Geology of the Mount Stephen Trilobite Beds and Adjacent Strata Field B.C., Yoho National Park — Exploration Ramifications From New Insights on a 129 Year Old Discovery

Abstract

Since their discovery 129 years ago, researchers have assumed that the Mount Stephen Trilobite Beds, found within the Ogygopsis Shale, were the southwestern extension of the Burgess Shale Beds exposed along the Kicking Horse River Valley mountainsides. The absence of Ogygopsis or equivalent shale within the adjacent local Burgess exposures, including those on Fossil Ridge (home of the Walcott Quarry) has perplexed researchers for over a century. The recent discovery of the post glacial Field Landslide and analysis of the landslide features, including the slide failure surface(s), led to the discovery of several previously unrecognized Cambrian depositional features and Canadian Rocky Mountain Main Range structural features. Aside from the discovery of the Field Landslide, the most significant findings include: 1) the discovery of the initial western Main Range thrusting event (the KTC) on the exposed surfaces of the Field Slide, separating the two Main Ranges into two distinct thrusting episodes, 2) the discovery of a major subaerial exposure surface at the contact between the Ogygopsis Shale and the underlying carbonate beds, 3) the recognition that the previously interpreted Cathedral Escarpment megaclasts or deep water carbonate mud mound features in the underlying carbonate beds are Cambrian patch reefs, part of the Basal Cathedral Formation (Upper Mount Whyte Formation) and 4) the redefinement of significant basement faulting both during and post western Main Range thrusting. Combined, the above findings challenge: a) the accepted Cambrian (Cathedral/Burgess Shale) depostional and stratigraphic models which were developed without the recognition of duplicated, laterally displaced Cambrian Strata, and b) the accepted theories regarding the structural history of the Main Ranges of the Canadian Rocky Mountains. Recognizing that the Cathedral Burgess section is a cyclic carbonate shale sequence comparable in character to those found within the productive Devonian sections in the Western Canadian Basin, and acknowledging the existence of early Cretaceous basement faulting opens up the potential for both conventional and resource play exploration within these Cambrian formations.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016