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Book Chapter

Middle to Outer Shelf

Published:
January 01, 1991

Abstract

The sediments of the Moyvoughly Beds within the Moyvoughly-Moate area of the Irish Midlands comprise ooid grainstones, skeletal ooid grainstones, and marine sandstones, punctuated by rarer calcareous mudstones. These sediments were deposited in agitated environments on a gently sloping south- or southeast-facing ramp. Core investigations and construction of isopach maps have shown changes of thicknesses within individual sedimentary units across known faults. These are interpreted as the result of synsedimentary faulting during sediment deposition. Changes in sediment lithologies can be related both to relative changes in sea level plus faulting activity, with the sandstones being sourced from erosion of local, active, fault-bounded highs. Relative sea-level highs are characterized by calcareous mudstones, with periods of lower sea level being characterized by grainstones or sandstones dependent on local siliciclastic sourcing. No major sequence breaks have been recognized with the Moyvoughly Beds. However, a regional change in sedimentation occurs at the base of the Moyvoughly Beds, where corals colonized the lithified surface of the underlying Micrite Unit. These lower sediments were deposited in a shallow lagoon, with periodic marsh progradation and subsequent exposure with paleosol formation. The Micrite Unit can be traced across the Irish Midlands and, although no regional detailed studies have yet been carried out, appears to be of similar lithologies throughout. In contrast, units within the Moyvoughly Beds, although correlatable within the area studied, cannot be traced to other areas, and their characteristics are more controlled by local tectonic movements.

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Contents

SEPM Core Workshop Notes

Mixed Carbonate-Siliciclastic Sequences

Anthony J. Lomando
Anthony J. Lomando
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Paul M. Harris
Paul M. Harris
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SEPM Society for Sedimentary Geology
Volume
15
ISBN electronic:
9781565762695
Publication date:
January 01, 1991

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