Vineyard and plot variation confuses our understanding of Burgundy
High on the upper slopes, the farthest away from the Saône Valley Fault, the magnitude of fracturing within the same vineyard can vary significantly, even within the span of a few meters. Not only that, but there is evidence that the farther one moves from the main fault, the occurrence of fracturing patterns widens in its spacing, being further and further apart, and more irregular in its distribution. This means that if the fracturing is unequal within a vineyard, so can it to be unequal within a parcel. Following this uneven fracturing distribution, it becomes quite clear that a wine produced from different vineyard sections may produce wines of differents weights, and possibly character. We can only assume that this kind of intermittent fracturing, hidden beneath the topsoil, has unequally affected not only the wine made by these plots but the reputation of the vignerons who farm these plots as well.
The patterns of fracture propagation
Looking back at Part 1.2 about the deformation and fracturing of limestone, the stress that causes the main fault, and many of the parallel faults also weakens the entire stone structure through deformation. Micro-fractures appear throughout the stone, independently of one another, usually in clusters. As the cracks propagate, they do so often in a tree-like pattern, forking and spreading upward from the origin fracture, deeper within the stone. Depending on the brittleness of the limestone and the direction of the strain, these microcracks will form tensile fractures (extensional strain) or shear planes (compressional strain). Additional strain will be concentrated on the most fractured, weakest part of the stone, and this becomes the path of the fracture. Because these areas have been forced to bend and ultimately fail, this movement causes the strain to localize, increased by the stone’s own failure, causing even greater fracturing. Alternately in the areas between the crack arrays, the stone will be only lightly fractured, and in some places, maybe not at all. It is this that makes plots within the same vineyard unequal, as much as the skill and style vignerons are unequal.
Clues to the Côte by examining another fault/escarpment
The Arugot Fault near Jerusalem is unique because the fractures to its dolomite slabs (limestone containing magnesium) lie above ground, not covered by sand or soil. Geologists are reasonably certain that the Arugot fault was an extensional occurrence (like the SaôneFault), not caused by slip-shear or other earthquake-related stresses. The Arugot fault, like the Saône Fault, was created an escarpment as the Dead Sea Basin pulled away, in ahorst/grabenrelationship. The area is prone to flash flooding, particularly through the deep canyons that bisect the escarpment (not unlike thecombesof the Cote), and it was the erosion that rapid water movement causes have left the vertically fractured dolomite uncovered and available to be studied. The general geographical similarities of the Saône and Arugot are marred by the fact that the Dead Sea escarpment is twice as tall (600 meters), and many times more steep, with very steep angles of 75% to 80% that drop into the Dead Sea depression.
The fault itself is believed to extend several hundred meters into the earth. Parallel to the fault, a series many extensional fractures were formed, marching up the escarpment away from the main fault. There is ample evidence that these fractures propagated from below, as the fractures are tree-like, branching vertically, splitting the rock into smaller and smaller divisions as they move toward the surface. They often, but not always, fracture through the top of the stone. Nearest to the Arugot fault itself, the fractures are very close together, and the farther away from the fault the wider the spacing between fractures until they discontinue hundreds of meters away from the main fault. The relevance of this increased space between fractures is that explains the variation between well-fractured sections of limestone, and poorly fractured sections, all within the space of a few meters. This variation extends to, and explains not only to the difference between two vineyards, but the difference between plots, or even within sections of the same plot.
Shallow topsoil over hard limestone: a site of struggle
As I touched on in the introduction of slope position in Part 3.2, there are significant variables effecting which vineyards can produce weightier wines further up the slope. However, as a general rule, the steep upper-slopes are far less capable of producing dense, weighty and fruit filled Burgundies that are routinely produced on the mid and lower slopes.
The lack of water, nutrients and root space
In many of these upper vineyards, the crushed, sandy, and in some places powdery, or typically firmer and more compact, the marly limestone topsoil overlies a very pure limestone, such as Comblanchien, Premeaux and Pierre de Chassagne. Here, the extent of that the stone is fractured determines the vines ability to put down a healthy volume of roots to support both growth and fruit bearing activity. Any gardener can tell you that insufficient root space, whether grown above a shallow hardpan or in a pot, will cause a plant to be root bound and less healthy.
Because these steeper vineyards can neither develop, nor hold much topsoil to its slopes. The topsoil, which can be measured in inches rather than feet, tends to be very homogeneous in its makeup; a single horizon of compact, marly limestone, with a scant clay content of roughly 10-15%. The infiltration of rainwater and the drainage are one and the same. Retention of the water is performed almost solely by this clay content, and evaporation in this confined root zone can be a significant hazard to the vine. Fortunately rain in Burgundy during the growing season is common, although rainfall from April to October, and particularly in July, the loss of water in the soil is swifter than it’s replacement from the sky (Wilson, “Terroir” p120).
Infiltration Rates of Calcareous Soils
A study by A. Ruellan, of the Ecole National Supérieure Agronomique, examined the calcareous (limestone) soils of Mediterranean and desert regions, where available water and farming can be at critical odds. He studied two major limestone soil types. The first was a light to medium textured, loamy, calcareous soil (60 – 80% CaCO3), and the second was a powdery and dry limestone soil with no cohesion. This second soil had a calcium carbonate content that exceeded 70%, and had 5% organic matter and a low clay content. The water holding capacity of this soil was a mere 14%. The depth of this soil was over 2 meters deep, which likely does not allow weathered clay accumulate near the surface, as it does in Burgundy.
Both limestone soils had very high permeability, with an infiltrate at a rate at a lightning fast 10 to 20 meters per day (or between 416 mm per hour and 832 mm per hour). Even if rainwater infiltrated at half that rate through Burgundy’s compact limestone soils, it would virtually disappear from the topsoil. This is the area where the majority of the vines root system exists, and part of the root system responsible for nutrient uptake is within this topsoil region. In this case of these soils, the vines must send down roots to gain water in the aquifer. Wittendal, who I wrote of in Part 3, suggests in that the vines literally wrap their roots around the stone, and suck the water from them. I have seen little evidence that limestone actually absorbs water due to many limestone’s high calcium content and lack of porosity. This would be particularly true on the upper slopes under consideration now. It would be up to the roots to attempt to penetrate the stone in search of the needed water.
The root zone
By design, vines rely on the roots established within the surface soil – which is where nutrients (ie nitrogen, phosphorus, potassium) are found – to gain the majority of their sustenance. They send down deeper roots to gain water when it is not available nearer the surface. However in Burgundy, many of the steeper slopes present planting situations where not only is the soil very shallow, but the nutrients are poor. The limestone in these vineyards often is hard and clear of impurities, and within the same vineyard may vary significantly in how fractured the stone is. Because of this, in some locations vines have difficulty establishing vigorous root penetration of the limestone base, and this can dramatically limit the vine’s root zone.
Additionally, because of the soil’s shallow depth, , and because of the soils high porosity and low levels of clay and other fine earth fractions, only a limited volume of water can be retained
Water is critical for both clay’s formation and its chemical structure, and the clay will not give up the last of what it needs for it own composition. The evaporation rate of what little water there might remain, can be critically swift.
Rainwater’s infiltration of the limestone base, and its retention of water can also be limited where significant fracturing has not occurred. Any water that cannot easily infiltrate either the soil or the limestone base, will start downward movement across the topsoil as runoff. That means any vine that has been established in shallow topsoil, or the topsoil has suffered significant losses due to erosion, will be forced to send roots down to attempt to supply water and nutrients.
Vine roots and a restricted root zone
In non-cultivated, non-clonal vines, powerful tap roots are sent down for the purpose of retrieving water when it is not available in from the surface soils. However our clonal varieties are more “highly divided” according to the “Biology of the Grapevine” by Michael G. Mullins, Alain Bouquet, Larry E. Williams, Cambridge University Press, 1992. The largest, thickest, roots develop fully in their number of separate roots, by the vine’s third year, and are called the main framework roots. Old established vines in good health may have main framework roots as thick as 100cm (40 inches) thick. This main framework root system, in normal soils, typically sinks between 30 cm (11 inches) and 35 cm (13 inches) below the surface. In shallow soils, they may hit hard limestone before full growth, and may have to turn away, or stop growing. Anne-Marie Morey, of Domaine Pierre Morey, echoes this in talking with Master of Wine, Benjamin Lewin, of their plot in Meursault Tessons. “This is a mineral terroir: the rock is about 30 cms down and the roots tend to run along the surface.”
From the main framework, grows the permanent root system. These roots are much smaller, between 2 and 6 cm, and may either grow horizontally (called spreaders) or they may grow downward (known as sinkers). From these permanent roots grow the fibrous or absorbing roots. These absorbing roots are continually growing and dividing, and unlike the permanent roots, are short-lived. When older sections absorbing roots die, new lateral absorbing roots to replace them.
Although the permanent sinker roots may dive down significant depths, the absorbing roots (which account for major portion of a vine’s root system account for the highest percentage of root mass, typically only inhabit the first 20cm to 50cm, or between 8 inch and 19 inches of a soils depth (Champagnol, Elements de Physiologie de la Vigne et de ViticultureGénérale 1984). Clearly this is an issue if the topsoil is only 30 cm (12 inches) to begin with. If the absorbing roots are not growing sufficiently on the sinkers, the vine must rely on the exceptionally poor topsoil of the marly limestone.
South African soil scientist Dr. Philip Myburgh found (1996) that restricted root growth correlated with diminished yields. He also found that the “critical limit’ of penetration by vine root was 2 MPa through a “growing medium”. Weakness in the bedrock, and the spacing of these weaknesses, contributed to a vines viability.
The vines on these slopes, on which there is limited fracturing of the harder, non-friable limestone, have difficulty surviving. These locations often shorten the lifespan of the vines planted there, compared to other, more fertile locations in Burgundy, where vines can grow in excess of 100 years. It is these vines, with barely sufficient nutrients that make wines that don’t have the fruit weight that I wrote of before, simply because they cannot gain the water and nutrients necessary to develop those characteristics. The amount of struggle the vine endures directly determines the wine’s weight, or lack of it.
It is ironic, that when we research the issues the catchphrases of wine describe, ie, the “vines must struggle”, or that a vineyard is “well-drained”, or the vineyards are “too wet to produce quality wine”, we see the simplicities, inaccuracies, or the shortcuts that those words cover up. Yet these catchphrases are so ingrained in wine writing, that we don’t even know to question them, or realize that they require significantly more nuance, or at minimum, point of reference. Yes, the vines on the upper-slopes are particularly well-drained. They do indeed struggle, sometimes to the point of producing vines are not healthy, and cannot the quality or the weight of wine that the producer (dictated by their customers) feels worthy of the price.
Extreme vineyard management
In Blagny, the Sous le dos d’Ane vineyard, which lies directly above the small cru of AuxPerrières, has seen at least one frustrated producer graft their vines from Pinot Noir to Chardonnay. The Pinot, from the red, shallow, marly limestone soils, was felt to be unsatisfactorily light in weight. Not only would a lighter-styled, and minerally Chardonnay be well received, the producer will be able to sell it much more easily – and for more money because he could then label it as Meursault, Sous le dos d’Ane, a much more marketable name.
Producers in the Côtede Nuits rarely have the option to switch varietals. They typically must produce Pinot Noir to label as their recognized appellation. In the premier cru of Gevrey-Chambertin “Bel Air”, and Nuits St-Georges “Aux Torey”, growers have gone to the extreme lengths and expense of ‘reconditioning’ their plots. To do this, they must rip out their vines, strip back the topsoil and breaking up the limestone below. In the adjacent photo, a field of broken Premeaux limestone and White Oolite has been tenderized, if you will. The soil is replaced and the vineyard replanted. The entire process requires a decade before useful grapes can be harvested once again from the site, costing an untold number of Euros spent, not to mention the money not realize had the old vines been allowed to limp on. The same has been done in Puligny Folatières in 2007 by Vincent Girardin, and there again in 2011 by another unknown producer. Ditto with Clos de Vergers, a 1er cru in Pommard in 2009.
In Part 3.1, I covered how the position and degree of slope determined the type of topsoil that lies there. In the next two sections, I will talk about how the position on the slope not only greatly influences topsoil composition but independent of winemaking decisions, is a significant determiner of the weight of the wine. In this section I will discuss this concept, focusing primarily on the vineyards below the slope, the flatlands vineyards most burgundy aficionados have traditionally ignored. This disdain for these lower-lying vineyards is changing because massive improvements in wine quality have made them relevant, and equally massive increases in wine prices have left them as the only wines tenable to those without the deepest of pockets. Additionally, sommeliers looking for high-quality wines of relative value, have begun to much more closely examine the wide-reaching Bourgogne appellations and the village level wines of the Côte d’Or. These are wines that fit price points and quality standards premier cru vineyards used to fill and often fill that void admirably.
The relationship of slope to wine weight
It has become increasingly apparent over the past decade, that there is a direct connection between the depth and richness of soil, to the weight of the wines produced from those vines. Vineyards that have a modicum of depth, and at least a fair amount of clay or other fine earth elements, coupled with a fractured limestone base, produce weightier wines. These vineyards typically exist from quite low on the slope to roughly mid-slope. The higher up the slope one goes, the more crucial it is that the stone below is well-fractured to be easily penetrated by vine roots. Softer limestone bases, like the friable, the fossil-infused crinoidal limestone, which is weakened by the ancient sea lilies trapped within it, or like clay-ladened argillaceous limestone, makes it possible to produce great wine from the steeper, upper-slopes. Examples of these vineyards include the uppermost section of Romanee-Conti and all of La Romanee, which sits above it. These appear to be rare exceptions, however.
Most wines produced from the steeper, upper slope vineyards, with shallower, marly-limestone (powdery, crushed-stone with low clay content) soils, lie over harder, purer limestone types like Comblanchien, Premeaux, and Pierre de Chassagne. These limestone types must have at least moderate fracturing and a high enough degree of ductile strain to plant above them. Wines from these types of vineyards are, without question, finer in focus and have greater delineation of flavor. It is not unusual for these wines to be described as spicier, more mineral laden, and have greater tannic structure. The short explanation is the upper-slope wines have less fruit to cover up their structure, while the wines from more gently sloped vineyards have more weighty fruit. This fruit provides the gras, or fat, that obscures the structure of these weightier, more rounded wines. The upper slope vineyards will be covered in greater depth in the upcoming Part 3.3.
Because of the weathering of limestone on the upper slopes, and subsequent erosion, the soils, and colluvium collect on lower on the slope, making the topsoil there both deep and heavy. They are full of a wider array of fine earth fractions, and more readily retain water and nutrients necessary for the vines health and propagation of full, flavorful, berries. On the curb of the slope they do this splendidly, with an excellent mix of clay and colluvium, giving the proper drainage for the typical amount of rainfall, yet retaining the right amount of water most times of year when rain does not fall.
The “highway” and the low-lying vineyards below
For decades we have been told that the low-lying vineyards of Burgundy, were too wet to grow high-quality grapes, and we could expect neither concentration nor quality, from these village and Bourgogne level vineyards. The reason, we were told, was grapes grown from these flat, low-lying vineyards became bloated with water, and the result was acidic, thin, and “diluted” village and Bourgogne level wines. Alternately we were told the wines from lower vineyards were too “flabby”, as James E. Wilson ascribes on in his groundbreaking book Terroir published in 1988 (p.128). Thusly, an entire swath of vineyards, from below the villages of Gevrey and Vosne, all along the Côte, all the way to down to Chassagne, were dismissed as thin and shrill, lacking both character and concentration. These wines were generally considered by connoisseurs to be unworthy of drinking, much less purchasing. At that time, given the poor quality being produced, that seemed perfectly reasonable.
This set in motion a series of generalizations and biases, many of which remain to this day. “The highway”, as Route Nationale 74 is often referred, became the demarcation between the possibility of good wine and bad. The notion that this roadway, something that is built for the sole purpose of moving from one village to the next, had become an indicator of wine quality, is so pervasive, that the grand crus with N74 at their feet, such as Mazoyères–Chambertin and Clos Vougeot, have been cast in a bad light simply due to their proximity to it. It has colored perceptions so much, that many people, to this day, equate being higher on the slope with being “better situated”. The fact that there are grand crus and premier crus on the upper slope, but none on the lower slopes only buttressed this idea. However…
We now know this is not true.
There are many Bourgogne level vineyards that are more than capable of producing wines with good concentration, so long as the vigneron sought to produce quality over quantity, and the plot is not in an excessively poor location. So why were these myths that Bourgogne level vineyards could only produce light, thin, acidic wines, propagated by winemakers, wine writers, and importers?
The optimist would point to a lack of technical knowledge in the field and cellar made this true. The optimist would also say that the long tradition of creating simple, inexpensive, quaffing wine made it acceptable.
But there were other factors. Cold weather patterns from the mini ice-age, which ended in the 1850s, certainly set up long-standing expectations of wine the wine quality that was capable from various vineyards. These expectations were absolutely cemented in after the widely influential book by Jules Lavalle, Histoire et Statistique de la Vigne de Grands Vins de la Côte-d’Or was published in 1855. In this revered reference, Lavalle classified the vineyards of Burgundy the same year the French Government classified the chateaux of Bordeaux. No doubt the timing of this gave Lavalle’s unsanctioned work credence. After the first half degree average temperature increase which occurred around 1860, the climate in central Europe only gradually grew warmer over the next 135 years until 1990 when global warming really began in earnest. Before that, the weather would not allow the consistent ripening patterns that routinely we see today.
Another major factor was that there was not a complete understanding of how to control and divert runoff. Nor, prior to 1990, was it likely the villages along the Côte wealthy enough to make the large-scale improvements that were necessary to control rainwater runoff. Until the prices of Burgundy began to rise, overall the region was experiencing some economic depressed. This economic struggle, coupled with the inevitable political obstacles required to spend sparse civic funds, could delay improvements a decade.
On the other hand, the skeptic would point to the problems of greed, and it’s accomplice, over cropping. Vignerons could achieve 3 to 5 times higher production levels from the same vines, which was profitable, and required far less knowledge, less diligence in the field, and other than taking up more labor in bottling and space in the cellars, far less work in the cellars. It was not only the Bourgognes that fell into this net of profit over quality, but the village level wines were often fairly low in concentration, with under-ripe fruit, and low in quality. Even now, a producer that has reduced yields by a division of 3 in order to make a quality village or Bourgogne, is making less money per hectare than they would if they still over-cropped – and working harder in the field to do it.
Overcoming wet soil issues
Excess water in lower vineyards is a serious issue, and each vineyard is not equal in its ability to contend with heavy rainfall. Although flat is the quickest descriptor, the topography of each vineyard varies, as does the bedding (layers of soil) of each vineyard. These variances can dramatically determine the challenges presented to each grower in each day, season, and year, be it rain storm or drought.
In farming, an infiltration rate of roughly 50mm of rainfall per hour is considered ideal. That is precisely what a well-structured loam can typically absorb at normal rainfall rates, without significant puddling and runoff. Clays, however, drain much more slowly, with an infiltration 10-20mm per hour. These optimal figures can all be thrown out the window, however, if the soil structure has been degraded through compaction or farming practices that commonly degrade the soil. Poorly structured clay soils can drain as slowly as 5-8-10mm per hour.
Alluvial soils, with their graded bedding, created by heavier gravel and sand falling out of water suspension before silt and clays, typically have good infiltration rates. Loam soils that have moved in from the SaôneValley pasture lands, and have weaved themselves into the fabric of the lower vineyards, have ideal infiltration rates. Sandy sections are likely to exist in some vineyards, will have very rapid infiltration and drainage, 150mm to 200+ mm per hour. Where solid layers of transported clay, in thick slabs have formed, drainage can be severely affected. These plastic-y clays may repel water as much as they slowly absorb it. I wrote a much more complete examination of soils in Part 2.2.
What is important to consider, is that in all but the upper-most vineyards, soils are layered in horizons of soil types. It is normal, around the world, that there are typically 5 horizons of soil and subsoil layers in any given place, although there may be more, or as on slopes, fewer. Each horizon will affect the drainage of the plot, depending on its soil makeup. Geologist Francois Vannier-Petit presided over an excavation of Alex Gamble’s village-level LesGrands Champs vineyard in Puligny-Montrachet. In this vineyard, she records two horizons within the 80 cms that they dug, and she noted most of the vines roots existed in this zone. At the time of the excavation, she noted the soil was damp, but not wet, with good drainage.
The calcium, which is freed from the limestone rubble with weathering on the upper slopes, is not as prevalent and effective in the farther-flung Bourgogne vineyards. The calcium which helps disrupt the alignment the clay platelets, and aiding is drainage, may not be carried far enough by runoff to sufficiently strengthen the soils of these more distant vineyards. Certainly, most of these vineyards are located beyond the SaôneValley fault, and the continuation of limestone that virtually sits on the surface of the Côte lays buried by at least a hundred feet of tertiary valley fill and has no effect on wine quality there, other than by its remoteness.
The most severe problems revolve around the maximum amount of water the soil or clay can hold and fail to drain quickly enough through to the unsaturated/vadose zone, through capillary action to the water table below. With clay, this is called the plastic limit, or the point just before the clay loses its structure and becomes liquid. Flooding would ensue, and large volumes of soil would become suspended in turbid flowing waters, causing massive erosion, particularly from vineyards up-slope. This would truly be the worst case event, and I won’t say it doesn’t happen.
Another, significant problem, at least for vintners, although less apparent to the wine drinking public, is less wet soil is that it causes the vines to have difficulty acclimating to colder weather, and affects their hardiness if severe weather sets in.
However, in many vineyards, the wet soil has now been addressed by investments in drainage. Large yields are eliminated and concentration is gained by pruning for quality, coupled with bud thinning or green harvest. Vigilance against rot is key in these lower vineyards, as well as odium, and other mildews, which thrive in humid wet vineyards. This is a key element in quality since rainfall during the growing season is very common in Burgundy. With all of these precautions, there are now many producers who now make excellent Bourgogne level wines. And despite the tripling and quadrupling of the prices of Bourgogne, they are now well-worth drinking – often equalling the premier cru wines of yesteryear in terms of quality.
It is often cited that Puligny-Montrachet has no underground cellars because of the high water table there. Yet Puligny is arguably the finest region for growing Chardonnay in the world. I submit that much of the success Puligny has enjoyed, is in part because the water table ishigh, coupled with the fact that the village and its vignerons have invested heavily in water control features to channel and redirect excess runoff.
Reshuffling the wine weight matrix
The revelation that well-concentrated wines can be produced from these “wet” vineyards, has thrown slope position into a far clearer focus. No longer did we have lighter-to-medium weight wines on the upper slopes, the heaviest wine on the curb of the slope, and the very lightest wines coming from the lowest and flattest areas of Burgundy. Now it was clear: the areas with deeper, richer soils, particularly those with clay to marl soils, can universally produce richer fuller-bodied wines. This increasing quality of Bourgogne and the lower-situated village wines has dramatically raised the bar of expectations of wines across the Côte d’Or. With Bourgogne’s challenging the more highly regarded village-level vineyard in terms of quality, and village wines posing a challenge in regards to quality to many of the premier crus, lackluster producers were now put on notice to raise their game in terms of coaxing harmony and complexity out of their wines. Now that wine weight can be achieved in vineyards all across the Côte, despite a low slope position below the highway, expectation that Bourgognes are the simple, light and often shrill wines of yesteryear has been largely shattered.
Additionally, there is adequate evidence that deeper soils, particularly those with moderate-to-high levels of clay (or other fine earth fractions), can be a positive factor, for their ability to retain water and nutrients for the vines. This allows them to develop anthocyanins and other flavor components within the grapes. The challenge in these low-lying vineyards is controlling, and dealing with excess water. In wet years, vignerons have demonstrated that adequate investment to direct and control runoff, even most lower vineyards will not be too wet to grow good to high-quality fruit. Examples abound of village crus, from top vignerons, costing more than many grand crus; and these producers Bourgognes are not far behind in price. It’s not magic; it’s investment and hard work, in a decent vineyard, that makes this kind of quality possible.
Author’s Note: To avoid misunderstanding, this is a discussion of wine weight and concentration, not wine quality or wine complexity. Too often these things are confused, along with the notion that increased enjoyment equals increased complexity or quality. The goal is to understand and appreciate the differences and nuances that each vineyard provides by its unique situation, not to make it easier to find the most hedonistic wine possible.
We all know what soil is, or at least we think we do. If I were to ask you what was in soil, what would you say?
by Dean Alexander
Soil: 45, 25, and 25%
Despite all the talk about limestone, to really understand the terroir of Burgundy, we really have to understand what soil is and the material from which it is eroded. The mineral component, or the part we think routinely of as soil, are typically only 45% of the soil matrix. The balance is actually 25% air, and a further 25% of water, with the last 5% being split between humus (4%), roots (.05% ), and organisms (.05). It would make sense that this percentage changes seasonally, depending on how much water is in the soil from rainfall (or the lack of it) which changes the ratio of minerals, water, and air. Further, these ratios can change based on soil compaction, which decreases the air in the soil, which in turn increases the percentage of the mineral and organic component. Why is this important? Because this is the environment that the vines live and they require a certain ratio of each of these components to produce high-quality grapes.
The 45%: Burgundy’s mineral makeup
The French refer to the loamy Saône Valley fill as Marne des Bresse. The earth there is very deep, and typically is too wet for high-quality grape production. Historically this been used for pasture land for sheep and cattle. With every storm, this rich loam from the valley intermixes a little bit more with the soils of the boundary vineyards, and even encroaches on the loose, stony soils of the Côtes lower slopes. ‘Interfingering’, was how geologist James E. Wilson described this mixing of soils in his 1990 book, Terroir: The Role of Geology, Climate, and Culture in the Making of French Wines.
Bore samples, according to Wilson, had indicated that this interfingering has reached westward, up the hill, to influence the soil construction of the lower sections of the grand cru Batard-Montrachet. With this information, he inferred that the Saône fault must be near. It is notable that in 1990 precise location Saône fault was not known, and around Puligny, it still may not be. I suppose the wealthy Puligny vintners have no need to explain why Puligny-Montrachet is great. Vannier-Petit however, does tacitly show the Saône fault in her map of Gevrey, which is represented by the abrupt end of the limestone bedding east of RN74.
Because the Côte is an exposure of previously buried, older limestone, younger soils line the divide on either side of the escarpment. The Saône Valley’s Marnes de Bresse brackets the Côte on the eastern, lower side of the slope, while younger rock and soil material that cover the tops of the hills, to the west, and beyond.
From the hilltops above, those younger soils have eroded down, bringing feldspar and quartz sand, silt, as well as phyllosilicate clay minerals, to help fill in and strengthen the rocky limestone soils of the Côte. In many places, geological faulting, coupled with runoff or streams, have created combes or ravines which have allowed substantial alluvial washes to extend the planting area of the Côte. A prime example of this is the Combe de Lavaux which is a dominate feature of the appellation of Gevrey-Chambertin. It has sent a large amount of alluvial material around and below the village of Gevrey, creating good planting beds for village-level vineyards. Alluvial soils are nothing more than a loose assortment of uncemented of soil materials that have been transported by rain or river water. These materials are typically sand, silt, and clay, and depending on the water flow, various sizes of gravel particles. It is this sand and gravel that has traveled with the water flow from the Combe, that provides these vineyards that protrude past the limestone of the escarpment the drainage the vines require. These are not, however, the soils that will produce the great premier cru, or grand cru, wines for which Burgundy is famed.
Soil suspension and graded bedding
Soil moves downslope by water erosion, the force of gravity, and even is transported by the force of significant wind. With movement, the particles within the topsoil are in a state of suspension. Geologists refer to this movement and suspension as turbidity. Because of their weight, gravel travels downward in the moving soil, creating a progressively sorted soil, with coarser pieces on the bottom, while the finer particles find their way to the top. The result of this is called a graded sediment bed. (1)
While it is easier to see how a graded bed might be created in a stream bed below a ravine like the Combe de Lavaux, I was somewhat perplexed how this might occur in Alex Gamble’s Les Grands Champs vineyard in Puligny-Montrachet, see Claypart 2.1. Here gravel bedding lay at 80cm, a little more than two and a half feet below the surface. Above the gravel, sat a foot and a half of heavy, yellow, clay-dominated soil. This was, in turn, topped by nearly a foot of loamy-clay soils. Vannier-Petit estimated these soil horizons, as geologists refer to them, were created between two and five million years ago by water runoff. What kind of run off? I realized that the kind of runoff that creates graded bedding happens often, like in this photo (below), taken in Pommard during the winter/spring of 2014, by winemaker Caroline Gros Parent.
Geologists talk about a soil’s parent material because every element of soil came from a different material, which was then weathered, both mechanically and chemically, into various sizes. These minerals will then accumulate, either poorly sorted into an aggregate material, or they can be well sorted by the wind, water, or gravity into size categories. Sand and silt are generally said to have been created by mechanical weathering, although chemical weathering is always a present force, as long as there will be rain. Sand can be made of any parent rock material, but in Burgundy, there are sands made of granite, in addition to plentiful limestone sand. (2) We know this because there is loam present (as well as graded bedding), in the Grands Champs vineyard from the Saône valley fill below. The water that carried this non-limestone, Côte-foreign material, would have carried quartz sand with it as well when it created the graded bedding there. This gives us a very important insight into the construction of the soils of Burgundy.
Fine earth fractions
Geologists grade soil minerals by size; the basis of which are particles that are 2 mm and smaller. These are called fine earth fractions and consist of sand, silt, and clay. In equal thirds of each of the three soil fractions is considered perfect for farming crops, and is termed loam. The various sizes of minerals in the soil makeup gives the soil its texture.
Clay, we have talked about in length in part 2.1, and differs from silt and sand because it is a construction from stone that has been chemically weathered, whereas silt and sand are derived from mechanically weathered rock. Additionally, clay is a construction of clay minerals that are bound with aluminum and oxygen by water and carries minerals within its phyllosilicate sheets. It is also important to mention that clay’s particles are considerably smaller in diameter, being less than 2 microns in size. Soils with more clay hold more water, so they require less frequent application. An overabundance of water in clay soils causes oxygen depletion in the root zone. This can limit root development. The abundant solvent calcium in the limestone soils Burgundy misaligned the clay platelets, loosening the soil, and allowing better drainage.
Silt is specifically formed from quartz and feldspar, and is larger than clay, being 0.05 mm-0.002 mm. We know that any feldspar in the soil, could not have come from weathered stone; neither limestone or granite, which was the dominant stone in the area when the limestone beds were forming, because it would have metamorphosed into a phyllosilicate clay mineral if it had. This means the feldspar has traveled onto the Côte, either from above or below the limestone strata.
While it might seem logical to assume the quartz in silt originated in the earth’s crust, and perhaps degraded from granite that was prevalent in the area, this may not be the case. The first problem is quartz is resistant to chemical weathering. And physical weathering like frost wedging of sand particles may continue to yield results beyond a certain size.
Researchers from the University of Texas at Arlington used (and I cut and pasted this) a “backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe.” They found that the 100% of silt quartz found in 370 million-year-old shales of Kentucky were made from the “opaline skeletons” of plankton, radiolarians, and diatoms. This, they reasoned, might explain the lack of these kinds of fossils during the same period. These tiny animals had all been incorporated into the then forming shale. This may also be the case for the silt quartz of Burgundy, itself too having once been a Jurassic, seaside resort. This, in fact, this information also suggests this quartz silt may come from weathered shale that is much older than the limestone of the Côte.
Sand is larger than silt. being less than 2 mm, and typically is constructed of quartz or limestone particles. The limestone sand will weather to solvent calcium carbonate, but the quartz will not weather and will remain as sand. It is likely that significant quartz sand has been washed down from the hillsides, and certainly is a major contributor to alluvial soils below the combes. Sand drains so quickly that vines grown in sandy soil have more frequent water requirements, but require a lesser amount of water. Adequate water maintains plant growth while minimizing the loss in the root zone.
Plant and animal soil contributors
Grasses, with their dense root systems, are positively impactful to the topsoil. In their decomposition, darker soils are created to deeper depths, and the resulting soils also tend to be more stable. In a monoculture of grapevines, many growers are finding this to be a significant advantage. In Australia, some grape growers are using grasses to help lower soil temperature in efforts to slow down ripening in an ever-warming climate.
Much is made by those practicing sustainable and organic cover crop encourage populations beneficial predator insects and birds, but grasses and cover crops also encourage subsoil organisms and microorganisms growth as well. Most common are bacteria and actinomycetes (rod-shaped microorganisms), which by weight have been found to be four times more present by weight than earthworms in healthy soils. While these are important to the quality of the wine, they are only an intricate part of terroir if it is practiced by the farmer.
The 25%: Air (and soil compaction)
The proper amount of airspace between mineral fragments is very important for vine growth and allow for water to penetrate and be retained by the soil. Soils with diminished airspace are said to have soil compaction, and compaction is difficult to correct once it has occurred. The Overly tight spacing between the mineral component of a soil restricts oxygen levels and contributes to a poor water holding capability. Rainfall itself can cause some soil compaction, but most commonly walking or operating farming equipment on moist soils does the most damage. In drought years, soil compaction can lead to stunted vine growth and decreased root development. In wet years, soil compaction decreases aeration of the soil and can cause both a nitrogen and potassium deficiency. Additionally, without adequate porosity to the soil, water cannot easily penetrate the soil during a rainstorm. Water that cannot infiltrate soils of flat terrain can stagnate, which further compacts the soil, or on sloped terrain will runoff, which can create erosion problems.
Positive effects of moderate compaction
Moderate compaction can have some desirable effects. Moderate compaction forces the plant to increase root branching and encourages secondary root formation. This additional root growth is the plant’s response to not finding enough nutrients with its existing root system. Plants with more extensive root systems are more likely to find nutrients that are not carried by water, like phosphorus. Obviously, more compaction is not better, because it impedes root growth, lessens the oxygen in the soil, and repels water from penetrating the soil.
While deep tillage 10-16 inches can shatter the hard packed soil, studies have shown that crop yields will not return to normal following the effort. While there are factors that might cause the soil to return to compaction, like a farmer, unintentionally re-compacting their soils, more than likely tilling does not return the airspace that was lost in the soil itself. Further continuous plowing and tilling at the same depth can cause serious compaction problems on the soil below the tilling depth.
The 25%: Water (the key to everything that Burgundy is)
It should be impossible to talk about soil without talking about water, given it is optimally 25% of soil’s makeup. It is certainly tempting to pass over the subject of groundwater and lump it into erosion, but that would really shortchange our understanding of the Cote. Part of Burgundy’s success can surely be attributed to relatively steady rainfall year round, coupled with the fractured limestone’s ability to hold water until its reserves of water which is held within the stone can be recharged by future storms.
Good drainage, well-drained? Let’s reset the dialogue.
The infiltration of rainfall by the soil is the first and perhaps most important factor in recharging groundwater levels. Like I wrote of compaction, the soil has to be porous enough to penetrate the topsoil and subsoils successfully. The buzz word in the wine world is drainage, with terms like well-drained, and good drainage appearing often. I suppose we picture the roots drowning in mud if there isn’t good drainage. But the idea of good drainage really simplifies the issue. Drainage can have to do as much to do with compaction as soil materials or slope. Soil drainage is important in fighting erosion as well not causing additional soil compaction. Good drainage, which is what happens with a well-aerated soil, allows the vines roots sufficient oxygen and nitrogen and allows the roots to take in nutrients like phosphorous and potassium. But none of this can happen if the soil releases rainwater too quickly, and the vine can perform none of these vital tasks. The reality is, it is not the fact that a soil well-drained, but rather it drains at the adequate rate for a given rainfall. Obviously, this will not always be a perfect equation since rainfall varies greatly depending on the year and the time of year.
The speed of drainage
The kinds of materials that make up the soils contribute greatly to the rate of water ability percolate through the material. The speed of the mater’s movement depends on the path the water is channeled in. The most direct path that is in line with gravitational pull will give the fastest drainage.
Sandy soils, as one might expect, drains quickly because it consists of only slightly absorptive, small pieces of stone, that allow the water to essentially slide right past.
Clay, on the other hand, is very dense and plasticity. These characteristics, as you might expect, would be resistant to allowing water to pass through, and large bodies of transported clay can redirect horizontally, the flow of water percolating through from above due to it’s slower absorption rate. But what isn’t obvious is that clay’s construction encourages capillary action. The clay body will distribute water throughout its mass, counter to gravitational pull, becoming completely saturated, before releasing excess water through to the material below.
Highly fractured limestone that is still in place, is often is fragmented in a prismatic pattern. However some limestones, like this soft argillaceous limestone to the right, with its high clay content, may fracture horizontally. The type of fragmentation would depend on the stresses upon the stone, the freeze-thaw effects of water and temperature, as well as the material of the stone’s construction. Clay based stones will tend to fragment horizontally and when they do, they are considered platy, and water will percolate more slowly than stones that fracture in a prismatic fashion.
Groundwater, the water table, and karst aquifers
In writings regarding Burgundy, very little is said about ground water, other than there are no cellars built underground in Puligny because the water table is too high there. A plentiful water supply may be one of the features that propel the vineyards of Puligny into the ranks of the worlds best. As my diagram above shows, water percolates through the soil and stone. This upper section is called the vadose zone, or unsaturated zone. Slabs of limestone, fissures, faults, and clay bodies all can change the course of the water flow. Each horizon of soil and each layer of stone have their own rate of percolation. With this much limestone, it is very likely there are karst aquifers or large caves caused by the carbonization of calcium carbonate beneath the Côte, but I could find no specific mention of aquifers in close proximity to the Côte. There is a mention in a European Academies Science Advisory Council‘s country report for France, that in Burgundy there are “karsified Jurassic limestone layers” somewhere in the region, but nothing more is elaborated upon.
There is a very famous and massive karst aquifer with seven very deep layers that spans from north of Burgundy across the Paris basin to the English channel. The deepest level of water is brackish. The uppermost section is called the Albian sands sits at than 600 meters, and was first was drilled into in 1840 taking well more than 3 years to achieve. The water there is 20,000 years old, and there has been discussion whether the water should be considered fossil, meaning there is a question whether there recharge from the water above, or not.
Next up: Understanding the Terroir of Burgundy, Part 3: Confluence of stone, soil, and slope
(1) Interestingly, larger stones, especially the flatter, rounded shaped stones that the French refer to as galets, tend move to the surface, probably because of their larger displacement values.
(2) Sand from other parent rock material is likely to be available as well.
For the past 35 million years, rainwater has endlessly and relentlessly washed across the limestone escarpment. To varying degrees, the limestone will absorb water through its pores, but stone that has been damaged by ductile deformation is much more easily infiltrated. Faster still, water fills the cracks and fissures created by geologic strain, finding freshly broken calcium carbonate to wetten, and begin the process of chemical weathering called carbonation.
Rain rainwater, it seems is more than just H2o. From the storm clouds above, H2obinds to with carbon dioxide (CO2) to formcarbonic acid (H2CO3). And although carbonic acid is typically a mild acid when carried by the rainwater, it does slowly act as a solvent to the calcium carbonate (CaCO3) that holds the limestone together. This carbonation frees the carbonate from the calcium, and will metamorphose the calcium into calcium hydrogen bicarbonate Ca(HCO3)2, which technically only exists in solution. (1) The material that remains behind once it is no longer bound by bonds of the stone, is whatever impurities that were in the stone when it formed. This could include clay, fossils, feldspar which is the most common mineral on earth), among many other possibilities.
Nature’s Highly Engineered, Deconstruction of Limestone
Calcium carbonate is more soluble in colder temperatures. If you aren’t paying attention, this, along with so many other pieces of information might seem fairly unrelated. But like everything else, it is an important piece of the puzzle. It is all part of nature’s finely detailed engineering, where every element directly is related to, and influences the next.
This fact that calcium is more soluble in colder temperatures folds beautifully together with the freeze-thaw fracturing of the limestone that I detailed in Limestone: Part 1.2. The acidic water enters the more porous limestone, where it then freezes. This exerts immense internal pressure on the rock, which causes it to split along the pores, can cause various types of fractures within the stone. Then when the acidic ice within the rock begins to melt, it erodes the stone along the fissures, being aided by the cold temperatures. The more acidic the rainwater, the more minerals the groundwater can dissolve and be held in solution. Interestingly, because lime is alkaline (a base as opposed to acid) it naturally balances the ph of the water, and thus the soil, which is good for the health the vines.
Clay Development = great vineyards
Every Burgundy vineyard that is considered to be great has at least some clay and some limestone in their makeup. But that is not surprising since clay,is the byproduct of the chemical weathering of stone. The silicate materials (essentially the building blocks almost all minerals) in the stone are metamorphosed into phyllosilicate minerals. Putting that more simply: after stone is eroded by acid, some of the weathered material (depending on what the stone was made of) is transformed into a material that will become clay – once it attracts the needed aluminum, oxygen, and water.
Clays first forms at the site (in situ) of the stone that is being weathered, and this typically is a form of surface weathering. This new material is a primary clay, and sometimes referred to as a residual clay. These primary clays tend to be grainy, lack smoothness, and do not typically have qualities that are described as plasticity. As primary clays are eroded, (typically by water) and are moved to reform in another location, they are called transported clays.
This transportation changes the clay’s properties; this is likely because the water carries the lighter, smaller gains together, away from the larger, coarser material that remains in the in situ location. When transported clay reforms, the reformation is called flocculation. This natural attraction that clays have toward homogeneous groupings,are due not only to their similar size but because they carry a net negative electrical charge, which the particles gain by adsorption. Adsorption is not to be confused with absorption, is like static-cling. Items are added, or adhered by an electrical charge, to the grains, not absorbed by the grains.
In flocculation, particles are attracted to one another, by their uniform size (typically very small, under 2 micrometers), and shape (tetrahedral and octahedral sheets). These phyllosilicate sheets organize themselves, layering one upon another, like loose pages of sheet music. Between these silicate sheets, aluminum ions and oxygen are sandwiched. These elements bind together to form a clay aggregate, even in the confluence of water. Clay formations can carry with them, varying mineral components such as calcium, titanium, potassium, sodium and iron and other minerals, making them available to the vines. To say that the chemistry of clay gets very complicated, very quickly, is an understatement.
Transported clay has plasticity, which primary clays do not. When a clay is very wet, beyond its liquid limit, (meaning the most water a clay structure can hold before it de-flocculates), the sheets slide apart, giving clay its slippery feeling. Any thick area of clay found at a location is likely to a be transported clay, as the adsorption characteristic of clay allows it to achieve significant mass.
Sand 0.02 – 2.00 mm in diameter
Silt 0.002 – 0.02 mm in diameter
Clay < 0.002 mm in diameter
The type of clay that is produced from the weathering of rock depends on the what minerals make up the stone. In the case of granite (the stone which existed in the Burgundy region, before the creation of limestone), is constructed of up to 65% feldspar, and a minimum of 20% quartz, along with some mica. While quartz will not chemically degrade in contact with the carbonic acid carried in rainwater, feldspar and mica will. Even though they originate from the same stone, these two minerals will metamorphose into two different of types clay, that belongs to two different clay family groupings. Feldspar weathers into Kaolinite clay minerals and mica weathers to an Illite clay mineral. These tend to be non-swelling clays. (3)
I probably spent twenty hours trying to figure out what kind of clay eroded from limestone, before I realized that it would depend on what impurities were mixed into the calcium carbonate when it was brewed up during the Jurassic period. Limestone can produce any of the four families of clay.
Kandites (of which Kaolin(ite) is a subgroup), are the most common clay type, because feldspar, which is the world’s most common mineral, metamorphoses intoit.
The other three clay groupings are smectite, illite, andchlorite.(4) Within these clay family groupings, there are 30 subtypes. As might be suggested by the example of the weathering of granite above, it is very common for different kinds clays reside adjacent to, or in layers with other clays. This layering of clay types is called a stacking sequence, and it can occur in either ordered or random sequences. Each are attracted to formations of its own type, by size weight, and electrical charge.
The Effect of Weathered Limestone on Soil Quality
There are a number of significant benefits to the high levels of limestone in the soils of Burgundy. The world over, farmers make soil additions of agricultural lime (which is made from grinding limestone or chalk), in order to balance and strengthen their soils. These are additions that are unnecessary in Burgundy. Soil salinity is increased by the calcium bicarbonate that is released by chemical weathering of limestone. This increase in soil salinity (which raises the pH) of the soil, is cited as a condition for the flocculation of the clay, allowing the phyllosilicates (clay minerals) to bind together into aggregates. But of course, citing a high ph is required for flocculation (as I have seen written by several authors) this is the chicken or the egg debate. The flocculation requires a low pH environment to occur because it creates that environment in process of its development.
Lime additions to agricultural lands are also beneficial in that it increases soil aeration, which in turn improves water penetration. The calcium loosened soils allow for better root penetration, and because of that root growth is improved. Additionally, agricultural lime strengthens vegetation’s cell walls, increases water and nitrogen intake, and aids in developing enzyme activity. Too much lime (and its accompanying salinity) in the soil, however, can be lethal to the vines, and various rootstock has been identified as being more resistant to the effects of high levels of limestone in the soil than others.
This loosening of soil by addition of lime/calcium carbonate is caused by the disruption of the alignment of the clay particles. Rather than doing a poor job paraphrasing an already excellent article from soilminerals.com, called “Cation Exchange Capacity,” which will I quote below. To put the article in a frame of reference, it explains to farmers interested in organic and biodynamic farming, the proper mineral balance for healthy soils. These are conditions often exist naturally in the best sections of the slope in the Cote d’Or.
“Because Calcium tends to loosen soil and Magnesium tightens it, in a heavy clay soil you may want 70% or even 80% Calcium and 10% Magnesium; in a loose sandy soil 60% Ca and 20% Mg might be better because it will tighten up the soil and improve water retention. If together they add to 80%, with about 4% Potassium and 1-3% Sodium, that leaves 12-15% of the exchange capacity free for other elements, and an interesting thing happens. 4% or 5% of that CEC will be filled with other bases such as Copper and Zinc, Iron and Manganese, and the remainder will be occupied by exchangeable Hydrogen , H+. The pH of the soil will automatically stabilize at around 6.4 , which is the “perfect soil pH” not only for organic/biological agriculture, but is also the ideal pH of sap in a healthy plant, and the pH of saliva and urine in a healthy human.” soilminerals.com
The industrial of use of limestone to control wet and unstable soil
The soil strengthening properties of lime is well known by the construction industry. It is used as a soil stabilizer in the construction of buildings and roadways, as well as being used to stabilize wet ground to improve the mobility of trucks and tractors. In the vineyard, soils with high levels of limestone provide the good porosity, soil structure, and drainage to clay soils, and as this construction advertisement depicts, the same for mud/dirt soils as well.
