SEDIMENT DISPERSAL DURING RIFT TO DRIFT TRANSITION IN THE CENTRAL NORTH ATLANTIC - INSIGHTS FROM U-PB-HE PROVENANCE DATA FROM THE LUSITANIA BASIN, PORTUGAL

The Iberian Atlantic continental margin and Newfoundland conjugate margin form one of the prototypical magma-poor continental margins. The Lusitania Basin unearths the record of the protracted history of Atlantic rifting related to the opening of the central Atlantic Ocean, Late Jurassic continental extension, and Early Cretaceous break-up in response to Grand Banks-Iberia separation. A stratigraphic succession of the western margin of the Lusitania basin (Atlantic coast of Portugal) exposes deposits related to post-Triassic thermal sag, Late Jurassic rifting, and Cretaceous break-up.

For this study, a siliciclastic succession between São Martinho do Porto and Nazaré that spans Kimmeridgian rifting to Albian-Cenomanian break-up was sampled for detrital zircon U-Pb and (U-Th)/He provenance analysis. Paleocurrent data show that sediment was sourced from the west (non-Iberian sources). Preliminary U-Pb-He data from composite samples along the coast of Portugal indicates an unroofing sequence of Variscan basement (~300 Ma) following Kimmeridgian deposits sourced from older Paleozoic crystalline rocks (~600 Ma). Kimmeridgian deltaic red beds deposited in areas of high accommodation that were generated during pre-rift extension yield a homogeneous U-Pb distribution of ~600 Ma grains. These data suggest a continuous source from Paleozoic basement rocks within the western fault block throughout the late Jurassic, possibly indicating pre-rift isolation from Newfoundland provenances. Better characterization of potential source regions is needed to further constrain this working hypothesis.

Fundamental questions remain regarding the timing of regional drainage network disruptions and source-to-sink dynamics during Grand Banks-Iberia separation. This study will lead to a better understanding of the multi-stage tectonic evolution of the Newfoundland-Grand Banks-Iberia magma-poor rift system as well as the prediction of Jurassic-Cretaceous reservoir distribution and quality in petroliferous rift basins of the central North Atlantic.