Pau Arbués¹, Santiago Sánchez-Villanueva², Marta Puig², Mariano Marzo², Josep Anton Muñoz²

(1) University of Barcelona, Barcelona, Spain
(2) University of Barcelona, Spain

ABSTRACT: The role of growing anticlines on the evolution of a turbidite channel complex: The Gerbe-Banaston system (Eocene Ainsa slope complex, Spanish Pyrenees)

The Gerbe-Banaston system occurs as the basal fill of one of the major canyon-like depressions carved by slumping during episodes of thrust induced oversteepening in the Ainsa foredeep. The geometry of the system is that of a rhomboidal prism being 870 m thick and up to 5 km wide. The preserved length of the system is over 22 km. The base and top correspond to angular unconformities; the margins occur as pinch-out onto hemipelagic slope mudstones or as sidelap onto canyon walls. Field-mapping (1:12,500) distinguished facies associations which correspond to: 1) channels filled largely with intraformational conglomerates, 2) channel-fills made of thick-bedded sandstone, 3) channel-margin and splay deposits, mostly thin sandstone/mudstone beds; 4) mudstone-dominated slump deposits and 5) slump and debris flow deposits made of limestone clasts. A transverse section across the system displays: 1) lateral migration of the depositional axis of the system, caused by rotation along the forelimb of a nearby growing anticline and 2) changes in facies and size, which can be explained as the response to cycles of relative fast/slow forelimb rotation. The dip section involves changes in net to gross, from 20% sandstone in the updip to 80% sandstone in relatively distal localities, which was caused by the downdip widening of the container canyon into an area where intrabasinal anticlines had not developed yet. We document these 3D relationships and discuss the transport, deposition and tectonic processes responsible for the thickest turbidite sandstone accumulation in the Ainsa basin.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado