The South-east Karst province of South Australia

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There is also evidence for historical changes in water tables of the order of ... together with heath and swamp vegetation in the swampier areas (Lange 1983). ...... exploration (Wopfner and Thornton, 1971) and suggested that there could be ...

Grimes, K.G., 1994: The South-east Karst province of South Australia. Environmental Geology 23: pp 134-148. This is my own layout & pagination, and the text may differ slightly from the published version.

The South-East Karst Province of South Australia K. G. Grimes Regolith Mapping, PO Box 362, Hamilton, Victoria 3300, Australia

Abstract The South-East Karst Province of South Australia is an extensive area of low relief with dolines, cenotes, uvalas, and a variety of cave types developed in the soft, porous, flat-lying Tertiary Gambier Limestone and also as syngenetic karst in the overlying calcarenite dunes of the Pleistocene Bridgewater Formation. The most spectacular surface karst features are the large collapse dolines, especially those that extend below the water table to form cenotes. Shallow swampy hollows occur in superficial Quaternary sediments. These are an enigmatic feature of the Bool Region, where all gradations appear to occur between definite karst dolines and nonkarstic hollows. Some depressions may be polygenetic – involving a combination of: (1) primary depositional hollows on coastal flats or in dune fields, (2) deflation, and (3) karst solution and subsidence. There are extensive underwater cave systems in the southern part of the province, and the bulk of the cave development there may well lie below the present water table, although these systems would have been at least partly drained during the lower sea levels of the last glacial period. Systematic variations within the province reflect differences in the parent rock types, the extent and nature of the cover and, most importantly, the hydrology – in particular the depth to the water table and its gradient. Key words: Karst, Dolines, Cenotes, Uvalas, Caves

Introduction The South-East Karst Province of South Australia is bounded by the coastline to the south and west, the Victorian Border to the east, and extends northwards to latitude 36° 20', although the bulk of the caves and karst features are limited to the area south of Naracoorte and east of Millicent (Figs. 1 and 2). The area also extends a short distance into Victoria in the southeast. There have been few karst studies of the area – most detailed is the regional study by Marker (1975). Others are the early summary by Sexton (1965) and the later honours thesis study of the Lower South-East by Lewis (1984). Thurgate (1992) described some selected cenotes and springs in the Lower South-East. Geological and geomorphological studies of relevance to the karst include those of Wopfner and Douglas (1971), Cook and others (1977), Schwebel (1983), and Twidale and others (1983). Blackburn (1983) summarized the soils of the area. The hydrology of the region was discussed by Waterhouse (1977), Holmes and Waterhouse (1983), and Love and others (1992). The present study is being done for the South Australian National Parks and Wildlife Service and involves an inventory of karst features on Crown land in the southeast of the state. This paper is a modified and reduced version of a review that appeared in the field guide to the IGCP 299 symposium on "Geology, climate, hydrology and karst formation" (Grimes 1992).

Geology and landforms Regional setting The South-East Karst Province lies in the Gambier Embayment in the northwestern part of the Cretaceous to Tertiary Otway Basin (Wopfner and Douglas 1971) and also extends a short distance north over the Padthaway Ridge in the Naracoorte area. The karst is developed on Tertiary marine Gambier Limestone, the younger Pleistocene calcareous dune limestones (Bridgewater Formation), and calcareous marine and coastal plain sediments of the interdune flats. Its development is also influenced by the thin younger sediments that partly cover the limestones. Figure 1 shows the distribution of the main geological units in the province. The area is mostly low and flat, with local relief provided by the dune ridges and the volcanic hills. Many of the flats were waterlogged for much of the year but have now been artificially drained. The gorge of the Glenelg River in the extreme southeast has provided sufficient relief to form the only known vadose stream caves in the province. Gambier Limestone The Gambier Limestone was deposited in a shallow marine embayment that flooded the region in the Oligocene and early Miocene. It is mainly composed of porous bryozoan limestones (Waterhouse 1977; Wopfner and Douglas 1971). The unit varies in thickness from 300 m at the coast to less than 100 m at Naracoorte but is reduced to nothing beneath parts of the Dismal Swamp where it has been uplifted and eroded above the Tarpeena-Dartmoor Upwarp (Fig. 4 below). The


Figure 1: The South-East Karst Province, its regions and geology. CF = Caroline Forest, GF = Gambier Forest, MF = Myora Forest, TF = Tantanoola Forest, K = Kalangadoo, N = Nangwarry, Mt.G = Mount Gambier, GL = Gambier Lineament.

limestone is poorly consolidated in the subsurface but develops case hardening and calcrete cappings on exposure. It is massive to well bedded with horizontal or gentle dips and is jointed with a dominant northwest trend. The influence of both the jointing and the bedding are exhibited in the cave passage forms. The Gambier Limestone forms the main unconfined aquifer in the area. At its base it is separated by a thin aquiclude from an older nonkarstic confined aquifer – the Eocene Knight Group. The limestone has been folded and faulted in places. The main structures are the Tarpeena-Dartmoor Upwarp and the associated Tartwaup Fault and Gambier Lineament, which lies to the north of Mount Gambier (Fig. 4 below). In the Naracoorte area, the edge of the uplifted Naracoorte Plateau follows the Kanawinka Fault (Fig. 3 below). The surface expression of the fault is now the Kanawinka Escarpment, an early Quaternary sea cliff that has been cut back up to 2.5 km to the northeast of the original fault line (Kenley 1971). Pliocene alluvial and marine deposits On the Naracoorte Plateau the limestone has a partial mantle of Parilla Sand, a partly lateritized fluvio-lacustrine unit of Pliocene age. In the Bool Region, to the southwest of the Kanawinka Scarp, the Gambier Limestone is mantled by late Pliocene marine calcareous quartz sands up to 17 m thick (Fig. 3 below)(Cook and others 1977). Towards the Victorian border these quartz sands are replaced by shelly calcareous sands and muds that might be equivalent to the Pliocene to early Pleistocene Whalers Bluff Formation. Bridgewater Formation and associated coastal deposits The Bridgewater Formation is a series of calcareous dune ridges that run parallel to the coast (Schwebel 1983). The ridges are coastal dunes and associated beach deposits that developed along shorelines during an overall uplift of the area and associated regression of the sea during the Quaternary. They form linear north-northwest trending ranges that rise up to 30 m above the adjoining plains. However, there are higher piles of dune sands in the Mount Burr area, where dunes have climbed up the sides of older volcanos, and to the southeast of Mount Gambier, where several dune ridges have coalesced.


The ridges are now partly consolidated calcarenites and contain syngenetic karst features. Within the study area, the innermost and oldest ridge is the East Naracoorte Range, where the dunes have climbed over the Kanawinka Escarpment cut into the Gambier Limestone (Fig. 3 below). This dune ridge has been dated at about 700,000 years old, and the ridges to the southwest become progressively younger towards the modern coast (Cook and others 1977; Idnurm and Cook 1980). Between the ridges there are extensive swampy plains. These are old coastal flats and comprise estuarine to lacustrine marls and clays up to 13 m thick (Fig. 3 below). These plains have many shallow swampy depressions of uncertain origin. The volcanics Quaternary volcanics in the area are the western end of the basaltic Newer Volcanics of Victoria (Sheard 1983). The main area of volcanics is centered on Mount Burr and ranges from about 2 million years to 20,000 years old. The isolated volcanos at Mount Gambier and Mount Schank are younger (4000-9000 years old). The older volcanos are partly buried by calcareous beach and dune sands of the Bridgewater Formation, but their form is still obvious and craters are preserved in some of them. The younger volcanos at Mount Gambier and Mount Schank postdate the Bridgewater Formation and have better preserved landforms. Blue Lake at Mount Gambier is a watertable lake in a large crater. Younger dunefields and sand sheets In the Bool Region the interdune flats have been covered in places by thin Pleistocene and Holocene alluvial deposits and aeolian sand sheets of several ages (equivalents of the Pleistocene Malanganee Formation and Holocene Molineaux Sand). The undulating to flat sheets of quartz and quartz-calcarenaceous sands are particularly common in the Nangwarry Region and in the eastern part of the Gambier Region. These are probably derived from reworking of the Bridgewater Formation. Sheets of Molineaux Sand on parts of the Naracoorte Plateau would have been derived from both the Parilla Sand and the Bridgewater Formation of the Naracoorte Range. The modern dunes of the coast are actively moving inland to form linear ranges that can be taken as a model for the development of the older dune ranges of the Bridgewater Formation.

Hydrology Natural surface drainage channels are absent over much of the province. Exceptions are in the far southeast, where the Glenelg River, an allogenic stream rising outside the province, has cut a gorge through the limestones, and in the north, where several creeks in the Naracoorte area have maintained their surface flow across the Naracoorte Plateau. The Gambier Limestone forms the main unconfined aquifer in the area. This has been referred to as one of the best aquifers in Australia (Holmes and Waterhouse, 1983). The porous nature of the Gambier Limestone means that much of the groundwater flow is via the primary porosity rather than in channels or fractures, and there is a well-defined watertable. The groundwater surface shows a general coastward slope with a high ridge beneath the Dismal Swamp area north of Mount Gambier and two belts of relatively steep gradients: one along the line of the Kanawinka Escarpment, and one beneath the Gambier Region (Figs. 2-4). The groundwater divide in the Dismal Swamp area is caused by thin and relatively less permeable aquifers above the Tarpeena-Dartmoor Upwarp. Marker (1975) considered that the nature of the groundwater regime is the most important control on the character and extent of karst development in the province. She correlated areas of strong cave development with the areas where the water table was at greater than normal depth and where there were steep water table gradients. The northern steep gradient zone corresponds to the line of the Kanawinka Fault. This is also a zone of major cave development (Fig. 2). The southern steep gradient zone passes northwest through Mount Gambier and is partly the result of the steep rise in the base of the Gambier Limestone, which thins over this area, and partly due to permeability changes within it (Waterhouse 1977; Holmes and Waterhouse 1983). This zone also has a significant concentration of caves. During glacial periods the lowering of sea levels would have caused the coast to retreat to the edge of the continental shelf and descend a way down the continental slope. This would have caused a significant drop in the groundwater levels in the Coastal and Schank regions (Fig. 4) (Love and others 1992). The reduced water table and extension of the steep gradient zone in the northern Schank Region may have been responsible for the concentration of cenotes and large cavities in that area (Lewis 1984). Reduced sea levels would have had less effect in the Gambier Region and the regions further inland where the distance from the coast would have reduced the sea level effect. In the Gambier Region, the local geological control, in particular the high levels of the aquiclude at the base of the Gambier Limestone, would have been the main factor that determined the water levels. Within the submerged caves there is evidence for major lowering of the water table at some stage in the past – for example, extensive mudcracks occur on the floor of Iddlebiddy Cave (L 250) in present water depths up to 15 m (Horne 1990), and submerged speleothems have been reported as deep as 22 m (Lewis 1984). There is also evidence for historical changes in water tables of the order of several metres. For example, Sheathers Cave (L 144) was almost completely flooded when first recorded in 1972, but the water level dropped over a metre during a period of five years between 1982 and 1987 (Horne 1988). This can be contributed to the growth of a pine plantation on the surface. By contrast, the levels in Mount Burr Bat Cave (L 69) have risen since the pine plantation in that area was


Figure 2: Water-table contours for the Gambier Limestone aquifer. The density of significant karst features is superimposed.

destroyed by a fire (A. P. Spate, personal communication). This difference in groundwater recharge between pine plantation areas and the surrounding country has been discussed by Allison and Hughes (1972). Exposed stromatolites on the walls of some cenotes also indicate higher water tables in the recent past. Much of the groundwater from the Mount Gambier area is discharged in major springs in the Piccaninnie Ponds and Eight Mile Creek areas on the southern coast and to lesser springs in the Kongorong area. Clisby (1972) reported a total flow of 5200 l/s from the coastal springs. Marker (1975) showed a line of small springs in the Millicent area, but the resurgence points further Figure 3: East-west geological cross section in the Naracoorte west are not well documented. area. Based on sections in Cook and others (1977) and Marker (1975).

