HR: 0800h
AN: V51C-0595    [Abstracts]
TI: The Impact of Diagenesis on the Sm-Nd Isotope Systematics of Black Shales
AU: Hannigan, R
EM: HANNIGAN@astate.edu
AF: Department of Chemistry, Arkansas State University, State University, AR 72467 United States
AU: * Abanda, P A
EM: pabanda@astate.edu
AF: Department of Chemistry, Arkansas State University, State University, AR 72467 United States
AU: Chakrabarti, R
EM: ramananda@earth.rochester.edu
AF: Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627 United States
AU: Basu, A R
EM: abasu@earth.rochester.edu
AF: Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627 United States
AB: We investigate the impact of diagenesis on Sm-Nd systematics in black shales. Here we report Nd-isotopic compositions of different isolated shale components (organic, silicate, carbonate, sulfide) using thermal ionization mass spectrometry (TIMS). This study uses time correlative black shales with different grades of thermal maturity from the Utica Shale Magnafacies (middle Ordovician) of Quebec (immature: Tmax 20$^{0}$C to 50$^{0}$C Ro $<$0.5), Ontario (mature: Tmax 50 $^{0}$C to 140 $^{0}$C Ro 0.5 - 0.8), and New York (post mature: Tmax $>$140 $^{0}$C Ro $>$1). The units chosen for this study share a common provenance and range in thermal maturity from: Quebec (immature: Tmax 20$^{0}$C to 50$^{0}$C), Ontario (mature: Tmax 50 $^{0}$C to 140 $^{0}$C), and New York (post mature: Tmax $>$140 $^{0}$C; Hannigan and Basu, 1998). $\epsilon$Nd(0) values for the whole rock samples range from -15.3 to -9.0 for the immature shales and from -19.2 to -12.9 for the mature shales. The $\epsilon$Nd(0) values for the organic fractions range from -12.5 to -12.7 for the immature shales and from -23.5 to -14.0 for the mature shale samples. The carbonate fractions have $\epsilon$Nd(0) values ranging from -7.7 to -11.6 for the immature shales and from -10.7 to -12.5 for the mature shales. T$_{DM}$ values for the whole rock samples range from 2.13 to 2.15 Ga and 1.9 to 2.6 Ga for the immature and mature shales, respectively. $\epsilon$Nd(0) values for the immature shales become progressively more negative from the carbonates, organics to the whole rocks However, for the mature shales, the organic fraction shows most negative values followed by the whole rock and the carbonates. Our results suggest that during early diagenesis (thermal maturation of organic matter and formation of authigenic mineral phases) of black shales there is a clear fractionation between Sm and Nd - Nd being more mobile. Finally, the T$_{DM}$ model ages of all the whole rock samples both mature and immature indicate late Archean to early Proterozoic provenance ages distinctly older than Grenvillean sources.
DE: 3675 Sedimentary petrology
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting