T33D-2964
Paleomagnetic and Environmental Magnetic Insights into the Middle to Late Pleistocene Stratigraphy of the 8o North Bengal Fan Transect, IODP Expedition 354
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Brendan T Reilly1, Peter A Selkin2, Laure Meynadier3, Jairo F Savian4, Michael E Weber5, Tilmann Schwenk6, Volkhard Spiess6, Joseph Stephen Stoner7, Christian France-Lanord8, Adam Klaus9 and Expedition 354 Shipboard Scientific Party, (1)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (2)U Washington, Tacoma, Tacoma, WA, United States, (3)Institut de Physique du Globe, Paris, France, (4)IAG Institute of Astronomy, Geophysics and Atmospheric Sciences, Sao Paulo, Brazil, (5)University of Cologne, Cologne, Germany, (6)University of Bremen, Bremen, Germany, (7)Oregon State Univ, Corvallis, OR, United States, (8)Organization Not Listed, Washington, DC, United States, (9)Texas A & M University College Station, College Station, TX, United States
Abstract:
IODP Expedition 354 cored seven sites along a ~320 km transect of the Bengal Fan at 8o N. Assessing the Pleistocene fan development and depocenter migration in the upper 150-220 m of the Bengal Fan was a primary goal of this expedition. Because any one site includes local variations in depositional processes, the transect approach and accurate stratigraphic correlation of sites is essential to understand overall fan development. Within this transect framework, integrating sediment fluxes across the fan allows for reconstruction of regional climate and tectonic signals through time. A hemipelagic unit deposited at ~1-2.5 cm/ka late in the Matuyama Chron, recording both the Cobb Mountain (1.173 – 1.185 Ma) and Jaramillo (0.988 – 1.072 Ma) Subchrons, was observed at all sites across the transect. This hemipelagic unit provides robust correlation between core derived chronologies and seismic imaging in the Middle Pleistocene. Correlation and orbital tuning of distinctive variations in physical properties (e.g. sediment lightness, wet-bulk density, and magnetic susceptibility) relative to paleomagnetic reversals indicate that turbidite deposition immediately below the base of this unit ceased relatively synchronously across the transect and turbidite deposition likely occurred elsewhere on the fan. The upper bound of the unit, however, is diachronous, with the timing of the onset of turbidite deposition in this part of the fan likely related to the infilling of accommodation space on the Middle Pleistocene fan surface. Stratigraphic constraints on the resumption of turbidite deposition to transect sites include the upper Jaramillo (0.988 Ma) and Matuyama-Bruhnes (0.780 Ma) polarity boundaries and the Oldest Toba Tephra (~0.800 ± 0.020 Ma). The Middle Pleistocene hemipelagic layer and directly overlying turbidites were continuously sampled (u-channels) during Expedition 354. We present initial u-channel magnetic and XRF results to refine the middle to late Pleistocene shipboard magnetostratigraphy, characterize the magnetic, geochemical, and geophysical properties of Bengal Fan sediments, and discuss the implication for Pleistocene fan development and sediment accumulation rates.
