Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 113.0 ± 1.0 Ma, approximately. The Aptian precedes the Albian, all part of the Lower/Early Cretaceous; the Aptian overlaps the upper part of the regionally used stage Urgonian. The Selli Event known as OAE1a, was one of two oceanic Anoxic events in the Cretaceous period, which occurred around 120 Ma and lasted 1 to 1.3 million years. The Aptian extinction was a minor extinction event hypothesized to have occurred around 116 to 117 Ma; the Aptian was named after the small city of Apt in the Provence region of France, known for its crystallized fruits. The original type locality is in the vicinity of Apt; the Aptian was introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1840. The base of the Aptian stage is laid at magnetic anomaly M0r. A global reference profile for the base had in 2009 not yet been appointed.
The top of the Aptian is at the first appearance of coccolithophore species Praediscosphaera columnata in the stratigraphic record. In the Tethys domain, the Aptian contains eight ammonite biozones: zone of Hypacanthoplites jacobi zone of Nolaniceras nolani zone of Parahoplites melchioris zone of Epicheloniceras subnodosocostatum zone of Duffrenoyia furcata zone of Deshayesites deshayesi zone of Deshayesites weissi zone of Deshayesites oglanlensisSometimes the Aptian is subdivided in three substages or subages: Bedoulian and Clansayesian. Examples of rock units formed during the Aptian are: Antlers Formation, Cedar Mountain Formation, Cloverly Formation, Elrhaz Formation, Jiufotang Formation, Little Atherfield, Mazong Shan, Potomac Formation, Santana Formation, Twin Mountains Formation, Xinminbao Group and Yixian Formation. Eogaudryceras Georgioceras Lithancylus Pictetia Salfeldiella Zuercherella Lower Ammonitoceras Australiceras Cheloniceras Cicatrites Colombiceras Dufrenoya Eotetragonites Helicancylus Melchiorites Parahoplites Procheloniceras Prodeshayesites Pseudosaynella Roloboceras Shastoceras Upper Acanthohoplites Acanthoplites Ammonoceratites Argonauticeras Beudanticeras Burckhardites Cloioceras Desmoceras Diadochoceras Diodochoceras Eodouvilleiceras Epancyloceras Epicheloniceras Gabbioceras Gargasiceras Gyaloceras Hamites Hulenites Hypacanthoplites Jauberticeras Kazanskyella Knemiceras Mathoceras Mathoceratites Megatyloceras Metahamites Miyakoceras Neosilesites Nodosohoplites Nolaniceras Protacanthoplites Protanisoceras Sinzovia Somalites Tetragonites Theganoceras Trochleiceras Tropaeum Uhligella Conoteuthis Vectibelus Lower Parahibolites Peratobelus Tetrabelus Carinonautilus Heminautilus Upper Zhuralevia Upper Euphylloceras Upper Adygeya Naefia Boluochia zhengi Changchengornis hengdaoziensis Chaoyangia beishanensis Confuciusornis sanctus Cuspirostrisornis houi Jeholornis prima Jixiangornis orientalis Largirostrornis sexdentoris Longchengornis sanyanensis Longipteryx chaoyangensis Sapeornis chaoyangensis Sinornis santensis/Cathayornis yandica Songlingornis linghensis Yanornis martini Yixianornis grabaui Sarcosuchus Hybodus Jinanichthys longicephalus Lycoptera davidi Lycoptera muroii Peipiaosteus pani Protosephurus liui Sinamia zdanskyi Amblydectes Anhanguera Araripedactylus dehmi Araripesaurus castilhoi Arthurdactylus conandoylei Boreopterus cuiae Brasileodactylus araripensis Cearadactylus atrox Chaoyangopterus zhangi Dsungaripterus weii Dsungaripterus brancai Eoazhdarcho liaoxiensis Eopteranodon lii Gegepterus changi Haopterus gracilis Hongshanopterus lacustris Huaxiapterus benxiensis Huaxiapterus corollatus Huaxiapterus jii Istiodactylus latidens Istiodactylus sinensis Jidapterus edentus Liaoningopterus gui Liaoxipterus brachyognathus Lonchodectes Longchengpterus zhaoi Ludodactylus sibbicki Nemicolopterus crypticus Nurhachius ignaciobritoi Ornithocheirus simus Ornithocheirus mesembrinus Pricesaurus megalodon Santanadactylus Sinopterus dongi Sinopterus gui Tapejara navigans Tapejara wellnhoferi Thalassodromeus sethi Tropeognathus mesembrinus Tropeognathus robustus Tupandactylus imperator Aptian extinction Gradstein, F.
M.. G. & Smith, A. G.. D'Orbigny, A. C. V. M.. GeoWhen Database - Aptian Mid-Cretaceous timescale, at the website of the subcommission for stratigraphic information of the ICS Stratigraphic charts of the Lower Cretaceous: and, at the website of Norges Network of offshore records of geology and stratigraphy
Tethys Ocean
The Tethys Ocean called the Tethys Sea or the Neotethys, was an ocean during much of the Mesozoic Era located between the ancient continents of Gondwana and Laurasia, before the opening of the Indian and Atlantic oceans during the Cretaceous Period. The name stems from the mythological Greek sea goddess Tethys and consort of Oceanus, mother of the great rivers and fountains of the world and of the Oceanid sea nymphs; the eastern part of the Tethys Ocean is sometimes referred to as Eastern Tethys. The western part of the Tethys Ocean is called Tethys Sea, Western Tethys Ocean, or Paratethys or Alpine Tethys Ocean; the Black and Aral seas are thought to be its crustal remains, though the Black Sea may, in fact, be a remnant of the older Paleo-Tethys Ocean. The Western Tethys was not a single open ocean, it covered many small plates, Cretaceous island arcs, microcontinents. Many small oceanic basins were separated from each other by continental terranes on the Alboran and Apulian plates; the high sea level in the Mesozoic flooded most of these continental domains.
As theories have improved, scientists have extended the "Tethys" name to refer to three similar oceans that preceded it, separating the continental terranes: in Asia, the Paleo-Tethys, Meso-Tethys, Ceno-Tethy are recognized. Neither Tethys Ocean should be confused with the Rheic Ocean, which existed to the west of them in the Silurian Period. To the north of the Tethys, the then-land mass was called Angaraland and to the south of it, it was called Gondwanaland. From the Ediacaran into the Devonian, the Proto-Tethys Ocean existed and was situated between Baltica and Laurentia to the north and Gondwana to the south. From the Silurian through the Jurassic periods, the Paleo-Tethys Ocean existed between the Hunic terranes and Gondwana. Over a period of 400 million years, continental terranes intermittently separated from Gondwana in the Southern Hemisphere to migrate northward to form Asia in the Northern Hemisphere. About 250 Mya, during the Triassic, a new ocean began forming in the southern end of the Paleo-Tethys Ocean.
A rift formed along the northern continental shelf of Southern Pangaea. Over the next 60 million years, that piece of shelf, known as Cimmeria, traveled north, pushing the floor of the Paleo-Tethys Ocean under the eastern end of northern Pangaea; the Tethys Ocean formed between Cimmeria and Gondwana, directly over where the Paleo-Tethys used to be. During the Jurassic period about 150 Mya, Cimmeria collided with Laurasia and stalled, so the ocean floor behind it buckled under, forming the Tethyan Trench. Water levels rose, the western Tethys shallowly covered significant portions of Europe, forming the first Tethys Sea. Around the same time and Gondwana began drifting apart, opening an extension of the Tethys Sea between them which today is the part of the Atlantic Ocean between the Mediterranean and the Caribbean; as North and South America were still attached to the rest of Laurasia and Gondwana the Tethys Ocean in its widest extension was part of a continuous oceanic belt running around the Earth between about latitude 30°N and the Equator.
Thus, ocean currents at the time around the Early Cretaceous ran differently from the way they do today. Between the Jurassic and the Late Cretaceous, which started about 100 Mya, Gondwana began breaking up, pushing Africa and India north across the Tethys and opening up the Indian Ocean; as these land masses crowded in on the Tethys Ocean from all sides, to as as the Late Miocene, 15 Mya, the ocean continued to shrink, becoming the Tethys Seaway or second Tethys Sea. Throughout the Cenozoic, global sea levels fell hundreds of meters, the connections between the Atlantic and the Tethys closed off in what is now the Middle East. During the Oligocene, large parts of central and eastern Europe were covered by a northern branch of the Tethys Ocean, called the Paratethys; the Paratethys was separated from the Tethys with the formation of the Alps, Dinarides and Elburz mountains during the Alpine orogeny. During the late Miocene, the Paratethys disappeared, became an isolated inland sea. In 1885, the Austrian palaeontologist Melchior Neumayr deduced the existence of the Tethys Ocean from Mesozoic marine sediments and their distribution, calling his concept Zentrales Mittelmeer and described it as a Jurassic seaway, which extended from the Caribbean to the Himalayas.
