Last glacial cycle hydrological change at Lake Tyrrell, southeast Australia

Lake Tyrrell is the largest playa in the Murray Basin of southeast Australia. Optical dating of transverse dune (lunette) sediments extends the lake's radiocarbon chronology to the last interglacial period. The highest lake level was attained 131,000 ± 10,000 yr ago, forming Lake Chillingollah, a megalake that persisted until around 77,000 ± 4000 yr ago. Pedogenesis of its sandy lunette continued until buried by a silty clay lunette deflated from the lake floor 27,000 ± 2000 yr ago. The dated soil-stratigraphic units correlate with the upper Tyrrell Beds and contain evidence that humans visited the lakeshore before 27,000 yr ago. The Lake Chillingollah megalake was synchronous with very high lake levels in monsoon-dominated Australia, yet it was not influenced by tropical monsoon systems. It was filled instead by increased winter rainfall from westerly low-pressure fronts. Greater effective precipitation across Australia is evident, the result of a weakened subtropical high-pressure zone.     

Late Neogene tectonics in northwestern Victoria: Evidence from the Late Miocene–Pliocene Loxton Sand

The Late Miocene–Pliocene Loxton Sand strandplain extends across the western part of the Murray Basin in southeastern Australia. Gamma logging on groundwater bores surrounding Lake Tutchewop, which lies close to the eastern limit of this strandplain, showed that a heavy mineral layer within the Loxton Sand is displaced across the northern extension of the Leaghur Fault. A crevasse splay sand within the overlying Pliocene Shepparton Formation is also displaced, indicating that tectonic activity along the Leaghur Fault occurred in the Early Pliocene. This coincides with the Kosciusko Uplift, a major phase of Neogene tectonism across southeastern Australia, which also resulted in movement along the Danyo, Hindmarsh, Tyrell and Avoca Faults in northwestern Victoria.     

The Early Lake Ontario barrier beach: evidence for sea level about 12.8–12.5 cal. ka BP beneath western Lake Ontario in eastern North America

An overstepped, concave‐eastward, barrier beach beneath Holocene mud in western Lake Ontario has been delineated by acoustic and seismic reflection profiles and piston cores, and related to Early Lake Ontario (ELO). The average ELO barrier depth below present mean lake level is 77.4 to 80.6 m, or about ?6 to ?2.8 m above present sea level. Trend surface analysis of Champlain Sea (Atlantic Ocean) marine limits defined the contemporaneous marine water surface, and projections of this surface pass ~25 m above the outlet sill of the Lake Ontario basin and extend to the ELO palaeo‐barrier, a unique sand and gravel deposit beneath western Lake Ontario. ELO was connected to the Champlain Sea above the isostatically rising outlet sill for up to three centuries after about 12.8 cal. ka BP, while the glacio‐isostatically depressed St. Lawrence River Valley was inundated by the Atlantic Ocean. During the period of this connection, ELO level was confluent with slowly rising sea level, and the lake constructed a transgressive beach deposit with washover surfaces. ELO remained fresh due to a high flux of meltwater inflow. The marine water level connection stabilized water level in ELO relative to its shore and facilitated shore erosion, sediment supply and barrier construction. Glacio‐isostatic uplift of the outlet sill, faster than sea‐level rise, lifted ELO above the Champlain Sea about 12.5 cal. ka. Shortly after, a hydrological deficit due mainly to a combination of diverted meltwater inflow and dry climate, well known from regional pollen studies, forced the lake into a lowstand. The lowstand stranded the barrier, which remains as evidence of sea level, the farthest inland in eastern North America north of the Gulf of Mexico at the time. The highest palaeo‐washover surface provides a sea‐level index point.     

Pliocene volcano-tectonics and paleogeography of the Turkana Basin,Kenya and Ethiopia

The distribution of hominin fossil sites in the Turkana Basin, Kenya is intimately linked to the history of the Omo River, which affected the paleogeography and ecology of the basin since the dawn of the Pliocene. We report new geological data concerning the outlet channel of the Omo River between earliest Pliocene and final closure of the Turkana Basin drainage system in the latest Pliocene to earliest Quaternary. Throughout most of the Pliocene the Omo River entered the Turkana Basin from its source in the highlands of Ethiopia and exited the eastern margin of the basin to discharge into the Lamu embayment along the coast of the Indian Ocean. During the earliest Pliocene the river’s outlet was located in the northern part of the basin, where a remnant outlet channel is preserved in basalts that pre-date eruption of the Gombe flood basalt between 4.05 and 3.95 Ma. The outlet channel was faulted down to the west prior to 4.05 Ma, forming a natural dam behind which Lake Lonyumun developed. Lake Lonyumun was drained between 3.95 and 3.9 Ma when a new outlet channel formed north of Loiyangalani in the southeastern margin of the Turkana Basin. That outlet was blocked by Lenderit Basalt lava flows between 2.2 and 2.0 Ma. Faulting that initiated either during or shortly after eruption of the Lenderit Basalt closed the depression that is occupied by modern Lake Turkana to sediment and water.Several large shield volcanoes formed east of the Turkana Basin beginning by 2.5–3.0 Ma, volcanism overlapping in time, but probably migrating eastward from Mount Kulal on the eastern edge of the basin to Mount Marsabit located at the eastern edge of the Chalbi Desert. The mass of the volcanic rocks loaded and depressed the lithosphere, enhancing subsidence in a shallow southeast trending depression that overlay the Cretaceous and Paleogene (?) Anza Rift. Subsidence in this flexural depression guided the course of the Omo River towards the Indian Ocean, and also localized accumulations of lava along the margins of the shield volcanoes. Lava flows at Mount Marsabit extended across the Omo River Valley after 1.8–2.0 Ma based on estimated ages of fossils in lacustrine and terrestrial deposits, and possibly by as early as 2.5 ± 0.3 Ma based on dating of a lava flow. During the enhanced precipitation in latest Pleistocene and earliest Holocene (11–9.5 ka) this flexural depression became the site of Lake Chalbi, which was separated from Lake Turkana by a tectonically controlled drainage divide.     

A new multi‐stage recession model for Proglacial Lake Humber during the retreat of the last British–Irish Ice Sheet

The single most prominent lake associated with the retreat phase of the last British–Irish Ice Sheet (BIIS) was Proglacial Lake Humber. The present research elucidates a revised regional history of Proglacial Lake Humber from its maximum elevation to its demise using a combination of landscape mapping and luminescence dating. The results of mapping multiple Lake Humber strandlines are now best described by an eight‐stage recessional model. Erosional highstands of the lake can be shown to post‐date the BIIS advance that deposited the Skipsea Till at around 17 ka whereas new OSL ages show that Lake Humber was nearing its demise by 15.5±0.8 ka, indicating a possible short‐lived lake. Multiple lake level stands are attributed to the switching of lake outlets from the Lincolnshire Gap to the Humber Gap and to oscillations of the BIIS blocking the latter on more than one occasion and subsequently at a lower elevation with till. The horizontal or near‐horizontal shorelines confirm that isostatic adjustment did not occur during the demise of Lake Humber, indicating that BIIS advances in the North Sea region and Vale of York were not only dynamic but of short duration.     

