Permian Mixed Carbonate-Siliciclastic Lagoon Coastal System In West-Central Gondwana

Although in recent years mixed carbonate-siliciclastic platforms have been increasingly recognized in the Permian of Western Gondwana, there is no detailed description of these mixed systems in West-Central Gondwana. This study focuses on the Permian of the Sergipe-Alagoas Basin (NE Brazil), with the aim of filling this knowledge gap. Based on sedimentological data and microfacies analysis, six facies associations (FA) were identified: FA1 is an eolian-fluvial system, composed of stratified sandstones, FA2 and FA3 represent a mixed tidal flat-lagoon system composed of microbialites, pelitic/micritic sediments and intraclastic packstones, FA4 represents shoreface wave deposits composed of laminated sandstones and silicified grainstones, and FA5 and FA6 are interpreted as a barrier-tidal inlet system, composed of oolitic/intraclastic grainstones, subtidal microbialites, and mixed rudstones. Facies associations reflect the paleoenvironmental conditions of a coastal environment, with dunes and small rivers adjacent to a mixed carbonate-siliciclastic ramp. This is defined as a lagoon system associated with tidal flats protected from the high-energy region by carbonate shoals and microbial constructions. These deposits represent the eastern portion of a shallow epicontinental sea that covered lowlands in West-Central Gondwana within the arid-semiarid belt, whose climate characteristics are reflected in eolian deposits, desiccation structures, mixed carbonate-siliciclastic facies, and fossil records. The main diagenetic feature observed in petrographic analyses was an early diagenetic silicification. Although the absence of spiculites and shelf configuration did not allow a correlation with the Permian glass ramp model, similarities were observed with Eocene glass ramps of Australia, and a relationship with the Permian Chert Event is suggested. (C) 2020 Elsevier B.V. All rights reserved.