Polystrate fossil: Difference between revisions

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==Geological explanation==

In [[geology]], such fossils are referred to as either upright fossil trunks, upright fossil trees, or ''T0 assemblages''. According to mainstream (actualistic) models of sedimentary environments, they are formed by rare to infrequent brief episodes of rapid [[Deposition (sediment)|sedimentation]] separated by long periods of either slow deposition, nondeposition, or a combination of both.<ref name="DiMichele+2011a"/><ref name=Gastaldo2004a>Gastaldo, R.A., I. Stevanovic-Walls, and W.N. Ware, 2004, ''Erect forests are evidence for coseismic base-level changes in Pennsylvanian cyclothems of the Black Warrior Basin, U.S.A'' in Pashin, J.C., and Gastaldo, R.A., eds., Sequence Stratigraphy, Paleoclimate, and Tectonics of Coal-Bearing Strata. American Association of Petroleum Geologists Studies in Geology. 51:219–238.</ref><ref name="ArcherOthers2016a">Archer, A.W., Elrick, S., Nelson, W.J. and DiMichele, W.A., 2016. ''Cataclysmic burial of Pennsylvanian Period coal swamps in the Illinois Basin: Hypertidal sedimentation during Gondwanan glacial melt-water pulses.'' In ''Contributions to Modern and Ancient Tidal Sedimentology: Proceedings of the Tidalites 2012 Conference: International Association of Sedimentologists. '' Special Publication (Vol. 47, pp. 217-231).</ref>

Upright fossils typically occur in layers associated with an actively subsiding coastal plain or [[Rift (geology)|rift]] basin, or with the accumulation of volcanic material around a periodically erupting [[stratovolcano]]. Typically, this period of rapid sedimentation was followed by a period of time - decades to thousands of years long - characterized by very slow or no accumulation of sediments. In [[river delta]]s and other coastal-plain settings, rapid sedimentation is often the end result of a brief period of accelerated subsidence of an area of coastal plain relative to sea level caused by [[salt tectonics]], global sea-level rise, growth faulting, [[continental margin]] collapse, or some combination of these factors.<ref name=Gastaldo2004a/> For example, geologists such as John W. F. Waldron and Michael C. Rygel have argued that the rapid burial and preservation of polystrate fossil trees found at [[Joggins, Nova Scotia]] directly result from rapid subsidence, caused by salt tectonics within an already subsiding [[pull-apart basin]], and from the resulting rapid accumulation of sediments.<ref name="Waldron+2005a">Waldron, J.W.F., and M.C. Rygel, 2005, ''Role of evaporite withdrawal in the preservation of a unique coal-bearing succession: Pennsylvanian Joggins Formation, Nova Scotia,'' Geology 33(5):337-340.</ref><ref name="Waldron+2005b">John W.F. Waldron, John C. White, Elizabeth MacInnes, and Carlos G. Roselli, 2005, ''Field Trip B7 Transpression and transtension along a continental transform fault: Minas Fault Zone, Nova Scotia.'' Geological Association of Canada Mineralogical Association of Canada - Canadian Society of Petroleum Geologists - Canadian Society of Soil Sciences Joint Meeting - Halifax, May 2005. Special Publication no. 33. Atlantic Geoscience Society, Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada. ISBN 0-9737982--2-X</ref> The specific layers containing polystrate fossils occupy only a very limited fraction of the total area of any of these basins.<ref name="Waldron+2005a"/><ref>Popular articles on their findings include (1.) [http://www.geotimes.org/july05/NN_Jogginstrees.html ''Sedimentology: Fossil forests sunk by salt''] by Sara Pratt, July 2005 Geotimes and (2.) [http://palaeoblog.blogspot.com/2005/04/joggins-fossil-forest.html ''Joggins Fossil Forest''] PaleoBlog, April 25, 2005</ref>