Jurassic tectono-sedimentary evolution of the northern lusitanian basin (offshore portugal)

摘要

The Lusitanian Basin is one of a series of rift-related basins developed during the rifting that led to the break-up of Iberia and Canada. The strong influence of halokinesis on the depositional evolution of its northern sector provides an analogue for the development of other evaporite-prone rift basins on Atlantic-type passive margins. In this paper, the pre-Valanginian evolution of the Northern Lusitanian Basin is documented based on regional seismic stratigraphy, isochron and time-structure maps tied with sonic and stratigraphic data from 10 exploration wells. The pre-salt structure of the study area is marked by two sets of faults: (i) a N-S to NE-SW striking set active throughout the Jurassic period and (ii) a NW-SE striking set active during the Late Jurassic. The latter defines five Late Jurassic sub-basins northeast of a basin-margin structure, the Marinha-Grande Fault. The development of half-graben basins in the Northern Lusitanian Basin during the Jurassic was overprinted by halokinesis over the Marinha-Grande Fault and other major marginal basement faults. Halokinesis climaxed during the Oxfordian-Kimmeridgian rifting with the formation of a 10 km long salt ridge over the Marinha-Grande Fault. The ridge limited the southward progradation of fluvial/deltaic units derived from hanging-wall drainage systems and restricted the syn-rift sediments to a 15 km long X 5 km wide bowl-shaped depocentre located 10 km west of the present coastline. In order to better characterise the Jurassic tectono-sedimentary evolution of the Northern Lusitanian Basin, the interpreted seismic data is compared with physical models for extensional forced folds above active normal faults and with stratigraphic information from well and outcrop.