Rainbow Basin is a geological formation in the Calico Peaks range, located 8 miles north of Barstow in the Mojave Desert in San Bernardino County, California. The Rainbow Basin has been designated a National Natural Landmark and is in the Bureau of Land Management managed Rainbow Basin Natural Area. Rainbow Basin is a mixture of private and public land, but it is managed by the Bureau of Land Management, it is accessible to the public via Irwin Road from Barstow to an unpaved loop road through the colorful basin. The basin is notable for: the fantastic and beautiful shapes of its rock formations: its fossil beds, which have provided scientists with valuable information about life during the middle Miocene epoch, between 12 and 16 million years ago. Underneath Rainbow Basin is the massive batholith. Made from a type of rock called quartz monzonite, this batholith dates to either the Cretaceous, or the late Jurassic period. Early in the Cenozoic Era this batholith was exposed in the area surrounding Rainbow Basin and bent downward as it underwent compression, to form a basin.
Sediments deposited in this basin became the sedimentary rocks that are most visible in Rainbow Basin today. Further compression and extension left these sedimentary formations folded, the most prominent fold being the Barstow Syncline; these same stresses produced several faults in the Rainbow Basin area. The thick sedimentary layers can be divided into three distinct formations; the lowest is called the Jackhammer Formation, it is composed of layers of sandstone, siltstone and conglomerate, all dating to the early Miocene Epoch. Above this is the Pickhandle Formation; the sediments making up this formation are of volcanic origin – tuff and andesite, indicating that they were laid down during a period of active volcanism. That time was during the early Miocene; the highest of the three formations is the Barstow Formation, made up of layers of conglomerate, limestone and shale. This formation dates to the middle to late Miocene and it contains one of the largest Cenozoic fossil assemblages in North America.
Most of the sediment that makes up the layers in this formation was stream-laid, but there is a white layer of rhyolitic tuff near the top. On top of everything else, is a thin layer of fanglomerate laid down during the late Pleistocene. Differential erosion of rocks of different hardness finished the job of sculpting the formations into the fantastic shapes that can be seen in Rainbow Basin today; the majority of the fossil beds in Rainbow Basin are found within the sedimentary rocks of the Barstow Formation. They include many animals not found in California today, including camels, horses and flamingos; this unique collection of animals is representative of the Barstovian Land Mammal age. In 1941 Rainbow Basin was designated the type reference for the Barstovian Land Mammal age by the North American Paleontological Society. Rainbow Basin is open to the public by means of a one-way dirt road. There is no camping within Rainbow Basin itself. Fossils cannot be collected without a permit. Anyone planning a trip to this natural landmark should keep in mind that it is a desert area, take appropriate safety precautions.
Bureau of Land Management 1991 Management Plan for the Rainbow Basin Natural Area. Barstow Resource Area, California Desert District, Bureau of Land Management, U. S. Department of the Interior, Barstow. Dibblee Jr. Thomas W. 1967 Areal Geology of the Western Mojave Desert, California. Geological Survey Professional Paper no. 522. United States Government Printing Office, Washington D. C. Dibblee Jr. Thomas W. 1968 Geology of the Fremont Peak and Opal Mountain Quadrangles, California. California Division of Mines and Geology, San Francisco. Lindsay, Everett H. 1972 Small Mammal Fossils from the Barstow Formation, California. University of California Publications in Geological Sciences Vol. 93. University of California Press, Berkeley. Official Rainbow Basin Natural Area website San Bernardino County Museum's "Barstow Fossil Beds: Motherlode of the Miocene" online slide show Rainbow Basin National Park Service
The Jurassic period was a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era known as the Age of Reptiles; the start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, the Tithonian event at the end; the Jurassic period is divided into three epochs: Early and Late. In stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, Upper Jurassic series of rock formations; the Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified. By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north, Gondwana to the south; this created more coastlines and shifted the continental climate from dry to humid, many of the arid deserts of the Triassic were replaced by lush rainforests.
On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life; the oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates. The chronostratigraphic term "Jurassic" is directly linked to the Jura Mountains, a mountain range following the course of the France–Switzerland border. During a tour of the region in 1795, Alexander von Humboldt recognized the limestone dominated mountain range of the Jura Mountains as a separate formation that had not been included in the established stratigraphic system defined by Abraham Gottlob Werner, he named it "Jura-Kalkstein" in 1799.
