Biofabric and porosity relationship in coquinas, Morro do Chaves Formation (Barremian/Aptian), Sergipe-Alagoas Basin, Brazil-NE

Abstract

Coquinas of Morro do Chaves Formation are analogous rocks of pre-salt reservoirs of Campos and Santos basins; they are mainly composed by shells and fragments of bivalves that present a great variability of biofabric and porous system, which allows the use of taphonomy to relate their depositional environment. The main taphonomic attributes in this work are: valve orientation; shell packing; granulometry and selection; degree of fragmentation, abrasion and roundness. The interpretation of data had as objective grouping the samples according to different taphonomic patterns and porosity, using the artificial neural networks method (Self-Organization Map — SOM) as auxiliary tool. The analysis of data resulted in 3 clusters: A1 with high porosity values (between 11 and 23%) whose taphonomic characteristics reveal a high energy environment; A2 with intermediate values of porosity (between 7 and 15%) whose taphonomic characteristics indicate a transition environment between high and low energy; finally,group A3 with lower values of porosity (between 0 and 7%) whose taphonomy indicates low energy environments. As a final result, the taphonomic characteristics reveal the energy of the depositional environment and it is possible to associate high energy environments with the high porosities for the Coquinas of the Morro do Chaves Formation.