The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 5.333 ± 0.005 Ma. It is followed by the Zanclean, the first age of the Pliocene; the Messinian overlaps the Turolian European Land Mammal Mega Zone and the Pontian Central European Paratethys stage. It overlaps the late Huayquerian and early Montehermosan South American Land Mammal Ages, falls inside the more extensive Hemphillian North American Land Mammal Age. During the Messinian, around 6 million years ago, the Messinian salinity crisis took place, which brought about repeated desiccations of the Mediterranean Sea; the Messinian was introduced by Swiss stratigrapher Karl Mayer-Eymar in 1867. Its name comes from the Italian city of Messina on Sicily, where the Messinian evaporite deposit is of the same age; the base of the Messinian is at the first appearance of the planktonic foram species Globorotalia conomiozea and is stratigraphically in the middle of magnetic chronozone C3Br.1r.
The Global Boundary Stratotype Section and Point for the Messinian is located in a section at Oued Akrech, near the Moroccan capital Rabat. The top of the Messinian lies with the top of magnetic chronozone Cr3; the top is close to the extinction level of the calcareous nanoplankton species Triquetrorhabdulus rugosus and the first appearance of nanoplankton Ceratolithus acutus. Gradstein, F. M.. G. Ogg. G. Smith. A Geologic Time Scale 2004. Cambridge University Press. Hilgen, F. J.. G. Langereis. J. Zachariasse; the Global Boundary Stratotype Section and Point of the Messinian Stage. Pp. 172–178. Hsü, K. J.. The Mediterranean Was a Desert. Princeton: Princeton University Press. Mayer-Eymar, Karl. Catalogue systématique et descriptif des fossiles des terrains tertiaires qui se trouvent du Musée fédéral de Zürich. Zürich. GeoWhen Database - Messinian Messinian online - living in an evaporitic world - Mediterranean area Neogene timescale, at the website of the subcommission for stratigraphic information of the ICS Neogene timescale at the website of the Norwegian network of offshore records of geology and stratigraphy
The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago. The Miocene was named by Charles Lyell; the Miocene is followed by the Pliocene. As the earth went from the Oligocene through the Miocene and into the Pliocene, the climate cooled towards a series of ice ages; the Miocene boundaries are not marked by a single distinct global event but consist rather of regionally defined boundaries between the warmer Oligocene and the cooler Pliocene Epoch. The Apes first evolved and diversified during the early Miocene, becoming widespread in the Old World. By the end of this epoch and the start of the following one, the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path during the final Messinian stage of the Miocene; as in the Oligocene before it, grasslands continued to forests to dwindle in extent. In the seas of the Miocene, kelp forests made their first appearance and soon became one of Earth's most productive ecosystems.
The plants and animals of the Miocene were recognizably modern. Mammals and birds were well-established. Whales and kelp spread; the Miocene is of particular interest to geologists and palaeoclimatologists as major phases of the geology of the Himalaya occurred during the Miocene, affecting monsoonal patterns in Asia, which were interlinked with glacial periods in the northern hemisphere. The Miocene faunal stages from youngest to oldest are named according to the International Commission on Stratigraphy: Regionally, other systems are used, based on characteristic land mammals. Of the modern geologic features, only the land bridge between South America and North America was absent, although South America was approaching the western subduction zone in the Pacific Ocean, causing both the rise of the Andes and a southward extension of the Meso-American peninsula. Mountain building took place in western North America and East Asia. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines.
Well studied continental exposures occur in Argentina. India continued creating dramatic new mountain ranges; the Tethys Seaway continued to shrink and disappeared as Africa collided with Eurasia in the Turkish–Arabian region between 19 and 12 Ma. The subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea near the end of the Miocene; the global trend was towards increasing aridity caused by global cooling reducing the ability of the atmosphere to absorb moisture. Uplift of East Africa in the late Miocene was responsible for the shrinking of tropical rain forests in that region, Australia got drier as it entered a zone of low rainfall in the Late Miocene. During the Oligocene and Early Miocene the coast of northern Brazil, south-central Peru, central Chile and large swathes of inland Patagonia were subject to a marine transgression; the transgressions in the west coast of South America is thought to be caused by a regional phenomenon while the rising central segment of the Andes represents an exception.
While there are numerous registers of Oligo-Miocene transgressions around the world it is doubtful that these correlate. It is thought that the Oligo-Miocene transgression in Patagonia could have temporarily linked the Pacific and Atlantic Oceans, as inferred from the findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation. Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography; the Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction. At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan; as the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time.
The asthenospheric window associated to the triple junction disturbed previous patterns of mantle convection beneath Patagonia inducing an uplift of ca. 1 km that reversed the Oligocene–Miocene transgression. Climates remained moderately warm, although the slow global cooling that led to the Pleistocene glaciations continued. Although a long-term cooling trend was well underway, there is evidence of a warm period during the Miocene when the global climate rivalled that of the Oligocene; the Miocene warming b
The Langhian is, in the ICS geologic timescale, an age or stage in the middle Miocene epoch/series. It spans the time between 13.65 ± 0.05 Ma during the Middle Miocene. The Langhian was a continuing warming period defined by Lorenzo Pareto in 1865, it was established in the Langhe area north of Ceva in northern Italy, hence the name; the Langhian is followed by the Serravallian stage. The base of the Langhian is defined by the first appearance of foraminifer species Praeorbulina glomerosa and is coeval with the top of magnetic chronozone C5Cn.1n. A GSSP for the Langhian stage was not yet established in 2009; the top of the Langhian stage is at the first occurrence of fossils of the nanoplankton species Sphenolithus heteromorphus and is located in magnetic chronozone C5ABr. The Langhian is coeval with the Orleanian and Astaracian European Land Mammal Mega Zones, with the upper Hemingfordian to mid-Barstovian North American Land Mammal Ages, with mid-Relizian to Luisian Californian regional stages, with the early-mid Badenian Paratethys stage of Central and eastern Europe, with the Tozawan stage in Japan, with the late Batesfordian through Balcombian to early Bairnsdalian Australian stages and with the mid-Cliffdenian to mid-Lillburnian New Zealand stages.
Turtles: Meiolania brevicollis Sharks, rays and relatives Chlamydoselachidae: †Chlamydoselachus tobleri Hexanchidae: Hexanchus griseus, Hexanchus nakamurai, Notorynchus cepedianus Perissodactyla Rhinocerotidae: † Dicerorhinus sansaniensis Rodentia Cricetidae: †Karydomys Sciuridae: †Palaeosciurus,? Ratufa Middle Miocene disruption Nördlinger Ries impact crater Gradstein, F. M.. G. & Smith, A. G.. Pareto, L.. PDF GeoWhen Database - Langhian Neogene timescale, at the website of the subcommission for stratigraphic information of the ICS Neogene timescale at the website of the Norwegian network of offshore records of geology and stratigraphy
The Pliocene Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58 million years BP. It is the youngest epoch of the Neogene Period in the Cenozoic Era; the Pliocene is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations within the Pleistocene, the Pliocene included the Gelasian stage, which lasted from 2.588 to 1.806 million years ago, is now included in the Pleistocene. As with other older geologic periods, the geological strata that define the start and end are well identified but the exact dates of the start and end of the epoch are uncertain; the boundaries defining the Pliocene are not set at an identified worldwide event but rather at regional boundaries between the warmer Miocene and the cooler Pliocene. The upper boundary was set at the start of the Pleistocene glaciations. Charles Lyell gave the Pliocene its name in Principles of Geology; the word pliocene comes from the Greek words πλεῖον and καινός and means "continuation of the recent", referring to the modern marine mollusc fauna.
H. W. Fowler called the term Pliocene a "regrettable barbarism" and an indication that "a good classical scholar" such as Lyell should have requested a philologist's help when coining words. To summarize the usage of these "regrettable barbarisms" in the labelling of the Cenozoic era: with the understanding that these are all new relative to the Mesozoic and Paleozoic eras. In the official timescale of the ICS, the Pliocene is subdivided into two stages. From youngest to oldest they are: Piacenzian Zanclean The Piacenzian is sometimes referred to as the Late Pliocene, whereas the Zanclean is referred to as the Early Pliocene. In the system of North American Land Mammal Ages include Hemphillian, Blancan; the Blancan extends forward into the Pleistocene. South American Land Mammal Ages include Montehermosan and Uquian. In the Paratethys area the Pliocene contains the Romanian stages; as usual in stratigraphy, there are many other local subdivisions in use. In Britain the Pliocene is divided into the following stages: Gedgravian, Pre-Ludhamian, Thurnian, Bramertonian or Antian, Pre-Pastonian or Baventian and Beestonian.
