Polystrate fossil: Difference between revisions

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

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{{Paleontology}}

[[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 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. 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==

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Geologists have recognized innumerable fossil soils ([[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. 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, geologistsit has 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===

Geologists find nothing anomalous about upright fossil trees found in Carboniferous coal-bearing strata being associated with marine or brackish-water fossils. Because they lived on subsiding coastal plains or pull-apart basins open to the coast, it was quite frequent for subsidence to periodically outpace the accumulation of sediments such that adjacent shallow marine waters would periodically inundate coastal plains in which the trees were buried. As a result, sediments containing marine fossils would periodically accumulate within these areas before being replaced by coastal swamps - either as sediments filled in the shallow sea or as the sea level fell. Also, according to [[Paleoecology|ecological reconstructions]] by geologists, specific assemblages of the types of trees found as upright fossils occupied brackish water, even saline coastal swamps much like modern [[mangrove]] swamps. Thus, finding marine and brackish water fossils associated with these trees is no different than finding brackish water or marine animals living in modern mangrove swamps.<ref name=falcon2005 /><ref name=falcon2006a /><ref name=falcon2006b />

A detailed study by Taylor and Vinn (2006) of the microstructure of fossils which have been traditionally identified as ''"Spirorbis"'' in the geological literature revealed that they consist of the remains of at least two completely different animals. Taylor and Vinn discovered that the ''"Spirorbis"'' fossils found in sedimentary strata, including the Joggins and other Carboniferous coal measures deposited from the [[Ordovician]] to [[Triassic]] periods are the remains of an extinct order of [[Lophophore|lophophorates]] (now called [[microconchids]]) unrelated to modern marine tube-worms ([[Annelid]]s) to which the genus ''Spirorbis'' belongs.<ref name=TaylorOthers2006a>Taylor, P.D. and O. Vinn, 2006, ''Convergent morphology in small spiral worm tubes ('Spirorbis') and its palaeoenvironmental implications''. Journal of the Geological Society, London 163:225–228.</ref> This contradicts arguments made by Harold Coffin and other creationists that ''"Spirorbis"'' fossils within strata containing polystrate fossils indicate their deposition in a marine environment, because these fossils are classified as the remains of extinct fresh and brackish water microconchids instead of the remains of the marine genera ''Spirorbis'' as they have been misidentified in the geologic literature.<ref name=ZatonOthers2012a>Zaton, M., O. Vinn, A.M.F. Tomescu, 2012, ''Invasion of freshwater and variable marginal marine habitats by microconchid tubeworms – an evolutionary perspective.'' Geobios. vol. 45, pp. 603-610.</ref>

===Quaternary examples===

Scientists interpret ''polystrate fossils'' as fossils buried in a geologically short time span - either by one large depositional event or by several smaller ones. Geologists see no need to invoke a global flood to explain upright fossils. This position of geologists is supported by numerous documented examples, a few of which are discussed in the paragraphs below, of buried upright tree-trunks that have been observed buried in the Holocene volcanic deposits of [[Mount St. Helens]], [[Skamania County, Washington]], and Mount Pinatubo, Philippines; in the deltaic and fluvial sediments of the [[Mississippi River Delta]]; and in glacial deposits within the midwestern United States. These buried upright trees demonstrate that conventional geologic processes are capable of burying and preserving trees in an upright position such that in time, they will become fossilized.<ref name="DiMichele+2011a"/><ref name="KaroweOthers1987a)">Karowe, A.L. and T.H. Jefferson, 1987, ''Burial of trees by eruptions of Mount St. Helens, Washington: Implications for the interpretation of fossil forests'', Geological Magazine 124(3):191-204.</ref>

====Volcanic deposits====