Dilliard, Kelly A.1, Michael C. Pope1, Stephen T. Hasiotis2,
Bruce S. Lieberman2
(1) Washington State University, Pullman, WA
(2) University of Kansas, Lawrence, KS
ABSTRACT: Sequence Stratigraphy of the Lower Sekwi Formation, Selwyn Basin, Northwest Territories, Canada
The Sekwi Formation in the Mackenzie Mountains, Northwest
Territories, Canada is the first carbonate unit deposited during the widespread Early
Cambrian transgression of the Cordilleran continental margin. A sequence stratigraphic
framework for the Sekwi Formation is established using ten detailed measured sections,
each up to 1 km thick. The Fallotaspis, Nevadella, and Bonnia-Olenellus trilobite zones
provide a chronostratigraphic framework for regional and global correlations. The
lowermost sequence (S1) is an eastwardly thinning wedge, (50 to >300 m thick) composed
predominantly of slope and basin deposits overlain by a thin, prograding ooid shoal
complex. The upper part of the Vampire Formation, underlying the Sekwi Formation, is
included within S1. Sequence 2 (S2; 150 to >275 m thick) includes shelf through basin
deposits, whereas sequences 3 through 7 are smaller-scale sequences (40-150 m thick) with
subtidal carbonate transgressive systems tracts (TSTs) and peritidal carbonate highstand
systems tracts (HSTs).
The TST of S1 consists of siliciclastic shelf deposits of the upper Vampire Formation and nodular carbonate of the lower Sekwi Formation. The maximum flooding zone occurs within black laminated mudstone intercalated with debris flow and turbidite deposits that overly nodular carbonate. Early HST debris flow deposits are composed predominately of slope-derived clasts with minor shelf-derived clasts. Conversely, late HST debris flow deposits contain oolitic grainstone and subtidal shelf sandstone clasts that track progradation of an ooid shoal complex.
The TST of S2 consists of shale and black laminated mudstone with allochthonous mud mounds. The HST records progradation of another ooid shoal complex.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.