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57-751: A number of studies defined the extent of the Ryukyu Arc geographically and morphologically into three parts: Northern Ryukyu, which includes the Ōsumi Islands ; Central Ryukyu, which includes Amami Islands and Okinawa Islands ; Southern Ryukyu, which includes Miyako Islands and Yaeyama Islands . The northernmost and southernmost parts of the Ryukyu Arc terminate in Kyushu and Taiwan, respectively. The geological and structural features of Southern Ryukyu are quite different from those of Northern and Central Ryukyu; Southern Ryukyu, and Northern and Central Ryukyu may have developed in disparate geological settings before

114-516: A quarry near Thouars. In Europe this period is represented by the upper part of the Lias . The base of the Toarcian is defined as the place in the stratigraphic record where the ammonite genus Eodactylites first appears. A global reference profile (a GSSP ) for the base is located at Peniche, Portugal . The top of the stage is at the first appearance of ammonite genus Leioceras . In

171-501: A clockwise rotation of Southern Ryukyu after 10 Ma. Seismic reflection surveys indicate initial rifting of the southern part of the Okinawa Trough in the early Pleistocene, which gave rise to distinct tectonic processes, i.e., sedimentation , crustal doming, erosion , and subsidence . The emergence of the Ryukyu Arc, together with the subsidence of the Okinawa Trough, may have occurred in the late Pleistocene (1.7–0.5 Ma) after

228-505: A democratic election, the local electorate chose a governor who pledged reversion to Japan (this also happened in other native governments of Ryukyu, namely those of Okinawa, Miyakojima , and Yaeyama ). The United States Civil Administration of the Ryukyu Islands (USCAR) was alarmed by this development, and reduced the power of native governments to that of a figurehead status. In 1952, USCAR founded another governmental body called

285-631: A late Eocene age. The Nosoko Formation is a 300m thick sequence of tuff , volcanic sandstone and breccia , and lavas with dykes , sills , and other small intrusions . This formation is widely exposed at the Nosoko peninsula in northern Ishigaki Island. It also lies conformably above the Miyara Formation. Paleomagnetic data of the Nosoko Formation indicate a mean deflection of the magnetic direction at about 30˚ clockwise away from

342-419: A lower member. The upper member (Shinzato) of late Miocene or Pliocene age consists of tuff and shale; the lower member (Yonabaru) of Miocene age contains shale interbedded with siltstone and sandstone. The Shimajiri Group is the first geological unit to be found across Northern, Central, and Southern Ryukyu. Northern, Central Ryukyu, and Southern Ryukyu may have had different basins and tectonic settings prior to

399-650: A minor amount of calcareous siltstone , tuffaceous and calcareous mudstone. Fossil records of ammonites and halobiids in this formation suggest a Late Triassic age. The Nakijin Formation can be found in Central Ryukyu, i.e., Sesoko Island and the northwestern part of the Motobu peninsula of Okinawa Island. This formation overlies the Yonamine Formation along a reverse fault. The Shimanto Group

456-562: A nobility class called the aji , who resided in castles called gusuku . Famous gusuku included Beru Castle in Kasari, Amami , and Yononushi Castle in Wadomari . Stronger aji battled each other to expand their territories. Local folklore states that some Taira clan members, having lost the Battle of Dan-no-ura in 1185, fled to Amami Ōshima. The historical accuracy of this claim

513-572: A style different from that of Ryukyu, and still remain as a part of their culture today. Under Satsuma's rule, names of Amami people underwent a great change, and they are today known for many unique one-character surnames. In 1871, after the Meiji Restoration , the Amami Islands were incorporated into Ōsumi Province , and then into Kagoshima Prefecture . During World War II , more than 20,000 Japanese soldiers were garrisoned in

570-689: Is a set of metamorphic rocks dated from Early Cretaceous to earliest Miocene which are associated with the Shimanto belt. The Shimanto belt is an accretionary complex in the Outer Zone of Southwest Japan which extends from Honshu , Shikoku , and Kyushu to Northern and Central Ryukyu. The group comprises sedimentary and metasedimentary rocks metamorphosed up to greenschist facies , including flysch -type sandstone and slate with mafic greenstones. Deformations such as northwest-dipping, isoclinal, overturned folds and SE-verging thrust faults can be found in

627-415: Is a south-southwest-dipping succession of conglomerate , sandstone, shale , and limestone deposited along the coast of Ishigaki Island. A large variety of marine fossils—e.g., calcareous algae, foraminifera, corals, echinoderms , bryozoans , and gastropods — have been preserved in the limestones, and molluscs were also found in the conglomerate. Foraminifera and calcareous algae in the limestones suggest

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684-600: Is distributed in Central and Southern Ryukyu and is marked by a distinct unconformity above the Shimajiri Group. The group comprises predominantly the Ryukyu Limestone and Terrace Deposits of sand and gravel. The Ryukyu Limestone is generally 40–60m thick and is characterised by post-depositional faulting, which resulted in the formation of terraces and the associated sediments (Terrace Deposits). Following

741-494: Is greater than other parts, is about 2200 m. The Okinawa Trough accommodates terrigenous sediments from the continental shelf of Asia and the Ryukyu Arc at a high rate. The Ryukyu Arc is a site of active seismicity characterised by shallow earthquakes, given the ongoing convergence between the Philippine Sea Plate and Eurasian Plate. Seismic data of earthquakes have been used to detect seismic structures below

798-402: Is the back-arc basin of the Ryukyu Arc, and has been formed by lithospheric extension of the continental Eurasian Plate. Extensional grabens , about 10 km wide and about 50–100 km long, with en echelon alignment can be found in the middle to southern parts of Okinawa Trough. Of the whole Okinawa Trough, the southern part is the most evolved and active, in that, its maximum depth, which

855-593: Is unknown. This gusuku period is sometimes called the Aji period ( 按司世 , Ajin'yu ) . Eventually the Amami aji were forced to pay tribute to stronger nations to retain autonomy. Ryukyuan records state that Amami aji paid tribute to Eiso , the king of Chūzan in Sanzan period Okinawa. Okinoerabu and Yoron fell under Hokuzan 's control. However, since Okinawa itself was still rife with civil wars, it could not control

912-763: The Amami language . It is divided into several dialects: the Kikai dialect, North Amami dialect, South Amami dialect, and Tokunoshima dialect. Dialects spoken in the southern islands of Okinoerabu and Yoron are part of the Kunigami language centered on Northern Okinawa Island. These dialects and languages all belong to the Northern Ryukyuan group of the Ryukyuan languages . Although the Ryukyuan languages belong to

969-551: The Azuchi-Momoyama period , led Shimazu Tadatsune , the ruler of Satsuma Domain in southern Kyushu, to invade the Ryukyu Kingdom in order to gain control of the shipping routes between Japan and China. In April 1609, Shimazu launched an invasion of the Ryukyu Kingdom. They landed on Amami Ōshima, then Tokuno, Okinoerabu, and Okinawa itself. Satsuma met fierce resistance, but eventually defeated Ryukyu, by capturing

1026-466: The Battle of Amami-Ōshima , which resulted in a Japanese victory. Download coordinates as: As a part of the Ryukyuan cultural sphere, Amami culture is closer to that of the other Ryukyu Islands than to that of mainland Japan. However, the islands' history is different from Okinawa as well. Okinawa, including the Sakishima Islands , had strong cultural influences from China, whereas Amami

1083-626: The Government of the Ryukyu Islands , in which "local leaders" were appointed by the American government. Amami residents were dissatisfied with these controls by the U.S. Moreover, the Amami economy suffered from separation from the Japanese market. Public funds of the U.S. administration were mostly used for heavily damaged Okinawa and the military bases there. The Amami Islands Homeland Restoration Movement, which had started immediately after

