Classification of the Sibumasu and Paleo‐Tethys tectonic division in Thailand using chert lithofacies
Yoshihito KamataKatsumi UenoHidetoshi HaraMegumi IchiseThasinee CharoentitiratPunya CharusiriApsorn SardsudKen‐ichiro Hisada
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Abstract:
Abstract 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.Keywords:
Radiolaria
Pelagic sediment
Lithology
Micrite
Basement
Devonian
Terrigenous sediment
Проведено петрографическое и геохимическое изучение известняков из маломощных прослоев среди хромитоносных терригенных отложений разрезов казанского яруса в Южном Предуралье. Установлено, что карбонатные породы из трёх разрезов (Сухой Изяк, Сабантуй и Кузьминовский известняковый карьер) представлены одним генетическим типом пород. Они отвечают микритовым и биокластово-микритовым известнякам структуры вакстоун, содержащим пелоиды, реликты мелководных морских организмов, и признаки развития микробиалитов. Литологические особенности свидетельствуют о кратковременной трансгрессии и установлении мелководно-морской литоральной обстановки на изучаемой территории в казанское время. Химический состав известняков подтверждает их генетическую близость, свидетельствуя о незначительных различиях во влиянии терригенно-глинистого или лагунно-хемогенного материала.
Petrographic and geochemical study of limestones from thin interlayers among chromite-bearing terrigenous deposits of sections of the Kazanian stage in the Southern Urals was carried out. It is established that carbonate rocks from three sections (Sukhoy Izyak, Sabantuy and Kuzminovka limestone quarry) are represented by a single genetic type of rocks. They correspond to micrite and bioclast-micrite limestones of the wackestone structure containing peloids, relics of shallow-water marine organisms, and signs of development of microbialites. Lithological features indicate a short-term transgression and a shallow-sea littoral environment in the studied area during the Kazan time. The chemical composition of limestones confirms their genetic proximity, indicating minor differences in the influence of terrigenous-clay or lagoon-chemogenic material.
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Chromite
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Radiolaria
Lithology
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Trough (economics)
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Provenances of pelagic sediments are a less well‐known and key problem of sedimentation in the deep sea. Two sediment cores from the south and middle Shikoku Basin are selected for grain size analysis and element geochemical analysis in this paper. Grain size analysis for the studied cores shows that the grain sizes become coarser upwards gradually, especially for subsurface sediments. It probably reveals the enhancement of terrigenous clastic material. Rare elements analysis reveals that two cores are enriched in Ba and Th. However, the other elements are more or less the same as those of the North American Shales (NAS). Through the NASC‐normalized REE distribution, curves are nearly aclinic, and there are no Ce and Eu anomalies. The geochemical characteristics of elements indicate that the sediments in the Shikoku Basin should mainly be regarded as hemipelagic and pelagic sediments. The comparison of samples from the Nankai Trough, Kyushu Ridge and Izu Island Arc and the analysis of DSDP and ODP cores jointly show that the sediments of the core SG1‐2 have an apparent ‘affinity’ with the Nankai Trough. The core SG1‐1 is influenced by the submarine volcanic activities, having a relatively complex provenance, and is possibly derived from the spreading centre of the Kyushu Ridge and the central Shikoku Basin. Copyright © 2016 John Wiley & Sons, Ltd.
Terrigenous sediment
Trough (economics)
Pelagic sediment
Island arc
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Over 500 previously unidentified, symmetric pointed stones of similar size, shape, color, and texture have been found on the barrier beach of Mantoloking, New Jersey, since 1940. Petrographic, stereo, and scanning electron microscopy analysis reveals that the stones are made of either a biomicritic packstone composed of 50% siliceous microfossil remains ( including sponge spicules and radiolaria) embedded in a micrite matrix or a limestone with abundant angular quartz grains (50–150 μm wide) surrounded by a calcite matrix. The distinctive shape of the Mantoloking stones is most similar to whetstones used for sharpening scythes. We conducted a worldwide search and discovered one producer of carbonate whetstones: a company in the town of Pradalunga in Northern Italy. Microscope analysis reveals that the Pradalunga source rocks are exact matches for the spicule-rich limestone and angular quartz-rich limestone found in the Mantoloking collection. The whetstones are most likely lost cargo from a wreck offshore of Mantoloking, but the exact source may never be known. © 2006 Wiley Periodicals, Inc.
Micrite
Radiolaria
Spicule
Chalcedony
Texture (cosmology)
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Radiolaria
Pelagic sediment
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Terrigenous sediment
Pelagic sediment
Sedimentation
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Terrigenous sediment
Sedimentation
Pelagic sediment
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Siliceous skeletal remains, principally of diatoms and radiolarians with smaller amounts of sponge spicules and silicoflagellates, constitute up to approximately 40 percent of some Recent pelagic sediments. The main factors controlling the contribution made by siliceous organisms to marine sediments are apparently (1) the rate of production of siliceous organisms in the overlying waters, (2) the degree of dilution of siliceous remains by terrigenous, volcanic and calcareous organic contributions to the sediment and (3) the extent of solution of the siliceous skeletons, most of which apparently occurs shortly after deposition. Depth of water is apparently not an important direct...
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Pelagic sediment
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Deposition
Sponge
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Micrite nodules are the only source of Radiolaria within the upper Tithonian to Aptian (Upper Jurassic-Lower Cretaceous) interval of Great Valley Supergroup (GVS), California Coast Ranges. Radiolaria recovered from GVS micrite nodules are either calcified or pyritized. This paper describes a method of extracting well preserved calcified radiolaria from micrites utilizing acetic acid. The same method resulted in the extraction of well preserved Upper Cretaceous planktonic foraminifera from indurated micrite within the Khoy ophiolitic complex of northwestern Iran; from micrite in the Green Horn Formation, Pueblo Colorado; from indurated chalk in the Austin Chalk, Dallas Texas, and from indurated micrite in Albian Duck Creek Formation of Texas. The preservation of extracted radiolaria and planktonic foraminifera from the indurated micrites and chalk is excellent and is often comparable to that found in most DSDP/ODP samples. Assumedly the clay content of the rock, and the chemical homogeneity of the calcified test are the principal reasons for differential solution of the acetic acid.
Micrite
Radiolaria
Concretion
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