CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
artículos
Título:
Stable isotopes (C, S) and hydrocarbon biomarkers in Neoproterozoic sediments of the upper section of Sierras Bayas Group, Argentina
Autor/es:
VELÁSQUEZ-BAGNOUD, M.1,§,*, SPANGENBERG, J. E.1, POIRÉ, D. G.2 AND GÓMEZ PERAL, L.E.2
Revista:
PRECAMBRIAN RESEARCH
Editorial:
ELSEVIER SCIENCE BV
Referencias:
Lugar: Amsterdam; Año: 2013 p. 388 - 400
ISSN:
0301-9268
Resumen:
Abstract The present study addresses the reconstruction of paleoenvironmental conditions for Ediacaran, post-Gaskiers shelf deposits (upper section of Sierras Bayas Group) and their changes as marked by the paleo-biodiversity. To this end, we use the elemental and isotopic geochemistry of the sedimentary rocks and their associated organic matter, as well as the distribution of hydrocarbon biomarkers. The occurrence of 34S enrichments within sulfides exceeding coeval D34SCAS values in the green micritic limestones of Loma Negra Formation is viewed as a combined product of globally low seawater sulfate, high rates of bacterial sulfate reduction and sulfate limitations under a stratified water column inherited from glaciations, particularly the lower water layer. The black micritic limestones of Loma Negra Formation were most probably deposited under oxidizing conditions in the water column as revealed by a clear negative Ce anomaly. However, reducing conditions were maintained into the sediments as evidenced by the record of trace elements and molecular biomarkers. A hopanes distribution with maxima in the C29 hopane indicates an anoxic source-rock depositional setting. The biomarker distribution in the micritic limestones of Loma Negra Formation points to a diverse microbial community including primary producers such as cyanobacteria (e.g., terminally-branched monomethylalkanes, hopanoid distribution), phototrophic bacteria (e.g., acyclic isoprenoids C> Ph). The lowest D13Ccarb-ker values coincided with the latest biomarker signal interpreted as the signature of green non-sulfur bacteria using a less 13C fractionation pathway.