Submarine Troughs: Examples from Deepwater Campos Basin, Offshore Brazil

Alexandre A. Grassi, Mario Carminatti, and Paulo de Tarso M. Guimaraes
Petrobras, Rio de Janeiro, Brazil

Analysis of 3-D seismic data, well logs and cores in Upper Paleocene of Campos Basin ultra-deep water (> 2000m) reveals the occurrence of very conspicuous and spectacular submarine troughs in slope-to-basin regions genetically associated with a huge volume of conglomerates supported by a coarse shell rich sandy matrix and massive thick-bedded sandstones deposits, which can not be classified as a classic deep-water turbidities depositional system. In this work we discuss sedimentary and morphological aspects which characterize the main elements of this depositional system, by focusing on: (1) submarine troughs morphology which are narrow (1-6km wide), deep (100-500m thick) and elongate (at least 180km); (2) unclear submarine trough-lobe transition zones; (3) main sedimentary facies. The character of Campos Basin Paleocene submarine troughs is outstanding and unique. Their origin is probably related to local tectonic uplift of the nearby Serra do Mar Range and associated alkaline magmatism during the Paleocene. A tectonically forced lowstand interconnected to climate instabilities is interpreted as the main scenario in which catastrophic events generated sedimentary gravity flows deposits in the slope and basin regions. Those deposits have been considered as important exploratory targets in deep and ultra-deep water regions.