|
Rattlesnake Formation
The Rattlesnake Formation is a Miocene to late Pliocene geologic formation found along the John Day River Valley of Oregon, in the Western United States. Description The formation is described in ''Geologic Formations of Eastern Oregon'' (1972) as follows: The unit is composed of up to 700 feet of fanglomerate and finer terrestrial sediments and a 40-foot thick ignimbrite unit which crops out in the middle of the section. The gravel is well rounded and consists of pebbles of basalt, chert, siltstone, diorite, rhyolite, and chert set in a medium-grained matrix of poorly indurated volcanic sandstone. The ignimbrite displays zonation typical of welded ashflow tuffs and is a prominent ridge former. Age The ignimbrite was radiometrically dated by the Potassium–argon method at 6.4 million years by Evernden and James (1964). Fossil content Middle and late Pliocene mammals have been recovered from beneath the ignimbrite. Fossils found here include '' Amebelodon sp.'', the extin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sedimentary
Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of detritus (geology), geological detritus (minerals) or detritus, biological detritus (organic matter). The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or Mass wasting, mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts (mainly shells) of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial planet, rocky planet or natural satellite, moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of volcanism on Venus, Venus, which cover ~80% of the surface, are basaltic; the lunar mare, lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Indarctos
''Indarctos'' is an extinct genus of bear, endemic to North America, Europe and Asia during the Miocene. It was present from ~11.1 to 5.3 Ma, existing for approximately . The oldest member is from Arizona (~11.1—7.7 Ma) and youngest is (~9.0—5.3 Ma) from Kazakhstan. In North America this animal was contemporary with ''Plionarctos'' (~10.3—3.3 Ma). Discovery, history and taxonomy Discoveries A molar (designated to MNA 1839/km-83) discovered from the Karabulak formation in 1988 was tentatively assigned to ''Indarctos sp''. In 2017 it was re examined and assigned to ''I. punjabensis.'' The tooth was found to belong to a young individual, which might possibly be a male, and is the largest tooth known from this species. This might be due to sexual dimorphism since extant male bears are larger than the females. Species ''Indarctos'' is known from several species spread widely across Eurasia, North America, and North Africa, however, most of them are known from fragm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Teleoceras
''Teleoceras'' (Greek: "perfect" (teleos), "horn" (keratos)) is an extinct genus of grazing rhinoceros. It lived in North America during the Miocene and Pliocene epochs during the Hemingfordian to the end of Hemphillian from around 17.5 to 4.9 million years ago. It grew up to lengths of 13 feet (4 meters long). Description ''Teleoceras'' had much shorter legs than modern rhinos, and a barrel chest, making its build more like that of a hippopotamus than a modern rhino. Based on this description, Henry Fairfield Osborn suggested in 1898 that it was semi-aquatic and hippo-like in habits. This idea persisted for about a century, but has recently been discounted by isotopic evidence. ''Teleoceras'' is now thought to have been a terrestrial grazer on C3 plants. ''Teleoceras'' had a single small nasal horn. Discovery ''Teleoceras'' is the most common fossil in the Ashfall Fossil Beds of Nebraska. In fact, its remains were so numerous and concentrated that the building housing the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mylohyus
''Mylohyus'' is an extinct genus of peccary found in North and Central America. It first evolved during the Late Miocene and became extinct at the end of the Pleistocene, around 12,000 years ago. Six species were known, the most famous being ''Mylohyus nasutus'', also known as the long-nosed peccary. The genus was slightly larger-bodied than any modern peccaries, with an estimated mass of . Isotope and anatomical studies have suggested that the diet of ''Mylohyus'' varied over geological time, from being primarily a C3 browser during the Blancan, with an increasing consumption of C4 vegetation during the Irvingtonian, with a relatively even mixture of C3 and C4 during the Rancholabrean The Rancholabrean North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from less than 240,000 years to 11,000 years BP, a p .... Suggestions have been made that it was fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amebelodon
