Fácies sedimentares dos depósitos glaciomarinhos aflorantes nos rios Urubu, Uatumã e Jatapu, borda norte da Bacia do Amazonas

Abstract

The Amazon Basin has a significant Paleozoic sedimentary record, partly exposed on the northern and southern edges. In recent years, sedimentological and stratigraphic studies have intensified on the northern edge of the basin, especially in the municipalities of Presidente Figueiredo, Rio Preto da Eva, and Urucará (AM), where marine and glacial sedimentary facies have been defined. The present study integrates sedimentological, palynostratigraphic, mineralogical, and microtextural data from outcrops in the Urubu, Uatumã, and Jatapu rivers, with the aim of defining correlation criteria. The results obtained allowed the identification of sedimentary facies characteristic of marine paleoenvironments (upper-lower shoreface and foreshore), intercalated with glacial deposits associated with the sedimentation of terminal moraines and subglacial-proglacial lagoons in the Nhamundá and Manacapuru formations. The recognized facies include sandstone with tabular cross-stratification (Act), sandstone with plane-parallel stratification bioturbated by Cruziana (Apbc), sandstone with plane-parallel stratification bioturbated by Skolithos (Apbs), sandstone with plane-parallel stratification (Ap), laminated pelite (Pl), as well as coarse polymictic (Dpp) and oligomictic (Dpo) diamictites and laminated pelite with dropstones (Pld). Glacial deposits were identified in five locations, related to the Early Silurian (Llandovery-Wenlock) glacial event, as well as a new glacial event positioned in the Late Silurian-Early Devonian (Pridoli to Lochkovian) interval. The presence of faceted clasts, dropstones, and diagnostic microtextures (such as parallel striations) reinforces the action of glacial processes during the Silurian-Devonian in the Amazon Basin. Therefore, the integration of the geological-palynological data from this study with regional studies allowed the geological map of the studied area to be drawn up, with the definition of six sub-ranges of the Autás Mirim, Nhamundá, Manacapuru, Ererê, Barreirinhas, and Itaituba formations, oriented in an E-W direction.