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Lithology is the basis of subdividing rock sequences into individual lithostratigraphic units for the purposes of mapping and correlation between areas. In certain applications, such as site investigations , lithology is described using a standard terminology such as in the European geotechnical standard Eurocode 7 .
The principles of lithostratigraphy were first established by the Danish naturalist, Nicolas Steno, in his 1669 Dissertationis prodromus. [1] A lithostratigraphic unit conforms to the law of superposition, which in its modern form states that in any succession of strata, not disturbed or overturned since deposition, younger rocks lies above older rocks. [2]
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. [2]
Stratigraphy is a branch of geology concerned with the study of rock layers and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks . Stratigraphy has three related subfields: lithostratigraphy (lithologic stratigraphy), biostratigraphy (biologic stratigraphy), and chronostratigraphy ...
Units of formation or higher rank are usually named for the unit's type location, and the formal name usually also states the unit's rank or lithology. A lithostratigraphic unit may have a change in rank over a some distance; a group may thin to a formation in another region and a formation may reduce in rank for member or bed as it "pinches out".
They are further divided into progressive gradual contacts where the change in lithology is more or less continuous, or intercalated contacts where thin beds of a new lithology appear at the base of the contact zone, become thicker upwards, and completely replaced the old lithology at the top of the contact zone. [4]
Petrology (from Ancient Greek πέτρος (pétros) 'rock' and -λογία 'study of') is the branch of geology that studies rocks, their mineralogy, composition, texture, structure and the conditions under which they form. [1] Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. [2]
In geology, a complex is a lithodemic unit consisting of two or more lithodemes of more than one genetic class (metamorphic, igneous or sedimentary).. The law of superposition is inapplicable to intrusive, highly deformed, or metamorphic bodies of rock lacking discernible stratification.