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PESA Vic/Tas August Technical Meeting: IODP Expedition 356: A Miocene-Pliocene record of reefs, climate and subsidence off Northwest Australia

Wednesday, August 16 @ 12:00 - 14:00

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Guest Speaker: Associate Professor Stephen Gallagher

Since completing his PhD at University College Dublin, Ireland and taking up a lectureship at the University of Melbourne, Associate Professor Stephen Gallagher has researched Carboniferous to Recent microfossils, sedimentology and stratigraphy globally.  His most significant contribution to stratigraphy and micropalaeontology is in the application of detailed microfossil analyses to solve stratigraphic problems and to interpret bathymetry & oceanography.  He is one of few workers in this field in Australia who is actively carrying out such applied stratigraphic research.  His research has contributed fundamentally to the interpretation of Cretaceous to Cenozoic shelf evolution in southeast Australia, leading to a better understanding of the Gippsland and Otway Basins. His work with Guy Holdgate has improved brown coal stratigraphy in Victoria. In the last ten years, he has become interested in the stratigraphy of Australia’s northwest margin, this has led to numerous publications and two major international expeditions to the area by the RV Joides Resolution (2015) (International Ocean Discovery Program) and the RV Sonne (2017) (German Science Foundation).  These investigations have revealed the stratigraphy in full cores of the upper 1km of the Northwest Shelf for the first time. He has published 64 international refereed journal papers, 10 book chapters and over 20 books/major reports. He has supervised 30 BSc Honours, 11 PhD, 1 MPhil and 9 MSc completions and is currently supervising 2 PhD, and 3 Masters students.

RSVP: COB, Friday 11 August 2017.

PLEASE NOTE: Registrants who have not prepaid, and who don’t give at least 48 hours notice of not attending, will be invoiced for the event.

 

Abstract:

International Ocean Discovery Program Expedition 356 cored sites along a latitudinal transect from 29°-18°S off northwest Australia to obtain a 5 m.y. record of the evolution of the Indonesian Throughflow (ITF), Indo-Pacific Warm Pool, subsidence and regional climate. Six sites were drilled from south to north: U1459, U1460, U1461, U1462, U1463 and U1464.

Sites U1459 and U1460, in the Perth Basin, yielded a Miocene to Quaternary upper-slope to outer-shelf carbonate section that will allow investigations of the relative roles of the Leeuwin Current (and the ITF) on the initiation and evolution of reef development on the Rottnest Shelf and Carnarvon Ramp system. The clay mineralogy and pollen record of the high-recovery, Pleistocene section at Site U1460 is likely to yield a 2 m.y. orbital-scale climate record of the winter-dominated rainfall regime.  When combined with similar records from the high-recovery Pliocene record at site U1459, this will greatly increase understanding of how Australia’s subtropical to warm temperate climate responded to Pliocene warmth through to the Middle Pleistocene Transition and onset of icehouse conditions.   Sites U1461 and U1462, in the Northern Carnarvon Basin, are near a series of drowned reefs at ~22°S. Both sites yielded well-constrained ages and well logs that permit both calibration of regional seismic profiles and dating of reflectors beneath these reefs, thereby constraining reef onset. Marine ooids present in the Pleistocene strata of Sites U1461 and U1462 indicate that shallow-water, carbonate-supersaturated, arid, tropical conditions prevailed. Further analyses will constrain the age of these key tropical indices and enhance understanding of the onset of aridity and reef development in northwestern Australia.  Site U1461 yielded potentially one of the best sampled paleoceanographic and climate archives along the western continental margin of Australia. Another archive with excellently preserved calcareous microfossils was cored at Site U1463.  The very good preservation of foraminifera in the Pleistocene and Pliocene strata of this site is likely to facilitate orbital-scale paleoceanographic and palaeoclimate reconstructions using inorganic and organic geochemical analyses to yield an unparalleled 5 m.y. record of oceanic conditions immediately downstream from the ITF. Site U1464 in the Roebuck Basin is up-dip from a drowned shoal. Drilling revealed a detailed bio-chronostratigraphic framework enabling dating of the initiation and demise of this “failed” Rowley Shoal.  The presence of anhydrite in the Miocene strata at U1464 suggests drier conditions prevailed before the Australian monsoon intensified during the Pliocene.

The Northwest Shelf of Australia is an ideal location to constrain the spatial and temporal patterns of vertical motions caused by the interaction between plate motion and convection within the Earth’s mantle, known as dynamic topography as it is positioned on the fastest moving continent since the Eocene, on the edge of the degree two geoid anomaly and is known to have experienced significance anomalous subsidence in the last 10 million years. Coring obtained a well-constrained stratigraphic framework that will allow high-resolution subsidence curves to be generated for the last 10 million years.  Preliminary shipboard analyses revealed significant palaeobathymetric variations from terrestrial to upper bathyal palaeodepths suggesting a complex subsidence history for the region.  Ongoing post-cruise analyses are combining age models and palaeobathymetric data from each site with both laboratory and wireline logging physical properties measurements of lithology-dependent properties such as density and porosity.  Combining these borehole data with seismic interpretations will allow accurate subsidence estimates over 10° of latitude.  Resolving whether northern Australia is moving with/over a time-transient or long-term stationary downwelling within the mantle will vastly improve our understanding of deep-Earth dynamics and their impacts on surficial processes.

Details

Date:
Wednesday, August 16
Time:
12:00 - 14:00
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Venue

Henry & The Fox
525 Little Collins Street, Melbourne, Victoria 3000 Australia

Organizer

VIC-TAS Secretary
Email:

Registration Details

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