Is an entrance to an underground mine which is horizontal or nearly horizontal, by which the mine can be entered, drained of water, and ventilated.
Is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships (i.e. younging direction) between various strata are unknown, the term antiform must be used.On a geologic map, anticlines are usually recognized by a sequence of rock layers that are progressively older toward the center of the fold because the uplifted core of the fold is preferentially eroded to a deeper stratigraphic level relative to the topographically lower flanks. The strata dip away from the center, or crest, of the fold.If an anticline plunges (i.e., is inclined to the Earth's surface), the surface strata will form Vs that point in the direction of plunge. Anticlines are typically flanked by synclines although faulting can complicate and obscure the relationship between the two. Folds typically form during crustal deformation as the result of compression that accompanies orogenic mountain building.
Is a geologic eon before the Paleoproterozoic Era of the Proterozoic Eon, before 2.5 Ga (billion years ago, or 2,500 Ma). Instead of being based on stratigraphy, this date is defined chronometrically. The lower boundary (starting point) has not been officially recognized by the International Commission on Stratigraphy, but it is usually set to 3.8 Ga, at the end of the Hadean Eon. In older literature, the Hadean is included as part of the Archean.
Is a soft, deep blue copper mineral produced by weathering of copper ore deposits.The mineral has been known since ancient times. The blue of azurite is exceptionally deep and clear, and for that reason the mineral has tended to be associated since antiquity with the deep blue color of low-humidity desert and winter skies.
Is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium.
Is an absorbent aluminium phyllosilicate, in general, impure clay consisting mostly of montmorillonite. There are different types of bentonites, and their names depend on the dominant elements, such as potassium (K), sodium (Na), calcium (Ca), and aluminum (Al). As noted in several places in the geologic literature, there are some nomenclatorial problems with the classification of bentonite clays. Bentonite usually forms from weathering of volcanic ash, most often in the presence of water. However, the term bentonite, as well as a similar clay called tonstein, has been used for clay beds of uncertain origin. For industrial purposes, two main classes of bentonite exist: sodium and calcium bentonite. In stratigraphy and tephrochronology, completely devitrified (weathered volcanic glass) ash-fall beds are commonly referred to as K-bentonites when the dominant clay species is illite. Other common clay species, and sometimes dominant, are montmorillonite and kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically associated with coal.
Is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which is usually consolidated (shingled) and further forged into wrought iron. The bloomery has now largely been superseded by the blast furnace, which produces pig iron.
Is a transitional period between the Stone Age and Iron Age, characterized by the creation of bronze from raw materials, the widespread use of bronze tools and weapons, and the continued development of pictogramic or ideogramic symbols and proto-writing. In archeology, the Bronze Age is the 2nd principal period of the three-age system created by Christian Jürgensen Thomsen for classifying and studying ancient societies, particularly the regional societies of the Mediterranean and Near East. The archaeological cultures are characterized by advance metalworking and the widespread cultural use of bronze. This could either be based on the local smelting of copper and tin from ores, or trading for bronze from production areas elsewhere. Copper/tin ores are rare, as reflected in the fact that there were no tin bronzes in western Asia before the third millennium BCE. Many, though not all, Bronze Age cultures flourished in prehistory. Some cultures developed extensive written records during their Bronze Ages.
Are a phylum of marine animals that have hard "valves" (shells) on the upper and lower surfaces. Most species of brachiopod went extinct during the P–T extinction over 250 million years ago, but many survive today. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and more complex muscles. In a typical brachiopod a stalk-like pedicle projects from an opening in the hinge or from a hole in the larger valve, attaching the animal to the sea bed but clear of silt that would obstruct the opening. Brachiopods have a mantle that secretes and lines the shell, and encloses the internal organs. The body occupies typically about one-third of the internal space inside the shell, nearest the hinge. The rest of the mantle encloses a water-filled space containing the lophophore, a crown of tentacles that filters food particles out of the water. In all species the lophophore is supported by cartilage and by a hydrostatic skeleton.
In geology is the smallest division of a geologic formation or stratigraphic rock series marked by well-defined divisional planes (bedding planes) separating it from layers above and below. A bed is the smallest lithostratigraphic unit, usually ranging in thickness from a centimeter to several meters and distinguishable from beds above and below it. Beds can be differentiated in various ways, including rock or mineral type and particle size. The term is generally applied to sedimentary strata, but may also be used for volcanic flows or ash layers.
Is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470 °C, and vaterite is even less stable.
Is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.The supercontinent Columbia broke up during the Calymmian some 1500 Mya.
Is the first geological period of the Paleozoic Era, lasting from 542 ± 0.3 to 488.3 ± 1.7 it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätten. These are sites of exceptional preservation, where 'soft' parts of organisms are preserved as well as their more resistant shells. This means that our understanding of the Cambrian biology surpasses that of some later periods.
Is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya (million years ago), to the beginning of the Permian Period, about 299.0 ± 0.8 Mya The Carboniferous was a time of glaciation, low sea level and mountain building, diversification and extinction; a minor marine and terrestrial extinction event among animals and plants (Carboniferous Rainforest Collapse) occurred in the middle of the period caused by climate change
Is a type of speleothem, a concretion of calcium salts which forms in limestone caves. They may be any shape but are formed of concentric layers, reaching up to 15 cm (5.9 in) in diameter. Most are smaller than 1 cm (0.39 in) wide. They can be found singly or grouped. A cave pearl forms as calcite crystallizes on a nucleus such as a grain of sand, in much the same way that a biological pearl forms within a mollusc. A cave pearl is formed when a current of water provides a rotation to the nucleus in such a way that it is coated evenly. In this manner it may form a sphere or a cylinder or any of several other shapes. The cave pearl then sinks and is buffed to a high gloss by the motion of the water. It sinks to the bottom of the pool, and while the motion of the water often keeps it from adhering, several cave pearls may stick together to form stone which looks like a bunch of grapes. Cave pearls often degrade when allowed to dry. There may be microbial action involved in the formation of cave pearls. Cave pearls are generally not considered to be a type of oolite.
Is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. It is marked by the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and the end of the Mesozoic Era. The Cenozoic Era is ongoing
Is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color (from white to black), but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements present in the rock, and both red and green are most often related to traces of iron (in its oxidized and reduced forms respectively).
Is any member of the molluscan class Cephalopoda. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.
Is a geological term used to describe a clastic sedimentary rock that is composed primarily of clay-sized particles
Is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is ubiquitous in copper ores, it is found in limited abundance and is not an important ore of copper itself, although it is well known to mineral collectors.As described for the mineral pyrite, the assignment of formal oxidation states (or charges) to the atoms that constitute covellite is deceptive. The mineral is associated with chalcocite in zones of secondary enrichment (supergene) of copper sulfide deposits. Commonly found with and as coatings on chalcocite, chalcopyrite, bornite, enargite, pyrite, and other sulfides, it often occurs as pseudomorphic replacements after other minerals. Despite the very rare occurrence as a volcanic sublimate, the initial description was at Mount Vesuvius by Nicola Covelli (1790–1829)
is a geologic period and system from circa 145.5 ± 4 to 65.5 ± 0.3 million years (Ma) ago. In the geologic timescale, the Cretaceous follows the Jurassic Period and is followed by the Paleogene Period of the Cenozoic Era. It is the youngest period of the Mesozoic Era, and at 80 million years long, the longest period of the Phanerozoic Eon. The end of the Cretaceous defines the boundary between the Mesozoic and Cenozoic eras. In many languages this period is known as "chalk period".
Are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). They live both in shallow water and in depths as great as 6,000 meters. Sea lilies refer to the crinoids which, in their adult form, are attached to the sea bottom by a stalk. Feather stars or comatulids refer to the unstalked forms. Crinoids are characterized by a mouth on the top surface that is surrounded by feeding arms. They have a U-shaped gut, and their anus is located next to the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognized, most crinoids have many more than five arms. Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults. There are only a few hundred known modern forms, but crinoids were much more numerous both in species and numbers in the past. Some thick limestone beds dating to the mid- to late-Paleozoic are almost entirely made up of disarticulated crinoid fragments.
Is a geologic period that lasted from 850 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
Is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria .
The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early reducing atmosphere into an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of oxygen-intolerant organisms. According to endosymbiotic theory, chloroplasts in plants and eukaryotic algae have evolved from cyanobacterial ancestors via endosymbiosis.
Dolostone or dolomite
Rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater, but it can still develop solution features over time.
Is a geologic period and system of the Paleozoic Era spanning from 416 to 359.2 million years ago It is named after Devon, England, where rocks from this period were first studied. During the Devonian Period the pectoral and pelvic fins of lobe-finned fish evolved into legs as they started to walk on land as tetrapods around 397 Ma.Various terrestrial arthropods also became well-established.