Predicting Early Cretaceous deepwater turbiditic successions in the offshore Aaiun-Tarfaya Basin, southern Morocco: constraints from new data from Fuerteventura

Abstract

This paper re-examines the sedimentology and biostratigraphy of the Early Cretaceous Main Clastic Unit (Steiner et al., 1998) exposed in Fuerteventura, and provides a correlation to the proximal equivalent of the system onshore Morocco, to assess the implications for the petroleum system and potential reservoir distribution.

Lower Cretaceous coarse clastic-dominated continental to shallow-marine successions are extensively exposed in the onshore Aaiun-Tarfaya Basin, Morocco. The deep-water distal counterparts of these systems are less well-documented, and only exposed on Fuerteventura, where they have been exhumed by tectonic uplift associated with volcanism. The studied section is dated as pre-late Berriasian based on previous work and the discovery of a well-preserved ammonite as part of this study. It is made of thin bedded clastic turbidites with occasional coarser and thicker bedded intervals exposed in a succession of overturned and sub-vertical outcrops, intruded by igneous bodies, with local repetitions of the succession due to tectonic folding.

Three large-scale cycles can be identified; two coarsening-upward, interpreted to represent the progradation of lower and middle lobes of a large submarine fan and an overall fining-upward cycle with increasing contribution of calciturbidites and limestone beds. The latter is interpreted to reflect the sea-level rise during Aptian and Albian times and the associated development of carbonates on the shelf, resedimented into the deep basin as calciturbidites.

The sand content in the lower part of the three cycles can reach up to 95 %, deposited as high density turbidites. This can be correlated with the low stand wedge seen in seismic, draping the older Jurassic carbonate platform. Detailed logging and new biostratigraphy further constrain understanding of these depositional systems and their evolution, helping to reduce uncertainty in exploration for these important reservoir systems that are targets for offshore exploration.