Soils Blackburn (1983) presented a detailed description of the soils of the province. Six great soil groups are widespread in the area. Podzols are developed on the quartz sands that mantle most of the dune ridges and dune sheets in the area. Humus Podzols occur in the lower waterlogged parts of the quartz sand sheets. Rendzinas together with Solodized Solonetz and Solodic soils are characteristic of the flats that lie between the dune ridges of the Bool and Millicent regions. The last two soil types also occur on the limestones and younger covering sediments on the Naracoorte Plateau. Terra Rossa soils occur


Figure 4: North-south cross section along longitude 140°40' showing the base of the Gambier Formation, present and past water tables, and selected cave depths. L-42 = Ten-Eighty Cenote and associated cave, L-72 = the shaft at Piccaninnie Pond.

on exposed areas of the Gambier Limestone, in particular in the Schank Region and the Glencoe Area, and also on some of he calcareous dune ridges and on the younger limestones near Coonawarra. Calcareous sands are poorly developed soils on the younger calcareous dunes of the Coastal Region. Some subsidiary soil groups include soliths and humic gleys and gleyed podsolic soils in the waterlogged southern part of the Bool Region, and peat soils in the swamps of the Coastal Region.

Climate The climate of the region is a Mediterranean one (Csb in the Köppen system) with wet winters and cool dry summers. Penney (1983) provided a useful summary of the rainfall, evaporation, solar radiation, winds, and temperatures of the region. The annual rainfall decreases from 800 mm in the south to 550 mm in the Naracoorte area. The Mount Burr volcano (240 m asl) causes a local orographic peak in rainfall with a slight rain shadow to its east. Mean annual temperatures range from 14.4°C at Naracoorte to 13.2°C at Mount Gambier. During the Quaternary the present type of climate would have alternated with colder, drier, and windier climates during the peaks of the glacial stages (Colhoun 1991). The windy periods would be responsible for the lunettes and possibly for deflation of some of the enigmatic shallow hollows in the Bool Region. Much of the area would have been intermittenly flooded by the sea during the interglacial periods of the early Quaternary.

Vegetation The original (pre-European and pre-Aboriginal) vegetation is poorly documented, but would seem to have been a soiland topographically-controlled mosaic that included moderately dense forest and woodland, mallee woodland, open forest, together with heath and swamp vegetation in the swampier areas (Lange 1983).

Karst landforms Karst landforms comprise the caves and a suite of surface features that have resulted directly or indirectly from solution of the limestones.

Syngenetic karst Syngenetic karst (Jennings 1968) is an important feature of the province. In the calcareous dunes of the Bridgewater Formation, karst features have developed at the same time as the sand was being consolidated into a calcarenite. The main characteristics of syngenetic karst are the development of a calcreted caprock, of vertical solution pipes, and of low, wide, horizontal cave systems at the level of the adjoining swampy plains. The poorly consolidated nature of the rock means that collapse plays an important role from an early stage. Solutional, subsidence, and collapse dolines can occur on the surface, but the former two can be difficult to distinguish from primary dune hollows. Solution pipes are vertical cylindrical tubes, typically 0.3-1 m in diameter, which can penetrate anything from less than a metre to 20 m into the soft limestone. They occur as isolated features or in clusters with spacings as close as a metre or so. They commonly have a cemented rim that is harder than the surrounding rock, and they may be empty or filled with a reddish soil. In some the soil fill has been cemented to form a solid plug. At the surface these pipes may be flush with a rocky pavement or at the base of a conical subsidence doline developed in a sandy soil cover. Within some caves the presence of many sand cones reaching to the chamber ceilings indicates the abundance of sand-filled pipes. Jennings (1968) postulated that the pipes formed around tree roots penetrating the soft calcareous sand and that they contributed to the consolidation of the dune. Calcareous rhizomorphs are a common feature in the younger, partly consolidated, dunes.


Figure 5: Syngenetic karst cave in a dune calcarenite at Bat Ridges, western Victoria. Note the soft sandy floor, the flat roof (cut at an old water table), and a phreatic sculptured pendant extending below the roof.

Syngenetic karst development is typical of the Quaternary dune calcarenites; however, the Gambier Limestone is a relatively soft porous limestone, and consequently it also shows some of the features of syngenetic karst, in particular the development of solution pipes and calcreted caprocks. Not all karst features in the Bridgewater Formation are syngenetic. Subjacent karst can occur where the formation overlies the Gambier Limestone. There are a number of caves and dolines that have their main development in Gambier Limestone but extend up into the overlying Bridgewater Formation.

Caves Typical syngenetic caves in the calcareous dunes are shallow horizontal systems developed beneath the caprock. They have multiple entrances (often via solution pipes or the collapse of the surface crust) and an irregular outline of chambers, pillars, and short connecting passages, generally with a roof height less than 1 m throughout. Caves are best developed at the levels of the adjoining swamps but also occur higher in the dune ridges. Those near the swamps show obvious control by water tables (Fig. 5) and are low horizontal irregular systems. They tend to have thicker roofs than the higher caves in the dune ridges and may have multiple levels tied to older water tables. Most syngenetic caves show extensive instability, so that collapse domes and rubble-filled passages are common. The caves in the dune limestone generally lack strong joint control.

Figure 6: Map of Engelbrecht Cave (L-19): a typical large, part-submerged, phreatic system with much collapse modification; located beneath the city of Mount Gambier. The north-northwest alignment is a common feature of the caves in the region and follows a dominant joint trend. Note the highway directly above the large collapse dome.


The caves in the Gambier Limestone are dominantly horizontal phreatic systems – the limited relief means that vadose features are restricted to a few caves in close proximity to the incised Glenelg River. Both joint and bedding plane control can be seen, but because the bedding planes are horizontal, it can be difficult to distinguish their influence from that of solution at temporary water-table levels. Joint control is less obvious in the Naracoorte Plateau than in the southern regions. Because of the soft nature of the parent limestone, some syngenetic characters also occur in these caves. Many of the primary phreatic caverns and passages have been modified by breakdown, and collapse domes and passages are common. Entrances can be vertical joint-controlled fissures, collapse windows above chambers, or vertical solution pipes. In the southern part of the region, the bulk of the cave development may be below the present water table, although these passages would have been at least partly drained during the low sea levels of the last glacial period. On the Naracoorte Plateau, the caves range from small solution pipes and chambers to large complex systems. The larger caves tend to be linear to maze-like systems of interconnected large chambers and smaller passages. The large chambers are mainly collapse domes, but some phreatic features are preserved locally, especially in the lower levels, near the present water table. Only a few caves actually reach down to the present water table. The caves of the southern regions are more variable in character – reflecting the variable parent materials and topography. They range from simple solution pipes and small fissures to extensive horizontal underwater systems of large phreatic and collapse passages (Fig. 6). Other phreatic caves are irregular in plan and typically consist of chambers and low flatteners. In the Schank Region, there are spectacular large flooded collapse domes up to 80 m high and 130 m across, some of which have extensive horizontal development. The large collapse domes may penetrate to the surface to form cenotes. The original cave passages appear to have been large phreatic tubes, but these have been extensively modified by collapse.

Dolines The most spectacular surface karst features are the collapse dolines, especially those that extend below the water table to form cenotes (see below). These have formed above large phreatic caverns. They reach widths of 130 m and depths of up to 46 m. Large conical to basin-shaped dolines up to 500 m across and 8 m deep occur in areas of stronger relief in parts of the Gambier and Naracoorte regions. This type was referred to as funnel dolines by Marker (1975), but in this paper are referred to as basin dolines, as that is the more usual shape. Some of these contain small active "run-away holes" where the surface runoff soaks into the sandy soil. These dolines appear to be a combination of solution and of subsidence of surface soil into large cavities. The larger dolines tend to have a less regular form and grade to uvalas. Smaller versions also occur and are discussed below. More numerous are the many small shallow hollows that occur throughout the province, but are particularly common in the Bool, Nangwarry, and parts of the Naracoorte and Gambier regions. There are four main types of these small hollows. The first type of hollows are smaller versions of the basin dolines described above. These are typically 1-3 m deep and generally less than 100 m across. As with the larger versions, they appear to be mainly subsidence dolines in either soft soil or superficial sediments over buried karst cavities in limestone, although where the cover is thin some might be simple solutional dolines. Most are dry, but about a third hold water, even near the end of the dry season. These ponds can occur on ridge tops and also in close proximity to the dry holes, so the water must be perched on an organic or clay horizon which has built up beneath the sandy topsoil. A second type of hollows are the swamp dolines of Marker (1975), which consist of shallow flat-floored, and swampy hollows. These are most common in the Bool Region, where they form extensive fields, but examples occur in all the regions. They are typically less than a metre or two deep and can be from 50 m to over 500 m across. They are generally swampy and may have seasonal lakes. The shallow swampy form is probably due to restriction on vertical development as a consequence of a shallow water table and the thin limestone beds in which they have formed. Where they occur in association with deeper basinal dolines, this could indicate a local perched water table. A third type of hollows are the shallow lunette lakes seen in the Bool Region. These are a larger variant of the flatfloored swampy hollows. Lunettes are a special feature of lakes in southern Australia (Twidale and others, 1983). They form as clayey crescentic ridges at the eastern margins of shallow lakes in the interdune flats. The lunettes are not karst features, but the associated lakes have been interpreted as such by some previous authors as there is limestone or marl at shallow depth. However, many of the larger lakes could be primary coastal depressions, such as are commonly seen on the flats behind foredunes on modern coasts. Bool Lagoon is a large complex of these lunette lakes. Fourth, some ill-defined swampy areas with irregular outlines are an extreme end member of the flat-floored swampy type. These are probaby not karst features. All gradations between the four end members occur, and when interpreting the smaller features on aerial photographs it was difficult to distinguish the types. Only the basin types are definite karst features. In some places (e.g., the Naracoorte Region) most of the flat-floored type are karst, with the depth limited by the water table or by sedimentation that has filled in an old saucer type, but in the Bool Region the flat-floored hollows and lunette lakes may be mainly the result of other processes. Some depressions may be polygenetic, involving a combination of primary depositional hollows on coastal flats or in dune fields, deflation hollows, and karst solution or subsidence. Subjacent karst effects inherited from the buried Gambier Limestone or the younger marls and limestones of the Bool region may also contribute.


Figure 7: 7a: detail of a typical cenote (Goulden Hole) in the Schank Region. The prior water level is deduced from the height of exposed stromatolites. From a survey by P. Horne (CEGSA) in 1981. 7b: Some cenotes and related features in the Gambier and Schank regions. Black is water. Note the higher water tables in the two examples from the Schank Region. The Shaft is a large collapse dome that is currently connected to the surface by a small solution pipe and illustrates the situation prior to collapse of the roof to form a cenote. From CEGSA and CDAA surveys.

Figure 8: Little Blue Lake (L-9), a cenote in the Schank Region. The cliffs extend 6 m above water, but the water depth is 40 m (cf. Fig. 7b)

Figure 9: Stromatolites on the wall of a cenote, exposed by a recent drop in water table. The Sisters (L-44), Schank Region. 10-cm scale


Cenotes The term cenote has been used fairly broadly in the southeast to include not only steep-walled collapse dolines that extend below the water table, but also dry collapse dolines that have water in associated caves or for mainly submerged caves with entrances that are not strictly collapse dolines. Part of the nomenclature problem comes from the emphasis by the cave divers on the presence of deep water in any situation and part from Marker's (1975, 1976) use of the term cenote as a synonym for any collapse doline with sheer walls, regardless of the presence of water. I will follow the usages of Monroe (1970) and Jennings (1985), who restricted cenote to collapse dolines that contain a water-table lake. Cenotes are restricted to the southern regions: The southern half of the Gambier Region and the Schank and Coastal regions. All gradations occur, from dry collapse dolines through those with just a small pool under an overhang or water in an associated cave, to the "true" cenote with a large deep lake and possible underwater cave extensions (Fig. 7). The drier versions are more common in the Gambier region where the water tables are deeper, The cenotes typically have sheer walls, sometimes pocketed with horizontal solution tubes in the upper levels. The presence of a lake enhances the visual impact, and these are favoured sites for both passive and active recreation (Fig. 8). The deep water has attracted cave divers and indirectly led to a numberof safety and management problems. An interesting feature of some of the cenotes is the existence of stromatolites: underwater calcareous growths formed by algae (Thurgate 1992). These are growing actively to depths of over 10 m, and some occur as deep as 25 m. A zone of well-preserved stromatolites is exposed up to 2 m above the present water surface in several of the cenotes (Fig. 9). This indicates a drop in the water table in fairly recent times – possibly since European settlement.

Uvalas Uvalas are composite hollows. They are most common in the Naracoorte Plateau, the Nangwarry Region, and the Gambier Region. They have formed in part by the coalescence of simple solution or subsidence dolines, in part as chains of hollows along old dry valleys, and in part by the karst modification of primary dune hollows. They can be difficult to distinguish from dune hollows.

Dry valleys In the Naracoorte Plateau and in the southeastern end of the Gambier region, there are old surface drainage lines that have been abandoned as a result of underground capture of their flow. Most are just chains of dolines and uvalas and are not immediately obvious; however, there are two better-defined examples. The first, in the Naracoorte Plateau, is a deep meandering dry valley that cuts across the East Naracoorte Range at Jerboa, east of Struan. This is a good example of superimposed drainage – a prior stream managed to maintain its course and cut a deep valley as the range was uplifted. Subsequent underground capture of the water has left the valley dry. A line of dolines and uvalas running to the northeast of this old valley marks a continuation of it across the Naracoorte Plateau. Mosquito Creek, where it crosses the East Naracoorte Range, is also an example of superimposed drainage, but in this case the surface stream is still active. The second example is Dry Creek near the Glenelg River in the Gambier Region, which is a well-preserved incised meandering valley that now has no surface drainage and a number of shallow closures within its thalweg.

Springs There are many springs in the Coastal Region. Most rise out of small submerged dolines or caves and feed small creeks, swamps, or a series of artificial drains. A few are known to bubble out of the sands on the modern beach and some may also occur offshore on the sea floor (Marker 1975). Clisby (1972) reports a total discharge of 5200 l/s from all measured springs east of Port MacDonnell. There are no tufa deposits associated with the springs. Springs are also known in the Millicent Region, but flows are much less and they are not well documented. Most of the surface ponds have a circular to elliptical plan and a basin- or funnel-shaped floor. These are probably either solutional dolines or degraded collapse dolines formed when the water table was lower. The associated caves are joint controlled fissures with some small phreatic chambers and minor collapse modification. The largest is the cave beneath Piccaninnie Ponds (L 72), which extends to a depth of at least 75 m. This shows excellent phreatic sculpturing of the walls.

Karren and other small-scale surface forms The Shank Region has the best development of karren fields. These show extensive exposures of rounded subsoil karren with some areas of sharper surface solutional sculpturing (Marker 1975). Apart from the Schank Region, karren are not well developed in the province, mainly because of the lack of extensive bare karst. At Dry Creek in the far southeast there are moderately extensive limestone outcrops in linear ridges and pavements. These show rounded subsoil karren forms and some rain pits and poor-quality rillenkarren. Karren also occur on the coastal cliffs (see below).

Coastal karst Coastal karst and related features are well developed on many of the low limestone cliffs along the coast. They include small pits, sharp hackly pinnacles, tide notches and platforms, and sea caves. The small-scale solutional forms are produced by the sea spray, assisted in many cases by the biological solution of algal hyphae and other small plants to form phytokarst


(Jennings 1985; Folk and others 1973). The small sea caves that occur in the coastal cliffs are formed primarily by wave action, but some of them show well-developed horizontal slots near the high water mark that could be partly solutional in origin. Some of the coastal cliffs have good exposures of solution pipes developed in calcareous bands. These are seen both in plan and in section in the cliff faces.

Quasikarst forms Primary dune hollows occur in the high dunes – these are not true karst, but may have had some modification by karst processes. All sizes and depths occur up to a maximum length of several kilometres and depths of 15 m or more. They are typically smoothly rounded basins or closed valleys, but where the base of the dunefield has been limited by a water table, they may have flat swampy floors. In places they have been pitted by smaller subsidence dolines to form uvala-like features. Dune hollows can be difficult to distinguish from true karst dolines; all gradations occur. Areas referred to as hummocky terrain occur in several places in the Mount Gambier Region. These areas consist of an irregular to elongated pattern of rounded hills separated by broad basin-shaped hollows. The hills are built partly of calcareous dune limestone, but the lower parts are in Gambier Limestone. The larger hummocks, in the immediate vicinity of Mount Gambier, have a vertical relief ranging from 10 to 25 m and a "wavelength" of between 300 and 700 m. The hollows are nearly always dry – indicating a well-developed underground drainage. This terrain seems to be a dune topography that has been modified by karst processes, as the bottoms of the hollows commonly extend well below the contact between the old calcareous dunes and the underlying limestones. To the northwest of Mount Gambier the hummocks are gradational to a high dune topography in the Gambier Forest and also grade to true karst dolines and uvalas in the nearby Wandilo area. A smaller version of this hummocky terrain occurs to the east in the Myora Forest where the vertical relief is generally less than 5 m (and commonly only 1 m) and the "wavelength" is between 50 and 200 m. These small hummocks grade into a gently undulating dune sand sheet.

Karst regions Marker (1975) recognized seven regions within the South-East Karst Province (Fig. 1), for which her subdivisions have been adopted, but with some modifications to the boundaries so as to better reflect the geological and hydrological setting. In particular, the Dismal Swamp as a distinct region has been abandoned and combined with the Bool Region, and two new regions – Nangwarry and Millicent – have been recognized. The Glencoe–Gran Gran region of Marker (1975) is regarded as part of the Gambier Region.

Naracoorte Plateau The Naracoorte Plateau lies in the northeastern part of the province at an elevation of 85-100 m asl. It is a plateau of Gambier Limestone uplifted to the east of the Kanawinka Fault. A thin cover of soil, laterite, alluvium, and aeolian sand sheets up to 6 m thick blankets part of the plateau. Some ridges on the plateau are possibly old coastal dune lines of late Pliocene or early Pleistocene age. Along the western margin there is a pair of large dune ridges (Bridgewater Formation). The westernmost ridge (the West Naracoorte Range) is a thick calcareous dune sand and has little karst development, although it would have potential for syngenetic karst. The eastern ridge (the East Naracoorte Range) is perched above the old sea cliff of the Kanawinka Escarpment and has only a relatively thin dune cover over Gambier Limestone (Fig. 3). The water table is relatively deep beneath the plateau – averaging 16 m below the surface. It is deepest in a zone of relatively steep gradients along the line of the Kanawinka Escarpment at the western margin of the region. This is where the water descends from the intake areas on the plateau down to the level of the Bool Region. The main concentration of caves is along a zone of deep water tables and steep gradient beneath the East Naracoorte Range. The caves range from small solution pipes and chambers to large complex systems such as Victoria Fossil Cave (U 1) with 3000 m of passages. Joints are present in the limestone, but joint control on the overall form of the caves is not as obvious as in the southern regions. Most of the larger rounded hollows in the Naracoorte Ranges appear to be primary dune hollows rather than karst, but smaller karst dolines do occur. The best development of dolines occurs on the main plateau, east of the Naracoorte Ranges, but caves are less common here. The dolines vary from small saucer-, basin-, or conical-shaped subsidence depressions in the soft soil or dune-sand cover to larger basins and shallow, flat-floored hollows that may be swampy or form intermittent to permanent lakes. Collapse dolines are rare; those that do occur are in the form of small roof windows above cave chambers. The larger basin dolines grade to uvalas, and there are several chains of dolines and uvalas marking old dry valleys in the southeast of the plateau. A deep meandering dry valley cuts across the East Naracoorte Range east of Struan. There are some small areas of karst pavements or karren, but no good examples occur in this region.

Bool Region The Bool Region corresponds to the Bool Lagoon- Kalangadoo Region of Marker (1975). It has been extended it to include all the interdune flats in the province north of the Gambier Region along with the smaller linear dune ridges that occur within the flats. This region is the most extensive one within the South-East Karst Province. The lines of dune ridges mark old Quaternary coast lines, while the flats are developed on the alluvial, swamp, lagoon, estuarine, and shallow marine deposits of the old coastal plains that formed behind the ridges. The dune ridges are calcareous sands and have the potential to develop syngenetic karst. The deposits of the flats include estuarine and lacustrine marls and limestones that also have some karst potential. Parts of the flats are covered by quartzose sand sheets and have little karst development. Even where


the underlying sediments are calcareous, karst development on the flats appears to be restricted to shallow depths by the high water tables, poor drainage, and the nature of the host sediments. Prior to an extensive artificial drainage program, much of the flat country was flooded for extensive periods each wet season. Many of the shallow hollows still hold water for much of the year. Known cave development is restricted to syngenetic cavities in the better drained calcareous dune ridges, and to a pair of small caves in the flats at the southern end of the region. These latter are very small, shallow, phreatic cavities that appear to be developed in calcreted Gambier Limestone or Whalers Bluff Formation beneath a thin sandy cover. The flat plains have numerous shallow surface depressions that are somewhat enigmatic (see discussion above in Karst Landforms section). They range from small well-defined basin dolines that appear to be definite karst features, through shallow flat-floored swamp "dolines," only some of which may be karstic, to lunette lakes and ill-defined irregular-shaped swamps that probably have no karst significance. Some of the hollows have a composite form and could be referred to as uvalas if one were sure of their origin. The linear dune ridges contain hollows, but these are mainly aeolian in origin, although some small subsidence dolines are known.

Nangwarry Region This newly named region incorporates the pine plantations and adjoining parts of the Nangwarry area (Fig. 1). It includes parts of Marker's Bool Region, and some areas that she excluded from the karst province. It is a low undulating sand plain, but differs from the sandy plains of the Bool Region in having a stronger relief and a relatively thick cover of quartz sand. The undulating surface appears to be a dune sheet, and degraded irregular to linear dune ridges can be recognized in places. It comprises quartz sand and clay up to 8 m thick and overlies Pliocene and Pleistocene coastal and marine calcareous deposits similar to those beneath the Bool Region (Ludbrook 1966, unpublished report). A few slightly higher areas of calcareous dune ridges (Bridgewater Formation) also occur. The Gambier Formation occurs at depths of about 20 m but pinches out over the Tarpeena-Dartmoor Upwarp and is replaced by a noncarbonate Eocene sequence. The water table is at shallow to moderate depths, generally less than 5 m, but the gradients are low and flow rates would be sluggish. No collapse dolines or caves are known in the area: probably the thick sandy surface soil clogs any potential entrances, and the relatively shallow and sluggish water table would limit the development of large cavities. Shallow dune hollows are common throughout the region. Southwest of Nangwarry, the dune hollows have a linear form up to 3 km tong and appear to be swales between linear dunes. Small saucer and basin dolines and larger flat-floored swampy dolines are common throughout much of the region, and locally abundant in the southwest and some parts of the east. Many of the dune hollows are pocketed by small subsidence dolines, which give them a uvalalike form.

Gambier Region The Gambier Region of Marker (1975) is a composite area comprising several different geological and geomorphic zones. Marker recognized an inlier, the Glencoe Region, as a separate entity. This area is discussed separately below, but it probably should be included as part of the Gambier Region. High dune ridges, together with exposures of Gambier Limestone and some flatter swampy country, form the Mount Burr and Gambier Forest areas. The northern part of the Tantanoola Forest also is dune country, but the southern part is a series of low beach ridges that form only a thin cover over Gambier Limestone. About Mount Gambier itself there is a strong hummocky terrain in which hills built partly of calcareous dune limestone stand above hollows in Gambier Limestone. Further east the hummocks become much smaller and are difficult to see under the dense pine plantations of the Myora and Caroline forests. The low-lying country there is interrupted by scattered higher dunes. The southern part of the Caroline Forest is a composite series of high coastal dunefields that separate into several discrete dune ridges further to the northwest. A major west-northwest trending structural lineament associated with the Tartwaup Fault runs along the core of the region. Marker referred to this as the Gambier Lineament (Fig. 1) and pointed out differences in the karst style to north and south – in particular, most of the large collapse dolines and associated cenotes and deep underwater caves lie to the south of this line. A line of elongated dolines and uvalas follows the surface trace of the fault. Marker (1975) reported water-table depths varying from up to 15 m in the north to as much as 26 m in the south of the region. There is a steepening of the water-table gradient as it crosses the Gambier lineament – in contrast to the almost flat gradients of both the Bool Region to the north and the Schank Region to the south (Figs. 2 and 4). The degree of cover above the limestones varies from fairly thick (up to 7 m) beneath the high dunes, to quite thin in lower areas where Gambier Limestone is exposed or occurs beneath a thin dune limestone. Some bare limestone pavements occur in the Dry Creek area in the far southeast. A variety of caves occur both in the Gambier Limestone and as syngenetic karst in the dune limestones. In the Victorian part of the region, the Glenelg River has incised its channel sufficiently to allow vadose streams to flow through the fissure caves in the base of the river cliffs. These are the only active vadose stream caves in the province. A number of spectacular large collapse dolines occur, some of which extend below the water table to form cenotes. The


largest example of a cenote in the Gambier Region is Hells Hole (L 40), which is a collapse hole 45 m across found on the upper slopes of a dune ridge in the Caroline Forest (Fig. 7b). It penetrates about 10-15 m of dune limestone and then Gambier limestone to reach the water table at a depth of 27 m. Below the water the hole bells out into a large collapse dome with a maximum water depth of 33 m. With a few exceptions, the smaller basin-shaped and flat-floored swamp dolines are absent from the high dunes and from the hummocky terrain, but they are common in the southeastern part of the Glencoe area. Good examples of solutional uvalas occur to the northwest of Mount Gambier. Dry valleys occur in the Dry Creek area in the far southeast. Karren are not well developed in the region, the best examples being in the Dry Creek area near the Glenelg River. The Up and Down Rocks, in the Tantanoola Caves Conservation Park, are an old sea cliff (Tindale 1933).

Glencoe area This is a small area of Gambier Limestone with moderate to thin soil cover that lies within the Gambier Region. Marker (1975) gave it a separate status because of its distinctive character. The region comprises uvalas and small dolines, including stream sinks and blind valleys taking water derived from the adjacent volcanic hills. The water table is typically 6 m below the surface, and the soil cover is thickest at the margins (8 m) and in the southeast but thinner towards the center. Caves are moderately common in the region. They are a mix of collapse, phreatic, and joint-controlled systems developed mainly in Gambier Limestone, although some may intersect overlying areas of dune limestone. Most have watertable pools or small lakes. A few small collapse dotines are associated with cave entrances. The region has many small to medium-sized basin dolines, and some flat-floored swamp dolines. Flat-floored hollows are particularly common in the flat and swampy Honans Scrub area, southeast of Glencoe. This swampy area has many similarities to the Bool Region. It has been attributed to an old course of the Glenelg River, which was supposed to have run westwards from Victoria through the Dismal Swamp area and then south through this area to the sea (Sprigg 1952; Boutakoff 1963). There are many uvalas in the area, some very extensive. The largest is a broad, but shallow, irregular hollow about 4 km across. A typical uvala visited in the Wombat Holes area was an irregular oval basin 290 m long and 14 m deep. There were several perched ponds within it, but the lowest point was dry.

Schank Region This region is an area of relatively bare karst on a flat, stripped Pleistocene coastal plain to the south of the Gambier Region. The narrow Coastal Region separates it from the sea. Much of the region has thin soil or bare pavements of Gambier Formation. Chert gravels form beach ridges in the west. The water table is generally 5-9 m below the surface and has a gentle seawards gradient. Cenotes are a characteristic feature of this region and include some impressive views of unexpected deep clear lakes within an otherwise monotonously flat plain (Figs. 7 and 8). Most of the collapse dolines contain water and are therefore classed as cenotes, but there are a few small, shallow, dry ones with degraded edges. There are occasional subsidence dolines, and small solutional dolines are associated with the karren fields. The Schank Region has the best limestone pavements in the province. These are mostly stripped subsoil karren, together with some surface karren types. The region has a number of shallow air-filled caves, but the most extensive systems are beneath the present water table. There is evidence for substantial reductions in the water levels during the glacial periods (see Hydrology section).

