MICROFOSSILS IN ALBIAN TO CENOMANIAN FOREDEEP SETTINGS OF THE WESTERN INTERIOR SEA, CANADA: INTEGRATING BIOSTRATIGRAPHY FROM LITHOSTRATIGRAPHY INTO ALLOSTRATIGRAPHY

The Rocky Mountain Foredeep in eastern British Columbia and western Alberta preserves an expanded Albian to Cenomanian interval in outcrop and subsurface that documents a nearly complete sea-level record of the Western Interior Sea. Currently detailed foraminiferal subzonations are linked to the lithostratigraphic framework and cannot be correlated to areas of less accommodation space such as the forebulge. An extensive subsurface database in this region resulted recently in a new allostratigraphic framework that forms the basis for our new biostratigraphic correlations. Faunal changes can now be linked to allostratigraphic surfaces and vice versa. Lateral faunal assemblage distribution correlates remarkably well to allomember architecture. Missing zones can be explained by major erosional surfaces linked to basin topography and varying subsidence rates.

The Albian to Cenomanian foraminiferal assemblages in this region consist entirely of agglutinated species. As facies change, tests of certain tolerant species vary with grain size of their substrate resulting in intraspecific variability. In the past, this variability has led to great taxonomic confusion hampering biostratigraphic correlations. By combining a critical taxonomic review with the new allostratigraphic framework, we attempt to distinguish times of major faunal turnover from more subtle facies-related faunal changes. Results demonstrate that the Western Interior Sea in Canada was overall a shallow, but dynamic basin. During Albian time new faunal elements arrived with each major transgression resulting in rich and diverse assemblages. In contrast, Cenomanian paleoenvironments appear inhospitable and seem to be controlled by watermass properties such as low oxygen content.