A Storm-Influenced Shoreface Succession Within the Cambrian Mount Clark Formation of the Mackenzie Mountains, Northwest Territories

Abstract

The Cambrian Mount Clark Formation is potential reservoir-quality sandstone within the Central Mackenzie Valley of the Northwest Territories, Canada. The succession lies unconformably over Proterozoic rocks and represents a shoreface to offshore setting, and it is flanked by paleotopographic highs to the West (Mackenzie Arch) and East (Mahony Arch). 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. To produce a detailed sedimentological framework, four outcrops within the Mackenzie Mountains were measured and described to identify characteristic ichnological assemblages and sedimentological fabrics. In general, the Mount Clark Formation is represented by a regressive parasequence set. Base-level changes are expressed at parasequence boundaries, these are demarcated by sharp erosional contacts separating highly bioturbated lower shoreface strata from hummocky and trough cross-stratified middle to upper shoreface strata, and the presence of a localized Glossifungites-demarcated omission assemblage. Observed trace fossils include Skolithos, Palaeophycus Striatus, Diplocraterion, Asterosoma, Planolites, Phoebichnus, Rosselia?, Rhizocorallium?, Teichichnus, Phycodes, and Chondrites. Depending on the proximity of the studied locales to the paleo-shoreline, trace fossils tend to represent the distal Skolithos Ichnofacies in proximal settings and the archetypal Cruziana Ichnofacies in more distal positions. Bioturbation intensity and ichnological diversity tends to increase towards the offshore. Importantly tempestite beds, indicating a storm-influenced depositional setting, are observed. Unlike well-studied Mesozoic tempestites, these exhibit poorly developed to non-existent post-storm tempestite colonization trace fossil suites. Our observations firmly place the studied sections of the Mount Clark Formation in the shallow marine (offshore to shoreface) realm. Characteristically, the unit appears to have deposited during a late highstand systems tract, where accommodation was low, thus leading to the progradation and amalgamation of these units. Future work is aimed at refining the depositional and stratigraphic framework.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015