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18-653: Shan–Thai is c. 4,000 km (2,500 mi) long and bounded by the Indochina terrane to the east and the South China terrane to the north. It is one of a series of continental blocks or terranes that were rifted off eastern Gondwana during the Ordovician ( 495 to 443 Ma ), long before the formation of Pangaea . Today these blocks form south-east Asia but the different timing of their journeys has given them distinct geologic histories. Shan–Thai

36-419: A facies ( / ˈ f eɪ ʃ ɪ . iː z / FAY -shih-eez , US also / ˈ f eɪ ʃ iː z / FAY -sheez ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formation) and the changes that may occur in those attributes over

54-415: A distinct kind of sediment for that area or environment. Since its inception in 1838, the facies concept has been extended to related geological concepts. For example, characteristic associations of organic microfossils, and particulate organic material, in rocks or sediments, are called palynofacies . Discrete seismic units are similarly referred to as seismic facies. Sedimentary facies are described in

72-514: A geographic area. A facies encompasses all the characteristics of a rock including its chemical, physical, and biological features that distinguish it from adjacent rock. The term "facies" was introduced by the Swiss geologist Amanz Gressly in 1838 and was part of his significant contribution to the foundations of modern stratigraphy , which replaced the earlier notions of Neptunism . Walther's law of facies, or simply Walther's law, named after

90-435: A group of "facies descriptors" which must be distinct, reproducible and exhaustive. A reliable facies description of an outcrop in the field would include: composition, texture, sedimentary structure(s), bedding geometry, nature of bedding contact, fossil content and colour. The sequence of minerals that develop during progressive metamorphism (that is, metamorphism at progressively higher temperatures and/or pressures) define

108-587: A larger plate, and is relatively buoyant due to thickness or low density. When the plate of which it was a part subducted under another plate, the terrane failed to subduct, detached from its transporting plate, and accreted onto the overriding plate. Therefore, the terrane transferred from one plate to the other. Typically, accreting terranes are portions of continental crust which have rifted off another continental mass and been transported surrounded by oceanic crust, or they are old island arcs formed at some distant subduction zones. A tectonostratigraphic terrane

126-436: Is a fault-bounded package of rocks of at least regional extent characterized by a geologic history that differs from that of neighboring terranes. The essential characteristic of these terranes is that the present spatial relations are incompatible with the inferred geologic histories. Where terranes that lie next to each other possess strata of the same age, they are considered separate terranes only if it can be demonstrated that

144-407: Is also an older usage of the term terrane , which described a series of related rock formations or an area with a preponderance of a particular rock or rock group. A tectonostratigraphic terrane did not necessarily originate as an independent microplate , since it may not contain the full thickness of the lithosphere . It is a piece of crust that has been transported laterally, usually as part of

162-427: Is different from the surrounding areas—hence the term "exotic" terrane. The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault . A sedimentary deposit that buries the contact of the terrane with adjacent rock is called an overlap formation . An igneous intrusion that has intruded and obscured the contact of a terrane with adjacent rock is called a stitching pluton . There

180-522: Is the vertical stratigraphic succession that typifies marine transgressions and regressions . Ideally, a sedimentary facies is a distinctive rock unit that forms under certain conditions of sedimentation , reflecting a particular process or environment. Sedimentary facies are either descriptive or interpretative. Sedimentary facies are bodies of sediment that are recognizably distinct from adjacent sediments that resulted from different depositional environments. Generally, geologists distinguish facies by

198-632: Is transitional between the other two. The internal parts of Shan–Thai merged with Laurasia 265 Ma when the Nan - Uttaradit suture closed. Oceanic basins separated the other elements of Shan–Thai until the Late Triassic–Early Jurassic Late Indochina Orogeny. The collision between India and Eurasia during the Oligocene and Miocene resulted in clockwise rotation of south-west Asia, severe deformation of south-east Asia, and

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216-457: The aspect of the rock or sediment being studied. Facies based on petrological characters (such as grain size and mineralogy ) are called lithofacies , whereas facies based on fossil content are called biofacies . A facies is usually further subdivided. The characteristics of the rock unit come from the depositional environment and from the original composition. Sedimentary facies reflect their depositional environment, each facies being

234-913: The orogenic belt where they had eventually ended up. It followed that the present orogenic belt was itself an accretionary collage, composed of numerous terranes derived from around the circum- Pacific region and now sutured together along major faults. These concepts were soon applied to other, older orogenic belts, e.g. the Appalachian belt of North America.... Support for the new hypothesis came not only from structural and lithological studies, but also from studies of faunal biodiversity and palaeomagnetism . When terranes are composed of repeated accretionary events, and hence are composed of subunits with distinct history and structure, they may be called superterranes . Africa Asia Taiwan Tibet Australasia Europe Fennoscandia North America South America Facies In geology ,

252-413: The ability of crustal fragments to "drift" thousands of miles from their origin and attach themselves, crumpled, to an exotic shore. Such terranes were dubbed " accreted terranes " by geologists . Geologist J. N. Carney writes: It was soon determined that these exotic crustal slices had in fact originated as "suspect terranes" in regions at some considerable remove, frequently thousands of kilometers, from

270-578: The extrusion of Shan–Thai and Indochina blocks. These two blocks are still crisscrossed by the faults from this collision. This palaeogeography article is a stub . You can help Misplaced Pages by expanding it . Terrane In geology , a terrane ( / t ə ˈ r eɪ n , ˈ t ɛr eɪ n / ; in full, a tectonostratigraphic terrane ) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured " to crust lying on another plate. The crustal block or fragment preserves its distinctive geologic history, which

288-428: The geologic evolutions are different and incompatible. There must be an absence of intermediate lithofacies that could link the strata. The concept of tectonostratigraphic terrane developed from studies in the 1970s of the complicated Pacific Cordilleran orogenic margin of North America , a complex and diverse geological potpourri that was difficult to explain until the new science of plate tectonics illuminated

306-403: The geologist Johannes Walther , states that the vertical succession of facies reflects lateral changes in environment. Conversely, it states that when a depositional environment "migrates" laterally, sediments of one depositional environment come to lie on top of another. In Russia the law is known as Golovkinsky-Walther's law, honoring also Nikolai A. Golovkinsky . A classic example of this law

324-482: Was an archipelago on the Paleo-Tethys Ocean spread over several latitudes. It can therefore be subdivided into several portions with different palaeo-geographical histories. The internal "Thai" elements, bordering the Indochina block, are of Cathaysian type and characterised by palaeo-tropical warm-water facies . The external "Shan" part has Gondwanan cold-water facies whilst the central "Sibumasu" part

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