Many of Ausralia's finest red wines are made in Coonawarra and it is one of the country's few world class wine producing areas. Coonawarra, like most of the world's great vineyard areas, is a clearly defined, localised, geographic setting. This setting and the other influences that make up the terroir may explain the particular wine flavours that make Coonawarra wines so popular with consumers. All vineyard areas can make delicious and affordable wine, but very few have the terroir to make wines for which consumers will pay greatly increased prices.
The Coonawarra vineyards lie on a flat plain in the South-eastern corner of South Australia on the Limestone Coast. The Limestone Coast formed during the last one million years in a geologic period called the Quaternary. This large area of the coast, about 350 km by 100 km, is underlain by limey soils and rocks. Many vineyards grow on the Limestone Coast, usually associated with red soils known locally as terra rossa.
Coonawarra is characterised by these terra rossa soils, forming a thin, linear shape more than 20 km long. The Coonawarra soils differ from the other vineyard areas on the Limestone Coast in this thin, continuous shape and in the colour intensity of the red soil. Coonawarra barely rises out of the surrounding plains. Most of the other vineyard sites on the Limestone Coast stand well above the plain. Clearly, Coonawarra has a different origin and it seems that the conditions that created this area occurred only once.
Compared to the classical Old World vineyards, with vines clinging to steep hillsides, Coonawarra appears a most unlikely site for great red wine. It is the high quality of grapes that grow on the terra rossa soils that makes Coonawarra so interesting for winemakers. Consumers also are curious as to why such small areas of red soil are associated with such special wines.
Why do these soils occur here; why are they confined to a narrow band; and when did these strange soils form? The scope of this paper is to explain the origin of the Coonawarra land surface and it does not deal with vineyards, wineries and wine quality. It was thought worthwhile, though, to include a short summary of the history of settlement and farming at Coonawarra, taken from current accounts, which includes a table of the vineyard plantings at 2000, to give focus to these important issues.
A BRIEF HISTORY OF WINE GROWING AT COONAWARRA
By 1850-1860 settlers at Penola, on the southern end of Coonawarra soil, found the climate and soils favourable for fruit trees.No doubt a few vines were planted.
In 1861 John Riddoch purchased the 14,170 ha pastoral property Yallum Park which covered a large area north of Penola. By 1880 Riddoch had built an imposing homestead a few kilometres to the west of Penola. He planted fruit trees and vines around the homestead. The area of Yallum Park continued to expand and by 1880 extended from Coonawarra to Mount Gambier, an area of 695 square kilometres.
In 1890 Riddoch founded the Penola Fruit Colony and in 1891 commenced subdivision of 465 ha of Yallum Park, north of Penola, centred on what is now the town of Coonawarra. Twenty-six settlers took up blocks, from 4 ha to 32 ha, and the planting of fruit trees, mostly apples, and vines commenced.By 1897 the settlers had 89 ha of vines planted and Riddoch had planted 52 ha. The main grape varieties were Shiraz, Cabernet Sauvignon, Malbec and Pinot Noir.
The first vintage was made at the Riddoch cellars in 1897, in the building which is now the Wynns winery. At about this time Riddoch changed the name of the Penola Fruit Colony to the Coonawarra Fruit Colony. The initial orchardists did not prosper but the history of viticulture in the region had begun.
In 1901, 14-year-old Bill Redman arrived in the district. In 1908 he purchased 16 ha from the Riddoch estate and went on to complete 45 vintages. These were difficult times. By the mid 1930s the Coonawarra vineyards had been reduced to 121 ha, from 365 ha, at the turn of the century. Most of the grapes were distilled.
In 1951 Samuel Wynn purchased the old Riddoch winery and vineyards. It was about this time that a small number of winemakers and consumers recognised the region's potential, but had to wait for a larger number of Australian consumers to discover wine before the area could expand.
Recognition by wine consumers of the area's huge potential came as late as the mid 1970s to early 1980s.
