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Polystrate fossil
A polystrate fossil is a fossil of a single organism (such as a tree trunk) that extends through more than one geological stratum.〔MacRae, A., 1997, (''"Polystrate" Tree Fossils'' ). (TalkOrigins Archive. )〕 This term is typically applied to "fossil forests" of upright fossil tree trunks and stumps that have been found worldwide, i.e. in the Eastern United States, Eastern Canada, England, France, Germany, and Australia, typically associated with coal-bearing strata.〔DiMichele, W.A., and H.J. Falcon-Lang, 2011, (''Pennsylvanian 'fossil forests' in growth position (T0 assemblages): origin, taphonomic bias and palaeoecological insights.'' ) Journal of the Geological Society, 168(2):585-605.〕 Within Carboniferous coal-bearing strata, it is also very common to find what are called ''Stigmaria'' (root stocks) within the same stratum. Stigmaria are completely absent in post-Carboniferous strata, which contain either coal, polystrate trees, or both. The word ''polystrate'' is not a standard geological term. This term is typically found in creationist publications.〔〔Gastaldo, R.A. 1999. ''Debates on Autochthonous and Allochthonous Origin of Coal: Empirical Science versus the Diluvialists,'' In Manger, W.L., ed., The Evolution-Creation Controversy II: Perspectives on Science, Religion, and Geological Education, The Paleontological Society Papers, v. 5, p. 135-167.〕
==Geological explanation==
In geology, such fossils are referred to as upright fossils, trunks, or trees. Brief periods of rapid sedimentation favor their formation.〔〔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.〕 Upright fossils are typically found in layers associated with an actively subsiding coastal plain or 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 deltas 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.〔 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 was the direct result of rapid subsidence, caused by salt tectonics within an already subsiding pull-apart basin, and resulting rapid accumulation of sediments.〔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.〕〔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〕 The specific layers containing polystrate fossils occupy only a very limited fraction of the total area of any of these basins.〔〔Popular articles on their findings are (1.) (''Sedimentology: Fossil forests sunk by salt'' ) by Sara Pratt, July 2005 Geotimes and (2.) (''Geologists probe mystery behind Nova Scotia’s fossil forests'' ) PhysOrg, June 7, 2005〕
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