Abstract

The Triassic succession in the Western Canada Sedimentary Basin contains extensive evidence, both direct and indirect, for an aeolian influence on sedimentation. Paleogeographic and paleoclimatic reconstructions for western Canada in Triassic time show that northeast trade winds would have been the expected prevailing wind system during the arid summer season. This is confirmed by southwesterly dip of crossbeds in dune sands in the Charlie Lake Formation, particularly when corrected for Triassic plate rotation. A west-flowing jetstream may also have influenced sediment transport, similar to northwest Africa today. Arid coastal and inland desert or semidesert conditions provided a source for "desert loess" (silt fines) and very fine sand. Specific evidence for aeolian processes in the Triassic of western Canada includes bimodal or coarse-grained deflation lags in the Montney, Charlie Lake, Baldonnel and Pardonet formations and crossbedded dune sands in the Artex Member and other members of the Charlie Lake Formation. In addition (and more conjecturally), thick accumulations of relatively well sorted siltstones in the Montney, Baldonnel and Pardonet formations, and probably in all other Triassic units, may have formed at least in part by fallout from aeolian suspension ("loessite" model). For the Montney at least, basinward aeolian sediment bypass is suggested by the presence of coarse-grained aeolian deflation lags at the tops of some lowstand coquinal units. By comparison with Quaternary analogues of aeolian-marine turbidite sands in the Atlantic Ocean off the west coast of northwest Africa (offshore Saharan Desert) and in at least two other west-facing continental margin settings, bypassed well sorted aeolian silts and sands may have contributed to the formation of turbidites and extensive fluidized/downslope-displaced sandstones and siltstones in the Montney. The limited fine grain size, high detrital dolomite and feldspar composition, and high degree of sorting of many very fine-grained sandstones and siltstones in the Montney and in other Triassic units, are all consistent with aeolian source and transport mechanisms and also have direct impact on reservoir quality and petrophysical log characteristics.

You do not currently have access to this article.