ABSTRACT: Sea Level Control on Platform and Basin Development, Upper Devonian of Western Canada
David J. McLean
The geometric and sedimentologic relationships between buildup margins and their flanking basin sediments in the Rocky Mountains suggest that superimposed short-term and long-term sea level fluctuations controlled buildup stratigraphy. Preliminary correlation of cycle stacking patterns from one margin to another reveals an ordered hierarchy of possibly three magnitudes of sea level change: tentatively fifth, fourth, and third order.
The Flume platform and overlying upper Cairn biostrome consist of meter-scale shallowing-upward cycles. These cycles are interpreted to have been deposited during short-term high-frequency (fifth-order?) sea level oscillations. Superimposed on this high-frequency cyclicity are larger, broadly shallowing-upward trends in which dominantly subtidal meter-scale cycles gradually pass upward into peritidal cycles of comparable thickness. These intermediate cycles (tens of meters thick) may represent fourth-order eustasy. The Flume, upper Cairn, and overlying Peechee members, together with their time-equivalent basin-filling strata, represent low-frequency, third-order depositional sequences. The various cycles are best developed in the Main Ranges, where greater subsidence allowed for incre sed sediment accumulation.
Abrupt margins are common to all localities investigated. At least three major episodes of fourth-order sea level rise (backstepping), punctuated by relative stillstands (prograding tongues of stromatoporoid rudstone into Perdrix basin shales), dominated middle Frasnian Peechee sedimentation. Pervasive dolomitization prohibits resolution of finer scale cycles. Onlap of the Peechee buildup margins by overlying Mt. Hawk argillaceous limestones and shales indicates an important basin-filling episode during a probable stillstand and/or lowering.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990