Punctuated Aggradational Cycles: A General Hypothesis of Episodic Stratigraphic Accumulation

According to the hypothesis of punctuated aggradational cycles presented here, the stratigraphic record consists of small-scale (1-5 m thick) shallowing-upward cycles (PACs) separated by surfaces marked by abrupt change to deeper facies. This motif, pervasive in time and environment, is produced by relatively long periods (tens of thousands of years) of base-level stability punctuated by geologically instantaneous relative base-level rises of at least basin-wide extent. As basin-wide lithologic time-stratigraphic units, PACs are fundamental to all aspects of stratigraphic analysis including correlation, paleoenvironmental interpretation, and paleogeographic reconstruction. Of several possible allogenic mechanisms for a pervasively cyclic stratigraphic record, glacial eustasy driven by orbital perturbations is preferred. The PAC hypothesis is presented as a comprehensive model to be tested and modified by examination of the stratigraphic record from an episodic perspective.