Late Cretaceous sequences in Mato Grosso State: a synthesis.

Abstract

The Late Cretaceous of the State of Mato Grosso are registered in the thick and well exposed stratigraphic sequences of the Bauru and Parecis groups, with restricted outcrops on the south and north of the Paraguai Belt, respectively, both formed of volcano-clastic-chemical deposits. In the last decades the studies on these groups have been intensified since they constitute the secondary source of diamond-bearing Quaternary deposits. An extensive intrusive-extrusive magmatic event of basaltic composition occurred at ca. 85 My in the Bauru and Parecis basins. The basaltic rocks are included in the Paredão Grande Formation, and mainly occur at Paranatinga, Chapada dos Guimarães, Dom Aquino, Poxoréu, General Carneiro and Serra de São Vicente. Volcano-clastic-chemical deposits derived from basaltic rocks were identified in both basins. They are represented in the Bauru basin by the Quilombinho, Cachoeira do Bom Jardim and Cambambe formations of the Bauru Group. In the Parecis basin they are included in the Salto das Nuvens and Utiariti formations and the Tapirapé Sequence, which represent the Parecis Group. The Cambambe, Utiariti and Tapirapé units are devoid of igneous activities, but contain fossil fragments, like the Cachoeira do Bom Jardim Formation. The Late Cretaceous sequence of the State of Mato Grosso is related to events of the South America-Africa separation, starting with the impact of the Trindade plume and the individualisation of the Rio das Mortes rifts. The works until now accomplished about the Late Cretaceous stand up the need of elaboration of a single stratigraphic column for both basins. The Bauru Group is suppressed in Mato Grosso, and the Paredão Grande, Salto das Nuvens, Cachoeira do Bom Jardim and Utiariti formations in the Parecis Group.