Depositional history of the coal-bearing Upper Jurassic-Lower Cretaceous Kootenay Formation, Southern Rocky Mountains, Canada

摘要: The coal-bearing Kootenay Formation of Late Jurassic-Early Cretaceous age in Alberta and British Columbia is a classic example sedimentary sequences built by delta progradation. formation composed 3,500 ft cyclicly alternating sandstone, shale, coal, with few conglomerate beds. sandstone beds are poorly to moderately sorted, fine- medium-grained lithic graywacke proto-quarzite. Shale illitic composition minor amounts kaolinite. These Upper Jurassic-Lower sediments were derived mainly from the sedimentary-rock terrains located Purcell Mountains Shuswap Complex. Direction transportation was northeast. Deposition initiated epeirogenic uplift source area Jurassic time. Terrigenous initially deposited on low-lying coastal plain, which advanced seaward accretion processes into shallow sea eastern Canadian Cordillera miogeosyncline. In vertical section, siltstone mudstone open marine environment grade upward transitional prodelta facies Fernie sandstones siltstones containing trace fossil Thalassinoides. deposits turn front sheet sand Rhizocorallium. overlying well-sorted highly burrowed barrier bar “misch” tidal flats contains Arenicolites, grades lower plain deposits. ranging up 50 thickness represent channel fill point bars meandering distributaries, laterally interfingered interdistributary sequences. Coal, as much 30 thick formed peat marshes fresh-water swamps basins plain. Within upper more common, coal flood basins. delta-plain alluvial characterized occurrence form conglomerate, silty decreased individual cyclothems. Increased frequency alternation rock units explained increase instability tendency river channels braided system. This system provided unfavorable conditions for development. Uplifting depositional Neo-comian time terminated sedimentation denudation previously sediments. During additional strong uplifting inland area, rejuvenated piedmont-plain represented Cadomin spread over eroded surface Formation. study demonstrates use sedimentological studies tool exploration evaluation