In the Netherlands the Pliocene is divided into these stages: Brunssumian C, Reuverian A, Reuverian B, Reuverian C, Tiglian A, Tiglian B, Tiglian C1-4b, Tiglian C4c, Tiglian C5, Tiglian C6 and Eburonian. The exact correlations between these local stages and the ICS stages is still a matter of detail; the global average temperature in the mid-Pliocene was 2–3 °C higher than today, carbon dioxide levels were the same as today, global sea level was 25 m higher. The northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma; the formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds. Mid-latitude glaciation was underway before the end of the epoch; the global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas. Continents continued to drift, moving from positions as far as 250 km from their present locations to positions only 70 km from their current locations.
South America became linked to North America through the Isthmus of Panama during the Pliocene, making possible the Great American Interchange and bringing a nearly complete end to South America's distinctive large marsupial predator and native ungulate faunas. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean. Africa's collision with Europe formed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean; the border between the Miocene and the Pliocene is the time of the Messinian salinity crisis. Sea level changes exposed the land bridge between Asia. Pliocene marine rocks are well exposed in the Mediterranean and China. Elsewhere, they are exposed near shores. During the Pliocene parts of southern Norway and southern Sweden, near sea level rose. In Norway this rise elevated the Hardangervidda plateau to 1200 m in the Early Pliocene.
In Southern Sweden similar movements elevated the South Swedish highlands leading to a deflection of the ancient Eridanos river from its original path across south-central Sweden into a course south of Sweden. The change to a cooler, seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species worldwide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, grasslands spread on all continents. Tropical forests were limited to a tight band around the equator, in addition to dry savannahs, deserts appeared in Asia and Africa. Both marine and co
Geochronology is the science of determining the age of rocks and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as palaeomagnetism and stable isotope ratios. By combining multiple geochronological indicators the precision of the recovered age can be improved. Geochronology is different in application from biostratigraphy, the science of assigning sedimentary rocks to a known geological period via describing and comparing fossil floral and faunal assemblages. Biostratigraphy does not directly provide an absolute age determination of a rock, but places it within an interval of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand, however, to the point where they share the same system of naming rock layers and the time spans utilized to classify layers within a stratum; the science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.
By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material. A number of radioactive isotopes are used for this purpose, depending on the rate of decay, are used for dating different geological periods. More decaying isotopes are useful for longer periods of time, but less accurate in absolute years. With the exception of the radiocarbon method, most of these techniques are based on measuring an increase in the abundance of a radiogenic isotope, the decay-product of the radioactive parent isotope. Two or more radiometric methods can be used in concert to achieve more robust results. Most radiometric methods are suitable for geological time only, but some such as the radiocarbon method and the 40Ar/39Ar dating method can be extended into the time of early human life and into recorded history; some of the used techniques are: Radiocarbon dating. This technique measures the decay of carbon-14 in organic material and can be best applied to samples younger than about 60,000 years.
Uranium–lead dating. This technique measures the ratio of two lead isotopes to the amount of uranium in a mineral or rock. Applied to the trace mineral zircon in igneous rocks, this method is one of the two most used for geologic dating. Monazite geochronology is another example of U–Pb dating, employed for dating metamorphism in particular. Uranium–lead dating is applied to samples older than about 1 million years. Uranium–thorium dating; this technique is used to date speleothems, corals and fossil bones. Its range is from a few years to about 700,000 years. Potassium–argon dating and argon–argon dating; these techniques date metamorphic and volcanic rocks. They are used to date volcanic ash layers within or overlying paleoanthropologic sites; the younger limit of the argon–argon method is a few thousand years. Electron spin resonance dating A series of related techniques for determining the age at which a geomorphic surface was created, or at which surficial materials were buried. Exposure dating uses the concentration of exotic nuclides produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created.
Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure. Luminescence dating techniques observe'light' emitted from materials such as quartz, diamond and calcite. Many types of luminescence techniques are utilized in geology, including optically stimulated luminescence, cathodoluminescence, thermoluminescence. Thermoluminescence and optically stimulated luminescence are used in archaeology to date'fired' objects such as pottery or cooking stones and can be used to observe sand migration. Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed or floating. Dendrochronology Ice cores Lichenometry Varves A sequence of paleomagnetic poles, which are well defined in age, constitutes an apparent polar wander path; such a path is constructed for a large continental block. APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age.
For paleomagnetic dating, it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP. Two methods of paleomagnetic dating have been suggested Rotation method. First method is used for paleomagnetic dating of rocks inside of the same continental block; the second method is used for the folded areas. Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and/or volcanic rocks by comparison to the magnetic polarity timescale; the polarity timescale has been determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, astronomically dating magnetostratigraphic sections. Global trends in isotope compositions Carbon 13 and strontium isotopes, can be used to corr