Abstract: The carbonate sediments of the Western Australian shelf in the Indian Ocean host diverse assemblages of benthic foraminifera. These shelf environments are dominated by the southward-flowing Leeuwin Current, which impacts near-surface circulation and influences biogeographic ranges of Indo-Pacific warm-water foraminifera. Analyses of outer-ramp to upper-slope sediments (127–264 m water depth) at four different sites (some with replicates) revealed 185 benthic species. A shift from benthic to planktonic foraminifera was accompanied by a decrease in “larger” benthic foraminifera below the lowermost euphotic zone. Fisher α and proportions of buliminid and textulariid taxa increased with water depth, as miliolids and rotaliids decreased in proportion. Cluster analyses on the 125 to 250 μm and 250 to 850 μm size fractions revealed distinct assemblages, with the former distinguishing between deeper and shallower sites, and the latter distinguishing between the Carnarvon Ramp site and the three sites on the northwestern shelf (NWS). The assemblage shift with depth was likely caused by rapidly changing physical conditions in the upper thermocline. The assemblage differences between the NWS and the Carnarvon Ramp site indicate limited horizontal transport and migration rates on the outer shelf below the influence of the Leeuwin Current. Similarity in bottom-water temperature at the studied sites indicates that water mass characteristics, biogeographic history, and/or possibly diversity in benthic shelf habitats, rather than temperature and depth, are responsible for differences between the two regions.

Abstract: The continental shelf of southwest Australia is part of a passive continental margin which is open, wave-dominated and characterised by cool-water carbonate sedimentation. The Houtman Abrollios coral reefs comprise three shelf-edge carbonate platforms which together form the discontinuously rimmed AbroLhos Shelf at latitude 28-29.5°S. This shelf lies in a biotic transition zone between northern tropical and southern temperate environments. There is also a regional transition between warm-water sediments to the north and the cool-water carbonate shelves of southwestern and southern Australia. There is a marked contrast between Abrolhos platform facies and adjacent shelf sediments. Platform sediments are aragonite-dominated coral framestones and aragonite/Mg calcite sand sheet facies composed of coral and coralline algal debris, with lesser amounts of bryozoans, foraminifers and molluscs. Shelf sediments are dominated by bryozoans and coralline red algae, with lesser molluscs and foraminifers, and are Mg calcite and calcite-rich. There are no ooids, and Halimeda is present only in trace amounts on the shelf. The abundance of corals imparts a warm-water character to the platform deposits, whilst the shelf sediments are indistinguishable from other cool-water shelf deposits which extend from Australia’s southern margin to the western margin, at least to the latitude of the Abrolhos shelf. A poleward-flowing warm-water current (the Leeuwin Current) influences the biotic transition and the relatively high southerly latitude of the Abrolhos reef platforms, which are near the temperature limits for reef-building coral growth. During Tertiary to Quaternary time, there was a vertical transition from cool-water ramp sedimentation to reefal platform development near the shelf edge at the Abrolhos, as a result of Australia’s northward drift and establishment of the Leeuwin Current. Such facies transitions owe their existence to regional patterns of oceanographic circulation, driven in the long term by changes in paleolatitude, and have been an integral part of carbonate platform evolution during the Phanerozoic.

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 western margin of Australia provides a regional latitudinal and climatic gradient from the macrotidal tropical north to the microtidal temperate south, modulated by the poleward-flowing warm Leeuwin Current. Coral-reef systems, discontinuously developed during the late Tertiary-Quaternary, vary from fringing reefs to isolated reefs which rise from deep-ramp settings. Quaternary evolution of the reef systems is being documented using regional mapping, seismic imaging, coring and U-series dating. The well-constrained sea-level data from the Houtman Abrolhos carbonate platforms (at 28–29° S) have also been applied to the less known North West Shelf reefs. The Ningaloo fringing reef at 20–22° S records Holocene and last-interglacial phases of reef growth in a tectonically stable environment. It overlies Tertiary carbonates of the Cape Range, which is flanked by uplifted Plio-Pleistocene terraces and reefs. Scott Reef (at 14° S) is a macrotidal, isolated reef which overlies a carbonate platform and a major gas discovery. Seismic profiles reveal a last-interglacial (ca. 125,000 year) reef system, but reefs which apparently grew to sea-level are 30 m below present sea-level, indicating significant subsidence in the late Quaternary. Contemporary reefs grew during the Holocene in the accommodation space provided by subsidence and are up to 35 m thick. The Rowley Shoals (15–17° S) comprise one of the most perfect morphological series of reefs known, and these emergent, annular reefs rise from depths of 200–400 m. Seismic profiles suggest that late Quaternary subsidence has been an important control on reef growth, while differential subsidence has influenced reef morpho1ogy. Differential geomorphic and physical process settings, seismic stratigraphy, sea-level history, and subsidence are keys to patterns of reef growth which can be seen as responses to these controls.

Abstract: The neritic stratigraphic record in southern Australia sorts into four cycles or sequences which resemble global second-order cycles based on sequence stratigraphy. The record is highly incomplete at the second order, due especially to a 9 my gap in the middle Eocene and poor and restricted records of the early Oligocene and the late Miocene series, and at the third order where hiatuses become more apparent as stratigraphy advances. Correlations and age determinations are based mostly on micropalaeontology and are limited by the neritic facies, the extratropical situation and the lack of a local or regional geomagnetic pattern. In this composite regional succession, we have had to proceed from regional stages based only loosely on fossils, to biostratigraphic ranges and formal zones (of planktonic foraminifera), to faunal associations based on transgressions and regressions, so that we are but a short step from a revision of the regional stages in terms of sequence biostratigraphy. This geochrono- logical scaffolding is important not only to the neritic realm itself, but to the neritic-oceanic link and ODP drilling in one direction and to the terrestrial environmental and paleobiological realm in the other. The Cenozoic record of global climatic deterioration has temporary reversals punctuated by four sharp coolings (“chills”) in the early middle Eocene, earliest Oligocene, middle Miocene and late Pliocene, and they too are chronologically consistent with the regional neritic record. In the oldest cycle, the sediments are marginal marine siliciclastics with several very brief transgressions with marine microfaunas and rare macrofossils but no limestones. Extratropical carbonates begin abruptly in the late middle Eocene series at the base of the second cycle and the Wilson Bluff transgression, which is the Khirthar Restoration of the Indo-Pacific region. At the same time there develops a distinction between warmer and cooler intermediate watermasses in the Indian Ocean, and the Leeuwin Current is born. These events are responses to accelerated Australia/Antarctica separation from 43- 42 Ma. The third-order components of this cycle are marked by marine transgressions; they are consistent in number and timing with the putative late Eocene global pattern. The third cycle is the Miocene oscillation which begins in late Oligocene time and peaks in sea level and warming at the Miocene climatic optimum in early middle Miocene time. As shown in a correlation chart, the extratropical “cool-water carbonates” are mostly in the second and third cycles, although there are carbonates in the extensive marine horizons of the Pliocene reversal. The Eocene-Miocene neritic carbonate record comprises third-order sequences, seen most clearly as marine transgressions. The transgressions can be related to third-order glaciations and eustatic cycles in plausible if not always compelling correlations. Horizons of warming, upwelling, and siliceous facies complete a framework of an outstanding extratropical, neritic carbonate record.