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The late Paleozoic and early Mesozoic Indosinian Orogeny in Southeast Asia was characterized by subduction in the Paleo-Tethys and collisions among continental blocks and fragments. The Khorat Plateau Basin in northeastern Thailand covers much of the Indochina Block and was subjected to complex tectonic activity during the late Paleozoic and Mesozoic. The Mesozoic sequence of the basin comprises thick, gently folded non-marine sediments that include red beds and is separated from the underlying upper Paleozoic sequence by the major angular unconformity of the Permo-Triassic boundary, which we refer to as the “Indosinian I event” in the Khorat Plateau Basin. Seismic and well data acquired for oil and gas exploration indicate that the upper Paleozoic sequence is heavily faulted and structurally complex. Our study showed that in some areas about 2000 m of the upper Paleozoic sequence has been eroded at the Indosinian I unconformity, although thicknesses of up to ∼6000 m of upper Paleozoic rocks remain in some areas. Previous interpretations of oil and gas exploration data attribute the erosional event to back-arc closure due to collision of the Indochina and Sibumasu blocks during subduction in the Paleo-Tethys Ocean. However, our detailed structural mapping indicated that the Indosinian I unconformity was a consequence of the collision of the Indochina and South China blocks during the late Permian to Middle Triassic. We propose that this collision initiated the Indosinian Orogeny in mainland Southeast Asia.

The Upper Triassic Langjiexue Group, which lies immediately south of the Yarlung-Tsangpo Suture Zone in the Shannan area of southeastern Tibet, represents an important part of the Tethyan Himalayan...

Triassic foraminifers are reported for the first time from limestones in the upper part of the Nam Sam Suite distributed in the Sam Neua area of northern Laos. The study area is located in the northern part of the Indochina Block, based on the basic geotectonic subdivision of mainland Southeast Asia. The fauna consists of 17 taxa and includes age-diagnostic Pilammina densa, Pilamminella grandis, Citaella dinarica, C.? deformata, Arenovidalina amylovoluta, and Diplotremina astrofimbriata. It is referable to the middle Anisian (Pelsonian) of the Middle Triassic. The microfacies of the studied samples are subdivided into three types, suggesting low wave-energy uppermost subtidal, moderately wave-agitated uppermost subtidal, and intertidal environments, respectively. Two species are specific to the intertidal microfacies. A notable paleontological feature is the dominance of P. densa, shown by the large number of individuals in the foraminiferal assemblage. This could be related to its opportunistic nature in the stressful conditions of the intertidal environment. We also consider that C.? deformata may be ecologically adapted to a hypersaline environment. The Sam Neua fauna shares several important species, such as C. dinarica, P. densa, P. grandis, and A. amylovoluta, with those found in the Sibumasu Block, Sukhothai Zone, and South China Block, suggesting that these major geotectonic domains in mainland Southeast Asia formed a single paleobiogeographic province during Anisian time. In view of paleogeography, the present results point toward a rather restricted (narrow) Paleo-Tethyan ocean basin allowing faunal interchanges among separated Eastern Tethyan continental blocks during the Middle Triassic.

Provenance analysis and U–Pb dating of detrital zircons in Permian–Triassic forearc sediments from the Sukhothai Arc in northern Thailand clarify the evolution of a missing arc system associated with Paleo-Tethys subduction. The turbidite-dominant formations within the forearc sediments include the Permian Ngao Group (Kiu Lom, Pha Huat, and Huai Thak formations), the Early to earliest Late Triassic Lampang Group (Phra That and Hong Hoi formations), and the Late Triassic Song Group (Pha Daeng and Wang Chin formations). The sandstones are quartzose in the Pha Huat, Huai Thak, and Wang Chin formations, and lithic wacke in the Kiu Lom, Phra That, Hong Hoi and Pha Daeng formations. The quartzose sandstones contain abundant quartz, felsic volcanic and plutonic fragments, whereas the lithic sandstones contain mainly basaltic to felsic volcanic fragments. The youngest single-grain (YSG) zircon U–Pb age generally approximates the depositional age in the study area, but in the case of the limestone-dominant Pha Huat Formation the YSG age is clearly older. On the other hand, the youngest cluster U–Pb age (YC1σ) represents the peak of igneous activity in the source area. Geological evidence, geochemical signatures, and the YC1σ ages of the sandstones have allowed us to reconstruct the Sukhothai arc evolution. The initial Sukhothai Arc (Late Carboniferous–Early Permian) developed as a continental island arc. Subsequently, there was general magmatic quiescence with minor I-type granitic activity during the Middle to early Late Permian. In the latest Permian to early Late Triassic, the Sukhothai Arc developed in tandem with Early to Middle Triassic I-type granitic activity, Middle to Late Triassic volcanism, evolution of an accretionary complex, and an abundant supply of sediments from the volcanic rocks to the trench through a forearc basin. Subsequently, the Sukhothai Arc became quiescent as the Paleo-Tethys closed after the Late Triassic. In addition, parts of sediments of supposed Devonian–Carboniferous age within the Sukhothai Arc were revised as the Triassic Lampang Group, and the Early Cretaceous Khorat Group.

The Carboniferous–Permian Kano-yama limestone in the Jurassic Chichibu Accretionary Complex, central Japan, contains an algal-microbial mound composed of Anthracoporella, Palaeoaplysina, Tubiphytes, Archaeolithoporella, and bryozoans. The limestone is characterized by abundant micrite, implying a low-energy back-reef depositional environment. The fusuline fauna includes Daixina sokensis, Carbonoschwagerina minatoi and C. morikawai, which are representative of the Gzhelian Stage of the Carboniferous. Anthracoporella and Palaeoaplysina are interpreted to be the main bafflers in the mound. The lower horizon of the mound is characterized by a binding structure of Tubiphytes, Archaeolithoporella and bryozoans, which enabled the formation of this Anthracoporella and Palaeoaplysina mound. Compared with the Akiyoshi–Taishaku limestone, a well-documented Panthalassan atoll-type carbonate, the occurrence of Palaeoaplysina is a common feature of these limestones. Based on their accretion ages, the Kano-yama limestone is estimated to have been located several thousand kilometers west of the Akiyoshi–Taishaku limestone in the Panthalassa Ocean during the latest Carboniferous. The occurrence of Palaeoaplysina in both the Akiyoshi–Taishaku and Kano-yama limestones indicates that the distribution of Palaeoaplysina, which is known to be a cool-water genus, extended over thousands of kilometers in the Panthalassa during the period of the Gondwana glaciation.

This paper presents a newly found fauna of Ladinian (Middle Triassic) radiolarians from the Hong Hoi Formation of the Lampang Group, Sukhothai Zone, northern Thailand. The Ladinian age determined by the radiolarian fauna concords with the age previously determined by mollusks. The study section consists of intercalated sandstone and shale in the lower part and a thick conglomerate in the upper part. The radiolarian-bearing siliceous beds are intercalated within the lower unit. The lithic sandstone of the lower unit consists mainly of volcanic rock fragments, quartz, and feldspar, whereas the thickly bedded conglomerate of the upper unit is characterized by abundant gravel-sized clasts of volcanic rock and limestone. These lithic features of the study section suggest that during deposition the Hong Hoi Formation was located near a supply of volcanic materials. A forearc basin close to the Sukhothai Arc would be the most suitable environment for the deposition. The Ladinian age determined by the radiolarian fauna supports the occurrence of intensive volcanic activity within the Sukhothai Arc during the Middle Triassic.

The Upper Triassic Langjiexue Group, which lies immediately south of the Yarlung-Tsangpo Suture Zone in the Shannan area of southeastern Tibet, represents an important part of the Tethyan Himalayan Sequence (THS). Its provenance and palaeogeography have been the subject of debate. We present new data on petrographic composition, whole-rock geochemistry, and detrital zircon U–Pb geochronology to constrain the provenance of the Langjiexue Group. The dominance of quartz grains and felsic volcanic lithic fragments suggests that the sandstones are litho-quartzose. The trace element geochemical signatures (V–Ni–Th*10, Co/Th–La/Sc, Eu/Eu*–Th/Sc) suggest derivation from felsic igneous sources. The detrital zircon age spectra display three major peaks: a Meso-to-Neoproterozoic peak (1200–900 Ma, 7–18%), a Neoproterozoic-to-Late Cambrian peak (750–500 Ma, 32–65%), and a Late Carboniferous-to-Late Triassic peak (300–200 Ma, 11–33%). The maximum depositional age of early Carnian (236–235 Ma) is obtained by calculating weighted average ages of the youngest zircons (≤250 Ma). The youngest age cluster (300–200 Ma) is incompatible with sources from neighbouring terranes, including the South Qiangtang terrane, Lhasa terrane, THS, and Higher Himalayan Crystalline. Correlations of the Permian–Triassic zircons with those of time-equivalent strata in northwest Australia, west Burma, and the Banda Arc unveil a potential connection to the Tasmanides along the convergent margin of eastern Australia. The New England Orogen (300–230 Ma) could have supplied the Langjiexue Group with magmatic materials via continent-scale drainage systems or a submarine fan complex. This scenario provides a new perspective into the transport of detritus from distal orogens to sedimentary basins thousands of kilometres away.

The fine clastic and siliceous sedimentary successions distributed in the Hat Yai area, southeastern peninsular Thailand were examined using radiolarian biostratigraphy, lithology, and stratigraphy. The studied succession was essentially divided into two kinds of fine-grained sedimentary rock units: the lower shale unit and the upper chert unit. The lower shale unit and the upper chert unit yielded late Middle to early Late Permian and Early to Middle Triassic radiolarians, respectively. We clarified that the sedimentary rocks distributed in the study area are not entirely Carboniferous, but contain some sediments from the Permian and Triassic. This age determination suggests that the clastic–chert succession distributed in the study area should be distinguished from the Carboniferous Yaha Formation and correlated with the Permian to Triassic Semanggol Formation. Lithological change with increasing siliceous composition was observed in the uppermost part of the lower shale unit, and the geological age based on the radiolarians indicates a nearly conformable stratigraphic relationship for the lower shale unit and the upper chert unit. The stratigraphy and lithology of the Permian to Triassic succession in the study area, together with geological correlation around southernmost Thailand and northern Malaysia, suggest that the Triassic chert should be interpreted as continental slope sediments overlying Permian clastic and/or calcareous facies, rather than typical pelagic deep-water sediments formed on an abyssal plain. The depositional environment of the chert in this area was likely restricted to the vicinity of a continental slope. Considering with the wide distribution of Triassic platform carbonates over southeastern peninsular Thailand, the continental margin of the Sibumasu along the Paleo-Tethys was represented by a stable passive margin during the Middle–early Late Triassic time. On the basis of the sedimentary setting and stratigraphy in the Permian and Triassic, it is suggested that the closure of the Paleo-Tethys between the Sibumasu and Indochina continental blocks took place at least after the Middle Triassic in southeastern peninsular Thailand.

The characteristics of tropical storm washover deposits laid down during the years 2007 to 2011 along the southern peninsular coast of the Gulf of Thailand (GOT) were described in relation to their different geomorphic conditions, including perched fan, washover terrace and sheetwash lineations preserved behind the beach zone within 100 m of the shoreline. As a result, washover terrace and sheetwash lineations were found where the beach configuration was uniform and promoted an unconfined flow. Non-uniform beach configurations that promoted a confined flow resulted in a perched fan deposit. Washover sediments were differentiated into two types based on sedimentary characteristics, including (i) a thick-bedded sand of multiple reverse grading layers and (ii) a medium-bedded sand of multiple normal grading layers. In the case of thick-bedded washover deposits, the internal sedimentary structures were characterized by the presence of sub-horizontal bedding, reverse grading, lamination, foreset bedding and wavy bedding, whereas, horizontal bedding, normal grading, and dunes were the dominant structures in the medium-bedded washover sand. Rip-up clasts were rare and recognized only in the washover deposits in the bottom unit, which reflects the condition when a mud supply was available. All washover successions were found in the landward inclined-bedding with a basal sharp contact. A high elevated beach ridge associated with a large swale at the backshore proved suitable for a thick-bedded washover type, whereas a small beach ridge with uniformly flat backshore topography promoted a medium-bedded washover sediment.

