CHANGXINGIAN (UPPER PERMIAN) RADIOLARIAN FAUNA FROM MEISHAN D SECTION, CHANGXING, ZHEJIANG, CHINA, AND ITS POSSIBLE PALEOECOLOGICAL SIGNIFICANCE

Journal of Paleontology, Mar 2005 by He, Weihong, Feng, Qinglai, Gu, Songzhu, Jin, Yuxi

ABSTRACT-

A well-preserved radiolarian fauna reported from the Changxing Formation in the Meishan D Section, Changxing, Zhejiang, China, mainly includes abundant Entactinia itsukaichiensis, Grandetortura nipponica, Copicyntra robustodentata, Lepingosphaera stauracanthus, and a few Entactinia meishanensis n. sp., Entactinia? sp., Entactinosphaera cimelia, Triaenosphaera sp., Tetragregnon sp., Paracopicyntra ziyunensis, Copicyntroides sp. cf. C. asteriformis, Copicyntroides sp., and Ishigum trifustis, with the conodont Neogondolella subcarinata Zone. One new species, Entactinia meishanensis, is described in this paper. This radiolarian fauna is characterized by low abundance and low diversity, and apparently occurred in a water depth of 150-200 m.

INTRODUCTION

BEFORE THE Meishan D section, Changxing, Zhejiang, China (Fig. 1), was defined as the Global Stratotype section of the Permian-Triassic Boundary, the Changxing Formation had been investigated in detail and received much international attention (Zhang, 1995; Zhang et al., 1995; Yin et al., 1996, 2001; Hansen et al., 1999). An abundance of information about taxonomy, biostratigraphy, ecostratigraphy, and related sea-level changes in this section has been gathered (Yang et al., 1991; Zhang, 1995; Zhang et al., 1995, 1997). However, there have been few detailed reports on the radiolarian fauna in this section, except that Flustrella (Yang and Jiang, 1980) and a radiolarian fauna with nine species in nine genera (Yang et al., 1997) were reported from the upper part of the Changxing Formation without descriptions or figures. In order to push research on the radiolarian biostratigraphy in the Meishan D section forward, this paper describes the radiolarian fauna in detail.

As a result of new information about modern radiolarian ecology (Anderson, 1983; Tan and Chen, 1999), people began to conduct research in the ecology of ancient radiolarians (Catalano et al., 1991; Afanasieva and Zamilatskay, 1993; Kozur, 1993). However, because of the morphological differences between modern radiolarians and ancient ones, it is difficult to reconstruct precisely the ecology of ancient radiolarians. At the present time there are a number of divergent opinions concerning the paleoecology of radiolarians. For example, based on research on conodonts and trace fossils from cold, deepwater conditions, Kozur (1993) recognized four radiolarian ecological zones: 1) from 0-50 m deep water, this zone consists almost exclusively of Copicyntrinae; 2) from 50-200 m deepwater, Entactinaria dominates, accompanied by Copicyntrinae; 3) from 200-500 m deepwater, Entactinaria dominates, accompanied by Copicyntrinae and Albaillellacea; 4) below 500 m deepwater, this zone is characterized by Albaillellacea, accompanied by Entactinaria, Ruzhencevispongacea, and Phaenicosphaera. Conversely, Afanasieva and Zamilatskay (1993) conducted research in the lithofacies and organism associations from Artinskian time in the northeastern Pricaspian Basin and preUralian Depression and pointed out that the shallow-water basin was more favorable for the radiolarian and foraminifera. In order to advance the study of radiolarian paleoecology, this paper summarizes the characteristics of radiolarian fauna from the Changxing Formation of the Meishan D section and infers some characteristics of marine water in which the radiolarian fauna from this paper occurs, based on previous lithology and paleobiology research (Yang et al., 1991; Zhang, 1995).

GEOLOGICAL SETTING AND STRATIGRAPHY

The Meishan D section, near the juncture of Anhui, Zhejiang, and Jiangsu Provinces, 20 km northwest of Changxing County, can be reached by railway or by highway from Hangzhou and Shanghai (Fig. 1). Tectonically, the Meishan D Section is located in the Lower Yangtze Block. In Changxingian time, the Lower Yangtze Block could be subdivided into three paleogeographic parts: the carbonate platform facies characterized by the Changxing Formation limestone in the southeast; the slope facies dominated by the Changxing Formation limestone along the edge of carbonate platform; and the siliceous mudrock facies dominant in the Dalong Formation in the northwest. The Changxing Formation from the Meishan D Section was deposited in the slope facies in Changxingian time (Fig. 2).

The Changxing Formation in the Meishan D Section is subdivided into the Baoqing Member and the Meishan Member in ascending order. The Baoqing Member is characterized by gray to grayish black thin-medium bedded limestone intercalated with siliceous limestone, cherty banding, and claystone, and the Meishan Member is characterized by the gray to grayish black, thin-medium bedded limestone, intercalated with siliceous limestone, siliceous mudrock, and claystone (Fig. 3). The Baoqing Member covers Bed 2-16 and the Meishan Member includes Bed 17-24 (Fig. 3). In terms of the conodont biostratigraphy it has been established that the Baoqing Member can be assigned to the Neogondolella subcarinata Zone and the Meishan Member to the N. changxingensis Zone (Fig. 3). According to the division of conodont biozones, the Baoqing Member and the Meishan Member of the Changxing Formation should be assigned to Changxingian in geological time.