Lime is also the binding agent in cement. The first known use of lime in construction was 4000 BC when it was used for plastering the pyramids, and later the Romans extensively used lime in the preparation of mortar for various constructions. They found that mortars prepared from lime, sand, and water, would harden to a man-made limestone, with exposure to the carbon dioxide provided by the air. This, of course, sounds very familiar, knowing the formation and chemical weathering of stone.
Next Up Soil Formation: Part 2.2, Soil, Slope and Erosion
(1) I should note, that within the span of this short paragraph, carbon has seen several forms: in the air (in carbon dioxide CO2), as an acid (in carbonic acid CO3) carried by water, in stone as calcium carbonate CaCO3, as a mineral bi-product (as calcium bicarbonate Ca(HCO3)2 which exists in liquid solutions. This is all part of the carbon cycle, where carbon is regenerated in the air we breath, the water we drink, the earth we grow our food in.
(2) The fact that CO3 is now carried by water, is important in terms of vineyard development.
(3) Kaolinite clays are the type used in pottery.
(4) As Granite was the primary stone formation in the region prior to the development of limestone, it is likely that Kaolinite and Illites are the most common clay families in Burgundy today.
Burgundy’s story really is one of stone into the earth, and pivots on a cast of geological stress, sub-freezing temperatures, and the simple, transformative power of water. Just how the forces of nature may have acted upon the limestone and transformed it into the great wine region it is today, is the subject of this article. Meanwhile, the ultimate goal of this series explains the intimate relationship limestone has with the wines of Burgundy.
I suspect that we all have this image of the Côte, post-Fault Event (however long that took), to be this raw 400-meter face of sheared limestone. But even then, the Côte was not a solid piece of stone. The incredible extensional forces the broke the Côted’Or free from the Saône would have caused significant tension fracturing throughout the Côte before this much more massive fault gave way.
Just Add Water
This tensile fracturing, which surely was extensive, would allow rainwater to deeply infiltrate these fine crevices of the stone. And then, upon each surface that the water contacted, depending on the specific porosity and permeability of the limestone, rain water would penetrate the surface of the stone. This contact with water would set the stage for two very different yet significant developments in the stone.
With winter temperatures below freezing, the water in the stone will expand between 8 and 11 percent. This will yield 2000 pounds per square inch, or 150 tons per square foot of internal pressure which is more than enough to cleave the stone. Geologists call this frost wedging, a form of mechanical weathering which breaks apart the stone due to thermal expansion and further with the eventual contraction. Thermal expansion has a culprit in shattering the stone: the cold. Most materials are inherently brittle in colder temperatures, and the limestone which has more elastic than brittle tendencies is more vulnerable to fracturing in freezing temperatures. Frost wedging is so successful in nature that the stone industry mimics it as a non-explosive technique to separate pieces of stone.
The effect of successive freeze thaw cycles, even upon undamaged exposed stone can cause the development of micro-fissures that influence the stone’s fatigue strength, and can produce vertical cracking called exfoliation joints, as well as flaking, and spalling. All along the Côte, there are numerous scars on hillsides where limestone has in the past loosened, to slide off of even moderate slopes, sending scree down the hillside to rest at the curb of the slope. Geologists refer to this rubble pile as colluvium, and it has proved a near perfect vineyard soil solution. The sliding and falling of rock further degrades the stone, abrading it as it slides, and breaking as it falls, allowing fresh broken surfaces for water to act on. Frost wedging which in part created this colluvium rubble pile, is considered mechanical weathering, and isthe first development that I mentioned water would bring. Equally important to vineyard formation, is the second significant development that rainwater brings, is chemical weathering. The acid carried by the rainwater, will metamorphose these freshly broken limestone surfaces. And like magic, it will slowly dissolve the calcium carbonate which binds the stone, leaving behind clay minerals and other material. (This process will be covered in Part 1.3 Clay and Soil Development)
Exfoliation and Other Theories on Geologic Structures with Unobservable Change
Consider for a moment: most significant geologic changes occurs over a time frame that is far longer than the entire the evolution of mankind. This fact alone might best explain the difficulties of studying events that happen so slowly that change is not observable. These are geologic forces that can not be seen, felt, or measured. If we didn’t have evidence that these changes had occurred, we would
never know they were still continuing to occur around us. The scale of time and shear size and immobility of the objects makes many traditional scientific methods impossible.
Exfoliation Theory: G.K. Gilbert 1904
We know that exfoliation joints exist, but scientists are at odds about how they occur. It is agreed that mechanical strain results in large horizontal sheets of stone separating itself from the mother rock. Half Dome in Yosemite has achieved its shape in this manner. The first, and once long-held theory, was put forth by the ground breaking U.S. geologist Grove Karl Gilbert. Gilbert’s theory of Mechanical Exfoliation concerned stone formations that had previously been buried in the earth’s crust, which were later were forced to the surface by geological up-shifts. The theory explained that the removal of the overburden (the weight of the rock or earth above)had causedunloading of stress in one direction. The resulting release of stress once on the surface and not confined upwardly, caused expansion and tensile cracking along unloading joints, eventually creating loose sheets of stone on the upper surface of these rock structures. These outer layer of stone were thusly being exfoliated. This website for Girraween National Park in Queensland, Australia, has an excellent explanation of exfoliation weathering.
Challenges to Exfoliation Theory
However, this theory has had it challenges by the mid 20th century, and is to some extent (depending on the point of view), muted or discredited. Situations were sited that didn’t fit all of the theory’s criteria, like rocks that with exfoliation joints which have never been deeply buried, and evidence that many exfoliation joints exist in compressive stress environments, rather than being produces by extensional stress as the theory suggests. Alternative theories are thermal expansion, (and even wide diurnal expansion), and hydraulic expansion, , (which I discussed above with frost wedging), compressional stress, and in the case of Half Dome, the weight of gravity, or a combination of all of the above, including exfoliation weathering.
Along the same lines, theories revolve around minerals that are created in an anaerobic environment. These stipulate some minerals molecular structure are changed (metamorphized) when exposure to oxygen, creating new minerals. While oxygen is the most common element in the earth’s crust, most of it is bonded with silicates and oxide materials and is not free to act as a weathering agent. But when minerals are exposed to free O2 above ground, they undergo chemical weathering, that produces new minerals that are stable on the surface. The most obvious example is when iron ions lose an electron with exposure to oxygen, rust is formed.
In many ways, I’ve put the cart before the horse by talking about the escarpment, before covering even more fundamental ideas. But that is how storytelling goes: sometimes you have to fill in the back story.
The world was a very different place 160 million years ago. This was five million years before the Allosaurus and Apatosaurus (formerly known as the Brontosaurus) roamed the earth. The limestone of the Côte, being a sedimentary material, was laid down in big, flat, shallow beds between the reef barrier that protected the lagoon, and the shore. Each layer was put down, one at a time, chronologically by age, marking millions of years. As the seas receded, and this is the main point, this would become a wide, flat valley of young, sedimentary limestone. It is likely that this bedding would eventually, be completely covered by wind-blown soils. We don’t know what happened to this young Burgundian stone in the intervening 130 million years between formation and the Fault Event, 35 million years ago, but it is unlikely it remained there unchanged. As geological stress acted upon the bedding, it would be pulled, pushed, deformed, and in all likelihood, in some way, fractured.
Author’s Note: For the remainder of this article, I will describe the stress and deformation, and potential fracturing of the stone in the body of the text, and in the photos I will show some of the results (that I am aware of), of that stress. Hopefully the two together will paint a complete picture.
It takes more than just ‘X’ to fracture
I would love to be able to write that a particular limestone will fracture under the “X” conditions, but just doesn’t seem to be that simple. First, there are too many variables. How stone reacts to geological stress is directly related to its composition and construction as well as: its temperature, the amount of stress, multiplied by the duration of stress. Most materials tend to be more elastic under higher temperatures and more brittle in low temperatures. It would be reasonable to assume that there was significantly more geological fracturing during ice ages because stone is more brittle in cold temperatures. At least in warmer temperatures, calcium carbonate stones tend to have good elasticity, depending on how pure their construction, as the chemical bonds in CO3 will move if pressure is applied very slowly. However, that elasticity is finite before the stone is structurally damaged as it passes its elastic limit; but more on that later.
Secondly, like I mentioned before, science cannot measure the stress, but rather the deformation due to the stress. For this geologists use a strainmeter, which they measure changes in the distance between two points. For greater distances technology has brought the laserinterferometer. These tools allow the scientist to measure frequencies that represent deformation. Over short periods of time, they record tides (I had never before considered the stress created by a 1.5 quintillion tons of water moving position above earth) and the seismic waves of earthquakes, while over longer periods of time, it can record the gradual accumulation of stress of rock formations.
The mission of this article? What I am looking for here, are some kind of answers these two questions: What conditions would make it possible for vine roots to bed into limestone bedrock? and What limestone types will fracture enough to allow this to happen? Anything learned along the way will be a bonus.
Stresses and the resulting strain
Stress causes strain of various types. Like I mentioned before, we are not able to measure the stress itself, rather only its effect by measuring the stone’s deformation. Below are the basic stresses upon objects and the resultant strains and deformations associated with them. Any deformation is considered flow (as science calls this) and it is domaine of an interdisciplinary study called Rheology. Here it is again, more simply, because its getting more complicated: Stress first. It, in turn, causes strain. The result can be deformation, and this deformation is studied as if it were a liquid: as flow by Rheologists (a group of engineers, mathematicians, geologists, chemists, and physicists), who work together in an attempt to answer questions that transcend all of these disciplines.
6 Most Common Geologic Stresses (the first two are the most relevant to Burgundy)
Tensile, Tension, or extensional stress which stretch the rock or lengthen an object, will cause longitudinal or linear strain, and its effect is to lengthen an object, and can pull rocks apart. Like a rubber band pulled longitudinally, this is known as extensional rheology. As the rubber band breaks, that is called shearing flow. Rocks are significantly weaker in tension than in compression, so tensile fractures are very common. Tension stress formed the Côte d’Or.
Compressional stress that squeezes the rock and the resulting strain shortens an object. This too can be a linear or longitudinal strain. Stone under compressional stress can either fold (as in the photo to the right) or fault.
Normal Stress (can be either compressional or extensional) Normal stress that acts perpendicular to the stone.
Directed stress is typically a compressional stress, that comes from one direction with no perpendicular forces to counteract it. The higher the directed pressure the more deformation that occurs.
Lithostatic> and hydrostatic stresses are the compressional pressure of being underground or underwater. The force of the stress is uniform, causing compression from all sides.
Interestingly, the effects of hydrostatic stresses upon an object are mitigated by oppositional forces. For example, the stress from below counteracts much of the force from above, and the forces from the right side counteracted by those from the left as they push against each other. So unlike directed stress, (the kind of stress that a 2 ton object exerts on top of a man), hydrostatic stress is like a scuba diver in the ocean. The stress of water upon the diver can be the same as the heavy weight upon the man, but because of counteracting stresses, strain is not expressed in the same way.
Shear stress is that which is parallel to an object. Shear strain (caused by shear stress) changes the angle of an object. It can cause slippage between two objects when the frictional resistance is exceeded, or even failure within an object. Faulting is an example of slippage under shear stress. I would be remiss to note that faults in Burgundy, at least to my anecdotal eye, often occur between limestone types.
The Magnitude of Strain
Elastic strain and ductile deformation
There are two levels of strain. Elastic strain, in the effects of the strain, are reversible. The stone will change shape or deform under stress, with minimal damage to its structure, and then return to its original shape and position.
Ductile strain, is the area of strain once past the elastic level. The stone is now developing microscopic fissuring, and the stone can not return completely to its original size, shape, or position. Although the stone may not appear to be visibly damaged, any deformation into the ductilerange, will harm the stone’ structural integrity. Additionally, in comparison to the deformation of the stone in the elastic range, the speed and ease of ductile deformation increases quickly (in structural geologic terms). The deformation is now the result of micro-fissures that have emerged throughout the stone, and are now both propagating and enlarging. It is during this phase of rapid deformation that the stone can achieve dramatic folding from what had previously been flat, sedimentary stone.
By The Numbers: limestone limits
Author’s note: The measuring of deformation and the related stress involved becomes a bit more technical, and requires a number of lingo words to be used in the same sentence. I resist this as much as possible, because it requires the reader to be very familiar with the terms. Skip ahead if this doesn’t interest you, but it gives a numerical frame of reference for limestone fracturing.
The deformation under applied pressure is called flow, and the material’s resistance to deformation is measured (in newtons). The measurement of a stone’s elasticity is called it’s Elastic Modulus (a.k.a. Young’s Modulus).
The Elastic Modulus measures the tensile elasticity, meaning when a material is pulled apart by extensional stress.This resistance to deformation is expressed in gigapascals(GPa) which are one billion newtons per square meter.
Additionally, there is Bulk Modulus, the measurement of a stone’s lithostatic (compressed from all sides) elasticity. This is expressed in Gigapascals, (GPa) or one million newton units.
And Shear Modulus, also known as the Modulus of Rigidity, in which the elasticity of a stone under shear forces is measured. It is defined as “the ratio of shear stress to the displacement per unit sample length (shear strain)”.
I gave the MPa compressional strength (loads that tend to shorten) of various limestone types in part 1.1. Note here MPa is used, or one million newtons per square meter. The elastic modulus of most limestone can be as low as 3 GPa for very impure limestone (we don’t know what was sampled), and up to 55 GPa depending on purity of the calcium carbonate. As a comparison of elastic modulus: Dolomite (limestone with a magnesium component) typically ranges between 7 to 15 GPa, while Sandstone typically runs 10 to 20 GPa.
General Limestone Modulus Ranges (the range of deformation before fracture)
The strain rate is important: which is expressed as elongation over time (e/t). The longer the period of time, the more the material can “adapt” to the strain. The faster the stress is applied exceeding the plastic elastic limit, the shorter the plastic region. The plastic region fracture where the material breaks and is considered brittle behavior.
Brittle materials can have either a small (or a large) region of elastic behavior, but only a small region of ductile behavior before they fracture.
Ductile materials have a small region of elastic behavior and a large region of ductile behavior before they fracture.
From Strain to Total Failure of Stone
The description of how stone reacts to crushing pressures reminds me of those submarine movies, where the hull is slowly being strained with a chorus of creepy groaning sounds, rivets popping and water spraying from leaks in the hull. In the laboratory, geologists study stones they crush, in order to understand what has occurred to rock materials over hundreds of thousands, to several million of years.
Infinitesimal strains refer to those that are small, a few percent or less, and is part of a mathematical approach material that is “assumed to be unchanged by the deformation” (Wikipedia). As deformation increases, micro-cracks and pores in the stone are closed and depending on the orientation of the pores in relation to the direction of the stress, this can cause the stone to begin to deform in a coaxial manner. This non-linear deformation is obvious in weaker or more porous stone.
While in the elastic region, stone adjusts to the pressure applied to it. Micro-cracks don’t appear in the stone until it reaches the 35%-40% way-point in elastic region. At this point structural strain is largely recoverable with little damage. At 80% of the elastic limit, micro cracks are developing independently of one another, and are evenly dispersed throughout the stone’s structure, despite the fact that the stone is at maximum compaction with no volume change. As the stone nears its elastic limit, micro-cracks are now appearing in clusters as the their growth accelerates in both speed and volume. The stones appearance and size remains intact as it passes its peak strength, although the structure is highly disrupted. The crack arrays fork and coalesce, as they begin to form tensile fractures or shear planes, depending on the strength” of the limestone.(1) The rock is now structurally failing, and considered to have undergone “strain softening”. Additional strain will be concentrated on the most fractured, weakest segments of the stone, creating strain and shear planes in these specific zones, which as it nears the fracture point will essentially become two or more separate stones, ironically bound together only by frictional resistance and the stress that divided them. information source: Properties of Rock Materials, Chapter 4 p.4-5, (LMR) at the Swiss Federal Institute of Technology, Lausanne
The Bottom Line on the Fracturing of Limestone
The truth is that we don’t have any records detailing the condition of the limestone base that lies below the topsoil. Certainly the limestone base has been exposed often enough over the past century, that had some academic organization wanted to catalog this kind of information, there would now be a large database to refer to by now. Moreover this would be a substantial advance in the knowledge of how to farm these vineyards. Today, the most progressive vignerons are now making these inquiries themselves, digging trenches to find out what lies below in order to make the best replanting and farming decisions possible. But it is unlikely that even these recent efforts are being catalogued, as they investigated.
Vineyard Development: Limestone
Limestone fracturing and shallow soiled vineyards
Since deeper soils do not require the vine to penetrate the bedrock in order to have a successful vineyard, fracturing there is not required for vineyard vitality.
However any vineyard where there is shallow soil, the limestone below must be compromised structurally, to some degree, for the vines to penetrate the stone. In this way, the vines themselves are a contributor to mechanical weathering of stone in the vineyards. Limestone varieties with a high percentage of impurities, are typically more easily fractured; although they may actually be soft enough, or porous enough stone for the vines to penetrate on their own. It is documented that composite formations with heavy fossilization (like crinoidal), or clay content (like argillaceous limestone) are less elastic than purer limestones with high levels of CaCO3, and are much more friable. You can read about limestone construction in Limestone: part 1.1.
With a harder stone, would significant ductile deformation with fissuring make the stone weak enough for the vine roots to penetrate? Or does a limestone based vineyard need to be significantly fractured before vines can sufficiently take root? That answer to this question is not apparent with the information available at this time, but the answer is probably yes.
Vineyards like Mazy-Chambertin and Ruchottes-Chambertin give evidence that the more brittle Premeaux limestone (with its lower compressive strength, and higher porosity), if fractured enough, can support vineyards, despite there being very shallow topsoil. There are a number of linear, east-west oriented, limestone outcroppings in these two vineyards, indicating this area has seen significant compressional stress to the bedrock there over the last 35 million years, in addition to the tensile faulting caused by extensional stress that created the region. These two stresses would have created vertical dip joints, and horizontal, strike joints, and very possibly diagonal oblique joints, and fissuring in the bedrock. Enough for the vines to survive well enough for these two vineyards to be awarded grand cru status in the late 1930s.There has been a question in my mind whether Comblanchien, which is so dense that water cannot penetrate enough to effect freeze thawing, and is also very elastic due to its 98% calcium carbonate content, would fracture enough in a vineyard location to support a vineyard in shallow soils. In fact that has been a driving question throughout this piece, and which I was inclined to believe the answer was no, until evidence proved otherwise. Apparently that has happened.
The Rise of Colluvium
In terms of vineyard soil development itself, geologic pressures have worked extensively to prepare the limestone bedrock. Primarily with extensional stress, but also exerting compressional stress, the strain significantly weakened and fractured the limestone bedding. This deformation and the ensuing fracturing allowed water to infiltrate its cracks and crevices. During periods of cold weather it would freeze within the fissuring, causing frost wedging. Exfoliation would ensue, ultimately causing significant limestone debris to be pulled away by gravity, itself a powerful force of mechanical weathering, to slide (and tumble) down the hillside. As the stones fell, they would further break and abrade into yet smaller pieces. Abrasion is another agent of weathering. There they would stop at the curb of the slope, where eventually they form deep, limestone-based “colluvium” soils. This is what Coates is speaking of when he wrote “rock and more limestone on the section closest to the over-hang, and there is some sand” in Amoureuses. These are the colluvium soils that would with enough time would generate the vineyards upon the the red grand cru vines of the Cote de Nuits would grow.
But first, the story of chemical weathering would have to play out, creating clay and soil needed to feed the vines. The slopes of the Cote d’Or would slowly evolve geologically for millions of years, awaiting the arrival Roman agriculturalists who would recognize and exploit the vinous wealth of this thin strip of the hillside.
Next up: Part 1.3 Amoureuses and Parallel Evidence of Shallow Soils over Comblanchien
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(1) Because it is often difficult to distinguish between the different types of fractures and faulting once the fracture has occurred, I will leave it at this. There are 3 kinds of fractures born from the three major stresses: Shear, tensile, and extensional.
(2) I have not been able to determine if crystallization is a definition of Comblanchien limestone, or if the Comblanchien limestone in the villages Corgoloin and Comblanchien just happen to have been metamorphosed into marble, and that is why it is quarried there.
As the Burgundy legend has it, it is the limestone that sets Burgundy apart, and makes the wine that comes from there so special. But what does all of this limestone really do? Does it impart flavor, as some people say, imparting a minerality, or does it create a perfect growing condition for the vines? How does it interplay with what is possibly the most important component of farming, the clay, and what is its relationship with the limestone? Then there is the scree, or gravel, intermixing with what geologists sometimes refer to as colluvium. Together this makes soil, but how it got there, and how it is changing perhaps most important. The forces of erosion that constantly tear down the geological structures with its wind and rain and freezing temperatures. This is where the rubber meets the road of terroir, and I will look at all of these factors quite carefully over the next few writings. But first, for Part 1.1, it’s all about the formation and types of limestone that makes up the escarpment.
From the beginning
We typically think of hillsides as being pushed up, and indeed the hills of the Hautes-Cotes de Nuits were formed by folds in the sedimentary bedding. But the Cote itself was formed when the Sôane Valley was pulled down and away from the Côte d’Or Burgundy 35 million years ago by a large fault that runs near the highway RN74, as the Saône Valley dropped away as a graben. The Côtes d’Or is actually the broken facewall of the horst. But before that, the story of Burgundy started with a sea, teeming with unbridled marine life.
Just how much marine life has impacted this planet is represented by the vast majority of limestone formations that have grown here, constituting 10% of the total volume sedimentary rock, which represents 75% of all geological formations. Most limestone is credited to biologically produced calcium carbonate that is naturally extracted from eroding shells sea animals. Shell production, for defense against predators, began in the Cambrian period (500 million years ago.) This occurred with a change in the ocean chemistry which allowed the calcium compounds to become stable enough for allow for shell production. While at the same time (give or take a few million years), the animals adapted through mutation, to produce the needed proteins and polysaccharides, and the ability to produce shells for protection against predators. The success of this new animal life led to an explosion of species, and the warm shallow seas that covered central France were densely populated. The seas of the Jurassic period were filled with calcium producing crinoids, ammonites, oysters, and as corals. As the exoskeletons of generations dead sea creatures accumulated on the seabed, eroding, the waters filled with high concentrations of calcite and (or) metastablearagonite, (depending on the water chemistry of the period), where it precipitatedinto a thick, jelly-like solution at the bottom of calm lagoons and shallow seas. Eventually, this layer would solidify and compression would indurate (or harden) the (CaCO3) into limestone. Non-marine limestone is less common, with calcium being deposited in a location by the water, or calcium carbonate can accumulate at the bottom of lake beds, forming limestone.
