Early Devonian marine invertebrates from the Lolén Formation (Ventania System), Southern Ranges of the Buenos Aires Province, Argentina

SICCARDI, ARÓN; URIZ, NORBERTO; CINGOLANI, CARLOS; RUSTÁN, J.J.

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2012

The Ventania System is located in the south-western Buenos Aires province, Argentina and is classically correlated to units of similar age outcropping in the Malvinas Islands, the Cape Fold Belt (South Africa) and Ellsworth Mountains (Antarctica). It is characterized by an intense folding of the entire Paleozoic siliciclastic sedimentary record. Three sedimentary units are known as Curamalal, Ventana and Pillahuincó Groups. The Ventana Group (1300 m thick) is part of a Middle Ordovician-Middle Devonian marine siliciclastic sedimentary sucession and is unconformably overlain by diamictites of the Pennsylvanian Gondwanan glaciations. Four lithostratigraphic units have been recognized within the Ventana Group, from base to top: Bravard, Napostá, Providencia and Lolén. The Lolén Formation is mainly composed of lithic, feldspar, quartzose and micaceous sandstones, wackes, and interbedded black shales, with shallow marine sedimentary structures. The lower section of the Lolén Formation contains marine invertebrates (mainly brachiopods and bivalves) assigned to the Emsian age and correlated with the Bokkeveld Group from South Africa and other outcrops in Gondwana that characterized the Malvinokaffric realm. A new record of invertebrates shown a first coarse grained sandy level bearing Proboscidina sp, interpreted as a supratidal environment; and a second sandy level with fossils like Proboscidina sp, Scaphiocoelia sp and a Muttationellid indet., interpreted as a tidal channel. A third sandy level with shale intercalations belongs to a subtidal environment showing a diverse fossil assemblage, including the already mentioned fauna plus bivalves like Nuculidae, Mallettidae and Nuculanidae, some gastropod (Plectonotus? sp) and abundant trace fossils.