GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 44-3
Presentation Time: 8:35 AM


BOTTERILL, Scott E.1, CHEN, Qi2, DUVALL, Michael1, GINGRAS, Murray K.2, KUGLER, Jared C.2, ZHANG, Wenbo2 and ZONNEVELD, John-Paul3, (1)Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada, (2)Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada, (3)Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada

The Gog Group (Lower Cambrian) comprises a thick succession (up to 3000 metres) of predominantly clastic rock. It is subdivided into four main formations (McNaughton, Mural, Mahto & Hota / Peyto fms), the upper two of which are carbonate-rich. This paper is focused on mixed siliciclastic-carbonate strata in the upper units of the Gog Formation (the Hota-Peyto Member) in the Whirlpool Point area, west of the Kootenay Plains & north of the David Thompson Highway, Alberta, Canada. Sandstone units in the study interval are dominantly fine to medium-grained with medium & coarse-grained beds & laminae. Large-scale cross-beds; herringbone cross-strata; bi-directional current ripples & numerous reactivation surfaces characterize clastic units. Channelized scours, up to 3 metres deep, locally incise clastic sandstone beds occur interbedded with carbonate-rich sandstone beds. These beds are typically fine-grained to medium-grained with abundant out-sized carbonate grains (up to 1 mm x 3 mm) & range in the overall proportion of carbonate grains to clastic grains from ~<1:2 to >2:1. The carbonate grains observed in the study area include locally abundant oncoids (up to several cm across), ooids & fragmentary / abraded skeletal debris (including mollusc, archaeocyathid & possible brachiopod fragments). Carbonate-rich beds also typically exhibit large-scale cross-stratification, along with bi-directional current ripples & reactivation surfaces. Both clastic-dominated & carbonate-dominated end-members are interpreted to have been deposited in tidally influenced intertidal to shallow subtidal depositional settings. The scale of the bedforms, the occurrence of numerous reactivation surfaces, & the scale of localized channel units indicates a mesotidal or macrotidal setting. Mixing of carbonate & clastic sediments within the study interval is interpreted to be a function of variable sediment delivery to the coastline. A high proportion of clastic sediment indicates deposition proximal to a fluvial point source. Increased proportion of carbonate sediment likely occurred when the clastic depocentre shifted away from the study area, allowing development of carbonate banks, & increased preservation of reworked abraded / fragmentary skeletal debris in cross-stratified sandstone units.