1140-593: The Japan Coast Guard agreed on February 15, 2010, to use the name of Amami-guntō ( 奄美群島 ) for the Amami Islands. Prior to that, Amami-shotō ( 奄美諸島 ) was also used. The name of Amami is probably cognate with Amamikyu ( 阿摩美久 ) , the goddess of creation in the Ryukyuan creation myth . The Amami Islands are limestone islands of coralline origin and have a total area of approximately 1,240.28 square kilometres (478.87 sq mi), of which 308.3 square kilometres (119.0 sq mi) constitute

1197-523: The Japonic family along with Japanese , they are often not mutually intelligible between each other and Japanese. Because of the education system put in place during the Meiji period, all Amami people today speak standard Japanese. However, the de facto common speech among Amami people under 60 is Amami Japanese , a dialect of the Japanese language that uses an Amami accent and some words and phrases from

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1254-673: The Tokara Islands to Japan in February 1952, and the Amami Islands on December 25, 1953. The U.S. government called it "a Christmas present to Japan". This period is called the American period ( アメリカ世 , Amerika-yo ) . Although the Amami Islands were returned to Japan in 1953, Okinawa remained under American control until 1972. Because of this, Amami people who worked in Okinawa suddenly became "foreigners", making their situations difficult. The Japanese government promulgated

1311-478: The pentatonic scale of Ab, C, Db, Eb, G - that is, a hemitonic scale with intervals 2-0.5-1-2-0.5 (leading note) - Amami folk songs use the scale of C, D, E, G, A - an anhemitonic scale with intervals 1-1-1.5-1-1.5 (the same as the Greek pentatonic scale). Singers use a falsetto voice when singing. Each community has multiple utaki shrines for the native religion , as well as Shinto shrines established by

1368-476: The Amami Islands Promotion and Development Special Measures Law. However, the economic gap between the islands and the mainland still exists to this day. The law did help residents by improving the island's infrastructure. However, its bureaucratic system has been criticized as causing unnecessary destruction of nature. In 2001, there was a small naval exchange between North Korea and Japan in

1425-523: The Amami Islands, although the islands were never invaded, and experienced only small scale airstrikes . This period, until 1945, is called the Yamato period ( 大和世 , Yamatun'yu ) . After the surrender of Japan , the Amami Islands fell under direct American military control, with American documents referring to the Amami Islands as the "Northern Ryukyu Islands". The Japanese government believed this indicated an American intention to permanently separate

1482-930: The Amami language, locally referred to as Ton-futsūgo ( トン普通語 , lit. "Potato standard") . The speech is different from Uchinaa-Yamatuguchi ( Okinawan Japanese ), the Okinawan equivalent used in Okinawa. Ton-futsūgo is affected not only by standard Japanese, but also by the Kagoshima dialect and the Kansai dialect . The local folk songs in Amami are called shima uta . Although shima means "island" in Japanese, it means "community" in Amami. Thus shima uta literally means "communities' songs". Singers of shima uta are called utasha  [ ja ] (lit. "singer"). Some utasha also sing pop songs as well, examples include Chitose Hajime , Kousuke Atari , Rikki , and Anna Sato  [ ja ] . Some believe that

1539-598: The Ishigaki Island and Taketomi Island of the Yaeyama Islands in Southern Ryukyu, comprises weakly metamorphosed olistromal rocks : allochthonous blocks of chert, mudstone , sandstone, and limestone are embedded in a muddy matrix . The metamorphic age of this formation ranges from 145 to 130 Ma (Early Cretaceous ) and was determined by K-Ar phengitic micas dating. Radiolaria data show that

1596-985: The Japan Island Arc, including the Ryukyu Arc, developed from accretions pertinent to the subduction during the Jurassic. Fossil and paleomagnetic evidence from the Shimanto Group suggests that subduction of a young oceanic plate occurred in the Late Cretaceous (about 70 Ma) to the Paleogene. Subduction and accretion may have stopped in late Eocene prior to the deposition of the Neogene-Quaternary Shimajiri Group. Deposition of continental shelf sediments (the Yaeyama Group) took place in Southern Ryukyu, which at

1653-540: The Japanese government, whereas Buddhist temples are less common than in Japan. As in Okinawa, priestesses called noro exist, and the people worship according to the native religious norms. There are three Ryukyuan tomb styles: the house style, the turtle style, and the cave style. Most tombs in Amami use the house style, unlike in Okinawa where the turtle style is more prevalent. However, there are tombs called "Shiroma Tofuru" tombs, which were built 400 years ago, that use

1710-559: The Late Miocene (the age of deposition of the group). Despite being widely distributed across the East China Sea, the Ryukyu Arc and its forearc , the group does not occur in the southern Okinawa Trough. Rifting of the southern Okinawa Trough preceded the deposition of the group. The Ryukyu Group is Pleistocene deposits formed after the development of the Shimajiri Group but before Holocene sediments had been deposited. It

1767-576: The Motobu Formation and contains Permian corals. The Tomuru Formation is distributed in the Iriomote and Ishigaki Islands of the Yaeyama Islands, Southern Ryukyu. The formation has an age of 220–190 Ma (million years ago) (Late Triassic -Early Jurassic ) and comprises ultramafic rocks and high pressure/temperature (P/T) metamorphic rocks, i.e., metagabbro and mafic , siliceous , and pelitic schists . The Fusaki Formation, located at

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1824-540: The Northern Amami Islands. Aji from Tokuno and further north just paid tribute to Okinawan kingdoms, and continued to remain independent. After 1429, Shō Hashi unified Okinawa Island , founding the Ryukyu Kingdom . During the 1430s and 1440s, Ryukyu expanded into the Amami Islands. By 1450, Ryukyuan forces had reached deep into the Tokara Islands and conquered all but Kikai Island , which

1881-466: The Ryukyu Arc are herein summarised. The Motobu and Yonamine Formations are Permian rocks that constitute the basement of the Motobu peninsula of Okinawa Island , Central Ryukyu. The Motobu Formation consists mainly of limestone interbedded with chert and phyllite . The limestone contains foraminifera fossils of Permian age. The Yonamine Formation, with strata of interbedded phyllite, slate , sandstone , limestone, greenstone, and chert, underlies

1938-587: The Ryukyu Arc. Low seismic velocity zones , which are possibly associated with the upwelling of magma, have been discovered beneath active volcanoes and the Okinawa Trough. An active volcanic front lies 100 km above the Wadati-Benioff zone (a planar zone of seismicity at the interface between the subducting and overriding plates) in Northern Ryukyu and gradually fades off in Central and Southern Ryukyu. Major, but not all, geological units of

1995-607: The Shimanto Group of Central and Northern Ryukyu. In Okinawa Island, Central Ryukyu, the Shimanto Group is separated into the Nago Formation and the Kayo Formation. The Nago Formation comprises pelitic and mafic schist, phyllite, and slate, with minor chert and limestone, and crops out most of northern Okinawa Island. Though only trace fossils have been found in the formation, it is thought to be Cretaceous to early Eocene in age by correlations with other formations in

2052-496: The arc toward south. Global Positioning System data show that southern Kyushu and the Ryukyu Arc migrate southeastward (toward the Ryukyu Trench) relative to Eurasia, as compared to the westward-northwestward migration of other arcs of Japan. Permian-Jurassic accretionary prisms accumulated along the eastern side of Pangea , where the ancient Pacific Plate subducted under the ancient Asian continental block. Vast regions of

2109-482: The capital of Shuri . Ryukyu ceded the Amami Islands to Satsuma Domain in 1611. Satsuma started to directly rule the islands from 1613, sending a daikan commissioner. However, it was still nominally treated as Ryukyuan territory, and bureaucrats from the kingdom were dispatched as well. Satsuma control over the islands was formally recognized by the Tokugawa shogunate in 1624. At first, Satsuma's administration