The current vineyard area within the proposed Coonawarra Geographic area at the end 2000 is:
COONAWARRA: A PART OF THE LIMESTONE COAST
Coonawarra is part of the Limestone Coast, a South Australian coastal plain developed over the last one million years. Coonawarra lies towards the eastern edge of this plain. Across the limestone coastal plain lie a series of parallel fossil sand dunes, about 15 metres high, trending northwest/ south-east. These dunes make the Limestone Coast a complex record of the rise and fall of the world's oceans. The onset of the current cooler period in the Earth's history, which commenced about 2.5 million years ago, triggered a series of ice ages causing sea levels to repeatedly rise and fall.
Coonawarra sits between two dune ranges, the West Naracoorte Range to the west and the Harpers-Stewarts Range to the east. The Harpers-Stewarts Range dune formed some 680,000 years ago. The West Naracoorte Range may well be made of a number of dunes that lie on top of one another. The youngest of these has a date of less than 780,000 years.
A quarry exposure of the West Naracoorte Dune before it was excavated to
form the Gartner Winery. Note the blocky nature of the sediments and the relatively steep dip of the dune sediments. (Reference point 1 on map).
The unconsolidated sediments that underlie the black soil plains to the West of Coonawarra. Excavated rubble at the surface which overlies black soil rubble and seams of black soil lower down. (Reference point 2 on map).
An important feature of the West Naracoorte Range is its partial abutment against a cliff, termed the Kanawinka Escarpment. This escarpment separates two dunes, the East and West Naracoorte Ranges. It marks
a fault line that first moved
millions of years ago. This
fault shifted again about
780,000 years ago. The country
to the west of the fault fell
about 40 metres, perhaps
under the sea. It was against
this cliff face that the
Southern Ocean deposited
the dunes comprising the
West Naracoorte Range.
The fault line can be dated
using the magnetic polarity of
the East and West Naracoorte
Ranges. Tiny particles of magnetite
within the dunes
aligned themselves with the
Earth's magnetic field. The Earth's magnetic field frequently
reverses; 780,000 years ago (+/- 20,000 years) a reversal, the
Brunhes-Matuyama, named after early pioneers of this dating
method, occurred. As the East and West Naracoorte
dunes have a different magnetic polarity, the Brunhes-
Matuyama reversal can be used to date the fault. This date
helps anchor all the dates for dune ranges to the west of the
fault. The East Naracoorte Range is older than 780,000
years, and may be as old as 860,000 years. This fault line
marks a natural divide between the Limestone Coast and its
vineyards and the Naracoorte tableland, on which the
Wrattonbully vineyard district has grown.
From the period of warmth, during which the West
Naracoorte Range dune was deposited at the base of the Kanawinka Escarpment, the Earth began to cool. As the ice caps grew, the ocean retreated westward over the plain on
which Coonawarra now sits. The ocean shore re-formed far to
the south-west, well out on the continental shelf.
As the Earth's weather again began to warm, the ice sheets
at the poles began to melt. The sea level rose and water once
more covered the limestone plain. While the sea was in
retreat the Australian crust in this area had been slowly rising.
Since the formation of the West Naracoorte Range, this dune
and the surrounding country had risen about 7 metres.
Hence the new seashore was not as before the West
Naracoorte Range but 10 km
to the south-west. Here, a new
coastal dune, the Harpers-
Stewarts Range, began to form.
While the age of the
lagoonal sediments east of the
Harpers-Stewart Range is
similar to the age of that
range, 680,000 years, marine
sedimentation would have
ceased with the retreat of the
ocean and the formation of
the next westerly dune, the
at 570,000 years.
To begin to understand
Coonawarra the best place to
start is on top of the Harpers-
Stewart Range dune. The dune
rises about 15 metres above
plains to the east and west.
The view eastward towards
Coonawarra is of a flat, dullgrey,
treeless surface, passing
over Coonawarra to the fading,
grey-green hills of the
West Naracoorte Range. With
the winter rains these plains
become waterlogged and boggy. Closer examination of the
plains will show small scoops and depressions, some of which
are rimmed on the eastern edge with a slight rise. These have
been hollowed out by wind. The larger lagoons may be rimmed
by sediments 10-20 metres high.