Calcium carbonate is soluble in groundwater containing relatively low acid levels and is responsible for the chemical weathering that forms limestone caverns and sinkholes. Interestingly, the calcium carbonate in limestone is more soluble in low-temperature environments than in warmer tropical climates that it began in. In a cycle that will likely continue during earth’s lifespan, limestone is formed, and then eroded (and been transported) by groundwater, to reform in another location. Limestones are sedimentary rock formations that contain at least 50% calcium carbonate in the form of calcite and or aragonite. The higher the percentage of calcium, the harder, the less porous, and more water-resistant the limestone becomes. Even the hardest limestone of Burgundy contain at least some silica, which after the chemical weathering of limestone becomes phyllosilicate minerals, the primary element in clay. However, the higher the percentage of silica and other impurities renders a stone that is more porous and more easily friable (the ability to fracture or crumble) It is my belief that it was these impurities that have allowed Burgundy to become the great growing region it is today. Had all the limestone been the pure hard Comblanchien that the region is so famed for, I suspect there would not have been enough viable, arable land to have any significant grape growing area. But that is supposition on my part. Back to more fact-based information.
There are a number of common limestones in Burgundy, each which contain varying percentages of calcium and differing levels of impurities. The harder limestones are typically named after the towns that they were quarried for building materials, while softer, non-commercial limestones can be named for their fossilized sea life contained in them, or by the shape of their construction. Don’t be confused by names like Bajocian limestone and Bathonian limestone: these are not types of limestone, rather they are periods of time within the Jurassic when the limestone was formed. It is easy to be confused. I recently read this snippet from a knowledgeable, professional wine critic trying to explain the geological differences between the Côte de Beaune and Côte de Nuits. They wrote “…the Comblanchien limestone to the north and the Jurassic rock formation to the south…” apparently unaware that Comblanchien is a limestone formed during the Jurassic period. I mention this only because it highlights the confusion even highest-level of wine professionals have about terroir and the geology of Burgundy.
Limestone Types (that you may read about)
Calcaire: The fact that English speaking wine writers use the word calcaire, is simply confusing to almost everyone trying to actually learn something. Calcaire is nothing more than the French word for Limestone. We say limestone, they say calcaire.
Comblanchien is a name bandied often by wine writers as if it is an attribute in a wine’s character. But the facts point to this stone having a negligible if any effect on the vines grown directly above it. Comblanchien is 99% pure calcium carbonate, often giving the stone a white color. As a building material that is commonly referred to as ComblanchienMarble. It is so dense and fine-grained that it can be polished. It can be white (clair), beige, or slightly pink.
Comblanchien formed from still water lagoons that were hyper-rich in calcium, and relatively void of sea creatures that would cause impurities. Presumably, the calcium solution was so concentrated that sea life did not live there, and generally did not disturb the (CaCO3) sludge in the areas where Comblanchien was forming. The spots in Comblanchien are not fossils or impurities, but the trails of worms that wiggled through the thickening lime ooze. The hole made by the passing worm was then filled by pure, clear calcium carbonate, and like a glue, it cemented the whole into a solid, amazingly dense block of stone.
Most defining in its role in terroir picture is Comblanchien’s exceptionally low-level of porosity. The stone virtually does not absorb water so it will not crack when frozen. Vine roots cannot penetrate Comblanchien if it has not already been fractured, which tends not to happen since it is so water-resistant. Where a vineyard grows over Comblanchien, (1) there is a need for a deep layer of topsoil for the vine roots to inhabit. Where Comblanchien reaches the surface at the top of the vineyards in the Gevrey-Chambertin, no vines are grown (or can grow?) A strata of Comblanchien sit at the top of the Côte de Nuits‘ vineyard as a cap rock, and it’s hardness and resistance to decomposition keeps the hill above from eroding. The result kept the depth of vineyards there, (this is particularly evident above the grand crus of Gevrey) in a very narrow band An opposite example would be the Côte de Beaune. In Beaune the cap rock (if in fact there is one) is much softer. Because of that, the hillside is eroding at a much faster rate, a creating lower hill lines and much deeper (east to west) growing areas. Off topic, but not have to rehash this later, writers often contribute Beaune’s faster erosion rate to its younger limestone makeup (mid-Jurassic compared to upper-Jurassic which younger), but I believe it is the impurities or the porosity of the limestone, not the age (curing) of the limestone, are the factors of its faster erosion.
Premeaux is another hard limestone used in construction, but it is not quite as hard as Comblanchien. I have not found any reference as to how much calcium carbonate is in Premeaux Limestone, but as evidenced in this photo, it does crack and fracture. This is due to the fact that it will absorb 12 to 18 times more water than Comblanchien, which when permeated, then frozen, will crack stone. Premeaux, unlike Comblanchien limestone, is found at very shallow depth under vineyard land, most notably the Grand Crus of Ruchottes and Mazy-Chambertin, where in places the vineyard was dynamited in order to allow the plants to gain a foothold.
Premeaux technical statistics: Water Absorption: 6-9 By Vol.% Compressive Strength: 120-180 MPa Density:2400 – 2500 kg/m3
Crinoidal Limestone is closely associated with the Bajocian period and is named for the Crinoids that team its construction. Crinoids are multi-armed sea creatures that are filter feeders. Anemones, starfish, and urchins are among the 600 species of Crinoids found in today’s seas, but during the middle Jurassic there were many times more species, and they densely populated the shallow lagoons of Burgundy. Crinoidal limestone is friable, meaning it can be broken or crumble, because of its heavy fossilization. The hillside of premier crus, including Lavaux, Estournelles and Clos St Jacques in Gevrey-Chambertin is entirely made of crinoidal limestone. This formation continues above the Route de Grand Crus, underneath Chapelle, Griotte, Latricieres, Charmes-Chambertin, as well as the lower half of Chambertin itself and Clos de Beze. To my mind, this is ample evidence that Crinoidal limestone is one of, if not the finest limestone for growing vines.
Oolitic Limestone formations are unique and fascinating composition. Oolites are formed of oval calcium pellets called ooids that gained their shape as they were rolled around by the wave actions the ancient Burgundian seas of the Jurassic that are super-saturated with calcium carbonate. The ooid spheres begin with as a seed, such as a very small shell fragment, and as this seed rolls around the ocean floor, it chemically attracts layers of calcium to it from the water. The size of the individual oodid corresponds to the amount of time they had to form before they were covered by dirt. While the word ooid typically refers to forms made from calcium carbonate and aragonite, the name means egg so the name ooids can be used to refer to other materials in the same small oval shape. These ooids bonded under a secretion of a calcium cement forming the stone. The grand cru Ruchottes-Chambertin is famous for the ooids found it its topsoil, and presumably oolitic limestone formations are there also along with the more prevalent Premeaux limestone.
Nantoux is an oolitic limestone is named by the late geologist James E. Wilson as being the stone that was once quarried in and above Meursault- Les Perrieres. Named after a village nestled in a valley above Pommard, it appears on Vannier Petit’s Pommard map, just north of the village, very low on the slope. She labels it as an oolitic stone, Wilson gave no details of the stone other than its former quarry location. I have seen no other reference to Nantoux other than these two brief references.
Other limestone types that rarely, if ever, appear in writings. Of the more common: Chassagne and Ladoix both appear on Francoise Vannier-Petit’s Pommard map, but there is little reference to them elsewhere. Both stones are available commercially as building materials, and both stones have pages dedicated to them on the Contactstone.com website, listing these stones density, strength, and water absorption similar to that of Comblanchien. However, they list Ladoix being an alternate name for Comblanchien limestone (as well as an alternate name for Corton Limestone), so it is not clear what the differences actually are at the geological level.
Argillaceous Limestone consists of larger amounts of clay, often making them quite soft and friable. In many ways, it is like a hardened version of marl. The stone may appear silvery due to the substantial amount of clay component. The vineyards of Chambertin and Clos des Beze both have sections in the heart of those vineyards that is made up of argillaceous material, as well as the lower third of Lavaux St-Jacques and Clos St-Jacques. Vannier-Petit labels these sections as Calcaires Argilleux (Hydraulique) on her Gevrey map which can be found at www.joyaux-cotedenuits.fr/
Bioturbated Limestone is not actually a limestone but a disturbance to the forming stone that before it completely set. Whether calcium deposit was disturbed by an animal, a wave, or geologic action, churns the curing material. This agitation, or Bioturbation, creates weakness in the limestone and can cause it to be quite friable depending on the impurities and the amount of disruption to its structure.
Travertine is not a maritime derived stone. It is a terrestrial calcium carbonate formation that is created by geothermally heated springs. Travertine is a very porous stone (that is filled and sealed by the stone industry for use in construction), and that porosity is caused either by calcium dioxide evasion or by organisms that have grown on the stone’s surface. As far as I am aware there are no Travertines in Burgundy.
Tufa is a calcium carbonate formation similar to Travertine, but Tufa is even more porous due to its large macro biological component. Tufa has no relation to the volcanic rock Tuff, which is often referred to as “tufa”. As far as I am aware there are no Tufas of either sort in Burgundy.
Marble is a limestone that has undergone a major geological event involving high pressure and or heat. In this process, limestone carbonate materials are recrystallized, very commonly calcite or dolomite. The colors in marbles are from the metamorphosed impurities in the stone that have become new minerals.
This hopefully gives a fairly detailed overview how limestone was created, and how susceptible it is to damage. In Part 2.2 I’ll look at how this limestone has been fractured and eroded, creating the basis for what would, over millions of years, become great vineyard land.
Up Next: Understanding the Terroir of Burgundy, Part 1.2 Limestone deformation and fracturing. (click here)
Previous: Understanding the Terroir of Burgundy, Introduction(click here)
Despite the scores of books written about Burgundy, if you really break down what is being written specifically about each climate, the information can be pretty sparse. For a handful of the greatest vineyards, extraordinary efforts are made to explore the grandness of these few plots.(1) However, these vineyards probably represent less than one half of one percent of Burgundy. Little coverage is given to the physicality of the rest of Burgundy’s sites,including many highly-regarded premier crus. Beyond listing most vineyard’s size, what the name means in French, sometimes an inane fact (like some wild bush used to grow in that spot) and who the top producers are, most crus don’t seem to warrant the effort. How does Puligny’sLes Combettes differ from LesChamps-Canet, which sits directly above it? It is not likely you find the answer by reading a book about Burgundy.
Of these vineyard entries, writers typically ignore the soil makeup and limestone below;the most primary elements of terroir. Perhaps this is due to a lack of information. (2) However,I have no doubt that if as much effort was given to researching these appellations as is given to tasting Armand Rousseau’s latest barrel samples, we’d have a lot more understanding about Burgundy than we do today. Typically when a comment regarding a particular vineyard’s soil is made by a wine writer, it is simply as a notation, with no connection to the style of wine that comes out of that vineyard. It sits there like a pregnant pause, as though it were quite important, but no explanation follows. And that explanation is what I hope to supply by my upcoming article. I can’t do what the top wine writers can: go to Burgundy and walk the vineyards with the winemakers, talk to the professors at LycéeViticole de Beaune. But I wanted these answers for myself; what it all that means the limestone and “marl” and clay, and what did for the wine. If I could. Did I dare?
While I am critical of the much of the wine writing produced – for its lack of deeper educational and intellectual content, I understand that wine writers must produce what consumers are willing to pay for. We are a consumer-driven society, and readers are really looking for buying guides wrapped up in a little bow of information. The capitals of 19th century Europe were famed for their starving intelligentsia, but no one wants to scrape-by in a land of plenty, regardless of how romantic. Wine writers write what the public wants.
After more than a year of researching Burgundy vineyard information for the marketing part of my job, I thought I could do a quick write-up about the terroir of Burgundy. I had come to some interesting conclusions and felt I could write a piece with a unique perspective on vineyard orientation, slope, the general soil types determined by that, and how it all relates to a wine style.
