Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earths surface. Geomorphologists work within disciplines such as geography, geodesy, engineering geology, archaeology. This broad base of interests contributes to many styles and interests within the field. Earths surface is modified by a combination of processes that sculpt landscapes, and geologic processes that cause tectonic uplift and subsidence. Many of these factors are strongly mediated by climate, the broad-scale topographies of the Earth illustrate this intersection of surface and subsurface action. Mountain belts are uplifted due to geologic processes, denudation of these high uplifted regions produces sediment that is transported and deposited elsewhere within the landscape or off the coast. On progressively smaller scales, similar ideas apply, where individual landforms evolve in response to the balance of additive processes, these processes directly affect each other, ice sheets and sediment are all loads that change topography through flexural isostasy.
Topography can modify the climate, for example through orographic precipitation. Many geomorphologists are particularly interested in the potential for feedbacks between climate and tectonics, mediated by geomorphic processes, in addition to these broad-scale questions, geomorphologists address issues that are more specific and/or more local. Fluvial geomorphologists focus on rivers, how they transport sediment, migrate across the landscape, cut into bedrock, respond to environmental and tectonic changes, and interact with humans. Soils geomorphologists investigate soil profiles and chemistry to learn about the history of a landscape and understand how climate, biota. Other geomorphologists study how hillslopes form and change, still others investigate the relationships between ecology and geomorphology. Because geomorphology is defined to comprise everything related to the surface of the Earth and its modification, geomorphologists use a wide range of techniques in their work. These may include fieldwork and field data collection, the interpretation of remotely sensed data, geochemical analyses, geomorphologists may rely on geochronology, using dating methods to measure the rate of changes to the surface.
Practical applications of geomorphology include hazard assessment, river control and stream restoration, planetary geomorphology studies landforms on other terrestrial planets such as Mars. Indications of effects of wind, glacial, mass wasting, meteor impact and this effort not only helps better understand the geologic and atmospheric history of those planets but extends geomorphological study of the Earth. Planetary geomorphologists often use Earth analogues to aid in their study of surfaces of other planets, other than some notable exceptions in antiquity, geomorphology is a relatively young science, growing along with interest in other aspects of the earth sciences in the mid-19th century. This section provides a brief outline of some of the major figures
Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea level. The opposite of subsidence is uplift, which results in an increase in elevation, ground subsidence is of concern to geologists, geotechnical engineers and surveyors. Subsidence frequently causes problems in karst terrains, where dissolution of limestone by fluid flow in the subsurface causes the creation of voids. If the roof of these voids becomes too weak, it can collapse and this type of subsidence can result in sinkholes which can be many hundreds of meters deep. Several types of mining, and specifically methods which intentionally cause the extracted void to collapse will result in surface subsidence. Mining-induced subsidence is relatively predictable in its magnitude and extent, mining-induced subsidence is nearly always very localized to the surface above the mined area, plus a margin around the outside. Where mining activity is planned, mining-induced subsidence can be successfully managed if there is co-operation from all of the stakeholders and this is accomplished through a combination of careful mine planning, the taking of preventive measures, and the carrying out of repairs post-mining.
If natural gas is extracted from a gas field the initial pressure in the field will drop over the years. The gas pressure supports the soil layers above the field, if the pressure drops, the soil pressure increases and this leads to subsidence at the ground level. Since exploitation of the Slochteren gas field started in the late 1960s the ground level over a 250 km² area has dropped by a current maximum of 30 cm, the Geospatial Information Authority of Japan reported immediate subsidence caused by the 2011 Tōhoku earthquake. In Northern Japan, subsidence of 0.50 m was observed on the coast of the Pacific Ocean in Miyako, Tōhoku, while Rikuzentakata, in the south at Sōma, Fukushima,0.29 m was observed. The maximum amount of subsidence was 1.2 m, coupled with horizontal diastrophism of up to 5.3 m on the Oshika Peninsula in Miyagi Prefecture, the habitation of lowlands, such as coastal or delta plains, requires drainage. The resulting aeration of the leads to the oxidation of its organic components, such as peat.
This applies especially when water levels are periodically adapted to subsidence, in order to maintain desired unsaturated zone depths. In addition to this, drained soils consolidate as a result of increased effective stress, in this way, land subsidence has the potential of becoming self-perpetuating, having rates up to 5 cm/yr. Water management used to be tuned primarily to such as crop optimisation but, to varying extents. When differential stresses exist in the Earth, these can be accommodated either by geological faulting in the brittle crust, or by flow in the hotter. Where faults occur, absolute subsidence may occur in the wall of normal faults
A seamount is a mountain rising from the ocean seafloor that does not reach to the waters surface, and thus is not an island. Seamounts are typically formed from volcanoes that rise abruptly and are usually found rising from the seafloor to 1. They are defined by oceanographers as independent features that rise to at least 1,000 m above the seafloor, the peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. Seamounts and guyots are most abundant in the North Pacific Ocean, in recent years, several active seamounts have been observed, for example Loihi in the Hawaiian Islands. Because of their abundance, seamounts are one of the most common marine ecosystems in the world, interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton, corals and marine mammals alike.
Their aggregational effect has been noted by the fishing industry. There are ongoing concerns on the impact of fishing on seamount ecosystems. 95% of ecological damage is done by bottom trawling, which scrapes whole ecosystems off seamounts, because of their large numbers, many seamounts remain to be properly studied, and even mapped. Bathymetry and satellite altimetry are two technologies working to close the gap, there have been instances where naval vessels have collided with uncharted seamounts, for example, Muirfield Seamount is named after the ship that struck it in 1973. Seamounts can be found in every ocean basin in the world, a seamount is technically defined as an isolated rise in elevation of 1,000 m or more from the surrounding seafloor, and with a limited summit area, of conical form. If small knolls and hills less than 1,000 m in height are included there are over 100,000 seamounts in the world ocean. Most seamounts are volcanic in origin, and thus tend to be found on oceanic crust near mid-ocean ridges, mantle plumes, and island arcs.
Overall and guyot coverage is greatest as a proportion of area in the North Pacific Ocean. The Arctic Ocean has only 16 seamounts and no guyots, the 9,951 seamounts mapped cover an area of 8,088,550 km2. The largest seamount has an area of 15,500 km2, guyots cover a total area of 707,600 km2 and have an average area of 2,500 km2, more than twice the average size of seamounts. Nearly 50% of guyot area and 42% of the number of guyots occur in the North Pacific Ocean, the largest three guyots are all in the North Pacific, the Kuko Guyot, Suiko Guyot and the Pallada Guyot. Seamount chain redirects here, for a broader coverage related to this topic, Seamounts are often found in groupings or submerged archipelagos, a classic example being the Emperor Seamounts, an extension of the Hawaiian Islands
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin, for these reasons, in geology and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term volcanic is often applied to what are strictly metavolcanic rocks, Volcanic rocks are among the most common rock types on Earths surface, particularly in the oceans. On land, they are common at plate boundaries and in flood basalt provinces. It has been estimated that volcanic rocks cover about 8% of the Earths current land surface, lava Tephra Volcanic bomb Lapilli Volcanic ash Volcanic rocks are usually fine-grained or aphanitic to glass in texture. They often contain clasts of other rocks and phenocrysts, phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a fine grained matrix.
Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava, pumice is a highly vesicular rock produced in explosive volcanic eruptions. Most modern petrologists classify igneous rocks, including rocks, by their chemistry when dealing with their origin. The fact that different mineralogies and textures may be developed from the same initial magmas has led petrologists to rely heavily on chemistry to look at a volcanic rocks origin. The chemistry of volcanic rocks is dependent on two things, the composition of the primary magma and the subsequent differentiation. Differentiation of most volcanic rocks tends to increase the silica content, the initial composition of most volcanic rocks is basaltic, albeit small differences in initial compositions may result in multiple differentiation series. The most common of these series are tholeiitic, calc-alkaline, most volcanic rocks share a number of common minerals. Differentiation of volcanic rocks tends to increase the silica content mainly by fractional crystallization, more evolved volcanic rocks tend to be richer in minerals with a higher amount if silica such as phyllo and tectosilicates including the feldspars, quartz polymorphs and muscovite.
While still dominated by silicates, more volcanic rocks have mineral assemblages with less silica, such as olivine. Bowens reaction series correctly predicts the order of formation of the most common minerals in volcanic rocks, occasionally, a magma may pick up crystals that crystallized from another magma, these crystals are called xenocrysts. Diamonds found in kimberlites are rare but well-known xenocrysts, the kimberlites do not create the diamonds, Volcanic rocks are named according to both their chemical composition and texture. Basalt is a common volcanic rock with low silica content
Aphanite, or aphanitic as an adjective, is a name given to certain igneous rocks that are so fine-grained that their component mineral crystals are not detectable by the unaided eye. This geological texture results from rapid cooling in volcanic or hypabyssal environments, as a rule, the texture of these rocks is not the same as that of volcanic glass, with volcanic glass being non-crystalline, and having a glass-like appearance. Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass or matrix, the large inclusions are called phenocrysts. They consist essentially of very fine-grained minerals, such as feldspar, with hornblende or augite, and may contain biotite, quartz. Andesite Basalt Basanite Dacite Felsite Phonolite Rhyolite Trachyte This article incorporates text from a now in the public domain, Hugh
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can refer generally to the study of the features of any terrestrial planet. Geology gives insight into the history of the Earth by providing the evidence for plate tectonics, the evolutionary history of life. Geology plays a role in engineering and is a major academic discipline. The majority of data comes from research on solid Earth materials. These typically fall into one of two categories and unconsolidated material, the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three types of rock, igneous and metamorphic. The rock cycle is an important concept in geology which illustrates the relationships between three types of rock, and magma. When a rock crystallizes from melt, it is an igneous rock, the sedimentary rock can be subsequently turned into a metamorphic rock due to heat and pressure and is weathered, eroded and lithified, ultimately becoming a sedimentary rock.
Sedimentary rock may be re-eroded and redeposited, and metamorphic rock may undergo additional metamorphism, all three types of rocks may be re-melted, when this happens, a new magma is formed, from which an igneous rock may once again crystallize. Geologists study unlithified material which typically comes from more recent deposits and these materials are superficial deposits which lie above the bedrock. Because of this, the study of material is often known as Quaternary geology. This includes the study of sediment and soils, including studies in geomorphology and this theory is supported by several types of observations, including seafloor spreading, and the global distribution of mountain terrain and seismicity. This coupling between rigid plates moving on the surface of the Earth and the mantle is called plate tectonics. The development of plate tectonics provided a basis for many observations of the solid Earth. Long linear regions of geologic features could be explained as plate boundaries, mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, were explained as divergent boundaries, where two plates move apart.
Arcs of volcanoes and earthquakes were explained as convergent boundaries, where one plate subducts under another, transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes. Plate tectonics provided a mechanism for Alfred Wegeners theory of continental drift and they provided a driving force for crustal deformation, and a new setting for the observations of structural geology
Exfoliation joints or sheet joints are surface-parallel fracture systems in rock often leading to erosion of concentric slabs. Divide the rock into sub-planar slabs, joint spacing increases with depth from a few centimeters near the surface to a few meters Maximum depth of observed occurrence is around 100 meters. Host rock is generally sparsely jointed, fairly isotropic, and has high compressive strength, can have concave and convex upwards curvatures. Many different theories have suggested, below is a short overview of the most common. This theory was proposed by the pioneering geomorphologist Grove Karl Gilbert in 1904 and is widely found in introductory geology texts. The description of this mechanism has led to terms for exfoliation joints. Laboratory studies show that simple compression and relaxation of rock samples under realistic conditions does not cause fracturing, Exfoliation joints are most commonly found in regions of surface-parallel compressive stress, whereas this theory calls for them to occur in zones of extension.
