When commenting about wine regions it's not a simple task to write about the geology and the origin of landscapes and soils. Consider this example of the confusion that one region has managed.
Heathcote, the Victorian region noted for fine shiraz makes great use of the districts red soils in selling and marketing. Some say the best vineyards are located on the red soils, and it's suggested, they produce the best wines. Here are nine recent comments.
1. From the Gourmet Traveller Wine, January - February 2011, Ken Gargett had a Regional Profile titled; 'Heathcote's BOW'; and made the following comment:
"Because of the larger size than some originally anticipated [the GI area called Heathcote], the soil is not uniform but undoubtedly the ancient red Cambrian/greenstone influence is a major factor on many of the wines. This soil has gradually moved down from its origins on the Mount Camel ridge half a billion years ago. The Cambrian soils are effectively an elongated spine..."
2. From the Heathcote Shiraz web site:
"Over the past 30 odd years the pioneers of the Heathcote district have extolled the virtues of having their vineyard planted on Cambrian earth – the soils are the result of a very long weathering process, having been formed from Cambrian rocks which are over 500 million years old."
"These ancient soils, geologists inform us, are around 100 million years old. The Cambrian earth exists as two narrow bands that run parallel to the Mount William fault line. The Cambrian earth starts approx 5km South of the Heathcote township and extends North for approx 35km. The bands of earth are quite narrow, no more than 2km across and are not continuous, although they extend to the Northern end of the region."
There is also a very confusing summary of the local geology on this site.
3. From the Wine Australia site there are comments titled:
A Case In Point: Stephen Shelmerdine, Chief Executive, Shelmerdine, Heathcote.
"With a climate reminiscent of the Rhone Valley and its diversity of soil types, geology and topography, Heathcote produces a range of wines, but is most renowned for the complex, rich and intense Shirazes grown on the 500-million-year-old, Cambrian-era red soils north of Heathcote along the Mt Camel Range."
4. From the Ellis Wines web site:
"Whilst sitting upon the ancient Cambrian soil, pondering the land and studying the complex local geology, Bryan and Joy Ellis realised their undulating land had the potential to generate a variety of microclimates suitable for viticulture".
5. From the Taltarni web site:
"The 500 million year old volcanic soil that makes up Heathcote's unique topography has long been regarded as the reason for such exceptional shiraz. Known as Cambrian earth, the red soil of Heathcote,"
6. From the Melbourne Wine Tours:
"People often ask what it is about the Cambrian soil that makes Heathcote wine so special. As Ron Laughton of Jasper Hill says 'This land was meant for vines' The soil, estimated to be 500 million years old, is the oldest in Victoria and derived from rock of the Cambrian age."
7. From Wine Wisdom by Sally Easton:
"Heathcote shiraz is all about the Cambrian (500 million years old) soils which lie over basalt bedrock."The tortured geology is important. Two parallel faults run close together in Heathcote which lifted and exposed the volcanic rock which formed the Cambrian soils – decomposed basalt high in iron. "Minerals are mixed in the Cambrian soils, and the building blocks for the molecules of colour and flavour come from the ground" Laughton said."[the later being a reference to a district pioneer, Ron Laughton of Jasper Hills]
8. From the Heathcote Wine Growers Association site:
"As well as premium Australian Shiraz, the famous ancient red Cambrian soils of Heathcote produce...."
9. And lastly from a Dan Murphy advertisement, March, 2011*:
On the front label of a wine called Cambrian Rock I noted; "Wine from the ancient soils of the five hundred million year old Cambrian Rock.", while the advertising copy read; "Heathcote's prized ancient Cambrian soils took 500 million years to perfect..."
I have been reading remarks similar to these for over a decade and it's time to put the record straight.
The Cambrian is a geological period that spans 545 million years to 495million years. Within the Heathcote area, now defined as a GI or Geographical Zone, there are indeed rocks of Cambrian age. Some of these are termed greenstones with many being marine lava flows, that is, they flowed over the ocean floor. They grade upward into marine sedimentary rocks.
In the Heathcote region this pile of Cambrian and younger rocks has been cut, sliced and deformed on several occasions spanning several hundred million years. The rocks may have been pushed up to the surface and perhaps down again before assuming the position they have now. These 500 million years of geological history are of great interest but for the practical purpose of talking about why your vineyard for example slopes the way it does and has variable thicknesses of soil it is the most recent slice of this long history which contains the clues.
Naturally the underlying geology imposes its character on the landscape and is of use in explaining the origin of any wine region.
So for Heathcote vignerons and others to refer to Cambrian rocks is correct though they do not warrant the term ancient as 500 million years is about 11% of the earth's age - the term an 'early teen' may be used. Volcanic rocks frequently weather to a bright red soil so it is also correct to relate the soil to the local Cambrian rocks. This may seem obvious but in many vineyard regions the soils are not related to the local or underlying rocks. It is not correct to say or suggest that the soils are of a similar age to the rocks. The soils do not warrant the term ancient and neither are they 100 million years old as has been suggested. The position of the pile of Heathcote rocks 100 million years ago would be difficult to unravel. There is some evidence that a great, rolling, peneplain covered Southern Australia at this time and this was associated with a thick covering of enriched ironstone rock often called laterite. Any soils which sat above this covering have been removed long ago.
When explaining the soils they may be called Cambrian soils, as a usage term, if it's meant they are recently derived from the Cambrian rocks. This is a simple and easily understood concept tying together rocks and soil and a useful marketing tool.
Soils by their very nature are generally young and the chances that they can develop and survive for much more than several million years, is I think very low. Most then are far younger than this.
Even a stable continent like Australia is constantly moving and flexing. Couple this with the pronounced periods of climate change over the last few million years and this means that, with rare exceptions, soils were being constantly eroded and replaced. The replacement in many incidences is from the underlying rock which is slowly crumbling from weathering.
Much more can be said about soils and this will be tackled another time.
Footnote: I might add you could debate that where it can be proven the parent bedrock has continuously weathered to produce and replenish - this soil at this spot - for 'pick a number' years you could infer the soils are of that determined age. Even so I wonder how many places across the globe there are where these conditions have existed for longer than say 10 million years. I might also add that soils of great age do strange things as excessive leaching turns many back into a surface rock. Soils need constant renewal.
* While I am at it, in the Dan Murphy advertisement referred to above, the vineyard picture behind the Leconfield Coonawarra Cabernet is not from Coonawarra. The use of any old clip art to represent famous wine regions has irritated me for years and is very common.