Rapid changes in the level of Kluane Lake in Yukon Territory over the last millennium

The level of Kluane Lake, the largest lake in Yukon Territory, was lower than at present during most of the Holocene. The lake rose rapidly in the late seventeenth century to a level 12 m above present, drowning forest and stranding driftwood on a conspicuous high-stand beach, remnants of which are preserved at the south end of the lake. Kluane Lake fell back to near its present level by the end of the eighteenth century and has fluctuated within a range of about 3 m over the last 50 yr. The primary control on historic fluctuations in lake level is the discharge of Slims River, the largest source of water to the lake. We use tree ring and radiocarbon ages, stratigraphy and sub-bottom acoustic data to evaluate two explanations for the dramatic changes in the level of Kluane Lake. Our data support the hypothesis of Hugh Bostock, who suggested in 1969 that the maximum Little Ice Age advance of Kaskawulsh Glacier deposited large amounts of sediment in the Slims River valley and established the present course of Slims River into Kluane Lake. Bostock argued that these events caused the lake to rise and eventually overflow to the north. The overflowing waters incised the Duke River fan at the north end of Kluane Lake and lowered the lake to its present level. This study highlights the potentially dramatic impacts of climate change on regional hydrology during the Little Ice Age in glacierised mountains.     

A 6000-year record of ecological and hydrological changes from Laguna de la Leche, north coastal Cuba

Laguna de la Leche, north coastal Cuba, is a shallow (≤ 3 m), oligohaline (∼ 2.0-4.5‰) coastal lake surrounded by mangroves and cattail stands. A 227-cm core was studied using loss-on-ignition, pollen, calcareous microfossils, and plant macrofossils. From ∼6200 to ∼ 4800 cal yr BP, the area was an oligohaline lake. The period from ∼ 4800 to ∼ 4200 cal yr BP saw higher water levels and a freshened system; these changes are indicated by an increase in the regional pollen rain, as well as by the presence of charophyte oogonia and an increase in freshwater gastropods (Hydrobiidae). By ∼ 4000 cal yr BP, an open mesohaline lagoon had formed; an increase in salt-tolerant foraminifers suggests that water level increase was driven by relative sea level rise. The initiation of Laguna de la Leche correlates with a shift to wetter conditions as indicated in pollen records from the southeastern United States (e.g., Lake Tulane). This synchronicity suggests that sea level rise caused middle Holocene environmental change region-wide. Two other cores sampled from mangrove swamps in the vicinity of Laguna de la Leche indicate that a major expansion of mangroves was underway by ∼ 1700 cal yr BP.     

Holocene Foraminifera as Indicators of Relative Estuarine–Lagoonal and Oceanic Influences in Estuarine Sediments of the River Murray, South Australia: Volume 53, Number 3 (2000), pages 378–391

In southeastern South Australia, the River Murray debouches through a coastal barrier separating euryhaline estuarine-lagoonal waters from the Southern Ocean. Depending upon the relative freshwater outflow of the river and ingress of the ocean, water salinity varies greatly within the lower estuary. Ammonia beccarii and Elphidium articulatum are euryhaline species of foraminifera that characterize the estuary and back-barrier Coorong Lagoon. The inner-shelf marine environment hosts an assemblage in which Discorbis dimidiatus, E. crispum, E. macelliforme, and various cibicidid species predominate. In cored sediments recovered from the shallow lower estuary, the relative abundance of A. beccarii + E. articulatum was compared with that of D. dimidiatus + E. crispum + E. macelliforme + other species. These data, and AMS radiocarbon ages determined for foraminifera and ostracods, provide evidence of a change from maximum oceanic influence (5255 ± 60 yr B.P.) to maximum estuarine influence (3605 ± 70 yr B.P.). Over this same time interval, sea level fell relatively by about 2 m. However, the event was also contemporaneous with falling water levels in several Victorian lakes, and it is thus attributed to onset of climatic aridity. Reduced precipitation in the River Murray catchment and reduced freshwater outflow enhanced development of the flood-tide delta and constriction of the mouth.     

