Classification of the Sibumasu and Paleo-Tethys tectonic division in Thailand using chert lithofacies |
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| Authors: | Yoshihito Kamata Katsumi Ueno Hidetoshi Hara Megumi Ichise Thasinee Charoentitirat Punya Charusiri Apsorn Sardsud and Ken-ichiro Hisada |
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| Institution: | Research Institute for Time Studies, Yamaguchi University, Yamaguchi, 753-8512 (email: ),;Department of Earth System Science, Fukuoka University, Fukuoka 814-0180,;Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567,;Shogakukan Junior High School, Nobeoka, Miyazaki, 882-0001, Japan,;Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330,;Bureau of Geological Survey, DMR, Bangkok 10400, Thailand, and;Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8571, Japan |
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| 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. |
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| Keywords: | chert hemipelagic Mesozoic Paleo-Tethys Paleozoic pelagic radiolaria Sibumasu Thailand |
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