A FORMAÇÃO SALINAS NA ÁREA-TIPO, NE DE MINAS GERAIS: UMA PROPOSTA DE REVISÃO DA ESTRATIGRAFIA DA FAIXA ARAÇUAÍ COM BASE EM EVIDÊNCIAS SEDIMENTARES, METAMÓRFICAS E IDADES U-Pb SHRIMP

Abstract

THE SALINAS FORMATION IN THE TYPE-AREA, NORTHEASTERN MINAS GERAIS: A PROPOSAL TO REVIEW THE STRATIGRAPHY OF THE ARAÇUAÍ BELT ON SEDIMENTARY, METAMORPHIC AND U-Pb SHRIMP EVIDENCES The Salinas Formation has been considered to be a stratigraphic unit of the Macaúbas Group. This group comprises the rift to passive margin sequences of the precursor basin of the Neoproterozoic Araçuaí Orogen, eastern Brazil. However, new roadcuts show extensive and spectacular outcrops with very well-preserved sedimentary structures, allowing detailed studies in the type-locality of this formation, located in the Salinas town and surroundings, northeast Minas Gerais State. In its type-locality, the Salinas Formation consists of graywacke, pelite and clast-supported conglomerate, metamorphosed in the greenschist facies. The sedimentary lithofacies are grouped into three facies association (shelf, slope and deep-sea), indicating sedimentation from shelf deposits to deep-water turbidites. The shelf sedimentation was influenced by storm-wave during deposition. The slump and deep-sea deposits were generated by gravitational flows and high- to low-concentration turbidity currents. Shelf sandstone, clast-supported conglomerate and proximal to distal turbidites outline a submarine fan system. U-Pb SHRIMP data from detrital zircons of graywacke samples indicate a maximum sedimentation age of ca. 568 Ma. Thus, the Salinas Formation is much younger than the Macaúbas Group, and represents late orogenic deposits (ca. 568- 500 Ma). The distal, passive margin unit of the Macaúbas Group is now called Ribeirão da Folha Formation (ca. 800 Ma).