HR: 12:06h
AN: B32B-08    [Abstracts]
TI: High-resolution C-N-S-Fe isotope chemostratigraphy of the terminal Proterozoic Huqf Supergroup, Sultanate of Oman: reorganization of global biogeochemical cycles and the progressive oxygenation of the ocean
AU: * Fike, D A
EM: dfike@mit.edu
AF: Department of Earth, Atmosherphic, & Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Grotzinger, J P
EM: grotz@mit.edu
AF: Department of Earth, Atmosherphic, & Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Summons, R E
EM: summons@mit.edu
AF: Department of Earth, Atmosherphic, & Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Pratt, L M
EM: prattl@indiana.edu
AF: Department of Geological Sciences, Indiana University, 1001 E. 10th St., Bloomington, IN 47405 United States
AU: Poulton, S W
EM: s.poulton@biology.sdu.dk
AF: Danish Center for Earth System Science, Institute of Biology, University of Southern Denmark, Campusvej 55, Odense, 5230 Denmark
AB: We present a high resolution study of the terminal Neoproterozoic to Cambrian Huqf Supergroup of Oman using drill core and cuttings. The Huqf Supergroup overlies approximately 800Ma crystalline basement and is composed in ascending order of siliciclastics and glacio-marine diamictites (Ghadir Manquil Formation), carbonate-siliciclastic packages (Masirah Bay, Khufai, Shuram, and Buah Formations), and a thick carbonate-evaporite sequence (Ara Group). The ratio of highly reactive iron to total iron and the presence of significant Fe-carbonate, Fe-magnetite, and Fe-(oxyhydr)oxide species in the Neoproterozoic Huqf sediments indicates deposition under an anoxic ferrous water column, rather than under oxic or euxinic conditions. The speciation of highly reactive iron changes approaching the Precambrian/Cambrian boundary, suggesting a change in water column redox. Carbonate-associated sulfate (CAS) from these units is found to increase in abundance from less than 100pm in the lower units to several thousand ppm in the Ara Group. CAS d34S indicate a general increase up to 39 permil at the Precambrian/Cambrian boundary, followed by a decrease at the top of the Ara Group. The coincidence of CAS d34S and anhydrite d34S from the Ara Group provide confidence that the observed CAS d34S isotope signal is primary. The rise in sulfate d34S observed during terminal Proterozoic time and subsequent steady decline across the Precambrian/Cambrian boundary suggests a progressive shift in the balance of sulfur burial from sulfides to sulfates. There are two significant negative excursions in carbonate d13C from this section: an 8 permil excursion at the Precambrian/Cambrian boundary; and a 13 permil excursion in the Shuram Formation. The latter excursion extends through $>$500m of section, suggesting a long term perturbation to the C-cycle. Both excursions have correlative representations in globally distributed sections, improving confidence that our observations reflect significant, global changes to biogeochemical cycling of carbon during the terminal Neoproterozoic. Here we present organic d13C and d15N with a focus on outlining their behavior during these excursions. Taken together, these data indicate a massive reorganization of the global C-N-S-Fe biogeochemical cycles likely due to changing redox conditions (e.g., oxygenation) of the deep ocean.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1055 Organic geochemistry
DE: 1010 Chemical evolution
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting