South Australian geology

The Lochiel Landslip was initiated in August 1974. It was the result of heavy winter rains, but was facilitated by the occurrence of hydrophilic clay interbedded with the quartzitic country rock. Monitoring has shown that whereas most of the minor features within the mass movement have been degraded and subdued, the headwall region remains active. The backing bluff that defines the tension scar has receded between 5 and 10 m during the last decade. The development of fissures some 90 m upslope from the present headwall suggests that this trend will continue. The widening of fissures located laterally and along the hillslope suggests that it too will fail. These changes illustrate the importance of reinforcement mechanisms in landform development. Seepage was facilitated once fissures had formed and the initial slippage left the strata upslope unbuttressed.

A geomorphological approach to landform design aims to pattern constructed landforms in erodible materials on natural landforms. These natural landforms represent a mature geomorphic condition subject to a slow rate of evolution. Most commonly, stable alluvial landforms in the local environment are utilised as analogues. Unfortunately, few landforms constructed in mining overburden in New South Wales, Australia, have an overall geometry that allows for alluvial analogues to be directly applied; that is, the post mining landforms are frequently too steep. To address this challenge, approaches used internationally range from very sinuous drainage lines to flatten gradients, through to wide grassed drains to reduce velocities, and the use of rock armouring in drainage lines. Each of these approaches has some challenges. Overly sinuous designs move away from a dendritic drainage layout and are overly complex to construct. They are also vulnerable to piping failures. Wide grassed drains can develop preferential flow paths and can also impact unfavourably on the overall drainage density. Rock armouring is not generally favoured by geomorphologists since armouring represents a rigid conveyance system without self-healing capabilities. The strategy adopted by the authors is to design drains using a vegetated rock matrix approach. Effectively, a dendritic drainage layout is used at a desired drainage density, and the drain widths and/or longitudinal slopes adjusted to ensure that the drains have velocities below 3 m/s even for the design event (typically the 1:100-year event). These drains are wider and shallower than a typically optimised trapezoidal drain and, for frequent flood events, the rock is primarily required for the roughness it adds to the surface. With relatively low design velocities, sediment accumulates within the rock voids and revegetation of this material significantly increases the rock stability. The embedded rock and revegetated matrix are then able to withstand extreme flood events well above the original design event. This larger flood event is more in line with that expected for the required design life of these surfaces. It is noted that, because the rock size required is proportional to the velocities, increasing the drain perimeter by designing a flatter, wider drain does not necessarily increase the cost of the lining because smaller rock sizes result in reduced thicknesses of the rock lining.

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Fracture formation in fill was observed to occur rapidly, in just a few years at the WillowCreek Landfill site. The soil science and geomorphology literature does not discuss the formation of fractures in glacial fill. Observations (which are often the first step in developing a research effort) of fractures formed in fill derived from fine-grained Ohio glacial soils and tills by Weatherington-Rice at the WillowCreek site and in earthen dams by Sherard are here presented. Questions regarding the applications of these observations to potential impacts and failures of the built environment, that is, landfill construction and leachate generation (HELP model), earthen dams, highway construction, and general construction sites, are raised. Recommendations are made for the need for inter-disciplinary research and literature sharing.

Fracture formation in fill was observed to occur rapidly, in just a few years at the WillowCreek Landfill site. The soil science and geomorphology literature does not discuss the formation of fractures in glacial fill. Observations (which are often the first step in developing a research effort) of fractures formed in fill derived from fine-grained Ohio glacial soils and tills by Weatherington-Rice at the WillowCreek site and in earthen dams by Sherard are here presented. Questions regarding the applications of these observations to potential impacts and failures of the built environment, that is, landfill construction and leachate generation (HELP model), earthen dams, highway construction, and general construction sites, are raised. Recommendations are made for the need for inter-disciplinary research and literature sharing. OHIO J SCI 106 (2):27-34, 2006 Manuscript received 6 September 2004 and in revised form 28 September 2005 (#04-01F). INTRODUCTION Fractures in in situ fine-gr...

The Troubridge Basin in South Australia is a late Paleozoic sedimentary basin, extending from the Coorong area across Fleurieu Peninsula and Kangaroo Island to Yorke Peninsula (Alley and Bourman 1995; Fig. 1). The basin contains the Cape Jervis Formation, which crops out extensively in these areas. The formation is also widely distributed in the subsurface below Yorke and Fleurieu peninsulas, Gulf St Vincent, Investigator Strait, Backstairs Passage, the Coorong area, Kangaroo Island and on the continental shelf to the east of Kangaroo Island (Alley and Bourman 1995). In some areas the formation forms a blanket of sediment and, in others, significant thicknesses are preserved in glacially eroded troughs or local tectonic depressions.

Catchments in northern Australian have undergone dramatic land-use changes from traditional Aboriginal management to widespread cattle grazing post-European settlement. Quantifying the soil erosion impacts of these changes is essential to the future sustainable management of the soils in these catchments. Rates of gully erosion in alluvial soils were measured using recent GPS surveys and historical air photographs. The results indicated that median erosion rates currently and historically are within the same order of magnitude (0.1 to 1m per year). Historic air photo analysis demonstrated rapid increases in gully area of 2 to 10 times their initial 1949 area. Extrapolation of gully area growth trends backward in time suggested that most gullies initiated between 1880 and 1950. European cattle were introduced into the lower Mitchell catchment in the 1880's, suggesting the contribution of land use intensification to either gully initiation or acceleration. It is hypothesized that intense cattle grazing concentrated in the riparian zones during the dry season decreased perennial vegetation cover along hollows and steep river banks, increasing the potential for gully erosion. Once initiated on steep banks into dispersible sub-soils, alluvial gullies can rapidly progress in consuming and degrading the most productive part of the landscape, the riparian zone.

Water flow Water quality Water clarity Streamside vegetation Local jobs Cost This appears to be a list of six attributes, 4 relating to physical items and two to economic, but is actually nine attributes. The apparent divergence in number of attributes arises because water flow incorporates four separate attributes, as described below. Nine attributes is at the higher end of the norm for the number of attributes included in this type of study. Water Flow Key informants indicated strong concerns about water flow levels. Concerns were raised about the frequency of days without flow, particularly in the summer months, and the levels of flow at times when there is water in the river. Four flow levels were defined:

A new subdivision for the Cambrian Kanmantoo Group into a basal Carrickalinga Head Formation and overlying Inman Hill, Brown Hill and Wattaberri Subgroups is proposed for the type section. Investigations have shown that the stratigraphic subdivision formerly erected and utilized in the Nairne area is inappropriate when applied to the type section of the Kanmantoo Group. The Nairne Pyrite Member is correlated with part of the Talisker Calc-siltstone and does not occur in the type section of the Kanmantoo Group in the position as shown on recently published maps. We identify rocks in that position as belonging to the lower parts of the Brown Hill Subgroup which, in the Nairne-Catlington region, are 3,000-4,000 m above the true Nairne Pyrite Member.

Rubidium-strontium and strontium isotope data for eight whole-rock samples of granite varieties from the Encounter Bay area, South Australia, yield an isochron age of 487 ± 37 m.y. Two specimens of albitised granite, formed as a result of latestage metasomatic alteration of original megacrystic granite, conform to this isochron. These data support a genetic relation between granites and late-stage metasomatic alteration as suspected from field, petrographical and geochemical studies. Eight samples from contiguous Kanmantoo Group metasedimentary rocks have an isochron age of 487 ± 60 m.y. Thus this metamorphic event is coincident with emplacement of the Encounter Bay Granite. The initial Sr 87 Sr 86 ratio for the Encounter Bay Granite (0.719) is significantly higher than initial ratios for the Palmer (0.709) and Anabama (0.705) Granites from the same region and can be attributed to either remobilisation or incorporation of strontium from older crustal material in the intrusion. The apparent initial Sr 87 /Sr 86 ratio for the Kanmantoo Group metasedimentary rocks (0.722) can not be distinguished from that for the Encounter Bay Granite within the analytical uncertainties. Compatability of ages and high initial Sr 87 Sr 86 ratios suggest that the granites formed by remobilisation of associated crustal rock.

A new subdivision for the Cambrian Kanmantoo Group into a basal Carrickalinga Head Formation and overlying Inman Hill, Brown Hill and Wattaberri Subgroups is proposed for the type section. Investigations have shown that the stratigraphic subdivision formerly erected and utilized in the Nairne area is inappropriate when applied to the type section of the Kanraantoo Group. The Nairne Pyrite Member is correlated with part of the Talisker Calc-siltstone and does not occur in the type section of the Kanmantoo Group in the position as shown on recently published maps. We identify rocks in that position as belonging to the lower parts of the Brown Hill Subgroup which, in the Nairne-Catlington region, are 3,000-4,000 m above the true Nairne Pyrite Member.

The occurrence and movement of groundwater are controlled by various hydrogeological, hydrological and climatological factors. Reasonably accurate assessment of groundwater recharge and discharge components is not easy because no direct measurement techniques are presently available. Therefore, indirect methods are generally employed for assessment of groundwater resources. Groundwater is a dynamic and replenishable resource which is normally estimated based upon the annual groundwater recharge. It is subjected to withdrawal for various uses such as irrigation, domestic, industrial etc. This article presents the norms for various groundwater recharge components for estimation of groundwater resources in India.

