ALLOCYCLIC CONTROL ON LATE DEVONIAN BUILDUP DEVELOPMENT, SOUTHERN CANADIAN ROCKY-MOUNTAINS

Parasequence stacking patterns in Upper Devonian Fairholme Group reef complexes of the southern Canadian Rocky Mountains suggest that deposi tion and buildup stratigraphy were controlled by superimposed short-te rm and long-term fluctuations in relative sea level. Correlation of th ese stacking patterns from one reef complex to another reveals a hiera rchy of fifth-order and third-order sea-level changes. The Flume platf orm and overlying Upper Cairn biostrome consist of meter-scale shallow ing-upward parasequences. These are interpreted to have been deposited during short-term, high-frequency (fifth-order) oscillations of relat ive sea level. Superimposed on this high-frequency cyclicity are large r, broadly shallowing-upward trends in which dominantly subtidal meter -scale parasequences or subtidal noncyclic intervals gradually (someti mes abruptly) pass upward into peritidal parasequences of comparable t hickness. These sequences are regionally correlative and are the produ ct of third-order driving mechanisms of extrabasinal origin. Collectiv ely, the Flume, Upper Cairn, and overlying Peechee members represent a single depositional sequence (sensu Vial et al. 1977). The various or ders of cyclicity are best developed in the eastern Main Ranges, where greater syndepositional subsidence allowed for increased sediment acc umulation. The development of entirely subtidal parasequences, and the regional correlation of larger-scale groups of vertically stacked sub tidal and peritidal parasequences, suggest a syndepositional allocycli c control on buildup development rather than an autocyclic one. Howeve r, large uncertainties in the calculated durations of both the high-fr equency parasequences and the larger-scale sequences, and assumptions inherent in the calculations, obscure the evidence for possible Milank ovitch control on the development of the Cairn Formation. Instead, Lat e Devonian differential subsidence related to the formation of the Ant ler flysch basin is invoked to explain the regionally correlative larg e-scale groupings of parasequences.