School of Earth Sciences - Research Publications
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ItemQuaternary environments and monsoonal climate off northwest Australia: Palynological evidence from Ocean Drilling Program Site 765(Elsevier, 2021-05-01)The bathyal Ocean Drilling Program Site 765 at 5725 m water depth, offshore northwest Australia at 16°S is directly under the influence of the Australian monsoon during the Austral summer and is the recipient of continental dust during the Austral winter. It is downstream of the Indonesian Throughflow, which is a major arm of the global thermohaline circulation. As such it is ideally situated to record the climate and oceanic consequences of Quaternary climate variability. Despite being over 400 km from northwest Australia, palynomorphs (pollen and spores) are relatively common in this section, sourced via aeolian (during the dry winter) and benthic transportation processes and sediment plumes (during the summer monsoon). Detailed palynological analyses of this flora in the upper part of this core reveals intermittent snap shots of environmental and climate change over the last 300 kyrs. Interglacial stages are interpreted to be characterised by palynomorph-rich turbidite and calcareous ooze deposition whereas palynomorph-poor slowly accumulating siliceous oozes (deposited below the Calcium Carbonate Compensation Depth) are present during glacials. The dominance of Poaceae sourced from the Australian mainland in interglacial periods suggests that vegetation during these periods was similar to today. Interglacial palynofloral assemblages suggest a more intense wet season (Australian monsoon) with higher rainfall that allowed more active erosion and deposition onto the shelf. The presence of Indonesian sourced pollen and fern spore taxa, as well as warm water dinoflagellate species suggest enhanced Leeuwin Current and monsoonal intensity during interglacials times. The youngest part of the core is dominated by siliceous ooze, likely deposited during the Last Glacial Maximum and the early Holocene. The lack of calcareous ooze near the top of the core is likely caused by Holocene to Recent erosive processes or core disturbance. The presence of common charcoal in all samples over the last 300 kyrs shows that fire was a constant feature of the landscape in northwest Australia prior to human occupation of the region 65,000 years ago.
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ItemDating the Northwest Shelf of Australia Since the Pliocene(AMER GEOPHYSICAL UNION, 2021-03)Abstract Accurate dating of marine sediments is essential to reconstruct past changes in oceanography and climate. Benthic foraminiferal oxygen isotope series from such sediments record long‐term changes in global ice volume and deep‐water temperature. They are commonly used in the Plio‐Pleistocene to correlate deep ocean records and to construct age models. However, continental margin settings often display much higher sedimentation rates due to variations in regional depositional setting and local input of sediment. Here, it is necessary to create a regional multi‐site framework to allow precise dating of strata. We create such a high‐resolution regional framework to determine the ages of events for the Northwest Shelf (NWS) of Australia, which was cored by International Ocean Discovery Program (IODP) Expedition 356. We employ benthic foraminiferal oxygen and carbon isotopes to construct an astronomically‐tuned age model for IODP Site U1463 (5.16–1.69 Ma). The age model is applied to the IODP Site U1463 downhole‐logging natural gamma radiation (NGR) depth‐series, which was then correlated to NGR depth‐series of several IODP sites and industry wells in the area. This approach allows assigning ages to regional seismic reflectors and the timing of key climate‐related siliciclastic phases in a predominantly carbonate‐rich sequence, like the late Miocene‐Pliocene Bare Formation. This age model is also used to chronologically calibrate planktonic foraminiferal biostratigraphic datums showing that the Indonesian Throughflow (ITF) had shoaled enough in the early Pliocene to act as biogeographical barrier between the Pacific and Indian Ocean.
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ItemPalaeobiogeographical affinities and palaeoceanographical significance of late Cretaceous Ostracoda (Crustacea) from Voluta-1, Otway Basin, southeastern Australia(TAYLOR & FRANCIS LTD, 2020-10-01)A continental shelf to upper continental slope ostracod fauna is documented from the late Cretaceous (late Turonian to Santonian) Belfast Mudstone in Voluta-1 of the Otway Basin, southeastern Australia. The fauna has palaeobiogeographical affinities with mid-late Cretaceous ostracod faunas of Western Australia, New Zealand, the Antarctic Peninsula and the Falklands Plateau. This distribution pattern probably reflects dispersal influenced by the opening of the Australo-Antarctic Gulf, and by clockwise gyre currents in the proto Southern Ocean. The presence of Philoneptunus sp. in this fauna suggests that the Australo-Antarctic Gulf was an important locus for deep sea colonization by Gondwanan neritic ostracod clades.
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ItemPlio‐Pleistocene Indonesian Throughflow Variability Drove Eastern Indian Ocean Sea Surface Temperatures(American Geophysical Union (AGU), 2020-10)Ocean gateways facilitate circulation between ocean basins, thereby impacting global climate. The Indonesian Gateway transports water from the Pacific to the Indian Ocean via the Indonesian Throughflow (ITF) and drives the strength and intensity of the modern Leeuwin Current, which carries warm equatorial waters along the western coast of Australia to higher latitudes. Therefore, ITF dynamics are a vital component of global thermohaline circulation. Plio‐Pleistocene changes in ITF behavior and Leeuwin Current intensity remain poorly constrained due to a lack of sedimentary records from regions under its influence. Here, organic geochemical proxies are used to reconstruct sea surface temperatures on the northwest Australian shelf at IODP Site U1463, downstream of the ITF outlet and under the influence of the Leeuwin Current. Our records, based on TEX86 and the long‐chain diol index, provide insight into past ITF variability (3.5–1.5 Ma) and confirm that sea surface temperature exerted a control on Australian continental hydroclimate. A significant TEX86 cooling of ~5°C occurs within the mid‐Pliocene Warm Period (3.3–3.1 Ma) suggesting that this interval was characterized by SST fluctuations at Site U1463. A major feature of both the TEX86 and long‐chain diol index records is a strong cooling from ~1.7 to 1.5 Ma. We suggest that this event reflects a reduction in Leeuwin Current intensity due to a major step in ongoing ITF constriction, accompanied by a switch from South to North Pacific source waters entering the ITF inlet. Our new data suggest that an additional ITF constriction event may have occurred in the Pleistocene.
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ItemA Cenozoic Great Barrier Reef on Australia's North West shelf(ELSEVIER, 2020-01-01)The Great Barrier Reef of Australia is the largest modern coral reef system on Earth. However, a similar-sized barrier reef (~2000 km long) existed on Australia's north-western margin in the middle Miocene and to some extent, still exists today. Seismic profiles reveal that this reef system was first initiated in the late Paleogene (~34–28 Ma) and reached its zenith as a prograding barrier reef during the middle Miocene (16–15 Ma). This giant reef system backstepped in the late Miocene (~10 Ma), forming a series of isolated atolls and pinnacle reefs. These remaining reefs were gradually extinguished, leaving only a few surviving isolated atolls today (Rowley Shoals, Scott Reef, Seringapatam Reef and Ashmore Reef). The distribution of these extant reefs therefore outlines the former presence of the mid-Miocene Great Barrier Reef of the Australian North West Shelf. This middle Miocene shallow-water rimmed-reefal shelf grew contemporaneously on a deeper-water heterozoan ramp, producing an unusual mixed heterozoan/photozoan carbonate system for most of its length. The initiation of reef growth appears related to Australia's northward drift into lower latitudes, combined with warm mid-Miocene climatic optimum conditions. However, the sudden and simultaneous initiation of reef growth in the mid-Miocene across the North West Shelf was probably also related to changes in paleoceanography (increased aragonite saturation and/or nutrient-depletion) perhaps influenced by changing climatic conditions (increased aridity). From the late Miocene (~10 Ma) to Holocene, high rates of subsidence across the North West Shelf probably set the scene for ultimate demise of this giant barrier reef system and led to widespread backstepping with the development of a series of isolated atolls and pinnacle reefs. It is likely that other paleoceanographic and climatic events (like nutrient supply, carbonate saturation, eustasy etc) combined with continued high subsidence rates acted to gradually extinguish the reef system in a series of steps over a period of 10 million years. The onset (~1 Ma) of a strong Leeuwin Current (with the delivery of warm and nutrient depleted water from the north) and its effect on the Quaternary reefs of the Western Australian coast is a good example of a paleoceanographic process that would be difficult to recognize in an ancient setting. It is likely that similar paleoceanographic events have controlled the rich and complex history of reef growth and drowning since the mid-Miocene on the North West Shelf.
