Paleo-climatic and paleo-environmental evolution of the Neoproterozoic basal sedimentary cover on the Río de La Plata Craton, Argentina: Insights from the δ13C chemostratigraphy

GOMEZ PERAL, L.,SIAL, A., ARROUY, M.J., RICHIANO, S., FERREIRA, V., KAUFMAN, A., POIRÉ, D.

SEDIMENTARY GEOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2017

0037-0738

The Sierras Bayas Group of the Tandilia System constitutes the Neoproterozoic sedimentary cover of the Río de LaPlata Craton in Argentina that accumulated amid the breakup of the Rodinia supercontinent and subsequentassembly of Gondwanaland. Evidence for glaciation in the Villa Mónica Formation (VMF) at the base of the successioncomes in the form of iron-rich laminated sediments containing dropstones composed predominantly of basementcrystalline rocks and quartzites that, are sequentially overlain by a phosphatic mudstone and a ~40 m thickstromatolitic dolomite. Subtidal facies preserve columnar forms similar to post-glacial tubestone stromatolitesseen in the Neoproterozoic records. Thesemorphologies suggest rapid growth associated with elevated seawater alkalinityand high rates of carbonate accumulation records. The VMF dolomites in our four studied sections nearOlavarría-Sierras Bayas area reveal a pronounced negative-to-positive δ13C up section that is similarly to these capcarbonates and others worldwide. Our sedimentological and geochemical study of the VMF sections reveal consistentcarbon and oxygen isotope trends that may be useful for detailed intra-basinal correlations. Samples of the VMFfabric-retentive dolomite preserve an unusually narrow range of non-radiogenic strontium isotopic compositions(0.7068 to 0.7070) that are consistent with Cryogenian limestone facies in the potential Namibian and Brazilianequivalents. Exceptional preservation of 87Sr/86Sr compositions suggest the possibility of primary dolomite precipitationin post-glacial seawater, and furthermore that REE patterns and distributions may yield similar insights toredox conditions in the depositional basin. In particular, the VMF dolomites reveal depleted LREE abundances, a negativeCe anomaly, positive La and Gd anomalies, and low Y/Ho values. As a whole, these observations suggest oxidizingpost-glacial seawater conditions associated with significant freshwater inputs into the basin. Global warmingand increases in primary productivity and organic carbon burial linked to the buildup of oxygen, the positive δ13Ctrend and the increase in stromatolite biodiversity in the VMF.