Architecture of a Tide-Dominated, Regressive Marginal Marine Succession, Drumheller, Alberta, Canada
An examination of the literature suggests there is a bias in perception that tide-dominated clastic depositional environments are generally associated with landward-stepping or transgressive systems. Here, we present an example of a seaward-stepping ancient succession, which is dominated by discrete regressive packages that exhibit abundant evidence of tidal processes.
The Campanian Bearpaw-Horseshoe Canyon Formation transition is three-dimensionally exposed near Drumheller, Alberta. These clastic marine to marginal marine sediments were deposited in mixed-process (wave-, tide- and fluvial-influenced) depositional environments. The deposits are subdivided into seven, relatively thin (10m average) allostratigraphic members. Each contains a transgressive and regressive phase, making the allomembers effectively Transgressive-Regressive (T-R) sequences. Forty-seven sedimentary logs were acquired from the outcrop interval. Four nearby cored wells with accompanying wireline log data were described in sedimentological and ichnological detail and correlated into the outcrop log sections. The outcrop study area is surrounded by oil and gas wells with wireline log data across the stratigraphic interval of interest. Seventy-five of these wells were selected within an area of 22 x 16km, and correlated to the cored wells and outcrop data, in order to generate a 3D geocellular model. This model was used to analyse the stratigraphic architecture and evolution of the area.
The hierarchical WAVE architectural classification system was applied to the deposits. Twenty-one Element Complexes (EC) were identified. These complexes form parts of 12 Element Complex Assemblages (ECA), which in turn form portions of Regressive or Transgressive Element Complex Assemblage Sets (RECAS and TECAS, respectively). The EC and ECA levels of the hierarchy are classified by the dominant, secondary and tertiary depositional processes. For example, a wave-dominated, tide-influenced, and fluvial-affected ECA would be classified as a Wtf-Assemblage. All of the ECs and ECAs exhibit some evidence of tidal processes. The whole succession can thus be termed “tide-dominated”.
Tidal dominance of the entire depositional system during regression is attributed to shelf geometry. The relatively low local shoreline accommodation (water depths averaging 10m), if extended across a wide shelf, may have amplified the tidal wave and enhanced the regularly alternating current velocities in nearshore settings.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California