LATE ORDOVICIAN?EARLY SILURIAN IN THE PRECORDILLERA OF ARGENTINA: INSIGHTS FROM C-, N-ISOTOPE AND Hg CHEMOSTRATIGRAPHY

SIAL, ALCIDES N.; PERALTA , SILVIO H.; GAUCHER, CLAUDIO; FERREIRA, VALDEREZ P; PEREIRA, NATAN S; SANTOS, N.T.S.

Porto Alegre

Congreso; Brazilian Geological Congress; 2016

Sociedad Geológica de Brasil

High-resolution δ13Corg and δ15N and Hg chemostratigraphy was studied in geological sections in three localities of the Precordillera, Argentina, where sedimentary successions (carbonates, shales, siltites) have recorded the Ordovician?Silurian (443.7 Ma) boundary (OSB): (a) Los Baños de Talacasto, (b) Cerro La Chilca and (c) Villicum. The Sandbian and Katian stages are absent in the Los Baños de Talacasto section, being Darriwilian carbonates of the San Juan Formation unconformably overlain by the Hirnantian transgresive basal cherty pebbly conglomerate of the La Chilca Formation, which in turn is covered by fine-grained siliciclastic shallow marine deposits of the La Chilca Formation bearing graptolites of Hirnantian?Rhuddanian age. In the Villicum section, the Lower Hirnantian Member of the Don Braulio Formation is composed by siltstones/shales with calcareous lenses bears Normalograptus persculptus and brachiopods of the Hirnantia Fauna, which are overlain by yellowish/ocher bioturbated mudstones (12 m thick Ocher Member) which includes the Hirnantian?Rhuddanian bourndary, which is paraconformably overlay by 12 m of ironstones and graptolite-rich black shale interbedded of the Upper Ironstone Member of the Don Braulio Formation.