Robert P. Bourman

Perennial problems in the study of laterite: A review

There are perennial problems in the investigation of laterite. (i) The development of an acceptable terminology to describe the forms and processes associated with laterite genesis. Some workers consider that the use of the term laterite should be discontinued, because of its genetic connotations and the uncritical application of the term to a wide variety of materials. The terms ferricrete or lateritic duricrust are sometimes preferred. (ii) Identifying and classifying lateritic materials. (iii) The mode of formation of the laterite; by in situ weathering, relative or absolute accumulation or by continual weathering and erosion of a long exposed landscape. The relationships of laterite to zones of mottled and bleached bedrock and sediment are critical. (iv) Determining the age of the laterite and the weathering processes responsible for its formation and its relationship to the age of the surface on which it rests. Critical investigations include determining the age of the underlying materials, the age o...

Facies architecture of a last interglacial barrier: a model for Quaternary barrier development from the Coorong to Mount Gambier Coastal Plain, southeastern Australia

Abstract The last interglacial Woakwine Range, a linear, barrier shoreline complex of temperate bioclastic carbonate origin, in the southeast of South Australia, occurs essentially uninterrupted over a distance of 300 km and up to 10 km inland from the present coastline. Mapping of the internal facies architecture of the barrier as revealed in McCourts Cutting southeast of Robe, reveals the presence of transgressive and regressive facies associated with the last interglacial maximum (Oxygen Isotope Substage 5e), as well as an older aeolianite within the core of the barrier, correlated herein with Oxygen Isotope Stage 7. Amino acid racemisation and thermoluminescence dating indicate that volumetrically, the majority of the Woakwine Range is of last interglacial age. The bulk of the barrier structure comprises aeolian facies in the form of landward-migrating coastal dunes. The internal facies appear to record the culmination of the post-Stage 6 marine transgression at the onset of Substage 5e, and possibly the termination of Substage 5e based on the shallow seaward dip of the discontinuity between regressive littoral and sublittoral facies.

Foraminiferal biofacies eco-succession and Holocene sealevels, Port Pirie, South Australia

Abstract At Port Pirie, on the eastern coast of Northern Spencer Gulf, South Australia, 10 cores taken along a 3 km transect recovered a succession of Holocene marine sediments. Facies representing shallow subtidal Posidonia seagrass and intertidal sandflat, mangrove and back-storm ridge coastal lagoon environments are recognized on the basis of lithological characteristics and their preserved foraminifera. An assemblage dominated by Nubecularia lucifuga , Peneroplis planatus and Discorbis dimidiatus signifies sediments of shallow subtidal Posidonia seagrass meadows. Subtle changes in the numerical distribution of these species upcore are used to infer the change from subtidal to intertidal sandflat facies; Elphidium crispum and Elphidium macelliforme become more numerous across this transition. The mangrove facies is characterized by Trochammina inflata . This species is present significantly in only one seaward core where modern mangrove woodland continues to grow today and no equivalent biofacies are recognized in other cores. The lagoonal sediments preserve a rich assemblage of species of euryhaline foraminifera. Together with those of the mangrove woodland, they exhibit an ecological succession which can be related to decreasing intervals of tidal inundation and increasing salinity. Helenina anderseni , with subordinate Ammonia beccarii , and Elphidium cf. articulatum are the pioneer species in the euryhaline setting, giving way to Trichohyalus tropicus and Miliolinella schauinslandi . Late stages of hypersaline sedimentation are characterized by Triloculina inflata + Triloculina oblonga . In the mangroves, H. anderseni , A. beccarii and Elphidium cf. articulatum are replaced by Trochammina inflata as the dominant species. In turn, as further sediment aggradation leads to ever shorter intervals of tidal inundation at the landward side of the mangrove woodland, Trochammina inflata is overtaken by Ammobaculites barwonensis . Quantitative foraminiferal biofacies analysis confirms and refines the sedimentological interpretation of intertidal sediment facies from macro-observations of the core materials. It provides independent estimates of the elevation of key facies boundaries in cores and confirmation of a general relative fall in sealevel in Northern Spencer Gulf over the past 7000 yr.

A critique of the Schellmann definition and classification of ‘laterite’

Abstract Schellmans definition and classification of ‘laterite’ are based on the SiO2, Al2O3 and Fe2O3 contents of weathered formations in comparison to the chemical composition of the underlying rocks, from which the weathered materials are assumed to be derived. This approach is open to misinterpretation because many regolith materials have formed by lateral transport, both physical and chemical; it ignores the role of absolute accumulation; it pays little attention to the morphological characteristics of ‘laterites’ that give clues to their origins; it ignores the detailed mineralogical compositions of weathered materials and ‘laterite’; and it does not permit field identification. Understanding of geology, stratigraphy, geomorphic evolution, mineralogy and micromorphology are essential ingredients of regolith investigations. Chemical analysis alone is insufficient. Schellmanns chemical classification seems appropriate only to a small subset of potential ‘laterites’ in which the whole profile is of bedrock and saprolite, and where there has been no lateral movement of solids or solutions. Schellmanns definition demands formation by tropical weathering, which eliminates ferruginous duricrusts formed outside the tropics. His approach produces confusion by grouping disparate ferruginous/aluminous materials together as ‘laterite.’ The range of applications of the term ‘laterite’ is so broad that it has become meaningless and the Schellmann approach has not resolved this issue.

Mid Pleistocene arid shift in southern Australia, dated by magnetostratigraphy

In coastal sections at Hallett Cove and Sellicks Beach, south of Adelaide, and at Redbanks section on Kangaroo Island, the Brunhes/Matuyama polarity transition (780 ka) is identified in the strongly oxide-mottled Ochre Cove Formation. At all 3 sections, the Ochre Cove Formation is overlain by a calcareous grey-green aeolian clay, called Ngaltinga Clay, which in turn is overlain by calcareous sediments of the Taringa and Christies Beach Formations. The marked change from an oxide-dominated weathering regime to a carbonate-dominated weathering regime, estimated to have occurred at about 500–600 ka, is interpreted as a major arid shift in regional climates. Similar arid shifts are known from Lake Bungunnia in the Murray Basin and Lake Lefroy in southern Western Australia, where changes from lacustrine clays to evaporites and dune sediments are estimated to have occurred between 400 and 700 ka, and about 500 ka, respectively. An increase in aeolian dust accession in south-eastern Australia, consistent with increased aridity in the interior source area, occurred after 780 ka, and was probably coeval with increased dust input to Tasman Sea sediments since 350 ka. Between 600 and 900 ka, oxygen isotope fluctuations in deep-sea cores showed a pronounced change in frequency, from a 40 ka (obliquity dominated) to a 100 ka (eccentricity dominated) pattern. At the same time, glacial-interglacial amplitudes increased, with a marked enrichment of glacial d18O values consistent with larger continental based ice-sheets. Colder global temperatures, and lower sea levels during glacials, may have played a part in the mid Pleistocene arid shift recorded in southern Australia. Associated variations in the strength of the warm Leeuwin Current may also have affected regional rainfall patterns in southern Australia.

Geography and Environmental Studies in Australia: Symbiosis for Survival in the 21st Century?

This paper presents the results of a detailed survey into the reasons for the spate of mergers between Geography and Environment Studies that took place in Australian universities from 1989 to 1999. The results, from a 1998 survey, suggest that the development of a symbiotic relationship between the two areas of study is merely a veneer masking a complexity of underlying factors. These include financial reasons, internal university politics, staff changes and mobility, and only in some cases, a genuine academic rationale for a merger. The paper concludes that the superficial appearance of a symbiosis between Geography and Environment Studies generally masks an opportunistic pragmatism which is very site specific in its complexity. The result has been a series of departmental mergers which, although providing a firmer financial footing, raise questions about the academic implications for the development of both study areas as we move into the third millennium.

Holocene palaeofire records in a high-level, proximal valley-fill (Wilson Bog), Mount Lofty Ranges, South Australia

An elevated valley-fill peat bog (Wilson Bog) near Mount Lofty, South Australia, failed in November 2005 following a flooding event, and exposed representative sections of the sediment infill. Two distinct units were revealed: 2 m of coarse-grained, siliciclastic sand/gravel, overlain by 2 m of peat. A simple charcoal extraction technique based on floatation and skimming was developed to extract coarse charcoal from coarse-grained gravels to determine the palaeofire record at a proximal site of sedimentation. Optically stimulated luminescence (OSL) dating of basal sediments revealed a minimum age of deposition of 7.02 +0.50 —0.56 ka, while the oldest charcoal peak yielded a radiocarbon age of 6000—5740 cal. yr BP. The lower half of the siliciclastic unit contains three distinct charcoal peaks suggesting there were infrequent but intense fires associated with wetter conditions during the Holocene climatic optimum 8000—5000 years ago. The period from 4000 to 2000 cal. yr BP is characterised by more frequent charcoal peaks and higher background levels of charcoal, which is consistent with more regular but less intense fires during drier, cooler conditions. The sharp transition from siliciclastic sedimentation to peat formation began ~1200 cal. yr BP, which may relate to a return to wetter conditions. However, fire frequency appears to have increased in this time suggesting augmentation by anthropogenic or ENSO-related factors. Charcoal-rich layers in the siliciclastic unit are associated with poorly sorted, bimodal sediments with high proportions of clay, silt and gravel, which supports the hypothesis that there is an association between past fire events and rapid, coarse-grained, post-fire aggradation. By analogy with active colluvial aggradation following recent fires at nearby Mount Bold, it is evident that fire plays a significant role in hillslope destabilization and subsequent sediment movement, leading to rapid valley-fill aggradation — a chain of events to which we apply the term ‘pyrocolluviation’.

Last interglacial (MIS 5e) sea-level determined from a tectonically stable, far-field location, Eyre Peninsula, southern Australia

ABSTRACT The last interglacial maximum (Marine Isotope Substage 5e [MIS 5e], 128–116 ka) is a distinctive event in recent Earth history. Shoreline successions of this age are important for calibrating climate models and defining the overall behaviour of the crust–mantle system to fluctuating ice and ocean-water volumes. In a global context, the recently intensified interest in last interglacial shoreline successions has revealed considerable variability in the magnitude of sea-level rise during this time interval and highlighted the need to examine paleosea-level evidence from tectonically stable, far-field settings. Situated in the far-field of continental ice sheets and on the tectonically stable Gawler Craton, the 300 km coastal sector of western Eyre Peninsula between Fowlers Bay and Lake Newland in southern Australia represents an important region for defining the glacio-eustatic (ice-equivalent) sea-level attained during the last interglacial maximum based on the relative sea-level observations from this region. Low-energy, shoaling upward, peritidal bioclastic carbonate successions of the last interglacial (locally termed Glanville Formation) formed within back-barrier, estuarine–lagoonal environments in the lee of eolianite barrier complexes (locally termed Bridgewater Formation) along this coastline. The well-preserved shelly successions (coquinas) contain diverse molluscan fossil assemblages including species no longer living in the coastal waters of South Australia (e.g. the Sydney cockle Anadara trapezia and the benthic foraminifer Marginopora vertebralis). The extent of amino acid racemisation (a measure of fossil age based on increasing d/l value) in a range of species, and in particular A. trapezia and Katelysia sp., confirms the time equivalence of the isolated embayment-fill successions, correlated with the informal type section of the Glanville Formation at Dry Creek, north of Adelaide. Preliminary U-series analyses on A. trapezia also suggest a correlation with the last interglacial maximum, but further highlight the complexity in dating fossil molluscs by the U-series method in view of their open-system behaviour. The shelly successions of the Glanville Formation occur at elevations higher than attained by sea-level in the current, Holocene interglacial. A higher sea-level of between 2.1 ± 0.5 and 4 ± 0.5 m above present sea-level is inferred for the last interglacial maximum (MIS 5e) along this coastline based on the elevation of sedimentary successions host to the shallow subtidal–intertidal fossil molluscs Katelysia sp., and Anadara trapezia. The paleosea-level observations place a lower limit on the sea-level attained during the last interglacial maximum and suggest that caution be exercised in the definition of the upper limit of sea-level during this interglacial.

