Sachiko Agematsu

Panthalassan Seamount-Associated Permian-Triassic Boundary Siliceous Rocks, Mino Terrane, Central Japan

Abstract. We describe the lithology and age of an intact section (NF 1212R) and two reference sections of Panthalassan seamount-associated Permian-Triassic boundary (PTB) siliceous rocks. The sections occupy the upper part of the Hashikadani Formation of the Mino terrane in the Mt. Funabuseyama area, central Japan. Section NF 1212R comprises a lower unit of gray chert (ca. 1.7 m thick), a middle unit of dark gray to black chert (ca. 0.8 m) with a pyrite-rich layer at the top (ca. 0.1 m), and an upper unit of black claystone with thin, intermittent beds of black to dark gray chert (ca. 1.2 m), in ascending order. The chert of the lower and middle units is rich in radiolarian remains with minor siliceous sponge spicules. The black chert of the middle unit is carbonaceous and includes tiny pyrite grains. The black claystone consists of microcrystalline quartz and clay minerals rich in carbonaceous matter. The chert of the upper unit is also carbonaceous and rich in radiolarian remains. The lower and middle units are correlated with the Neoalbaillella optima Zone (Changhsingian). The basal part of the upper unit is referable to the Hindeodus parvus Zone (basal Griesbachian), and the major part of the upper unit is possibly correlated with the middle to upper Dienerian. We position the PTB at the sharp lithologic boundary between the upper Upper Permian chert and lower Lower Triassic black claystone. The examined PTB siliceous rocks are stratigraphically attributed to the upper part of the Hashikadani Formation, reconstructed as an oceanic rock unit characterized by Lower Permian to Lower Triassic siliceous rocks that accumulated upon the lower flank of a mid-oceanic seamount in a pelagic realm of the Panthalassa Ocean. Our results present the worlds first record of deep-marine PTB siliceous rocks associated with a Panthalassan seamount.

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.

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.

Global Upper Ordovician correlation by means of delta C-13 chemostratigraphy: implications of the discovery of the Guttenberg delta C-13 excursion (GICE) in Malaysia

Apart from a single study of the early Katian δ 13 C chemostratigraphy in two regions in China, no investigations of the Sandbian and Katian chemostratigraphy have been published from anywhere in Asia. A recent study of the conodont biostratigraphy of the classical Ordovician succession on Langkawi Islands, peninsular Malaysia, showed the presence there of strata coeval with those having the Guttenberg Carbon Excursion (GICE) on the Yangtze Platform. In an effort to establish for the first time the presence of this widespread δ 13 C excursion in southern Asia, a series of samples from the upper part of the Kaki Bukit Formation was isotopically analysed. This resulted in the discovery of a conspicuous δ 13 C excursion with peak values of ~ 2 ‰ above the baseline values. The excursion is located just above the Baltoniodus alobatus Subzone and near the level of the first appearance of Hamarodus europaeus , hence the same stratigraphic position as the GICE on the Yangtze Platform. Using the GICE, the Malaysian study interval is closely correlated with the GICE intervals at three localities representing an approximately 23 000 km long transect from Malaysia across Baltoscandia to central North America. This shows the usefulness of δ 13 C chemostratigraphy to clarify previously obscure stratigraphic relationships between geographically very widely separated localities.

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.

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.

Stratigraphy and Age of the Permian-Triassic Boundary Siliceous Rocks of the Mino Terrane in the Mt. Funabuseyama Area, Central Japan

Abstract. This paper presents the litho- and biostratigraphy of the Permian-Triassic boundary (PTB) siliceous rocks that accumulated on the lower flank of a seamount in a mid-oceanic realm of the Panthalassa Ocean. The study section correlates with the upper part of the Lower Permian to Lower Triassic Hashikadani Formation of the Mino terrane in the Mt. Funabuseyama area, central Japan. The lithologic succession comprises a lower unit (ca. 6.2 m thick) dominated by gray chert with small amounts of black chert and black claystone, middle unit (ca. 0.7 m) of black chert with subordinate black claystone and gray chert including pyrite nodules near the top, and upper unit (ca. 0.9 m) characterized by black claystone with thin black chert beds. The lithologic change from the middle unit to the upper unit is sharp and abrupt. The lower and middle units correlate to the upper Wuchiapingian to Changhsingian (Neoalbaillella ornithoformis to N. optima zones). The upper unit includes the lower Induan, as the black chert bed in its middle part yields Hindeodus parvus. These beds also yield Triassospongocyrtis? sp., a primitive Mesozoic-type Nassellaria, with several types of the sphaeroid spumellarians. The Permian radiolarians exhibit a marked loss in diversity across the lithologic boundary between the middle and upper units. We hypothesize that this lithologic boundary marks the main extinction horizon of the Permian radiolarians. Also a profound faunal turnover of radiolarians occurred at this level. On the basis of the Global Boundary Stratotype Section and Point (GSSP) designation, it is reasonable to position the PTB at the bottom of the H. parvus-yielding chert bed in the upper unit. Nevertheless placing the PTB at this level remains tentative, because age-diagnostic fossils are absent from the lower part of the upper unit. Alternatively, with the emphasis upon correlation with the recently reported PTB section of the Hashikadani Formation, the PTB of the study section is preferably positioned at the sharp lithologic boundary between the middle and upper units. Given this alternative, the PTB corresponds to the main extinction event of Permian radiolarians, which, in turn, is thought to correspond to significant environmental changes.

Lower and Middle Ordovician conodonts from the Thung Song and Thung Wa areas, southern peninsular Thailand

ABSTRACT Lower and Middle Ordovician conodonts from the Thung Song Group, in the Thung Song and Thung Wa areas of southern peninsular Thailand, are described and illustrated here for the first time. These conodonts are divided into faunas A, B, and C, which are middle to late Arenigian, middle Arenigian to Darriwilian or Caradocian, and late Arenigian to early Caradocian, respectively. Fauna A resembles faunas in Australia, South China, the Argentine Precordillera, and North America. Fifteen species belonging to twelve genera were studied systematically.

Ordovician-Silurian boundary graptolites of the Satun area, southern peninsular Thailand

ABSTRACT Black shale exposed north of Satun, southern peninsular Thailand, lies upon Upper Ordovician limestone and includes abundant graptolites. This fauna contains Normalograptus pseudovenustus pseudovenustus (Legrand, 1986) and Normalograptus sp. N. pseudovenustus is a reliable index species of an interval containing the Ordovician-Silurian boundary. Based on the range of this species, the graptolite-bearing black shale is inferred to be of latest Ordovician age, with the study section including the O/S boundary. The taxonomy of these two graptolite species is discussed in this study.