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Silurian radiolarians from the Sepon Mine, Truong Son Terrane, central Laos and their palaeogeographic and tectonic significance

Thassanapak, H, Udchachon, M and Burrett, C 2018 , 'Silurian radiolarians from the Sepon Mine, Truong Son Terrane, central Laos and their palaeogeographic and tectonic significance' , Geological Magazine, vol. 155, no. 8 , pp. 1621-1640 , doi: 10.1017/S0016756817000425.

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Abstract

A Silurian radiolarian fauna based on 18 species is described from cherts from three sections in two quarries in the Sepon Mine area, central Laos. Each section contains distinctive assemblages but Futobari morishitai, F. solidus, Zadrappolus yoshikiensis and Z. tenuis are found in all three sections and are characteristic of the Ludlow–Pridoli Z. yoshikiensis Assemblage. In addition, the Hoei Yang pit section contains Zadrappolus hitoeganensis, Pseudospongoprunum sagittatum, Futobari sp. and Secuicollacta sp. Section CQ contains Pseudospongoprunum sagittatum, P. tazukawaensis, Praespongocoelia parva, P. sp., Rotasphaera sp. cf. R. quadrata, Secuicollacta sp. cf. cassa. Section QM also contains Pseudospongoprunum parvispina, P. sp., Zadrappolus sp. and Devoniglansus (?) seponensis new species Thassanapak is common. Evidence from Silurian and Devonian strata of the southern Truong Son Terrane indicates deepening towards the southern margin as defined by the Thakhek–Danang Shear Zone and exemplified by deep-marine Ludlow–Pridoli radiolarian cherts in the south, shallowing to fossiliferous, shallow-water sediments to widespread Old Red Sandstone type terrestrial facies 85 km further NE. The radiolarian cherts are in faulted contact with probable Llandovery limestone and Upper Ordovician – Llandovery graptolitic shales. The graptolitic shales are overlain with slight angular unconformity by the submarine fan, volcaniclastic-dominated, Namphuc Formation of Llandovery age. This fan received andesitic materials from the nearby Long Dai Volcanic Arc which extends eastwards to the Tamky Suture in Vietnam. This plutonic–volcanic arc was probably maintained by northwards subduction along the trend of the Permian–Recent Thakhek–Danang Shear Zone.

Item Type: Article
Authors/Creators:Thassanapak, H and Udchachon, M and Burrett, C
Keywords: chert, Indochina, palaeogeography, Ludlow–Pridoli, Llandovery
Journal or Publication Title: Geological Magazine
Publisher: Cambridge Univ Press
ISSN: 0016-7568
DOI / ID Number: 10.1017/S0016756817000425
Copyright Information:

Copyright Cambridge University Press 2017

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