It was all going along quickly and easily until I wanted to clarify a couple of points about geology. What had initially looked like a weekend project, has taken 9 months of daily work. This article has become something of a Leviathan, but the exploration has taken me to uncover some enlightening information, as the pieces started falling into place. The original piece first became two parts, and ironically, now it is four parts, each divided into articles of a more manageable size of 2,000 to 4,000 words. The result of this is untold hours of research and writing.
Unfortunately, sections of Part One have ended up being so technical that I no longer really know who will want to read it. Any hope of an audience is slim. Most wine professionals are so burnt by the end of the week, that they would rather paint their house than read about wine. However, this is a unique article that looks at the breadth of the factors that influence vine growth in Burgundy and ultimately influence wine character.
A Path of Discovery and Frustration
One of the first surprises was difficulty justifying the satellite images with some of the vineyard maps that I had been so diligently studying. Sometimes they just didn’t look like the same place. The vineyard maps often gave little sense of topography of the hillsides, despite paying particular attention to the elevation lines. I believe that the amount of slope in vineyards that are not terraced, like in Burgundy, is critically important to the profile of a wine.
What looked like roads on a map, at times were not, and in many places, there were entire sections which were shown as vineyard were actually unplanted, inhabited only by trees, scrub or rock. This I found to be very illuminating information regarding adjacent vineyard land, and how that might define a wine’s character. At times, the shapes and sizes of vineyards depicted on maps appeared to be different from the photos, perhaps changed to fit the artist’s needs. After a while, I started making my own maps using Google Maps’ satellite images and adding the information that I found relevant to the needs of my job. Perhaps the most telling visual information has come by utilizing Google Maps’ street view, to see a vineyard and its slope, the topsoil, quickly and easily, and often from multiple angles. It is an amazing tool, I highly recommend using it in addition to maps when studying wine regions.
Am I a Skeptic or Just Paranoid?
I noticed that the information I was reading, from multiple sources, wine writers, importers, etc, was all starting to seem repetitive, using similar wording, ideas, phrasing. Increasingly, the information seemed more and more borrowed, shallow and canned. For instance, it is common for a writer to state that a vineyard is “a mix of limestone and marl” or the vineyard is made up of “marly clay.” And then there was this from one of the definitive Burgundy reference books regarding the soils of Mazy-Chambertin: “there is a lot of marl mixed in the with the clay and limestone.”
Marl is generally defined as a mix of clay and limestone. When they refer to limestone in this fashion, they don’t mean solid stone, they mean rock that has been mechanically eroded, of varying sizes (from a fine sand to fairly large stones) that are mixed into the soil. The ratio of these two major elements of marl can be a range of 35% of one, to 65% of the other. (3) The more I read, the more I question what I am reading. (4)
Below is an example kind of “soil information” that I’m talking about. At first blush, the passage below sounded like I’d found the holy grail of explaining what kind of soils for which Pinot and Chardonnay were best suited, but later I realized it was anything but. The following was written by an authority on the subject.
“•Pinot Noir flourishes on marl soils that are more yielding and porous, that tend towards limestone and which offer good drainage. It will produce light and sophisticated or powerful and full-bodied wines, depending on the proportion of limestone, stone content, and clay on the plot where it grows.” “•Chardonnay prefers moreclayey marly limestone soils from which it can develop sophisticated, elegant aromas in the future wine. The clay helps produce breadth in the mouth, characteristic of the Bourgogne region’s great white wines.”
With the Pinot, he starts off well. Marl (a combination of clay and limestone in varying percentages) with very high levels of calcium carbonate(limestone) is has a correspondingly high-rate of infiltration by rainwater. And he is right again as he writes that the weight of the wine is dictated by the “proportion of limestone, stone content, and clay on the plot where it grows.”
The problem occurs when he tries to differentiate the conditions in which Chardonnay thrives. “Chardonnay,” he writes, “prefers more clayey marly limestone soils from which it can develop sophisticated, elegant aromas in the future wine.” If we compare the soils and bedrocks of the finest Pinot and Chardonnay vineyards, there are tremendous commonalities, and both varietals seem to flourish on the same soils. Every aspect of what he said about Pinot equally applies to Chardonnay. Second, as marls increase in their clay content (which is what he was trying to say with the utterly confusing description of “clayey marly limestone soils“), these denser soils, which typically occur at the curb of the slope, are still capable of excellent drainage. We will look at this in depth later, but for an immediate explanation see below (6),
To make this passage more accurate, he should have led with drainage. The porosity of the soil allows drainage: in other words, it has a causal effect of good drainage. It is not an axillary attribute as he suggests when he writes “and which offer good drainage.”
Secondly, it seems that the writer is suggesting that Chardonnay does not do as well as Pinot Noir in porous limestone dominated soils, and vice-versa. I believe vineyards like Les Perrières in Meursault, that have very poor, and very porous, limestone soils, with little clay content, contradicts that notion. Additionally, in Chassagne Montrachet, Chardonnay has replaced much of the Pinot Noir on the upper slopes of the appellation, while Pinot Noir has remained in the heavier, clay-infused soils lower on the slope.
“Now every piece of information had to pass the smell test, and preferably it needed to be corroborated by another source, that clearly wasn’t of the same origin.”
I plodded on with my inquiry. Now every piece of information had to pass the smell test, and preferably it needed to be corroborated by another source, that clearly wasn’t of the same origin. I had read enough to identify “family trees” of bad information, and I often believed that I could often identify the original source. Just how easy it is to pass on incorrect information is illustrated by this next example. I found an error (in my opinion) in one Master of Wine’s book on Burgundy, saying that the “white marl” of a vineyard was found on the upper slope, producing a richer, fuller wine, and while the calcareous (limestone) soils were down below, and produced a lighter wine. It was an obvious mistake if you just thought about it for a second, as the forces of gravity and subsequent erosion drive clay to the lower-slopes where it reforms via flocculation. Later I would find the same information, but in more detail, in another Master of Wine’s article, again containing the same error.(6) The source of the error was either a mistranslation of a conversation with a vigneron or a typo. While this is a simple mistake, having two of our most revered Master of Wines citing the same information can only confuse an already misunderstood subject, even further. I can envision a whole generation of Sommeliers reciting that the upper-slope of Les Caillerets produces heavier, more powerful wine than sections of Caillerets farther down the slope.
It was clear I wasn’t going to find the answers I was looking for in the English language Burgundy books I had access to. Ultimately my questions would become more and more specific, pushing my inquiry of terroir to an elemental level – delving into the construction of the earth and stone, and how it breaks down, and how it might influence the wine we ultimately drink. I still have a tremendous number of questions that will simply go unanswered for quite some time,(7) either due to the lack of research, or that this information is not available in an accessible, English-language format.(8)
Part One of the article is the result of searching out, reading, and trying to understand small, maybe inconsequential details. Since I’m putting it out there on the internet, I have made a concerted effort to attempt to get it right. Obviously not a geologist, so despite reading about clay and clay formation dozens of times, from dozens of sources, the complexity of the science makes it easy to over-simplify, to misunderstand it, and definitely, easy to misrepresent. Making this process more difficult, I could find no articles that (for instance) were specific to the clay and clay formations of Burgundy. (9)
It’s not sexy reading, but I’ve done my best to pull it all together into one place. If nothing else, I hope this can be a jumping off point for others to research, and expand our cumulative understanding of terroir.
(1) Even with the top vineyards, publications heavily link the greatness of the wine to the producer, rather than the vineyard. The mantra for the past 30 years has been: producer, producer, producer. Whilethere is a historical reason for this producer-driven focus, I feel the vast improvements in viticulture and winemaking knowledge over the past two decades, coupled with the concurrent global warming, has changed the paradigm and significantly leveled the playing field between producers. There are now much smaller differentials in quality from the top producers and the lower level producers. I feel that the focus should now return to the vineyards of Burgundy, each with a distinct set of characteristics due to its orientation, slope, and soils. Nowhere else in the world is this kind of classification so rigorously defined. And because of that, nowhere else in the world is this kind of ‘study’ possible.
(2) The mapping of Limestone has never really been done before the geologist Francoise Vannier-Petit began her work a number of years ago. She has now mapped Pommard, Gevrey, Marsannay, and Maranges, for the trade associations that have been willing to pay for her services.
(3) The fact that mud/mudstone (and this is substance is sometimes referred to as shale) is introduced as a term by Wikipedia, see table certainly confuses the issue, but they also indicate that this mud is a clay element.
(4) To give credit where credit is due: When I first started doing an overview of our producers, I had summarized this idea, (Pinot liked preferred limestone soils and Chardonnay preferred more clay-rich soils.) My boss, Dr. George Derbalian (with his background in failure analysis) looked at the statement and said, “I don’t know about that.” He asked where I had obtained this information, and when I couldn’t immediately produce the source, he warned: “You have to be very, very, careful about these things. As an importer, we have to be completely sure we are right when we say something. I would like to remove this sentence.” I thought he was being over-reactive at the time, and 100% accuracy wasn’t important for the marketing piece I was working on, but later, with much more research under my belt, I would revisit his words with far more respect.
(5) The word marl has a very poorly defined meaning because it is a very old word that was used somewhat indiscriminately. Wikipedia lists marl as a calcium carbonate-richmud with varying amounts of clay and silt in their of the definition. To make matters more confusing Wikipedia’s definition of mud says it has clay in it. Is mud part of marl? Is clay part of mud? Does it really matter?
6) This is for two reasons: first, because of the shards limestone, in the soil, weathering of that material by rainwater produces an abundance of freed calcium. This is sometimes referred to as “active” limestone. This calcium, which is mixed by plowing with the clay, misaligns the platelets in clay causing the clay to lose its plasticity. This misalignment greatly increases the infiltration rate (IR) of water through the clay. So while clay alone has very poor IR’s, clay that has been mixed with calcium has much-improved drainage. The second reason that these richer marls, meaning an equal or higher percentage of clay than limestone in the mix, produces richer wines is there is more root space in the vineyards which our author is writing about, (ie le Montrachet and Batard-Montrachet). This occurs because of the location in which clay increases in the soil, happens in places where the slope is leveling off. These locations are where gravity has sent the hills colluvium. Here is where the hillside’s scree, sliding down, due to erosion or from man’s working the land, sits, and upon it, water runoff and gravity have sent the clay, eroded from the hillside above, to this same spot. This convergence of higher proportion of clay in the topsoil and limestone colluvium, together, provide a deep, rich soil that has excellent drainage for the level of slope. Of course, we will get into the science of this in much greater detail, later.
(7) The quote from the second Master of Wine’s write up of Les Cailleret. I have added the (er) to here to make the passage more clear. “Up at the top of the slope, there are outcrops of bare rock. He(re) we find mainly a white marl. This will give the wine weight. Lower down there is more surface soil and it is calcareous, producing a wine of steely elegance. A blend of the two, everyone says, makes the best wine.”
(8) The list of questions I have that don’t have answers seems limitless. Here are my top questions with no answers at the present: 1) How pervasive is is the fracturing of limestone in the top crus, 2) what kind of limestone is it? 3) does the limestone there to fracture and is thus friable? 4) how much water do these limestones hold? 5) how much groundwater is available to the vines? 6) How does the groundwater circulate, and 7) how quickly through different types of soil? 8) Where are the faults in the various top climates, 8) are the faults often at the boundaries dividing limestone types? 9) how deep are the drop-offs (covered by the topsoil) created by the various faultlines?
(9) The University, LycéeViticole de Beaune is likely to be active in this kind of research, but so far I have not been able to access what might be available, and correct translation from French to English can be problematic if it isn’t done by the author who wrote it, and many times more so if using a translating program (software).
(10) Therefore I’m unable to discuss the types of primary clays, called kaolins which may have formed there, in situ, instead focusing on transported clay that has been derived from the erosion of limestone of the vineyards, called Chlorites.