Lake George revisited: New evidence for the origin and evolution of a large closed lake,Southern Tablelands,NSW, Australia

Lake George contains the longest continuous sedimentary record of any Australian lake basin, but previous age models are equivocal, particularly for the oldest (pre-Quaternary) part of the record. We have applied a combination of cosmogenic nuclide burial dating, magnetostratigraphy and biostratigraphy to determine the age of the basal (fluvial) unit in the basin, the Gearys Gap Formation. Within the differing resolutions achievable by the three dating techniques, our results show that (i) the Gearys Gap Formation, began accumulating at ca 4 Ma, in the early Pliocene (Zanclean), and (ii) deposition had ceased by ca 3 Ma, in the mid late Pliocene (Piacenzian). Whether the same age control provides an early Pliocene (Zanclean) age for the formation of the lake basin is uncertain. During the Piacenzian, the vegetation at the core site was a wetland community dominated by members of the coral fern family Gleicheniaceae, while the surrounding dryland vegetation was a mix of sclerophyll and temperate rainforest communities, with the latter including trees and shrubs now endemic to New Guinea–New Caledonia and Tasmania. Mean annual rainfall and temperatures are inferred to have been ～2000–3000 mm, although probably not uniformly distributed throughout the year, and within the mesotherm range (>14°C <20°C), respectively. Unresolved issues are: (1) Does the basal gravel unit predate uplift of the Lake George Range and therefore provide evidence that one of the proposed paleo-spillways of Lake George, that above Geary's Gap, has been elevated up to 100–200 m by neotectonic activity over the past 4 million years? (2) Did a shallow to deepwater lake exist elsewhere in the lake basin during the Pliocene?     

Abrupt shifts in the Indian monsoon during the Pliocene marked by high-resolution terrestrial records from the Yuanmou Basin in southwest China

A 650-m-thick sequence of fluvio-lacustrine sediments from the Yuanmou Basin in southwest China was analyzed at 20-cm intervals for grain-size distribution to provide a high-resolution terrestrial record of Indian summer monsoon variations during the Pliocene. The concentrations of the clay and clay-plus-fine-silt fractions are inferred to reflect the water-level status of the lake basin related to the intensity of the Indian summer monsoon and high concentrations reflect high lake levels resulting from the intensified summer monsoon. The frequency of individual lacustrine mud beds is considered to reveal the frequency of the lakes developed in the basin associated with the variability of the Indian summer monsoon and an increased frequency of the lakes reveals an increased variability of the summer monsoon. The proxy data indicate that the Indian summer monsoon experienced two major shifts at 3.57 and 2.78 Ma and two secondary shifts at 3.09 and 2.39 Ma during the Pliocene. The summer monsoon displayed a general trend of gradual intensification during the period of 3.57–2.78 Ma, coeval with an accelerated uplift of the Tibetan Plateau, implying a close link between the monsoon intensification and the plateau uplift. At 2.78 Ma, the summer monsoon was markedly weakened, synchronous with the formation of extensive Northern Hemisphere ice sheets, denoting a quick response of the monsoon regime to the Northern Hemisphere glaciation. The variability of the summer monsoon decreased at 3.09 Ma and increased at 2.39 Ma, presumably suggesting that variations of the Indian monsoon would be modulated by the initiation and periodic fluctuations of ice-sheet covers in Northern Hemisphere high latitudes.     

内蒙古狼山山前台地成因及其新构造运动意义

内蒙古狼山地处阴山造山带西段、河套断陷带的西北缘,晚新生代以来狼山山前断裂广泛发育、构造抬升强烈。研究晚更新世以来狼山的构造隆升对深入了解河套断陷带的形成演化机制及其隆升过程对河套盆地古地理格局的影响具有重要的意义。狼山山前翁格勒其格和乌兰敖包台地的沉积学、地貌学和年代学研究表明,T1台地形成于47.4 kaB.P.,其沉积物为晚更新世河套古大湖沉积;T2台地形成于69 kaB.P.,其沉积物可能为黄河流经狼山山前的冲积物。台地特征的分析显示,狼山山前台地主要由构造抬升形成,两级台地记录了狼山晚更新世晚期(Qp^3-2)以来的构造隆升过程。69 kaB.P.到47.4 kaB.P.翁格勒其格和乌兰敖包地区的隆升速率分别为1.34 m/ka和1.25 m/ka,47.4 kaB.P.以来分别为0.81 m/ka和1.18 m/ka,狼山南段(翁格勒其格地区)构造抬升有减小的趋势。晚更新世晚期(Qp^3-2)以来由于狼山的快速隆升,导致黄河河道不断东迁,河套平原的古河道是其迁移的证据。狼山山前湖岸阶地的研究进一步证实晚更新世晚期河套地区发育统一古大湖。     

Groundwater flow and solute transport at the Mourquong saline-water disposal basin, Murray Basin, southeastern Australia

Saline groundwater and drainage effluent from irrigation are commonly stored in some 200 natural and artificial saline-water disposal basins throughout the Murray-Darling Basin of Australia. Their impact on underlying aquifers and the River Murray, one of Australia's major water supplies, is of serious concern. In one such scheme, saline groundwater is pumped into Lake Mourquong, a natural groundwater discharge complex. The disposal basin is hydrodynamically restricted by low-permeability lacustrine clays, but there are vulnerable areas in the southeast where the clay is apparently missing. The extent of vertical and lateral leakage of basin brines and the processes controlling their migration are examined using (1) analyses of chloride and stable isotopes of water (²H/¹H and ¹⁸O/¹⁶O) to infer mixing between regional groundwater and lake water, and (2) the variable-density groundwater flow and solute-transport code SUTRA. Hydrochemical results indicate that evaporated disposal water has moved at least 100 m in an easterly direction and that there is negligible movement of brines in a southerly direction towards the River Murray. The model is used to consider various management scenarios. Salt-load movement to the River Murray was highest in a "worst-case" scenario with irrigation employed between the basin and the River Murray. Present-day operating conditions lead to little, if any, direct movement of brine from the basin into the river. Electronic Publication     

Palaeoenvironmental change recorded in the palaeodunefields of the western Murray Basin,South Australia – New data from single grain OSL-dating

This study is concerned with the reconstruction of the palaeoenvironmental history of southeastern Australia for the last ～300 ka by establishing a luminescence chronology of dune sand deposition in the western Murray Basin (South Australia). In the study area, vast fields of palaeodunes, stabilised by vegetation, provide evidence of past environmental change. In total 98 samples were collected from dune sand layers at 13 different dune sections. The time of their deposition was determined using optically stimulated luminescence dating of single quartz grains, accounting for the impact of post-depositional mixing by the use of a finite mixture model. The oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western Murray Basin, ranging up to at least 380 ka. Phases of substantial dune sand deposition were identified for the periods 18–38 ka and 63–72 ka. Older depositional phases also exist, but are poorly resolved due to relatively large errors of the luminescence ages. Aeolian deposition during the last termination and the Holocene is relatively limited, with a slight clustering of ages at the time of the Antarctic Cold Reversal and from 5–8 ka. Two modern ages give evidence of very recent dune sand deposition. Comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases. Thus, although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward, the palaeodunes of the western Murray Basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction.     

罗布泊东部阿奇克谷地第四纪古地理

通过对罗布泊东部阿奇克谷地中部AK1孔及露头剖面第四纪沉积特征的综合研究,初步分析了阿奇克谷地第四纪以来的沉积环境与古地理演化。结果表明,阿奇克谷地第四纪古地理受上新世以来区域构造控制,谷地两侧北山及阿尔金山的隆升,一方面为其提供了丰富的物质来源,同时也控制了其沉积环境的演化。其中第四纪以来阿奇克谷地沉积环境有两次明显变化,早更新世中期谷地中开始出现湖相沉积;中更新世晚期湖相沉积范围扩大,为罗布泊湖的大发展期。晚更新世谷地两侧普遍出现砾石层,与中更新世呈不整合接触,表明构造抬升造成湖泊退缩。晚更新世以来湖泊沉积环境波动变化加快。     

Timing and cause of water level fluctuations in Kluane Lake, Yukon Territory, over the past 5000 years

We reconstructed late Holocene fluctuations of Kluane Lake in Yukon Territory from variations in bulk physical properties and carbon and nitrogen elemental and isotopic abundances in nine sediment cores. Fluctuations of Kluane Lake in the past were controlled by changes in climate and glaciers, which affected inflow of Slims and Duke rivers, the two largest sources of water flowing into the lake. Kluane Lake fluctuated within a narrow range, at levels about 25 m below the present datum, from about 5000 to 1300 cal yr BP. Low lake levels during this interval are probably due to southerly drainage of Kluane Lake to the Pacific Ocean, opposite the present northerly drainage to Bering Sea. Slims River, which today is the largest contributor of water to Kluane Lake, only rarely flowed into the lake during the period 5000 to 1300 cal yr BP. The lake rose 7-12 m between 1300 and 900 cal yr BP, reached its present level around AD 1650, and within a few decades had risen an additional 12 m. Shortly thereafter, the lake established a northern outlet and fell to near its present level.     

Architecture and evolution of the Kushiro submarine canyon in the Kurile Trench forearc slope,North‐western Pacific

An air‐gun survey, conducted over a total distance of 4356 km in the western end of the Kurile Arc offshore, has revealed the architecture and evolution of the Kushiro submarine canyon and Tokachi submarine channels of the Tokachi‐oki forearc basin. The Kushiro submarine canyon, which runs along the eastern margin of the forearc basin, is characterized by an entrenchment of up to several hundred metres in depth. The Tokachi submarine channels, by contrast, occupy the centre of the basin and consist of small, branching and levéed channels. The Kushiro submarine canyon is not connected to the Tokachi River, which has the largest drainage area in eastern Hokkaido, with a catchment area of approximately 9010 km² that includes high mountains and a volcanic region. Instead, the Kushiro submarine canyon exhibits an offset connection/quasi‐connection (probably having been connected during a prior sea‐level lowstand) with the Kushiro River (drainage area of 2500 km²) which contains the Kushiro Swamp at its mouth. To understand this unusual arrangement of rivers and submarine channels, acoustic facies analysis was undertaken to establish the seismic stratigraphy of the area. Subsurface strata can be divided into six seismic units of Miocene to Recent age. Analyses of seismic facies and isopach maps indicate that: (i) the palaeo‐Kushiro submarine canyon, which was ancestral to the Kushiro submarine canyon, was an aggradational levéed channel; and (ii) the palaeo‐Tokachi submarine channel was much larger than the present‐day channel and changed its course several times. Both the palaeo‐Kushiro submarine canyon and palaeo‐Tokachi submarine channel were fed predominantly by the ancestral Tokachi River, whereas the present‐day channels are no longer connected or quasi‐connected to the Tokachi River. Entrenchment of the Kushiro submarine canyon began in its distal reaches during the Early Pleistocene and propagated landward over time, which was possibly caused by base‐level fall (i.e. subsidence of the trench floor) or uplift of the forearc basin. Entrenchment of the upper part of the Kushiro submarine canyon began during the Middle Pleistocene, which may have been related to: (i) depositional progradation; (ii) uplift of the coastal area; or (iii) a change in source area from the ancestral Tokachi River to the Kushiro River.     

A chronology of environmental changes in the Lake Vättern basin from deglaciation to its final isolation

During and after deglaciation, Lake Vättern developed from a proglacial lake situated at the westernmost rim of the Baltic Ice Lake (BIL), into a brackish water body connecting the North Sea and the Baltic Sea, and finally into an isolated freshwater lake. Here we present geochemical and mineralogical data from a 70‐m composite sediment core recovered in southern Lake Vättern. Together with a radiocarbon age model of this core, we are able to delineate the character and timing of the different lake stages. In addition to a common mineralogical background signature seen throughout the sediment core, the proglacial sediments bear a calcite imprint representing ice‐sheet transported material from the limestone bedrock that borders the lake basin in the northeast. The proglacial fresh to brackish water transition is dated to 11 480±290 cal. a BP and is in close agreement with other regional chronologies. The brackish period lasted c. 300 years and was followed by a c. 1600 year freshwater period before the Vättern basin became isolated from the Initial Littorina Sea. Decreasing detrital input, increasing δ¹³C values and the appearance of diatoms in the upper 15 m of the sediment succession are interpreted as an overall increase in biological productivity. This mode of sedimentation continues until the present and is interpreted to mark the final isolation of the lake at 9530±50 cal. a BP. Consequently, the isolation of Lake Vättern was not an outcome of the Ancylus Lake regression, but rather because of ongoing continental uplift in the early Littorina period.     

Pliocene sedimentation in a shallow, cool-water, estuarine gulf, Murray Basin, South Australia

The Pliocene Norwest Bend Formation is a well‐preserved succession of terrestrial and shallow‐marine deposits in the Murray Basin, South Australia. Sediments in this unit consist of two discrete terrigenous clastic‐rich, decametre‐scale sequences, or informal members, which record episodes of marine incursion during the Early and Late Pliocene respectively. The base of each sequence is a transgressive lag and/or strandline deposit that is transitional upwards into a highstand, subtidal, terrigenous clastic and cool‐water carbonate sediment accumulation. The top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea‐level fell and terrestrial environments prograded basinward. Sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy. Differences in sedimentary style between these two sequences, however, reflect a major climatic change that took place in southern Australia during the mid‐Pliocene. The lower quartzose sand member is formed of siliciclastic sediment derived from prolonged, deep, subaerial weathering and contains a bivalve‐dominated, cool‐temperate, open‐marine mollusc assemblage. These sediments accumulated under an equitable, relatively warm, humid climate. The Murray Basin during this time, because of high fluvial discharge, was a salt‐wedge estuary with typical estuarine circulation. In contrast, the upper, oyster‐rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments. Strandline deposits contain a warm‐temperate skeletal assemblage. Contemporaneous aeolian sediments accumulated under warm, semi‐arid climatic conditions. Well‐developed ferricrete, silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern Australia today. Highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed. These Pliocene sediments support the notion that mollusc‐rich facies are the signature of cool‐water carbonate accumulations in inboard neritic environments. Unlike bryozoans that dominate the outer parts of Cenozoic cool‐water carbonate shelves, molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates.     

A late Quaternary sedimentary record of steryl alkyl ethers from offshore southeastern Australia

Steryl alkyl ethers (SAEs) have been reported from marine sediments ranging from Holocene to Lower Cretaceous and their production has been linked to upwelling of cold, nutrient-rich water. However, the lack of continuous stratigraphic records for them has complicated validation of the precise connection of their production, sedimentary distribution and survival to climatic conditions. Here, we report an SAE record that spans the last ca. 135 ka from a core taken offshore southeastern Australia in the Murray Canyons Group region. The SAEs are composed predominantly of C₂₇–C₃₀ steroid moieties with one or two double bonds, ether-bound to C₁₀–C₁₁ alkyl moieties. Some of the SAEs are identical to those reported in marine sediments, whereas others have not been identified previously. They do not exhibit any systematic change in distribution over the past 110 ka but sediments older than 110 ka possess a different assemblage, with a higher amount of constituents containing a C₁₁ alkyl moiety. The SAE accumulation rate increases rapidly during glacial episodes and for intervals characterized by a sharp decline in sea-surface temperature. The results suggest that SAEs may be related to marine eukaryotes that thrive when there is an influx of cold, deep waters in the Murray Canyons Group region, likely triggered by stronger westerlies over southeastern Australia forcing deeper water to reach the surface during glacials.