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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Intl. Symposium of the Devonian system: Papers, Volume II, 1967
Pages 1089-1099
Clastics

Sedimentation and Tectonic Setting of the Old Red Sandstone of southwest Ireland

D. Naylor, P. C. Jones

Abstract

In tectonic setting, geometry and environment of deposition, the Old Red Sandstone rocks of southern Ireland (probable equivalents of rocks in the Upper Old Red Sandstone Division of Britain) display many of the features of a molasse deposit. A non-marine sequence of coarse and fine clastics, exceeding a thickness of 20,000 feet, accumulated in an elongate trough which trended east-west across southwest and south-central Ireland, and developed on the folded terrain of the Caledonides. Sediment was derived from a tectonically active area to the north, and the axis of maximum subsidence lay near the northern margin of the basin, with the result that the body of sediments is strongly asymmetric in cross section. Conglomerates are abundant in the northern part of the basin, and the sequence becomes finer southward and upward in the section.

During Late Devonian time, much of southern Ireland formed a plain of low relief on which a sequence of fine sediments was deposited in lacustrine and flood-plain environments. In Cork Harbour a sequence of red and green beds shows well developed cyclothems beginning with channel-fill sandstones and culminating with a relic soil bed. Comparison with other stratigraphic models and present-day environments suggests that the cycles are a result of point-bar migration. The sequence correlates with a marine, possibly deltaic, succession to the south which has yielded a fauna of Famennian age.

A similar transition from non-marine red beds southward to a shallow-water marine sequence is revealed by coastal exposures farther west. Thus, at the end of Devonian time, marine conditions had transgressed northward onto the Old Red Sandstone continent approximately to a line joining the mouth of Cork Harbour to Glengarriff in west Cork.


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