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The Princeton Chert is a fossil locality in British Columbia, Canada, that represents one of the best preserved collections of Eocene Epoch floras in the world, with rich species abundance and diversity. It is located on the east bank of the Similkameen River, south of the town of Princeton in the Regional District of Okanagan-Similkameen.〔〔Miller, C.N. (1975) "Silicified cones and vegetative remains of ''Pinus'' from the Eocene of British Columbia." ''Contributions from the Museum of Paleontology, University of Michigan'', 24 (10): 101-118.〕 The site of the Princeton Chert (Ashnola in older sources) and its fossils have been known since the 1950s,〔Arnold, C. A. (1955). "A Tertiary Azolla from British Columbia". ''Contributions from the Museum of Paleontology, University of Michigan'' 12 (4): 37–45.〕〔Boneham, R. F., 1968, Palynology of three Tertiary coal basins in south-central British Columbia. Ph.D. Dissertation, University of Michigan, Ann Arbor, Michigan〕 but have recently attracted increased attention. This may be due to the rare type of silica permineralized fossil Lagerstätten found, which has preserved plants and animals in minute 3D detail, with exceptional internal cellular detail.〔Pigg, KB, and RA Stockey. 1996. "The significance of the Princeton chert permineralized flora to the middle Eocene upland biota of the Okanogan Highlands." ''Washington Geology'' 24: 32-36.〕 This has meant anatomical descriptions and reconstruction of whole plants from isolated parts has been possible in many species.〔 Few plant fossils elsewhere in the world exhibit such excellence in both preservation and diversity. Similar aged fossil beds in Eocene lake sediments are found elsewhere in British Columbia, including in Driftwood Canyon Provincial Park near Smithers in northern British Columbia, and the McAbee Fossil Beds west of Kamloops, about NNW of the Princeton Chert beds. ==Location and geologic setting== The Princeton Chert is an interbedded sequence consisting of coal, shale, and chert in the Allenby Formation.〔 49 chert layers, ranging in thickness from have been recognized and described, though each is not unique in organisms preserved. Despite this, trends are evident throughout the outcrop, with certain taxa appearing and disappearing with time.〔 The Princeton Chert was originally considered to be Middle Eocene based on data from mammals, freshwater fish, and potassium-argon dates. Recently, more accurate radiometric techniques provided a date of 48.7 mya,〔 placing the Princeton Chert in the Ypresian stage (47.8–56.0 mya), consistent with the whole Allenby Formation being now dated radiometrically as being Early Eocene.〔 The climate at this time was warm; it had reached a maximum during a series of warming events during the Early Eocene with the Princeton Chert likely deposited after the Eocene Thermal Maximum 2 and during the Early Eocene Climatic Optimum.〔 During this time the sea warmed approximately 4 °C and terrestrial temperatures were several degrees warmer than today, meaning little or no ice was present. The temperature difference between poles and equator was small. This long term warmth is thought to be due to increased greenhouse gases, particularly CO2 trapping more heat.〔〔Bijl, P. K., Houben, A. J. P., Schouten, S., Bohaty, S. M., Sluijs, A., Reichart, G., Damsté, S. & Brinkhuis, H. (2010) Transient Middle Eocene Atmospheric CO2 and Temperature Variations. ''Science'', 330(6005), pp 819–821.〕 The reason for this sudden increase in CO2 is unknown, but it is hypothesised that it was due to an increase in ocean floor being recycled via volcanic arcs and metamorphic decarbonation reactions.〔 This happened because the ocean between India and Asia was disappearing and being replaced by the Himalayas and the Tibetan plateau due to the collision of tectonic plates. Also at the time, Australia, which was joined to Antarctica, was beginning to move northwards.〔Scotese, C. R. (2003) Paleomap Project. (). Available from: http://www.scotese.com/ (18/03/2012 ).〕 The Princeton Chert fossils indicate that the area was an aquatic ecosystem, growing in tropical to subtropical conditions.〔 Several of the smaller chert layers degrade to volcanic ash, indicating nearby volcanic activity. It is thought that fossils were pervaded with silicic acid due to this volcanic activity. Subsequently, water charged with minerals flowed from springs or geysers into the low lying basin where the Princeton chert was located. Here, the water surrounded organisms as they grew, along with plant debris which had been accumulated.〔 Many organisms were preserved in situ, in the lake or small pond environment in which they lived.〔 The preservation must have been rapid, due to the minute cellular detail which has been conserved. This sequence of events is thought to have been replicated up to 50 times, as the basin allowed peat to reaccumulate each time,〔 producing the multiple layers. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Princeton Chert」の詳細全文を読む スポンサード リンク
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