The name "Jura" is derived from the Celtic root *jor via Gaulish *iuris "wooded mountain", borrowed into Latin as a place name, evolved into Juria and Jura. The Jurassic period is divided into three epochs: Early and Late. In stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, Upper Jurassic series of rock formations known as Lias and Malm in Europe; the separation of the term Jurassic into three sections originated with Leopold von Buch. The faunal stages from youngest to oldest are: During the early Jurassic period, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana; the Jurassic North Atlantic Ocean was narrow, while the South Atlantic did not open until the following Cretaceous period, when Gondwana itself rifted apart. The Tethys Sea closed, the Neotethys basin appeared. Climates were warm, with no evidence of a glacier having appeared; as in the Triassic, there was no land over either pole, no extensive ice caps existed.
The Jurassic geological record is good in western Europe, where extensive marine sequences indicate a time when much of that future landmass was submerged under shallow tropical seas. In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface. Though the epicontinental Sundance Sea left marine deposits in parts of the northern plains of the United States and Canada during the late Jurassic, most exposed sediments from this period are continental, such as the alluvial deposits of the Morrison Formation; the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus common, along with calcitic ooids, calcitic cements, invertebrate faunas with dominantly calcitic skeletons; the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, South America, Japan and the United Kingdom.
In Africa, Early Jurassic strata are distributed in a similar fashion to Late Triassic beds, with more common outcrops in the south and less common fossil beds which are predominated by tracks to the north. As the Jurassic proceeded and more iconic groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are neither well studied in Africa. Late Jurassic strata are poorly represented apart from the spectacular Tendaguru fauna in Tanzania; the Late Jurassic life of Tendaguru is similar to that found in western North America's Morrison Formation. During the Jurassic period, the primary vertebrates living in the sea were marine reptiles; the latter include ichthyosaurs, which were at the peak of their diversity, plesiosaurs and marine crocodiles of the families Teleosauridae and Metriorhynchidae. Numerous turtles could be found in rivers. In the invertebrate world, several new groups appeared, including rudists (a reef-formi
Shale is a fine-grained, clastic sedimentary rock composed of mud, a mix of flakes of clay minerals and tiny fragments of other minerals quartz and calcite. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility, it is the most common sedimentary rock. Shale exhibits varying degrees of fissility, breaking into thin layers splintery and parallel to the otherwise indistinguishable bedding plane because of the parallel orientation of clay mineral flakes. Non-fissile rocks of similar composition but made of particles smaller than 0.06 mm are described as mudstones or claystones. Rocks with similar particle sizes but with less clay and therefore grittier are siltstones. Shales are composed of clay minerals and quartz grain, are grey. Addition of variable amounts of minor constituents alters the color of the rock. Black shale results from the presence of greater than one percent carbonaceous material and indicates a reducing environment.
Black shale can be referred to as black metal. Red and green colors are indicative of ferric oxide, iron hydroxide, or micaceous minerals. Clays are the major constituent of other mudrocks; the clay minerals represented are kaolinite and illite. Clay minerals of Late Tertiary mudstones are expandable smectites whereas in older rocks in mid- to early Paleozoic shales illites predominate; the transformation of smectite to illite produces silica, calcium, magnesium and water. These released elements form authigenic quartz, calcite, ankerite and albite, all trace to minor minerals found in shales and other mudrocks. Shales and mudrocks contain 95 percent of the organic matter in all sedimentary rocks. However, this amounts to less than one percent by mass in an average shale. Black shales, which form in anoxic conditions, contain reduced free carbon along with ferrous iron and sulfur. Pyrite and amorphous iron sulfide along with carbon produce the black coloration; the process in the rock cycle which forms shale is called compaction.
The fine particles that compose shale can remain suspended in water long after the larger particles of sand have deposited. Shales are deposited in slow moving water and are found in lakes and lagoonal deposits, in river deltas, on floodplains and offshore from beach sands, they can be deposited in sedimentary basins and on the continental shelf, in deep, quiet water.'Black shales' are dark, as a result of being rich in unoxidized carbon. Common in some Paleozoic and Mesozoic strata, black shales were deposited in anoxic, reducing environments, such as in stagnant water columns; some black shales contain abundant heavy metals such as molybdenum, uranium and zinc. The enriched values are of controversial origin, having been alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow accumulation from sea water over long periods of sedimentation. Fossils, animal tracks/burrows and raindrop impact craters are sometimes preserved on shale bedding surfaces.
