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Quaternary alluvial and colluvial sediments infill major river valleys and form alluvial fans and colluvium-filled bedrock depressions on the range fronts and within the Mount Lofty Ranges of south...

In contrast to the detection and resolution of Late Pleistocene interstadials (Marine Isotope Stages; MIS 5c, 5a and 3) in marine and ice core-based oxygen isotope records, accurately defining palaeosea-levels for these events from sea level indicators remains a challenge. Commonly, such investigations have been undertaken in tectonically active, subduction-related settings, on emergent marginal marine-coastal successions above present sea level, given that the higher ice volumes during these Marine Isotope Stages resulted in ice-equivalent sea levels significantly below present, particularly in far-field settings. Delineation of palaeosea-levels for this period, has accordingly involved an assumption about the long-term rate of coastal uplift. Core SV#23 collected from the tectonically highly stable, remote far-field setting of southern Gulf St Vincent, southern Australia, in a present water depth of 40 m obtained a 3.89 m undisturbed sedimentary record of Late Pleistocene to Holocene age. The basal 2.39 m of the sediment record is of Late Pleistocene interstadial age, as it overlies the Last Interglacial Glanville Formation (128–118 ka; MIS 5e) and occurs beneath the Holocene St Kilda Formation. The extent of aspartic acid and glutamic acid racemization in the benthic foraminifer Elphidium macelliforme sampled at 2 cm intervals continuously from the interstadial succession in Core SV#23, confirms the relative age interpreted from lithostratigraphy. A mean amino acid racemization (AAR) age of 75 ± 13 ka indicates a correlation with MIS 5a, and highlights the utility of E. macelliforme as a species for AAR geochronology. As the foraminifers more closely define the timing of sedimentation, the interstadial succession is regarded as beyond the range of radiocarbon dating (>50 kyr), as revealed in a comparison of radiocarbon ages of fossil molluscs with AAR ages for E. macelliforme from the same depth intervals within the interstadial succession. All of the radiocarbon ages for fossil marine molluscs from the interstadial succession represent minimum ages, resulting from contamination by trace levels of modern radiocarbon. The foraminiferal faunal assemblages within the interstadial succession reveal changes of water depth at the time of deposition, pointing to millennial-scale sea level variability. In particular, the ratio of Elphidium crispum to E. macelliforme indicates several oscillations in relative sea level within a bandwidth of 26 to 24 ± 4.6 m below present sea level (BPSL). Notwithstanding the large uncertainty associated with palaeosea-level estimation based on the Elphidium ratio, the inferred relative sea level record is in accord with the sea level records of Barbados and the Red Sea, and points to Sub-Milankovitch interstadial sea level variability as noted in Greenland and Antarctic ice cores. Refereed/Peer-reviewed

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 ...

Over the past several decades, a group of like-minded Earth scientists have made some useful contributions towards understanding the Quaternary coastal geology and geomorphology, particularly of South Australia, but also within a much wider Australian context.

A geochronological framework for the sequential development of coastal barrier aeolianite complexes in the mouth region of the River Murray, Australia's largest river system is presented based on amino acid racemization and thermoluminescence dating. The sedimentary successions represent a foreshortened and condensed sequence of coastal barriers compared with those of the Coorong Coastal Plain in southern South Australia where the barrier complexes are more widely separated in response to tectonic uplift. The barriers have formed during interglacial sea-level highstands and are correlatives of genetically equivalent landforms of the Coorong Coastal Plain. Thermoluminescence dating and the extent of amino acid racemization in aeolianite 'whole-rock' sediment samples, reveal a general increase in age of the barriers landwards from the modern coastline. In detail, however, the individual barriers represent composite structures having formed in more than one interglaciation, due to the reoccupation of Pleistocene shoreline positions during sea-level highstands of similar amplitude, in a zone of gradual basin subsidence. The most seaward Pleistocene aeolianite at Surfer Beach is of interstadial age (Marine Isotope Stage 5c, 105 ± 5 ka; MIS 5c), and correlates with the Robe Range of the Coorong Coastal Plain. The last interglacial shoreline (130 ± 15 ka; MIS 5e) is particularly well-defined in the River Murray mouth region. It is represented by a complex association of coastal parabolic dunes superimposed on a transverse dune system, which runs parallel with the former coastline, and also includes associated estuarine, lagoonal and open ocean beach facies. Landward of the last interglacial succession are distinct barriers relating to the penultimate interglaciation (215 ± 35 ka; MIS 7), as well as earlier interglaciations (350 ± 65 ka; MIS 9 or 11 and 470 ± 70 ka; MIS 11 or 13). The coastal barriers have been successively breached by the ancestral River Murray at times of lower sea level during glacial cycles. Former mouths of the River Murray during interglacial sea-level highstands are likely to have existed near Tauwitchere Island during MIS 7, and between Goolwa and Hindmarsh Island and near the southern-most part of Lake Albert during the last interglacial (MIS 5e). The River Murray mouth region represents a failed delta as the limited sediment brought to this area since late middle Pleistocene time has been either rapidly incorporated within aeolian deposits during sea-level highstands, or transported to the edge of the Lacepede Shelf during glacial maxima. The Holocene and modern River Murray has not established a marine delta, but deposits its load in the settling basins of the terminal lakes. Only a small digitate delta has formed where the river enters Lake Alexandrina. © 2009 Elsevier B.V. All rights reserved.

