Polystrate or upright fossil describes fossils of single organisms (such as tree trunks) that run through more than one geological strata. Entire "fossil forests" have been discovered. They are found all over the world— they are very commonin the Eastern United States, Eastern Canada, England, France, Germany, and Australia — but especially in areas where coal seams are present. Within Carboniferous coal-bearing strata, it is also very common to find what are called Stigmaria (root stocks) in this 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, and is found most often in creationist materials.
In case of the polystrate trees of the Yellowstone petrified forest, which occur buried within the lahar and other volcanic deposits comprising the Lamar River Formation, the periods of rapid sedimentation are regarded by them to be the result of 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 occurs, 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. As is the case of modern lahar deposits, the sedimentary layers containing polystrate trees of the Yellowstone petrified forest and the individual forests, which these polystrate trees comprise, are discontinuous and very limited in their areal extent. Individual layers containing polystrate trees and individual buried forests, which these polystrate trees compose, occupy only a very, very small fraction of the total area of Yellowstone National Park.
Geologists have recognized innumerable fossil soils (paleosols) throughout the strata containing polystrate fossils at Joggins, Nova Scotia, Yellowstone petrified forests, coal mines of the Black Warrior Basin of Alabama, and 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 polystrate fossils found in sedimentary rocks exposed in various outcrops for the last 30 years have described polystrate fossil trees as being deeply rooted in place and typically rooted in recognizable paleosols. This is in sharp contrast to the claims made by creationists such as Harold Coffin and N. A. Rupke. Geologists, such as Falcon and Rygel et al., have published detailed field sketches and pictures of polystrate tree fossils with intact root systems, which are rooted within recognizable paleosols. In case of polystrate fossil trees of the Yellowstone petrified forests, geologists, —again in sharp disagreement with creationists like Harold Coffin— found that the polystrate fossil trees, except for relatively short stumps, are rooted in place within the underlying sediments. Typically, the sediments within which polystrate trees are rooted have paleosols developed within them Either pictures or diagrams of the Yellowstone polystrate fossil trees having intact root systems developed within paleosols found within these strata have been published in Retallack (1981, 1997).
Geologists have also found that some of the larger polystrate trees found within Carboniferous coal-bearing strata show evidence of regeneration after being partially buried by sediments. In the case of these polystrate trees, they were clearly alive when partially buried by sediments. Because of their size, the sediment, which accumulated around them, was insufficient to kill the trees. As a result, they developed a new set of roots from their trunks just below the new ground surface and grew higher to compensate for the part of the trunk buried by sediment. Until they either died or were overwhelmed by the accumulating sediments, these polystrate would likely continue to regenerate by adding height and new roots with each increment of sediment, eventually leaving several of meters of former "trunk" buried underground as sediments accumulated
Geologists find nothing anomalous about polystrate 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 polsytrate trees were buried. As a result, sediments, containing marine fossils, would periodically accumulate within these areas before being replaced by coastal swamps as sediments either filled in the shallow sea or sea level fell. Also, according to ecological reconstructions by geologists, specific assemblages of the types of trees found as polystrate fossils occupied brackish water, even saline coastal swamps much like modern mangrove swamps. Thus, finding marine and brackish water fossils associated with these polystrate trees is no different than finding brackish water or marine animals living in modern mangrove swamps.
A detailed study of the microstructure of fossils, which have been traditionally identified as “Spirorbis” in the geological literature, by Taylor and Vinn revealed that they consist of the remains of at least two completely different animals. They 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 lophophorates totally unrelated to modern marine tube worms (Annelids) to which the genera Spirorbis belong. Thus, the arguments by Harold Coffin and other creationists that the presence of "Spirorbis" fossils within strata containing polystrate fossils indicate their deposition in a marine environment are invalid because these fossils are actually the remains of extinct fresh and brackish water lophophorates instead of the remains of the marine genera Spirorbis as they have been misidentified in the geologic literature.
According to scientists, polystrate fossils are just fossils which were buried in a relatively 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 examples, which have been found at numerous locations, of polystrate, upright, trees completely buried within either late Holocene or historic sediments. These polystrate 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.
At this time, the best documented occurrences of unfossilized polystrate trees are found within historic and late Holocene volcanic deposits of Mount St. Helens, Skamania County, Washington, and Mount Pinatubo, Philippines. At Mount St. Helens, both unfossilized and partially fossilized polystrate trees were observed in many outcrops of volcanic debris and mud flows (lahars) and pyroclastic flow deposits, which date from 1885 to over 30,000 BP., along the South Toutle and other rivers. Late Holocene forests of polystrate trees have also been observed as occurring within the volcanic deposits of other Cascade Range volcanoes. In a few years after the eruption of Mount Pinatubo in 1991, the erosion of loose pyroclastic deposits covering its slopes created a series of volcanic lahars, which ultimately buried large parts of the countryside along major streams draining these slopes beneath several meters of volcanic sediments. The repeated deposition of sediments by volcanic lahars and sediment filled rivers not only created innumerable polystrate trees, but also “polystrate” telephone poles, churches, and houses, over a period a few years. The volcanic deposits enclosing these modern polystrate trees are often virtually identical in their sedimentary structures, external and internal layering, texture, buried soils, and other general character to the volcanic deposits containing the Yellowstone buried forests. As in case of modern forests buried by lahars, the individual buried forests of the Yellowstone Petrified Forest and the layers containing them are very limited in their areal extent.
Within excavations for Interstate Highway 10, borrow pits, landfills, and archaeological surveys, unfossilized polystrate trees have also been found buried within late Holocene, even historic, fluvial and deltaic sediments underlying the surface of the Mississippi River Delta and the Atchafalaya Basin of Louisiana. In one case, borrow pits dug in the natural levees of Bayou Teche near Patterson, Louisiana, have exposed completely buried, 4 to 6-foot (1.2 to 1.8 meters) high, upright trunks of cypress trees. Northeast of Donaldsonville, Louisiana, a borrow pit excavated for fill used to maintain nearby artificial levees, exposed three levels of rooted upright tree trunks stacked on top of each other lying completely buried beneath the surface of Point Houmas, a patch of floodplain lying within a meander loop of the current course of the Mississippi River. While searching for buried archaeological sites, archaeologists excavated a 12 ft (3.6 meter) high upright rooted cypress tree completely buried within a natural levee of the Atchafalaya River within the Indian Bayou Wildlife Management Area just south of Krotz Springs, Louisiana. Radiocarbon dates and historic documents collected for this archaeological survey, during which this and other polystrate trees were found, of the Indian Bayou Wildlife Management Area demonstrated that these polystrate trees were buried sometime during the 1800s during the initial diversion of Mississippi River's flow into the Atchafalaya River.
Unfossilized, late Pleistocene polystrate trees have been found buried beneath glacial deposits within North America along the southern edge of the Laurentide ice sheet. These polystrate forests were created when the southern edge of the Laurentide ice sheet 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 with sediments, which quickly buried and preserved the submerged forests lying within them. One forest of in situ, 24,000 year-old unfossilized polystrate trees was exposed by excavations for a quarry near Charleston, Illinois. Excavations for a tailings pond about Marquette, Michigan, exposed an in situ forest of unfossilized polystrate trees, which are about 10,000 years old, buried in glacial lake and stream sediments.
Two of the reasons Creationists assert that massive amounts of strata must have been laid down rapidly is the fact that polystrate fossil trees are found crossing numerous layers of strata: including sandstone, shale, clay, and even coal seams; another is because some of the "layers" are the size of Texas.
They also assert this because of the absence of any visible sign of roots in the majority of these trees, and because the trees that do possess roots are almost always truncated. In addition, the stigmaria roots that are sometimes found attached to these type of trees are very commonly missing their rootlets. Stigmaria roots get their name from the fact that they often possess scar marks left behind from the missing (or broken off) rootlets. Stigmaria roots are also usually fragmented and not attached to a tree. Lesquereax described 30-foot thick deposits containing broken up stigmaria roots in Pennsylvania, and said that the strata containing them had no upright fossil trees at all. His conclusion was that they had to have been broken off and redeposited. In addition, most of the rootlets found in the coal strata are buried individually, (i.e. apart from being attached to larger roots or trees).
Creationists claim that only 1 out of 50 such fossil trees possesses both roots and rootlets. This figure is the result of counting the number of trees that were missing their roots as recorded by Dawson in his book, Acadian Geolody. See Berg, Randy S., "The Fossil Forests of Nova Scotia" Parts one and two.
One of the rare trees that did have both roots and rootlets is discussed in detail in Part Two of the above referenced article. The author concluded that it also was probably not in situ because it was filled with white sandstone, while none of the surrounding sediments that buried it, or that were above it were white sandstone, and because other trees in this section were said by Brown to be buried obliquely to the horizontal strata.
Leo Lesquereux said that: "Fragments of Stigmaria, trunks, branches and leaves, are generally found embedded in every kind of compound, clay, shales, sandstone, coal, even limestone, in Carboniferous strata ... They are always in large proportion, far above that of any other remains of coal plants..."
For these and other reasons, creationists argue that virtually none of the upright trees that are buried in the coal strata are in situ.