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Ceja Formation
The Ceja Formation is a Pliocene to Pleistocene geologic formation exposed near Albuquerque, New Mexico. Description The formation consists of weakly consolidated sandstone and conglomerate, varying in color from light yellowish-brown to reddish-yellow or pink. It consists of fluvial deposits with paleocurrent directions from the west. The lower beds are predominantly interbedded sandstone and mudstone while the upper beds are predominantly sandstone to conglomerate with occasional small boulders. The formation lies disconformably on the Arroyo Ojito Formation and its top beds are gravels capping the Llano de Albuquerque geomorphic surface. The lower beds sometimes contain white micritic carbonate pebbles interpreted as reworked caliche of the underlying Arroyo Ojito Formation. Total exposed thickness is . Well logs indicate that the Ceja thickens to more than in the subsurface on the western margin of the Rio Grande valley, where it likely interfingers with the Sierr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Formation (stratigraphy)
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exposed in a geographical region (the stratigraphic column). It is the fundamental unit of lithostratigraphy, the study of strata or rock layers. A formation must be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by the thickness (geology), 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 a geologic formation goes back to the beginnings of modern scientific geology. The term was used by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, W. H. Freeman, 2nd ed, 529 pp. The term ''mudstone'' is also used to describe carbonate rocks (limestone or dolomite) that are composed predominantly of carbonate mud. However, in most contexts, the term refers to siliciclastic mudstone, composed mostly of silicate minerals. The NASA Curiosity rover has found deposits of mudstone on Mars that contain organic substances such as propane, benzene and toluene. Definition There is not a single definition of mudstone that has gained general acceptance,Boggs 2006, p.143 though there is wide agreement that mudstones are fine-grained sedimentary rocks, composed mostly of silicate grains with a grain size less than . Individual grains this size are too small to be disting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Argon–argon Dating
Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of argon isotopes. 40Ar/39Ar dating relies on neutron irradiation from a nuclear reactor to convert a stable form of potassium (39K) into the radioactive 39Ar. As long as a standard of known age is co-irradiated with unknown samples, it is possible to use a single measurement of argon isotopes to calculate the 40K/40Ar* ratio, and thus to calculate the age of the unknown sample. 40Ar* refers to the radiogenic 40Ar, i.e. the 40Ar produced from radioactive decay of 40K. 40Ar* does not include atmospheric argon adsorbed to the surface or inherited through diffusion and its calculated value is derived from measuring the 36Ar (which is assumed to be of atmosphe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lava Flow
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from . The volcanic rock resulting from subsequent cooling is also often called ''lava''. A lava flow is an outpouring of lava during an effusive eruption. (An explosive eruption, by contrast, produces a mixture of volcanic ash and other fragments called tephra, not lava flows.) The viscosity of most lava is about that of ketchup, roughly 10,000 to 100,000 times that of water. Even so, lava can flow great distances before cooling causes it to solidify, because lava exposed to air quickly develops a solid crust that insulates the remaining liquid lava, helping to keep it hot and inviscid enough to continue flowing. The word ''lava'' comes from Italian and is probably derived from the Latin word ''labes'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ma (unit)
A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn and winter. In tropical and subtropical regions, several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked. A calendar year is an approximation of the number of days of the Earth's orbital period, as counted in a given calendar. The Gregorian calendar, or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars. For the Gregorian calendar, the average length of the calendar year (the mean yea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanic Ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer to all explosive eruption products (correctly referred to as ''tephra''), including particles larger than 2 mm. Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The force of the gases shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, causing the water to explosively flash to steam leading to shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometres away. Due to its wide dispersal, ash can have a number of impacts on society, including animal a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiometric Dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. The use of radiometric dating was first published in 1907 by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features, including the age of fossilized life forms or the age of Earth itself, and can also be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geologic time scale. Among the best-known techniques are radiocarbon dating, potassium–argon dating and uranium–lead dating. By al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the ''fossil record''. Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years old to 4.1 billion years old. Early edition, published online before print. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sierra Ladrones Formation
The Sierra Ladrones Formation is a geologic formation exposed near the Rio Grande Valley in New Mexico. It preserves fossils of Pliocene to Pleistocene age. Description The formation consists of three facies representing different depositional environments. These are piedmont slope and alluvial fan deposits, typically composed of light-brown to light-reddish-brown sandstone and fanglomerate; axial stream deposits, which are composed of light-gray to light-yellowish-brown fine- to medium-grained sand and sandstone with fluvial cross-bedding and cut-and-fill channels; and interbedded basalt flows with a K-Ar age of 4.5 +/-0.1 million years ( Ma. The total thickness is in excess of . The formation unconformably overlies or is in fault contact with the Popotosa Formation or older formations. Its age is early Pliocene to middle Pleistocene (2 Ma to 5 Ma.) The formation is interpreted as fanglomerates shed from the flanking uplifts of the Rio Grande Rift and channel and floodplai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interfingering
A geological contact is a boundary which separates one rock body from another. A contact can be formed during deposition, by the intrusion of magma, or through faulting or other deformation of rock beds that brings distinct rock bodies into contact. The geologic subdiscipline of stratigraphy is primarily concerned with depositional contacts,Boggs 2006, p. 401 while faults and shear zones are of particular interest in structural geology. Faults and shear zones can be regarded as a form of secondary structure in the rock beds.Davis and Kluth 2011, p.21 Types of contacts Depositional Conformable Conformable contacts represent no time gap in the geologic record. They are usually planar, though they may have slightly irregular topography. These contacts represent continual, uninterrupted deposition and accumulation of sedimentary rocks, or represent lava flows. A conformable contact can be ''abrupt'', where the contact separates beds of distinct lithology. Abrupt contacts coi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rio Grande Valley
The Lower Rio Grande Valley ( es, Valle del Río Grande), commonly known as the Rio Grande Valley or locally as the Valley or RGV, is a region spanning the border of Texas and Mexico located in a floodplain of the Rio Grande near its mouth. The region includes the southernmost tip of South Texas and a portion of northern Tamaulipas, Mexico. It consists of the Brownsville, Harlingen, Weslaco, Pharr, McAllen, Edinburg, Mission, San Juan, and Rio Grande City metropolitan areas in the United States and the Matamoros, Río Bravo, and Reynosa metropolitan areas in Mexico. The area is generally bilingual in English and Spanish, with a fair amount of Spanglish due to the region's diverse history and transborder agglomerations It is home to some of the poorest cities in the nation, as well as many unincorporated, persistent poverty communities called ''colonias''. A large seasonal influx occurs of "winter Texans" — people who come down from the north for the winter and then re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Caliche
Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, including in central and western Australia, in the Kalahari Desert, in the High Plains of the western United States, in the Sonoran Desert, Chihuahuan Desert and Mojave Desert of North America, and in eastern Saudi Arabia at Al-Hasa. Caliche is also known as calcrete or kankar (in India). It belongs to the duricrusts. The term ''caliche'' is Spanish and is originally from the Latin ''calx'', meaning lime. Caliche is generally light-colored, but can range from white to light pink to reddish-brown, depending on the impurities present. It generally occurs on or near the surface, but can be found in deeper subsoil deposits, as well. Layers vary from a few inches to feet thick, and multiple layers can exist in a single location. A caliche laye ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