Shales may contain concretions consisting of pyrite, apatite, or various carbonate minerals. Shales that are subject to heat and pressure of metamorphism alter into a hard, metamorphic rock known as slate. With continued increase in metamorphic grade the sequence is phyllite schist and gneiss. Before the mid-19th century, the terms slate and schist were not distinguished. In the context of underground coal mining, shale was referred to as slate well into the 20th century. Bakken Formation Barnett Shale Bearpaw Formation Burgess Shale Marcellus Formation Mazon Creek fossil beds Oil shale – Organic-rich fine-grained sedimentary rock containing kerogen Shale gas Shale gas in the United States Wheeler Shale Wianamatta Shale Media related to Shale at Wikimedia Commons
Rhyolite is an igneous, volcanic rock, of felsic composition. It may have any texture from glassy to aphanitic to porphyritic; the mineral assemblage is quartz and plagioclase. Biotite and hornblende are common accessory minerals, it is the extrusive equivalent to granite. Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock, outcrops of rhyolite may bear a resemblance to granite. Due to their high content of silica and low iron and magnesium contents, rhyolitic magmas form viscous lavas, they occur as breccias or in volcanic plugs and dikes. Rhyolites that cool too to grow crystals form a natural glass or vitrophyre called obsidian. Slower cooling forms microscopic crystals in the lava and results in textures such as flow foliations, spherulitic and lithophysal structures; some rhyolite is vesicular pumice. Many eruptions of rhyolite are explosive and the deposits may consist of fallout tephra/tuff or of ignimbrites. Eruptions of rhyolite are rare compared to eruptions of less felsic lavas.
Only three eruptions of rhyolite have been recorded since the start of the 20th century: at the St. Andrew Strait volcano in Papua New Guinea, Novarupta volcano in Alaska, Chaiten in southern Chile. Rhyolite has been found on islands far from land. Etsch Valley Vulcanite Group near Bolzano and the surrounding area Gréixer rhyolitic complex at Moixeró range Vosges Iceland: all active and extinct central volcanoes, e.g. Torfajökull, Leirhnjúkur / Krafla, Breiddalur central volcano Papa Stour in Shetland Copper Coast Geopark in southeast Ireland various locations around Snowdonia, Wales Massif de l'Esterel, France the Thuringian Forest consists of rhyolites and pyroclastic rocks of the Rotliegendes Saxony the north west Saxony-Anhalt north of Halle Saar-Nahe Basin e.g. the Königstuhl on the Donnersberg mountain Black Forest e.g. on the Karlsruher Grat Odenwald Andes Cascade Range Cobalt, Ontario Sheep Creek, Idaho Rocky Mountains Jemez Mountains Rhyolite, Nevada was named after a rhyolite deposit that characterised the area.
Wichita Mountains within the Southern Oklahoma Aulacogen St. Francois Mountains Mount Jasper, New Hampshire Yellowstone Crater Lake, Oregon Palisade Head, a formation found at Tettegouche State Park, Minnesota; the Taupo Volcanic Zone in New Zealand has a large concentration of young rhyolite volcanoes Glass House Mountains National Park, Australia the Gondwana Rainforests of Australia World Heritage Area contains rhyolite-restricted flora along the Great Dividing Range the Flinders Peak Group in the Teviot Range in the Fassifern Valley is a rhyolite of varying colours. The Malani Igneous Suite, India; the Yandang Shan mountain chain, near the town of Wenzhou, Zhejiang province, China Tambora, Indonesia Mount Kilimanjaro, Kenya/Tanzania The name rhyolite was introduced into geology in 1860 by the German traveler and geologist Ferdinand von Richthofen from the Greek word rhýax and the rock name suffix "-lite". In North American pre-historic times, rhyolite was quarried extensively in eastern Pennsylvania in the United States.
Among the leading quarries was the Carbaugh Run Rhyolite Quarry Site in Adams County. Rhyolite was mined there starting 11,500 years ago. Tons of rhyolite were traded across the Delmarva Peninsula, because the rhyolite kept a sharp point when knapped and was used to make spear points and arrowheads. Comendite – A hard, peralkaline igneous rock, a type of light blue grey rhyolite List of rock types – A list of rock types recognized by geologists Pantellerite – A peralkaline rhyolite type of volcanic rock Thunderegg – A nodule-like rock, formed within rhyolitic volcanic ash layers University of North Dakota description of rhyolite Information from rocks-rock.com
Conglomerate is a coarse-grained clastic sedimentary rock, composed of a substantial fraction of rounded to subangular gravel-size clasts, e.g. granules, pebbles and boulders, larger than 2 mm in diameter. Conglomerates form by the lithification of gravel. Conglomerates contain finer grained sediment, e.g. either sand, clay or combination of them, called matrix by geologists, filling their interstices and are cemented by calcium carbonate, iron oxide, silica, or hardened clay. The size and composition of the gravel-size fraction of a conglomerate may or may not vary in composition and size. In some conglomerates, the gravel-size class consist entirely of what were clay clasts at the time of deposition. Conglomerates can be found in sedimentary rock sequences of all ages but make up less than 1 percent by weight of all sedimentary rocks. In terms of origin and depositional mechanisms, they are related to sandstones and exhibit many of the same types of sedimentary structures, e.g. tabular and trough cross-bedding and graded bedding.
Conglomerates may be named and classified by the: Amount and type of matrix present Composition of gravel-size clasts they contain Size range of gravel-size clasts presentThe classification method depends on the type and detail of research being conducted. A sedimentary rock composed of gravel is first named according to the roundness of the gravel. If the gravel clasts that comprise it is well-rounded to subrounded, it is a conglomerate. If the gravel clasts that comprise it are angular, it is a breccia; such breccias can be called sedimentary breccias to differentiate them from other types of breccia, e.g. volcanic and fault breccias. Sedimentary rocks that contain a mixture of rounded and angular gravel clasts are sometimes called breccio-conglomerate. Conglomerates are composed of gravel-size clasts; the space between the gravel-size clasts is filled by a mixture composed of varying amounts of silt and clay, known as matrix. If the individual gravel clasts in a conglomerate are separated from each other by an abundance of matrix such that they are not in contact with each other and float within the matrix, it is called a paraconglomerate.
Paraconglomerates are often unstratified and can contain more matrix than gravel clasts. If the gravel clasts of a conglomerate are in contact with each other, it is called an orthoconglomerate. Unlike paraconglomerates, orthoconglomerates are cross-bedded and well-cemented and lithified by either calcite, quartz, or clay; the differences between paraconglomerates and orthoconglomerates reflect differences in how they are deposited. Paraconglomerates are either glacial tills or debris flow deposits. Orthoconglomerates are associated with aqueous currents. Conglomerates are classified according to the composition of their clasts. A conglomerate or any clastic sedimentary rock that consists of a single rock or mineral is known as either a monomict, oligomict, or oligomictic conglomerate. If the conglomerate consists of two or more different types of rocks, minerals, or combination of both, it is known as either a polymict or polymictic conglomerate. If a polymictic conglomerate contains an assortment of the clasts of metastable and unstable rocks and minerals, it called either a petromict or petromictic conglomerate.
In addition, conglomerates are classified by source as indicated by the lithology of the gravel-size clasts If these clasts consist of rocks and minerals that are different in lithology from the enclosing matrix and, thus and derived from outside the basin of deposition, the conglomerate is known as an extraformational conglomerate. If these clasts consist of rocks and minerals that are identical to or consistent with the lithology of the enclosing matrix and, penecontemporaneous and derived from within the basin of deposition, the conglomerate is known as an intraformational conglomerate. Two recognized types of type of intraformational conglomerates are shale-pebble and flat-pebble conglomerates. A shale-pebble conglomerate is a conglomerate, composed of clasts of rounded mud chips and pebbles held together by clay minerals and created by erosion within environments such as within a river channel or along a lake margin. Flat-pebble conglomerates are conglomerates that consist of flat clasts of lime mud created by either storms or tsunami eroding a shallow sea bottom or tidal currents eroding tidal flats along a shoreline.
Conglomerates are differentiated and named according to the dominant clast size comprising them. In this classification, a conglomerate composed of granule-size clasts would be called a granule conglomerate. Conglomerates are deposited in a variety of sedimentary environments. In turbidites, the basal part of a bed is coarse-grained and sometimes conglomeratic. In this setting, conglomerates are very well sorted, well-rounded and with a strong A-axis type imbrication of the clasts. Conglomerates are present at the base of sequences laid down during marine transgressions above an unconformity, are known as basal conglomerates, they are diachronous. Conglomerates deposited in fluvial environments are well rounded and well sorted. Clasts of this size are carried as only at times of high flow-rate; the maximum clast size decreases as the clasts are transported fu
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones. Siltstone is a clastic sedimentary rock; as its name implies, it is composed of silt sized particles, defined as grains 2–62 µm or 4 to 8 on the Krumbein phi scale. Siltstones differ from sandstones due to their smaller pores and higher propensity for containing a significant clay fraction. Although mistaken as a shale, siltstone lacks the fissility and laminations which are typical of shale. Siltstones may contain concretions. Unless the siltstone is shaly, stratification is to be obscure and it tends to weather at oblique angles unrelated to bedding. Mudstone or shale are rocks that contain mud, material that has a range of silt and clay. Siltstone is differentiated by having a majority silt, not clay. Cosmetic palette—made exclusively out of siltstone with a few exceptions Folk, R. L. 1965, Petrology of sedimentary rocks PDF version. Austin: Hemphill’s Bookstore. 2nd ed. 1981, ISBN 0-914696-14-9 Williams, Francis J. Turner and Charles M. Gilbert, 1954, Petrography, W. H. Freeman
Beetles are a group of insects that form the order Coleoptera, in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, distinguishing them from most other insects; the Coleoptera, with about 400,000 species, is the largest of all orders, constituting 40% of described insects and 25% of all known animal life-forms. The largest of all families, the Curculionidae with some 70,000 member species, belongs to this order. Found in every habitat except the sea and the polar regions, they interact with their ecosystems in several ways: beetles feed on plants and fungi, break down animal and plant debris, eat other invertebrates; some species are serious agricultural pests, such as the Colorado potato beetle, while others such as Coccinellidae eat aphids, scale insects and other plant-sucking insects that damage crops. Beetles have a hard exoskeleton including the elytra, though some such as the rove beetles have short elytra while blister beetles have softer elytra; the general anatomy of a beetle is quite uniform and typical of insects, although there are several examples of novelty, such as adaptations in water beetles which trap air bubbles under the elytra for use while diving.
