--> --> Abstract: Diachronous Rifting: A Model Built from Tectono-Stratigraphic Relationships for the Opening of the South Atlantic, by Steven G. Henry, Al Danforth, and Sujata Venkatraman; #90082 (2008)

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Diachronous Rifting: A Model Built from Tectono-Stratigraphic Relationships for the Opening of the South Atlantic

Steven G. Henry1, Al Danforth2, and Sujata Venkatraman3
1RIFTT, Las Cruces, NM
2Consultant, Houston, TX
3GX Technology, Houston, TX

Various models have been proposed for the South Atlantic opening which provided useful insights into possible responses of the crust and overlying basin formation. Regional deep reflection seismic data (16sec.) has been processed to provide pre-stacked depth migrated images, which are placing new constraints on rifting models. In this paper we will present a model of diachronous rifting based on the interpretation of these deep (15-25km) reflectors and tectono-stratigraphic relationships in the overlying basins.

Data from West Africa (CongoSPAN) and Brasil (BrasilSPAN), has imaged reflectors that have been used to interpret the base of the oceanic and continental crust (Moho), continental transition zone (CTZ), lower crustal reflectors, top continental basement, and most importantly the sediments within the overlying basins that record the tectonic history. The diachronous rifting model consists of a series of rifting events beginning in the Jurassic, a second attempt to separate the continents in the Valanginian, with the successful separation in the Barremian.

The failed attempts to separate are recorded in sag basins that can be large (100 x1000km, 3km thick) and can contain rich source rocks. Thicker (15-20km) sections of continental crust act as mini-cratons, and are onlapped by sag basin sediments. The relative ages of the rifting episodes have been determined using the stratal relationships between these highs and sag basins.

This diachronous model for the opening of the South Atlantic can be used to explain the apparent wide (150-200km) zones, long duration (75Ma)and modeled extreme stretching of the crust, as a series of more normal dimensioned (50-100km) rifts spread through time. The observed deep reflectors and overlying sediments are providing a data set that needs additional interpretation, and will continue generating new ideas on rifting.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery