In trying to understand the effect of ‘terroir’ on the wines of Burgundy, only ‘clay’ has been a keener form of frustration than ‘marl’. But that isn’t because marl is a difficult concept to grasp, but rather because few wine writers seem to really know what marl is. The word is thrown around, even by people regarded as experts, with such seeming abandon, that almost anyone who attempts to understand the word can be hopelessly confused.
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 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.(1) This would be fairly simple, but Wikipedia lists marl as a calcium carbonate-rich mud with varying amounts of clay and silt.
Deep into researching vineyards, I began to realize that much of the information I was reading on soils, (and particularly about marl) was sounding borrowed, shallow and canned. I’ve seen marl written of in myriad ways including that a vineyard had “a mix of limestone and marl” or the vineyard is made up of “Marly clay.” This one, from one of the more definitive of Burgundy reference books, stated that the soils of Mazis-Chambertin have “a lot of marl mixed in the with the clay and limestone.” But the prize of goes to this gem that spoke of “clayey marly limestone soils”, written by an authority on the subject.
“Chardonnay prefers more clayey marly limestone soils from which it can develop sophisticated, elegant aromas in the future wine.” –unnamed author
Since we already know that marl is a mix primarily of clay and limestone, you don’t have to think very long and hard to see this statement is contradictory at its core. A soil can be a clay-heavy marl or a limestone-dominate marl, but it can not be a “clayey marly limestone soil.” All this kind of language does is confuse a difficult subject, and make Burgundy more inaccessible to students of this already arcane subject.
I am not alone in this criticism. On researching marl and clay, I found this article “On marls and marlstones” by geologists Stephen K. Donovan and Ron K. Pickerill that confirmed I wasn’t going completely off base.
“As enthusiastic editors, we cringe whenever we trip over lax use
of terminology and language that authors make, repeatedly, in the
geological literature. We have over 50 years editorial experience
between us and present this note as a brief suggestion for wider
consideration. We have commented on the subject of this paper before
(Pickerill et al., 1998), but, sadly, identifying the disease hasn’t
facilitated the cure, at least so far.”
I could go on and on, and in fact I have. Visit my long 2600 word post: Preface to my upcoming article: “Understanding the Terroir of Burgundy”) for more. Some of the above is excerpted from that post.
(1) 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.