SEDIMENTOLOGY, ICHNOLOGY AND SEQUENCE STRATIGRAPHY OF THE LOWER CAMBRIAN GOG GROUP, SOUTHERN ROCKY MOUNTAINS, CANADA

Shallow-marine sandstone of the Gog Group in the southern Rocky Mountains comprise part of the vast terrace of siliciclastic deposits that rimmed the continental margin of western Canada, indeed almost contiguously around Early Cambrian Laurentia. It lies at the base of one of the thickest Cambrian sections in the world and records the initial phases of the early Paleozoic transgression onto the craton. Seemingly monotonous, the Gog Group can help trace the depositional and paleocological evolution of the broad Cambrian shelf in this region.

An integrative study including sedimentologic, ichnologic and sequence-stratigraphic information has enabled: 1) revision of its stratigraphic nomenclature; (2) documentation of the sedimentary facies; (3) identification of facies assemblages and their interpretation in terms of sedimentary processes and environments; (4) characterization of sandstone body geometries; (5) development of a sequence-stratigraphic framework; (6) documentation of trace-fossil occurrences; and (7) characterization of different trace-fossil assemblages in terms of colonization trends and prevailing paleoenvironmental conditions.

Through the revision of the lithostratigraphy of the Gog Group, new members are now established, allowing future detailed studies to be placed in a better nomenclatural context. Forced-regressive tidal flats are described for the first time from the rock record. The response of tide-dominated coastlines to a forced regression is now better understood, and this expands the implication of falling-stage systems tracts. The study of pipe-rock ichnofabrics allowed the characterization of early mixground ecosystems and ascertain paleoecologic controls in sand-sheet complexes. Finally, the study of compound cross-stratified sandstone variability in an environmental context has permitted a more complete classification of subtidal sandbodies.

The detailed study of the Gog Group has “awakened a giant”, and these rock now play a major role in our understanding of Cambrian shallow-marine systems.