Late Permian to Middle Triassic radiolarian faunas from northern Thailand
Katsuo SashidaHisayoshi IgôShuko AdachiKatsumi UenoYoshimichi KajiwaraNikorn NakornsriApsorn Sardsud
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Abstract:
Moderately well-preserved Late Permian to Middle Triassic radiolarians are identified in chert beds that occur in the Shan-Thai Block of northern Thailand. These radiolarians are identical to the faunas of the Late Permian Neoalbaillella ornithoformis and N. optima Assemblage Zones and the Triassic Parentactinia nakatsugawaensis and Triassocampe coronata Assemblage Zones reported in chert sequences of Japan. We discovered the radiolarian faunas, apparently indicating Late Permian and Early Triassic ages, in almost continuous sequences of chert and shale exposed in the north of Chiang Mai. The occurrence of these radiolarian faunas provides important data to solve the P/T (Permian/Triassic) boundary in pelagic sequences. Our present discovery also furnishes significant data to reconstruct the paleobiogeography of Mainland Thailand during Late Permian to Middle Triassic times. Fifty species belonging to 35 genera, including three unidentified genera, are investigated taxonomically. Four new species Pseudospongoprunum ? chiangdaoensis, Cenosphaera igoi, Cenosphaera ? rugosa, and Tlecerina ? apsornae are described.Keywords:
Radiolaria
Early Triassic
Conodont
Biochronology
Conodont
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Fifty-seven new conodont collections from the Nechako NATMAP area contribute to a conodont biostratigraphic framework for the region. Most collections are from the Pope unit of the Cache Creek complex and are early Late Carboniferous (Bashkirian-Moscovian) to Middle Permian (Wordian). The most extensive carbonate buildup is Bashkirian-Moscovian, whereas latest Carboniferous to Permian limestone is much less common and Middle Permian buildups are known only in the north. The Sowchea clastic-volcanic unit is Late Permian to Late Triassic (Norian); it includes unique records of (?)Changshingian, Griesbachian, and Smithian fauna, and the first records of Middle Triassic Tethyan Gladigondolella in Canada. At two widely separated localities, breccia containing mixed conodont faunas show that Paleozoic and Triassic strata were reworked during or after the Late Triassic. Late Triassic conodonts are also reported from the Tezzeron unit and adjacent Takla Group.
Conodont
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Conodont
Radiolaria
Stratotype
Section (typography)
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The study of conodont biostratigraphy in central Jilin Province has made some progress in recent years.The depositional age of the Erdaogou,Shoushangou,Daheshen and Fanjiatun formations as well as Monodiexodinafauna has been determined by conodonts.New conodont data have been recovered from Jilin Province,but much more work remains,and there is virtually no information about Silurian and Devonian conodonts in Jilin Province.Future work should focus on the Shifeng,Wanyue,and Shihuiyao formations in the Yiyun area and on the Wangjiajie Formation in Yongji County.The Mopanshan section should be targeted for a detailed analysis of Carbonifeous conodont biostratigraphy.We recommend a more extensive collection of conodont samples,and greater efforts to improve fossil extraction techniques,especially for slightly metamorphosed rocks.
Conodont
Devonian
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Conodont
Devonian
Section (typography)
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Conodont
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Sequence (biology)
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Conodont
Early Triassic
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Conodont
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Conodont
Early Triassic
Extinction (optical mineralogy)
Trias
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Silurian conodonts have been widely reported and many species have worldwide distribution. However, present zonations utilizing them have many limitations and no single scheme provides a suitable standard. A good standard zonation for Silurian conodonts is desirable, but impossible at our present state of knowledge. Environmental differentiation, the rapid evolution of several unrelated conodont lineages and the lack of distributional data are the principal factors producing this situation. Existing Silurian conodont zonations are evaluated, and zonal schemes based on well documented phylogenetic lineages are advocated. Eight datum planes are proposed as an additional biostratigraphic framework in the system. These are the Distomodus staurognathoides Datum, Pterospathodus amorphognathoides Datum, Pterospathodus Extinction Datum, Kockelella walliseri Datum, Kockelella variabilis Datum, Ancoradella ploeckensis Datum, Kockelella Extinction Datum and Ozarkodina crispa Datum. Six of these datum planes are based on the evolutionary appearance of the datum-defining species. Extinction datum planes correspond to a significant level of extinction amongst the conodont-bearing animals.
Conodont
Extinction (optical mineralogy)
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