Caracterização sedimentológica dos carbonatos albianos do reservatório quissamã na porção meridional da bacia de campos

Abstract

Albian carbonates rocks of Quissamã Formation from the southern of Campos Basin (RJ) and the Outeiro Formation are described in detail, with emphasis on petrology, petrography, cycles, paleoenvironments and diagenesis. Six lithofacies were recognized in the Quissamã Formation, mainly grainstones and packstones (rare wackestones) with carbonate grains composed of ooids, oncoids, peloids and some bioclasts (mollusks, echinoids, benthonic microfossils). This study confirms previous interpretations that the Quissamã Formation was deposited in a shallow carbonate ramp with a set of banks oriented parallel to the coast composed of carbonate grains. The other facies (mainly packstones) represent the flanks of banks and interbank regions, deposited under lower energy conditions. Rudaceousoncoids were most commonly formed in the protected areas at the western flank of the bank, where microbial communities found the most favorable life conditions. There is evidence of reworking of grains by storms. Successions composed of peloidal/bioclasticpackstones grading to grainstones are similar to typical high-frequency cycles which represent the transition from a relatively deep/low energy to a shallow/higher energy depositional environment (shallowing upwards successions). The Outeiro Formation has mudstones and wackestones, with distal marine planktonic organisms becoming more abundant from the base. This unit is ascribed to a transgressive context in gradually deeper environments. The diagenetic history of the rocks encompassed, during the eodiagenesis, micritization, mechanical compaction, dissolution, cementation (mainly fringe, mosaic and sintaxial cementation) and, during mesodiagenesis, chemical compaction and blocky cementation in fractures.