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16-661: The Taynton Limestone is a geological formation in Oxfordshire in the United Kingdom . It dates to the Middle Jurassic , mid- Bathonian stage. It predominantly consists of ooidal grainstone . The term " Stonesfield Slate " refers to slaty limestone horizons within the formation that during the 18th and 19th centuries were extensively quarried for use in roof tiling within the vicinity of Stonesfield , Oxfordshire . Previously these were thought to belong to

32-611: A geologic formation goes back to the beginnings of modern scientific geology. The term was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at

48-542: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

64-419: A particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the standard of reference for unlayered rocks is the type locality . Also it can be defined as "The particular sequence of strata chosen as standard of reference of a layered stratigraphic unit." When a stratigraphic unit is nowhere fully exposed,

80-617: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

96-449: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

112-408: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Stratotype A stratotype or type section in geology is the physical location or outcrop of

128-560: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

144-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

160-568: The Sharp's Hill Formation , but boreholes and shaft sections suggest that at least three horizons within the Taynton Limestone were quarried for the slate. These horizons are well known for producing a diverse set of fossils including those of plants, insects as well as vertebrates, including some of the earliest known mammals, pterosaurs as well as those of first dinosaur ever described, Megalosaurus . Blapsium The flora known from

176-577: The Stonesfield Slate comprises a relatively diverse flora, with 25 morphospecies present. It primarily represents a coastal environment, perhaps seasonally dry with mangrove like environments. It is a noticeably different assemblage than the Yorkshire floras of equivalent age, possibly because the latter is thought to represent a deltaic, wetland environment. Formation (geology) A formation must be large enough that it can be mapped at

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192-550: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

208-522: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

224-450: The original type section may be supplemented with reference sections covering the full thickness of the unit. A reference section may also be defined when the original type section is poorly exposed, or for historical units which were designated without specifying a type section according to more modern standards. This palaeogeography article is a stub . You can help Misplaced Pages by expanding it . This article about stratigraphy

240-643: The surface are fundamental to such fields as structural geology , allowing geologists to infer the tectonic history of a region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils

256-432: 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

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