Coastal Landscapes of South Australia

Introduction People commonly have close affinities with coastlines, whether for recreation (swimming, fishing, boating, surfing, sunbathing), enjoying their generally milder climates, investigating their historical and cultural connections, admiring their inherent beauty or questioning the nature and formation of coastal landscapes. This book aims to assist people in interpreting coastal landforms, revealing how the coast has evolved and is continuing to do so under the influences of a range of processes acting upon a variety of geological settings. Developing an understanding of the ways in which coastlines have changed through time, by interpreting rock strata, landforms and coastal and marine processes, can add much to the enjoyment of coastal experiences. Study of coastal environments also offers opportunities to reconstruct past environments and to monitor ongoing changes that may relate to climatic changes. An understanding of coastal processes and development can also provide critical information relevant to the vulnerability of predicted rises in sea level and coastal flooding. Coasts are very complex environments, representing the interaction of physical, chemical and biological processes. Located at the boundary between land and sea, coasts are among the most dynamic environments on Earth as tides, winds, waves, weathering processes and currents modify landscapes and produce a range of erosional and depositional landforms, the stability and fragility of which may also be influenced by flora and fauna. Repeated sea level changes over the past 2.6 million years, coupled with crustal movements, add to the complexity of coastal development. Thus the coastline of South Australia must be considered as a dynamic system in a state of constant flux. In addition, some coastal features are inherited from coastlines that were formed during past ages. According to Geoscience Australia, the South Australian mainland coast is 3816 km long, with islands providing an additional 1251 km of coast, giving a total coastline of just over 5000 km. South Australian coastal landforms include cliffs, rocky outcrops and shore platforms, mangrove woodlands, mudflats, estuaries, extensive sandy beaches, coastal dunes and coastal barrier systems, as well as numerous nearshore reefs and islands. These coastal landforms have developed under the influence of a range of tidal conditions and wave regimes, varying from high energy on exposed open ocean coasts (for example, the west coast of Eyre Peninsula) to low energy in protected shorelines with high tidal ranges (such as in the northern gulfs).

Age and origin of alluvial sediments within and flanking the Mt Lofty Ranges, southern South Australia: a Late Quaternary archive of climate and environmental change

Quaternary alluvial sediments occur within and on the flanks of the Mt Lofty Ranges of southern South Australia. Within the ranges they occupy colluvium-filled bedrock depressions, alluvial-fan sequences at hill/plain junctions and river terraces that flank major streamlines in both locations. Sediments ranging in age throughout the Quaternary have been identified, but this paper focuses on those deposits of Late Quaternary age. Luminescence dating has verified a Last Interglacial age (132–118 ka) for the most widespread of the alluvial units, the Pooraka Formation. A younger, Marine Isotope Stage 3, alluvial unit, in places containing bones of the extinct marsupial Diprotodon, has also been identified. Deposition of the alluvial sediments is associated with relatively warmer and wetter conditions, whereas the valleys that they occupy were eroded under drier climatic conditions. A more widespread occurrence of Stage 3 units is expected to be present but has not yet been verified. Cold, arid environments are inferred from the presence of dunes (∼18 ka) deposited during the Last Glacial Maximum when stream valleys were incised. Grey/black mid-Holocene alluvium (Waldeila Formation), forming present-day floodplains and low river terraces, equates with the Holocene Hypsithermal. The sequence of climatic changes revealed by these sediments is correlated with evidence of Late Quaternary climatic change from other Australian locations. The identification of equivalent units in different tectonic settings reveals that sedimentation is largely climatically driven although active tectonism may accelerate the supply of sediments available for transport.