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Geology and terroir in the Western Cape winelands
Abstract
Terroir and geology are indirectly linked through the formative effects of geological processes on landscapes, their soil assemblages and associated climates. In contrast to this passive linkage, the effects on vine performance and wine style of those aspects of the terroir environment which are imposed by, or are consequences of geological processes, such as altitude, aspect, insolation, soil mineralogy and particle size range, and by those climate characteristics which are conferred by landform, are both direct and active.
Introduction
Although geology is sometimes described as a terroir or wine-style affecting factor, the term is too broad to be meaningful. Nevertheless, every landscape is a product of a long history of geological processes. This article briefly examines the relationship between geology and terroir.
Terroir
Terroir is 'a quintessentially French term' which underlies and defines the French Appellation Contrôlée system, and which seeks to embrace and describe the total natural environment of a viticultural site (Gladstones & Smart, 1994). In evident agreement with this view, Wilson (1998) maintained that 'answers' (to the question of why great vines grow where they do) 'are not in one or two elements, but in the totality of the elements of the vineyard habitat', which totality he considered to be 'the very essence of terroir'. More practically, and in keeping with the analytical approach favoured by South African wine researchers, Carey (2001) noted that a terroir may be defined in terms of the complex of natural factors which are expressed in the final product (wine). Stripped of the mysticism with which terroir is occasionally endowed (Hancock, 1997), the terroir concept is founded on the common observation that 'the quality of a plant' and, by inference, that of wine derived from it 'depends on where you grow it' (Hancock, 1999). Early recognition of the implied link between vineyard location and wine is reflected by the tradition of naming wines by their place of origin, such as Bordeaux or Constantia, rather than by cultivar. Scientific evidence that variation in natural terroir-determining factors affects wine style under Western Cape conditions is now accumulating (Carey, 2001; Conradie et al., 2002), and vineyards are increasingly being planted outside the traditional wine growing areas to take advantage of a greater diversity of environmental conditions, as in the case of the area-specific wines now being produced in the Elgin area.
Demarcation
Implicit in the terroir concept is the need to accurately demarcate homogenous terroir units. In the older European wine producing areas terroir demarcation was an evolutionary process based on the successes and failures of preceding generations, sometimes extending back to Roman times. In South Africa, although viticulture dates back to the mid 1650s, too little information was acquired for this historical approach to demarcation to be useful in other than restricted areas. An alternative approach was therefore necessitated. This alternative, which forms the basis of most South African terroir studies, entails the identification and quantification of those factors which define a terroir (Saayman, 2003). If the predictive value of the selected factors is verified by field testing, then the factors may be used as criteria in the demarcation of new terroirs, even though no wine has previously been produced in the areas thus demarcated. The net effect of the combination of factors which successfully defines a terroir, such as that shown in Figure 1, will be that wine produced from that terroir will be true to type, and will have a distinctive character which will be recognisable from season to season despite variations in cultivation practice and management of the vinification process.
Geology and landscape
In South Africa, soil and climate are regarded as having marked effects on wine style, and have been used for ward delimitation purposes for some years (Saayman, 1977). As the concept of terroir developed, topography (aspect, altitude, terrain morphology) was added to soil and climate, and zoning is now primarily based on climate and on patterns in soil and geology (Saayman, 2003). Geology was also linked with terroir by Wilson (1998), and by Haynes (1999). However, geology, which Hancock (1994) defines 'mainly as the study of the earth's crust' is too vague a term to be useful unless further qualified. Difficulties in relating geology to terroir are exacerbated by the fact that most geological maps are compiled at scales that inadequately depict vineyard conditions (Morlat, according to Hancock, 1997). In the Western Cape there is nevertheless a close relationship between natural vegetation (fynbos), physiographic subregion and geology (Lambrechts, 1979). It is also true that the landscapes of the Western Cape owe many of their characteristics to geological processes. Indeed, Dr J.L. Scholtz, in his presidential address to the Geological Society of South Africa in 1946, stated that the south western part of the Western Cape is unusual because, in the absence of such modifying factors as Quaternary glaciation, the surface form as revealed by erosion and denudation 'is practically entirely dependent on the geological structure of the area'. Scholtz also made the intriguing statement that 'removal of the Cape System' by erosion 'has exposed the underlying Malmesbury Series and its intrusives' on which the vineyards of the Stellenbosch, Paarl and Wellington areas, amongst others, are based '? for the second or third time during geological history'. This suggests that the geological history of the Western Cape has been unusually diverse, has contributed greatly to the formation of present-day landscapes, together with their associated mesoclimates, to the nature of the soil parent materials, and to their effective depth. Scholtz' comment also implies that, rather than being thought of as static, landscapes should be regarded as representing only the present stage of adaptation in an ongoing evolutionary process that already has a 4.56 thousand million year long history. In practice, landscapes often change at rates which are appreciably slower than climatic and other environmental changes. This explains the occurrence of landscapes and soils which are relics of past events. The presence of a variety of landscape features within a given area may have no significant effect on viticulture. In other cases, as, for example, where water holding capacity varies across a region, such as may happen where cobbles and gravel in outwash fans or terraces adjoin alluvium or clay-rich soils derived by weathering of shale in situ, the effects on viticulture may be marked. Where landscapes have not as yet evolved to the point where equilibrium has been reached with the conditions which prevail at the present day, further change is inevitable. Although most landscape changes are slow in human terms, floods, landslides and earthquakes, such as that in the Ceres / Tulbagh area in 1969 which measured 6.3 on the Richter scale (Truswell, 1977), are reminders that we live and farm on an active planet where rapid changes are possible.
Geology, terroir and wine internationally
Recognition that geology, terroir and wine are linked, even though the effects of geology are invariably indirect (Saayman, 1992; Gladstones & Smart, 1994; Conradie et al., 2002), acting via such factors as soil depth, water holding capacity (Carey, 2001; Hancock, 1999) and clay fraction mineralogy (Van Schoor, 2001), led to geological criteria being used as key elements in the demarcation of the 'Inités Terroir de Base' of the Loire Valley (Morlat, 1996). Subsequently, work by Haynes (2000) showed that the terroirs of the Niagara Peninsula, Canada, have a geological basis. Descriptions of the geology of the Walla Walla Valley and Red Mountain appellations of Washington State were published by, respectively, Meinert & Busacca (2000) and Meinert & Busacca (2002). Wilson (1998) has written extensively concerning the geology of French vineyards. Recently, in the 'Geology and wine' series published in Geoscience Canada, Taylor, Longerich & Greenough (2002) showed that cluster analysis of trace element concentrations in wines, as affected by vineyard geology, climate and environment, may be used to provide proof of vineyard of origin. Similar 'fingerprinting' work is in progress in South Africa, and an article concerning geology and wine production in South Africa currently awaits publication (Bargmann, 2003).
Aspects (factors) of terroir: geological basis
According to Laville (1990), definable aspects of the vineyard environment which are of specific importance from a terroir viewpoint include soil hydrology (soil moisture relations), geology / pedology [top- and subsoil depth, texture, granulometry (distribution of particle sizes), induration, mineralogy and chemistry], geomorphology (altitude, slope, aspect), morphoclimatology (insolation, or solar energy influx ) and climatology (rainfall and temperature). Wind and other climatic effects associated with coastlines and topography are also terroir-contributory factors (Bonnardot et al., 2002). Recent reports from Australia suggest that the source and mineral content of water used for irrigation may also be important, and that some wine characteristics may be influenced more by water composition than by the solid soil material, particularly in vineyards that have a long history of irrigation (Rees, 2003). Water mineral composition is strongly influenced by the mineral material through which it percolates. Soil is thought to affect vine growth pattern and wine characteristics mainly through its physical and water regulating properties (Saayman, 1992). However, clay fraction mineralogy, which reflects soil parent material, has marked effects on potassium buffering (Wooldridge, 1990) which may in turn affect juice pH (Iland, 1988).
Many terroir-influencing factors reflect geology and geological history in so far as deposition of sediments, emplacement of igneous rocks and the shaping of continents and landscapes, with their associated drainage systems and mesoclimates, are processes that are essentially geological in nature. Soil, and soil parent material granulometry and mineral composition, tend to reflect source area geology, possibly even dating back to earlier cycles of rock formation, erosion, sorting, and deposition. Similarly, the evolution of macroclimates reflects the effects of continental drift on the location and relative distribution of continents, ocean basins and ocean currents relative to the poles and to global atmospheric circulation patterns. In the Western Cape, changing climates, at times associated with ocean ridge- or ice-related changes in sea level measurable in tens, and occasionally hundreds of metres, and in drainage base levels, have affected weathering patterns, landscape form, soil parent materials and pedogenesis (Hendey, 1983; Lambrechts, 1983; Schloms, Ellis & Lambrechts, 1983). In effect, geological processes create the physical settings within which terroirs may come to be demarcated. Since the range of processes is considerable, most terroirs will have geological histories, and combinations of landscape, climatic and soil factors, that are uniquely their own, as is the case for the vineyard shown in Figure 1. Apart from the visual impact of its location and scenery, this terroir is uniquely defined by factors which include altitude, aspect, slope, mesoclimate, including exposure to sea breezes, soil characteristics and, in a temporal sense, by its geological history.
Conclusions
Landscapes and their terroirs are products of sequences of earth processes that date from the beginning of the geological record to the present day. Landscapes are shaped by their geological histories, and may acquire terroir-determining features during the course of these evolutionary histories. The effects of geological processes on terroir are therefore formative rather than dynamic. In contrast, the effects on vine performance and wine style of those aspects of the terroir environment which have been imposed by geological processes, such as altitude, aspect, soil mineralogy and granulometry, and by those climate characteristics which are conferred by landform, will nevertheless be direct and active.
This article, in which links were established between geology and terroir, will be followed in future WineLand publications by articles dealing with the geology of specific wine growing regions.
For further information contact John Wooldridge at Nietvoorbij on: (021) 809-3330, 083 662 4742, John@infruit.agric.za.
Geologie en terroir in die Wes-Kaapse wynlande
Terroir en geologie word indirek deur die effek van geologiese prosesse op die vorming van landskappe, hul grondsamestellings en geassosieerde klimaat verbind. Hierteenoor het die terroir omgewingsfaktore wat veroorsaak word deur, of wat die gevolg is van, geologiese prosesse byvoorbeeld hoogte bo seespieël, aspek, straling, grond mineralogie en deeltjie grootte, asook klimaatseienskappe wat veroorsaak is deur landskapsvorming, 'n direkte sowel as aktiewe effek op wingerdprestasie en wynstyl.
References
Bargmann, C.J., 2003. Geology and wine production in the Coastal Region, Western Cape Province, South Africa. Geology and wine series no. 7. Geoscience Canada. In press. |
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This Sauvignon blanc vineyard on the estate Thelama is located on a saddle of high ground which links Simonsberg (background) to the Jonkershoekberge on the western margin of the Cape Fold Mountain Belt. The precipitous, wheathering-resistant sandstones which form the upper part of Simonsberg rest on an older landscape composed of Malmesbury sediments and granite. The gravelly vineyard soil consists of a mixture of gravity-transported sandstone fragments and wheathered granite, and owes its red colour to intense wheathering under humid conditions during a period of high sea level in the tertiary era which began about 65 million years ago. - Photograph: Phillip Olivier, ARC Infruitec-Nietvoorbij.
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