Mass transport complexes and tectonic control on confined basin-floor submarine fans, Middle Eocene, south Spanish Pyrenees
Published:January 01, 2005
Kevin T. Pickering, Jordi Corregidor, 2005. "Mass transport complexes and tectonic control on confined basin-floor submarine fans, Middle Eocene, south Spanish Pyrenees", Submarine Slope Systems: Processes and Products, David M. Hodgson, Stephen S. Flint
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The syn-tectonic deep-marine Ainsa fans (Eocene of the Ainsa basin, Spanish Pyrenees) were confined by lateral thrust ramps and influenced by intra-basinal growth anticlines. Mass transport complexes (MTCs) constitute a major component of the stratigraphy and represent an integral part of the evolution and depositional style of the deep-marine clastics. Using an integrated study of outcrop data from sedimentary logs and mapping, with core data from eight wells and micropalaeontological and palynomorph analyses, we demonstrate the lateral step-wise migration of sandy channelized submarine fans, as a foreland-propagating clastic wedge on a time-scale of hundreds of thousands of years. The deep-marine expression of the inferred tectonic pulses began with the large-scale basin-slope collapse as sediment slides and debris flows that formed much of the seafloor topography for each fan and contributed to their lateral confinement. The uppermost slope and any shelf-edge, including the narrow shelf, then collapsed, redepositing unconsolidated sands and gravels into deep water. This is overlain by an interval of mainly channelized and amalgamated sandy deposits, passing up into several tens of metres of less confined, non-amalgamated, medium- and thin-bedded, finer grained sands and marls. These deposits represent the phase of most active fan growth, initially by erosional channel development, sediment bypass and backfill (in several cycles), giving way to non-channelized, finer grained sandy deposition, interpreted as a response to the flushing out of the coarser clastics from the coastal and near coastal fluvial systems. During this latter stage in active fan growth and when sediment accumulation rates probably remained high, the degraded submarine slope was regraded and healed by finer grained depositional events. The high amount of woody material and the high non-marine palynomorph signal in these sandy deposits suggest direct river input as both turbidity currents and hyperpycnal flows for the silty marls. In the upper few metres, a thinning-and-fining-upward sequence shows a return to background marl deposition, representing fan abandonment. Many sequences are overlain by intraformational sediment slides that attest to the increasing seafloor gradients associated with the regrading and healing stage in slope development. These organized, predictable vertical sedimentary sequences provide a testable generic model for submarine fan development where fan growth is strongly influenced by tectonic processes.
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Submarine Slope Systems: Processes and Products
Submarine slopes provide the critical link between shallow-water and deep-water sedimentary environments. They accumulate a sensitive record of sediment supply, accommodation creation/destruction, and tectonic processes during basin filling. There is a complex stratigraphic response to the interplay between parameters that control the evolution of submarine slope systems, e.g. slope gradient, topographic complexity, sediment flux and calibre, base-level change,tectonic setting, and post-depositional sediment remobilization processes. The increased understanding of submarine slope system has been driven partly by the discovery of large hydrocarbon fields in morphologically complex slope settings, such as the Gulf of Mexico and offshore West Africa, and has led to detailed case studies and improved generic models for their evolution. This volume brings together research papers from modern, outcrop and subsurface settings to highlight these recent advances in understanding of the stratigraphic evolution of submarine slope systems.