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Dale A Leckie1, Claudia Schröder-Adams2, John Bloch3
(1) Canadian Occidental Petroleum Ltd, Calgary, AB
(2) Carleton University, Ottawa, ON
(3) Scealu Modus, Albuquerque, NM

Abstract: Influence of basin-scale structure and paleotopography on the Late Albian and Cenomanian sea-level record in Western Canada

In Western Canada, a major paleoenvironmental change at the Albian/Cenomanian boundary is related to a eustatic sea-level rise overprinted by a relative sea-level fall in conjunction with pre-existing topography within the basin. Lateral variability of sedimentology, paleoecology and biostratigraphy of the latest Albian to Cenomanian interval is the result of paleotopography caused by a collapsed arch in the north and volcanic buildup in the south. This basin structure created antecedent paleo-topography prior to the transgression. Faunal assemblages and facies distribution indicate greater amounts of erosion and coarser-grained deposition in the southwest, associated with the paleohigh. Northwards and eastwards, greater accommodation space was associated with the collapsed Peace River Arch, less erosion associated with the unconformity, and finer-grained sediment. A 1000 km traverse resolves the enigmatic occurrence of chert, quartz and bioclastic pebbles associated with black anoxic shale within the Fish Scales (Barons/Mowry) Fm. Conglomerate in SW Alberta represents proximal shelf sedimentation of material flushed out during sea-level lowstand and subsequently reworked by the Belle Fourche transgression. Northwards, the Fish Scales Fm is bounded by unconformities and conglomerate indicating multiple sea-level fluctuations and deposition on a wave-influenced shelf. In west-central Alberta, deposition was in a nearshore setting. Distally to the north the coarse component is predominantly gravel-sized fish and vertebrate debris.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana