Diápiros de lama na Bacia do Recôncavo: interpretação sísmica 3D e sua possível influência no sistema petrolífero

Abstract

Mud diapirs are present in different tectonic environments around the globe and are particularly prevalent in large deltas. The onshore, Jurassic-Cretaceous Recôncavo Basin NE Brazil, represents an atypical example of mud diapir occurrence in a rift basin. The intensity of mud diapirism is different in the three sectors of the basin, with the central sector exhibiting the best development In the southern sector, diapirism is less significant, and it is practically non-existent in the northeast sector. 3D and 2D seismic, geochemical, outcrop and well data were used to geomorphologically characterize the onshore mud diapirs in the central and south sector of the Recôncavo Basin and correlate them with the structural and morphological aspects of the basin, in addition to elucidating the possible origins of their movement. The Cinzento diapir was seismically interpreted in the southern sector, and four mud diapirs were identified in the central sector of the basin, named Apraius-Miranga Norte, Pedra do Salgado, Biriba and Carijó. Two internal seismic facies were identified in the diapirs, called F1 and F2. Facies F1 presents more disruptive features and facies F2 is composed of reflection-free features. The eastern diapirs, positioned close to the basin border fault conglomerates, are dominated by the disruptive seismic facies (F1). Facies F2 (reflection-free) predominates in the western diapirs. The diapiric movement is probably related to the paleo-seismicity of the basin and the rupture of an ancient delta front, associated with the Pitanga and Caruaçu members. The rapid advance of conglomerates towards the basin during the active rift phase also played an important role in triggering the diapiric movement. In the central sector, the Biriba diapir was possibly the first to develop, followed by the Carijó, Apraius-Miranga Norte and finally the Pedra do Salgado diapir. Analyses of TOC, S, RI, Rock-Eval Pyrolysis, and stable organic carbon isotopes showed that the possible source rocks observed in outcrop are thermally immature and that they were deposited in a lacustrine environment with salinity variations.