Devonian Transgressive-Regressive Cycles and Biostratigraphy, Northern Antelope Range, Nevada: Establishment of Reference Horizons for Global Cycles

Abstract

The physical boundaries of global Devonian transgressive-regressive (T-R) cycles are located for the first time at reference sections in central Nevada. Early Devonian (Pragian and Emsian), deepening events defining T-R cycle bases resulted in deeper subtidal facies overlying peritidal or shallow subtidal facies. Middle and earliest Late Devonian deepening events resulted in slope facies overlain by basinal facies, or deep ramp overlain by basinal facies (with or without interbedded debris flows). Brachiopod and coral biofacies changes reflect these deepening events. Environmental change also affected conodont diversity, which is highest in slope or slope-derived deposits. Icriodus is poorly represented or absent in basinal facies in the Middle Devonian of central Nevada. Conodont zonal correlations for the defining deepening events are: Ia, base of sulcatus Zone; Ib, approximately base of dehiscens Zone; Ic, high in serotinus Zone; Id, mid costatus Zone revised from low in australis Zone; Ie, mid kockelianus Zone; If, upper ensensis Zone; IIa, in Middle varcus Subzone; IIb, approximately base of norrisi Zone. The deepening event at the base of the Woodpecker Limestone in Nevada is at the base of T-R Ie, revised downward from the base of T-R If. It correlates with the Delaware-Oatka Creek deepening in Ohiomore » and New York. The basal T-R Ie deepening also correlates with the base of the Kacak Member of the Srbsko Formation, Bohemia, and with a level immediately above the top of the Man Member of the Gustalapiedra Formation, northwest Spain. 34 refs., 5 figs., 2 tabs.« less