Gulf St Vincent is one of a pair of elongate, triangular, shallow water embayments into the southern coast of continental Australia. From the southern floor of this embayment, within a shallow basin-like depression where present-day water depth is about 40 m, vibracore SV23 recovered c. 4 m of late Quaternary sediments. The uppermost 1.5 m of this core comprises postglacial (Holocene) marine deposits; six radiocarbon ages for the interval 64-130 cm downcore are all around 10 000 cal. yr BP, while two for 18-24 cm are several thousand years younger. Radiocarbon analysis of an oyster shell at 154 cm yielded a minimum age of c. 37 000 cal. yr BP. Well-preserved benthic foraminifera are abundant in all the recovered sediments. The early phase of Holocene marine sedimentation in Gulf St Vincent was marked by the development of a marginal marine, perhaps lacustrine to estuarine environment, as signified by the presence of oogonia, gypsum crystals and the foraminifera Miliolinella labiosa and Elphidium cf. articulatum. Development of seagrass meadows followed; these were inhabited by Nubecularia lucifuga and Discorbis dimidiatus. As the marine transgression proceeded, the environment remained somewhat restricted, as indicated by Ammonia beccarii, but numbers of this species declined giving way to Massilina milletti as conditions began to resemble those of the modern Gulf St Vincent. Culmination of the transgression provided the conditions necessary for the dominance of Ammobaculites reophaciformis and Flintina triquetra. A. reophaciformis and F triquetra therefore record the final episode of the transgression and transition to the modern, deeper water environment. At several lower horizons they also occur as conspicuous spikes, equivalent to their modern abundance. These spikes, which coincide with equivalent decreased numbers of A. beccarii, are interpreted to represent downward bioturbation of the overlying deeper water sediment.

Studies of past sea levels based on radiocarbon-dated field samples suffer variously from compilation of information from disparate locations and the imprecise nature of the dated indicators. Geographic segregation and systematic elimination of poor samples from time–depth data sets leads to improved interpretation of Holocene sea-level history. An example is presented from Southern Australia, where this is achieved through selection of higher-resolution palaeoenvironmental indicators, separation of transgressive from regressive populations, and geographic regionalisation of data. In Southern Australia, fossil sea-level indicators preserved in prograding coastal plain settings include seagrass, sandflat, mangrove, samphire and chenier ridge organo–sedimentary remains. These provide sea-level time–depth data points with a variety of elevational and dating errors. Preserved organic remains at the transition from Posidonia seagrass to intertidal sandflat environment, and from sandflat to Avicennia mangrove environment provide the most precise local data for tracing sea-level change. Time–depth plots of 233 dated sea-level indicators from South Australia generate a broad sea-level envelope tracing the Southern Australian transgression from 10,000 to ca. 6000 radiocarbon years BP, followed by a more or less consistent level to the present. Finer details of sea-level behaviour are only apparent after systematic selection, separation and regionalisation of the data. The data indicate a very rapid sea-level rise in the early Holocene, at about 16 mm/year, reaching present levels at 6400 years BP. This was followed by regionally variable regression and emergence of the land of 1–3 m, a process that continues to the present. The systematic increase from 1 to 3 m in the elevation of the 6400-year BP highstand with distance away from the shelf margin is consistent with a hydro-isostatic origin for the emergence as predicted by geophysical models.

