LOWER PERMIAN PERRINITID AMMONOID FAUNAS FROM THAILAND

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

CONCLUSIONS

There are two successive perrinitid zones in Thailand, the Metaperrinites Zone below and the Perrinites Zone above, which belong to the Artinskian and Kungurian Stages, respectively. The occurrence of Thailand perrinitids more fully shapes their beltlike distribution in the East Hemisphere.

The E-Lert and Nan Mahonam Formations of the Ratburi Group in the Loei area of northcentral Thailand are synchronous or at least partially synchronous, representing the facies differentiation between the fusulinid-bearing limestone and ammonoidbearing shale during the Artinskian.

The Nong Pong and Khao Khad Formations of the Saraburi Group in Saraburi area of southcentral Thailand are at least partially synchronous, representing the deposits of the Kungurian.

The Permian Formations mentioned above should not be in an exactly overlying and underlying relation, as shown in the geological maps of Changwat Eoei (scale 1:250,000, by Charoenpravat et al., 1976) and Changwat Pranakhon Si Ayutthaya (scale 1: 250,000, by Hinthong et al., 1976). Further biostratigraphic study is necessary if the tectonic evolution of Southeast Asia in Early to Middle Permian is to be understood fully.

REPOSITORY

Specimens with prefix NIGP before catalog numbers are reposited in the Nanjing Institute of Geology and Paleontology, Chinese Academia of Sciences, Nanjing, China. Specimens TF 2347 and TF 2348 tire reposited in the Geological Survey Division, Department of Mineral Resources, Bangkok, Thailand.

SYSTEMATIC PALEONTOLOGY

Definitions of genera and systematics are based on Treatise on Invertebrate Paleontology revision volume (Permian ammonoids) manuscript, coauthored by B. F Glenister, W. M. Furnish, and Zuren Zhou, 1992.

Superfamily MEDLICOTTIOIDEA Karpinsky, 1889

Family PRONORITIDAE Frech, 1901

Subfamily NEOPRONORITINAE Weyer, 1972

Genus NEOPRONORITES Ruzhencev, 1936

Goniatites (Pmnorites), KROTOW, 1885, p. 201 (part); Prenantes KARPINSKY, 1889, p. 4 (part); 1891, p. 42 (part); 1945, p. 49 (part); TCHERNOW, 1939, p. 161; Parapronorites KARPINSKY, 1889, p. 16 (part); 1891, p. 42 (part); 1945, p. 49 (part); TCHERNOW, 1907, p. 335 (part); 1939, p. 163 (part); DIENER, 1921, p. 8 (part); SMITH, 1929, p. 68; Neopronorites RUZHENCEV, 1936, p. 1076; 1938, p. 230; 1949, p. 72; 1950, p. 61; 1956, p. 83; MAXIMOWA, 1938, p. 12 (part); ZAKHAROV, 1984, p. 25; ANDRIANOV, 1985, p. 117; LEONOVA, 1988, p. 107; 1989, p. 82; Epipronorites MAXIMOWA, 1938, p. 25; RUZHHNCEV, 1938, p. 240.

Type species.-Parapronorites permicus Tchernow, 1907, p. 344; original designation; Artinskian Stage, Us'va River, Urals, Russia.

Diagnosis.-Conch subdiscoidal, involute to intermediate involute, with flattened flanks and evenly rounded venter; umbilicus small; suture characterized by irregular serration in prongs of mature external lateral lobe and one to three adjacent umbilical lobes; dorsal and adjacent internal lobe bidentate; seven or eight pairs of umbilically derived lobes in external suture, one-half as many internally; suturai formula: (V^sub 2^V^sub 1^V^sub 2^)(L^sub 1^L^sub 1^)UU^sup 1^U^sup 2^U^sup 4^U^sup 6^U^sup 8^. . . U^sup 7^U^sup 5^U^sup 3^I(D^sub 1^D^sub 1^).