Early Ordovician conodonts from the Dumugol Formation in the Baegunsan Syncline, eastern Yeongweol and Samcheog areas, Kangweon-Do, Korea

Samples from the Dumugol Formation were collected from eight measured sections and two cores in the so-called Baegunsan Syncline, located between eastern Yeongweol and Samcheog areas, Kangweon-Do, South Korea. A total of 7,813 identifiable conodonts were recovered from 146 samples. They are classified into 24 multielement species referable to 16 genera, and 37 form species belonging to 17 genera; six species are newly described: Distacodus dumugolensis, Parapanderodus acontiformis, Scolopodus longibasis, Scolopodus n. sp. A, Triangulodus dumugolensis, and Oistodus(?) sp. The Dumugol Formation is divided biostratigraphically into four conodont zones, viz, Chosonodina herfurthi-Rossodus manitouensis, Glyptoconus quadraplicatus, Paracordylodus gracilis, and Triangulodus dumugolensis zones in ascending order. These zones are correlated with those of the early Ordovician conodont faunas of North America, northern Europe, China, Australia, and Iran. The Dumugol Formation ranges from late Tremadocian to early Arenigian in age. The boundary between these two series lies between 70 and 100 m above the base of the Dumugol Formation in each of the sections.

Sphenothallus (“Vermes”) from the Tremadocian Dumugol Formation, Korea

Specimens of Sphenothallus ruedemanni (Kobayashi, 1934), which were originally assigned to Serpulites, are described from the Asaphellus Zone (Tremadocian) of the Dumugol Formation, Korea. Previously, Sphenothallus was known to occur in Middle Ordovician to Permian rocks, thus making Sphenothallus ruedemanni the earliest record of this genus. This species is characterized by a distally expanding tube with smooth to variously wrinkled surface. The tube is presently composed of quartz, chlorite, and/or muscovite, which appear to have replaced calcium phosphate. The zoological affinity of this tube-building animal is still uncertain.