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Litoestratigrafia, sistemas deposicionais e icnofósseis do Grupo Caacupé, (Ordoviciano da Bacia do Paraná) na Cordilheira de Los Altos, Paraguai oriental

2004; Sociedade Brasileira de Geologia; Volume: 34; Issue: 3 Linguagem: Inglês

10.5327/rbg.v34i3.1129

2317-4889

Renato Paes de Almeida, Cláudio Riccomini, Liliane Janikian, Antônio Romalino Santos Fragoso-Cesar, Victor Fernandes Velázquez,

Paleontology and Stratigraphy of Fossils

The Caacupe Group is composed of sandstones and conglomerates of presumable Ordovician age cropping out in the uplifted areas in the vicinity of the Assuncion Rift, Eastern Paraguay. This group is considered to be the lowermost unit of the Parana Basin, deposited prior to the glaciation registered in the Iapo Formation in Brazil, and thus representing the onset of the Ordovician-Silurian subsidence cycle of the basin. Stratigraphic and facies analyses of representative outcrops of the unit, mainly in the Cordilhera de los Altos region, have led to the revision of its formal lithostratigraphy and paleogeographic interpretation. This paper maintain the original lithostratigraphic subdivision of the Caacupe Group. This division considers two formations: Paraguari (lower conglomerates and pebbly sandstones) and Piribebui (upper cross-stratified sandstones and pelitic lenses), the latter abandoned without proper justification. Eleven facies are described and interpreted, leading to the characterization of a westwards flowing braided river paleosystem for the conglomeratic succession (Paraguari Formation), and a nearshore depositional paleosystem dominated by tidal bars migrating towards the northwest (ebb currents) for the sandy succession (Piribebui Formation). An abundant ichnofauna supports the interpretation of a coastal origin for the Piribebui Formation and brings additional sedimentological information. The interpreted depositional systems suggest a wide sedimentary basin devoid of proximal tectonically active margins during the deposition of the Caacupe Group, a general characteristic of the subsequent Paleozoic subsidence cycles of the basin.