Abstract Australia's western margin is adjacent to a low–moderate-relief, semi-arid hinterland extending from northern tropical to southern temperate latitudes. Swell waves occur throughout, and cyclonic storms and tidal influences decline from north to south. The margin is influenced by the poleward-flowing, warm, nutrient-poor Leeuwin Current. There is limited upwelling and localized downwelling of saline water on to the shelf. The North West Shelf (NWS) is an ocean-facing ramp with palimpsest sediments – formed during Marine Isoptope Stage (MIS) 3 and 4; stranded ooids and peloids formed early during the post-Last Glacial Maximum (LGM) sea-level rise – and Holocene particles. Changing oceanography during sea-level rise profoundly affected sediment character. The SW Shelf (SWS) comprises the subtropical sediment-starved Carnarvon Ramp in the north and the incipiently rimmed, flat-topped, steep-fronted Rottnest Shelf in the south. The inner Carnarvon Ramp includes the Ningaloo Reef and hypersaline Shark Bay. The mid ramp is relict or stranded foraminifer-dominated sand, and represents attenuated carbonate production due to downwelling incursions of Shark Bay water on to the ramp; the outer ramp is planktic foraminiferal sand or spiculitic mud. Rottnest Shelf has coralline algal-encrusted hardgrounds, larger symbiont-bearing foraminifers with abundant cool-water elements including bryzoans, molluscs and smaller foraminifers. The SWS is transitional between warm- and cool-water carbonate realms.

Abstract The Port Willunga Formation is a cool–water, marine, quartzose, clay–rich, biosiliceous, and calcareous sedimentary succession of Early Oligocene age that accumulated in a series of proximal estuarine paleoenvironments along the eastern side of the St. Vincent Basin, South Australia. Coeval strata in two of the paleo–embayments are interpreted to record deposition during one ~ 3.5 My–long eustatic sea–level fluctuation. Transgressive facies above a ravinement surface comprise quartzose sands (subaqueous marine tidal dunes) that grade upward into fossiliferous floatstones and mudstones (shoreface to shallow basin–floor environments) that accumulated in a protected embayment. Highstand sediments are distinctly cyclic at the meter scale and consist of epifaunal bryozoan–pecten–echinoid clay–rich floatstones that become less fossiliferous but more spiculitic and chert–rich upward in each cycle. Whereas cyclic sediments in one embayment (Willunga) are interpreted to have accumulated on a current–swept, illuminated seafloor, those in the other (Noarlunga) are thought to have been deposited in a lower–energy, sub–photic setting. Cyclicity is interpreted to record the increasing influence of fluvial fresh water in the system during each sea–level fluctuation. Comparison with underlying strata reveals a striking similarity in depositional style and stratigraphic packaging between Late Eocene and Early Oligocene deposits; both are interpreted as paleoestuarine. Differences between the dark, organic–rich, biosiliceous, and low–diversity Eocene highstand deposits and the light, more calcareous, and more diverse Oligocene highstand deposits are interpreted to be due to local depositional controls. An important implication of local controls is that several postulated unconformities in the succession are not due to global eustatic changes but are ravinement surfaces related to estuarine sedimentation dynamics. Such controls, specifically terrestrial climate, hydrodynamic energy, and trophic resource levels were more important in determining sediment composition than eustasy and Southern Ocean cooling. Similar biosiliceous–carbonate sedimentary facies are a recurring feature of cool–water deposition throughout the Phanerozoic.

Abstract: The storm-dominated, high-energy, cool-water Lincoln Shelf occupies the central part of the southern Australian continental margin. Carbonate sediments on this modern distally-steepened ramp were produced by slow deposition during the Terminal Quaternary Sea-level Cycle (0 75 Ka), a high-amplitude, asymmetric cycle of sea-level change. The 50 to 150-mwd (meters water depth), 120-170 km-wide surface is a rocky substrate covered by a patchy, m-scale, palimpsest sediment veneer composed mostly of bryozoans, molluscs, foraminifers and coralline algae. Facies of the condensed Terminal Quaternary Sequence are interpreted to reflect accumulation during different parts of the Terminal Quaternary Sea-level Cycle that are now variably mixed. Accumulation during early stages of the Terminal Quaternary Regression, Isotope Stage-3/4 (IS-3/4), when sea level fluctuated between 30- and at least 60-mwd, took place in a series of shallow marine to paludal environments. Small-scale, 5th-order sea-level fluctuations resulted in recurring deposition, surf-zone reworking and exposure. Such conditions generating Relict Particles, brown- colored, abraded grains filled with carbonate precipitates, that are now concentrated on the middle to inner shelf (< 100-mwd). The Terminal Quaternary Lowstand (early IS-2) at 120-mwd resulted in deposition on the outermost shelf and exposure of the middle and inner shelf. This was a period of mesotrophic conditions and overall upwelling, leading to prolific bryozoan growth and the formation of a bryozoan biostrome at the shelf edge. These conditions continued during the early Terminal Quaternary Transgression (late IS-2) resulting in shelf facies rich in articulated coralline algal particles and rhodolites. Rapid sea-level rise, coupled with a change to more oligotrophic conditions during the late Terminal Quaternary Transgression (early IS-1), drowned these environments and resulted in belts of Stranded Particles on the middle to outer shelf. The modern setting, during the present Terminal Quaternary Highstand, reflects a complex oceanography. Waters are mildly oligotrophic, with yearly incursion of warm, oligotrophic waters from the west, seasonal upwelling of mesotrophic waters and annual outflow of cold, saline bottomwaters from the large shallow embayment of Spencer Gulf. Recent Particles are diverse: bivalves dominate inner-middle shelf sediments; bryozoans are most abundant on the outer shelf; shelf sediments opposite Spencer Gulf saline outflows are rich in benthic foraminifers; and corallines are most abundant inshore. The moribund biostrome is now populated by a rich and diverse suite of deeper water bryozoans and ahermatypic corals. Sediments on the western part of the shelf, with scattered large foraminifers, illustrate the sporadic influence of warmer waters.

Abstract: Many modern continental shelves are areas of calcareous faunal and floral growth and subsequent carbonate accumulation. These de- positional environments can be subdivided into three major zones: (1) tropica I/warm-water; (2) temperate/cool-water and (3) polar/cold-water. Our research focused on the temperate environment. We analysed 51 samples of corals, coralline algae and bryozoans and 9 calcitic cements from bottom sediment samples from the Lacepede Shelf, South Australia for their mineralogy, oxygen and carbon isotopes, and distribution of major, minor and trace elements. Azooxanthellate corals are depleted in 8 18 0 and 8 I3 C in comparison to equilibrium values but less so than their tropical counterparts. Coralline algae are enriched in 8 18 0 and 8 I3 C compared to tropical samples. Both azooxanthellate corals and coralline algae display a positive correlation between their isotopes. The bottom temperature versus S ls O curve for the aragonitic bryozoan Adeona sp. parallels the equilibrium aragonite curve. These B 1S 0 values are in equilibrium with the ambient water but differ from those for Adeona sp. from the Indian (tropical) Ocean. Its 8 13 C content is almost in equilibrium and higher than its tropical counterpart, despite lower 8 13 C values for dissolved inorganic carbon (DIC) in the study area. This study shows that carbon isotope disequilibrium of carbonate-rich biota is greater than that of oxygen isotopes. Furthermore, the isotopic ratios for similar organisms are different from one environment to another. Even more importantly, diverse organisms living in the same environment may have dissimilar isotope values. This can be attributed to either metabolic processes or kinetic effects. For the former, photosynthesis is the major cause of 8 I3 C enrichment in photosynthetic organisms, and respiration induces some depletion. Extrinsic factors (e.g., depth, salinity, temperature, turbidity, substrate, and oxygen levels, etc.) variably mediate differences. Organisms with aragonitic mineralogy, such as corals and some bryozoans, have higher Sr and lower Mg, Fe and Mn concentrations than calcitic ones (e.g., coraUine algae). These differences may be functions of various combinations of the following processes: (a) mineralogical discrimination against some trace elements, (b) skeletal formation process, (c) environmental variables and (d) physiology of the organism. Differences between temperate and tropical biotic geochemistry may be useful for differentiating between temperate and tropical environments in the rock record, providing diagenesis has not altered the primary signatures.

Abstract: The mineralogy of living bryozoans and recent bryozoan skeletal particles on the cool-water Lacepede Shelf between water depths of 38 and 180 m is variable, with growth forms composed of aragonite and/or calcite with low or intermediate amounts of magnesium. The MgC0 3 content of LMC (low-magnesium calcite) and 1MC (intermediate-magnesium calcite) bryozoans is not temperature dependent, so that the composition of the same species is constant to water depths of 180 m. Stable carbon and oxygen isotopes values from CaC0 3 in these same bryozoans indicate that most, but not all, probably precipitate their skeletons close to isotopic equilibrium with ambient seawater. All morphotypes, except fenestrate and flat robust branching aragonite morphotypes, are potentially useful for paleotemperature and paleoenvironmental interpretation purposes if the mineralogy of the skeletons has not been changed. The most geologically useful forms, if the sediments have been altered to low-Mg calcite (LMC), are delicate branching cyclostomes or, if the original mineralogy can be determined to have been intermediate-Mg calcite (IMC), articulated branching cheilostomes. Such results indicate that bryozoans may be useful throughout the geological record as additional proxies for the determination of paleoceanographic parameters.

Abstract: The Oligocene-Miocene Port Vincent Limestone is one of several Tertiary units exposed along coastal cliffs on the western side of the St. Vincent Basin and can be traced off-shore via bore holes, where it reaches a maximum thickness of 125 m. The limestone has a cool-water bryozoan- dominated skeletal assemblage. It exhibits contrasting physical characteristics, with soft and friable, highly porous bryozoan limestone punctuated by several sharp and distinctive 0.5- to I-m-thick layers of hard calcarenite. Sedimentologically, the succession is divided into three informal members. The lower member comprises two transgressive facies, a bryozoan miliolid-echinoid packstone/rudstone and a bryozoan bivalve floatstone. The middle member is the largest and comprises five, meter-scale, hardground-bounded, asymmetric, warming-upward subtidal cycles. Wanning was brought about by an overall temperature rise in the environment (climatic changes and/or oceanic currents), acting in concert with a relative fall in sea level which brought the depositional surface into shallower and warmer near-shore illuminated environments. Marine cementation at the top of each cycle created a hard substrate, which dictated the type of fauna and flora above. The upper member comprises fine, highly abraded bryozoan- Eponides grainstone facies, which represents deposition on an outer middle ramp. Lateral and vertical facies analysis indicate that the Port Vincent Limestone was deposited in a transgressive cool-water carbonate ramp environment, extending from the inner ramp to an outer middle ramp. Cyclicity suggests that episodic warmer water interruptions brought about by fluctuating sea level (relative fall/rise) and climatic changes, occurred several times during deposition. Lithological and petrophysical variations are attributed to regional environmental changes and were later accentuated by selective diagenesis.