AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
An Ancient "Source-to-Sink" Example in Piggyback Basins, Pyrenean Fold and Thrust Belt
(1) ExxonMobil Exploration Co., Houston, TX.
(2) ExxonMobil Upstream Research Co, Houston, TX.
Middle Eocene (Lutetian) strata contained in piggyback basins of the Pyrenean Fold and Thrust Belt (PFTB) were studied to characterize a source-to-sink depositional system. These strata are used to: 1) refine sequence stratigraphic models linking continental, shelf and deepwater settings; 2) understand external controls on sediment flux; 3) evaluate the effect of multiple sediment entry points; and 4) construct a model for the interactions of depositional systems and growing compressional structures.
In the Lutetian, the PFTB comprised a series of small, linked basins that were connected to the Atlantic Ocean to the west. These basins formed in a piggyback setting during south-directed thrusting. East-west transitions between basins are defined by lateral ramps associated with thrusts. Deposition in these basins recorded the interaction of tectonics and sedimentation from fluvial/shelf EODs (Tremp Basin) to slope (Ainsa Basin) and basin (Jaca Basin). Sediment transport was both axial and transverse with respect to the major structural fabric of the PFTB.
In the early Lutetian, the lateral ramp of the Montsec thrust in the core of the Mediano anticline, formed a structurally-controlled shelf/slope transition between the Tremp and Ainsa basins. Strata of the Montañana Group (Tremp basin) include fluvial-shallow marine sediments transported to the WNW, as well as coarse-grained 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 that form a Lowstand Composite Sequence Set, capped by a Composite Maximum Flooding Surface. This MFS approximates a time of basin reorganization; the overlying Highstand deposits of the Sobrarbe deltaic complex were transported to the NNW, around and parallel to the Mediano anticline. Further west, the Boltaña Anticline marks the boundary between the Ainsa slope channel systems and the Jaca basin-floor fans. The timing and nature of basin reorganization, including the relationships between the oldest Sobrarbe delta-front channel systems and the slope channel systems observed at Ainsa, as well as the relationships between Ainsa channel systems and Jaca fans, are the focus of ongoing research. Additional work will address the regional to sub-regional linkage of marine environments, including contemporaneous clastic and carbonate EOD's, refine the sub-EOD architecture, and place these observations into a larger climatic/tectonic framework.