Lithofacies, taphonomy, and brachiopod assemblages in the Silurian of Western Argentina: A review of Malvinokaffric Realm communities

SÁNCHEZ, T.M. ; WAISFELD, B.G.; BENEDETTO, J.L.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1991 vol. 4 p. 307 - 329

0895-9811

Distribution of faunal associations in the Silurian sequences of the Precordillera and Northwestern Basins of Argentina is integrated with sedimentologic and taphonomic data, demonstrating that marked temporal and spatial changes in the Malvinokaffric brachiopod assemblages are related mainly to the type and intensity of the hydraulic regime of the shelf environment. The vertical arrangement of associations within each basin is controlled by local fluctuations in water depth, whereas the spatial variations are linked to minor environmental changes (substrate type and oxygen content). The basal strata of the Middle-Upper Silurian Los Espejos Formation of the Precordilleran basin are mudstones of an open-shelf environment. These pass upward into facies of a storm-dominated shelf and shoreface. Four brachiopod assemblages have been recognized in the muddy facies: the Harringtonina Low-Diversity and the Australina- Dominated associations characterize distal storm beds; the Harringtonina High-Diversity and Coelospira-Dominated communities occur in the fine-grained rocks of proximal tempestites. Storm shell beds, which dominated the middle-upper part of the sequence are represented by allochthonous and parautochthonous coquinas. The Clarkeia Association flourished in shallow-water, high-energy, nearshore environments. Silurian rocks in the Northwestern basin were deposited in an offshore, low-energy, restricted environment, and two main faunal assemblages have been recognized: a more distal Heterorthella Association and a relatively more proximal Ancillotoechia Association.