Polystrate fossil: Difference between revisions

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{{short description|Creationist term for a fossil that extends through more than one geological stratum}}

{{Paleontology}}

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[[File:Lycopsid joggins mcr1.JPG|thumb|Ancient ''in situ'' [[w:lycopsid|lycopsid]], probably [[w:Sigillaria|''Sigillaria'']], with attached [[w:stigmaria|stigmarian roots]]. Specimen is from the Joggins Formation ([[Pennsylvanian (geology)|Pennsylvanian]]), Cumberland Basin, Nova Scotia.]]

[[Image:Stigmaria Bear Valley upright.jpg|thumb|Upright ''[[Sigillaria]]'' in dipping beds of [[Pennsylvanian (geology)|Pennsylvanian]] [[Llewellyn Formation]] in [[Bear Valley Strip Mine]], [[Northumberland County, Pennsylvania]]]]

A '''polystrate fossil''' is a [[fossil]] of a single organism (such as a [[tree trunk]]) that extends through more than one geological [[stratum]].<ref name="MacRae1997a">MacRae, A., 1997, [http://www.talkorigins.org/faqs/polystrate/trees.html ''"Polystrate" Tree Fossils'']. [http://www.talkorigins.org/ TalkOrigins Archive.]</ref> This term is typically applied to "[[fossil forest]]s" of upright [[Petrified wood|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.<ref name="DiMichele+2011a">DiMichele, W.A., and H.J. Falcon-Lang, 2011, [http://si-pddr.si.edu/dspace/handle/10088/15971 ''Pennsylvanian 'fossil forests' in growth position (T0 assemblages): origin, taphonomic bias and palaeoecological insights.''] Journal of the Geological Society, 168(2):585-605.</ref> 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 [[Geology|geological]] term. This term is typically found in [[creationist]] publications.<ref name="MacRae1997a"/><ref name="Gastaldo+1999a">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.</ref>

This term is typically applied to "fossil forests" of upright [[Petrified wood|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.<ref name="DiMichele+2011a">DiMichele, W.A., and H.J. Falcon-Lang, 2011, [http://si-pddr.si.edu/dspace/handle/10088/15971 ''Pennsylvanian 'fossil forests' in growth position (T0 assemblages): origin, taphonomic bias and palaeoecological insights.''] Journal of the Geological Society, 168(2):585-605.</ref> 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.

==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>

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===Fossil soils===

Geologists have recognized innumerable [[fossil soil]]ssoils ([[paleosol]]s) throughout the strata containing upright fossils at Joggins in Nova Scotia, in the Yellowstone petrified forests, in the coal mines of the [[Black Warrior Basin]] of [[Alabama]], and at many other locations. The layer immediately underlying [[coal seam]]s, often called either "[[seatearth]]" or "[[underclay]]", typically either consists of or contains a paleosol. Paleosols are soils which were formed by [[subaerial]] [[weathering]] during periods of very slow or no accumulation of sediments. Later, renewed sedimentation buried these soils to create paleosols. These paleosols are identified on the basis of the presence of structures and microstructures unique to soils; animal burrows and molds of plant roots of various sizes and types; recognizable soil-profile development; and alteration of minerals by soil processes. In many cases, these paleosols are virtually identical to modern soils.

Geologists, who have long studied upright fossils found in sedimentary rocks exposed in various outcrops for decades, have described the upright fossil trees as being deeply rooted in place and typically rooted in recognizable [[paleosol]]s. This is in sharp contrast to the claims made by creationists such as Harold Coffin and N. A. Rupke. Geologists,Researchers such as Falcon<ref>Falcon-Lang, H.J., 2003a, ''Late Carboniferous dryland tropical vegetation, Joggins, Nova Scotia, Canada'', Palaios 18:197– 211.</ref><ref>Falcon-Lang, H.J., 2003b, ''Early Mississippian lycopsid forests in a delta-plain setting at Norton, near Sussex, New Brunswick, Canada'', Journal of the Geological Society, London 161:969–981.</ref><ref name=falcon2005>Falcon-Lang, H.J., 2005, ''Small cordaitalean trees in a marine-influenced coastal habitat in the Pennsylvanian Joggins Formation, Nova Scotia'', Journal of the Geological Society 162(3): 485-500.</ref><ref name=falcon2006a>Falcon-Lang, H.J., 2006a, ''Latest Mid-Pennsylvanian tree-fern forests in retrograding coastal plain deposits, Sydney Mines Formation, Nova Scotia, Canada'', Journal of the Geological Society 163(1): 81-93.</ref><ref name=falcon2006b>Falcon-Lang, H.J., 2006b, ''Vegetation ecology of Early Pennsylvanian alluvial fan and piedmont environments in southern New Brunswick, Canada'', Palaeogeography, Palaeoclimatology, Palaeoecology 233(1-2): 34-50.</ref> and Rygel et al.,<ref>Rygel, M.C., M.R. Gibling, and J.H. Calder, 2004, ''[[Vegetation-induced sedimentary structures]] from fossil forests in the Pennsylvanian Joggins Formation, Nova Scotia'', Sedimentology 51:531– 552.</ref> have published detailed field-sketches and pictures of upright tree-fossils with intact root systems, which are rooted within recognizable paleosols. In the case of the upright fossil trees of the [[Yellowstone National Park|Yellowstone]] petrified forests, geologists – again in sharp disagreement with creationists like Haroldit Coffinhas –been found that the upright fossil trees, except for relatively short stumps, are rooted in place within the underlying sediments. Typically, the sediments within which trees are rooted have paleosols developed within them.<ref name="Amidon, L. 1997"/><ref name=Retallack1981>Retallack, G.J., 1981, ''Reinterpretation of the depositional environment of Yellowstone fossil forest: Comment'', Geology 9:52-53.</ref><ref name=Retallack1997>Retallack, G.J., 1997, ''A Colour Guide to Paleosols.'' John Wiley and Sons. {{ISBN|0-471-96711-4}}</ref> Retallack (1981, 1997) has published pictures and diagrams of the Yellowstone upright fossil trees having intact root systems developed within paleosols found within these strata.<ref name=Retallack1981 /><ref name=Retallack1997 /><ref>Since 1997, geologists agree with Harold Coffin that his "organic levels" are not paleosols. Neither Harold Coffin nor other creationists discuss the layers which geologists currently recognize as being paleosols in their papers about the Yellowstone petrified forests. Geologists such as Amidon (1997) have documented the presence of structures, microstructures, profile development, and mineralogical alteration either characteristic or of consistent with a buried-soil profile within numerous thin layers, which are identified as paleosols, found within the strata containing Yellowstone petrified forests</ref>

===Formation by regeneration===

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===Formation by Carboniferous deglacial meltwater-pulses===

In addition, part of the Carboniferous Period was a period of extensive and thick continental [[ice sheet]]s. During the Carboniferous ice age, the repeated [[Glacial period|glacial]] – [[interglacial]] cycles caused major changes in the thickness and extent of continental ice sheets. When these ice sheets expanded in extent and thickness, [[eustatic sea level]] typically fell by over a {{convert|100|m|ft|sp=us}}. When these ice sheets shrank in extent and thickness, eustatic sea level typically rose again by typically over a {{convert|100|m|ft|sp=us}}.<ref name="Heckel1986a">Heckel, P.H., 1986. ''Sea-level curve for Pennsylvanian eustatic marine transgressive-regressive depositional cycles along midcontinent outcrop belt, North America.'' Geology, 14(4), pp.330-334.</ref><ref name="VeerversOthers1987a">Veervers, J.T. and Powell, C.M., 1987. ''Late Paleozoic glacial episodes in Gondwanaland reflected in transgressive-regressive depositional sequences in Euramerica.'' Geological Society of America Bulletin, 98(4), pp.475-487.</ref> As occurred during the [[Holocene]] Epoch for [[Meltwater pulse 1A]] and [[Meltwater pulse 1B]],<ref name="Gornitz2009a">Gornitz, V., 2009. ''Sea level change, post-glacial.'' In ''Encyclopedia of paleoclimatology and ancient environments'' (pp. 887-893). Springer Netherlands. In: Encyclopedia of paleoclimatology and ancient environments (Ed. V. Gornitz) pp. 887–893. Springer, Dordrecht, The Netherlands.</ref> brief episodes of rapid melting of Carboniferous, Gondwanan continental ice sheets likely caused very rapid rises in sea level that would have abruptly inundated low-lying coastal swamps and drowned the forests growing on them. Based on the sedimentology of roof strata of surface and underground coal mines and cyclothems containing the fossils of upright and ''[[in situ]]'' tree trunks, geologists proposed that the flooding of coastal swamp by [[Deglaciation|deglacial]] [[meltwater]] pulses resulted in the rapid flooding of coastal forests, particularly along preexisting coastal rivers and streams, over large areas of coastal swamp. During and after their submergence, upright trunks of drowned coastal forests were buried by tidally influenced sedimentation.<ref name="ArcherOthers2016a"/><ref name="CecilOthers2014a">Cecil, C.B., DiMichele, W.A. and Elrick, S.D., 2014. ''Middle and Late Pennsylvanian cyclothems, American Midcontinent: Ice-age environmental changes and terrestrial biotic dynamics.'' Comptes Rendus Geoscience, 346(7), pp.159-168.</ref>

===Association with marine fossils===

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====Glacial deposits====

Unfossilized, late [[Pleistocene]] upright trees have been found buried beneath [[glacial deposit]]s within North America along the southern edge of the [[Laurentide iceIce sheetSheet]]. These buried forests were created when the southern edge of the Laurentide iceIce sheetSheet locally dammed valleys. As a result, meltwater lakes filled these valleys and submerged forests within them. Sediments released by the melting of the adjacent ice sheet rapidly filled these lakes, which quickly buried and preserved the submerged forests lying within them. One forest of ''in situ'', 24,000-year-old unfossilized upright trees was exposed by excavations for a quarry near [[Charleston, Illinois]].<ref>Hansel, A.K., R.C. Berg, A.C. Phillips, and V. Gutowski, 1999, ''Glacial Sediments, Landforms, Paleosols, and a 20,000-Year-Old Forest Bed in East-Central Illinois'', Guidebook 26. Illinois State Geological Survey.</ref> Excavations for a tailings pond about [[Marquette, Michigan]], exposed an ''in situ'' forest of unfossilized trees, which are about 10,000 years old, buried in glacial lake and stream sediments.<ref>Pregitzer, K.S., D.D. Reed, T.J., Bornhorst, D.R. Foster, G.D. Mroz, J.S. Mclachlan, P.E. Laks, D.D. Stokke, P.E. Martin, and S.E. Brown, 2000, ''A buried spruce forest provides evidence at the stand and landscape scale for the effects of environment on vegetation at the Pleistocene/Holocene boundary". Journal of Ecology 88(1):45-53

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Illustrated articles about unfossilized upright trees found within glacial deposits of North America include： (1.) [http://www.museum.state.il.us/muslink/forest/htmls/how_bury.html ''How Do We Know?:Buried Forests'']; (2.) [http://www.admin.mtu.edu/urel/breaking/2000/forest.html ''Researchers Study 10,000-Year-Old Buried Forest'']; and (3.) [http://www.geo.msu.edu/geogmich/chippewa.html ''Glacial Lake Chippewa and Stanley''].

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==References==

==Notes and references==

{{reflist|2}}