Burgundian Rocks

The Burgundian sensibility is naturally obsessed with rocks.   What is valued is the celebration of difference - how one place, for whatever reason, produces wine that has certain features every vintage that distinguishes it from a wine produced from any other place, even from land directly adjacent. Those who have caught the terroir “bug” seek to understand within available limits the reasons for these distinctions.  And the most evident starting point for doing that is to understand the soils and bedrock in which the vines take root. Hence the obsession with rocks.

Although it would be fabulous if I could find the time to study this geology as a subject in detail I am resigned to having to do the best I can with the available published sources.  Fortunately there are now several useful books on the subject of the rock strata of the Cote d’Or and we now finally also have Francoise Vannier Petit’s extraordinary and long overdue visual depictions of what lies underneath the most important vineyards of Burgundy.

As an illustration of how these graphics bring this subject to life, below is a depiction from Francoise Vannier-Petit, showing the outline of the Grand Crus of Gevrey and their underlying bedrock.  

One point I would recommend to those just starting out is to be precise in use of language. There is soil - in several distinct layers but normally at least two - and then there is bedrock, being the deepest relevant material the vine can (in some cases) penetrate.  Soil and bedrock are of course not the same but these terms are too often used interchangeably - so when people loosely talk of “soil” they often really mean the bedrock and vice versa.

The other point to make at the outset is that there is still a remarkable absence of consensus as to what bedrock actually lies under particular vineyards or parts of vineyards in Burgundy.  The sources are very inconsistent when you get into detail.   And even now that we have Francoise Vannier-Petit’s excellent pictograms, the accuracy of even these representations is disputed by some growers of noted repute who have been farming their vineyards for more than four generations. So not all is definite or universally agreed.

The laying down of the bedrock

All limestone is formed by the land having previously been under water.  Lime is deposited in various forms at the bottom of these seas and is pressured over an unimaginably long time to form differing types of limestone of various composition, purity and hardness. Broadly it takes a million years to create 10 meters of sediment rock. This is so for the Cote d’Or, the relevant rock formations of which were laid down below waters of varying depth from about 165 to 150 million years ago, spanning the Bajocian, Bathonian and Callovian stages in the Middle Jurassic series and the Oxfordian stage in the more recent Upper Jurassic series.  These seas varied in depth and turbidity/ wave motion, which influences the type of sedimentation. There were shallow lagoons, shores and beaches as well as places and times when the waters were deeper.  As an example it appears that the waters that formed the Cote de Nuits strata experienced a ‘wave motion” before a quieter ‘lagoon period”, whereas in the waters that were above the Cote de Beaune that sequence was reversed. This is of course results in different layering of strata in different locations. To illustrate, broadly, the crinoidal limestone layer of strata would have been formed when the seas experienced significant wave acton - presumably deeper waters - whereas the ostrea accumulata layer results from sedimentation in calmer, shallower and more sheltered waters. Since at the periphery there was always some land above the water - including part of what is now called the Massif Central - differing degrees of mud from rivers flowed into these waters, impacting the purity of the limestone sedimented.

The sea  retreated 65 million years ago during the Tertiary Period as pressure from the Africa plate pushed Burgundy upwards.  Some 23 million years ago there was a huge fault that created a drop on the level of the earth to the east of what is now the Cote d’Or. This depression  stretching east all the way to the Jura mountains - “the Bresse Graben”. The Soane river flowed along this fault  so creating the valley. This drop exposed about 500 meters of vertical escarpment on the eastern edge of the Massif Central - the plateau that dominates the center of France. Then came the Glaciers of the Ice Age some 20,000 years ago, fracturing rocks and dragging debris down the hillsides.  The following warming allowed vegetation to grow and the formation of topsoil. On that east facing escarpment, much fissured and fractured, lie the vineyards of the Cote d’Or.

The types of strata 

Although when one gets into details and what exactly lies under specific vineyards there are still many question marks, it does seem worth the effort is to understand the basic characteristics of the types of bedrock that form the Cote. The key issue to grasp is that at the northern end of the Cote de Nuits the strata underlying the mid slope are very old. As we move south to the Cote de Beaune these layers sink lower and are replaced at the mid slope level by younger rock formations, which in Gevrey are present only at the very top of the slope or not at all, having been entirely eroded away. These older strata re-emerge at mid slope to replace the younger rock at Meursault. This is what is called the “Volnay Syncline” - the dip of the older rocks far below the mid slope line at Volnay and correspondingly the “Gevrey Anticline” representing the high point of these older strata at the mid slope level at Gevrey. Simplistically, the Cote de Nuits is made up of Bajocian and Bathonian limestones and the Cote de Beaune from Callovian and Oxfordian limestones.

Looking at the Cote de Nuits, from oldest (and so presumptively deepest in the strata layering absent faults and other irregularities) to youngest, I set out below the main bedrock types. I am grateful to Remington Norman’s “Grand Cru”, from which much of the below is sourced and which I believe to contains the most comprehensible description (to the layman) of this difficult topic

The Cote de Nuits (from oldest/deepest to youngest) 

1. Sandy marls - clay and limestone mix, present as outcrops only in the very north - Couchey and Marsannay
2. Crinoidal Limestone / “Calcaire Entroque” -  Part of the Bajocian set of limestones - being formed between 171 and 167 million years ago. This is an important strata formation, created by the decomposition of marine urchins - which are really lilies -  the stalks and skeletons of which contain a lot of calcium. Compressed by pressure this formation is only a narrow strip but sits under a 150m wide swarth of Grand Crus - including Clos de Beze and Bonnes Mares and well as many sites stretching north from Gevrey. On the Vosne side however it has started to bury itself deeper to be replaced at the critical mid slope level by younger strata.  
3. Ostrea Accumulata Marl  - Also from the Bajocian period this is made up of oysters accumulated in mud. Very friable and subject to erosion.  In Gevrey it appears only very high on the slope - by the forest but it underpins the upper part of Bonnes Mares, Romanee Conti and La Tache.  An extremely important layer.  
4. Shaly Limestone.  This looks like horizontal layers of slate but is almost yellow in color.  More limestone than marl / clay in composition. Apparently at mid slope in the southern end of Vosne and, for example in Nuits Boudots, consistent with the gradual sinking of the older strata as one moves further south.  
5. Premaux Limestone - Part of the younger Bathonian period - being 167 to 164 million years ago - unlike all the strata referred to above, this rock is extremely hard - being formed of limestone rich mud under high pressure from the strata above. It is pink in color.  It is very prevalent at the higher levels along the whole Cote de Nuits - from Ruchottes Chambertin through La Tache
6. “White Oolite” - Also Bathonian,  this is created in shallower (ie more recent) seas by wave action acting on small pieces of sand/debris which gathered limestone - like a pearl. The result is soft/ friable limestone that has the appearance of being made up of fish eggs bonded together.  Rests under really only the highest part of the Cote de Nuits slopes at the mid/ southern end - Petits Monts in Vosne and Mont Luisants in Morey, for example and perhaps there is some at the very top of the Clos de Beze.
7. Comblanchien limestone.  Also from the Bathonian period, this is not unlike Premeaux limestone - being formed from limestone rich mud compressed by strata above. Very pure limestone and very hard. It forms the dramatic sides of the combes in the Cote de Nuits.  As you might expect only found at the uppermost limits in the Cote de Nuits - basically is the cap rock. An exception is in Chambolle Musigny, where Comblanchien limestone inexplicably underpins parts of Les Amoureuses and vineyards on the northern side of the Combe d’Ambin, and in the upper part of Clos Vougeot and possibly above the Clos de Beze. To be viable for viticulture it really needs to have been eroded or be faulted somewhat and mixed with strata containing some clay.  

The above sequence of layering one on top of the other is to be presumed and unless interrupted, should be the natural sequence of the layering of the bedrock strata. Despite major rifting 30 million years ago, this presumption holds. But one has to understand that there are faults - and some of these can be so significant as to have the result that the strata sequence set out above is interrupted.  For example, Remington Norman asserts that Premeaux limestone is present lower on the slope than Calciare Entroque and Ostrea Accumulata in the Clos St Jacques, which inverts the historical layering sequence. And, due to faulting, what underlies the Clos St Jacques is not the same as what underlies the adjacent Cazetiers vineyard. The biggest, most visible faults seem to run north-south ie along the line of the slope. The largest one of all lies broadly along the D974, on the ‘Bourgogne” easterly side of which the soil is very deep whereas on the “Village” level designated westerly side perhaps only extending 2 or 3 meters down before you get to the bedrock. There is also a most evident and visible fault above the Montrachet vineyard.

The Cote de Beaune

Until you get to its very southern end, the bulk of the Cote de Beaune is made up of younger rock strata, the older formations of the Middle Jurassic present at mid slope in the Cote de Nuits sinking below the slope from about Ladoix.  The Cote de Beaune bedrocks are mostly from the later Middle Jurassic’s Callovian period - 165 to 161 million years ago or the Upper (ie more recent) Jurassic period known as Oxfordian , being 161 to 158 million years ago. 

Because of its less compact shape and greater expanse, articulating succinctly the Cote de Beaune’s rock formation is difficult and the available sources, on my reading, are less clear as the the exact sequencing of the strata layers.  Its probably true that less specific research has been done on most of these vineyards, absent Montrachet itself. As one moves south many different types of bedrock replace the type slightly further north. I have not been able to be precise about the names of all the rock types.  The best visualization I have found is the graphic on page 116 of James Wilson’s book “Terroir” 

At the base of the Corton Hill and stretching to mid slope the bedrock is the “Dallee Nacree” set from the Bathonian and Callovian Periods - the “pearly slab”.  Broadly between Aloxe Corton and Volnay the ‘Dalle Nacree” strata has gone 20 meters deeper and so at Volnay this only is present at the every base of the slope, being replaced at mid slope by younger white marls of the Upper Jurassic - ie Oxfordian marls. On this are grown the lighter styled reds of the Cote de Beaune. These strata have more clay than the purer limestone further north. The strata of the Middle Jurassic resurface around mid slope at Meursault and are present all the way to Santenay.  Hence the term “Volnay Syncline”, representing the dip beneath the slope of the Middle Jurassic strata at Volnay and “Gevrey Anticline”, representing the high point of the older strata at the village of Gevrey. This is why some firmer styled reds - reminiscent of the Cote de Nuits - are made in Santenay and Maranges, at the southern most end of the Cote de Beaune. 

The Cote de Beaune is difficult to pin down geologically because one has to explain the Hill of Corton, the mid section stretching from Beaune to Volnay and then from Meursault south.  Though I have a lot less confidence in the accuracy of this sequence I set out below relative to that that for the Cote de Nuits strata set out above, as I understand it from oldest to youngest in the Cote de Beaune the strata sequence is as follows  - 

1. “Dalee Nacree” - full of fossils, a pearly flagstone - shiny oysters in mud - at the base             under the Hill of Corton
2. Ferriginous oolite - a thin strata layer - red from the presence of iron minerals.
3. Dolomitic Limestone - like the Comblancien layer further north but with more magnesium
4. Pernand or Pommard Marl (depending on how far south ) - thick deposits of calcareous             clay - often interfingered with limestones richer in clay. Prominent in Pernand, Pommard             and Volnay
5. Ladoix Limestone - “laves” (so used for roof tiles) - results from sandy deposits present in             a tidal environment. Per Remmington Norman resent in the upper part of Volnay                         Caillerets and in adjacent parts of Monthelie.  
6. Nantoux Limestone, which forms the ‘cap” at the top of the southern slopes.  Above this l            lies St Romain marl