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Depositional Architecture of a Sand-Rich, Channelized Turbidite System: The Upper Carboniferous Ross Sandstone Formation, Western Ireland

By
Trevor Elliott
Trevor Elliott
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Published:
December 01, 2000

Abstract

The Ross Sandstone Formation is a 380m thick sand-rich turbidite system deposited in an intracratonic basin during a period of ca. 500,000 years. In overall terms, the system has a net aggradational/progradational trend, but this trend has been interrupted repeatedly by glacially-forced fluctuations in sea level that produced a series of condensed sections and interpreted sequence boundaries. Sheet-like turbidites, turbidite channels, megaflute surfaces, mudstone-filled gullies, and slides/slumps are recognised in the turbidite system. Channels dominate the mid to upper parts of the system and show considerable variability. The most widely developed type is a sandstone-dominated channel which comprises two sectors: (1) a locally developed channel axis defined by a master basal erosion surface; and (2) laterally extensive channel wings that overlie megaflute erosion surfaces that flank the channel axis. Channel axes are dominated by massive, highly amalgamated turbidites whereas the equivalent channel wings comprise turbidites having varying degrees of amalgamation and a pronounced thickening upwards trend above the megaflute erosion surface. This trend records the late expansion phase of the channel that followed initial aggradational filling of the channel axis. The ratio of channel axis to channel wing is around 1:10 minimum, resulting in a dominance of sheet-like, channel wing bedsets bounded by megaflute erosion surfaces. Vertically stacked channel wings can be correlated using megaflute erosion surfaces that are laterally extensive and link with axial erosion surfaces.

Sinuous, meandering turbidite channels characterized by lateral accretion surfaces also are recognized. The prime example is 7.5 m deep, 130 m wide, and migrated laterally to produce a meander belt 380m wide, giving a channel width to meander belt ratio of 1:3. Most of the channels in this turbidite system are single-story, but a sandstone-dominated, compound channel is recognized towards the top of the succession. Permeability barriers and baffles in the turbidite system comprise a hierarchical series in terms of lateral extent and potential effectiveness.

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Contents

GCSSEPM

Deep-Water Reservoirs of the World

Paul Weimer
Paul Weimer
Houston, Texas
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SEPM Society for Sedimentary Geology
Volume
20
ISBN electronic:
978-0-9836097-0-4
Publication date:
December 01, 2000

GeoRef

References

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