In 1893, the Austrian geologist Eduard Suess proposed the theory that an ancient and extinct inland sea had once existed between Laurasia and the continents which formed Gondwana II. He named it the Tethys Sea after the Greek sea goddess Tethys, he provided evidence for his theory using fossil records from the Africa. He proposed the concept of Tethys in his four-volume work Das Antlitz der Erde. In the following decades during the 20th century, "mobilist" geologists such as Uhlig and Daque regarded Tethys as a large trough between two supercontinents which lasted from the late Palaeozoic until continental fragments derived from Gondwana obliterated it. After World War II, Tethys was described as a triangular ocean with a wide eastern end. From 1920s to the 1960s, "fixist" geologists, regarded Tethys as a composite trough, which evolved through a series of orogenic cycles, they used the terms'Paleotethys','Mesotethys', and'Neotethys' for the Caledonian and Alpine orogenies, respe
Tithonian
In the geological timescale, the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 152.1 ± 4 145.0 ± 4 Ma. It is followed by the Berriasian stage; the Tithonian was introduced in scientific literature by German stratigrapher Albert Oppel in 1865. The name Tithonian is unusual in geological stage names. Tithonus was the son of Laomedon of Troy, he fell in love with Eos, the Greek goddess of dawn and finds his place in the stratigraphy because this stage, the Tithonian, finds itself hand in hand with the dawn of the Cretaceous. The base of the Tithonian stage is at the base of the ammonite biozone of Hybonoticeras hybonotum. A global reference profile for the base of the Tithonian had in 2009 not yet been established; the top of the Tithonian stage is marked by the first appearance of small globular calpionellids of the species Calpionella alpina, at the base of the Alpina Subzone. The Tithonian is subdivided into Lower/Early and Upper/Late substages or subages.
The Late Tithonian is coeval with the Portlandian stage of British stratigraphy. The Tithonian stage contains seven ammonite biozones in the Tethys domain, from top to base: zone of Durangites zone of Micracanthoceras micranthum zone of Micracanthoceras ponti or Burckardticeras peroni zone of Semiformiceras fallauxi zone of Semiformiceras semiforme zone of Semiformiceras darwini zone of Hybonoticeras hybonotum In the ocean of Tethys, the Tithonian has a calcareous facies with a typical cephalopod fauna; the Solnhofen limestone of southern Germany, known for its fossils, is of Tithonian age. Gradstein, F. M.. G. & Smith, A. G.. Oppel, C. A.. GeoWhen Database - Tithonian Jurassic-Cretaceous timescale, at the website of the subcommission for stratigraphic information of the ICS Stratigraphic chart of the Upper Jurassic, at the website of Norges Network of offshore records of geology and stratigraphy
Spitidiscus
Spitidiscus is a genus of ammonites placed in the family Holcodiscidae. List of species within Spitidiscus: Spitidiscus hugii Spitidiscus kilapiae Rawson and Aguirre-Urreta, 2012 - Argentina Spitidiscus oregonensis Imlay, 1960 - Oregon Spitidiscus riccardii Leanza, Wiedmann, 1992 - Argentina Spitidiscus rotulia - England Spitidiscus simitiensis Haas, 1960 - Colombia Spitidiscus vandeckii Member species have a rather evolute shell in which the whorl section is more or less circular, venter broadly rounded and dorsum deeply impressed. Close, fine low, single or branching ribs are interspersed by frequent straight or sinuous, moderately deep but wide constrictions; the first appearance of the species Spitidiscus hugii or Spitidiscus vandeckii are proposed to be the marker for the beginning of the Barremian. Spitidiscus has been found in the Lower Cretaceous of Europe, as well as of Morocco, Argentina and Mexico; the type species S. rotulia is from the Hauterivian of England. W. J. Arkell et al..
Mesozoic Ammonoidea in Treatise on Invertebrate Paleontology, Part L, Ammonoidea. Geological Society of America and Univ Kansas Press
Coniacian
The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma. The Coniacian is followed by the Santonian; the Coniacian is named after the city of Cognac in the French region of Saintonge. It was first defined by French geologist Henri Coquand in 1857; the base of the Coniacian stage is at the first appearance of the inoceramid bivalve species Cremnoceramus rotundatus. An official reference profile for the base had in 2009 not yet been appointed; the top of the Coniacian is defined by the appearance of the inoceramid bivalve Cladoceramus undulatoplicatus. The Coniacian overlaps the regional Emscherian stage of Germany, coeval with the Coniacian and Santonian stages. In magnetostratigraphy, the Coniacian is part of magnetic chronozone C34, the so-called Cretaceous Magnetic Quiet Zone, a long period with normal polarity. After a maximum of the global sea level during the early Turonian, the Coniacian was characterized by a gradual fall of the sea level.
