Relationship of Sea Level Changes and Intrabasinal Tectonics on Upper Cretaceous Depositional Sequences, Tremp Basin, Pyrenees, Spain

A. Simo

Well-exposed Upper Cretaceous rocks in the Tremp basin display the effects of subsidence and sea level changes. Subsidence and a net sea level rise control the sequence geometry and the cyclicity of transgressive-regressive units. In addition, subsidence, sea level, and sediment supply control the facies framework. The Tremp basin, where specific depositional processes can be related to basin evolution, is proposed as a reference section to compare tectonism vs. sea level changes.

Five depositional sequences recognized are seismic-stratigraphic in scale and are correlatives of global rhythms. Sequences are separated by unconformable or correlative conformable surfaces. Most of the surfaces in the area are concordant, characterized by a sharp transition upward from shallower to deeper facies. Sea level drops exposed the inner shelf but not the shelf margin; they did, however, result in submarine erosion and basin-restricted wedge deposition. The three oldest sequences are carbonate-rich. Each sequence exhibits very little coastal onlap; however, each successively younger carbonate platform backsteps the former. Thermal subsidence (6.3 cm/1,000 yr) created depositional space in the basin, and uplift reduced shelf onlap. The fourth sequence is carbonate-rich on th shelf and siliciclastic-rich in the basin. Subsidence first increased (shelf = 5.13 cm/1,000 yr; basin = 15.4 cm/1,000 yr) because of thrusting west of the area, resulting in coastal onlap over 60 km and accompanying backstepping of the carbonate platform. Subsidence later decreased, resulting in platform progradation. The fifth depositional sequence shows an overall siliciclastic regression, in response to regional thrusting and uplift.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.