''Amebelodon'' is a genus of extinct proboscidean belonging to Amebelodontidae (the so-called shovel-tuskers), a group of proboscideans related to the modern elephants and their close relative the mammoth. The most striking attribute of this animal is its lower tusks, which are narrow, elongated, and distinctly flattened with the degree of flattening varying among the different species. Two valid species are currently placed within this genus, which was endemic to North America. Other species once assigned to ''Amebelodon'' are now assigned to the genus ''Konobelodon'', which was once a subgenus. Taxonomy ''Amebelodon'' first appeared in the Great Plains and Gulf Coast regions of North America during the late Miocene, roughly 9 million years ago, and apparently became extinct on this continent sometime around 6 million years ago. The youngest record of ''Amebelodon'' is from a 5-million-year-old site in North America.Lambert, W. D., and J. Shoshani, 1998. The Proboscidea. In Ja ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles (including birds) from which they diverged in the Carboniferous, over 300 million years ago. Around 6,400 extant species of mammals have been described divided into 29 orders. The largest orders, in terms of number of species, are the rodents, bats, and Eulipotyphla (hedgehogs, moles, shrews, and others). The next three are the Primates (including humans, apes, monkeys, and others), the Artiodactyla ( cetaceans and even-toed ungulates), and the Carnivora (cats, dogs, seals, and others). In terms of cladistics, which reflects evolutionary history, mammals are the only living members of the Synapsida (synapsids); this clade, together with Saur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rattlesnake Formation Mural
Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small animals such as birds and rodents. Rattlesnakes receive their name from the rattle located at the end of their tails, which makes a loud rattling noise when vibrated that deters predators or serves as a warning to passers-by. Rattlesnakes are the leading contributor to snakebite injuries in North America, but rarely bite unless provoked or threatened; if treated promptly, the bites are seldom fatal. The 36 known species of rattlesnakes have between 65 and 70 subspecies, all native to the Americas, ranging from British Columbia through Ontario in southern Canada, to central Argentina. The largest rattlesnake, the eastern diamondback, can measure up to in length. Rattlesnakes are preyed upon by hawks, weasels, king snakes, and a variety of o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
K–Ar Dating
Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium is a common element found in many materials, such as feldspars, micas, clay minerals, tephra, and evaporites. In these materials, the decay product is able to escape the liquid (molten) rock, but starts to accumulate when the rock solidifies ( recrystallizes). The amount of argon sublimation that occurs is a function of the purity of the sample, the composition of the mother material, and a number of other factors. These factors introduce error limits on the upper and lower bounds of dating, so that the final determination of age is reliant on the environmental factors during formation, melting, and exposure to decreased pressure or open air. Time since recrystallization is calculated by measuring the ratio of the amount of accumulated to ... [...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] |
Cliff-former
A cliff-former is a geological unit of bedrock that is more resistant to erosion than overlying or underlying strata and consequently produces outcrops with high slope angles. It is more or less equivalent to ''ridge-former'', and may be contrasted with slope-former. In humid environments, sandstones are typically cliff-formers. In arid environments, limestones are often cliff-formers also. Recent lavas may be cliff-formers as well. In the Ridge-and-Valley Appalachians of the eastern United States the major ridge-formers are the Tuscarora Tuscarora may refer to the following: First nations and Native American people and culture * Tuscarora people **''Federal Power Commission v. Tuscarora Indian Nation'' (1960) * Tuscarora language, an Iroquoian language of the Tuscarora people * ..., Pocono, and Pottsville Formations. References {{geomorph-stub Erosion landforms Geomorphology ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, ''tuffaceous sandstone''). Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the ''moai'' statues on Easter Island. Tuff can be classified as either igneous or sedimentary rock. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms. Tuff is often erroneously called tufa in guidebooks and in television programmes. Volcanic ash The material that is expelled in a volcanic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.jpg "Click for more on -> Rattlesnake Formation Mural")
