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Petrography and stratigraphy of the late paleozoic rocks in thw wildhay River - Rock Lake Area, Alberta Dawson, Robin Humphrey

Abstract

This paper describes the Mississippian. Exshaw, Banff and Rundle units, a remnant of ? Pennsylvania strata and cherty sandstones of the Permian Ishbel Group; paleontological details include information on the megafossils, foraminifers and algae. The Exshaw Formation includes a sanidine bearing tuffaceous sandstone. The Banff was subdivided into four rock units - Basal Shale, Cherty Unit, Crinoidal Unit and Upper Unit. The Rundle Group was divided into the Pekisko, Shunda, Turner Valley and Mount Head Formations. The term Jasper Lake Formation is applied to a sequence of crinoidal biosparites and dolomites at the South Berland River section which are bank-marginal lateral equivalents of eastern Shunda micrites. The Mississippian rocks of the three stratigraphic sections upon which this study is based are assigned to eight main petrographic facies and six petrographic subfacies. Facies A - calcisiltite: argillaceous crinoidal biomicrite and associated calcareous shales Facies B - an interbedded sequence offacies A and B Facies C - calcarenite: argillaceous crinoidal biomicrite Facies D - calcarenites: crinoidal biosparite Subfacies Da - calcarenite: ‘mature’ crinoidal intrasparite Subfacies Db - calcarenite: intraclast bearing crinoidal biosparite Facies E - oolitic and/or grapestone bearing calcarenites Subfacies Ea - fossiliferous intraclast bearing oosparite Subfacies Eb - intrasparites and sparry intramierites; four lithotypes are recognized (1) oolitic micritic crinoidal intrasparite (2) grapestone bearing intrasparite (3) oolite bearing partially merged intrasparite (4) grapestone and oolite bearing, sparry intramicrite Facies F - pure limestone micrites Subfacies Fa - crinoidal micrite Subfacies Fb - micrites, pelsparites, pelmicrites and dismicrites Facies G - unfossiliferous micrograined dolomite, commonly with microbedding Facies H - dolomite breccias The progression through the facies and subfacies from A to H reflects a change in depositional environment from that of normal marine deep quiet waters to lagoonal and evaporitic conditions; modern sedimentation of the Bahama Banks is used as a partial model. The facies distribution pattern for the Rundle carbonates of the area shows a tendency toward lagoonal facies in the east (Mturtm Creek section), bank-marginal facies in the west (South Berland River section) and intermediate facies at the Eagles Nest Pass section.

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