Upper Devonian Catskill Delta margin cyclic sedimentation: Brallier, Scherr, and Foreknobs Formations of Virginia and West Virginia

Abstract

This study documents the applicability of the PAC hypothesis to the clastic sediments of the Upper Devonian Catskill Delta sequence in Virginia and West Virginia. Detailed studies of the type sections of the Back Creek Siltstone Member of the Brallier Formation, the Minnehaha Springs Member of the Scherr Formation, and the Foreknobs Formation show that the deposition of these sequences was strongly influenced by astronomically controlled sedimentary cycles with a dominant 100,000-yr period and superimposed 40,000- and 20,000-yr variations. Estimated water depths during the deposition of the Foreknobs Formation vary from 0–50 m and show an over-all shoaling trend as average uncompacted sediment accumulation rates increased from ∼40 to 140 cm/1,000 yr during the 2-m.y. duration of deposition of the formation. Deposition of the Foreknobs Formation appears to have been influenced by 413,000-yr variations due to eccentricity, and possibly by a 2.0-m.y. duration eccentricity cycle. All of these variations, in turn, are superimposed on the pulse of sedimentation and basin filling produced by the third tecto-phase of the Acadian orogeny.