The Araras Group of Neoproterozoic age, exposed in the southern Amazon Craton and North Paraguai Belt, central region of Brazil, is a predominantly carbonate succession with sporadic siliciclastic. These rocks overlap diamictites of the Puga Formation, related to Marinoan glaciations, included in the model of snowball Earth / Earth slushball. The base of the Araras Group consists of the Mirassol d'Oeste and Guia formations. This work is developed on deposits of the Guia Formation considered the limestone portion of the Puga cap carbonate. The Guia Formation consists of thin bituminous limestones, bituminous shales, pelites and cementstones with calcite fans and pseudomorphs of aragonite. This unit is described in the southern part of the Amazon Craton, Mirassol d'Oeste region and Tangara da Serra, and along the Paraguai Belt, region of Nobres. The study area is located in the Paranatinga region, approximately 250 km east of Nobres, which is still part of the Paraguay Belt. In the Paranatinga region, the Guia Formation constitutes an approximately 15m succession thick, composed mainly of calcareous thin laminated, gray to black limestones, and subordinate sandstones and carbonate breccia. 6 sedimentary facies/microfacies were described: a) Sandstone with hummocky cross-lamination (Ah); b) Shale with sand grans (Fl); c) Microsparite with terrigenous grains (Mt); d) Pseudosparite with terrigenous grains (Pt); e) Carbonate breccia with tabular clasts (Bt) Rudstone, and; f) Limestone Breccia (Bc) Floatstone, which been grouped into two facies associations. Association 1 (AF1) represented by transitional deposits shoreface/offshore and association 2 (AF2) represented by offshore deposits. Isotopic analyse of Pb-Pb suggest age of 476 ± 93 Ma, which goes against the isotope data obtained for the Tangara da Serra of 622 ± 33 Ma. The age of 476 ± 93 Ma found for the Guia Formation in the Paranatinga region suggests a pre-Ordovician event, which would have deformed the Neoproterozoic units (Cuiabá Group, Puga Formation, Araras Group and Alto Paraguai Group), and could be associated with the formation of the Paraguay Belt (?).
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