Driving across the plain towards Coonawarra, the soils are
a dirty grey-black colour, about a half to two metres thick.
Below are 10-15 metres of friable, weakly bedded, chalky sediments,
so soft that the term bedrock does not seem appropriate.
These chalky sediments lie on older, well-washed,
creamy-white, sandy, unconsolidated marine sediments.
Beneath these sediments lie the basement rocks.
The dull, grey-black soil of the plain is littered in some areas
with fragments, small discs and plate-sized stones of white calcrete.
This tough calcareous-rich rock is a feature of
Coonawarra. These areas of calcrete rubble are usually, but not
exclusively, associated with a slight rise of 1-1.5 metres. In most
places, the unconsolidated chalky sediment grades directly
upward into the black soil. However, in places it is thinly
veneered with a calcrete cap, millimetres to centimetres thick.
It is rare to find a pronounced cap up to 30 cm thick.
Fragments of this cap work their way to the surface, probably
through farming activities, forming areas of calcrete rubble.
The soil associated with these rises covered in calcrete
rubble is usually grey-black, but in places a noticeable
browning or reddening may occur. The elevated
rises begin to take on the ferruginous
tint of terra rossa. A few of these rises look
promising enough to plant with vines.
Beach sediments exposed in a quarry east of Penola. These are overlain by C
colour red-brown soils, some of which have been rolled into mud balls by
water and are surrounded by paler wind blown siliceous sandy soils swept
into the water at the same time. The soil and rubble at the top is from recent
excavation. (Reference point 3 on map).
The Western end of Drain C looking south east. At this point C colour soils
grade into B colour soils which coincides with a thickening of the calcrete cap
and a 1 to 1.5 metre lift in elevation. (Reference point 4 on map).
Indeed, in the middle of this plain a
vineyard has been positioned on a local rise
where the soils show a noticeable reddening.
In many quarry exposures a slight
browning-reddening of the soil can be seen
at the interface of the calcrete and the soil.
Small patches of red-brown soil, several
centimetres thick, are not infrequent.
Approaching Coonawarra, the sediments
slowly change. The unconsolidated, crumbly,
creamy to dirty grey limestone begins to
show faint, but distinct, bedding lines. And it
is always thinly veneered with a calcrete cap,
which thickens quickly as the soil reddens.
Continuing the journey west, the land
begins to rise after the Mount Gambier rail
line is crossed. As the ground lifts the colour
of the soil, over several hundred metres,
changes to a grey, brown-red, then a brighter
red-brown and then, opposite Wynns, a
fierce rust colour. Coonawarra is identified
with the famous Wynns Winery. Wynns and
the town of Coonawarra sit in the centre of
the famous red soils about 1.5 to 2 metres
above the plain. Here plates of calcrete are
common at the surface. The land now levels
out and travelling past Coonawarra, a darkening
and toning down of the soil colour
occurs. Crossing the main north-south road,
not far from the Brands winery, the soil again
brightens to a rust colour and then fades to a
brown-red chocolate colour, before quickly
fading to brown again and finally returning to
the grey-black colour of the plains. The width
of this strip of red soils is about 1.6 km. The
ground does not dip again, but rolls into the
flat plains of eastern Coonawarra. The land
surface seems different to the western plains.
The western edge of Coonawarra has a
distinct boundary. The 1 to 2 metre lift
from the grey-black soil plains is often sudden.
In contrast the eastern boundary dips
and rolls away into small gullies. In other
places the brown soils level off into a flat,
black coloured soil plain.
MAPPING THE RED SOILS OF COONAWARRA
The soils of Coonawarra have been mapped
by their colour (see map at right). The divisions
on this map are not those that experts
in soils would use. They were selected to
highlight, if it existed, the underlying geological grain of
Coonawarra. In this way the width, length and trend of
Coonawarra is revealed and magnified. The colour boundaries
are quite precise and the change, in general, occurs over a few
metres. Five soil colours have been identified. They are:
A colour soils - Soils with distinctive terra rossa colour associated
with Coonawarra. Brown-red to a bright iron-rust red,
distinctive, at times almost glowing with brightness.
Frequently associated with rubbly calcrete. Much of this calcrete
may have been brought to the surface by deep ripping
prior to vineyard planting. This ripped calcrete is angular.
Calcrete brought to the surface naturally is rounded and
smooth and occurs in areas where the soil cover is thin, often
less than 10 centimetres. The amount of calcrete brought to
the surface by vineyard preparation depends on the soil
depth and the length of the ripping device. The A coloured
soils occur at the high point of the Coonawarra rise.
B colour soils - Browner than the A colour soils, although
patches of A colour occur. Likewise, patches of B coloured
soils are seen in the A zone, usually associated with slight
dips and lower scoops. The soils range from rusty brown to
deep red- brown and are deeper in colour than the Acolour
soils. In places, near the boundary between the A and B
zones, A coloured soils have been washed onto the B
coloured soils. There is less calcrete rubble on the surface
and large areas have no surface rubble.
C colour soils - C coloured soils are dominated by brown and
grey colours. Soil redness is never present for long stretches,
although slight ground rises often show a weak reddening.
The soils are darker than the A and B colours. Calcrete
is common as tiny fragments and rubbly areas are small. The
C coloured soils represent a transitional soil to the plains on
either side of Coonawarra.
D colour soils - These are the soils of the black limestone
plains. Black to grey in colour and mostly without surface
calcrete, except on small rises. A weak reddening in colour
may be observed as the black soil passes into the thin calcrete
cap or the underlying soft bedrock. Many of the new
vineyard plantings on this soil show extensive calcrete rubble
from the deep ripping preparation. Where the soils
change quickly from C coloured soils, or rapidly through
the sequence from A to D, there is a drop in elevation. This
is most readily observed along the western edge of the
E colour soils - A grey, light- grey to dirty-white coloured
soil, generally seen east of a central line through Coonawarra.
These soils are wind-blown sands that overlie other soil
colours. Because of the patchy nature of this soil it has not
been mapped separately. The E colour soils vary in thickness
from 10 centimetres to several metres and thicken rapidly to
the east of Coonawarra. This soil is not contiguous, but lines
the dips and gullies along the eastern edge of Coonawarra.
In a quarry east of Penola mud balls of C colour soil are
found embedded in E colour sandy soils. These mud balls
probably formed in a shallow water-filled depression. When
the water dried, the mud cracked and flaked and was rolled
into balls by wind and water action. The wind-blown E soils
swept in at a similar time.
DISCUSSION OF THE COONAWARRA SOIL COLOUR MAP
The red soils of Coonawarra can be traced for 23 km along a
north-west line. The maximum width of the red soils measuring
to the C coloured soils is about 1.75 km and stretches for 14 km.
The brightly coloured A soils stretch for 17 km. At the
southern end of the area the red soils pinch out at Penola.
The northern end can be traced to the Sharefarmers block,
where brown colours begin to dominate the red. The soils
may continue north although calcrete is poorly developed,
indicating the trend is fading quickly. The northern end also
shows an arm trending to the north-east. The reason for
this arm and whether it has a geological significance is not
known. The S. Kidman vineyard and the trend of its red
soils is also uncertain. It is not known whether this vineyard
lies on the north-east split although this is unlikely as such
a connection would cut across the geological trend revealed
by the alignment of salt pans and marshes. Along the eastern
edge, three vineyard areas trend to the east. The most
northerly, the Penley block is on soils that are part of a weak
east-west ridge. Much of this ridge is covered with windblown
E coloured soils.
Looking East along Drain C. Lagoonal sediments merge upwards into thick
calcrete and A colour soils. (Reference point 5 on map).
Beach sediments exposed in the Penley quarry east of the Penola-
Coonawarra road, near the Penley Estate winery. (Reference point 6 on map).
