ABSTRACT: Recognition of Eustatic Control on Sequence Development Around the Late Cambrian Pericratonic Platform

D. A. Osleger, J. F. Read

Several orders of cyclicity can be recognized within Late Cambrian carbonates of the Cordilleran and Appalachian passive margins, the Texas cratonic embayment, and the incipient southern Oklahoma aulocogen. Interbasinal correlation suggests that several roughly synchronous third-order sequences exist in all four locations, strongly suggesting a eustatic control. The sequences are 2-6 m.y. long and consist of (1) an erosional or, more commonly, a conformable sequence boundary, (2) a basal thin transgressive internal exhibiting multiple hardgrounds, glauconite, and other evidence of suppressed sedimentation and incipient drowning, (3) an interval of maximum flooding, usually composed of meter-scale shale- or mudstone-based cycles or noncyclic fine-grained limestones, and (4 highstand grainstone- and boundstone-dominated meter-scale cycles.

Graphic correlation of the sequences reveals a good degree of synchroneity between the four locations. Both sequence boundaries and intervals of maximum flooding can be correlated, implying a strong eustatic control to sequence development. Subsidence modeling indicates two distinct orders of synchroneity: a long term (>70 m.y.) interval that corresponds to the Sauk sequence and a third-order scale that corresponds to six distinct 2-6-m.y. sea level events further supporting a eustatic origin. Only in the southern Oklahoma aulocogen is a tectonic influence recognized where small-scale cyclicity becomes indistinct but longer term sequences can still be identified. Two-dimensional computer modeling is helping to define potential rates and amplitudes of sea level fluctuations that sim late sequences developed in each of the tectonic settings. Differences in shelf morphology, antecedent topography, and driving subsidence appear to be critical variables in the development of individual sequences.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990