Katsuo Sashida

Occurrence of paleozoic and early mesozoic radiolaria in Thailand (preliminary report)

Abstract Paleozoic and Early Mesozoic radiolarians are newly recovered from chert and associated fine-grained clastic rocks in Thailand. This study clarifies the geologic age of these radiolarian rocks and their paleogeographic and geotectonic significance. Devonian, Early Carboniferous and Permian radiolarians were found in the “Fang Chert” which outcrops along the Chiang Mai-Fang Road, upper north Thailand, Early Carboniferous radiolarians were recovered from a sequence of tuffaceous shale and chert exposed in the Pak Chom area along the Mekong River, and well-preserved Late Devonian and Early Carboniferous radiolarians were also recovered from cherts exposed along the Pak Chom-Loei Road near Phu Laem, north of Loei, in northeast Thailand. These Devonian to Carboniferous radiolarian faunas are apparently identical with those reported from eastern and western Australia. Well-preserved Early Triassic conodonts and radiolarians were obtained from a limeston exposed near Patthalung, southern Thailand. Most of the radiolarian species of this fauna show close affinity with those reported from the Upper Paleozoic rocks, and are new species except for some spicule-type forms. Based on the above-mentioned newly obtained micropaleontological evidence, the geotectonic significance of these radiolarian rocks are briefly discussed in relation to the paleography of the Palaeo-Tethys Ocean, Sibumas and Indochina Terranes, and Australia during the Late Devonian to Middle Permian times.

Triassic radiolarian faunas from the Mae Sariang area, northern Thailand and their paleogeographic significane

Abstract Early to Late Triassic (Spathian to Carnian) radiolarians were obtained from the bedded chert sequence of the Mae Sariang Group distributed in northern Thailand. Based on the similarity of radiolarian fauna and petrographical characteristics, it is inferred that the fine-grained siliceous and calcareous sediments of the Mae Sariang Group are equivalent to those belonging to the eastern marginal facies of the Sibumasu Block. Moreover, the occurrence of an early (?) Carnian radiolarian assemblage from bedded chert shows that the closure of the Paleotethys Ocean between the Sibumasu and Indochina Blocks in northern Thailand occurred after the early Carnian.

Ordovician conodonts from the Satun area, southern peninsular Thailand

Abstract Well-preserved Ordovician conodonts are described from a micritic limestone sequence exposed in the Satun area of southern peninsular Thailand. The faunas represented by these conodonts have North Atlantic Realm affinities and are identical to those reported from North Atlantic Middle to Upper Ordovician successions. Representative conodonts of some of these faunas have also been reported from South China. In ascending order, three conodont zones are discriminated in the Satun sequence: the Pygodus anserinus range Zone, the Baltoniodus sp. cf. B. variabilis range Zone, and the Hamarodus europaeus range Zone. Strata between the B. sp. cf. B. variabilis and H. europaeus zones are not zoned. The conodont-bearing limestone is thought to have been deposited on the continental margin of northeastern Gondwana. Sixteen species belonging to 12 conodont genera, and two unidentified coniform elements, are systematically investigated.

Middle Triassic radiolarians from West Timor, Indonesia

Moderately well-preserved Middle Triassic radiolarians were recovered from bedded limestone exposed at about 3 km west of Kefamenanu, West Timor, Indonesia. This limestone probably from the Aitutu Formation is considered to be an allochthonous block and is embedded in the Neogene Bobonaro Complex. The radiolarian fauna in this limestone is characterized by abundant radiolarians of typical Tethyan forms and is identical to that of the early Fassanian (early Ladinian) of European Tethys and other related faunas reported from the Philippines, Russian Far East, and Japan. The Aitutu Formation is thought to be deposited in an ocean environment dominated by a warm-water current system originating from the low latitude Tethyan realm. Fifty-nine species belonging to 34 genera, including five unidentified genera, are systematically treated, among them, five new species; Parentactinia suparkai, Pseudostylosphaera timorensis, Cryptostephanidium? megaspinosum, Tetrarchiplagia compacta, and Planospinocyrtis kefaensis.

Biostratigraphy and Paleobiogeography of Middle and Late Ordovician Conodonts from the Langkawi Islands, Northwestern Peninsular Malaysia

Abstract The Middle and Upper Ordovician sequence of the Langkawi Islands, northwestern peninsular Malaysia, contains 20 species of conodonts belonging to 15 genera and four unidentified species, which are described and illustrated. The following four biostratigraphic zones are established for the study area: the Scolopodus striatus assemblage zone, the Periodon sp. A range zone, the Baltoniodus alobatus range zone, and the Hamarodus europaeus range zone, in ascending order. The Middle Ordovician fauna belongs to the low-latitude, warm-water Australian Province. Conodonts of the H. europaeus zone represent the HDS (Hamarodus europaeus-Dapsilodus mutatus-Scabbardella altipes) biofacies, which has been reported from the cool-water North Atlantic Faunal Region. The middle Arenigian limestones in the study area were deposited on a shallow-water shelf, whereas the late Arenigian to middle Darriwilian limestones formed in hemipelagic deeper-water conditions on an outer shelf or slope.

Discovery of Lower Permian Radiolarian and Conodont Faunas from the Bedded Chert of the Chanthaburi Area Along the Sra Kaeo Suture Zone, Eastern Thailand

Abstract. Lower Permian (Asselian to Sakmarian) radiolarians and conodonts are identified from the bedded chert of the Chanthaburi area along the Sra Kaeo Suture Zone in eastern Thailand. The radiolarian and conodont-bearing bedded chert including radiolarian species such as Parafollicucullus bulbosus, P. lomentarius, P. u-formus, Pseudoalbailella scalprata, and others is exposed as large-size exotic blocks within the Thung Kabin mélange. This radiolarian fauna further includes Triplanospongos musashiensis, Triaenosphaera minuta, Latentifistula texana, Latentibifistula asperspongiosa and others, which have previously been reported from the Middle to Upper Permian. Except for these Middle to Upper Permian species, this radiolarian fauna is quite similar to those from Japan, Oregon, South China, West Texas, Cis-Urals and Central and Northeastern Thailand. Asselian to Sakmarian conodont faunas represented by Streptognathodus constrictus which have been reported from the Southern Urals and South China, and several sponge spicules are also contained in this bedded chert. Occurrence of these Lower Permian conodonts is the first record from the Sra Kaeo Suture Zone. This radiolarian- and conodont-bearing bedded chert was probably deposited in the Palaeotethys /or Palaeotethyan back-arc basin which is thought to have been a pelagic environment at low latitudes of the Southern Hemisphere.

Middle Jurassic radiolarian fauna from Rotti Island, Indonesia

Abstract A well-preserved Middle Jurassic radiolarian fauna was discriminated from calcareous shale of the Wai Luli Formation on Rotti Island, Indonesia. This fauna is characterized by the presence of Tricolocapsa plicarum, Tricolocapsa ? fusiformis, Stichocapsa japonica, S. convexa, Cyrtocapsa mastoidea, Protunuma turbo, Transhsuum maxwelli, Eucyrtidiellum sp., Archaeodictyomitra sp. A. and others. These radiolarians represent the T. plicarum Assemblage reported from Bajocian and early Bathonian (Middle Jurassic) sequences in Japan and southeastern Europe. Based on accumulated micropaleontological evidence in Timor Island contributed by the present authors, Rotti Island was probably positioned within a warm water current system originating in the low latitude Tethyan realm through the Middle Jurassic. Fifteen species belonging to seven genera are systematically investigated. Among them, Tricolocapsa multispinosa and Tricolocapsa matsuokai are described as new.

Ordovician Sea-Level Change and Paleogeography of the Sibumasu Terrane Based on the Conodont Biostratigraphy

Abstract. Conodont biostratigraphy, paleobiogeography, and depositional environments reveal detailed eustatic changes and paleogeography of the Sibumasu terrane during the Ordovician. Based on lithologic data, the Ordovician sequences on the Sibumasu terrane are classified into two types. One was deposited in the Thong Pha Phum-Li basin, which extends from northern to western Thailand, and the other formed in the Tarutao-Langkawi basin ranging from southern Thailand to northern Malaysia. Five regressive events, RE 1 to 5, and a transgressive event TE 1 are recognized in these basins. On the basis of the conodont biostratigraphy, RE 1, 2, 4, and 5 are correlated with the Peltocare Regressive Event, the Ceratopyge Regressive Event, the Basal Whiterockian Lowstand interval, and the global regression caused by the end-Ordovician glaciation, respectively. TE 1 continued through Darriwilian time. The faunal affinity of Ordovician conodonts makes it clear that the Sibumasu terrane was close to both Australia and North China, which were located in low paleolatitudes. The Darriwilian transgressive event, TE 1, led to a remarkable conodont faunal change from a shallow-water to a deeper, cool-water assemblage.

Discovery of Middle Triassic radiolarian fauna from the Nan area along the Nan-Uttaradit suture zone, northern Thailand

Abstract A Middle Triassic radiolarian fauna is present in the siliceous rock section at the Nan area along the Nan-Uttaradit suture zone, northern Thailand. The radiolarian fauna is composed of Triassocampe deweveri, T. nishimurai, Annulotriassocampe campanilis, Cenosphaera igoi, and other species and corresponds to the Anisian (Middle Triassic) Triassocampe deweveri fauna reported from Japan, Hungary, Italy, Austria, Far East of Russia, and northern and eastern Thailand. More than fifteen radiolarian species belonging to eight genera are investigated. The radiolarian-bearing rocks were probably deposited in a pelagic environment within the Nan-Uttaradit back-arc basin between the Simao and Indochina blocks during Middle Triassic time. This suggests that the Nan-Uttaradit back-arc basin, the Palaeo-Tethys ocean and Panthalassa ocean were probably connected by seaways at this time and might have shared the same oceanic circulation system. Furthermore, the complete closure of the Nan-Uttaradit back-arc basin between the Simao and the Indochina blocks is thought to have occurred at least after the Middle Triassic.

Reinterpretation of Early and Middle Ordovician conodonts from the Thong Pha Phum area, western Thailand, in the context of new material from western and northern Thailand

ABSTRACT Early and Middle Ordovician conodonts are described and illustrated from the Thong Pha Phum and Kanchanaburi areas in western Thailand and the Li area in northern Thailand. The Thong Pha Phum fauna consists of 14 species representing ten genera and one unidentified species, and from the Kanchanaburi and Li sections two and five species, respectively, have been recovered. Two conodont zones, the Triangulodus larapintinensis and Aurilobodus leptosomatus zones, are established in the Thong Pha Phum section. The fauna from the T. larapintinensis Zone includes Panderodus nogamii, Triangulodus larapintinensis, and species of Juanognathus, and the A. leptosomatus Zone is characterized by A. leptosomatus, Histiodella holodentata, and Plectodina onychodonta. Two regression events are recorded in a lower part of the Thong Pha Phum section. The conodont biostratigraphy indicates that the regressions took place in latest Early Ordovician and earliest Middle Ordovician.