--> Abstract: Deconvolving Tectono-Climatic Signals in Deep-Marine Siliciclastics, Eocene Ainsa Basin, Spanish Pyenees: “Seesaw Tectonics” Versus Eustasy, by Kevin T. Pickering and Nicole J. Bayliss; #90082 (2008)

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Deconvolving Tectono-Climatic Signals in Deep-Marine Siliciclastics, Eocene Ainsa Basin, Spanish Pyenees: “Seesaw Tectonics” Versus Eustasy

Kevin T. Pickering and Nicole J. Bayliss
Department of Earth Sciences , University College London, London, United Kingdom

The Eocene deep-marine siliciclastic fill of the Ainsa basin, Spanish Pyrenees, gives unprecedented temporal resolution of the causes and timing of coarse clastic sediment supply to a deep-marine basin. Early Eocene tectonic subsidence linked to Pyrenean orogenesis created the Ainsa basin, with water depths of ~400-800 m above a foundered shallow-marine mixed carbonate / clastic shelf. The ~25 sandy channelized submarine fans in the basin were controlled by the ~400-kyr Milkankovitch frequency with modes, at ~100 kyr and ~41 kyr (possibly stacked ~23-kyr) influencing bottom-water conditions in the basin, causing periodic stratification in the water column across a submarine sill at the western basin margin (early Boltaña anticline). Intrabasinal tectonics defined and controlled the position of 8 sandy systems and their constituent fans, in a process of "seesaw tectonics" by: (i) Westward lateral offset-stacking of sandy fans due to growth of the eastern side of the basin, represented by the Mediano anticline, and (ii) Eastward (orogenwards) "back-stepping" of the depositional axis of each sandy system, due to phases of relative uplift of the Boltaña anticline. During basin infill, uplift of the Boltaña anticline led to increasing basin-narrowing and depositional-confinement. Unlike the earlier depositional systems, the youngest deep-marine system, was fed from a more southerly sediment source between the growth anticlines, as was the overlying deltaic system. All the older deep-marine sandy systems were fed from SE point sources, from "canyons" and erosional lower-slope channels eroding the growing Mediano anticline. The depositional style outlined in this presentation might be common to other active margins where siliciclastic basins evolve between active thrusts and/or other growth structures.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery