Rocky Mountain Section - 69th Annual Meeting - 2017

Paper No. 10-6
Presentation Time: 3:40 PM


DILLIARD, Kelly A., Department of Physical Sciences and Mathematics, Wayne State College, 1111 Main Street, Wayne, NE 68787, POPE, Michael C., Department of Geology & Geophysics, Texas A&M University, College Station, TX 77843 and CONIGLIO, Mario, Department of Earth Sciences, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada,

The Early Cambrian Sekwi Formation in the Selwyn Basin of the Northwest Territories, Canada, represents a well-exposed carbonate platform that records the Early Cambrian transgression of the Cordilleran continental margin. The Sekwi Formation is well-exposed in easterly-directed thrust sheets emplaced during the Late Paleozoic. Ten measured sections were described in a bed-by-bed fashion, examining surfaces and stacking patterns, with several sections up to 1 km in thickness. These detailed measured sections in conjunction with trilobite biostratigraphy and chemostratigraphy enable the construction of a sequence stratigraphic framework across these closely spaced thrust sheets.

The Sekwi Formation is composed of two 2nd-order cycles that help to differentiate an informal lower and upper part. The lower Sekwi Formation records predominantly deep-water deposition in a basin influenced by syndepositional faulting, whereas the upper Sekwi Formation is composed mostly of shallow-water deposition on a homoclinal ramp with little to no evidence of tectonism. The upper Sekwi Formation, typical of other Lower Cambrian carbonates of western Laurentia, includes a series of facies deposited on either side of a ramp crest composed of ooid shoals and/or algal-archeocyathan mounds that separates the inner ramp from basinward open marine conditions. Deposits of the inner ramp include mixed siliciclastic-carbonate lagoonal sediments, siliciclastic and carbonate tidal flat deposits, and terrestrial siliciclastics. Outer ramp facies include skeletal wackestone/packstone, interbedded shale and calcisiltstone, and black carbonate mudstone. Many of these facies contain distinct trace fossils. The upper Sekwi Formation consists of multiple 3rd-order sequences consisting of sandy bases, deep ramp transgressive systems tracts capped by shoal water or tidal flat deposits in high-stand systems tracts. 4th- and 5th-order high-frequency sequences, or parasequences, are common in the Sekwi Formation but they are difficult to correlate across the platform.