The reason for the other two easterly protrusions of red
soil to the south is more difficult to understand. The ridge
extending east of the Majella block is sculptured into
smooth gullies and numerous low-lying pans, evidence of
wind and water erosion. The ridge continues to the east and
is covered in wind-blown sands. The other prominent high
area extends east of Bowen Estate. It also has been sculptured
by wind and water erosion, though wind-blown sands
are less of a feature. Looking at the map (Page 33), there is a
weak indication that the vineyards along the eastern side,
associated with isolated patches of C coloured soil, have a
common geological control. The new developments south
of Penola occur on patches of soil that are similar to the C
coloured soils developed to the east of Coonawarra.
Possibly these are all linked in some manner.
On the western side of Coonawarra, over the rail line,
higher areas of ground are common. Many of these have
reddened to a brown-red C coloured soil. There are also
rises on the plain, several kilometres further west. Many
show strong calcrete development which has helped preserve
them from erosion.
The map highlights the extent of all vineyard development
either on the Coonawarra ridge or to either side. The
data is several years old and plantings have expanded over
the last few years. Many plantings extend onto D coloured
soils, though usually where associated with a slight elevation
increase. Plantings now occur well away from the terra rossa
soil, characterising the central rise of Coonawarra. Most of
these plantings will, though, lie within the new boundary of
the Coonawarra wine region.
A CLOSER LOOK AT THE SOIL RELATIONSHIPS OF COONAWARRA
On the surface, and on the map, the soil colours to the east
and west of Coonawarra appear identical. However, examining
pits and quarries on the eastern side of Coonawarra
shows the underlying bedrock to be a mottled, creamybrown
coloured, clayey, unstratified, unconsolidated sediment,
different to that of the western side. Also surface calcrete
is uncommon east of Coonawarra. A recent publication
on the land systems of Coonawarra also notes the
change in landforms to the east and west of Coonawarra.
A feature of the C and D coloured soils to the east is the
presence of pisolitic iron stones. These are tiny, pea-sized,
They may join together to form lumps. The new vineyards
south of Penola have uncovered large football-sized clumps
of these pisolites. Pisolites are very rare west of the A
coloured soils. This change in the soil type to the east of
Coonawarra suggests that the underlying bedrock has
changed under the rise of Coonawarra. The map shows a
continuous stretch of red soils some 23 km long, with 15 km
having a width of about 1.7 km; a continuous soil feature
which straddles the change in the underlying bedrock. This
cannot be a coincidence.
The Clues from a Cutting Across Coonawarra know as Drain C
There is an east-west cutting across Coonawarra that allows
us to examine the soils and sub-surface in great detail. Drain
C, as this cutting is called, crosses Coonawarra north of the
town. The 2 km walk along this drain is the most informative
walk any student of the wines of Coonawarra can take.
Starting on the grazing land to the west of the Mildara
Vineyards, C coloured soils are underlain by soft, friable,
chalky muds. The calcrete horizon between the two is poorly
formed. The change from C coloured soils to B coloured
soils occurs over a few metres and coincides with a lift in
the surface of about 1.5 metres. It also coincides with the
start of vineyard plantings.
Strolling eastwards, the faintest bedding planes appear in
the chalky muds. Small pellets of limey mud often occur on
the same horizon. The calcrete cap separating the red soil
and the chalky mud thickens.
The bedding planes become more distinct as one moves further
east. Pelletal, limey muds form continuous lines and link
together to form nodular, platey, firm layers that separate softer
muds. Under the A coloured soils the calcrete cap is half a
metre thick and is spectacularly eroded in places, allowing long
pipes of brilliant-coloured red earth to penetrate down. East of
the Acoloured soils and close to the main road the bedrock is
now slabby and stratified and passes into strongly stratified,
nodular, hard limestone east of the main road.
The characteristics of this limestone are best seen in
quarries, like that on Penley Estate, and along the eastern
side of Coonawarra. These quarries expose a flat-lying, slabby,
nodular, limestone of creamy to yellow-brown colour
with rust staining. Gently dipping beds are common.
The rock is densely fossiliferous with gastropods, scallops
and other bivalves of the sort found on beaches today. This
limestone is compacted enough to form metre-wide slabs.
