FÁCIES SEDIMENTARES E SISTEMAS DEPOSICIONAIS DAS FORMAÇÕES ALTO GARÇAS E VILA MARIA NA REGIÃO DE CHAPADA DOS GUIMARÃES (MT), BORDA NOROESTE DA BACIA DO PARANÁ

Abstract

The Ordovician-Silurian interval of the Paraná Basin, outcropping in the Chapada dos Guimarães, Campo Verde and Santo Antonio do Leverger counties (MT), is represented by the Alto Garças and Vila Maria formations. This interval is characterized by sixteen lithofacies and two ichnofacies. Among these lithofacies, nine ruditics, six arenitics and one lutitic are identified. The ruditics lithofacies are named massive conglomerate (Cm), conglomerate in tabular beds (Ct), conglomerates and sandstones interbedded in tabular beds (Ct(H)), conglomerate with cross-stratification (Cc), massive diamictite (Dmm), massive diamictite with evidence ofressedimentation (Dmm(r)), stratified diamictite (Dms), stratifieddiamictite with evidence of current reworking (Dms(c)) and stratified diamictite with evidence of ressedimentation (Dms(r)); the arenitics ones are named massive sandstone (Am), sandstone in tabular beds (At), sandstone with climbing-ripple cross-lamination (Acl), sandstone with cross-stratification (Ac2), sandstone with ripple cross-lamination (Ao) and sandstones and shales interbedded inflaser, wavy and linsen bedding (Ao(H)); and finally the lutitic lithofacies is named shale with dropstone (Fid). The identified ichnofacies are Skolithos (Sko), by the presence of Skolithos linearis, Arenicolites ichnosp. and Diplocraterion ichnosp., and Cruziana (Crz), by the presence of Arthrophycus alleghaniensis, Palaeophycus tubularis, Aulichnites ichnosp., Lockeia ichnosp., Chondrites ichnosp. and Teichichnus ichnosp. Those facies were related in four depositional systems: Fluvial System (SF-facies Cc), Rudaceous Shallow Marine System (SMRrud-facies Ct, Ct(H), Cm, At, Ac2, Crz), Arenaceous Shallow Marine System (SMRarn-facies Am, At, Ac2, Ao, Ao(H), Sko) and Glaciomarine System (SG-facies Dmm, Dmm(r), Dms, Dms(r), Dms(c), Acl, Fid, Crz). The Alto Garcas Formation, based on the association of the facies At, Am and Sko, is interpreted as the SMRarn system. The Vila Maria Formation is characterized by a succession of (i) beds of the Cc facies, interpreted as the SF system; (ii) beds of the Ct(H) facies, interpreted as deposits of a beach-face of the SMRrud system; (iii) beds of the Ct and At facies, interpreted as proximal shoreface deposits dominated by storms of the SMRrud system; (iv) beds of the At, Ct and Crz facies, interpreted as distal shoreface deposits dominated by storms of the SMRrud system; (v) beds of the diamictite facies, and Fid, Crz and Acl facies, all together interpreted as SG system; (vi) beds of the At, Crz, Ct and Ac2 facies, interpreted as proximal and distal shoreface deposits dominated by storms of the SMRrud system; (vii) and beds of the At, Sko, Ao and Ao(H) facies, interpreted as lagoonal and proximal shoreface deposits dominated by storms of the SMRarn system.