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Spears Group
The Spears Group is a group of geologic formations exposed in and around the northeast Mogollon-Datil volcanic field of southwestern New Mexico. It has a radiometric age of 33 to 39 million years, corresponding to the Eocene to Oligocene epochs. Description The group is composed primarily of volcaniclastic beds, deposited in alluvial fans or braided streams, with minor basaltic andesite to dacite lava flows. It contains some lacustrine delta deposits at its base. The total thickness is as much as . The group grades below into the Baca Formation and interfingers with lava flows and ash flow sheets of the Mogollon Group and Datil Group. K-Ar and fission track dating suggest an age of 33 to 39 million years. The Dog Springs Formation shows striking sedimentary structure indicating that the debris flow beds making up most of the formation slumped over distance scales of miles on the underlying Baca Formation beds. In some locations, clastic dikes derived from the Baca Formation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Group (stratigraphy)
In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into supergroups. Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying the stratigraphy of large regions. Geologists exploring a new area have sometimes defined groups when they believe the strata within the groups can be divided into formations during subsequent investigations of the area. It is possible for only some of the strata making up a group to be divided into formations. An example of a group is the Glen Canyon Group, which includes (in ascending order) the Wingate Sandstone, the Moenave Formation, the Kayenta Formation, and the Navajo Sandstone. Each of the formations can be distinguished from its neighbor by its lithology, but all were deposited in the same vast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dacite
Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. It is composed predominantly of plagioclase feldspar and quartz. Dacite is relatively common, occurring in many tectonic settings. It is associated with andesite and rhyolite as part of the subalkaline volcanic rock, subalkaline tholeiite, tholeiitic and calc-alkaline magma series. Composition Dacite consists mostly of plagioclase feldspar and quartz with biotite, hornblende, and pyroxene (augite or enstatite). The quartz appears as rounded, corroded phenocrysts, or as an element of the ground-mass. The plagioclase in dacite ranges from oligoclase to andesine and labradorite. Sanidine occurs, although in small proportions, in some dacites, and when abundant gives rise to rocks that form rhyodacite, transitions to the rhyolites. The rel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palm Park Formation
The Palm Park Formation is a geologic formation in southern New Mexico. It preserves fossils dating back to the Eocene epoch. Description The formation consists of reddish clastic sediments, including some beds of boulder conglomerate with individual boulders up to in diameter. The red color is attributed to a source in the Abo Formation. The upper beds contains considerable latite to andesite breccia interbedded with tuffaceous claystone and siltstone. The Palm Park Formation rests gradationally on the Love Ranch Formation, is unconformably overlain by the Bell Top Formation, Rincon Valley Formation, or Santa Fe Group, and has a thickness of about . The original age estimate, based on radiometric ages of intrusions and interbedded flows, ranged from 42 to 51 million years. More recent high-precision U-Pb dating gives an age of 45.0±0.7 Ma for an ash fall tuff in the lower part of the formation in the Robledo Mountains and an age of 39.6±0.5 Ma for an ash fall tuf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rubio Peak Formation
The Rubio Peak Formation is a geologic formation located in southwestern New Mexico. It is thought to have been deposited in the Eocene Epoch. Description The formation is volcanic, consisting mostly of flows of amphibole latites to pyroxene andesites and associated volcaniclastics and tuffs. The flows have a silica content of 59-63%. The appearance is highly variable, from pinkish gray to red to brown to black, with large to small phenocrysts and with glassy to fully crystalline texture. However, the chemical composition is reasonably uniform across the formation. The maximum thickness is as much as . It lies on older Tertiary intrusive rocks and is overlain and interfingers with the Sugarlump Tuff. Oxygen isotope ratios suggest that the magma from which the formation solidified had its origin in the Earth's mantle and underwent a degree of fractional crystallization. The formation has not been directly dated. However, the overlying Sugarlump Tuff has been radiometrically da ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clastic Dike
A clastic dike is a seam of sedimentary material that fills an open fracture in and cuts across sedimentary rock strata or layering in other rock types. Clastic dikes form rapidly by fluidized injection (mobilization of pressurized pore fluids) or passively by water, wind, and gravity (sediment swept into open cracks). Diagenesis may play a role in the formation of some dikes. Clastic dikes are commonly vertical or near-vertical. Centimeter-scale widths are common, but thicknesses range from millimetres to metres. Length is usually many times width. Clastic dikes are found in sedimentary basin deposits worldwide. Formal geologic reports of clastic dikes began to emerge in the early 19th century.Cross, W., 1894, Intrusive sandstone dikes in granite, GSA Bulletin, 5, p. 225-230 Terms synonymous with clastic dike include: ''clastic intrusion, sandstone dike, fissure fill, soft-sediment deformation, fluid escape structure, seismite, injectite, liquefaction feature, neptunian dike ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slump (geology)
A slump is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or a rock layer moves a short distance down a Grade_(slope), slope. Movement is characterized by sliding along a concave-upward or planar surface. Causes of slumping include Earthquake, earthquake shocks, thorough wetting, freezing and thawing, undercutting, and loading of a slope. Translational slumps occur when a detached landmass moves along a planar surface. Common planar surfaces of failure include joints or bedding planes, especially where a permeable layer overrides an impermeable surface. Block slumps are a type of translational slump in which one or more related block units move downslope as a relatively coherent mass. A rotational slump occurs when a slump block, composed of sediment or rock, slides along a concave-upward slip surface with rotation about an axis parallel to the slope. Rotational movement causes the original surface of the block to become less steep, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debris Flow
Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally have bulk densities comparable to those of rock avalanches and other types of landslides (roughly 2000 kilograms per cubic meter), but owing to widespread sediment liquefaction caused by high pore-fluid pressures, they can flow almost as fluidly as water. Debris flows descending steep channels commonly attain speeds that surpass 10 m/s (36 km/h), although some large flows can reach speeds that are much greater. Debris flows with volumes ranging up to about 100,000 cubic meters occur frequently in mountainous regions worldwide. The largest prehistoric flows have had volumes exceeding 1 billion cubic meters (i.e., 1 cubic kilometer). As a result of their high sediment concentrations and mobility, debris flows can be very des ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sedimentary Structure
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different particle sizes are deposited on top of each other. These beds range from millimeters to centimeters thick and can even go to meters or multiple meters thick. Sedimentary structures such as cross-bedding, graded bedding, and ripple marks are utilized in stratigraphic studies to indicate original position of strata in geologically complex terrains and understand the depositional environment of the sediment. Flow structures There are two kinds of flow structures: bidirectional (multiple directions, back-and-forth) and unidirectional. Flow regimes in single-direction (typically fluvial) flow, which at varying speeds and velocities produce different structures, are called bedforms. In the ''lower flow regime'', the natural progression is from a f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fission Track Dating
Fission track dating is a radiometric dating technique based on analyses of the damage trails, or tracks, left by fission fragments in certain uranium-bearing minerals and glasses. Fission-track dating is a relatively simple method of radiometric dating that has made a significant impact on understanding the thermal history of continental crust, the timing of volcanic events, and the source and age of different archeological artifacts. The method involves using the number of fission events produced from the spontaneous decay of uranium-238 in common accessory minerals to date the time of rock cooling below closure temperature. Fission tracks are sensitive to heat, and therefore the technique is useful at unraveling the thermal evolution of rocks and minerals. Most current research using fission tracks is aimed at: a) understanding the evolution of mountain belts; b) determining the source or provenance of sediments; c) studying the thermal evolution of basins; d) determinin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Datil Group
The Mogollon-Datil volcanic field is a large () silicic volcanic field in western New Mexico (Mogollon Mountains-Datil, New Mexico). It is a part of an extensive Eocene to Oligocene volcanic event which includes the San Juan volcanic field in southwestern Colorado, the Trans-Pecos volcanic field in west Texas and north central Mexico, the Boot Heel volcanic field in the bootheel of southwestern New Mexico and adjacent areas of Arizona and Mexico; and the vast volcanic field of the Sierra Madre Occidental of western Mexico. The Mogollon-Datil volcanic field was formed in "four discrete pulses representing synchronized activity of two separate cauldron complexes". Geologic history The volcanic activity of the Mogollon-Datil began near present-day Las Cruces, New Mexico about 36.2 million years ago (mya) with the eruption of the Cueva Tuff from the Organ Caldera. Activity spread to the northwest to the Mogollon caldera by 34.0 mya, and this first pulse of activity died down around ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mogollon Group
The Mogollon-Datil volcanic field is a large () silicic volcanic field in western New Mexico (Mogollon Mountains-Datil, New Mexico). It is a part of an extensive Eocene to Oligocene volcanic event which includes the San Juan volcanic field in southwestern Colorado, the Trans-Pecos volcanic field in west Texas and north central Mexico, the Boot Heel volcanic field in the bootheel of southwestern New Mexico and adjacent areas of Arizona and Mexico; and the vast volcanic field of the Sierra Madre Occidental of western Mexico. The Mogollon-Datil volcanic field was formed in "four discrete pulses representing synchronized activity of two separate cauldron complexes". Geologic history The volcanic activity of the Mogollon-Datil began near present-day Las Cruces, New Mexico about 36.2 million years ago (mya) with the eruption of the Cueva Tuff from the Organ Caldera. Activity spread to the northwest to the Mogollon caldera by 34.0 mya, and this first pulse of activity died down around ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
