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Abstract: Megaflute Surfaces in Channelized Turbidite Systems: Their Nature, Genesis and Significance

Elliott, Trevor - University of Liverpool

Widespread erosion surfaces characterized by large, flute-like scours and overlain by fine-grained facies are a prominent and distinctive feature of a sand-rich Upper Carboniferous turbidite system in western Ireland. These surfaces are traceable for >1000m laterally, display erosional relief of up to 5m and are locally ornamented by megaflutes that are 1 m to several 10?s m across. The surfaces erode underlying turbidites and are overlain by 1 m thick units of fine-grained facies that onlap the erosional surface. Megaflute surfaces can be traced into deeper erosional surfaces that define sandstone-filled turbidite channels whereupon it becomes clear that the megaflute surfaces define laterally extensive wings to the channels. Wings are characterized by an upwards thickening trend composed of the fine-grained onlapping facies and an overlying unit of amalgamated turbidites that links laterally to the upper part of the channel fill. Megaflute surfaces define discrete periods of widespread turbulent erosion during which a new generation of turbidite channels is created. Once formed the channels provide a pathway for subsequent, smaller volume turbidity currents whilst the flanking, raised sectors of the megaflute surface receive predominantly fine-grained sediment via overbank and flow stripping processes. As the channels fill, subsequent turbidity currents are more prone to overbank spilling and create the channel wings that overlie the megaflute surfaces. The surfaces, are an integral part of the evolution of the turbidite system and contribute to its reservoir architecture in establishing a high resolution correlation framework and defining important permeability barriers.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil