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Gravel Point Formation
The Gravel Point Formation is a geologic formation in western Michigan. It preserves fossils dating back to the middle Devonian period and correlates with the Long Lake Limestone and Alpena Limestone. Description The Michigan Basin was a shallow marine shelf during the middle Devonian, located between 30º South and 20º North latitude in central Laurasia. According to stratigraphic and paleontological examination, the sediments of the Gravel Point Formation were deposited in a shallow lagoonal reef environment. Fossil content Vertebrates Acanthodians Bony fish Placoderms Invertebrates Several species of ostracods, an unidentified arthropod 'hook', crinoid columnals and several species of polychaetes and scolecodonts are known from the formation. Brachiopods Bryozoans Cnidarians Sponges Tentaculitans Trilobites Flora Algal colonies are known from the formation. Acritarchs Plants See also * List of fossiliferous stratigraphic units in Michigan This ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geological Formation
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exposed in a geographical region (the stratigraphic column). It is the fundamental unit of lithostratigraphy, the study of strata or rock layers. A formation must be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by the thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of a geologic formation goes back to the beginnings of modern scientific geology. The term was used by Abraham Gottlob Wer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
