Maastrichtian-Paleocene foreland-basin stratigraphies, western Canada: a reciprocal sequence architecture

Abstract

Palynological and magnetostratigraphic chronostratigraphic correlations of lower Maastrichtian to Paleocene strata along an east-west Western Canada Basin transect allow for the recognition of a reciprocal sequence architecture in nonmarine strata. Reference sections include three Canadian Continental Drilling Program Cretaceous-Tertiary Boundary Project core holes and outcrops in Alberta, southern Saskatchewan, and north-central Montana. The spatial and temporal position of the third-order sequences provides evidence for the correlation of proximal sector regional disconformities and sedimentary wedges with distal sector sedimentary wedges and regional disconformities, respectively. The boundary between the two sectors is represented by a hingeline, which separates the foreland-basin "syncline" from the "peripheral bulge." The stratigraphies defined by reciprocal third-order sequences are complicated by fourth-order boundaries, developed within proximal sedimentary wedges and with no correlative distal strata. These results support tectonic control on foreland-basin sedimentation. A model for interpreting the various types of sequences in terms of foreland-basin evolution, vertical tectonics, and orogenic cycles is provided. It is argued that nonmarine sequence boundaries (times of maximum uplift in the foreland region) may be expressed as disconformities, incised valleys, top of mature paleosol levels, or base of fluvial channels, whereas nonmarine equivalents of marine maximum flooding surfaces (times of maximum basinal subsidence) may be indicated by extensive coal seams and (or) lacustrine sediments.