ARBUES, PAU¹, JORDI CORREGIDOR² , CAI PUIGDEFABREGAS³, JOSEP ANTON MUNOZ¹, and MARIANO MARZO^1
1Univ. Barcelona, Spain
²Barcelona, Spain
³Institut Jaume Almera, CSIC, Barcelona, Spain

Abstract: Anatomy and Evolution of the Tectonically-Control led Ainsa Slope System. Eocene, South-Pyrenean Foreland Basin, NE Spain

During the Eocene the Ainsa basin accommodated an alluvial to slope clastic wedge about 4,000 m thick, 40 km long and 30 km wide. The slope and shallow marine components of the tract are dissected by at least three truncation surfaces, of basinal scale, that represent degradational slopes moulded by submarine mass wasting. The cause of generalised slope unstability and collapse is tectonically driven overstepening, promoted by increasing thrusting rates and concurrent flexurealong the active and passive basin margins respectively. The truncation surfaces play a role on dividing the basin fill as four main depositional cycles, each spanning 2-5 Ma.

The slope system within each cycle evolves upwards from: a backstepping slump complex, that onlaps the basal truncation, to a thicker (cf. 800-1,000 m) and prograding slope prism, consisting of thinly laminated mudstone and coarser grained turbidite lithosomes that correspond to intra-slope valleys and channel elements.

Further genetic stratigraphic subdivision of the slope is based on condensed sections and local unconformities. Within such genetic units, valley and channel fill elements are more abundant upwards. It is suggested that this organisation level is still recording thrust episodes, whereas higher frequency cyclicity better responds to autogenic processes.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas