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. 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.
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.
Geological explanation In geology, such fossils are referred to as either upright fossil trunks, upright fossil trees, or T0 assemblages. According to mainstream models of sedimentary environments, they are formed by rare to infrequent brief episodes of rapid sedimentation separated by long periods of either slow deposition, nondeposition, or a combination of both.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.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).
Upright fossils typically occur 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 directly result from rapid subsidence, caused by salt tectonics within an already subsiding pull-apart basin, and from the 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 include (1.) Sedimentology: Fossil forests sunk by salt by Sara Pratt, July 2005 Geotimes and (2.) Joggins Fossil Forest PaleoBlog, April 25, 2005
Yellowstone The upright fossil trees of the Gallatin Petrified Forest in the Gallatin Range and the Yellowstone Petrified Forest at Amethyst Mountain and Specimen Ridge in Yellowstone National Park, occur buried within the lahars and other volcanic deposits comprising the Eocene Lamar River Formation as the result of periods of rapid sedimentation associated with explosive volcanism. This type of volcanism generates and deposits large quantities of loose volcanic material as a blanket over the slope of a volcano, as happened during the 1991 eruption of Mount Pinatubo. Both during and for years after a period of volcanism, lahars and normal stream activity wash this loose volcanic material downslope. These processes result in the rapid burial of large areas of the surrounding countryside beneath several meters of sediment, as directly observed during the 1991 eruption of Mount Pinatubo.Newhall, C.G., and R.S. Punongbayan, 1996, Fire and Mud: Eruptions and Lahars of Mount Pinatubo, Philippines, University of Washington Press. As with modern lahar deposits, the sedimentary layers containing upright trees of the Yellowstone petrified forest are discontinuous and very limited in areal extent. Individual layers containing upright trees and individual buried forests occupy only a very small fraction of the total area of Yellowstone National Park.Amidon, L., 1997, Paleoclimate Study of Eocene Fossil Woods and Associated Paleosols from the Gallatin Petrified Forest, Gallatin National Forest, SW Montana. unpublished Master's thesis, University of Montana.
Fossil soils Geologists have recognized innumerable fossil soils (paleosols) 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 seams, 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 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 paleosols. Researchers such as FalconFalcon-Lang, H.J., 2003a, Late Carboniferous dryland tropical vegetation, Joggins, Nova Scotia, Canada, Palaios 18:197– 211.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.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.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.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. and Rygel et al.,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. 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 petrified forests, it 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.Retallack, G.J., 1981, Reinterpretation of the depositional environment of Yellowstone fossil forest: Comment, Geology 9:52-53.Retallack, G.J., 1997, A Colour Guide to Paleosols. John Wiley and Sons. 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.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
Formation by regeneration Geologists have also found that some of the larger upright fossil trees found within Carboniferous coal-bearing strata show evidence of regeneration after being partially buried by sediments. In these cases, the trees were clearly alive when they were partially buried by sediments. The accumulated sediment was insufficient to kill the trees immediately because of their size. As a result, some of them developed a new set of roots from their trunks just below the new ground surface. Until they either died or were overwhelmed by the accumulating sediments, these trees would likely continue to regenerate by adding height and new roots with each increment of sediment, eventually leaving several meters of former "trunk" buried underground as sediments accumulated.Gastaldo, R.A., 1992, Regenerative growth in fossil horsetails (Calamites) following burial by alluvium. Historical Biology, 6(3):203-220.
Formation by Carboniferous deglacial meltwater-pulses