Reciprocal Architecture of Cambrian-Paleocene Sequences, Southern Canadian-Northern U.S. Western Interior

Octavian Catuneanu, Arthur R. Sweet, and Andrew D. Miall

The Claggett, Bearpaw, and Cannonball successions (Campanian- Paleocene) of the Western Interior Foreland basin were deposited during series of regional second- and third-order transgressions and regressions locally modulated by fourth-order cycles. Regional sequence correlation and stacking patterns established with the use of bentonite mapping and palynostratigraphy reveal a history of reciprocal sedimentation driven by alternating flexural subsidence and relaxation. Sequences are markedly diachronous, with ages of sequence boundaries varying laterally by ~800 yr/km. Episodes of subsidence and sedimentation adjacent to the orogen correlate to episodes of uplift and erosion over the forebulge, and the reverse. The two sectors of the basin are separated by a hinge-line which defines the boundary between marine transgressive and regressive rhythms or between nonmarine sedimentary wedges and correlative sequence boundaries. The position of the hinge-line has been mapped in Alberta, Saskatchewan, Montana and Wyoming using geophysical, sedimentologic and biostratigraphic data for eight time-slices during the Campanian-Paleocene interval. Areally the hinge-line traces a semicircular pattern outlining the region of maximum foreland-basin subsidence. It migrated at ~10 km/Ma to the north in response to Late Cretaceous-Paleocene orogenic dextral transpression. The hinge-line also migrated eastward, away from the orogen, during the Campanian, in response to thrustsheet advance, and migrated westward during the Maastrichtian-Paleocene in response to visco-elastic depening and narrowing of the basin.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California