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.
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