An Eocene “Source-to-Sink” Example in Piggyback Basins, Pyrenean Fold and Thrust Belt, Spain
Abstract”
A well-exposed example of a source-to-sink depositional system was evaluated using Middle Eocene (Lutetian) strata contained in piggyback basins of the Pyrenean Fold and Thrust Belt (PFTB). The purpose of this study was 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 in a basin; and 4) construct a model for the interactions of depositional systems and growing compressional structures.
The Lutetian 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. Correlation of Lutetian strata throughout the depositional system was accomplished with extensive biostratigraphic analyses, as well as outcrop interpretation and mapping. Integration of published PFTB structural reconstructions allows a better understanding of the response of depositional systems to growing compressional structures.
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 mid-Lutetian 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.
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Jeffrey Geslin, Ph.D.
Geologist and Geophysicist
Jeffrey Geslin is a consultant and educator living in Durango, Colorado. He received his Ph.D. in geology from the University of California Los Angeles in 1993 after completing geoscience degrees from the University of Northern Colorado (BA) and Idaho State University (MS). Jeff held post-doctoral research positions with the USGS and Idaho State University before joining ExxonMobil in 1998. At ExxonMobil, Jeff held positions across the upstream, from research to exploration and production. He worked on projects in numerous locations globally, including southeast Asia, west Africa, eastern Canada, and eastern Russia. Jeff held several technical and managerial positions at ExxonMobil, and most recently was the corporation’s Senior Technical Consultant in Stratigraphy. He retired from ExxonMobil in late 2018. He is now the owner of Pictured Cliffs Geoscience LLC, and an Adjunct Professor of Geology at Fort Lewis College.
Jeff’s technical interests include: 1) Petroleum geology, specifically reservoir performance evaluation, stratigraphic controls on play elements, acreage and prospect evaluation, integrated conventional production activities, and stratigraphic controls on unconventional reservoir performance; 2) Sequence stratigraphic evaluation of clastic strata, including fluvial, shallow-marine and deep-marine environments; 3) Applied geophysics (seismic interpretation and seismic sequence stratigraphy); and 4) Teaching, advising and mentoring geoscientists. Jeff has published over 60 articles, abstracts and technical reports.