In geology, such fossils are referred to as upright fossils, trunks, or trees. Brief periods of rapid sedimentation favor their formation. 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. The specific layers containing polystrate fossils occupy only a very limited fraction of the total area of any of these basins.
Read more about this topic: Polystrate Fossil
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