Graptolite biostratigraphy of the Ordovician to Silurian boundary succession in the Khao Nui area, southern peninsular Thailand
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According to a new study of Silurian-Devonian conodont biostratigraphy and conodont fauna of Fengyi,Binchuan and Xiangyun area along the E shore of Erhai Lake,Dali,we think that the lithostratigraphic unit in traditional division must belong to Kanglang Formation,Qingshan Formation,Lianhuaqu Formation,Changyucun Formation,which must be from later period of Early Silurian to Early Carboniferous in the geological time.And the boundary between Devonian and Silurian must be fixed at the upper part of Qingshan Formation.
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Devonian
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Abstract Late Llandovery and Wenlock conodonts are still inadequately documented in China, with data collected chiefly from the Baizitian section in Yanbian County, Sichuan Province, south‐west China. A collection of over 32 000 conodont elements was recovered from 38 samples from the Xiabaizitian and Shangbaizitian formations at this classic locality. The conodont fauna is dominated by cosmopolitan species and can be assigned to 50 species representing 17 genera. Of these, one new species, Apsidognathus yanbianensis sp. nov., is proposed herein. Six conodont zones are recognized in this section, including the Pterospathodus eopennatus Zone, the Pt. amorphognathoides angulatus Taxon‐range Zone of the Pt. a. amorphognathoides Superzone, the Kockelella ranuliformis Zone, the Kockelella walliseri Taxon‐range Zone, and the Kockelella patula Taxon‐range Zone, in ascending order. These zones can be correlated with other conodont zones around the world based on the occurrences of the stratigraphically diagnostic species. Moreover, the stratigraphical ranges of Pterospathodus enable greater understanding of the correlation of the Telychian guide taxa. The conodont biodiversity changes and faunal turnover across the Silurian Ireviken Bioevent are here documented for the first time in the Baizitian section from the South China palaeoplate.
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Two Silurian sections were re-measured, one being situated on the northern bank of the Yinshuihe River and the other on the northern bank of the Shouxinghu Lake of the Lazhuglung area of Doima, Rutog, NW Tibet. The lower part of the Shouxinghu Formation is composed of grey-black carbonaceous shales and slates, which contain graptolites Spirograptus sp. and chitinozoans Ancyrochitina brevicollis and Conochitina sp., indicating a Llandovery age, rather than the Upper Ordovician mentioned previously. Real Ordovician rocks have not been found until now there. The Silurian rocks in that area were divided in ascending order into the Llandovery Yinshuihe and Shouxinghu Formations, the Wenlock Pur Co Formation and the Ludlow-Pridoli Yeniupo Formation, a new lithostratigraphic unit here established, on the basis of diversified faunas. The lowermost beds correspond to the Llandovery Spirograptus turriculatus and Streptograptus crispus graptolite zones, and the uppermost beds to the Kopaninoceras juncudum cephalopod zone and its coeval Neoprioniodus latidentatus-Ligonodina siluria conodont assemblage. So far the Lazhuglung sections have been known to be the best sections in North Tibet in both outcrop-completeness and fossil abundance. The erectness of the Silurian sequence there provides important data for the reconstruction of Tibetan Early Plaeozoic history and the Silurian correlation of Qinghai-Xizang Plateau.
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Little is known about Ordovician litho- and biostratigraphy in northern and western Thailand because outcrops are scarce in these mountainous areas. Biostratigraphic and biogeographic studies of conodonts are limited to the uppermost Floian to lower Darriwilian strata in western Thailand. This paper describes and discusses a new Middle Ordovician conodont fauna that includes nine species from the Thong Pha Phum area of western Thailand. This is the first report of Eoplacognathus suecicus, Pygodus lunnensis, Protopanderodus calceatus, Protopanderodus cooperi, and Protopanderodus graeai in Thailand and indicates that a cool-water fauna existed in western Thailand and in southern peninsular Thailand during the Middle to Late Ordovician. The Dapingian to early Darriwilian sea-level rise likely resulted in an immigration of this "cooler or deeper water" fauna to the Thong Pha Phum area.
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Abstract: Early Ordovician conodont faunas of the Thung Song Formation on Tarutao Island, southern peninsular Thailand, consist of 14 known species belonging to 17 genera, and eight undescribed species. Utahconus tarutaoensis and Filodontus tenuis are new species. Three conodont zones: the Rossodus manitouensis Zone, the Utahconus tarutaoensis Zone and the Filodontus tenuis Zone, in ascending order, are defined in the study sections. These are coeval with the interval from the Rossodus manitouensis Zone to the Acodus deltatus ‐ Oneotodus costatus Zone of the standard zonation in the North American Midcontinent. Based on the conodonts studied here and fossils previously reported from Tarutao Island, the Thung Song Formation is early Tremadocian to middle Arenig (Ibexian) in age. This formation is lithostratigraphically subdivided into the S1 to S5 members, and our study sections consist of the S1 to S3 members. These strata accumulated on a shelf in the Early Ordovician. The depositional environments of the limestones making up the S1 and S3 members were in deeper‐shelf conditions. Limestone and shale of the S2 member formed in a shallow‐water, high‐energy environment.
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Panderodus nogamii LEE, (formerly Scolopodus nogamii), first described from North Korea, occurs also in the Lower Ordovician of Thailand, Malaysia, North and South China, Australia and Argentina. It ranged through the Middle and early Upper Ordovician and was restricted to shallow water carbonates in tropical to subtropical palaeolatitudes of Greater Gondwana. Its distribution is similar to that of the Ordovician gastropod Peelerophon oehlerti and the Ordovician trilobite Asaphopsoides sp.
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Trilobite
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