Detailed Architectural Analysis of Overbank Deposits Associated With a Deep-Marine Channel-Levee Complex, Lower Isaac Formation (Windermere Supergroup) South Canadian Cordillera

Khan, Z.A.¹, Lilian L. Navarro², R.William C. Arnott¹ (1) University of Ottawa, K1N 6N5, Ottawa, ON (2) University of Ottawa, K1N 6M2, Ottawa, ON

Detailed analysis of overbank deposits associated with a deep-marine channel in the Isaac Formation identified five main architectural elements: distributive lobes, proximal outer-bend levees, inner-bend levees, distal levees and overbank splays.

A distributive lobe occurs at the base of the outer-bend levee and consists of coarse-grained strata in beds up to 1 m thick. Overlying these basal deposits and adjacent to the channel are four distinct levee packages, each up to 20 m thick. In their lower 5 - 10 m, strata consist of medium- to thick-bedded (up to 1 m), Ta-c turbidites that thin upward and laterally. Lateral thinning is particularly evident in beds >15 cm, which over 300 m thin to ~5 cm and then persist as such well into the distal levee (an additional 500 m laterally) where strata consist mostly of thin-bedded Tcde turbidites. The distal levee consists also of up to 3 m-thick overbank splay deposits composed of thick, laterally-extensive, coarse sandstone turbidites. Inner-bend levee deposits are thinner and finer compared to their outer-bend counterparts, but similarly thin laterally away from the channel.

Levee deposits are separated from the channel-fill by a surface extending the full exposed length (400 m) of the outer-bend margin. This surface exhibits a terraced geometry suggesting multiple episodes of cutbank erosion and attendant lateral channel migration followed by levee growth and then filling of the channel. The inner-bend margin, in contrast, exhibits a complex but continuous interfingering of channel-fill and levee strata.