Civilization would not have developed without the availability and use of natural resources. Mineral resources generally correspond to underground resources. They form a concentration of naturally occurring solid, liquid, or gaseous materials in the earth’s crust or on the surface. Ancient people used hard rocks at first and made hunting aids from these rocks. Then they spread out all over the world carrying tequnique, how to make hunting aids, in their hands. West Asia has produced a variety of mineral resources abundantly and has supported to form civilization.

The Phu Kradung and Phra Wihan formations of the Early Cretaceous Khorat Group were investigated to characterize the depositional system and paleoclimate, based on stratigraphy, paleosol features, paleosol profiles, and reworked deposits. The sediments of both formations are classified into 12 facies on the basis of their primary depositional attributes, such as bedding, grain size, texture, and sedimentary structures. Furthermore, these facies are grouped into eight architectural elements based on stratigraphic relationships and outcrop-scale macroforms. The proportions of each architectural element indicate that the depositional system was that of an anastomosing river. The anastomosing river system in the studied section is characterized by a high rate of vertical floodplain aggradation and the development of a relatively stable crevasse channel. Paleosols are developed mainly in floodplain deposits, and are characterized by the development of calcretes. A semi-arid to sub-humid paleoclimate is deduced from the occurrence of the calcretes. In addition, their microstructures suggest that these calcretes were formed under several different conditions, with micritic carbonate precipitating under relatively arid climates, and alveolar septal structures under semi-arid to sub-humid conditions. Using the thicknesses of the calcrete horizons, we conclude that the difference in the amount of precipitation between the wet and dry periods was highly variable, without any order, during deposition of the studied section. The thicknesses of intervals between successive calcrete horizons indicate that the inflow of fine materials occurred randomly across the floodplain. Partly superimposed, multiple calcrete horizons were developed during periods of low sediment supply. A random deposition of floodplain sediments appears to characterize the anastomosing river system of the Khorat Basin.

The provenance, source rock compositions, and sediment supply system for a convergence zone of the Paleo-Tethys were reconstructed based on the petrography and geochemistry of clastic rocks of the Inthanon Zone, northern Thailand. The clastic rocks are classified into two types based on field and microscopic observations, the modal composition of sandstone, and mineral compositions: (1) lithic sandstone and shale within melange in a Permo–Triassic accretionary complex; and (2) Carboniferous quartzose sandstone and mudstone within the Sibumasu Block. Geochemical data indicate that the clastic rocks of the melange were derived from continental island arc and continental margin settings, which correspond to felsic volcanic rocks within the Sukhothai Zone and quartz-rich fragments within the Indochina Block, respectively. The results of a mixing model indicate the source rocks were approximately 35% volcanic rocks of the Sukhothai Zone and 65% craton sandstone and upper continental crust of the Indochina Block. In contrast, Carboniferous quartzose sedimentary rocks within the Sibumasu Block originated from a continental margin, without a contribution from volcanic rocks. In terms of Paleo-Tethys subduction, a continental island arc in the Sukhothai Zone evolved in tandem with Late Permian–Triassic forearc basins and volcanic activity during the Middle–early Late Triassic. The accretionary complex formed contemporaneously with the evolution of continental island arc during the Permo–Triassic, supplied with sediment from the Sukhothai Zone and the Indochina Block.

Basaltic sandstone composed mainly of clay- to sand-sized fragments of glass and basaltic rock has been discovered in a pelagic chert sequence in northern Thailand. The sandstone conformably underlies and is partly intercalated with the Upper Permian (Wuchiapingian-early Changhsingian) radiolarian-bearing chert. Geological age dating based on radiolarians, petrographic examination of the bedded chert with the basaltic sandstone, and geochemical studies were conducted to investigate the origin and sedimentary mode of the lithologic sequence. The bedded chert overlying the basaltic sandstone yielded Late Permian radiolarians and was correlatable with the Wuchiapingian Follicucullus charveti–Albaillella yamakitai assemblage zone as well as the early Changhsingian Neoalbaillella ornithoformis assemblage zone. Lithofacies and microfacies of the bedded chert indicated deposition in a pelagic realm of the Paleo-Tethys. Although the tectonic setting was difficult to estimate based on geochemical features because of element mobility and alteration, the basaltic fragments likely originated as oceanic basalt such as oceanic island basalt. Microfacies and sedimentary structures of the chert and sandstone indicated that the studied sequence is composed of intermittent high sedimentation rates, mainly gravity currents of basaltic fragments, in a background setting of very slowly accumulating radiolarian chert. The sedimentary mode of the sequence, the rare terrigenous influx, and the presence of fusulinoidean or other foraminiferal tests indicate that the basaltic rocks fragment were originally sourced from an oceanic topographic high such as a seamount or an oceanic plateau, and that the volcanic activity occurred in the chert-accumulated oceanic basin of the Paleo-Tethys in the Wuchiapingian.

The Thung Yai Group extends over a large area of peninsular Thailand, along the eastern margin of the Shan Thai block. Bound by angular unconformities 300 m thick dominantly detritic brackish to non-marine deposits with few intercalated limestone beds between Triassic marine and Tertiary non-marine sediments, represent the Thung Yai Group that comprises four formations: Khlong Min, Lam Thap, Sam Chom, and Phun Phin Formations. In the Ao Luk–Plai Phraya (ALPP) area, the Khlong Min and Lam Thap formations yield marine, brackish-water and non-marine fossil assemblages. These include trace fossils and for the first time in peninsular southern Thailand, the bivalve Parvamussium donaiense Mansuy, 1914. Based on fossil determinations, the Thung Yai Group has a late Early Jurassic to Early Cretaceous age. Our new observations help unravel the tectonic history of Mesozoic Peninsular Thailand. After the complete closure of the Paleotethys in the Late Triassic, renewed inundation, from the late Early Jurassic to the early Middle Jurassic, brought a regime of shallow to open marine and lagoon sedimentation over northwestern, western and southern peninsular Thailand, in the eastern part of Sundaland bordering the Mesotethys to the west.

