Magmatism, sedimentation and stratigraphy of the northern region of the Santos Basin

Abstract

The Santos Basin, passive margin basin, had its sedimentary history disrupted by intra and extra-basinal tectonic activity that took place during the Eocene and Santonian-Campanian. Many authors have identified these events; however this matter still deserves an integrated study including basement and basin areas. Recent Ar/Ar geochronological data from intrusive and extrusive rocks in the Santos basin have identified two events precisely at 82 ± 1 Ma and 48,9 Ma. Among the depositional sequences individual-ized from seismic and well data in the Santos Basin, the K90 depositional sequence - of Santonian-Campanian age - is the best example to investigate magmatism, sedimentation and stratigraphy. Substantial volcanic building, intrusive and extrusive rocks can be observed in this sequence and have a strong impact on in the mineralogical and sedimentary composition of the siliciclastic deposits (sand-stones and shales). Subaerial and subaqueous volcanisms are well identified and its characteristics are described herein in terms of seismic facies, log facies and lithofacies. Siliciclastic depositional systems from the transgressive tract (shallow marine) and from lowstand (deep marine) of this sequence are lithic arkosean sandstones, composed mainly by quartz, K-feldspar, plagioclase and fragments of igneous rocks. An intensive diagenetic chloritization, probably due to the presence of ferromagnesian minerals, has a strong impact on the reservoir quality.