Beetles are endopterygotes, which means that they undergo complete metamorphosis, with a series of conspicuous and abrupt changes in body structure between hatching and becoming adult after a immobile pupal stage. Some, such as stag beetles, have a marked sexual dimorphism, the males possessing enormously enlarged mandibles which they use to fight other males. Many beetles are aposematic, with bright colours and patterns warning of their toxicity, while others are harmless Batesian mimics of such insects. Many beetles, including those that live in sandy places, have effective camouflage. Beetles are prominent in human culture, from the sacred scarabs of ancient Egypt to beetlewing art and use as pets or fighting insects for entertainment and gambling. Many beetle groups are brightly and attractively coloured making them objects of collection and decorative displays. Over 300 species are used as food as larvae. However, the major impact of beetles on human life is as agricultural and horticultural pests.
Serious pests include the boll weevil of cotton, the Colorado potato beetle, the coconut hispine beetle, the mountain pine beetle. Most beetles, however, do not cause economic damage and many, such as the lady beetles and dung beetles are beneficial by helping to control insect pests; the name of the taxonomic order, comes from the Greek koleopteros, given to the group by Aristotle for their elytra, hardened shield-like forewings, from koleos and pteron, wing. The English name beetle comes from the Old English word bitela, little biter, related to bītan, leading to Middle English betylle. Another Old English name for beetle is ċeafor, used in names such as cockchafer, from the Proto-Germanic *kebrô. Beetles are by far the largest order of insects: the 400,000 species make up about 40% of all insect species so far described, about 25% of all animals. A 2015 study provided four independent estimates of the total number of beetle species, giving a mean estimate of some 1.5 million with a "surprisingly narrow range" spanning all four estimates from a minimum of 0.9 to a maximum of 2.1 million beetle species.
The four estimates made use of host-specificity relationships, ratios with other taxa, plant:beetle ratios, extrapolations based on body size by year of description. Beetles are found in nearly all habitats, including freshwater and coastal habitats, wherever vegetative foliage is found, from trees and their bark to flowers and underground near roots - inside plants in galls, in every plant tissue, including dead or decaying ones; the heaviest beetle, indeed the heaviest insect stage, is the larva of the goliath beetle, Goliathus goliatus, which can attain a mass of at least 115 g and a length of 11.5 cm. Adult male goliath beetles are the heaviest beetle in its adult stage, weighing 70–100 g and measuring up to 11 cm. Adult elephant beetles, Megasoma elephas and Megasoma actaeon reach 50 g and 10 cm; the longest beetle is the Hercules beetle Dynastes hercules, with a maximum overall length of at least 16.7 cm including the long pronotal horn. The smallest recorded beetle and the smallest free-living insect, is the featherwing beetle Scydosella musawasensis which may measure as little as 325 µm in length.
The oldest known fossil insect that unequivocally resembles a Coleopteran is from the Lower Permian Period about 270 million years ago, though these members of the family Tshekardocoleidae have 13-segmented antennae, elytra with more developed venation and more irregular longitudinal ribbing, abdomen and ovipositor extending beyond the apex of the elytra. In the Permian–Triassic extinction event at the end of the Permian, some 30% of all insect species became extinct, so the fossil record of insects only includes beetles from the Lower Triassic 220 mya. Around this time, during the Late Triassic, fungus-feeding species such as Cupedidae appear in the fossil record. In the stages of the Upper Triassic, alga-feeding insects such as Triaplidae and Hydrophilidae begin to appear, alongside predatory water beetles; the first weevils, including the Obrienidae, appear alongside the first rove beetles, which resemb