The opening of the Paleo-Tethys are reconstructed, including the depositional setting and redox conditions, based on an analysis of radiolarian fossils and the geochemistry of a Devonian siliceous succession in the Chiang Dao area of northern Thailand. The succession is subdivided into the following five rock types (in ascending stratigraphic order): black shale (Lower Devonian), siliceous shale (Middle Devonian), tuffaceous chert and tuff (Middle/Upper Devonian), and chert (Upper Devonian). The succession was deposited in continental margin and pelagic environments between the Sibumasu Block and the Indochina–North China blocks. The concentrations of terrestrial-derived elements (Al2O3, TiO2, Rb, and Zr) suggest that the succession (except for the chert) was supplied with terrigenous material and volcanic ash from the adjacent continent, deposited within a SiO2-rich environment. Geochemical indicators of redox conditions (total organic carbon and the Th/U ratio) reveal a gradual change from anoxic to oxic oceanic conditions between the black shale and chert. Taking into account the interpreted depositional setting and redox conditions, the initial Paleo-Tethys developed as a small, closed anoxic–suboxic oceanic basin during the Early to Middle Devonian, located close to the continental margin. Black shale and siliceous shale were deposited in the basin at this time. Opening of the Paleo-Tethys started around the Middle and Upper Devonian boundary, marked by voluminous volcanic activity. The tuffaceous chert was deposited under oxic conditions, suggesting that ash and pumice within the chert were derived from a continental source. After the Late Devonian, the Paleo-Tethys developed as a deep, broad ocean in which pelagic chert was deposited.

The Tibetan Plateau is a key factor in controlling the present-day climate and atmospheric circulation pattern in Asia. The pattern of atmospheric circulation after the uplift of the plateau is well known, whereas direct evidence is lacking regarding the nature of the circulation pattern prior to the uplift. The distribution of desert directly reflects the position of the subtropical high-pressure belt, and the prevailing surface-wind pattern recorded in desert deposits reveals the position of its divergence axis. Cretaceous eolian sandstone of the Phu Thok Formation is extensively exposed in the northern Khorat Basin, northeastern Thailand. We conducted a sedimentological study on this formation to reconstruct temporal changes in the latitude of the subtropical high-pressure belt in low-latitude Asia during the Cretaceous. Spatio-temporal changes in the paleo-wind directions recorded in the Phu Thok Formation reveal that the Khorat Basin mainly belonged to the northeast trade wind belt and subtropical high-pressure belt was situated to the north of the Khorat Basin during the initial stages of deposition, shifted southward to immediately above the basin during the main phase of deposition, and then shifted northward again to the north of the basin during the final stages of deposition. The paleomagnetic polarity sequence obtained for the Phu Thok Formation comprises three zones of normal polarity and two of reversed polarity, correlating to chrons M1n to C34n of the geomagnetic polarity time scale. This result suggests that the Phu Thok Formation is mid-Cretaceous in age (from c. 126 Ma to c. 99–93 Ma), similar to the age of eolian sandstone in the Sichuan Basin, southern China (the Jiaguan Formation). These results, in combination with paleo-wind direction data, suggest the development of low-latitude desert and an equatorward shift of the subtropical high-pressure belt (relative to the present-day) in Asia during the mid-Cretaceous.

We reconstructed the accretion process related to Paleo-Tethys subduction recorded in northern Thailand, based on melange and thrust structures, and metamorphic temperatures derived from illite crystallinity data. Melange formation was characterized by hydrofracturing and cataclastic deformation, with mud injection under semi-lithified conditions followed by shear deformation and pressure solution. Illite crystallinity data suggest metamorphic temperatures below 250 °C during melange formation. The combined structural and metamorphic data indicate that during melange formation, the accretionary complex related to Paleo-Tethys subduction developed at shallow levels within an accretionary prism. Asymmetric shear fabrics in melange indicate top-to-south shear. After correction for rotation associated with collision between the Indian and Eurasian continents, the trend of the Paleo-Tethys subduction zone is estimated to have been N80 °E. We conclude that the Paleo-Tethys was subducted northward beneath the Indochina Block from the Permian to Triassic.

This paper describes the pedogenic features of paleosols in the upper Lower Cretaceous Shiohama Formation, the lowest unit of the Shimonoseki Subgroup, in Yoshimi, Yamaguchi Prefecture, southwest Japan. The paleosol profiles in the Shiohama Formation are compound and complex, characterized by the presence of abundant calcrete horizons. An analysis of these profiles reveals that the floodplain upon which the Shiohama Formation was deposited was part of an unstable aggradation system characterized by the intermittent influx of sediments and occasional erosion. Furthermore, the mean annual range of precipitation was less than about 30 mm, suggesting only minor seasonal change between wet and dry conditions during deposition of the Shiohama Formation. The microstructures of the observed calcretes include dense microfabric, floating detrital grains, micronodules, circum-granular cracks, and complex cracks. These features formed by chemical precipitation under dry conditions, with little bioactivity. The calcrete horizons are classified into seven types (I–VII) based on their modes of occurrence. Two processes of carbonate accumulation can be identified based on the size and abundance of nodules: VI–V–III–(II)–I and VI–(V)–IV–II–I. These processes represent the development of calcrete horizons from the early to late stages of calcretization. Type I represents the most highly developed stage of calcretization. Calcretes within the Lower Member sequence of the Shiohama Formation show repetitions of type I and types II and III. Thus, it is interpreted that the frequency of sediment supply to the floodplain changed repeatedly over time.

Geology, lithostratigraphy, petrography, sedimentary structures and depositional environment of marine Jurassic rocks of the Hua Fai Group (HFG) from the Mae Sot area of Tak Province, western Thailand have been studied in detail. Based mainly on five measured sections in the Mae Sot Basin, the group can be divided into three formations: Khun Huai; Doi Yot; and Pha De, in ascending order. Seventeen sedimentary rock units have been established with a total thickness varying from 200 to 832 m. According to the fossil assemblages, the HFG was deposited during Toarcian–Bajocian. Analysis of lithofacies associations in the sedimentary sequences of the group discerns shoreface, fan-delta, protected lagoon, intertidal, subtidal and inner to outer ramp environments with occasional carbonate platforms and reef flats. Toarcian rocks are represented by transgressive–regressive (T–R) cycles that in the Aalenian gradually changed to highest sea level and water depth. During late Aalenian to early Bajocian, sea level wa...