Horizontal stresses become aligned with the current ground surface as the stress drops to zero at this boundary. Thus large surface-parallel compressive stresses can be generated through exhumation that may lead to tensile rock fracture as described below, rock expands upon heating and contracts upon cooling and different rock-forming minerals have variable rates of thermal expansion / contraction. Daily rock surface temperature variations can be large, and many have suggested that stresses created during heating cause the near-surface zone of rock to expand. Large diurnal or fire-induced temperature fluctuations have been observed to create thin lamination and flaking at the surface of rocks, sometimes labeled exfoliation. However, since diurnal temperature fluctuations only reach a few centimeters depth in rock, mineral weathering by penetrating water can cause flaking of thin shells of rock since the volume of some minerals increases upon hydration. This type of fracturing has been observed in the laboratory since at least 1900, fractures formed in this way are sometimes called axial cleavage, longitudinal splitting, or extensional fractures, and are commonly observed in the laboratory during uniaxial compression tests.
High horizontal or surface-parallel compressive stress can result from regional tectonic or topographic stresses, recognizing the presence of exfoliation joints can have important implications in geological engineering. Most notable may be their influence on slope stability, Exfoliation joints following the topography of inclined valley walls, bedrock hill slopes, and cliffs can create rock blocks that are particularly prone to sliding. Especially when the toe of the slope is undercut, sliding along exfoliation joint planes is likely if the joint dip exceeds the joint’s frictional angle, foundation work may be affected by the presence of exfoliation joints, for example in the case of dams. Exfoliation joints underlying a dam foundation can create a significant leakage hazard, exfoliation joints can exert strong directional control on groundwater flow and contaminant transport. Exfoliating granite Media related to Exfoliation joints at Wikimedia Commons
Types of mass wasting include creep, flows and falls, each with its own characteristic features, and taking place over timescales from seconds to years. Mass wasting occurs on both terrestrial and submarine slopes, and has observed on Earth, Venus. When the gravitational force acting on a slope exceeds its resisting force, the slope materials strength and cohesion and the amount of internal friction between material help maintain the slopes stability and are known collectively as the slopes shear strength. The steepest angle that a slope can maintain without losing its stability is known as its angle of repose. When a slope made of loose material possesses this angle, its shear strength perfectly counterbalances the force of gravity acting upon it. Mass wasting may occur at a slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilized the surface. It may occur at high speed, such as in rockslides or landslides, with disastrous consequences.
Factors that change the potential of mass wasting include, change in angle, weakening of material by weathering, increased water content, changes in vegetation cover. Volcano flanks can become over-steep resulting in instability and mass wasting and this is now a recognised part of the growth of all active volcanoes. The failure of the flank of Mount St Helens in 1980 showed how rapidly volcanic flanks can deform. Water can increase or decrease the stability of a slope depending on the amount present, small amounts of water can strengthen soils because the surface tension of water increases soil cohesion. This allows the soil to resist erosion better than if it were dry, if too much water is present the water may act to increase the pore pressure, reducing friction, and accelerating the erosion process and resulting in different types of mass wasting. A good example of this is to think of a sand castle, water must be mixed with sand in order for the castle to keep its shape. If too much water is added the sand away, if not enough water is added the sand falls.
Water increases the mass of the soil, this is important because an increase in mass means that there will be an increase in velocity if mass wasting is triggered. Types of mass movement are distinguished based on how the soil, soil creep is a long term process. The combination of movements of soil or rock in different directions over time are directed by gravity gradually downslope. The steeper the slope, the faster the creep, the creep makes trees and shrubs curve to maintain their perpendicularity, and they can trigger landslides if they lose their root footing
Cross-cutting relationships is a principle of geology that states that the geologic feature which cuts another is the younger of the two features. It is a dating technique in geology. There are several types of cross cutting relationships, Structural relationships may be faults or fractures cutting through an older rock. Intrusional relationships occur when an igneous pluton or dike is intruded into pre-existing rocks, stratigraphic relationships may be an erosional surface cuts across older rock layers, geological structures, or other geological features. Sedimentological relationships occur where currents have eroded or scoured older sediment in an area to produce, for example. Paleontological relationships occur where animal activity or plant growth produces truncation and this happens, for example, where animal burrows penetrate into pre-existing sedimentary deposits. Geomorphological relationships may occur where a feature, such as a river. In a similar example, an impact crater excavates into a layer of rock.