The Coorong Coastal Plain in southeastern South Australia preserves a long Quaternary record of cool-water, temperate-carbonate sedimentation in the form of high wave energy, barrier shoreline deposits and associated back-barrier lagoon facies that formed during successive sea-level highstands. Whole-rock samples of bioclastic skeletal carbonate sand with subordinate quartz were collected from aeolian facies (modern and relict foredunes) of a Holocene embayment fill and from ten Pleistocene barriers across the coastal plain in a transect from Robe to Naracoorte. The extent of leucine racemization (total acid hydrolysate and free amino acids) in the Pleistocene skeletal carbonate sand (63–500 μm) increases monotonically with age and is consistently higher than for entire fossil molluscs from the same allostratigraphic units, reflecting the lengthy residence time for bioclasts in this high wave energy environment, and sediment recycling from the erosion of older barriers. The extent of racemization in the whole-rock samples conforms with a model of apparent parabolic racemization kinetics and the calculated ages largely agree with previously determined luminescence ages. Apart from a possible reinterpretation of the significance of the West Naracoorte Range, the coastal plain succession indicates that interglacial sea levels did not deviate by more than 6 m of present sea level for the Mid- and Late Pleistocene thus providing an important framework for quantifying ice volume during sea-level highstands and calibrating the oxygen isotope record.

The River Murray Estuary, a Ramsar Wetland Site, has experienced considerable rapid coastal change during the Quaternary. The interplay of aeolian processes, river flows, tidal oscillations, wave action and variations in relative sea-level due to global sea-level changes and land subsidence, provides the energy for the ongoing dynamism, often accelerated by human impacts. The estuary is the terminus of the Murray-Darling catchment, which covers 1.073 million km 2 of the Australian continent. Terminal Lakes Alexandrina, Albert and the Coorong Lagoon are Holocene features, occupying tectonically subsiding Quaternary interdune areas. They formed in response to eustatic sea-level rise following the Last Glacial Maximum (ca. 20 ka). The last interglacial shoreline (125,000 yr BP) parallels the modern shoreline several kilometres inland. Dislocation of the last interglacial shoreline demonstrates ongoing tectonic subsidence, as does historical seismic activity. The northern half of Hindmarsh Island formed during last interglacial times when it was the sink for dominant longshore transport from the southeast, which pushed the River Murray westward, partly explaining the large bend in the River Murray at Goolwa. The modern coastal barriers of Sir Richard Peninsula and Younghusband Peninsula formed from 7000 yr ago, following glacier melt and sea-level rise. Subsequently, the barriers have migrated landward, sporadically exposing lagoonal sediments on the ocean beaches. Differential loading of the soft lagoonal sediments by advancing dunes, possibly in conjunction with seismic events, has deformed and elevated them to up to 10 m above present sea-level (APSL). During the mid-Holocene an extensive sand flat, with associated dunes, formed immediately inland of the coastal barrier. At least six generations of Late Pleistocene dune systems occur in the region. For example, during last glacial times the climate was drier, colder and windier than at present and a system of parallel, west–east trending, yellow–red desert dunes developed around the lakes. Aeolian processes remain important with occasionally up to 5000 tonnes of sand being in motion along 10 km of the modern shoreline. During mouth migration, dunes up to 2 m high have been formed and vegetated in 12 months, directly inland from the mouth, and replicating the formation of older dunes on Hindmarsh Island. Elsewhere sand blown directly from the barrier system infills channels. Barrage construction on the beach facies of the last interglacial shoreline transformed the estuary into freshwater lakes with permanently raised water levels and reduced the tidal prism by 90%. Increased deposition, upstream and downstream, accompanied barrage construction, as have accelerated lakeshore erosion and the growth and consolidation of the flood tidal delta (Bird Island). These human accelerated changes provide rapidly formed analogues of older Quaternary features, and aid their interpretation. The shape and location of the Murray Mouth is constantly changing, migrating over 1.6 km since the 1830s. Migrations of up to 6 km over the past 3000 yr have influenced sedimentation on the landward shore of the back-barrier lagoonal system.

The arcoid bivalve Anadara trapezia ( Deshayes, 1840 ) is a eurythermal estuarine mollusc that flourishes at present in eastern Australia between Port Phillip Bay, Victoria and Townsville in northern Queensland. A. trapezia first appeared in the Australian Quaternary fossil record during Oxygen Isotope Stage (OIS) 7. In New Zealand, where it is now extinct, the earliest known occurrences are in the Rangitawa “fossil beds” and in uppermost Castlecliffian strata west of Wanganui, North Island (OIS 11, ca. 400 ka). The species had an extensive distribution during the Last Interglacial Maximum (OIS 5e) in both Australia and New Zealand and appears to have had a slightly wider than present geographic range in southeastern Australia during the Middle Holocene, as shown by records from Tasmania and western Victoria, where it no longer lives. Apart from an isolated population inhabiting Oyster Harbour, Western Australia, A. trapezia has not been confirmed living in coastal waters west of Port Phillip Bay, Victoria. It became extinct in New Zealand sometime after OIS 5e. The extensive distribution and abundance of A. trapezia and other fauna of subtropical affinity during the Last Interglacial Maximum, in areas where both are now extinct, appears to be associated with an enhanced Leeuwin Current at that time, coinciding with higher, less seasonally concentrated levels of precipitation and river discharge. The arrival of A. trapezia in Australasian coastal waters may have been a consequence of planktonic dispersal from southern South America. A. bravardi del Rio, from the Middle Miocene Puerto Madryn Formation, on the Valdes Peninsula, Argentina, may be a possible ancestor for A. trapezia.

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 McCourt's 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.

Coastal Robe Range, and adjacent Woakwine Range, situated 10–15 km inland, are the most southwesterly and youngest of a series of parallel, low altitude, Pleistocene beach-dune barriers in southeastern South Australia. In the early Holocene, the post-glacial marine transgression flooded the Robe–Woakwine Corridor, thus forming a shallow back-barrier lagoon, open to the Southern Ocean near the present towns of Robe and Beachport. Marine to lagoonal, bioclastic, carbonate-quartz sedimentation prevailed within the corridor from ca. 7500–2000 yr BP. Along the seaward side of Robe Range, transgressive sands were deposited initially as ephemeral sand flats, but were mostly redistributed as coastal dunes, which today remain active and blanket the Pleistocene core of the range. Sand was also transported along the coast and deposited within the protected embayments of Guichen and Rivoli Bays, in the form of prograded beach ridge plains, eventually isolating the back-barrier lagoon from the open ocean. Sediment aggradation within the lagoon, cessation of marine influence and regional uplift of 0.7 m during the Holocene, combined to transform the corridor to a lacustrine landscape. Fossil molluscs, foraminifera and ostracods are diagnostic of successive palaeo-environments, and thus signify stages in the rapid geomorphic evolution of the coastal Robe–Woakwine Corridor.

Coastal marine strata of last interglacial age are preserved extensively around the southern Australian coastline. The sedimentary facies have many features in common with adjacent Holocene coastal facies and contemporary peritidal environments, but are partly lithified, mostly elevated, and laterally displaced inland. Sediments are dominantly biogenic skeletal carbonates of cool-temperate water affinities (foram-mollusc-coralline alga association). Surficial calcrete development has aided preservation of morphostratigraphic forms and sedimentary structures. Large coastal barrier complexes comprising aeolian dune, foredune and back-barrier lagoon facies characterize exposed coastal tracts facing the Southern Ocean. In contrast, broad, low-gradient peritidal complexes, with a shoaling-upward sequence of subtidal, intertidal, and supratidal mud/sand flat facies, characterize protected shorelines of major gulfs and embayments. A similar upward-shoaling sequence is preserved in back-barrier lagoons. Along the more tectonically stable part of southern Australia, the last interglacial palaeo shoreline is consistently recorded at 2 m above present sea level. This is an important regional datum that is significantly below the +6 m level globally attributed to this sea level highstand. Elsewhere, neotectonic variations in shoreline elevation are clearly discernible with uplift of up to 18 m associated with Quaternary volcanism near Mount Gambier. The last interglacial strata contain a number of fossils with tropical affinities that no longer live in the local waters. The presence of these fossils is consistent with warmer coastal waters during the last interglaciation, but does not necessarily imply warmer oceanic waters or a warmer continental climate.

The extent of racemisation for a range of amino acids for the total acid hydrolysate and free fractions, calibrated against radiocarbon dating, indicates that the foraminifer Marginopora vertebralis, found within ‘modern’ tidal flat sediments between Wardang Island and Goose Island, South Australia, is reworked from the underlying Late Pleistocene Glanville Formation. Analyses of amino acids in the total acid hydrolysate and free fractions in conjunction with the determination of absolute concentrations of amino acid residues in fossils, provides an elegant method for assessing the validity of amino acid racemisation dating, and in identifying reworked fossils.

Benthic foraminifera are abundant in surficial sediment of Gulf St Vincent and the distribution of many species is related to water depth. For example, Nubecularia lucifuga is most abundant in shallow northern waters while Ammobaculites reophaciformis is more common in deeper southern parts of the gulf. Elphidium crispum, a shallow‐water species, and E. macelliforme, favouring deeper water, provide a useful numerical ratio. Their logarithmic relative abundance in the sediment size fraction 0.50–0.25 mm correlates closely with water depth, particularly for southern Gulf St Vincent. Vibrocore SV23 recovered an undisturbed section of Quaternary strata from one of the deepest parts (40 m) of the gulf. Late Pleistocene sediment (oxygen isotope stage 3) was in turn overlain by rapidly deposited lacustrine and restricted marginal marine sediment before development of more open Holocene marine conditions. Using the Elphidium ratios and other supporting foraminiferal data on a framework of 14C dates, a palaeosea‐l...

Concordant results for the extent of racemization of the amino acids, aspartic acid, leucine and valine and isoleucine epimerization in several mollusc genera support radiocarbon data that indicate an interstadial age (oxygen isotope stage 3: 45,000 to 30,000 yr B.P.) for a sequence of mollusc-rich, carbonate muds in Gulf St. Vincent, South Australia. A numeric age of 46,500 ± 9100 yr B.P. was obtained on marine molluscs from these sediments, using a model based on “apparent” parabolic racemization kinetics. In a global context, the sequence represents one of the few well documented occurrences of marine strata of this age from a tectonically quiescent setting. A sea level as high as −22 m is indicated for this interval. Amino acid racemization provides an important method for validating conventional, “finite” radiocarbon ages close to the practical limits of radiocarbon dating and in studies of reworking.

Marginal marine strata of last interglacial age occur in a range of morphostratigraphic settings around the Australian coastline. The lithofacies are similar to their Holocene equivalents but are partly lithified, elevated and laterally displaced inland. Uranium-series ages for corals and molluscs from widely separated localities around the Australian coastline are generally in accord with the accepted age for Oxygen Isotope Substage 5e (125,000 ± 10,000 BP), the value generally accepted for the last interglacial maximum. Amino acid racemisation has principally been applied to correlation of sequences with benchmark sites dated by the uranium-series method. Elevations of preserved last interglacial shorelines do not support the notion that Australia is a stable continent. Significant neotectonic anomalies include Cape Cuvier (+10.5 m), Fleurieu Peninsula (+6 m), the Coorong Coastal Plain (+10 m) and Tasmania (+32 m), each indicating contrasting degrees of local uplift. The Tasmanian sequences are the highest occurrence on the Australian continent and have been attributed to uplift as a result of mantle hotspot processes. With the exception of these tectonically uplifted sites, the height of the last interglacial sea surface around the Australian coastline is consistently below the 6 m level globally attributed to this high sea level stand. In Australia, the most consistent datum is from western Eyre Peninsula where a level 2 m above present mean sea level is ubiquitous. The more southerly limit of coral growth and wider distribution of subtropical molluscan fauna are in accordance with warmer ocean waters during Substage 5e (approximately 2°C). The extent of racemisation in molluscan fossils from southern Australia also excludes the possibility of a more equable latitudinal distribution of MAT during Substage 5e.

Amino acid racemization data for marine molluscs of the last interglaciation from southern Australia provide the basis for a predictive model for relative dating of late Quaternary sequences. Genera analyzed includeAnadarasp.,Katelysiasp.,Glycymerissp., andFulviasp. that exhibit moderate racemization rates. A genus effect on racemization is not evident in these taxa. Coefficients of variation for intershellD/Lratio variation for each deposit are generally less than 12%. The extent of racemization in molluscan fossils of the last interglaciation from temperate coastal settings in southern Australia represents an exponential function of temperature and is in general accord with data from Northern Hemisphere sites with similar contemporary mean annual temperature values. These data highlight the potential of amino acid racemization for global correlation programs. The amino acid data from southern Australia suggest, however, that a larger margin of variation may have to be accounted for in stratigraphic correlation, as indicated by the greater scatter of data around the oxygen isotope substage 5eisochron. These data have implications regarding the age-resolving power of amino acid racemization.

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.

Stratigraphic and chronologic studies of the coastal sediments of northern Spencer Gulf in the vicinity of Redcliff are described. Two Pleistocene marine units are recognised beneath an extensive Holocene peritidal sequence. The Holocene sequence is dominated by sediments of the Posidonia australis seagrass facies which form a distinctive carbonate bank fringing the coastline. Peritidal sedimentation commenced prior to 6600 radiocarbon yrs B.P. and a + 2.5 m higher relative sea level existed from about 6000 until around 1700 yrs B.P. The subsequent relative fall to present level probably resulted from local tectonic uplift. After the regression, mangrove and samphire colonization, and beach ridge progradation, occurred over the former seagrass bank.

Carbonate-dominant sediments are currently forming and accumulating over the extensive marine shelf of the passive margin of southern Australia. A dearth of continental detritus results from both a very low relief and a predominantly arid climate. The wide continental shelf is bathed by cold upwelling ocean waters that support luxuriant growths of bryozoans and coralline algae, together with sponges, molluscs, asteroids, benthic and some planktonic foraminifera. The open ocean coast is battered by a persistent southwest swell, resulting in erosion of calcrete-encrusted Pleistocene eolianites. Much sediment is reworked and overall shelf sedimentation rates are low. High-energy microtidal beach/dune systems occur between headlands and along the very long ocean beach in the Coorong region. The northern, more arid coastal areas also contain saline lakes that precipitate gypsum from infiltrated sea water, and display marginal facies of aragonite boxwork to fenestral carbonate crusts, with stromatolites and tepee structures. In contrast, the southern, seasonally humid Coorong region, has a predominantly continental groundwater regime where sulphate is rare, and the high summer evaporation precipitates dolomite, magnesite and aragonite muds. Fenestral crusts, breccias, tepees and some stromatolites are also present. St. Vincent and Spencer gulfs both afford some protection from ocean swell, but tidal amplitude and currents increase, and a depth and inundation-related zonation of plants and animals is established. Muddy carbonate sand accumulates on the sea floor below 30 m, where filter-feeding bryozoans, bivalves and sponges dominate. In shallower regions, seagrass meadows contain a rich fauna that results in rapid accumulation of an unsorted muddy bioclastic sand. Mangrove woodlands backed by saline marsh with cyanobacterial mats are common, and accumulate mud-rich and gastropod-bearing sediment. As tidal amplitude and desiccation increase northward into both gulfs, a supratidal zone bare of vegetation (sabkha) becomes the site for deposition of gypsum-rich and fenestral calcitic mud.

The seafloor morphology and lithology of northern Spencer Gulf, South Australia, is related to successive transgressions and regressions accompanying glacial and non-glacial periods. Vibrocoring has revealed a veneer of Holocene bioclastics and a sequence of Pleistocene marine strata which display varying degrees of pedogenesis, oxidation, decalcification and clay illuviation. The contact between the Holocene and Pleistocene sediments is marked by either a thin alluvial or aeolian horizon or by a soil horizon of variable development. The Pleistocene marine strata have been assigned to four Formations (older Pleistocene marine beds, Mambray Fm., False Bay Fm., and Lowly Point Fm.) based on superposition of lithofacies and intervening pedogenic horizons. A sequence of slightly altered, laminated lagoonal clays (Lowly Point Formation) and bryozoan rich limestones (False Bay Formation) has been encountered in deeper parts of the Gulf. Stratigraphically below these is a widespread, weathered marine unit (Mambray Formation) which contains abundant remains of the bivalve Anadara trapezia and the foraminifer Marginopora vertebralis, species absent from the present biota. This unit, in turn, is underlain by a sedimentary sequence strongly altered by pedogenesis and clay illuviation (older Pleistocene marine beds); its original marine character has been largely obliterated. A dearth of fluvial gravels and sand from the vibrocores, as well as evidence from palaeosols, indicate that a predominantly semi-arid to arid climate has persisted in the northern Gulf region since ca. 125,000 yrs ago, and that there has been little subsequent terrigenous material transported to the Gulf.

Research into estuarine and coastal fine sediment transport and sediment deposition is aided by a proposed routine for collection and analysis of hydrodynamic, particulate, and salinity data. Field measurements taken over a number of depth intervals and over one or more tidal cycles are used to calculate the point, depth-integrated, and net horizontal movements of water, suspended solids, and salt at a fixed sampling site.

Summary In hydraulic response terms, the total clastic load of a river is comprised of wash load and bed material load components. Bed material load includes sediment moving as actual bed load and as suspended material originating from the bed. Classical suspended sediment rating curves do not differentiate between wash load and suspended bed material and their indiscriminant use can therefore lead to ambiguous results. Wash load must be delineated from the total suspension when using a rating curve. This is particularly important for rivers draining tropical catchments as these transport a large proportion of fine sediment. For rivers in which a relationship exists between wash load concentration and discharge, an estimate of fine sediment delivery may be obtained from a wash load rating curve. The remaining bed material load may then be calculated from physical principles. This technique is applied to the Burdekin River of northeast Australia. The Burdekin River drains a tropical semi-arid hinterland and transports a predominantly silt and clay wash load. A wash load rating curve is established by applying correction factors for suspended bed material under different flow rates to a classical suspended sediment rating curve. The resulting estimate of mean annual wash load is 3.0 million tonnes of silt and clay. The use of a theoretical bed load equation (ACKERS & WHITE 1973) together with hydraulic parameters on the coastal plain yields an estimate of mean annual bed material load of 0.45 million tonnes of sand.

Four dating methods have been used to obtain chronological information about Holocene and Pleistocene coastal marine sediments in South Australia, and to check the stratigraphic reliability of each dating technique. Estimates of accumulation rates for Holocene seagrass bank deposits vary according to the time period over which they are averaged. The estimates vary from 2.0 to 2.7 mm yr −1 for measurements by the Pb-210 method (averaged over about 100 years) to 1.4-0.2 mm yr −1 for C-14 derived measurements (averaged over a period of 1000–7000 yrs). Radiocarbon age determinations on carbonate and organic fractions do not date the true sediment age. Shells, shell fragments and calcareous fines predate the sediment whereas organic and seagrass detritus postdate it. By dating sample pairs, their age can be adequately defined. Thermoluminescence age estimates correlate well with available C-14 ages where the sediment grains have experienced good exposure to sunlight prior to deposition. Amino acid racemization and thermoluminescence measurements indicate a late Pleistocene age of ca. 110,000 yrs for the Mambray Formation of Spencer Gulf. Amino acid racemization data also support a correlation with the late Pleistocene Glanville Formation of Adelaide.

New data are presented from the north Queensland coastal plain which indicate that present Holocene sea level was reached about 6000 years B.P. and has not deviated significantly since then. Together with negative geomorphic evidence for higher sea levels along the coastal plain, this implies that previous reports of evidence for higher stands may have resulted from misinterpretation of field evidence. Close agreement with sealevel data from central Queensland and New South Wales indicates that eastern Australia has followed a common relative sea-level history and has been an area of relative tectonic stability.

Surficial sediments of Gulf St. Vincent, South Australia, are predominantly bioclastic, cool-temperate carbonates. Benthic foraminifera are abundant and distribution of species is closely related to water depth. For example, Massilina milletti is most common at depths ca. 40 m, while Discorbis dimidiatus is characteristics of shallow, subtidal environments. Elphidium crispum, a shallow-water species, and E. macelliforme, favoring deeper water, provide a useful numerical ratio. Their logarithmic relative abundance, in the sediment size fraction 0.50–0.25 mm, correlates strongly with water depth. Vibrocores SV 4 and SV 5 recovered undisturbed sections of Quaternary strata from the deepest part (ca. 40 m) of Gulf St. Vincent. Amino acid racemization and radiocarbon age determinations show that late Pleistocene sections of the cores were deposited over the time ca. 45,000 to 30,000 yr B.P. Species of fossil foraminifera, recovered from these sections, are mostly extant in modern Gulf St. Vincent, thus allowing paleoecological inferences of late Pleistocene sea levels. These inferred sea-level maxima can be correlated with those determined from study of Huon Peninsula coral reef terraces. Initial estimates of tectonically corrected sea levels for transgressions in Gulf St. Vincent at 40,000 and 31,000 yr B.P. are −22.5 m and −22 m, respectively. The intervening regression lowered sea level to −28 m.

Northern Spencer Gulf is the landward extremity of a shallow marine embayment which occupies a structural depression that overlies a major Precambrian lineament. Situated in a warm temperate climate, the low rainfall and high evaporation have created high salinities resulting in an hydrological inverse estuary. Modern sedimentation is dominantly biogenic carbonate to mixed terrigenous-carbonate. It is controlled by a mesotidal regime with occasional storm surges, minor wave activity, and a prolific growth of seagrass in shallow water. The skeletal detritus consists of bivalves, gastropods, forams, echinoids, coralline algae and bryozoa. The subtidal zone between 10–25 m is divided morphologically into two provinces. The wide southern part has a relatively smooth floor, but the northern part is narrower, and the seafloor is either scoured free of loose sediment, or covered with wide belts of megaripples. The subtidal zone between 0–10 m is everywhere dominated by seagrass meadows. The seagrasses are largely Posidonia australis and P. sinuosa and occupy broad depositional platforms, and discrete offshore banks. The seagrass meadows produce and trap mollusc/foram detritus, resulting in the accumulation of very poorly sorted, organically bound structureless carbonate muddy sand. Intertidal and supratidal zone sediments are very extensive. The intertidal zone includes bare sand flats or those covered by the seagrass Zostera . Dense mangroves ( Avicennia marina ) from mean sea level to spring high-tide level are followed progressively by a halophytic (samphire) association and an Atriplex (saltbush) association. Extensive algal mats occur with the halophytes and extend into the mangrove forests. The sediments are muddy and only moderately calcareous. The supratidal zone consists mainly of bare carbonate flats, some stranded beach ridges, and coastal dunes. The carbonate flats contain discoidal gypsum crystals in weakly layered, fenestral, calcitic mud. Coastal changes during historic time are limited, and the dominant sedimentary regime in northern Spencer Gulf is the vertical growth of seagrass areas to form intertidal sand flats.

The mixed carbonate-terrigenous shelf system associated with the Great Barrier Reef covers an area of about 270,000 km2. Fluvial sediment delivery to the Province averages 10 tonnes per metre of coastline per year and dominates modern sedimentation on the shelf. The northward dispersion of sediment from individual river mouths results in a merging of coastal interdeltaic deposits and an inner shelf zone dominated by terrigenous mud sedimentation. Intermittent high turbidity on the inner shelf precludes significant reef construction. Modern fluvially derived sand is largely contained in the littoral zone, and the terrigenous sand and gravel component of middle- and outer- shelf sediments are of relict or palimpsest origin. Coastal sedimentation accounts for the bulk of the Holocene terrigenous sediment budget, with vertical accumulation at rates of up to 8.5 mm/yr and seaward progradation at rates of up to 4 mm/yr. Holocene reef growth has occurred at rates as high as 16 mm/yr, and the reef complexes represent a significant reservoir of autochthonous carbonate sediment. However, their contribution of allochthonous carbonate to the shelf is limited. In situ skeletal carbonate production on the middle- and outer- shelf floor is locally significant; however, seismic profiles and sea-bed cores confirm that much of the shelf floor is devoid of major Holocene sediment accumulation. Quaternary sea-level fluctuations have promoted terrigenous-carbonate intermixing, but have suppressed long-term carbonate production. The changing locus of maximum terrigenous sedimentation (the coastal zone) associated with fluctuating sea levels has resulted in an overwhelming dominance of terrigenous clastics in the subsurface of the shelf.