Paleogeography and Basement Controls on the West-Central Mississippian Platform (WCMP) of North America

Richard Brandley
Rock Research Inc, Calgary, AB

Depositional systems allow reconstruction of Mississippian paleogeography across WCMP from central Montana to northeast B.C.. Depositional systems include Estuarine, Cool Restricted Marine, Warm Restricted Marine, Bank and Shoal Complex, Open Marine, Slope, and Basin. The first three generally represent nearshore to peritidal muddy deposits in variable water temperatures. The Bank and Shoal system represents high-energy wave and current swept carbonate sands, usually in cool to cold water. The last three represent grainy to muddy offshore deposition in cool to cold water. Much of the carbonate platform appears to be in depositional lock-step due to regional changes in relative sealevel. Superimposed on this regional pattern are local depositional and stratigraphic anomalies that cross-cut regional trends. Anomalies include oceanic embayments, depocenters, submarine canyon systems, protected areas east of island arcs, and areas subject to open-ocean upwelling and wave sweeping between offshore land masses. Correlations with potential field data indicate that both local anomalies and regional trends correspond with major, known, basement-tectonic elements. Thus, the paleogeography appears to be controlled largely by basement-tectonic structures. A fundamental tectonic element is the crustal-scale ramp that forms the western margin of the Mississippian craton. It is intersected by other basement-tectonic structures at high angles. These create local anomalies and divisions of the platform. The paleogeography and its controls are significant, as they shows that WCMP was in a tectonically active setting, on a relative geographic high, with offshore directed winds, both warm and cold water influences, and a complex interplay between offshore land masses and deposition.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005