| 词条 | Elk Formation |
| 释义 |
| name = Elk Formation | image = | caption = | type = Geological formation | age = {{Fossil range|155|135|Late Jurassic to Early Cretaceous}} | period = Mesozoic | prilithology = Sandstone, conglomerate | otherlithology = Siltstone, mudstone, coal | namedfor = Elk River coal mine east of Fernie, British Columbia | namedby = C.B. Newmarch, 1953[1] | region = {{flag|British Columbia}} {{flag|Alberta}} | country = {{flag|Canada}} | coordinates = | unitof = Kootenay Group | subunits = | underlies = Cadomin Formation | overlies = Mist Mountain Formation | thickness = Maximum {{convert|590|m|ft|-1}} | extent = | area = | map = | map_caption = }} The Elk Formation is a stratigraphic unit of the Western Canada Sedimentary Basin that is present in southeastern British Columbia and southwestern Alberta.[2] It is probably of Early Cretaceous age, but in some areas its strata could be as old as Late Jurassic. It includes minor thin coal beds and was named for outcrops near the now-abandoned Elk River coal mine east of Fernie, British Columbia.[3] LithologyThe Elk Formation is a sequence of interbedded sandstone, siltstone, mudstone, shale, and chert-pebble or cobble conglomerate. Thin coal seams are present in some areas. Thick-bedded, cliff-forming sandstones and conglomerates are the most conspicuous lithologies.[3][4][5] Most of the Elk Formation coals are of high-volatile bituminous rank and most seams are less than {{convert|60|cm|in|-1}} thick. An unusual type of coal, referred to as "needle coal" occurs in very thin beds in the upper third of the formation. It consists of compacted masses of rod-like "needles" and has been shown to be of algal origin. "Needles" of vitreous coal are also found in some of the siltstones associated with the needle coals.[3] Environment of depositionThe Elk Formation is an eastward-thinning wedge of clastic sediments that were derived from mountains to the west, transported eastward by river systems, and deposited in alluvial plain environments. These include river channel, crevasse splay, overbank, and marsh environments. Conglomeratic units may represent alluvial fan and braided river deposits.[3] Paleontology and ageThe Elk Formation contains plant fossils, palynomorphs, bivalves, ostracodes, and ichnofossils, but none of these fossils are sufficiently time-sensitive to date the strata precisely. Palynomorph evidence suggests that the Elk Formation is mainly of Early Cretaceous age, but could be as old as Late Jurassic in some areas.[3] Thickness and distributionThe Elk Formation is present in the Rocky Mountain Front and foothills of the Canadian Rockies in southeastern British Columbia and southwestern Alberta. It can be traced from Flathead Ridge south of Fernie to Barrier Mountain near the Red Deer River in the foothills of western Alberta. Measured thicknesses range from a maximum of {{convert|590|m|ft|-1}} at Mount Allan in Alberta to {{convert|28|m|ft|-1}} north of Coleman, Alberta.[3] Farther to the east it was truncated by pre-Aptian erosion.[2][6] Relationship to other unitsThe Elk Formation is the uppermost unit of the Kootenay Group. It gradationally and conformably overlies the Mist Mountain Formation. It is disconformably overlain by the Cadomin Formation and to the east it was truncated by pre-Cadomin erosion. To the north Elk strata may correlate with part of the Nikanassin Formation. Correlation to the south in Montana has not been established, but it has been suggested that equivalent strata maybe absent due to erosion and/or nondeposition.[3] References1. ^Newmarch, C.B. (1953). Geology of the Crowsnest coal basin, with special reference to the Fernie area. British Columbia Department of Mines, Bulletin 33. 2. ^1 {{Cite web|url=http://ags.aer.ca/reports/atlas-of-the-western-canada-sedimentary-basin.htm|title=The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 18: Jurassic and Lowermost Cretaceous strata of the Western Canada Sedimentary Basin|author=Mossop, G.D. and Shetsen, I. (compilers), Canadian Society of Petroleum Geologists and Alberta Geological Survey|year=1994|accessdate=2016-06-20}} 3. ^1 2 3 4 5 6 Gibson, D.W. 1985. Stratigraphy, sedimentology and depositional environments of the coal-bearing Jurassic-Cretaceous Kootenay Group, Alberta and British Columbia. Geological Survey of Canada, Bulletin 357, 108 p. 4. ^{{Cite web|url=http://weblex.nrcan.gc.ca/weblex_e.pl?00053:011229|title=Lexicon of Canadian Geological Units|author=Natural Resources Canada|accessdate=2013-12-23}} 5. ^Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. {{ISBN|0-920230-23-7}}. 6. ^{{Cite web|url=http://www.ags.gov.ab.ca/publications/wcsb_atlas/a_ch19/ch_19.html|title=The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 19: Cretaceous Mannville Group of the Western Canada Sedimentary Basin|author=Mossop, G.D. and Shetsen, I., (compilers), Canadian Society of Petroleum Geologists and Alberta Geological Survey|year=1994|accessdate=2013-08-01|deadurl=yes|archiveurl=https://web.archive.org/web/20130814133127/http://www.ags.gov.ab.ca/publications/wcsb_atlas/a_ch19/ch_19.html|archivedate=2013-08-14|df=}} 7 : Geologic formations of Canada|Upper Jurassic Series|Stratigraphy of Alberta|Cretaceous Alberta|Cretaceous British Columbia|Stratigraphy of British Columbia|Lower Cretaceous Series of North America |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。