The Inman River Catchment sits within a well-defined geomorphological feature on the southern part of Fleurieu Peninsula, a relict of an ancient glaciation, which eroded a large east-west trending bedrock depression across Fleurieu Peninsula known as the ‘Inman Trough’.  The Inman Catchment contains a unique geology and distinctive landforms, some of which have been recognised as being of international scientific significance.  The key land-forming processes responsible for the location and setting of the catchment were related to a glaciation of Antarctic proportions, which occurred about 300 million years ago, during Permian times, when Antarctica was welded onto southern Australia.  As the ice melted great thicknesses of sediments were deposited onto the glaciated bedrock floor.  These glacigene sediments are currently being eroded by running water, re-exposing parts of the ancient glacial landscape, and moulding the present landscape. 

A long geological history, which established the ancient bedrock floor of the peninsula, preceded the Permian glaciation.  The oldest rocks that occur on the northern boundary of the catchment are part of the 2 billion year-old core of the region.  The remaining hard rocks forming the floor and sides of the catchment were originally sediments more than 24 km thick, deposited in ocean basins during Proterozoic and Cambrian times (more than 500 million years ago).  These sediments were transformed by heat and pressure, and folded about 500 million years ago to form a huge mountain range of Himalayan magnitude, into the base of which granites were intruded.  Over the ensuing 200 million years this mountain range was so severely eroded that during the Permian ice age the oldest, deepest rocks in the mountains were exposed at the surface.

After the retreat of the Permian ice sheet the catchment was subjected to prolonged weathering and erosion over many millions of years, producing a landscape of low relief that was intensely weathered to depths exceeding 70 m.  The progressive uplift of this surface of low relief and its ongoing weathering and erosion has produced the high plateau surface on the margins of the catchment such as at Spring Mount.  Throughout this early geological history Australia and Antarctica were joined together as part of the ancient super-continent Gondwana: they were the last of the continents to separate about 43 million years ago, following which there were tectonic movements and incursions of the sea.

The sea inundated parts of the southern Australian coastline several times from about 40 million years ago and tectonic activity formed the marine St Vincent and Murray Basins. Marine incursions onto Fleurieu Peninsula deposited fossiliferous limestones, remnants of which occur at high levels in the Myponga, Upper Hindmarsh Valley and Waitpinga areas.  Ongoing earth movements progressively uplifted the Mount Lofty Ranges following the rifting of Australia and Antarctica, elevating the fossiliferous limestones up to 240 m above sea level as they did so.  Throughout the tectonic uplift, rivers, streams and weathering processes continued to mould the landforms in the catchment.

Over the past 2.6 million years of the Pleistocene, global sea level fluctuated dramatically with sea level falling to about 125 m below present sea level and returning to near present sea level about 30 times.  Only the last major sea level fluctuation (125,000 years ago) is recorded in the catchment, producing river terraces and stranded shorelines in the lower reaches of the Inman River.  During the Holocene, the last 11,500 years of Earth history, alluvial sediments accumulated in channel bottoms forming floodplains and swamps.

The arrival of humans witnessed some major changes in the landscape.  Over many thousands of years Aboriginal occupants actively managed the landscape, particularly through the use of fire. This had significant impacts, with plants and animals adapting to the mosaic-burning regime, which produced open parkland environments in places.  These landscapes were very attractive to the first European settlers in the early 1840s but the practices that were implemented to establish settlements supported by agriculture, albeit initially on a comparatively small scale, severely disrupted the pre-existing landscape ‘equilibrium’. Clearing of vegetation, cessation of burning practices, single-furrow ploughing of land areas, and the introduction of livestock, rabbits and weeds triggered significant changes.  Thus, new landforms were generated as the landscapes adapted.  Some obvious expressions of change were soil nutrient depletion, various forms of erosion (slumping, gullying, stream incision, stream bank collapse) and alluviation.  Changes to hydrology and water quality in the catchment were additional consequences. 

The last few decades have witnessed progressive changes in landuse, with current land management strategies being focused on soil and land conservation, erosion repair through revegetation and watercourse controls, and the eradication of feral animals and plants.  Thus, the agricultural regime which triggered the disruption of pre-European settlement landscapes throughout the catchment has, over more than 100 years or so, progressively changed to a new agricultural landuse regime under which the dramatic earlier erosional features have been progressively stabilised and ‘healed’.