The Bedrock Controls The Soils
As can be seen from the cross-section in drain C, Coonawarra
coincides with a change in the underlying bedrock. The transitional
sediment type under Coonawarra assisted the formation
of a much thicker calcrete cap, than that formed on sediments
to the west or east. The thick calcrete cap would have
acted to preserve the underlying sediments from erosion. This
calcrete crust is thickest under the A coloured soils.
Northern vineyards, like Sharefarmers, while directly on
the Coonawarra trend, appear to be at the fading influence
of this bedrock change. Towards the south the rise from the
C to B coloured soils in the west is gentle, suggesting that
the effect of bedrock changes is fading. It is unlikely the
bedrock change continues south of Penola.
The lens-like shape of Coonawarra does not seem related
to topography, as there is a steady rise of about 6 metres
from Sharefarmers to Penola. Such a rise is significant in this
flat landscape. This height difference supports the view that
the soil colours and the location of Coonawarra are not due to
superficial weathering influences, such as topographical influences
and the introduction of wind-blown soil, but have an
underlying geological control.
ASSEMBLING THE CLUES ABOUT HOW COONAWARRA WAS FORMED
In 1983 Schwebel studied the Limestone Coast inland from
Robe. His descriptions are helpful for understanding
Coonawarra. He says in reference to sediments formed
behind a dune, "They were deposited around the margins of
the lagoon and represent low energy beach and near-shore
conditions. The framework most commonly consists of
either whole or fragmentary bivalves and gastropods." Later
he continues, "Asystematic distribution of lithologies is controlled
by the energy conditions prevalent in different parts
of the lake. Coarser grained, better sorted sediments occur
around the leeward margins of the lakes where wind-generated
waves winnow the sediment in beach environments.
Pelletal mudstones tend to occur on those shallow parts of
the lakes where seiching periodically removes the fine disaggregated
mud from the lake surface and promotes the formation
of laminated pelletal mudstones. Amorphous mudstones
appear to be representative of the more central lacustrine
conditions where surface water persists through severe
seasonal evaporative periods." While technical, it is hard to
imagine a better description for the setting of Coonawarra.
The richly fossilised, stratified limestones that occur along
the eastern edge of Coonawarra are beach deposits. This and
the sediment gradation westward, under Coonawarra and
beyond, imply deposition in a lagoon formed behind the
Harpers-Stewarts Range. Fifteen kilometres south of Penola
the Harpers-Stewart Range swings to the west and fades as it
approaches the Mount Burr group of volcanoes. This group of
volcanoes is about one million years old. They may have been
islands at the time of formation of the Harpers-Stewart
Range. It seems possible that the ocean entrance to the
lagoon was between the Mount Burr volcanic group and the
southern end of the Harpers-Stewart Range. How long the
lagoon had an ocean entrance is not known.
Further evidence for this lagoon, and perhaps its size and
shape, comes from recent radiometric mapping of the
Coonawarra region. These surveys measure radioactive
emissions from potassium, thorium and uranium. The map
shows a large eliptical shape that takes as its eastern side a
curve just to the east of the Coonawarra rise, circles around
Bool Lagoon and closes after a wide loop west on Penola.
Could this be the outline of the lagoon that existed west of
the Coonawarra rise and is now reduced to Bool Lagoon? The
implication might be that a lagoon of greater area, that had a
seaward entrance to the south, was reduced to the size suggested
by the radiometrics after the seaward entrance closed.
The Coonawarra can be compared to the Coorong, which
today has formed behind the coastal dune of the
Younghusband Peninsula and has an entrance to the sea at
the mouth of the Murray River.
EXPLAINING THE FORMATION OF COONAWARRA
The Harpers-Stewart Range was formed 680,000 years ago.
This dune marks the advance of the Southern Ocean, after
melting of continental ice sheets during global warming. It forms a continuous, north-west trending range, stretching more than 100 km along the Limestone Coast. Behind the
southern end of this dune a large saltwater lagoon was
impounded. The lagoon was initially open to the sea at its
southern end. Aradiometric map of the Coonawarra region
suggests that later the lagoon was oval-shaped and about
40 km long and 10-12 km wide. The freshwater Bool
Lagoon, north of Coonawarra, may be a remnant of this
lagoon. Along the central and south-eastern margin of this
large lagoon a beach deposit many hundreds of metres wide
was formed. Waves stirred the near-shore sediments and
gently rolled the limey muds into laminated pelletal mudstones.
This steady stirring washed the finer clay particles
deeper into the lake, beyond wave action.
The red soils of Coonawarra overlie many rock types: the
beach deposits (overlain by the Eastern C coloured soils);
the shallow water, bedded peletal deposits (overlain by the
Eastern B coloured soils); the deeper water, poorly bedded,
chalky muds (overlain by the A coloured soils); and the
unconsolidated, chalky muds further west in the deeper
parts of the lagoon (overlain by the Western B and C
coloured soils). The relationship of individual soil colours to
underlying rocks is only a guide, as geological processes are
far too complex for simple solutions.
However, the near-shore depositional environment of the
bedrocks is the key to understanding the soils and how they
formed. Sorting of the sediments by waves has created varying
physical and chemical properties in the bedrock in different
places. This change has allowed thicker calcrete to form under
the Acoloured soils. Similar marine, lagoonal beach sands and
deeper water deposits occur inland from Robe but none have
the length of Coonawarra and more importantly they have not
had the time to express themselves, like Coonawarra.
The soils to the east of Coonawarra have formed on sediments deposited in swamps, marshes and intermittent lakes.As the continent dried over the last 500,000 years, significant amounts of siliceous wind-blown sand has been added to
the sediments. As the country slowly rose the lagoon
became brackish and finally fresh, before drying out.
Intermittent lakes would have appeared on the plains during
wetter periods. Numerous small depressions, scalloped
out by wind, occur east and west of Coonawarra. These
occur in rows that follow the trend of the Coonawarra soils
and thus reflect their underlying bedrock.
As the lagoonal muds became exposed to the air the soil
forming process began. The soft sediments of this area did
not require the intensive chemical and physical attack that
is required to make soil on a hard granitic surface. Along
with soil development, calcrete formation occurred.
A feature of soft, calcium rich sediments is a reaction with
water to form weak, carbonic acid. This dissolves the soft limestone
which re-deposits as the smooth, firm, crusty skin,
termed "calcrete". This weather-resistant capping has preserved
the Harpers-Stewart Range and is of course a feature of
the inter-dunal areas where solution and re-deposition builds
tough, flat slabs of calcrete at the junction of the soil and the
bedrock. Calcrete formation is assisted by fluctuating water
tables, frequent flooding of the plains and periods of aridity.
Wind has been a powerful factor in modifying the landscape
of the Coonawarra region for a long time. A visit to
Bool Lagoon shows the power of wind erosion. On the leeward
shore a crescent-shaped dune 10 to 20 metres high has
been formed of sediment scooped from the lake. Lunettes
fringing the clay-salt pans of this area are common. The wind
blows predominately from the west and northwest. The
wind exposed the Coonawarra ridge by removing the plains
sediments to the west, in a process called deflation. The calcrete
cap has protected the bedrock of Coonawarra from the
corrosive effects of water erosion and stabilised it against
wind erosion. In dry periods when wind erosion was most
active, wind was unable to cut into the Coonawarra ridge.
Wind carrying siliceous sand particles, the E coloured
soils, flowed over the Coonawarra ridge and dumped some of
the load along the gullies and ridges that had been sculptured
along the eastern side of Coonawarra. The rises on the western
plain and to the east of Coonawarra are erosional remnants
of the former surface. The active role of water in this
region is more difficult to understand as gradients are small
and there is no outlet for streams to remove sediment.
Fluctuating watertables would have assisted wind erosion by
creating weaknesses in the bedrock. Wind and water erosion
working together seem to be the cause of the unusual rounded
gullies that exist along the eastern side of Coonawarra.
