Abstract
The parautochthonous, subproximal segment of the 'Belly River' clastic wedge is subdivided into five new formations, listed here from oldest to youngest: Lees Lake, Burmis, Connelly Creek, Lundbreck and Drywood Creek. The Pakowki Formation divides the 'Belly River' clastic wedge into a lower succession consisting of predominantly marine sediments (the Lees Lake and Burmis Formations) and an upper succession (the Connelly Creek, Lundbreck and Drywood Creek Formations). The lower succession including the Pakowki Formation belongs to the Alberta Group and the upper succession represents the Belly River Group. The formations have been mapped in the Foreland Thrust and Fold Belt west of Lundbreck, Alberta, and correlated with the subsurface distal, autochthonous formations of the Interior Platform. Early indications of Laramide tectonic activity in the source area are recorded by the turbidites of the Lees Lake Formation. An increase in the supply of sand during deposition of the Lees Lake Formation produced thick sandstone layers which were syndepositionally deformed and partly eroded by sediment-laden density currents. The contact between the Lees Lake Formation and the overlying Burmis Formation is unconformable because of submarine erosion. The Burmis Formation is recognized as a deltaic sequence containing a lateral transition from fluviatile through distributary channel-fill to distributary mouth-bar facies. The next phase of the Laramide Orogeny is recorded by the upper delta plain facies of the Connelly Creek Formation and the alluvial fan facies of the Lundbreck Formation. The fan-shape geometry and sedimentological features of the Lundbreck Formation, especially the ephemeral, high-energy channels, semi-arid paleosols and playa deposits indicate sedimentation on a semi-arid alluvial fan bordering the upper delta plain environment. Flash-flood deposition within the ephemeral channels and deep erosion of the alluvial plain during sedimentation of the Lundbreck Formation suggest significant syndepositional topography. The semi-arid alluvial fan environment suggested for the Lundbreck Formation implies an uplifted mountain front during its formation. Basinward progradation of the Connelly Creek/Lundbreck delta was caused by easterly propagation of the tectonic deformation that forced the Pakowki Sea to retreat from the Crowsnest Embayment.
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