Two types of chert are defined in Thailand based on lithology, faunal content, and stratigraphy. ‘Pelagic chert’ consists of densely packed radiolarian tests in a microcrystalline quartz matrix with no terrigenous material and is found as blocks embedded within sheared matrix. ‘Hemipelagic chert’ also has a microcrystalline quartz matrix, and contains not only scattered radiolarian tests, but also calcareous organisms such as foraminifers. The pelagic cherts range in age from Devonian to Middle Triassic, whereas hemipelagic chert is only from the Early to the Late Triassic. Lithological and stratigraphic characteristics indicate that the pelagic chert originated in the Paleo-Tethys, whereas the hemipelagic chert accumulated on the eastern margin of the Sibumasu Block. The hemipelagic and pelagic chert are exposed in two north-trending belt-like zones. The western zone includes the hemipelagic chert, as well as glaciomarine and other Paleozoic to Mesozoic successions, overlying a Precambrian basement that consists exclusively of Sibumasu elements. The eastern zone contains pelagic chert and limestone and should be correlated to the Inthanon Zone. The Inthanon Zone is characterized by the presence not only of Paleo-Tethyan sedimentary rocks, but also of Sibumasu Block elements that structurally underlie the Paleo-Tethyan rocks. The boundary between the Sibumasu and Paleo-Tethys zones is a north-trending, low-angle thrust that resulted from the collision of the Sibumasu and Indochina blocks.

金沢大学理工研究域自然システム学系, Peridotites exposed in the Yugu area in the Gyeonggi Massif, South Korea, near the boundary with the Okcheon Belt, exhibit mylonitic to strongly porphyroclastic textures, and are mostly spinel lherzolites. Subordinate dunites, harzburgites, and websterites are associated with the lherzolites. Amphiboles, often zoned from hornblende in the core to tremolite in the rim, are found only as neoblasts. Porphyroclasts have recorded equilibrium temperatures of about 1000°C, whereas neoblasts denote lower temperatures, about 800°C. Olivines are Fo 90-91 in lherzolites and Fo 91 in a dunite and a harzburgite. The Cr# (=Cr/(Cr + Al) atomic ratio) of spinels varies together with the Fo of olivines, being from 0.1 to 0.3 in lherzolites and around 0.5 in the dunite and harzburgite. The Na2O content of clinopyroxene porphyroclasts is relatively low, around 0.3 to 0.5 wt% in the most fertile lherzolite. The Yugu peridotites are similar in porphyroclast mineral chemistry not to continental spinel peridotites but to sub-arc or abyssal peridotites. Textural and mineralogical characteristics indicate the successive cooling with hydration from the upper mantle to crustal conditions for the Yugu peridotites. Almost all clinopyroxenes and amphiboles show the same U-shaped rare earth element (REE) patterns although the level is up to ten times higher for the latter. The hydration was associated with enrichment in light REE, resulting from either a slab-derived fluid or a fluid circulating in the crust. The mantle-wedge or abyssal peridotites were emplaced into the continental crust as the Yugu peridotite body during collision of continents to form a high-pressure metamorphic belt in the Gyeonggi Massif. The peridotites from the Gyeonggi Massif exhibit lower-pressure equilibration than peridotites, with or without garnets, from the Dabie-Sulu Collision Belt, China, which is possibly a westward extension of the Gyeonggi Massif. © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Asia Pty Ltd.

This paper describes lherzolite and harzburgite within shale-matrix melanges of the late Mesozoic Franciscan Complex at the western margin of central California. The Cr# ( = Cr/(Cr + Al) atomic ratio) of spinels in the lherzolite is extremely low (0.11 to 0.13), plotting at the low Cr# end of the abyssal peridotite field, although the moderate to high Cr# of spinels in the harzburgite leaves two possible origins as forearc or abyssal peridotite. The relationships between the Fo and NiO contents of olivines, plot along the mantle olivine array and indicate the residual character of the lherzolite. A high Mg# ( = Mg/(Mg + Fe 2+ ) atomic ratio) for clinopyroxenes is one of the characteristics of the lherzolite, reflecting low-temperature Mg–Fe redistribution with olivine beneath the ocean floor at around 700 °C. The rare earth element patterns of clinopyroxenes in sampled lherzolite show simple light rare earth element-depleted patterns with flat middle and heavy rare earth elements patterns, resembling those obtained for peridotites dredged from the Vulcan Fracture Zone at the American–Antarctica Ridge. This mineral chemistry, in combination with a lack of association with gabbros and sheet–dike complexes, implies that the lherzolite and harzburgite represent fertile abyssal peridotites along oceanic fracture zones near a slow-spreading ridge; the peridotites experienced a low degree of melting during their history. This origin is in contrast to that of the Coast Range ophiolite, the most extensive ophiolitic belt in California, which formed in a supra-subduction zone setting.

本研究では，白亜系関門層群塩浜層の堆積相解析と塩浜層中の古土壌の記載を行い，塩浜層の古土壌の形成環境を明らかにした．調査地域の塩浜層は，岩相をもとに下部層，中部層，上部層の3つに区分される．堆積相解析の結果，下部層では，古土壌が厚く累積して発達するような扇状地末端部，あるいは平原の河川システムの安定した氾濫原に堆積物重力流が流入する環境であった．中部層は堆積物重力流の流入が頻繁な扇状地中部から上流部であった．上部層は，シート状流などの水流による堆積物の卓越する扇状地の中部付近の環境であった．氾濫原堆積物に含まれる赤色岩層は下部層と上部層でよく発達し，古土壌の特徴を示す．カルクリートや鏡肌などの特徴から，本研究地域の古土壌は，雨季と乾季が繰り返す半乾燥～半湿潤気候下で形成されたと考えられる．

The 2004 Indian Ocean tsunami deposited a sheet of sand with surficial bedforms at the Andaman coast of Thailand. Here we show the recognition of bedforms and the key internal sedimentary structures as criteria of the tsunami supercritical flow condition. The presence of well-preserved capping bedforms implied a dominant tsunami inflow. Sets of internal sedimentary structures including parallel lamination, seaward and landward inclined-laminations, and downstream dipping laminae indicated antidune structures that were generated by a supercritical flow current in a depositional stage during the inflow. A set of seaward dipping cross-laminations containing sand with mud drape on the surface of one depositional layer are a unique indication of an outflow structure. A majority of deposits show normal grading, but in some areas, localized reverse grading was also observed. The recognition of these capping bedforms and determination of the internal sedimentary structures provides new key criteria to help derive a better understanding of tsunami flow conditions.

The Sindong Group was deposited in the north-south trending half-graben Nakdong Trough, southern Korean peninsula. The occurrence of detrital chromian spinels from the Jinju Formation of the Sindong Group in the Gyeongsang Basin means that the mafic to ultramafic rocks were exposed in its provenance. The chromian spinels from the Jinju Formation are characterized by extremely low TiO2 and Fe3+. Moreover, their range of Cr# is from 0.45 to 0.80 and makes a single trend with Mg#. The chemistry of chromian spinels implies that the source rocks for chromian spinels were peridotites or serpentinites, which originated in the mantle wedge. To more narrowly constrain their source rocks, the Ulsan and Andong serpentinites exposed in the Gyeongsang Basin were examined petrographically. Chromian spinels in the Andong serpentinite differ from those of the Jinju Formation and those in the Ulsan serpentinite partly resemble them. Furthermore, the Jinju chromian spinel suite is similar to the detrital chromian spinels from the Mesozoic sediments in the Circum-Hida Tectonic zone, which includes the Nagato Tectonic zone in Southwest Japan and the Joetsu Belt in Northeast Japan. This suggests that the basement rocks, which were located along the main fault bounding the eastern edge of the Nakdong Trough, had exposures of peridotite or serpentinite. It is possible that the Nakdong Trough was directly adjacent to the Circum-Hida Tectonic zone before the opening of the Sea of Japan (East Sea). © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Asia Pty Ltd.

Provenance and tectonic history of the Jurassic accretionary complex, Mino terrane, located in the Inner Zone of south-west Japan, were studied using sandstone framework composition and mudrock geochemistry. Modal analysis of sandstones shows that the tectonic setting of the source area for the studied Mino terrane clastic rocks was uplifted basement, largely dominated by high-grade metamorphic terrain composed of quartz and feldspar, especially plagioclase. The textural and mineralogical immaturity, extent of alkali and alkaline earth element leaching, low chemical index of alteration values and depleted rare earth element (REE) contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity. Factor analysis revealed that grain-size effects governed compositional heterogeneity in the studied sediments. Provenance of the sediments is interpreted as being plagioclase-enriched felsic basement rock, such as granodiorite, within a continental margin and evolved arc tectonic setting rather than active volcanic arc. Lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and/or erosion of arc volcanics and exposure of basement. Considering the previous studies on palaeogeography and palaeocurrent reconstruction, the north-eastern part of the Yeongnam massif in the Korean Peninsula is interpreted as the most probable source area for the studied turbidites. The results of mixing calculation for Mino terrane sediments suggest that Precambrian leucocratic granite and the basement rock of the Cretaceous Gyeongsang Basin shed large amounts of sediments to the Mino trench, whilst Precambrian granitic gneiss and the Triassic pluton supplied lesser amounts. The results of this study reveal that, although active subduction–accretion processes were occurring, the Mino trench was bordered by continental basement rocks. This knowledge contributes to enhanced understanding of the Jurassic palaeogeography of the east Asia continental margin.

Micro-thermometry of water-rich fluid inclusions from two syn-tectonic veins sets (D1 and D2 veins) in the Otaki Group, part of the Cretaceous Shimanto accretionary complex of the Kanto Mountains, central Japan reveals the following tectono-metamorphic evolution. Combining the results of microthermometric analyses of fluid inclusions from D1 veins with an assumed geothermal gradient of 20-50°C/km indicates that the temper- ature and fluid pressure conditions during D1 were 270-300°C and 140-190 MPa, respec- tively. Peak metamorphic conditions during the development of D2 slaty cleavage involved temperatures in excess of 300°C and fluid pressures greater than 270 MPa, based on analyses of microthermometry of water-rich fluid inclusions from the D2 vein and illite crystallinity. The estimated fluid pressure increased by approximately 80 MPa from D1 accretionary processes to metamorphism and slaty cleavage development during D2. Assuming that fluid pressure reached lithostatic pressure, the observed increase in fluid pressure can be accounted for by thrusting of the Jurassic Chichibu accretionary complex over the Cretaceous Shimanto accretionary complex. Following thrusting, both accretion- ary complexes were subjected to metamorphism during the latest Cretaceous.

The Tetori Group is a representative Middle Jurassic to Lower Cretaceous deposit in the northern central part of Honshu, Japan. The Tetori Group is divided into the Kuzuryu, Itoshiro and Akaiwa Subgroups with decreasing age. It consists mainly of a marine sequence in the lower part (Kuzuryu Subgroup) and non-marine sequence in the upper part (Akaiwa Subgroup) with transitional sequence in the middle part (Itoshiro Subgroup). Diagenesis of Tetori Group sandstones comprises compaction, cementation and replacement. Early diagenetic events include mechanical compaction, and pore-filling cementation of calcite, siderite, dolomite and formation of kaolinite. Late diagenesis includes formation of quartz cement and albitization of feldspar, and formation of illite, chlorite, calcite, ankerite and pyrite. Among the diagenetic minerals, carbonate forms the major cement in Tetori Group sandstones. Calcite of each subgroup is subdivided into two or three types based on cathodoluminescence. Tetori Group sandstones of marine, fresh-water, and mixed depositional environments are characterized by distinct chemical compositions of early diagenetic calcites. Late diagenesis seems to have been mainly influenced by detrital compositions of the sequence, burial temperatures and partially hydrothermal processes. Especially, late diagenetic carbonate and authigenic clay minerals seem to have formed mainly from ions released from clay mineral transformations in the adjacent shales. Based on the illite crystallinity (IC), the Kuzuryu Subgroup exhibits higher diagenetic grades than the overlying Itoshiro and Akaiwa Subgroups, indicating that the diagenesis of the Tetori Group was mainly affected by depth of burial.

