HR: 09:45h
AN: GP41A-08 INVITED     [PDF]
TI: A Sedimentary Magnetic Record of Cenozoic Antarctic Environmental Changes from the Victoria Land Basin, Ross Sea
AU: * Sagnotti, L
EM: sagnotti@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Roma, 00143 Italy
AU: Roberts, A P
EM: arob@soc.soton.ac.uk
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Florindo, F
EM: florindo@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Roma, 00143 Italy
AU: Florindo, F
EM: florindo@ingv.it
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: Department of Geology, University of California, One Shields Ave., Davis, CA 95616 United States
AU: Wilson, G S
EM: gary.wilson@stonebow.otago.ac.nz
AF: Department of Geology, University of Otago, Leith Street, Dunedin, PO Box 56 New Zealand
AB: Magnetic properties of peri-Antarctic sedimentary sequences can provide useful indications of variations in the weathering regime, and therefore of paleoclimatic conditions, on the Antarctic continent. The Victoria Land Basin (VLB) faces the Transantarctic Mountains in the Ross Sea and contains a sedimentary record of Cenozoic erosion from Antarctica. We synthesize environmental magnetic results from multiple analyses on samples taken at an average spacing of 0.5 - 1 m from a suite of sediment cores drilled since the 1980's over a total stratigraphic thickness of 2.2 km, which span an age range from ~37 m.y. to ~17 m.y. We critically examine whether the magnetic properties contain a record of paleoclimatic, diagenetic or provenance variations or a mixture of signals resulting from these processes. We recognize variations in the concentration, grain-size and composition of the magnetic minerals in the VLB sequences, on time scales of tens of thousands of years to a few million years, which delineate a magnetic property zonation for the cores. The magnetic properties of the VLB cores are dominated by large-scale variations in magnetite concentration. A consistent overall upward fining of magnetite particles is also observed, together with an increase in the relative concentration of high-coercivity minerals. In the Late Eocene and Early Oligocene, variations in magnetite concentration coincide with variations in detrital smectite concentration associated with paleoclimate cycles across the threshold favoring physical versus chemical weathering of source rocks (high magnetite and smectite concentrations indicate warmer and wetter continental climates and vice versa). Smaller scale variations in smectite/magnetite concentrations also occur in younger sediments, which suggests that there were significant fluctuations in weathering regime during the Late Oligocene and Early Miocene. However, after 24 Ma, increased activity of the McMurdo Volcanic Group dominates the magnetic properties of the VLB sediments and becomes the main source for the younger magnetite and smectite, compared to a Ferrar Dolerite source for the older sediments. This demonstrates that provenance variations are just as important as paleoclimate in controlling clay mineralogy and magnetic properties in the VLB.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 3344 Paleoclimatology
DE: 9310 Antarctica
DE: 9604 Cenozoic
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting