ABSTRACT

Parasequence stacking patterns in Upper Devonian Fairholme Group reef complexes of the southern Canadian Rocky Mountains suggest that deposition and buildup stratigraphy were controlled by superimposed short-term and long-term fluctuations in relative sea level. Correlation of these stacking patterns from one reef complex to another reveals a hierarchy of fifth-order and third-order sea-level changes.

The Flume platform and overlying Upper Cairn biostrome consist of meter-scale shallowing-upward parasequences. These are interpreted to have been deposited during short-term, high-frequency (fifth-order) oscillations of relative sea level. Superimposed on this high-frequency cyclicity are larger, broadly shallowing-upward trends in which dominantly subtidal meter-scale parasequences or subtidal noncyclic intervals gradually (sometimes abruptly) pass upward into peritidal parasequences of comparable thickness. These sequences are regionally correlative and are the product of third-order driving mechanisms of extrabasinal origin. Collectively, the Flume, Upper Cairn, and overlying Peechee members represent a single depositional sequence (sensu Vail et al. 1977). The various order of cyclicity are best developed in the eastern Main Ranges, where greater syndepositional subsidence allowed for increased sediment accumulation.

The development of entirely subtidal parasequences, and the regional correlation of larger-scale groups of vertically stacked subtidal and peritidal parasequences, suggest a syndepositional allocyclic control on buildup development rather than an autocyclic one. However, large uncertainties in the calculated durations of both the high-frequency parasequences and the larger-scale sequences, and assumptions inherent in these calculations, obscure the evidence for possible Milankovitch control on the development of the Cairn Formation. Instead, Late Devonian differential subsidence related to the formation of the Antler flysch basin is invoked to explain the regionally correlative large-scale groupings of parasequences.