Dados da Submissão

Título

INTRASLOPE ACCOMMODATION CONTROLLED BY SALT TECTONICS AND MASS TRANSPORT DEPOSITS IN THE EXTENSIONAL SALT DOMAIN OF CAMPOS BASIN

Texto do resumo

The study of the stratigraphic evolution of deep-water systems in intraslope depocentres of passive margin salt basins has focussed on confined minibasins dominated by contractional salt tectonics. In contrast, few studies document the changing accommodation and evolution of deep-water systems in intraslope depocentres in areas dominated by extensional salt tectonics or with both extensional and contractional salt tectonics. This limitation is here addressed through the investigation of a Cenozoic intraslope depocentre flanked by salt-cored structures in the distal extensional salt domain of Campos Basin. Seismic mapping and well data analysis were carried out to understand the large-scale controls on depocentre configuration, and the local-scale controls on accommodation affecting the evolution of a 150 m thick succession composed of intercalated mass transport complexes and sand-rich turbidite units. The external configuration of the intraslope depocentre was controlled by salt-cored structures at the edges of an underlying carbonate raft. These structures formed during extension but were reactivated by extension and contraction, creating seabed topography. The partial fragmentation of the raft induced the formation of an elongate salt-cored structure in the middle of the depocentre, which also accommodated contraction through inversion and uplift and, at other times, extension through subsidence. Thickness variations and architectural changes during the evolution of the deep-water succession are evident above this structure. Thinning and thickening of the mass transport complexes and turbidite units are interpreted to record deformational phases, reflecting the alternation of contraction and extension. In addition, changes in the depositional architecture related to loss of confinement (submarine channels to lobes) within an elongate trough during the deposition of the lower turbidite unit suggest a topographic control and subsidence imposed by the same structure. On the other hand, two smaller depocentres formed upstream of the same salt-cored structure during the deposition of the upper turbidite unit. This suggests a positive topography, here related to the uplift of this structure. In addition, the load of the lowermost mass transport complex is interpreted to have led to a transient increase on subsidence rates by compaction and amplification of the ongoing slope deformation. This also impacted accommodation patterns during the evolution of the older turbidite unit. Conversely, small- and large-scale rugosity at the top surface of the younger mass transport complex is a secondary control on accommodation affecting the upper turbidite unit. In conclusion, the evolution of the salt-cored structures at the fragmented area of the raft and the emplacement of large-scale mass transport complexes had a major impact on accommodation, which controlled local depocentres and depositional architecture, while the salt-cored structures at the edges of the raft controlled the formation and geometry of the larger depocentre. This study highlights complicated tectonic-sedimentary interactions in a deep-water succession controlled by the alternation of extension and contraction, and mass transport complexes emplacement. The work focuses on the impact of these controls on the evolution of an intraslope depocentre formed in the extensional salt domain during a mature phase of passive margin evolution, an overlooked setting in salt basins.

Palavras Chave

intraslope depocentres; deep-water systems; salt tectonics; Campos Basin