Melick, Jesse John¹, Giovanni Benevelli¹, Giorgio Cavanna¹, Roberto Tinterri¹, Emiliano Mutti¹ 
(1) University of Parma, Parma, Italy

ABSTRACT: The Lutetian Aínsa Sequence: An Example of Small Turbidite Systems Deposited in a Tectonically-Controlled Basin

The Lutetian Aínsa Sequence crops out in the south-central Pyrenees and constitutes the stratigraphically lowermost portion of the fill of a Lutetian to Priabonian piggy-back basin situated between two oblique-ramp anticlines (Mediano and Boltaña). The Aínsa Sequence, bounded by distinct unconformities related primarily to thrust propagation, comprises five smaller-scale depositional sequences (for simplicity herein termed units), each recording a southerly-fed forestepping-backstepping episode of turbidite sandstone deposition. These forestepping-backstepping sandstone units (100-400 m thick by 5-6 km wide) formed in a highly tectonically mobile basin, which experienced migration of markedly asymmetric depocenters. Within each unit, channelized deposits grade over very short distances into depositional lobes confined within structural depressions. Cross-current facies changes observed in these lobes highlight the very complex interaction between bipartite turbidity currents and basin topography. In particular, the denser portion of each turbidity current is forced to deposit coarse-grained and extensively scoured sandstone and pebbly-sandstone facies near the steeper margin of the asymmetric depression, whereas the overlying dilute and turbulent part of the same current continues and can climb the more gentle margin, depositing thin beds of fine-grained sandstone and mudstone. Because of its tectonic context and internal architecture, the Aínsa Sequence provides and excellent analog for many intra-slope basins of divergent continental margins associated with salt tectonics.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.