Early Ordovician Conodonts From Tarutao Island, Southern Peninsular Thailand

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, highenergy environment.

The first systematic description of Cambrian fossils from Myanmar: Late Furongian trilobites from the southern part of the Shan State and the early Palaeozoic palaeogeographical affinities of Sibumasu

“…The relatively deep water Upper Ordovician Pa Kae Formation in Satun province, Thailand shares multiple trilobite genera (including 4 species) and facies in common with the Pagoda Limestone of the South China Block (Fortey, 1997;Zhou et al, 2016). Studies of conodont faunas from Satun and northern Malaysia show a coincident shift from shelf assemblages in the Early and Middle Ordovician to deeper water forms (Agematsu et al, 2007(Agematsu et al, , 2008, consistent with the trilobite data (Fortey, 1997). Burrett et al (2016) suggested that faunal links to South China increased in association with Late Ordovician sea level rise, and they noted that there may be some regional biofacies differences within Sibumasu itself (see below).…”

“…8). Compared to that succession, the limestone facies may be slightly younger in the Canning Basin, as indicated by conodont fauna (Agematsu et al, 2008;Normore et al, 2018), possibly reflecting a transgressive succession in which Ko Tarutao was located somewhat further offshore. Comparable sandstone facies are also found in Bhutan, although the part of the Bhutanese succession that has been precisely dated is slightly older stratigraphically (Hughes et al, 2011;Greenwood et al, 2016) than the dated Sibumasu Cambrian succession.…”

New conodont species and biostratigraphy of the Santa Rosita Formation (upper Furongian–Tremadocian) in the Tilcara Range, Cordillera Oriental of Jujuy, Argentina

“…Identical observations can be made for the material described as U. longipinnatus by Agematsu et al . (, p. 1450, pl. 1, figs ).…”

Conodonts in Ordovician biostratigraphy

“…Recent work in the relatively thick Ordovician carbonate successions in Thailand and Malaysia by Agematsu et al . (,b) has led to the discovery of notable conodont faunas. Whereas those of Tremadocian and slightly younger age are of North American type, the Sandbian–Katian faunas are dominated by taxa best known from Baltoscandia.…”