Vincent Basin Research Articles

Earthquake-induced soft-sediment deformation in the Pleistocene succession, Noarlunga Embayment, South Australia

ABSTRACT A suite of soft-sediment deformation structures occurs within the basal sands and gravels in the non-marine Pleistocene succession in the Noarlunga Embayment of the Cenozoic St Vincent Basin south of Adelaide, South Australia, the significance of which has hitherto gone unrecognised. The inclusion of large, isolated blocks of well-bedded sands randomly encased within fluidised, structureless clayey sands indicates that the soft-sediment deformation was intense, occurring soon after deposition by liquefaction of a still saturated sediment. Seismic activity has been, and continues to be, a regular occurrence along the adjacent Adelaide fold belt. The intensity of the deformation is comparable to the thixotropic response to earthquake activity observed during the Christchurch (New Zealand) earthquakes of 2010 and 2011, the earthquakes and aftershocks near Quorn, South Australia, in January 1887, in the southeast of South Australia in May 1899, and west of Adelaide in April 1954. This, however, is the first record of an interpreted seismite in the St Vincent Basin, although its full extent is yet to be mapped.

Characteristics of sediments and regolith alterations in the Plio-Pleistocene succession, coastal cliff sections, St Vincent Basin, South Australia

Syn- and post-depositional alterations are distinguished in a detailed lithological and mineralogical study of the largely unconsolidated Plio-Pleistocene non-marine succession in coastal cliff sections in the St Vincent Basin south of Adelaide. At its base, the sequence interfingers with Late Pliocene estuarine marine sediments in places but mostly unconformably overlies older Cenozoic marine sediments or Neproterozoic bedrock. The fluvial and alluvial siliclastics have bioturbation, blocky-prismatic macro-peds and subtle Fe-mottling indicators of hiatuses in deposition, and imprints of soil and shallow groundwater environments. A relative abundance of kaolinite, illite and randomly interstratified illite-smectite reflects both sediment source and conditions in the local depositional environment. A thick deposit of aeolian calcareous silt with associated pedogenic calcretes blankets the succession. Conspicuous bleached Fe mega-mottled intervals and zones of alunite-halloysite within the sequence record post-depositional, groundwater-related alterations in regolith environments. These formed during incision and erosion of the sedimentary fill in the basin in response to regional falls in base level. Each marks a different time and specific geomorphic environment according to the chemistry of the discharge of local groundwaters from aquifers that were intersected by incision and scarp retreat.

Late Eocene Ostracoda of the Blanche Point Formation, South Australia

The Blanche Point Formation (late Eocene) was deposited in the geographically restricted St Vincent Basin, South Australia. The Ostracoda of the Gull Rock and the Perkana Members (of this formation) are characterized by many cytherellids, krithiids, pontocypridids, bythocypridids and many sighted trachyleberidids. These taxa indicate outer shelf or epibathyal depths. Most specimens are represented by single valves, probably mainly as a consequence of the relatively slow sedimentation rate. The basal part of the Gull Rock Member yields a striking dominance of autochthonous cytherellids (synchronous with a peak in dominance of uvigerinid foraminifera) and might perhaps reflect intensification of oxygen minimum conditions. Six new species are proposed: Bairdoppilata willungaensis sp. nov., Trachyleberis maslinensis sp. nov., Trachyleberis reticulopustulosa sp. nov., Actinocythereis? onkaparingaensis sp. nov., Werribeeleberis? mediacosta sp. nov. and Bradleya mypongaensis sp. nov.

First record of late Eocene ascidians (Ascidiacea, Tunicata) from southeastern Australia

Ascidian spicules are reported for the first time from the upper Eocene (Paleogene) biosiliceous marls and mudstones of the Blanche Point Formation in the St. Vincent Basin, southeastern Australia. The spicules that belong to the family Polycitoridae are identified as a Recent speciesCystodytescf.dellechiajei, andCystodytessp. and spicules of the family Didemnidae are indentified as representing generaLissoclinum, Didemnum, andPolysyncraton.Five other different morphological spicule types which can be classified only at the family level also belong to the Didemnidae. This study demonstrates that ascidians had a very wide distribution by the late Eocene and that ascidian fauna was already of a modern character.

