HR: 0800h
AN: PP41A-0635    [Abstracts]
TI: A Paleoenvironmental Record From High Latitude Eocene Nearshore Marine Sediments: Concretions from ODP Leg 189, Tasman Gateway
AU: * Malone, M J
EM: malone@iodp.tamu.edu
AF: Texas A&M University, Integrated Ocean Drilling Program, College Station, TX 77845 United States
AU: White, T S
EM: tswhite@essc.psu.edu
AF: The Penn State University, EMS Environment Institute, University Park, PA 16802 United States
AU: Martin, J B
EM: jmartin@geology.ufl.edu
AF: University of Florida, Department of Geological Sciences, Gainesville, FL 32611 United States
AB: Concretions from nearshore marine detrital sediments recovered west and south of Tasmania during ODP Leg 189 were sampled to investigate paleoenvironmental conditions of the high latitude Eocene during rifting of the Australia-Antarctic margin. Forty-six nodules from three sites were examined for XRD mineralogy, stable isotopic and trace element composition. In addition, 22 of the 46 samples were thin sectioned for petrographic examination. Stable isotopic composition of pore waters are used to constrain present-day diagenetic conditions. The most common concretion phase is calcite, which is present in almost all samples. Intermediate-Mg calcite is present in two samples from Site 1170 (7 and 9 mol% MgCO₃) whereas all other calcites are low-Mg (<4 mol%). Twelve samples contain siderite. With one exception, all siderite nodules also have some calcite. Francolite is present in 15 samples; 11 of which are from Site 1171. The petrographic character and geochemical composition of the concretions show wide variability by type and location. At the two locations closest to Tasmania (Sites 1168 on the west Tasman margin and 1170 on the west South Tasman Rise) concretions have elevated Sr and lower Fe and Mn contents, and oxygen isotopic values more positive than expected for present-day equilibrium conditions despite variable petrographic character. These data sets are consistent with concretions at these two sites having formed during early marine diagenesis either (1) at cooler temperatures (i.e., at much shallower burial depth than present day) and/or (2) from waters with a more positive oxygen isotope composition. Carbon isotopic values vary from slightly positive to very negative also indicating formation during early diagenesis within sediments with active microbially mediated organic matter alteration. In contrast, at Site 1171, the southernmost site occupied on the southern tip of the South Tasman Rise, concretions record a very different history. Carbonate concretions at Site 1171 all have negative oxygen isotope values (-1.8 to -12.6‰, mean = -7.9‰), lower Sr contents, and higher Fe and Mn values than at the other study sites. These results suggest formation by meteoric fluids sourced from a different region under different paleoenvironmental conditions than the other two sites in the Australo-Antarctic Gulf.
DE: 3036 Ocean drilling
DE: 4825 Geochemistry
DE: 4870 Stable isotopes (0454, 1041)
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005