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The extent to which scleractinian coral inhabited southern Australia during the warm intervals of the Quaternary is poorly understood because identifiable corals from interglacial sedimentary recor...

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 identification and correlation of a sequence of Pleistocene beach barriers located within the northern Coorong Coastal Plain, South Australia, is made difficult by long-term subsidence and extensive reworking. Associated shell beds, to all but the last interglacial barrier, are subsurface and not readily accessible. The whole-rock amino acid racemization method was found to be unsuitable for distinguishing age differences of the individual barriers due to the low calcium carbonate content of the sediments, concerns for the leaching or contamination as a result of the comminuted nature of the shelly component, and the potentially high content of reworked sediment. These difficulties prompted an investigation into the applicability of AAR analysis of single foraminifera tests to ascertain whether the relative age of beach barriers could be determined and whether sediment contribution from antecedent barriers could be identified. Foraminifera tests of multiple genera (including Cibicides corticatus and Rosalina bradyi) from numerous modern depositional environments were analyzed to establish aminozones of aspartic acid and glutamic acid D/L values representative of modern/Holocene foraminifera and to assess natural variability of Holocene D/L values between depositional settings. Tests of Lamellodiscorbis dimidiatus, common in the Pleistocene barriers, were analyzed from MIS 5 and MIS 7 sediments and aminozones identified, allowing correlation of non-contiguous barrier features and the identification of reworked foraminifera. Rejection criteria removed, on average, between 25 and 30% of analytical results. The Holocene aminozone for every genus analyzed falls within the same general constraint: D/L values less than 0.40 for aspartic acid and less than 0.20 for glutamic acid. The D/L values of approximately 15% of foraminifera from the modern sediments exceed the Holocene aminozone constraint and the tests are considered reworked. The range of D/L values representative of each interglacial aminozone decreases with age, reflecting the slowing rate of amino acid racemization with time. Pleistocene sediments are found to have a higher percentage of reworked tests. Thermoluminescence dating of the Pleistocene successions was used to evaluate the AAR results. This work illustrates that foraminifera tests are surprisingly robust and can survive potentially multiple phases of deposition and reworking.

The Willandra Lakes region sits on the southern margin of Australia’s arid core and is one of the oldest localities on the continent known to have been occupied by Australia’s First People. The archaeological traces that accumulated in the Lake Mungo lunette paint a picture of changing land use over the past ∼50 thousand years (ka) and some of these are likely to have been responses to changes in palaeoenvironmental conditions. This study set out to determine the finest temporal resolution that can be used to study the depositional and palaeoenvironmental history of the Lake Mungo lunette. The investigation focused on the depositional history documented within stratigraphy exposed in an eroding gully in the southern part of the lunette; Gully 10. A stratigraphic framework was developed using sedimentological and soil micromorphological analysis. This framework was then fixed in time by 56 single-grain optically stimulated luminescence (OSL) age estimates. These data sets were then combined into a Bayesian model that indicated three depositional phases: >100 ka (LU1), ∼65–33 ka (LU2–LU3), and from ∼30 to 16 ka (LU4–LU9), with the late Pleistocene and Holocene samples (LU10–11) not being modelled. Furthermore, the redating of thirteen Lower and Upper Mungo OSL samples from Bowler et al. (2003)’s study of the southern tip of the lunette yielded younger age estimates for twelve of these, bringing them into line with previously published independent age control as well as the ages presented in this study. This study provides an approach for future efforts to establish consistency in age estimation and palaeoenvironmental interpretation along the length of the lunette.

A geochronological framework based on amino acid racemisation (AAR) and constrained by previously reported optically stimulated luminescence (OSL) ages is presented for the evolution and paleosea-level record of the Pleistocene Bridgewater Formation of the Mount Gambier region, of southern Australia. Within the study area, the Bridgewater Formation is represented by late early Pleistocene [Marine Isotope Stage (MIS) 23 at 933 ka] to Holocene barrier shoreline successions deposited during sea-level highstands. Regional monotonic uplift (0.13 mm yr–1) and pervasive calcrete development during the Pleistocene have preserved the sequence of calcarenite (mixed quartz-skeletal carbonate sand) shoreline complexes from denudation. AAR analyses confirm that the barriers generally increase in age landwards and correlate with sea-level highstands associated with interglacials as defined by the marine oxygen isotope record. AAR analyses on the benthic foraminifer Elphidium crispum have proved more reliable than the w...

Significant differences in the elevation of late Pleistocene interstadial coastal strata have been noted at the global scale resulting from the combined effects of tectonism, proximity of field sites to Pleistocene ice sheets, and the variable effects of glacio-hydro-isostatic adjustment processes. Here we report the first recorded example of subaqueously deposited late Pleistocene interstadial coastal sediments above present sea level in Australia, in a far-field location to Pleistocene ice sheets and characterised by minimal to modest rates of vertical crustal movements. Located at Port MacDonnell, in Southern Australia, the sedimentary succession is represented by a flint conglomerate beach facies with interstratified shells. An optically stimulated luminescence (OSL) age of 53 ± 4 ka for an aeolianite unit that unconformably overlies the shelly deposit indicates that the beach facies is older than early MIS 3. OSL analysis also confirms that the MacDonnell Range, located 7 km inland from the present coastline, is of last interglacial age (124 ± 10 ka; MIS 5e). Radiocarbon dating on the operculum of Turbo undulatus from the shelly conglomerate yielded a minimum age of 47,905 ± 2106 yr BP [Wk-34733]. The extent of amino acid racemization (AAR) for Turbo sp. from the shelly unit beneath the aeolianite suggests an interstadial age (102 ± 16 ka). Uplift-corrected palaeo-sea level at the time of deposition of the shelly flint conglomerate was at least − 14 m during MIS 5c. These results are consistent with palaeo-sea level estimates from other far-field settings as well as oxygen isotope-inferred sea levels for this interval and further highlight the regional tectonic stability of Australian coastal landscapes in a global context.

Oolites crop out along the northwestern coast of Western Australia at Port Smith, about 80 km SWof Broome. An oolitic coastal ridge truncated by marine erosion exposes subtidal, intertidal, and supratidal (aeolian) facies. The deposits are firmly indurated and composed of about 75% tangentially and moderately thickly layered, aragonitic ooid grains with over 90% quartz nuclei. Subtidal sedimentary structures are exposed about a metre above the present high tide mark, hinting that sea level may have been somewhat higher when the shoreline was formed. However, the macrotidal range of up to 7 m, and the possibility of cyclonic surges along the coast, precludes unequivocal determinations on this point. Whole-rock amino acid racemisation (AAR) geochronology (epimerisation of isoleucine: d-alloisoleucine/l-isoleucine or A/I) on each facies of the oolite outcrop averaged 0.106F0.013 (N=10). The modern beach contains fewer ooids (~30%), and nearly half of these are stained brown, grey, or black, perhaps as a result of burial, reduction and/or mineralization. A higher (older) mean and large standard deviation in whole-rock amino acid ratio of 0.145F0.067 (N=2) supports our inference that ooids on the modern beach were reworked from fossil deposits. Reverse phase chronostratigraphy (RPC) on individual ooid grains holds tremendous promise in this preliminary study. RPC results show a narrow variation of d/l values (CV=6–11%), and yield nearly identical d/l Asp means from light coloured fossil ooids (0.307F0.018 (N=17)); light (0.323F0.026 (N=12)) and dark coloured ooids (0.298F0.027 (N=10)) from the active beach face. When compared to A/I ratios from 14 C dated mid-Holocene ooids in the Bahamas, the mean A/I from Port Smith reflects an age of ca. 3500–4500 years that is in agreement with a calibrated AMS 14 C age of 3370F50 calendar years BP on the same material. Thus, the ooids were formed, transported, emplaced, strongly cemented, and largely eroded from the beach ridge in only 3400 years. The environmental conditions that underlie a pulse of ooid deposition during a brief period of the mid-Holocene almost certainly involve extensive tidal inlets in the area, a possible mid-Holocene oscillation 1–2 m above present, and a subsequent fall to present level that terminated the process. Apparently, a unique combination of factors produced ooids here, and in only a handful of other sites in Australia and the Indian Ocean. D 2005 Elsevier B.V. All rights reserved.

Optically stimulated luminescence (OSL) dating is now commonly used to estimate the depositional age of Quaternary landforms along the southern Cape coast of South Africa. Due to the early onset of dose saturation in the quartz-rich sediments from this region, determining the age of deposits much older than the last three glacio-eustatic sea-level high stands has been a challenge. In this study, we explored the feasibility of using the thermally-transferred OSL (TT-OSL) dating method to obtain ages for aeolian and shallow marine deposits at three different localities that hold promise to further illuminate the long and complex Late Quaternary sea-level history of this region. The bleachability and behaviour of both the recuperated OSL (ReOSL) and the basic-transferred OSL (BT-OSL) signals were investigated, and used as independent chronometers to infer (a) the degree of bleaching of the sediments and (b) the stability of the ReOSL signal for dating of older samples. We examined the sensitivity of both signals to varying preheat temperatures and further developed the single-aliquot regenerative-dose procedure for TT-OSL dating of our samples. To verify our procedures, and to understand some of the underlying mechanisms responsible for the problems we observed, modern analogues and known-age Marine Isotope Sub-stage (MIS) 5e samples from the same localities were also measured. The Middle Pleistocene deposits investigated in this study produced statistically consistent ReOSL and BT-OSL ages compatible with sea-level high stands during Marine Isotope Stage 11. This result is of considerable significance, as it may yield new insights into maximum sea-level heights during this period, which is widely considered an appropriate analogue for future environmental conditions.

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’.