LOWER PERMIAN PERRINITID AMMONOID FAUNAS FROM THAILAND

Journal of Paleontology, Mar 2004 by Zhou, Zuren, Liengjarern, Malai

The Metaperrinites Zone contains the following taxa: Neopronorites cf. darvasicus Leonova, 1988; Metaperrinites ishibashii n. sp.; Prostacheoceras spp.; Popanoceras cf. sobolewskyanus de Verneuil, 1845; Batnyaniceras loeiense (Ishibashi et al., 1996), Sicanites cf. notabilis Ruzhencev, 1940; Akmilleria electraensis (Plummer and Scott, 1937), and Agathiceras sp.

Neopronorites darvasicus is abundant in the Yakhtashian Stage (Zygur and Chelamchin Formations) of the northern Pamirs (Darvaz), which is equivalent to the fusulinid Pamirina darvasicaChalaroschwagerina vulgaris Zone in the same area (Leven et al., 1992, p. 62).

Metaperrinites ishibashii n. sp. from Loei is relatively primitive within the 11 species of the genus, which ranged from the Artinskian to Kungurian stage. Therefore, it is inferred that the fossilbearing rock could be of Artinskian age. As shown in Figure 5, the genus Metaperrinites is broadly distributed worldwide. It has been reported from Texas, New Mexico, California, and Nevada in the USA; Pamirs in Tajikistan; Guizhou and Guangxi in South China; Xinjiang in Northwest China; Jilin in Northeast China; Timor in Indonesia; and Crimea in Ukraine.

Prostacheoceras spp. are poorly preserved as fragments in the fauna. The genus is long ranged and widespread, with a total of 16 species ranging from Asselian to Wordian. Their distribution covers the Urals in Russia and Kazakhstan; Crimea in Ukraine; Pamirs in Tajikistan; Sicily in Italy; Bamyan Mountains in Afghanistan; Perak in Malaysia; Jilin and Hunan in China; British Columbia in Canada; and Texas in the U.S.

Popanoceras sobolewskyanus characterizes the Artinskian, mainly the upper Artinskian in South Urals in Russia and Kazakhstan.

Bamyaniceras loeiense is a common form in the Loei ammonoid fauna, and represents a new record of the long-ranged and widespread genus. Bamyaniceras, known from 13 species, mainly derived from the Artinskian to Wordian in Southeast Asia: South China, Timor, and Thailand; Central Asia: Afghanistan and Pamirs; Europe: Crimea and Sicily; America: Texas, Nevada, and California; and Western Australia. The present species can be compared with the materials from Yakhtashian in Darvaz in both the numbers of the umbilically derived lobes and the basic shape of the conchs.

Sicanites notabilis is an Artinskian representative from the Aktyubinsk area in Kazakhstan. The forms in Thailand are similar to the holotype of the species in both conch form and suture characteristics: succession of subequal umbilically derived lobes, and the adventitiously subdivided lobules.

Agathiceras ranges from Upper Carboniferous (Moscovian) to Middle Permian (Wordian) and has global distribution. The unidentified species of the genus adds little to age determination.

On the basis of the biostratigraphic analysis, it could be concluded that the horizon of the Metaperrinites fauna in Loei should belong to the Artinskian Stage, probably the Upper Artinskian, i.e., the Baigendzhinian Substage. This would correspond to the Bitauni beds in Timor, the Chalaroschwagerina vulgaris-Pamirina darvasicus Zone, i.e., the Chelamchin Formation in Peter-1 and Trans-Alai Mountains, the Upper Yakhtashian Stage in Darvaz (northern Pamirs) and the Longying Formation in southwest Guizhou and northwest Guangxi, South China.