J. H. Cann

Biogeographic impact of the Leeuwin Current in southern Australia since the late middle Eocene

Abstract The Leeuwin Current can be tracked from the western margin of the Australian continent to the southern margin by the record of fossilized organisms typical of warm-water marine environments. This transport smudges the normal latitudinal asymmetry in the biotas of opposing oceanic and continental margins, in which the eastern margins of oceans are cooler than the western margins and warmer biotas are restricted to lower latitudes in the east. The most comprehensive record is in the large benthic foraminifera, although fossils of benthic invertebrates, nektonic nautiloids and planktonic protists are also informative. In addition, organic biomarker hydrocarbons in stranded bitumens and resins demonstrate that they have travelled the same route from their ultimate sources in Cenozoic sedimentary basins and modern tropical rainforests of the Indonesian Archipelago. The earliest spoor of the current is in the later middle Eocene, at which time the part-deflection of counter-gyral circulation in the Indian Ocean to the southeast was stimulated by the accelerated opening of the oceanic gap between Australia and Antarctica. Thus the origin of the Leeuwin Current is twice the age of the previously suggested origin in the Miocene. The current turns on and turns off in the Great Australian Bight during the late Quaternary in concert with the interglacials and the glacials at scales of 10 5 yr. The switch can be seen in the faunal succession of planktonic foraminifera which are consistent with the neritic benthic faunas of the central gulfs: both communities show that, at the warm peak of the last interglacial, the current transported biota across the Bight more strongly than it has during the Holocene. The Cenozoic record of the past 40 Ma is in the same mode at 10 6 yr scales: the relevant fossils are found concurrently at major marine transgressions and warming reversals of the overall fall in global temperature. However, the fossil pattern is due to transport on the activated Leeuwin Current, not merely to general warming and the spread of friendly environments to higher latitudes.

The significance of Marginopora vertebralis (Foraminifera) in surficial sediments at Esperance, Western Australia, and in last interglacial sediments in northern Spencer Gulf, South Australia

Abstract Surficial sediments at Esperance, on the southern coast of Western Australia, are predominantly bioclastic carbonates in which tests of foraminifera are a major constituent. The megascopic species Marginopora vertebralis is prolific, occupying relatively protected areas of algal turf and seagrasses. The abundance of this normally tropical foraminifer at southern latitudes can be attributed to the Leeuwin Current, which brings warm waters from the tropics to southwestern Australia, and then eastwards, past Esperance into the Great Australian Bight. The Leeuwin Current is significantly warmer than the cool interfacing waters of the Southern Ocean that otherwise characterise the southern Australian continental shelf. Last interglacial sediments of the Glanville Formation, in northern Spencer Gulf of South Australia, host an assemblage of fossil foraminifera which is similar to that of the modern environment at Esperance, especially the presence of M. vertebralis. Two bivalve molluscs, Anadara trapezia and Pinctada carchariarium, both characteristic of warm waters, are also present in the Glanville Formation. Marginopora vertebralis and other faunal elements migrated to South Australia by means of the last interglacial equivalent of the Leeuwin Current, which apparently had greater definition at that time. It may therefore be inferred that, during other times of global warming and corresponding higher sea levels, the palaeo-Leeuwin current had greater ecological influence across the continental shelf of Southern Australia. Thus, warm-water marine fossils in the Glanville Formation do not necessarily signify last interglacial water temperatures for the open Southern Ocean, beyond the continental shelf. Similarly, it cannot be assumed that these fossils necessarily indicate a last interglacial climate for terrestrial southern Australian that was warmer than presently prevails.

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.

LATE QUATERNARY PALEOSEALEVELS AND PALEOENVIRONMENTS INFERRED FROM FORAMINIFERA, NORTHERN SPENCER GULF, SOUTH AUSTRALIA

Spencer Gulf is an elongate marine embayment extending northwards ca. 300 km inland into southern continental Australia to the apex at Port Augusta, with a narrow estuarine extension northwards. Since the post-glacial sealevel maximum, prograding coastal sedimentation has been effective through the trapping and binding actions of seagrasses, mangroves and cyanobacterial mats, and a well-defined zonation of subtidal, intertidal and supratidal sedimentary facies is characteristic of the northern gulf. Mollusks and foraminifera are prolific, especially within seagrass meadows, and their abundant remains, entire and comminuted, form bioclastic carbonate sediments. Distinctive assemblages of foraminifera are associated with the various estuarine and marine environments. The hypersaline estuary north of Port Augusta is characterized by the textulariids Ammobaculites barwonensis and Trochammina inflata, the latter most common where mangroves are present. Two species of Triloculina, T. inflata and T. oblonga are the only common miliolids, while the rotaliids are represented by Ammonia beccarii, Elphidium articulatum and Nonion depressulus. South of Port Augusta, in euryhaline intertidal waters, Trochammina inflata, A. beccarii and E. articulatum are commonly associated. The shallow subtidal Posidonia seagrass meadows support an abundant fauna which is dominated by three species, Nubecularia lucifuga, Peneroplis planatus and Discorbis dimidiatus. These species continue into the deeper waters, ca. 20 m, where they are subordinate to Quinqueloculina lamarckiana, Massilina milletti, Elphidium crispum and E. macelliforme. A vibrocore from 20 m water depth in Northern Spencer Gulf recovered 4 m of late Quaternary fossiliferous sediment. Amino acid racemization (AAR) and radio-carbon ages derived from fossil mollusks revealed four chronostratigraphic packages of sediment: 400–360 cm, penultimate interglacial, oxygen isotope stage 7; 360–240 cm, last interglacial, oxygen isotope substage 5e; 240–180 cm, interstadial, oxygen isotope stage 3; and 180 cm to the top of the core, postglacial, oxygen isotope stage 1. Species of foraminifera within the core are mostly also living in the modern gulf, thus the preserved assemblages permit plausible interpretations of paleoenvironments and paleosealevels. Large numbers of Q. lamarckiana and M. milletti in the substage 5e interval indicate that the last interglacial sealevel in southern Australia was only slightly higher than that of today. N. lucifuga is abundant in the stage 3 sediment, thus paleowaterdepth at the core site was ca. ≤2 m. This evidence further supports interstadial paleosealevels above −30 m, as previously determined for Gulf St Vincent. Basal sediments of the postglacial interval preserve a monospecific assemblage of Miliolinella labiosa which signifies an estuarine setting having many of the characteristics of a saline lake. Maximum Holocene sealevel is signified by the acme of M. milletti at 90 cm. Subsequent local hydroisostatic relative fall of sealevel is shown by changes up-core from 90 cm in both the general foraminiferal record, for example by declining numbers of M. milletti, and also by reduced numbers of E. macelliforme compared with those of E. crispum.

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.

Contemporary benthic foraminifera in Gulf St Vincent, South Australia, and a refined Late Pleistocene sea‐level history

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...

Quaternary neotectonism and intra-plate volcanism: the Coorong to Mount Gambier Coastal Plain, southeastern Australia: a review

Abstract The Coorong to Mount Gambier Coastal Plain in southeastern South Australia preserves a lengthy record of Quaternary temperate carbonate sedimentation in the form of high wave energy barrier shoreline deposits and associated back-barrier lagoon facies. The barriers occur sub-parallel to the modern coastline and to each other and increase in age landwards. The age of the barriers is now generally well established within a framework of radiocarbon, thermoluminescence, uranium-series disequilibrium, amino acid racemization dating and the position of the Brunhes-Matuyama boundary between the East and West Naracoorte Ranges. This framework is in accord with the deep-sea δ18O record of global ice volume change and the inferred timing of sea-level highstands for this interval. Individual barriers such as the last interglacial Woakwine Range (oxygen-isotope substage 5e) may be traced laterally for distances up to 300km and record a history of neotectonism in the form of regionally varying epeirogenic uplift associated with Quaternary volcanism.

Amino acid racemization and radiocarbon dating of interstadial marine strata (oxygen isotope stage 3), Gulf St. Vincent, South Australia

Abstract 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.

The last interglacial shoreline in southern Australia: Morphostratigraphic variations in a temperate carbonate setting

Abstract 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.

Synergetic influence of water masses and Kangaroo Island barrier on foraminiferal distribution, Lincoln and Lacepede shelves, South Australia: A synthesis

The mid-latitude, cool-water, high-energy Lincoln and Lacepede Shelves along the southern Australian margin are covered with mixed Holocene and Pleistocene sediments. Foraminiferal specimens of Recent and Pleistocene age from dredge samples are strongly mixed. Eight assemblages in two major groups A and B were recognised from the inner shelf to the upper slope, and they appear to be depth-related. However, some are typical of localised environments such as an upwelling zone (assemblage A2) or areas strongly affected by a high accumulation of relict specimens indicative of previous lagoonal deposition (assemblages A3 and A4). Sediment starvation due to strong wave abrasion is largely responsible for the preservation of this mixed biofacies. The interaction between shelf waters (the Great Australian Bight Current), waters from the Spencer and St. Vincent Gulfs, oceanic waters and waters from the River Murray, is suggested as the main factor controlling the overall distribution pattern of foraminifera. A war...