--> Siliciclastic and Tectonic Controls on Carbonate Distribution Within the Early Cambrian Mount Clark Formation, Mackenzie Mountains, Northwest Territories, Canada

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Siliciclastic and Tectonic Controls on Carbonate Distribution Within the Early Cambrian Mount Clark Formation, Mackenzie Mountains, Northwest Territories, Canada

Abstract

The Cambrian Mount Clark Formation is a potential reservoir-quality interval within the Central Mackenzie Valley of the Northwest Territories, Canada. The succession lies unconformably over Proterozoic strata and is represented by a variety of environments within the study area. Siliciclastic shorelines are represented in the northwest and southeast portions of the basin, whereas mixed clastic carbonate successions occupy a 10 km long stretch within the central margin. Basin elements include two prominent arches; the Mackenzie Arch to the west and the Mahony Arch to the East. The Mount Clark Formation has been the subject of several regional studies, but detailed ichnological and sedimentological investigations have not been conducted. Depositional affinities are poorly understood with fluvial to shallow marine environments proposed within existing lithostratigraphic schemes. Furthermore, the mixed clastic carbonate intervals at Dodo Canyon, Echo Creek, Fan Creek, and Mirror Lake have not been studied in sufficient detail. To produce a detailed sedimentological framework of the mixed clastic carbonate successions, three outcrops within the Mackenzie Mountains were measured and described to identify characteristic ichnological assemblages and sedimentological fabrics. In general mixed carbonate lithologies consist of the following; graded iron oolite beds, hyolithid grainstones, archaeocyathid rudstones, bioturbated mudstones, and algal-laminated dolostones. Clastic lithologies are represented by heavily bioturbated glauconitic sandstones, hummocky cross-stratified sandstones, dolomitic bioturbated sandstones, trough cross-stratified sandstones, and convolute bedded sandstones. Observed trace fossils include Skolithos, Palaeophycus Striatus, Diplocraterion, Asterosoma, Planolites, Rosselia?, Rhizocorallium, Teichichnus, Phycodes, and Chondrites. Trace fossil assemblages tend to represent the distal Skolithos Ichnofacies in proximal settings (i.e. proximal offshore and proximal prodelta locales) and the archetypal Cruziana Ichnofacies in more distal positions (i.e. distal offshore). Our observations suggest a twofold zonation for the Mount Clark Formation; initial carbonate deposition aided through low siliciclastic input by relative tectonic quiescence and subsequent rifting leading to increased siliciclastic input disrupting the pre-existing carbonate factory and resulting in siliciclastic deposition through the end of Mount Clark Formation deposition.