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ItemDenuding a Craton: Thermochronology Record of Phanerozoic Unroofing from the Pilbara Craton, Australia(American Geophysical Union (AGU), 2020)Cratons are ancient regions of relatively stable continental fragments considered to have attained long-term tectonic and geomorphic stability. Low-temperature thermochronology data, however, suggest that some cratons have experienced discrete Phanerozoic heating and cooling episodes. We report apatite fission track, and apatite and zircon (U-Th)/He low-temperature thermochronology data from the Archean Pilbara craton and adjacent Paleoproterozoic basement, NW Australia. Inverse thermal history simulations of this spatially extensive data set reveal that the region has experienced ~50–70°C cooling, which is interpreted as a response to the unroofing of erodible strata overlying basement. The timing of cooling onset is variable, mainly ~420–350 Ma in the southern and central Pilbara-eastern Hamersley Basin and ~350–300 Ma in the northern Pilbara, while the westernmost Pilbara-central Hamersley Basin does not record a significant Paleozoic cooling event. These differences are attributed to variations in sedimentary thickness and proximity to adjacent rift basins, which lack Archean age zircons in their Paleozoic strata. The onset of Paleozoic cooling coincides with the timing of the episodic intraplate late Ordovician-Carboniferous Alice Springs Orogeny. This orogeny is thought to have resulted from far-field plate margin stresses, which in turn caused the opening of the adjacent Canning Basin, to the north and east of the craton. We propose that basin development triggered a change of base level, resulting in denudation and the crustal cooling event reported here. Our results provide further evidence for the transmission of far-field forces to cratons over hundreds of kilometers and support the view that cratons have experienced geomorphic changes during the Phanerozoic.
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ItemRapid expansion of meso-megathermal rain forests into the southern high latitudes at the onset of the Paleocene-Eocene Thermal Maximum(GEOLOGICAL SOC AMER, INC, 2021-01-01)Abstract Current knowledge of terrestrial ecosystem response to the Paleocene-Eocene Thermal Maximum (PETM; ca. 56 Ma) is largely based on the midlatitudes of the Northern Hemisphere. To more fully reconstruct global terrestrial ecosystem response to the PETM, we generated vegetation and biomarker proxy records from an outcrop section on the southern coast of Australia (∼60°S paleolatitude). We documented a rapid, massive, and sustained vegetation turnover as a response to regional PETM warming of ∼1–4 °C, abruptly transitioning from a warm temperate to a meso-megathermal rain forest similar to that of present-day northeastern Queensland, Australia. The onset of this vegetation change preceded the characteristic PETM carbon-isotope excursion (CIE) by several thousand years. The reconstructed ecosystem change is much stronger than in other Southern Hemisphere records, highlighting the need for consideration of regional paleoceanographic, paleogeographic, and biogeographic characteristics to fully understand the global terrestrial ecosystem response to PETM climate forcing.
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ItemReversible subsidence on the North West Shelf of Australia(ELSEVIER, 2020-03-15)The Northwest Shelf (NWS) of Australia is characterized by offshore basins associated with Permian and Jurassic rifting and was only slowly subsiding by the Neogene. International Ocean Discovery Program (IODP) Expedition 356 targeted this region by coring four sites in the Northern Carnarvon and Roebuck Basins and two sites in the Perth Basin to the south on the Australian western margin. We use detailed lithological, physical property and age data with paleobathymetric interpretations, to infer tectonic subsidence apparently confined to the NWS that reverses (uplifts) with about the same amplitude and rate as an earlier subsidence event. About 300 m of tectonic subsidence occurred over one million years from 6 to 5 million years ago and then reverses when 300 m of tectonic uplift occurred from 2 to 1 Ma. The along strike extent of this subsidence pattern is ∼ 400 km. The similarity of magnitude and duration of the subsidence and uplift phases suggest that the subsidence is reversible. The results cannot be explained by glacial eustatic variability nor can the uplift event be attributed to sediments filling the accommodation space generated earlier. Reversible subsidence is a key fingerprint of dynamic topography. Although the rates of subsidence and uplift are roughly ∼ 300 m/Myr, a substantial portion of the changes occur over less than 1 Myr and the rates inferred from a detailed least squares analysis can reach up to about 500 m/Myr. These rates are incompatible with dynamic topography associated with motion of Australia over large-scale convection (10 to 40 m/Myr) or that associated with instability of the base of the lithosphere (<15 m/Myr). The vertical motions are too large to be associated with simple flexure of a plate and plate buckling in that the required amplitudes would lead to permanent deformation of the plate. A new geodynamic mechanism is required to fit the observations.
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ItemPalynological-age determination of Early Cretaceous vertebrate-bearing beds along the south Victorian coast of Australia, with implications for the spore-pollen biostratigraphy of the region(Taylor & Francis, 2020)Palynology is used to provide new age controls for the coastal exposures yielding Early Cretaceous vertebrate faunas in the Otway and Gippsland basins, southeast Australia. This work shows all vertebrate-bearing deposits in the Otway Basin are Albian in age. On the eastern margin of Cape Otway, vertebrate-bearing deposits are attributed to the early Albian Crybelosporites striatus Zone, except for one in the younger Coptospora paradoxa Zone. To the west of Cape Otway, the sampled deposits range from the oldest zone in the Albian, the C. striatus Zone, to the C. paradoxa and Phimopollenites pannosus zones, providing a complete section of the Albian stage. In the Gippsland Basin, the structural setting of vertebrate deposits is more complicated and large portions of the coastal exposures consist of repeated sections controlled by small-scale faults. Sites in this region lie below or above the Barremian/Aptian boundary. However, owing to the paucity of age indicator species, some sampled deposits remain undated. In this basin, the ranges of certain key palynomorph species (e.g., Pilosisporites notensis and Pilosisporites parvispinosus) differed from those outlined in some previously published biostratigraphic schemes. The discovery of the angiosperm pollen Clavatipollenites hughesii in the lowermost Aptian deposits of the Gippsland Basin is consistent with its first occurrence elsewhere in Australia and shows it is a reliable indicator for the Aptian stage. This study shows that there is currently a collection bias towards vertebrate assemblages that are latest Barremian and early Albian in age.
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ItemEocene to Oligocene high paleolatitude neritic record of Oi-1 glaciation in the Otway Basin southeast Australia(Elsevier BV, 2020-08)Multiple stable isotope investigations from upper Eocene to lower Oligocene deep-water marine sequences record the transition from global greenhouse to the icehouse conditions (Oi-1 glacial). While Southern Ocean high latitude deep sea records of this transition are well known, their shallow marine equivalents are rare and have the potential to record the eustatic and oceanic consequences of Paleogene glacial variability. The well-known high paleolatitude (~55°S) neritic carbonate sequence at Browns Creek and Castle Cove in the Otway Basin in southeast Australia spans the Eocene-Oligocene boundary. During this time the area lay on the northeastern margin of the Australo-Antarctic Gulf facing the evolving Southern Ocean. The importance of this record has been hampered by a lack of a consistent stratigraphy and contradictory microfossil interpretations. To reconcile these issues we combine new bio-, chemo- and lithostratigraphic analyses of the outcrops and a new core (Colac- 2) with pre-existing data to revise the stratigraphy. This confirms the middle/upper Eocene boundary is near the base of the section. The overlying upper Eocene siliciclastic strata are truncated by an unconformity (of ~0.8 Ma in duration) and overlain by glauconitic sand (the Notrostrea greensand) deposited after ~35.9 Ma. Subsequently deepening to middle to outer neritic depths deposited cyclic carbonates. Shallowing after ~35 Ma deposited laterally variable calcareous siliciclastic facies. These strata were tilted and eroded prior to 34 Ma leading to shallow water facies that may have been subaerially exposed during uplift. Brachiopod strontium isotope dates and an 0.5‰ carbon isotope excursion above this unconformity suggests the top of the Browns Creek and the base of the Castle Cove section correlate to Eocene-Oligocene transition (EOT-1) at ~34 Ma. The subsequent persistence of positive C/O isotope values above this level records the transition to the Oi-1 glaciation at ~33.7 Ma. Strong cyclicity in the inner shelf Castle Cove limestone is interpreted to record the commencement of obliquity dominated glacio-eustacy during the Oi-1 glacial phase. The shallowing from outer to inner shelf palaeodepths from the late Eocene to the early Oligocene is likely related to the onset of cryosphere expansion, however, palaeodepth estimates are complicated by the onset of regional compressional tectonism at the Eocene/Oligocene boundary that caused localized tilting and an unconformity with possible antisiphoning effects in this near-field site.