Ocean Drilling Program, United States

On Ocean Drilling Program Leg 149, a transect of drill sites across the ocean/continent transition along the western margin of Iberia recovered Mesozoic synrift to Cenozoic postrift sedimentary sequences above a series of basement highs. Sand detrital modes were determined for samples taken from Jurassic to Pleistocene sandy turbidite layers from these sites. The terrigenous sand recovered on ODP Leg 149 is predominantly quartzofeldspathic with a lesser metamorphic and sedimentary lithic component. There appears to be a distinct link between grain size and composition within the Cenozoic samples, probably resulting from a combination of transport and depositional history. Fine sand detrital modes reflect the overall passive margin, rift-to-drift evolution and show a crude basement unroofing trend from the Mesozoic to the Cenozoic. The detrital modes of Cenozoic very fine sand are a function, to some degree, of a superposed regional compressional tectonic event that resulted in a minor increase in metamorphic lithic content during the Oligocene and Miocene, perhaps associated with enhanced uplift on the adjacent Iberian Peninsula. Overall, results from this study provide a preliminary model for passive margin sand provenance.