There are many strata containing quartzite clasts in the Japanese Islands, but the on-land geology of the Japanese Islands has no candidate for the source rocks of the quartzite clasts. This study deals with the provenance of quartzite clasts of the Tetori Group (Middle Jurassic and Early Cretaceous) distributed in northern central Japan. Quartzarenite clasts from conglomerate beds of the Tetori Group are texturally subdivided into three types; the most abundant is matrix-bearing quartzarenite (type 3), followed by poorly sorted feldspar-bearing quartzarenite (type 2) and by well-sorted pure quartzarenite (type 1). To identify the provenance of quartzarenite clasts in the Tetori Group characteristics of quartzarenite sequences distributed in North China and Korea were studied and compared with those of the Tetori quartzarenite clasts. Texturally and geochemically, the quartzarenite clasts of the Tetori Group are very similar to pre-Mesozoic quartzarenites distributed in the south central and east central Korean Peninsula. Considering the previous results of depositional environments, paleomagnetism and paleocurrent studies on the Tetori Group, this study suggests that during deposition of the Tetori Group, the northern part of central Japan was probably land-connected with the central region of eastern Korea.

関東山地北西部において山中白亜系白井層と蛇紋岩が不整合関係を示す露頭を発見した．これにより，関東山地の黒瀬川帯の蛇紋岩には，断層帯の構成要素としての蛇紋岩と，山中白亜系の基盤岩としての蛇紋岩が存在することが明らかになった．不整合面は凹凸をなし，白井層基底部は不整合面と高角に斜交してアバットしている．白井層に含まれる蛇紋岩礫はアンチゴライトを主体とすることが多く，下位の蛇紋岩と組織と構成鉱物の点で異なる．よって，蛇紋岩礫のほとんどは，堆積場の比較的近傍に露出していた，アンチゴライトを主体とする蛇紋岩体からもたらされたと考えられる．白井層の堆積年代であるHauterivianには，粗粒堆積物で構成されるような汽水域に蛇紋岩が露出していたと考えられる．

江戸崎観測井は茨城県稲敷郡江戸崎町で掘削され，掘削深度は1234.0ｍに達した．この観測井の層序は，上位より，下総層群，上総層群，先新第三系である．先新第三系は砂岩や泥岩からなり，正確な年代は不明なまま扱われてきた．この区間の砂岩のモード組成と砕屑性ザクロ石の化学組成を検討した．また江戸崎観測井先新第三系と比較のため，関東地方に分布する白亜系－暁新統の砂岩についてもそのモード組成を検討した．その結果江戸崎コアの砂岩は，QmFLt図ではDissected-Transitional Arc起源の砂岩組成領域に集中し，跡倉層にモード組成では比較的類似することが判明した．さらに砕屑性ザクロ石は跡倉層から報告されているその化学組成と一部類似している．跡倉層は，関東山地では三波川変成岩の上にクリッペとして累重していることから，江戸崎観測井は領家帯上ではなく，三波川帯上に位置していることを示唆する．

An Early Permian small ammonoid fauna consisting of Neocrimites sp., Agathiceras suessi Gemmellaro, A. girtyi Bose, Agathiceras? sp., and Miklukhoceras sp. was found in nodules of a fine sandstone bed exposed in the Phatthalung-Hat Yai area of southern peninsular Thailand. The ammonoid-bearing bed belongs stratigraphically to the uppermost part of the Kaeng Krachan Group, which is essentially a clastic-dominant, Late Carboniferous (?) to Early Permian stratigraphic unit, widely distributed in western and peninsular Thailand. This ammonoid fauna is considered to be of Bolorian (Kungurian) age and includes Agathiceras girtyi Bose, which is described for the first time from Thailand. The present discovery of Bolorian ammonoids suggests that the uppermost part of the Kaeng Krachan Group is slightly younger than previously considered and around the latest Early Permian. This further implies that the continental margin environment of the Sibumasu Block drastically changed at around Bolorian time from a cool, clastic-dominant shelf condition to a temperate to subtropical, carbonate platform due to rapid northward drift after middle Artinskian rifting.

Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son-Mae Sariang area, north-west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean-floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana-Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion. © 2004 Blackwell Publishing Asia Pty Ltd.

房総半島南部の下部中新統嶺岡層群八丁層および中部中新統佐久間層群から, 砕屑性クロムスピネルが新たに発見された. 両層群から得られた砕屑性クロムスピネルは, 化学組成の傾向が互いに似ており, それぞれ低Tiグループ (TiO2 1 wt%) に区分される. 低Tiグループのクロムスピネルの大部分は, 嶺岡型蛇紋岩に含まれるものと化学組成が類似しており, さらに, 背弧海盆かんらん岩起源であると考えられる. しかし, 一部の低Tiグループは嶺岡型蛇紋岩に含まれるものよりもCr#が高く, 前弧域のかんらん岩もしくはボニナイトから供給された可能性がある. 高Tiグループのクロムスピネルは, 嶺岡帯, 葉山帯, 小仏帯, 瀬戸川帯に分布するアルカリ玄武岩もしくはピクライト玄武岩に含まれるものとその化学組成が類似している. これらの砕屑性クロムスピネルの産出は, 嶺岡帯のオフィオリティックな岩石が, 前期中新世もしくはそれ以前に定置したことを示している.

Cretaceous sedimentary basins in Kyushu Island, Japan, are developed as half-grabens, which accommodated very thick clastic wedges of non-marine to shallow-marine facies. The Albian to Cenomanian Goshoura Group in western Kyushu (ca. 1000 m thick) consists of interbedded channel sandstone, conglomerate, and mudstone. The Cenomanian to Turonian Mifune Group in central Kyushu (ca. 2300 m thick) comprises red and drab sandstone, and intercalated siliceous ash-fall tuff. Different types of paleosols occur in the Goshoura and Mifune groups. Paleosols in the Goshoura Group contain diagnostic vertic features such as subangular blocky peds, irregularly directed slickensides, and downward tapering fissures. Few obvious calcic horizons are developed except for the calcretes of rhizogenic origin. Paleosols in the Upper Formation of the Mifune Group are composed of cyclic acidic tuff–vertic paleosol intervals with abundant pedogenic calcretes. Paleosols of the Goshoura Group belong to the order of vertic Inceptisols, and those of the Mifune Group can be classified as calcic Vertisols. In spite of diagenetic alteration of the paleosols, paleo-vertic soils of the Goshoura and Mifune groups show the exceptional preservation of a number of pedological features. Among various soil-forming factors, diversity in each paleosol is mainly attributed to differences in paleoclimatic conditions during the Middle Cretaceous. Our results show that the paleoclimatic conditions in the subtropical–warm-temperate region had changed from subhumid to semi-arid with time.

The Kanmon Group (Lower Cretaceous) is a non-marine sequence in the Inner Zone of southwest Japan and is divided into the lower Wakino (lacustrine) and the upper Shimonoseki (fluvial) subgroups. Major diagenetic changes in this group are compaction, iron-oxide cementation, calcite cementation and grain replacement, quartz overgrowth and pore-fill cementation, illite authigenesis, chlorite pore-fill cementation and grain replacement, albitization of feldspar, and grain replacement by pyrite. Two subgroups of the Kanmon Group present no significant differences in general diagenetic features, paragenetic sequence, or the degree of diagenetic changes despite differences in depositional environments (lacustrine vs. fluvial) and stratigraphic positions. However, some differences are recognized in the content and chemistry of authigenic minerals caused by different sandstone framework compositions. The content of authigenic clay minerals is higher in sandstones of the Shimonoseki Subgroup containing abundant volcanic rock fragments. In addition, the composition of chlorite, the most abundant authigenic clay mineral in Kanmon sandstones, is Mg-rich in the volcanoclastic Shimonoseki sandstones, compared to an Fe-rich variety in Wakino sandstones. The original sandstone composition played a significant role in pore-water composition and diagenetic reactions. The Wakino sandstones lost most of its porosity by compaction, whereas Shimonoseki sandstones are only compacted in the vicinity of the basin-bounding fault. The weakly compacted Shimonoseki sandstones, instead, were largely cemented by pore-filling calcite during early diagenesis; cementation prevented compaction during further burial. The Kanmon Group sediments were heated to about 300 °C based on illite crystallinity values.

Geoscientists have always considered the Neyriz region, located along the Zagros Suture Zone, an important area of interest because of the outcrops of Neotethys ophiolitic rocks. We carried out a modal analysis of the Cenozoic sandstones and geochemistry of the detrital Cr-spinels at Neyriz region in order to determine their provenance and tectonic evolution in the proximal part of Zagros Basin. Our data shows a clear change in provenance from the Late Cretaceous onwards. As from the Late Cretaceous to Eocene, lithic grains are mostly chert and serpentinite; and higher Cr# values of the detrital Cr-spinel compositions indicate that they originate from the fore-arc peridotites and deposited in an accretionary prism setting during this period. From the Late Oligocene to the Miocene periods, volcaniclastic and carbonate lithic grains show an increasing trend, and in the Miocene, metasedimentary lithic grains appear in the sediments. Ophiolite obduction caused a narrow trough sub-basin to be formed parallel to the general trend of the Zagros Orogeny between the Arabian and Iranian plates in Oligocene. From the Miocene onwards, the axial metamorphic complex belt was uplifted in the upper plate. Therefore, the collision along the Zagros Suture Zone must have occurred in the Late Oligocene.

Detrital chromian spinels in the Permian Nam Duk Formation, Thailand are examined to determine the petrological characteristics of eroded mafic-ultramafic rocks in the Phetchabun area. Detrital chromian spinels are found as one of accessory heavy minerals from turbiditic sandstones of the Nam Duk Formation. The detrital chromian spinels are generally deep brown to almost opaque in thin section due to their wide compositional variation, and are relatively small, about 20–190 microns across. They sometimes exhibit subhedral to euhedral shapes and rarely have inclusions. Thirty–five grains were chosen for microprobe analysis. They have relatively high Cr contents, the Cr#(=Cr/[Cr+Al] atomic ratio), being mostly higher than 0.50, and up to 0.83. TiO2 contents are generally low but variable from 0.02 to 1.16 wt%, and Fe3+ ratios are consistently low. The relatively high Cr# and low TiO2 contents of the Nam Duk detrital chromian spinels in the Permian sediments indicate their derivation from mafic-ultramafic rocks of are origin. The relatively small and euhedral to subhedral spinels with inclusions especially suggest their provenance from volcanic rocks. It is strongly inferred that igneous rocks, namely volcanics and peridotites, of arc origin were exposed in this region at the Permian at least. The Loei-Phetchabun-Ko Chang volcanic belt, interpreted to have been constructed by several magmatic episodes (Devonian, Permian, Triassic, and Late Tertiary), could be a good candidate for the source of detrital chromian spinels in the Nam Duk Formation.

Permian to Late Jurassic radiolarians were obtained from granules and pebbles in conglomerates of the Donghwachi and Gisadong formations of the Lower Cretaceous Hayang Group, southeastern Korea. Radiolarian faunas and the petrologic character of the pebbles resemble those of Jurassic accretionary complexes of East Asia. Considering lines of evidence such as the lithologic characters of pebbles, affinity of the radiolarian faunas, reconstructed paleocurrent direction in the Hayang Group, and the paleogeographic position of southwestern Japan, it may be inferred that these pebbles were derived from the accretionary complexes mainly of southwestern Japan and the Far East. New evidence for the occurrence of Late Jurassic radiolarians in the Gisadong Formation suggests that radiolarian-bearing pebbles would be not only chert but also siliceous shale or shale of the Jurassic accretionary complexes, and gives an exhumation age for the latest accreted units of the complexes.

The Upper Oligocene, distributed in the Makarov, Korsakov and Shmidt areas of Sakhalin, yields detrital chromian spinels. These detrital spinels are characterized by extremely low TiO2 and Fe3+ contents, and they were probably derived from highly to moderately depleted mantle peridotite and/or serpentinite (>0.4 in Cr#). The source peridotites are very similar to those now exposed at the Kamuikotan metamorphic belt, Hokkaido, Japan, a possible southern extension of the N-S trending serpentinite melange belts of Sakhalin. It is highly probable that some of their serpentinite bodies had provided detritus of serpentinite and chromian spinel to the sediments. The occurrence of detrital chromian spinels has been reported from the Cretaceous, Paleogene, and Miocene in the axial zone of Hokkaido, indicating that serpentinites were emplaced into the erosional level during these periods. This suggests a protrusion of serpentinite along the N-S trending fault line, probably the extension of some faults in Hokkaido, occurred in late Oligocene as a presage of Miocene transcurrent tectonics in Sakhalin and Hokkaido.