LOWER PERMIAN PERRINITID AMMONOID FAUNAS FROM THAILAND

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

ABSTRACT-The Artinskian Metaperrinites and Kungurian Perrinites faunas are recognized from the Ratburi Group of the Loei area, northcentral Thailand, and the Saraburi Group of the Saraburi area, southcentral of the country, respectively. They represent one of the chains of the Asia-European perrinitid belt that was distributed within the ancient Tethys from Crimea in the west to Timor in the east. A total of 14 species representing 11 genera in the perrinitid faunas are illustrated and described herein.

INTRODUCTION

PERMIAN AMMONOIDS were known from a few localities in Thailand, Southeast Asia. Glenister et al. (1990) recorded the occurrence of Permian ammonoids from an uncertain detrital limestone formation in Amphoe (District, in Thai) Muak Lek (formerly as Muaglek), Changwat (Province) Nakhon Ratchasima, approximately 150 km NE of Bangkok, southcentral Thailand. It is now known that the ammonoid-bearing detrital limestone is from the uppermost Nong Pong Formation, exactly at Khao Nong Hoi in the Amphoe, about 14�41'N and 101�E (Map 5238 III, Grid 248-390). Actually this locality is much closer geographically to Saraburi than Nakhon Ratchasima (Fig. 1). The "Saraburi area" is used herein.

Four species were identified in the Saraburi fauna. Miklukhoceras cf. pamiricum Pavlov, 1967; Agathiceras mediterraneum Toumanskaya, 1949; Perrinites cf. hilli (Smith, 1903); and Prostacheoceras cf. oshense (Toumanskaya, 1938b). The age was assigned as part of the Leonard/Road Canyon sequence of the American southwest, or the Artinskian/"Kungurian" Kochusu Suite (Formation) of the southeastern Pamirs, based mainly on the occurrence of Perrinites Bose, 1917. The assemblage was determined to be representative of the upper Artinskian Baigendzhinian Substage; however, this was merely an inference in response to the knowledge that the Russian Kungurian ammonoids were considered as late Artinskian and pre-Roadian by Bogoslovskaya (1976). Actually, the "upper" Artinskian sensu lato has already been assigned to the Bolorian in Pamirs with the Kungurian age (the Lower Permian), and is placed immediately under the Roadian Stage of the Guadalupian Series (the Middle Permian) in the current Permian time scale (Jin et al., 1997).

Ishibashi et al. (1996) described another Lower Permian ammonoid fauna from four exposures near Loei, northcentral Thailand, which were located along the northsouth-strike of the E-Lert Formation 9-12 km between the successive two. From north to south they are Wat Tham Pha Pu, Wat Chonlathararam, Ban Na Pong, and Huai I-Loet of the reservoir Huai Sam Pot (Figs. 1, 2). The ammonoid fauna contains Agathiceras aff. suessi Gemmellaro, 1887; Propinacoceras sp.; Popanoceras sp.; Properrinites boesei (Plummer and Scott, 1937); and Artinskia loeiensis Ishibashi, Fujikawa, and Nakornsri, 1996. It seems that the listed components of the fauna are contradictory to each other in geological range. Ishibashi et al. (1996) considered the ammonoid-bearing E-Lert Formation to be of Bolorian age based upon occurrence of Agathiceras aff. suessi and Propinacoceras sp., while they suggested Properrinites boesei, Popanoceras sp., and Artinskia loeiensis at Ban Na Pong indicated Sakmarian age of the ammonoid-bearing block of reddish calcareous shale, and then inferred them and the block to be exotic in origin.

At present all forms of Agathiceras suessi have been found only from the Wordian Stage, the Sosio Limestone of Sicily, the Cache Creek Series of British Columbia, the Wordian of Iraq, and the Baten Beni Zid Sandstone of Tunisia. However, Propinacoceras Gemmellaro, 1887 is a widespread and long-ranged genus (from Artinskian to Wordian). Therefore, merely based on an affinitive species of Agathiceras Gemmellaro, 1887 and an unidentified species of Propinacoceras it is insufficient to make a judgment of Bolorian age for the E-Lert Formation. In spite of this, the appearance of the fusulinid Pseudodoliolina ozawai Yabe and Hanzawa, 1932 in the formation at the southernmost locality Huai I-Loet of the reservoir Huai Sam Pot does provide an evidence of Bolorian (Kungurian) age for the stratum concerned. It is possible that the fusulinid-bearing limestone in that locality is really younger than the ammonoid-bearing yellow shale at the other three localities. In addition, the identification of the genera "Properrinites" and "Artlnskiu" in their paper is questionable, since the sutures in their text-figure 7 (TF 2347 to TF 2350) are rather deformed, judging from details shown in illustrations of the plate 12, and the sutures in their text-figure 8E seem to belong to two kinds of suturai patterns (the same lobule was drawn as s^sup 1^ or l^sup 1^, respectively), but improbably were assigned to the same individual (TF 2352).

A Chinese and Thai cooperative investigation of Permian ammonoids, fusulinids, and biostratigraphy was carried out by the present authors around the above-mentioned ammonoid localities in the Saraburi and Loei areas in the field seasons of February, 1997, and January, 1998, respectively (Fig. 1). It is the purpose of this paper to depict this research and to achieve more understanding of the ammonoid assemblages of Thailand.