TY - JOUR
T1 - The Sukhothai Zone (Permian–Triassic island-arc domain of Southeast Asia) in Northern Laos
T2 - Insights from Triassic carbonates and foraminifers
AU - Ueno, Katsumi
AU - Kamata, Yoshihito
AU - Uno, Koji
AU - Charoentitirat, Thasinee
AU - Charusiri, Punya
AU - Vilaykham, Khamseng
AU - Martini, Rossana
N1 - Funding Information:
We thank Elias Samankassou (University of Geneva, Switzerland) for valuable suggestion on carbonate microfacies interpretation. Fieldwork of this research was financially supported by Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (JSPS) (No. 25302010 to K. Ueno). We are grateful to the Department of Geology and Minerals, Lao P.D.R., for logistics support including permission for fieldwork. This research was also supported by the Swiss NSF project 200020_156422 to R.M. We also thank Michał Krobicki and an anonymous reviewer, and associate editor Ian D. Somerville for their useful comments and suggestions that have improved the final version of the manuscript. Part of this research was accomplished during sabbatical stay of the senior author at the University of Geneva. He thanks Fukuoka University for permitting the stay. The present work constitutes part of the IGCP589 Project.
PY - 2018/9
Y1 - 2018/9
N2 - In mainland Southeast Asia, Permian–Triassic successive subduction of the Paleo-Tethyan oceanic lithosphere formed an island-arc system called the Sukhothai Zone, along the margin of the Indochina Block. This zone has been considered to extend from Northern Thailand to southwestern Yunnan of China, but so far lacked concrete evidence from northern Laos in between. This makes basic geotectonic subdivision of mainland Southeast Asia ambiguous. In this study Triassic foraminifers from limestone distributed in the Long area of Luang Namtha Province (northwestern Laos) solve this problem. The relevant limestone has a kilometer-sized extent and was previously assigned to the Carboniferous–Early Permian based only on lithological grounds in regional geological mapping. Its Triassic age is demonstrated for the first time based on foraminifers. We discriminated from this limestone Aulotortus sinuosus, A. tumidus, Ophthalmidium danneri, Endotriada tyrrhenica, Endoteba obturata, Endotebanella kocaeliensis, Diplotremina astrofimbriata, Duostomina biconvexa, and Palaeolituonella majzoni, and concluded that the fauna is referable to the Carnian (early Late Triassic). Cement-rich reefal sediments consisting of Carniphytes multisiphonatus-microbial boundstone and sparse-allochem bioclastic grainstone containing abundant fragments of Plexoramea gracilis are common in this limestone. They suggest open-marine sedimentation on a shallow carbonate platform, possibly comparable to a cement-dominated upper-slope “Tubiphytes” reef environment found elsewhere in the Triassic. In neighboring mainland Thailand, Carnian limestone with similar lithological and paleontological properties is found only in the Doi Long Formation distributed in the Sukhothai Zone. This evidence provides a firm basis for the tectonostratigraphic correlation of the Sukhothai Zone, in northern Laos. Consequently, our study is critical in giving a clue to clarify the distribution and extension in northern Laos of a Permian–Triassic island-arc domain, the Sukhothai Zone, which is one of the major tectonostratigraphic units comprising mainland Southeast Asia. In this paper, we also described two encrusting foraminifers having multi-chambered (septate) shells, which have been seldom documented in Triassic foraminiferal literature.
AB - In mainland Southeast Asia, Permian–Triassic successive subduction of the Paleo-Tethyan oceanic lithosphere formed an island-arc system called the Sukhothai Zone, along the margin of the Indochina Block. This zone has been considered to extend from Northern Thailand to southwestern Yunnan of China, but so far lacked concrete evidence from northern Laos in between. This makes basic geotectonic subdivision of mainland Southeast Asia ambiguous. In this study Triassic foraminifers from limestone distributed in the Long area of Luang Namtha Province (northwestern Laos) solve this problem. The relevant limestone has a kilometer-sized extent and was previously assigned to the Carboniferous–Early Permian based only on lithological grounds in regional geological mapping. Its Triassic age is demonstrated for the first time based on foraminifers. We discriminated from this limestone Aulotortus sinuosus, A. tumidus, Ophthalmidium danneri, Endotriada tyrrhenica, Endoteba obturata, Endotebanella kocaeliensis, Diplotremina astrofimbriata, Duostomina biconvexa, and Palaeolituonella majzoni, and concluded that the fauna is referable to the Carnian (early Late Triassic). Cement-rich reefal sediments consisting of Carniphytes multisiphonatus-microbial boundstone and sparse-allochem bioclastic grainstone containing abundant fragments of Plexoramea gracilis are common in this limestone. They suggest open-marine sedimentation on a shallow carbonate platform, possibly comparable to a cement-dominated upper-slope “Tubiphytes” reef environment found elsewhere in the Triassic. In neighboring mainland Thailand, Carnian limestone with similar lithological and paleontological properties is found only in the Doi Long Formation distributed in the Sukhothai Zone. This evidence provides a firm basis for the tectonostratigraphic correlation of the Sukhothai Zone, in northern Laos. Consequently, our study is critical in giving a clue to clarify the distribution and extension in northern Laos of a Permian–Triassic island-arc domain, the Sukhothai Zone, which is one of the major tectonostratigraphic units comprising mainland Southeast Asia. In this paper, we also described two encrusting foraminifers having multi-chambered (septate) shells, which have been seldom documented in Triassic foraminiferal literature.
KW - Late Triassic foraminifera
KW - Northern Laos
KW - Sukhothai Zone
KW - Tectonostratigraphy
KW - “Tubiphytes”-microbial reefal limestone
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U2 - 10.1016/j.gr.2018.04.013
DO - 10.1016/j.gr.2018.04.013
M3 - Article
AN - SCOPUS:85047905170
VL - 61
SP - 88
EP - 99
JO - Gondwana Research
JF - Gondwana Research
SN - 1342-937X
ER -