Cross-cutting relationships may be compound in nature, for example, if a fault were truncated by an unconformity, and that unconformity cut by a dike. Based upon such compound cross-cutting relationships it can be seen that the fault is older than the unconformity which in turn is older than the dike, using such rationale, the sequence of geological events can be better understood. Cross-cutting relationships may be seen cartographically and microscopically, in other words, these relationships have various scales. A cartographic crosscutting relationship might look like, for example, a large fault dissecting the landscape on a large map, megascopic cross-cutting relationships are features like igneous dikes, as mentioned above, which would be seen on an outcrop or in a limited geographic area. Microscopic cross-cutting relationships are those that require study by magnification or other close scrutiny, for example, penetration of a fossil shell by the drilling action of a boring organism is an example of such a relationship.
Cross-cutting relationships can be used in conjunction with radiometric age dating to effect an age bracket for geological materials that cannot be dated by radiometric techniques. A radiometric age date from crystals in dike A will give the age date for the layer in question and likewise. This provides an age bracket, or range of possible ages, Principle of original horizontality Principle of lateral continuity Principle of faunal succession Cross Cutting. Ed. K. Lee Lerner and Brenda Wilmoth Lerner, nicolai Stenonis solido intra solidum naturaliter contento dissertationis prodromus. Florentiae, ex typographia sub signo Stellae Hutton, theory of the Earth,1795 Lyell, Charles
Intrusive rock is formed when magma crystallizes and solidifies underground to form intrusions, for example plutons, dikes, sills and volcanic necks. Intrusive rock forms within Earths crust from the crystallization of magma, magma slowly pushes up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the magma slowly cools into a solid, the different parts of the magma crystallize into rocks, many mountain ranges, such as the Sierra Nevada in California, are formed mostly from large granite intrusions, see Sierra Nevada Batholith. Intrusions are one of the two ways igneous rock can form, the other is extrusive rock, that is, an eruption or similar event. Technically speaking, an intrusion is any formation of igneous rock, rock formed from magma that cools. In contrast, an extrusion consists of rock, rock formed above the surface of the crust. Large bodies of magma that solidify underground before they reach the surface of the crust are called plutons, plutonic rocks form 7% of the Earths current land surface.
Coarse-grained intrusive igneous rocks form at depth within the earth are called abyssal while those that form near the surface are called subvolcanic or hypabyssal. The term intrusive suite seems near synonymous, there is, however, a modest difference, An intrusive suite is a group of plutons related in time and space. Intrusions vary widely, from mountain-range-sized batholiths to thin veinlike fracture fillings of aplite or pegmatite, when exposed by erosion, such batholiths may occupy large areas. A well-known example of an intrusion is Devils Tower, another is Shiprock, New Mexico, USA. Be the pluton is large, it may be called a batholith or a stock, Intrusive rocks are characterized by large crystal sizes, and as the individual crystals are visible, the rock is called phaneritic. This is as the magma cools underground, and while cooling may be fast or slow, cooling is slower than on the surface, if it runs parallel to rock layers, it is called a sill. If an intrusion makes rocks above rise to form a dome, as heat dissipation is slow, and as the rock is under pressure, crystals form, and no vitreous rapidly chilled matter is present.
The intrusions did not flow while solidifying, hence do not show lines, contained gases could not escape through the thick strata, thus form cavities, which can often be observed. Because their crystals are of the rough equal size, these rocks are said to be equigranular, there is typically no distinction between a first generation of large well-shaped crystals and a fine-grained ground-mass. Earlier crystals originated at a time when most of the rock was still liquid and are more or less perfect, crystals are less regular in shape because they were compelled to occupy the spaces left between the already-formed crystals. The former case is said to be idiomorphic, the latter is xenomorphic, there are many other characteristics that serve to distinguish the members of these two groups
Aeolian processes, spelled eolian or æolian, pertain to wind activity in the study of geology and weather and specifically to the winds ability to shape the surface of the Earth. Winds may erode and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture, although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts. The term is derived from the name of the Greek god Aeolus, wind erodes the Earths surface by deflation and by abrasion. Regions which experience intense and sustained erosion are called deflation zones, most aeolian deflation zones are composed of desert pavement, a sheet-like surface of rock fragments that remains after wind and water have removed the fine particles. Almost half of Earths desert surfaces are stony deflation zones, the rock mantle in desert pavements protects the underlying material from deflation. A dark, shiny stain, called desert varnish or rock varnish, is found on the surfaces of some desert rocks that have been exposed at the surface for a long period of time.
Manganese, iron oxides and clay minerals form most varnishes, deflation basins, called blowouts, are hollows formed by the removal of particles by wind. Blowouts are generally small, but may be up to kilometers in diameter. In parts of Antarctica wind-blown snowflakes that are technically sediments have caused abrasion of exposed rocks, grinding by particles carried in the wind creates grooves or small depressions. Ventifacts are rocks which have cut, and sometimes polished. Sculpted landforms, called yardangs, are up to tens of meters high, the famous Great Sphinx of Giza in Egypt may be a modified yardang. Particles are transported by winds through suspension and creeping along the ground, small particles may be held in the atmosphere in suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air, typical winds near Earths surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust or haze.
Saltation is downwind movement of particles in a series of jumps or skips, saltation normally lifts sand-size particles no more than one centimeter above the ground and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation, the grain may hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert, aeolian turbidity currents are better known as dust storms. Air over deserts is cooled significantly when rain passes through it and this cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward, people and possibly even climates are affected by dust storms
Stratigraphy is a branch of geology which studies rock layers and layering. It is primarily used in the study of sedimentary and layered volcanic rocks, stratigraphy has two related subfields, lithologic stratigraphy or lithostratigraphy, and biologic stratigraphy or biostratigraphy. The first practical application of stratigraphy was by William Smith in the 1790s. Another influential application of stratigraphy in the early 19th century was a study by Georges Cuvier, variation in rock units, most obviously displayed as visible layering, is due to physical contrasts in rock type. This variation can occur vertically as layering, or laterally, and these variations provide a lithostratigraphy or lithologic stratigraphy of the rock unit. Key concepts in stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries imply about their original depositional environment. The basic concept in stratigraphy, called the law of superposition, states, in a stratigraphic sequence.
Chemostratigraphy studies the changes in the proportions of trace elements and isotopes within. Carbon and oxygen isotope ratios vary with time, and researchers can use those to map subtle changes that occurred in the paleoenvironment and this has led to the specialized field of isotopic stratigraphy. Biostratigraphy or paleontologic stratigraphy is based on evidence in the rock layers. Strata from widespread locations containing the fossil fauna and flora are said to be correlatable in time. Biologic stratigraphy was based on William Smiths principle of succession, which predated. It provides strong evidence for the formation and extinction of species, the geologic time scale was developed during the 19th century, based on the evidence of biologic stratigraphy and faunal succession. One important development is the Vail curve, which attempts to define a global historical sea-level curve according to inferences from worldwide stratigraphic patterns, stratigraphy is commonly used to delineate the nature and extent of hydrocarbon-bearing reservoir rocks and traps of petroleum geology.
Chronostratigraphy is the branch of stratigraphy that places an absolute age, a gap or missing strata in the geological record of an area is called a stratigraphic hiatus. This may be the result of a halt in the deposition of sediment, the gap may be due to removal by erosion, in which case it may be called a stratigraphic vacuity. It is called a hiatus because deposition was on hold for a period of time, a physical gap may represent both a period of non-deposition and a period of erosion. A geologic fault may cause the appearance of a hiatus, magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences