Icnologia e Paleopedologia aplicadas ao estudo de planícies aluviais albianas da Bacia do Parnaíba, Brasil

Abstract

The Itapecuru Formation covers the continental Cretaceous deposits distributed in the central-western region of the state of Maranhão and is part of the stratigraphic record of the Parnaíba Basin. This lithostratigraphic unit is characterized by fine to very fine sandstones, interspersed with thin and sparse lamestones and limestone levels, deposited in alluvial and fluvial-estuarine environments, marked by long periods of subaerial exposure, attested by the frequency of paleosols in the sedimentary sequences. The Itapecuru Formation, as well as other geological units that appear in the Brazilian intracontinental basins, present important paleosols profiles and preserve biogenic structures of invertebrates, vertebrates and roots. In this study, will be icnological, sedimentological and paleopedological data will be integrated aiming at the paleoenvironmental reconstruction of the Albians deposits of the Parnaíba Basin. The defined sedimentary deposits were fine sandstone with flat-parallel lamination and heterolytic deposit. The paleosols form composite profiles, moderate to well developed, with redoximorphic features and pedogenic structures. The iconic data helped to recognize five invertebrate icnogenerous, one vertebrate ichnogenerous and root structures. Scoyenia is the ichnofacies related to the ichnofossiliferous set. The ichnofabric defined were: Outcrop Pequi, ichnofabric Planolites-Taenidium and Thalassinoides-Taenidium; outcrops Prata, ichnofábrica rizolith; and outcropping Jundiaí, ichnofabric Planolites-Taenidium. The paleodrenage study using redoxmorphic characteristics of the paleosols and the variation of the icnocenoses in the deposits evidenced moderately drained paleosols with short periods of water retention. The integration of the data helped to the paleoenvironmental characterization of an alluvial plain and a paleoclimate with a seasonal condition.