This cycle is in sequence stratigraphy seen as a first order cycle. During the middle Coniacian a shorter, second order cycle, caused a temporary rise of the sea level on top of the longer first order trend; the following regression separates the Middle from the Upper Coniacian substage. An shorter third order cycle caused a new transgression during the Late Coniacian. Beginning in the Middle Coniacian, an anoxic event occurred in the Atlantic Ocean, causing large scale deposition of black shales in the Atlantic domain; the anoxic event lasted till the Middle Santonian and is the longest and last such event during the Cretaceous period. The Coniacian is subdivided into Lower and Upper substages, it encompasses three ammonite biozones in the Tethys domain: zone of Paratexanites serratomarginatus zone of Gauthiericeras margae zone of Peroniceras tridorsatumIn the boreal domain the Coniacian overlaps just one ammonite biozone: that of Forresteria petrocoriensis Gradstein, F. M.. G. & Smith, A. G.. Meyers, P.
A.. M. & Forster, A.. GeoWhen Database - Coniacian Late Cretaceous timescale, at the website of the subcommission for stratigraphic information of the ICS Stratigraphic chart of the Late Cretaceous, at the website of Norges Network of offshore records of geology and stratigraphy
Hemihoplites
Hemihoplites is an extinct genus of ammonoid cephalopods belonging to the family Hemihoplitidae. These fast-moving nektonic carnivores lived in the Cretaceous period, from Hauterivian age to Barremian age. Hemihoplites feraudianus Hemihoplites mexicanus Imlay, 1940 Hemihoplites ploszkiewiczi Riccardi and Aguirre Urreta, 1989 Hemihoplites soulieri Hemihoplites varicostatus Riccardi and Aguirre Urreta, 1989 Fossils of species within this genus have been found in the Cretaceous rocks of southeastern France, Slovakia, South Africa and Trinidad and Tobago
Sedimentary rock
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of small particules and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface. Sedimentation is the collective name for processes; the particles that form a sedimentary rock are called sediment, may be composed of geological detritus or biological detritus. Before being deposited, the geological detritus was formed by weathering and erosion from the source area, transported to the place of deposition by water, ice, mass movement or glaciers, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and piling up on the floor of water bodies. Sedimentation may occur as dissolved minerals precipitate from water solution; the sedimentary rock cover of the continents of the Earth's crust is extensive, but the total contribution of sedimentary rocks is estimated to be only 8% of the total volume of the crust.
Sedimentary rocks are only a thin veneer over a crust consisting of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata; the study of sedimentary rocks and rock strata provides information about the subsurface, useful for civil engineering, for example in the construction of roads, tunnels, canals or other structures. Sedimentary rocks are important sources of natural resources like coal, fossil fuels, drinking water or ores; the study of the sequence of sedimentary rock strata is the main source for an understanding of the Earth's history, including palaeogeography and the history of life. The scientific discipline that studies the properties and origin of sedimentary rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps with other disciplines in the Earth sciences, such as pedology, geomorphology and structural geology. Sedimentary rocks have been found on Mars. Sedimentary rocks can be subdivided into four groups based on the processes responsible for their formation: clastic sedimentary rocks, biochemical sedimentary rocks, chemical sedimentary rocks, a fourth category for "other" sedimentary rocks formed by impacts and other minor processes.
Clastic sedimentary rocks are composed of other rock fragments that were cemented by silicate minerals. Clastic rocks are composed of quartz, rock fragments, clay minerals, mica. Clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions: gravel and mud; the classification of clastic sedimentary rocks parallels this scheme. This tripartite subdivision is mirrored by the broad categories of rudites and lutites in older literature; the subdivision of these three broad categories is based on differences in clast shape, grain size or texture. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel. Sandstone classification schemes vary but most geologists have adopted the Dott scheme, which uses the relative abundance of quartz and lithic framework grains and the abundance of a muddy matrix between the larger grains.
Composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks. All other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Quartz sandstones have >90% quartz grains Feldspathic sandstones have <90% quartz grains and more feldspar grains than lithic grains Lithic sandstones have <90% quartz grains and more lithic grains than feldspar grainsAbundance of muddy matrix material between sand grains When sand-sized particles are deposited, the space between the grains either remains open or is filled with mud. "Clean" sandstones with open pore space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes. Six sandstone names are possible using the descriptors for grain composition and the amount of matrix. For example, a quartz arenite would be composed of quartz grains and have little or no clayey matrix between the grains, a lithic wacke would have abundant lithic grains and abundant muddy matrix, etc.
Although the Dott classification scheme is used by sedimentologists, common names like greywacke and quartz sandstone are still used by non-specialists and in popular literature. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles; these fine-grained particles are transported by turbulent flow in water or air, deposited as the flow calms and the particles settle out of suspension. Most authors presently
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