The oldest South Australian cowries (Gastropoda: Cypraeidae) from the Paleogene of the St Vincent Basin

Yates, A.M., March, 2009. The oldest South Australian cowries (Gastropoda: Cypraeidae) from the Paleogene of the St Vincent Basin. Alcheringa 33, 23–31. ISSN 0311-5518. Two occurrences of cowries in the Paleogene of the St Vincent Basin are described. Two cypraeid internal moulds from the late Eocene (Aldingan) Blanche Point Formation comprise one such occurrence. These are among the oldest recorded Australian cypraeids. They bear some resemblance to the genera Zoila and Umbilia but insufficient details are preserved for accurate identification. The second occurrence consists of a series of internal and external moulds from the early Oligocene of the Port Willunga Formation. These represent a new species of the endemic subgenus Lyncina (Austrocypraea), here described as L. (A.) onkastoma. This species is the oldest known member of the subgenus but its apparently derived characteristics indicate that the subgenus had already diversified by this time.

Australian Cenozoic Bryozoa, 2: Free-living Cheilostomata of the Eocene St. Vincent Basin, S.A., including Bonellina gen. nov

Schmidt, R., March 2007. Australian Cenozoic Bryozoa, 2: Free-living Cheilostomata of the Eocene St. Vincent Basin, S.A., including Bonellina gen. nov. Alcheringa 31, 67-84. ISSN 0311-5518. Free-living bryozoans are diverse in the Eocene sediments of the St. Vincent Basin, South Australia. They include Bonellina pentagonalis gen. et sp. nov., Otionellina sp. cf. O. exigua (Tenison Woods), Otionellina sp. cf. O. cupola (Tenison Woods), Tubiporella magna (Tenison Woods), Celleporaria nummularia (Tenison Woods), and an indeterminate species only found as moulds. This diversity and abundance is highest in the sediments representing the initial transgressive marine facies, where they occur in ‘sand fauna’ bryozoan assemblages (e.g. with Melicerita and Siphonicytara). Free-living bryozoans decrease up-section and are absent from latest Eocene sediments, indicating a significant environmental shift. Rolf Schmidt [rschmid@museum.vic.gov.au], Museum Victoria, Melbourne, Vic 3001, Australia; received 18.3.2005, revised 14.12.2005.

Biogeography of Eocene bryozoans from the St Vincent Basin, South Australia

The first extensive and stratigraphically detailed taxonomic study of the Middle to Late Eocene Bryozoa of the St Vincent Basin has identified more than 200 species of Cheilostomata and 50 species of Cyclostomata. There are three biogeographic groups: basin endemic, Australian and global. Two-thirds (116) of the cheilostome species and seven genera are currently considered endemic to this basin. Most species are endemic to Australia and similar to those found in the Oligo-Miocene of Victoria. The Cellariidae are a common component of most Australian Cainozoic deposits, but the species are highly dissimilar, with 13 of the 17 species here being new. The global component indicates that biogeographic links with regions outside Australia still existed in the Eocene. The cyclostome genus Reticrescis is only known from the Australian and Antarctic Eocene. Ten genera have their first occurrence in the Eocene St Vincent Basin. The Phidoloporidae and Smittinidae represent the most diverse and ubiquitous groups at a geological time close to their time of origination. Contemporaneous sediments in Antarctica, eastern Europe and North America also have a diverse fauna of this family, pointing to a strong Tethyan link. Rhamphosmittina lateralis (MacGillivray) is still extant in New Zealand, having an exceptionally long time range of 40 million years. Overall, the fauna has a distinct Late Cretaceous character. A new genus of Onychocellidae appears similar to genera that were common in Cretaceous Tethyan faunas but rare during the Cainozoic. This similarity ends in the Oligocene, after which the Australian bryozoan became endemic

Eocene cool‐water carbonate and biosiliceous sedimentation dynamics, St Vincent Basin, South Australia

Middle and Upper Eocene biogenic sediments in the Willunga Embayment along the eastern margin of the St Vincent Basin are a series of warm‐temperate limestones, marls and spiculites. The Middle Eocene Tortachilla Limestone is a thin, coarse grained, quartzose, biofragmental, bryozoan–mollusc calcarenite of stacked metre‐scale depositional cycles with hardground caps. Lithification, aragonite dissolution and the filling of moulds by sediment and cement characterize early marine‐meteoric diagenesis. Further meteoric diagenesis at the end of Tortachilla deposition resulted in dissolution, Fe‐oxide precipitation and calcite cementation. The Upper Eocene Blanche Point Formation is composed of coccolith and spiculite marl and spiculite, all locally rich in glauconite, turritellid gastropods and sponges. Decimetre‐scale units, locally capped by firmgrounds, have fossiliferous lower parts and relatively barren upper parts. Carbonate diagenesis is minor, with much aragonite still present, but early silicification is extensive, except in the spiculite, which is still opal‐A. All depositional environments are interpreted as relatively shallow water: high energy during the Middle Eocene and low energy during the Upper Eocene, reflecting the variable importance of a basin‐entrance archipelago of carbonate highs. Marls and spiculites are interpreted to have formed under an overall estuarine circulation system in a humid climate. Basinal waters, although well mixed, were turbid and rich in land‐derived nutrients, yet subphotic near the sea floor. These low‐energy, inner‐shelf biosiliceous sediments occur in coeval environments across other parts of Australia and elsewhere in the rock record, suggesting that they are a recurring element of the cool‐water, carbonate shelf depositional system. Thus, spiculites and spiculitic carbonates in the rock record need be neither deep basinal nor polar in origin. The paradox of a shallow‐water carbonate–spiculite association may be more common in geological history than generally realized and may reflect a characteristic mid‐latitude, humid climate, temperate water, palaeoenvironmental association.

Cytheropterine ostracoda in view ofthe palaeoecology of the Palaeogene Port Willunga Formation, South Australia, and the palaeobathymetrical evolution of the Tasman Basin

The ostracods of the Palaeogene Port Willunga Formation (PWF), St Vincent Basin, South Australia, are dominated by bairdiids, pectocytherids, xestoleberidids, cytherurids and hemicytherids with common cytherellids, cytheridids and loxoconchids. The assemblage is shallow marine in character, probably deposited in a high energy environment (many broken shells). Sandy cross-bedded layers and eroded tops of many of the beds in the PWF were probably subjected to currents and vigorous wave action during deposition. An oscillating sea-level was probably characteristic for the palaeoenvironment in the PWF. A temporary increase in palaeodepth about 6 m above the base of the PWF, is indicated by the many trachyleberidids and the few hemicytherids found there. Of nine cytheropterine species identified in the PWF, three are erected as new: Cytheropteron ruwarungensis, Cytheropteron mchenryi and Oculocytheropteron ayressi. Some of the cytheropterine species found, e.g. O. australopunctatarum and O. microfornix, are relatively facies independent and geographically widespread being recorded also from the dysaerobic Eocene, Blanche Point Formation, St Vincent Basin, and from the Eocene of New Zealand.

Middle Eocene palynofloras from the One Tree Hill area, St Vincent Basin, South Australia

Palynofloras from an outlier of Tertiary sediments in the One Tree Hill area north of Adelaide are nonmarine and correlate with similar assemblages from Middle Eocene North Maslin Sands from Maslin Bay and Golden Grove. Although there are similarities with time-equivalent Lower Nothofagidites asperus Zone palynofloras in the Gippsland Basin, a number of species in the South Australian palynofloras do not extend below the Late Eocene in the Gippsland sequences. This indicates earlier appearances for these species in southcentral Australia. The sediments overlie a highly weathered bedrock palaeosurface, indicating that a phase of significant weathering occurred prior to the Middle Eocene. A number of selected taxa are illustrated and their distribution in the palynofloras is discussed. Two new species, Proteacidites mildenhallii and Proteacidites parrawirrensis, are described and one species, Rhoipites byfieldensis, is emended.

Foraminiferal turnover in neritic environments in the Oligocene of Southern Australia

This study explores an excellent mid-latitude Oligocene calcareous neritic succession that spans the Eocene/Oligocene boundary to the Miocene. Rapid changes in sea level and climate should have a palpable influence on macroevolution and the Eocene-Oligocene transition marks one of the most substantial changes for the Cainozoic.Stratigraphic ranges of some 130 benthic and 20 planktic species occurring in two contrasting marine environments, one relatively restricted (low plankton - Murray Basin) and another more open (high plankton - Otway Basin) to oceanic processes, were identified and correlated with signals derived from changes in the physical environment. The signals include: the ‘Exxon’ sea-level curve, deep sea stable isotope curves, and prominent lithological changes.There is a significant turnover of species at the Eocene/Oligocene boundary. This event impacts on all assemblages and correlation metrics indicate that there is an ‘across-the-board’ response. Interestingly, the turnover corresponds to a local Saint Vincent Basin lithological change from the grey-green, organic rich facies of the Blanche Point Formation to the red-yellow-brown, well oxidized, quartz and bryozoa rich facies of the Port Willunga Formation. This switch is in turn coincident with the saltatory positive deviation in the δ18O top and bottom water curves derived from oceanic sections.The turnover pattern is not repeated at the major sea level fall predicted for the mid Oligocene (at 30 million years), neither is there any comparable lithological transition. Geographically widespread species (common to all environments) cross this supposed prominent type one sequence boundary, there is a signal but the impact on the fauna is less than that detected for the Eocene/Oligocene boundary. Those faunas that were more restricted to open ocean processes exhibited shorter stratigraphic ranges and appeared to be controlled primarily by sea level fluctuation and salinity changes. There is evidence to suggest that foraminiferal faunas of the more restricted environment in southern Australia were less responsive to the well mixed, thermohaline driven ocean of the Oligocene. Generally, Oligocene benthic assemblages are dominated by Cibicides, Notorotalia and Buliminid species in consistently high numbers, indicating a high dominance of relatively few taxa, that is, large populations and low diversity. Faunas of open ocean assemblages demonstrate relatively subdued turnover patterns compared to those of more restricted environments.The Late Eocene displays parallel patterns of foraminiferal turnover and the Oligocene is characterised by inter-basin contrasts. In comparison to the Eocene, faunas appear to be more robust in the psychrosphere constrained ocean of the Oligocene. It is proposed that these patterns indicate that the Latest Eocene was dominated by species adapted to a specialist life strategy while the Oligocene reflect patterns more often associated with opportunist colonization.

The Pleistocene terrestrial carbonate mantle on the southeastern margin of the St Vincent Basin, South Australia

An extensive blanket of calcareous sediment and associated calcrete mantles Pleistocene non‐marine sediments in the St Vincent Basin. The nature of the carbonate mantle and its relationships with underlying sediments assigned to the Ngaltinga Formation have been studied in the Noarlunga and Willunga Embayments along the southeastern margin of the basin. The Ngaltinga Formation is comprised of clay‐rich sediments with channel sands and occasional gravels interpreted to be of fluvial origin. The clay‐rich sediments may represent flood‐basin or overbank deposits. Carbonate beds are present at intervals through the formation, especially within sands immediately below the carbonate mantle in the northern part of the Noarlunga Embayment. The form and mineralogical composition of these beds suggest they are the carbonate accumulation horizons of former soils or palaeosols. The carbonate mantle is interpreted as a complex sedimentary and pedogenic unit. The primary sediment contained both calcite and dolomite, wa...

Foraminiferal biofacies in a silica-rich neritic sediment, Late Eocene, South Australia

The highly siliceous Blanche Point Formation accumulated during the Late Eocene (Zones P15–P16) in the St. Vincent Basin, when the climate was warm. It differs from shelly, neritic carbonates above it and below it by higher but fluctuating numbers of benthonic foraminifera of the Family Uvigerinidae, and by high dominance in different horizons of infaunal crustacean traces and of infaunal gastropods. Within the Blanche Point Formation, changes from a banded siliceous (opal-CT) sediment to a homogeneous spongolite are paralleled by biofacies changes. High numbers of Uvigerinidae, and in part of the Formation high numbers of Robertinacea, Bolivinidae, Sphaeroidina, Cassidulina, are more consistent with generally lowered levels of oxygen at the sediment surface than with other forms of environmental stress. The study is consistent with a recent conclusion, based on mineralogy, that the abundant silica came from volcanic ash. It suggests too that restricted circulation permitted biogenic and other mechanisms of fix the silica in the St. Vincent Basin whilst silica was being flushed away from more open environments facing the nascent Southern Ocean.