Sedimentary Facies and Architecture of a Subtidal Sandbar Complex, Lower Cambrian Gog Group, Southern Rocky Mountains, Canada

Desjardins, Patricio R.¹, Luis A. Buatois¹, Brian R. Pratt¹, M. Gabriela Mangano¹ (1) University of Saskatchewan, Saskatoon, SK

During the Cambrian, sedimentation on the continental margin of western Laurentia evolved in a context of worldwide transgression. Thus the architecture, distribution and facies of sandstone bodies in the Gog Group provide important clues towards a better understanding of sand dynamics on a broad, transgressive continental shelf. Our study focuses on the lower portion of this unit which reaches some 320 m in thickness. This study is based on the integration of lithofacies and ichnofacies analysis, paleocurrent measurements, interpretation of photomosaics, and correlation between sections. Four units were recognized: 1) tabular bodies of planar and trough cross-stratified sandstone; 2) tabular to lenticular bodies of cross-stratified and plane-laminated sandstone intercalated with wavy to tabular packages of ripple cross-laminated sandstone and shale; 3) relatively thick, nearly tabular bodies of planar cross-stratified sandstone with domed-shaped tops; and 4) interbedded lenticular to wavy packages of sandstone and shale. Units 1 to 3 reflect strong uni-directional currents within sandbars. The lenticular geometry of some of the beds reveals storm reworking, but the reactivation of uni-directional currents may have erased most of the signals of wave action in specific areas. Protected areas or lagoons (unit 4) developed as an associated subenvironment. Two different ichnofacies were identified and characterized: 1) Skolithos ichnofacies within units 1 to 3; and 2) Cruziana ichnofacies within unit 4. These deposits record growth and migration of a subtidal sandbar complex over a low-gradient shelf above storm wave base. The Gog Group represents an instructive outcrop analogue for transgressive subtidal sandstone reservoirs.