The reddening of the soils at Coonawarra and on the surrounding
plains is associated with elevation. The low-lying
grey-black soils become waterlogged during wet winters
leaving them in an anaerobic state in which iron cannot be
oxidised. Rises in the landscape allowing ferruginisation to
begin escape this waterlogging. Not all rises have become
ferruginised and the reason for this is not known. The exposure
of Coonawarra, as a rise of one to two metres above the
western plains, was enough for the soils to avoid waterlogging
and become ferruginised.
The age at which the Coonawarra ridge became exposed
is not known, nor is the age of the colour change. It is likely
that both processes began around the same time. The
exposure of Coonawarra may have commenced hundreds of
thousands of years after the sediments were deposited. Red
soils can develop quickly as can been seen on the young
dunes at Robe (80,000 years old). Evidence from coastal
dunes in Victoria suggests about 30,000-40,000 years is
needed in forming red soils. However, these soils are not as
deep and rich as those at Coonawarra which suggests a much
longer period was needed to create the Coonawarra soils.
As noted, the limited range over which the red soils occur
and the unusual red colour suggests that chemical differences
in the underlying sediments have played an important
part in soil formation*.
This explanation of the origin of the soils of Coonawarra is
unlikely to be the final word. The discussion does, though,
tighten the boundaries for future research and suggests areas
for detailed investigation. Hopefully it will also assist those
with vineyard properties in the area to market Coonawarra in
a smarter way. No doubt all the world's great wine areas have
an exciting story to tell. How many, though, will have undergone
such a wonderful, complex series of events just to make
the soils? Think about the sequence of soil formation. Ice
ages were needed to make the bedrock, unusual marine, estuarine
conditions were required to make bedrock, gentle
crustal lifting followed to preserve the bedrock, fluctuating
water tables and periods of aridity were needed to form the
protective calcrete caps, then wind and water erosion left a
long narrow ridge exposed. And all of this had to occur in the
right sequence for the distinctive terra rossa soils to develop.
Knowing how these valuable soils developed does not
make the wine taste any better, but a profound understanding
of the site where wine was made transfers into a greater
pleasure and understanding of the wine. Also, this study may
help the vignerons of Coonawarra focus on those parts of the
vineyard that make the most complex and interesting wines.
In a future paper it is intended to relate features of the
terroir of Coonawarra, including the different soils, to wine
quality. It will be interesting to see how much of the unusual
terroir of Coonawarra is expressed in the taste.
Bestland, E.A. (2002) The Dirt on the Coonawarra (for the Flinders Journal),
Press release from Flinders University, January, 2002.
Billing, N.B. and Cann, M.A. (2000) Land Systems of Coonawarra,
Preliminary map. Primary Industries and Reources, South Australia.
Drexel, J.F. and Preiss, W.V. (Eds) (1995) The geology of South Australia. Vol.
2, The Phanerozoic. South Australia. Geological Survey. Bulletin 54.
Halliday, J. (1983) Coonawarra the history, the vignerons & the wines. Yenisey.
Mackenzie, D.E. (1999) Coonawarra wine growing region, Interpretation of
soils from airborne radiometric data. Unpublished map, Australian Geological
Survey Organisation, Canberra.
Schwebel, D.A. (1983) Quaternary dune systems. In: Tyler, M.J., Twidale,
C.R.,Ling, J.K. and Holmes, J.W. (Eds). Natural history of the South East.
Royal Society of South Australia. Occasional Publications, 3:15-24.
Tyler, M.J., Twidale, C.R., Ling, J.K. and Holmes, J.W. (Eds). (1983) Natural history
of the South East. Royal Society of South Australia. Occasional Publications.
*Recent unpublished research has shown that siliceous sand grains in soils collected from the West
Naracoorte Range were last exposed to sunlight 150,000 years ago. This implies that the terra rossa soils
were formed recently and that the soil sediment was not derived from the dune. Chemical analysis of the
terra rossa soil indicates it could not have been derived from the underlying dune and was deposited by
wind. The field observations do not support these views and these differences are unresolved.