Stratigraphy

upright=1.35|thumb|The Permian through [[Jurassic strata of the Colorado Plateau area of southeastern Utah demonstrate the principles of stratigraphy.]] Stratigraphy is a branch of geology concerned with the study of rock layers (strata) 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 (stratigraphy by age).

fracture or discontinuity in rock across which there is displacement

thumb|Coral reef at Nusa Lembongan, Bali, Indonesia thumb|Pamalican island with surrounding reef, [[Sulu Sea, Philippines]] thumb|A reef surrounding an islet thumb|Reefs off Vanatinai|Vanatinai Island in the [[Louisiade Archipelago]]

thumb|Strata in Salta province|Salta ([[Argentina)]] thumb|Goldenville strata in quarry in Bedford, Nova Scotia|Bedford, Canada. These are [[Middle Cambrian marine sediments. This formation covers over half of Nova Scotia and is recorded as being 8,800 m (29,000 ft) thick in some areas.]]

thumb|Eolianite carbonate facies (Holocene) on [[Long Island, Bahamas]]

commission of the IUGS tasked with the scientific definitions of geological stratigraphy of the Earth

Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. The primary objective of biostratigraphy is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at a different section. Fossils within these strata are useful because sediments of the same age can look completely different, due to local variations in the sedimentary environment. For example, one section might have been made up of clays and marl

thumb|''Hutton's Unconformity'' at [[Jedburgh, Scotland, illustrated by John Clerk in 1787 and photographed in 2003.]] An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger layer, but the term is used to describe any break in the sedimentary geologic record. The significance of angular unconformity (see below) was shown by James Hutton, who found examples of Hutton'

in geology, the crystalline rocks lying above the mantle and beneath all other rocks and sediments

Sapropel (a contraction of Ancient Greek words sapros and pelos, meaning putrefaction and mud (or clay), respectively) is a term used in marine geology to describe dark-coloured sediments that are rich in organic matter. Organic carbon concentrations in sapropels commonly exceed 2 wt.% in weight.

Chronostratigraphy is the branch of stratigraphy that studies the ages of rock strata in relation to time.

boundary of a stage on the geologic time scale

thumb|upright=1.3|The Permian through [[Jurassic lithostratigraphy of the Colorado Plateau area of southeastern Utah that makes up much of the famous prominent rock formations in protected areas such as Capitol Reef National Park and Canyonlands National Park. From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area, Utah.]

cylindrical section of a naturally occurring substance, usually obtained by drilling into it with special drills

law stating that newer strata stack above older ones

alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data

A chronozone or chron is a unit in chronostratigraphy, defined by events such as geomagnetic reversals (magnetozones), or based on the presence of specific fossils (biozone or biochronozone). According to the International Commission on Stratigraphy, the term "chronozone" refers to the rocks formed during a particular time period, while "chron" refers to that time period.

In stratigraphy, paleontology, geology, and geobiology, an erathem is the total stratigraphic unit deposited during a certain corresponding span of time during an era in the geologic timescale.

thumb|250px|The Khulsan locality, which is the stratotype of the Barun Goyot Formation, [[Mongolia]] In geology, a stratotype or type section is the physical location or outcrop of 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.

idealized composite unit of the geologic record representing the totality of rock strata laid down during a certain period of the geologic time scale

The Subatlantic is the current climatic age of the Holocene epoch. It started about 2,500 years BP and is still ongoing. Its average temperatures are slightly lower than during the preceding Subboreal and Atlantic. During its course, the temperature underwent several oscillations, which had a strong influence on fauna and flora and thus indirectly on the evolution of human civilizations. With intensifying industrialisation, human society started to stress the natural climatic cycles with increased greenhouse gas emissions.

stratigraphic subdivison

diagram used in geology to show the vertical sequence of rock units

Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization (ChRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because volcanic flows acquire a thermoremanent magnetization and sediments acquire a depositional remanent magnetization, both of which reflect the direction of the Earth's field at the time of formation.

diagram of a 2D or 3D cross section through geological structures

powerful burst of cosmic rays

volume of rock defined by its petrographic, lithologic or paleontologic features

geologic term regarding rock types, stratigraphic units or mineral species

fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances

observed increase of 1.2% in the concentration of carbon-14 isotope in tree rings dated to 774 or 775

layers of sediment are deposited approximately horizontally under the action of gravity

Caprock or cap rock is a hard, resistant, and impermeable layer of rock that overlies and protects a layer of softer material. In petroleum geology the softer lower layer may be a reservoir of oil or natural gas. The caprock acts similarly to the crust on a pie where the crust (caprock) prevents leakage of the soft filling (softer material). In landforms like mesas and buttes the caprock consists of sturdy erosion-resistant rock like granite or basalt that resists weathering more strongly than its supporting rock and results in differential erosion. It also influences hydrology by creating wat

principle of geology that states that the geologic feature which cuts another is the younger of the two features

In sedimentary geology and geomorphology, progradation is the growth of a river delta further out into the sea over time. This occurs when the volume of incoming sediment is greater than the volume of the delta that is lost through subsidence, sea-level rise, or erosion.

entirety of the layers of rock strata

In geology, Neocomian was a name given to the lowest stage of the Cretaceous system. It is generally considered to encompass the interval now covered by the Berriasian, Valanginian and Hauterivian, from approximately 145 to 130 Ma. It was introduced by Jules Thurmann in 1835 on account of the development of these rocks at Neuchâtel (Neocomum), Switzerland. It has been employed in more than one sense. In the type area the rocks have been divided into two sub-stages, a lower, Valanginian (from Valengin, Pierre Jean Édouard Desor, 1854) and an upper, Hauterivian (from Hauterive, Eugène Renevier,

American geologist (1904–1975)

thumb | right|Scheme describing a retrogradation depositional pattern of coastal (shore or deltaic) sediments: t1-2-3 are consecutive sedimentation times. Ideal lithostratigraphic sections along the depositional system are reported. Retrogradation is the landward change in position of the front of a coastal depositional system (such as a river delta) with time. This occurs when the mass balance of sediment into a delta or a beach system is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. As a result,

Chemostratigraphy, or chemical stratigraphy, is the study of the chemical variations within sedimentary sequences to determine stratigraphic relationships. The field is relatively young, having only come into common usage in the early 1980s, but the basic idea of chemostratigraphy is nearly as old as stratigraphy itself: distinct chemical signatures can be as useful as distinct fossil assemblages or distinct lithographies in establishing stratigraphic relationships between different rock layers.

thumb|222px|The nature of sediments can vary in a cyclic fashion, and these cycles can be displayed in the sedimentary record - here visible in the colouration and resistance of strata thumb|Milankovitch variations, solar forcing, and glacial cycles. Image by Robert A. Rohde, under the CC BY-SA 3.0 license. Cyclostratigraphy is a subdiscipline of stratigraphy that studies astronomically forced climate cycles within sedimentary successions.

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sequences of sedimentary rocks that are characterised by repetitive patterns of different rock types (strata) or facies within the sequence

solar storm

creationist term for a fossil that extends through more than one geological stratum

a bedding surface where there is marked change in the lithology within a sequence of sedimentary or volcanic rocks or a distinctive layer or thin bed with a characteristic lithology or fossil content within a sequence

permanent magnetic property of rocks and sediments

organization