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"Source-to-Sink" in a Thrust/Foreland Setting: Middle Eocene South Pyrenean Foreland Basins

Abreu, Vitor 1; Geslin, Jeff 1; Demko, Tim 2
1 ExxonMobil Exploration Company, Houston, TX.
2 ExxonMobil Upstream Research Company, Houston, TX.

The objectives of this study are to refine and develop sequence stratigraphic models linking continental, shelf and deepwater settings, and to understand the external controls on sediment flux from continent to basin, focusing on when and where sediment is stored in shelf environments, and when and how it is transported to deepwater.

The well-exposed outcrops of the Pyrenean foreland basins (PFB) in northern Spain offer a unique opportunity for a source to sink analysis in a thrust/foreland setting. In early Lutetian time (Middle Eocene), this area comprised a series of linked basins that were connected to the Atlantic Ocean to the west. These basins were formed due to the interaction of the African and European plates with the Iberian micro-plate during the Cenozoic, resulting in south-directed thrusting. The middle Eocene deposition in the PFB recorded the interaction of tectonics and sedimentation from shelf (Tremp Basin) to slope (Ainsa Basin) and basin (Jaca Basin). At that time, deposition was in piggy-back (wedge top) basins as the fore-deep moved to the South.

The lateral ramp of the Montsec thrust, in the core of the Mediano anticline, formed a structurally-controlled shelf to slope transition between the Tremp and Ainsa basins. Lutetian sediments of the Montañana Group in the Tremp basin include fluvial-deltaic sediments transported to the west-northwest, as well as coarse-grained alluvial fan deposits shed to the south off of the Pyrenean axial zone. The Montañana Group is coeval to 4 deepwater composite sequences in the Ainsa Basin: Gerbe-Banaston, Ainsa, Morillo, and O’Grau. They form a Lowstand Composite Sequence Set that is capped by a Composite Maximum Flooding Surface, which could represent basin reorganization. This MFS separates these sequences from the overlying Highstand deposits of the Sobrarbe Deltaic Complex, composed of seismic-scale (~150-250m) clinoforms. The Boltaña Anticline marks the boundary between the Ainsa slope channel systems and the Jaca basin-floor fans. The genetic and stratigraphic relationships between the oldest Sobrarbe delta-front channels and the larger slope channels observed at Ainsa, as well as the Ainsa channels and Jaca fans are the focus of ongoing research.

This research will enable us to not only address the regional to sub-regional linkage of marine environments and fine-scale sub-EOD architecture, but also to place these observations into the larger climatic and tectonic framework.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009