2166-410: The city ( -shi ) of Amami, and 931.9 square kilometres (359.8 sq mi) constitute the district ( -gun ) of Oshima. The highest elevation is Yuwandake with a height of 694 metres (2,277 ft) on Amami Ōshima . The climate is a humid subtropical climate ( Köppen climate classification Cfa ) with very warm summers and mild winters. Precipitation is high throughout the year, but is highest in

2223-399: The current Amami. The tenth kentō-shi mission (Japanese Imperial embassies to China ) traveled to Tang dynasty China via Amami Ōshima. Among locals, this prehistoric period is called the Amami period ( 奄美世 , Aman'yu ) . Agriculture came to the islands around the 12th century, and the people shifted to farming from hunting. As on Okinawa Island , this resulted in the development of

2280-548: The deposition of the Ryukyu Limestone, prevalent northwest–southeast faulting across the Ryukyu Arc resulted in an episode of dome-like uplifting of basement rocks in the Ryukyu Islands, named the 'Uruma Movement'. Along the Ryukyu Trench, the Philippine Sea Plate is subducting northwestward under the Eurasian Plate at an estimated velocity of 5–7 cm/year. The subduction angles become increasingly oblique to

2337-689: The development of the Shimajiri Group and before that of the Ryukyu Group. The back-arc rifting and associated sedimentation in the southern Okinawa Trough have continued since 2 Ma. Amami Islands The Amami Islands ( 奄美群島 , Amami-guntō ) is an archipelago in the Satsunan Islands , which is part of the Ryukyu Islands , and is southwest of Kyushu . Administratively, the group belongs to Kagoshima Prefecture , Japan . The Geospatial Information Authority of Japan and

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2394-506: The expected pole. This data, coupled with radiometric ages, suggest that Southern Ryukyu might have rotated about 25˚ with respect to the Asian continent in the Miocene at 6–10 Ma. The Yaeyama Group is a set of sedimentary rocks comprising primarily sandstone with interbeds of conglomerate, limestone, mudstone, and coal seams, and cropping out the Yaeyama Islands, Southern Ryukyu. The age of

2451-707: The formation accreted in the Toarcian in the Early Jurassic. This formation is part of an accretionary complex of a Middle Jurassic subduction zone. On Ishigaki Island, this formation is thrusted beneath the Tomuru Formation along the Sokobaru thrust and is intruded by Oligocene granitic rocks, named the Omoto Pluton. The Nakijin Formation is a 450–500m thick deposit of limestone, basalt, and

2508-474: The group is early Miocene, as suggested by paleontological data. Coal seams, cross laminae, and trace fossils reveal that the group is possibly derived from sediments in a continental shelf. The group shows less deformation such as tilting and folding than the Eocene formations of Southern Ryukyu, suggesting that Southern Ryukyu has been stable since the early Miocene. The Shimajiri Group consists of an upper and

2565-405: The island. The Kayo Formation features beds of turbidite containing mudstone, sandstone, and nummulite fossils that indicate middle Eocene age. ] It underlies the Nago Formation along a northwest-dipping thrust fault. Thrust-folding and metamorphism of the formation suggest a trench origin. The Eocene Miyara and Nosoko Formations crop out the Yaeyama Islands, Southern Ryukyu. The Miyara Formation

2622-739: The islands from Japan, and in response, stressed to the American occupation authorities that the islands were an integral part of Kagoshima Prefecture. In February 1946, the Amami Islands were officially separated from Japan. In October, the Provisional Government of the Northern Ryukyu Islands  [ ja ] was founded, formed by local leaders. It changed its name to the Amami Gunto Government  [ ja ] in 1950. However, under

2679-552: The main islands of Japan, but later, a style original to Amami, known as "Usuki Lower Style", was developed. Among Japanese literature, mention of the islands first appeared in the late 7th century. The Nihon Shoki contains an entry dated 657 referring to Amami-shima ( 海見嶋 , "Amami Island") , and to the Amami-bito ( 阿麻弥人 , "Amami people") in 682. The Shoku Nihongi refers to Amami ( 菴美 ) in 699 and Amami ( 奄美 ) in 714. All of these are believed to be identical to

2736-599: The middle Miocene . Accretionary complexes in Northern and Central Ryukyu are considered as the extension of the Outer Zone of Southwest Japan, whereas metamorphic rocks in Southern Ryukyu are associated with the Inner Zone of Southwest Japan. The arc might be united into the present configuration in the Pliocene - Pleistocene due to different rates of southeastward migration as tectonics proceeded. The Okinawa Trough

2793-506: The months of May, June and September. The area is subject to frequent typhoons . The population of the Amami Islands on 1 October 2020 was 104,281, of which 41,390 were in the city of Amami- shi and 62,891 were in the district of Oshima- gun . Islanders started to produce earthenware from 6,000 years ago, affected by the Jōmon culture in Kyushu . Initially, the styles were similar to those of

2850-568: The previous Pliensbachian age. It is believed to have ended with a global cooling event known as the Comptum Cooling Event, although whether it represented a worldwide event is controversial. The Toarcian takes its name from the city of Thouars , just south of Saumur in the Loire Valley of France . The stage was introduced by French palaeontologist Alcide d'Orbigny in 1842, after examining rock strata of this age in

2907-416: The separation, became stronger. The Amami Communist Party , formed in 1947, also favored reunification. Among locals over 14 years old, 99.8% of them signed in a bid toward reversion. Some municipalities and communities went on a hunger strike after the example of Mahatma Gandhi . The Treaty of San Francisco in 1952 put the Amami islands under trusteeship as part of the Ryukyu Islands. The U.S. returned

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2964-431: The time was stable and had no crustal movement, during early Miocene. After a cessation of subduction around 10–6 Ma, the Philippine Sea Plate resumed subducting since the late Miocene (about 6 Ma), leading to back-arc spreading of the Okinawa Trough. Initial rifting of the northern Okinawa Trough may have caused a counterclockwise rotation in Northern Ryukyu and southern Kyushu after 6 Ma. Meanwhile, paleomagnetic data record

3021-790: The turtle style. Toarcian The Toarcian is, in the ICS ' geologic timescale , an age and stage in the Early or Lower Jurassic . It spans the time between 184.2 Ma (million years ago) and 174.7 ±0.8 Ma. It follows the Pliensbachian and is followed by the Aalenian . The Toarcian Age began with the Toarcian Oceanic Anoxic Event , a major anoxic event associated with marine extinctions and increased global temperatures that sets its fossil faunas apart from

3078-415: The word shima uta originally referred to Amami folk songs only, and is therefore now mistakenly used for Okinawan folk songs. The Japanese rock band The Boom 's 1992 hit song called Shima Uta , which incorporated some Okinawan styles and thus causes confusion as to the precision of the term. Others argue the word was used for Okinawan folk songs as well even before 1992. While Okinawan folk songs use

3135-453: Was a mild one, but as the financial deterioration of the domain became worse, the administration changed to one of exploitation. Satsuma imposed high taxes payable in sugar. This resulted in sugarcane monoculture , which often resulted in severe famines. During these times, the Amami people found their joys in local liquors made from sugarcanes, awamori bought from Ryukyu, and folk songs sung with sanshin . Their folk songs evolved into

3192-442: Was affected more by Japan. Because of this, the Amami people themselves regard their culture as distinct from that of Okinawa. The Amami people treat the area between Kikai, Amami Ōshima, and Tokuno as part of their own cultural sphere. On the other hand, islanders from Yoron, just 22 km away from Okinawa, have much closer cultural ties to Okinawa. Idiolects spoken in a large part of the Amami Islands are collectively known as

3249-454: Was invaded in 1466. Satsuma Domain of Japan attempted to invade Amami Ōshima in 1493, but Ryukyu defeated them. During the 16th century, there were three rebellions on Amami Ōshima that Ryukyu put down: one in 1536, one in 1537, and one in 1571. This period is called Naha period ( 那覇世 , Nahan'yu ) , after the major port of Ryukyu. Ryukyu's direct control lasted just over 170 years. Trade with Ming dynasty China, which flourished in

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