Millicent Region This newly named region lies to the west of the Gambier and Schank regions. It has many similarities to the Bool Region, being a flat swampy plain with occasional dune ridges marking old coastlines. However, it lacks the numerous shallow hollows that characterize the Bool Region. Karst features are restricted to a few syngenetic caves in the dune ridges. A line of springs lies along its eastern boundary. This region was not studied in any detail.

Coastal Region The Coastal Region is a narrow belt of land that extends up to 6 km inland from the present coast. It consists of a low erosional coastal plain developed on Gambier Limestone and is partly covered by coastal dunes and beach ridges. The water table is close to the surface. The region has numerous springs, many of them rising from submerged dolines and caves. The caves in this region are either completely submerged in spring-fed ponds or have water at shallow depth. Those caves that are not completely flooded tend to be either joint fissures or small collapse domes. In addition to the completely drowned dolines of the springs, there are several collapse dolines and cenotes in the area. Coastal karst and related features are well developed on many of the low limestone sea cliffs. They include small pits, sharp hackly pinnacles, tide notches and platforms, and sea caves (see Karst landforms section).


Controls on karst development Marker (1975) referred to the South-East Karst Province as a doline and uvala karst region with dominantly covered karst. She discussed the possible controls on the overall distribution and nature of the karst features within the province, including the hydrology, topography, overburden (thickness and character), lithology and rock structure, age of the land surfaces, past and present climates, and vegetation. She concluded that the main control on variations in karst character within the province is the hydrology, in particular, the depth to the water table and the water-table gradient. The nature and structure of the parent rock has also contributed to the distribution and character of the caves and surface karst, as has the extent and nature of the surface cover. Unlike some karst areas, a regional water table can be readily recognized. The groundwater surface shows a general coastward trend with a high ridge beneath the Dismal Swamp area north of Mount Gambier and two belts of relatively steep gradients: along the line of Kanawinka Escarpment and beneath the Gambier Region (Fig. 2). The areas of best cave and surface karst development are all areas of relatively deep water tables. The greater depth would promote vertical drainage and therefore surface percolation, which promotes solution. In the Coastal and Schank regions the deeper water levels that would have existed during the glacial periods may have been important factors in the development of the large cavities that underlie the cenotes (Lewis 1984) (Fig. 4). The two belts of steep water-table gradient may also be significant as they would have accentuated lateral water movement and thus promoted solution. The southern steep gradient zone would have been more extensive during the reduced sea levels of the glacial periods. The karst features of the province are typified by development on relatively soft and porous parent rocks: the Gambier Limestone and the dune calcarenites of the Pleistocene Bridgewater Formation. Dolines in the flat parts of the Bool Region and in the Nangwarry Region may be developed on thin Pliocene and younger carbonates. The Gambier Limestone is poorly bedded but shows moderately good jointing in places. The Bridgewater Formation has well-developed dune forset bedding in places and shallow-dipping medium to thin beds elsewhere. It shows only minor jointing. Most of the caves and large collapse dolines are developed in the Gambier Limestone, but some are partly or wholly developed in the Bridgewater Formation. Joints in the Gambier Formation provide strong control on the orientation and character of many caves in the southern part of the province, but joint control is less obvious in the north and is almost absent in caves in the dune calcarenites. The Tartwaup Fault has a line of elongated dolines and uvalas developed along it. Most of the karst is covered, but some extensive areas of bare karst occur in the Schank Region. The cover is of Quaternary age and consists of partly calcareous coastal swamp and lagoonal deposits, quartzose and calcareous sand dunes and aeolian sand sheets, and minor alluvial flats. Thicknesses can be up to 30 m. Thick cover can have an inhibiting effect on surface karst and thick soil cover can clog any potential cave entrances. The extensive shallow hollows of the flat areas of the Bool Region are developed on a relatively thick partly calcareous cover. It is not certain how many of these hollows should be regarded as karst, and if they are karst, whether they should be regarded as forming in the calcareous cover sediments or as subjacent karst effects originating in the underlying Gambier limestone. The age of the land surface puts a limit on the age of the surface features, but not necessarily the deep caves, which could predate the surface landforms. During the Quaternary the sea level fluctuated but showed an overall withdrawal to the southwest so that the oldest land surfaces and, therefore, surface karst features are on the Naracoorte Plateau, and they become progressively younger towards the present coast. Age of the landforms does not appear to have had a strong influence on karst development, although caves are absent from the youngest of the dune ridges. Lewis (1984) referred to the reserves of carbon dioxide gas found at depths between 2500 and 2800 m during oil exploration (Wopfner and Thornton, 1971) and suggested that there could be movement of this gas along fractures into the karst aquifer. Wopfner and Thornton (1971) attributed the carbon dioxide to the volcanic activity in the area. Lewis noted the proximity of a cluster of dolines and cenotes to the Mount Schank volcano and pointed out that lineaments in the area might indicate geological fractures. He therefore suggested that the movement of the gas into the groundwater may have been responsible for the increased solution in the area. The argument is interesting, but rather tenuous, and there are other explanations for this area of enhanced karst development, such as the reduced and steeper water tables during the glacial periods. There are some similarities with the Nullarbor Karst Region (also developed on extensive soft flat-lying Tertiary limestone), but the climate in the South-East Karst Province is wetter (at present) and the karst development here is complicated by the younger dune ridges and superficial sediments as well as the peculiarities of the water table.

Acknowledgments This report draws heavily on the previously published reports cited herein and also on the unpublished maps and records of the Cave Exploration Group, South Australia (CEGSA). Without the extensive exploration, mapping, and documentation efforts by numerous CEGSA members over the last 30 years, this project could never have been attempted. Additional information, maps, and airphotos were provided by individual members of CEGSA and by the South Australian National Parks and Wildlife Service, Department of Mines and Energy, and Lands Department. The study was funded by a National Estate grant to the SANPWS.


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