Role of Stratigraphic Discontinuities in Episodic Development of Paleogeography, Helderberg Group, Central Appalachians

Peter W. Goodwin, Edwin J. Anderson

The Lower Devonian Helderberg Group is segregated into paleogeographically significant packages by stratigraphic discontinuities at two scales. All stratigraphic sections are completely divisible into punctuated aggradational cycles (PACS) whose boundaries are synchronous stratigraphic discontinuities produced by rapid sea level rises that recurred at intervals of thousands or tens of thousands of years. Environmentally disjunct facies were superimposed basin-wide at each PAC boundary. Facies within PACs represent a continuous spectrum of paleoenvironments that coexisted and evolved through aggradation. At a larger scale, correlation of PACs reveals cryptic unconformities with a recurrence interval of hundreds of thousands of years. At these stratigraphic discontinuities, PACs are locally or regionally missing as a result of nondeposition or erosion associated with major sea level falls (and subsequent rises). Large basin-wide facies changes across these discontinuities indicate major reorganizations of paleogeography. Therefore, Helderbergian paleogeography developed episodically in response to allogenic stratigraphic events at two scales and two frequencies. Recognition of the paleogeographic significance of these allogenic events emphasizes the need to distinguish between stratigraphic and sedimentologic processes in stratigraphic analysis. Facies architecture and paleogeographic patterns were determined by stratigraphic processes, not sedimentologic processes, and therefore require stratigraphic models for interpretation.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.