Paleontology and sedimentology of Middle Eocene rocks in Lago Argentino area, Santa Cruz Province, Argentina

Silvio Casadío, Miguel Griffin, Sergio Marenssi, Laura Net, Ana Parras, Martín Rodriguez Raising, Sergio Santillana

Abstract


Sedimentological and paleontological study of the Man Aike Formation at the Estancia 25 de
Mayo, SW of Santa Cruz Province, Argentina, represents the evolution of an incised valley from fluvial to
marine environment during the late middle Eocene. At the base of the unit there is an unconformity that
corresponds to fluvial channels which cut down into the underlying Maastrichtian sandstones of the
Calafate Formation. The fauna of invertebrates (mostly molluscs) illustrated herein was collected from
shell beds interpreted as tidal ravinement surfaces. The fauna includes terebratulid brachiopods, bivalves
of the families Malletiidae, Mytilidae, Pinnidae, Ostreidae, Pectinidae, Carditidae, Crassatellidae,
Lahillidae, Mactridae, Veneridae, and Hiatellidae, and gastropods of the families Trochidae and
Calyptraeidae, and a member of Archaeogastropoda of uncertain affinities. The similarities of this fauna
with that recorded in the Upper Member of the Río Turbio Formation, together with 87Sr/86Sr ages, suggest
a late Middle Eocene age for the Man Aike Formation.

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