In geology, a key bed (syn marker bed) is a widespread sedimentary layer that formed at a single time, such that it is useful for geologic correlations and dating over a large area. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit This article deals with the general meaning of the term "synonym" Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Examples of key beds are massive ashfalls, such as those produced by nearby normal volcanic eruptions, and far away in supervolcanic eruptions, as well as tills deposited by continental glaciers, and the global iridium layer deposited at the K–T boundary. Plate tectonics and hotspots Divergent plate boundaries At the A supervolcano or super volcanic eruption is a Volcanic eruption which is Orders of magnitude greater than any volcano in historic times (generally accepted to be Till is unsorted glacial sediment Glacial drift is a general term for the coarsely graded and extremely heterogeneous Sediments of glacial origin A continent is one of several large Landmasses on Earth. They are generally identified by Convention rather than any strict criteria with seven regions "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. Iridium (ɪˈrɪdiəm is a Chemical element that has the symbol Ir and Atomic number 77 The K-T boundary is a geological signature usually a thin band dated to 65
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- Stanley, Steven M. Radiometric dating (often called radioactive dating) is a technique used to date materials usually based on a comparison between the observed abundance of a naturally occurring Before the advent of Absolute dating in the 20th century Archaeologists and Geologists were largely limited to the use of relative dating techniques Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) Earth System History. New York: W. H. Freeman and Company, 1999. ISBN 0-7167-2882-6 pp. 170-1
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