Mud diapirs in a continental extensional basin: 3D seismic interpretation of the Central Recôncavo Basin (northeast Brazil)

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 in northeast 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 nonexistent in the northeast sector. The 3D seismic, outcrop, and well data are used to geomorphologically characterize the onshore mud diapirs in the central 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. After seismic interpretation, four mud diapirs are identified in the study area: Apraius-Miranga Norte, Pedra do Salgado, Biriba, and Carijó. Two internal seismic facies are identified as F1 and F2, with F1 having more disruptive features and F2 being more reflection-free. The eastern diapirs, close to the border fault conglomerates, are dominated by disrupted seismic facies (F1). The diapiric movement is associated with paleoseismicity and the rupture of an ancient delta front, together with the rapid basinward advancement of conglomerates during an active rifting phase. The Biriba diapir is possibly the first to arise, followed by Carijó and Apraius-Miranga Norte, and finally, Pedra do Salgado; this variable timing influences the location and migration of the depocenters in the area.