Paleoecology of marine ostracods from the lower portion of the Corumbataí Formation (Permian of Paraná Basin), Goiás State, Brazil

Abstract

Outcrops of the Corumbataí Formation (Passa Dois Group) in the northern sector of the Paraná Basin expose marine neritic rocks deposited under slightly limnic influence and represent storm events to some extent. Ostracod occurrences confirm the Kungurian age of these rocks. Other authors working with samples from other portions of the basin could determine that the depositional system switched to shallow lakes in the Roadian. The studied material came from outcrops in southwestern Goiás State, in the northeast area of the Santa Rita do Araguaia Municipality. The eight ostracod species identified in the Corumbataí Formation belong to the families Bairdiocyprididae, Cytherideidae, Bairdiidae and Knoxitidae: Silenites sp. 1, Silenites? sp. 2, Basslerella sp. 1, Basslerella sp. 2, Saumella? sp. 1, Bairdiacypris sp. 1, Bairdiacypris sp. 2, Langdaia? sp. 1. With the exception of the Family Bairdiocyprididae, the other family group taxa have been reported exclusively from marine paleoenvironments. The ostracod assemblage is composed exclusively by neritic species that lived in a terrigenous substrate (muddy to sandy) in warm waters. Regarding salinity, all species are stenohaline, except Silenites sp. 1 and Silenites? sp. 2. Euhaline conditions may have occurred too. The presence of common Tethys genera, such as Silenites, Basslerella and Bairdiacypris corroborate the hypothesis of connections between the depositional system of the Corumbataí Formation and other marine coeval paleoenvironments. The low ecologic diversity of ostracod was probably due to restriction of the connection of this paleoenvironment with oceanic waters and the "restricted marine environment" is a more precise interpretation when compared with the "coastal lagoon" interpreted in previous works. This hypothesis is confirmed by the low abundance of Silenites species, the high abundance of which is indicative of coastal lagoon paleoenvironments. The frequent occurrence of ostracods in bioclastic lenses suggests a paleoenvironmental model of occasional storm events in the Corumbataí Formation.