A geologic formation is a formally named rock stratum or geological unit. Formations are Lithostratigraphic units which are defined by primary lithology. The rocky side of a mountain creek near Orosí, Costa Rica. ... Goldenville Strata exposed at a quarry in Bedford, Canada. ... A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ... A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ... Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. ...

The concept of formally defined layers or strata is central to the geologic discipline of stratigraphy. Stratigraphy, a branch of geology, studies rock layers and layering (stratification). ...

Usefulness of formations

Formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata. the are cool The Geologist by Carl Spitzweg A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth and planets of the solar system (see planetary geology). ... Outcrop is a geological term referring to the appearance of bedrock exposed at the surface of the Earth. ... Goldenville Strata exposed at a quarry in Bedford, Canada. ...

Formations were initially described to be the essential geologic time markers based on relative ages and the law of superposition. The divisions of the geological time scale were the formations described and put in chronological order by the geologists and stratigraphers of the 17th and 18th centuries. The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ... The law of superposition (or the principle of superposition) is an axiom that forms one of the bases of the sciences of geology, archaeology, and other fields dealing with stratigraphy. ... The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ...

Modern revision of the geologic sciences has restricted Formations to lithologies, because lithological units are formed by depositional environments, some of which may persist for hundreds of millions of years and will transgress chronostratigraphic intervals or fossil-based methods of correlating rocks. For example, the Hammersley Basin is a Proterozoic sedimentary basin where up to 1200 million years of sedimentation is preserved within the intact sedimentary stratigraphy, with up to 300 million years represented by a single lithological unit of banded iron formation and shale. Three small ammonite fossils, each approximately 1. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ...

Geologic formations are usually sedimentary rock layers, but may also be metamorphic rocks and volcanic flows. Igneous intrusive rocks are generally not divided into Formations. This article does not cite its references or sources. ... Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means change in form, derived from the Greek words meta, change, and morphe, form. The protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound... This article is about volcanoes in geology. ...

Defining lithostratigraphic formations

Formations are the only formal lithostratigraphic units into which the stratigraphic column everywhere should be divided completely on the basis of lithology.

The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region and the detail == needed for geologic mapping and to work out its geologic history.

Formations must be able to be delineated at the scale of geologic mapping practiced in the region. The thickness of formations may range from less than a meter to several thousand meters.

Geologic formations are typically named for the geographic area in which they were first described.

Strictly, formations cannot be defined on any other criteria except primary lithology. However, it is often useful to define Biostratigraphic units based on paleontological criteria, Chronostratigraphic units based on the age of the rocks, and Chemostratigraphic units based on geochemical criteria. A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ... Paleontology, palaeontology or palæontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ... A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ... A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ...

Sequence stratigraphy is a concept which challenges the idea of strict lithostratigraphic units by defining units based on events in sedimentary basins such as oceanic regressions and transgressions. These sequences are a combination of chronostratigraphic units, linked by time, and depositional environment linked by the geologic events which occurred at that time, regardless of the grain size of the sediments. This article may be too technical for most readers to understand. ... Generally, regression is related to moving backwards, and the opposite of progression. ... Transgression refers to an action that breaks some code or set of rules, that is, goes across or against basic assumptions or norms. ...

The term "formation" is often used informally to refer to a specific grouping of rocks, such as those encountered within a certain depth range in an oil well.

"Formation" is also used informally to describe the sometimes odd shapes (forms) that rocks acquire through erosional or depositional processes. Some well known cave formations include stalactites and stalagmites. Lechuguilla Cave, New Mexico A cave is a natural underground void large enough for a human to enter. ... Water droplet coming out of the central canal of a stalactite A stalactite (Greek stalaktos, (Σταλακτίτης), dripping or dropped), or dripstone, is a type of speleothem that hangs from the ceiling or wall of limestone caves. ... The Witchs Finger in the Carlsbad Caverns A stalagmite (from the Greek stalagma (Σταλαγμίτης), drop or drip) is a type of speleothem that rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate. ...

See also: List of fossil sites