摘要
本文研究的腕足类材料采自安徽中部巢湖南岸高林村塘埂(插图1)五通群擂鼓台组上部的一层粉砂质粘土岩中,其下紧伏富含Cyclostigma cf,kiltorkense Haughton等植物化石的地层,向上距离含大量腕足类Eochoristites neipentaiensis Chu,Ptychomaletoechia Kinglingensis(Grabau)等的金陵组灰岩层16.5m。与腕足类共生的还有双壳类、腹足类、介形类以及少量植物化石碎片。所有腕足类化石个体微小,属种单调,但保存尚好,属种组合颇具特色,在确定地层时代、进行地层对比和研究腕足类的古生态方面较有意义。
A Lower Carboniferous small brachiopod fauna recently discovered from the upper part of the Leigutai Formation in Chaohu, Anhui (Text-fig. 1) consists of Schuchertella chaohuensis Liao (sp. nov.), Yanguania pingtangensis Yang, Ptychomaletoechia kinglingensis (Grabau), P. gaolingensis Liao (sp. nov.), an P. cf. xuanchengensis (Ching) occurring in thin- to medium-bedded siltpelites associated with bivalves, gastropods and ostraoods, The characters of the brachiopod fauna can be recognized: as: (1) It is low in diversity but quite abundant, in individuals; (2) Almost all forms are small or tiny in size with the largest one only 15mm in length; (3) Most of them appear to have preferred argillaceous and fine-grained sedimentary substrates, that is, a low energy environment; and (4) Associated with them are other shelly fossils, almost without representatives of stenohaline groups, such as corals, cephalopods and echinoderms. The transgression during the Late Devonian and the Devonian—Carboniferous transition in the Lower Yangtze Valley is reflected by the presence of a few marine fossils-bearing beds and the high content of fine-grained sediments, Of the Upper Leigutai Formation from the Tanggeng section, the boron content of the brachiopod-bearing matrix is 75.5—78.5 ppm. Such a low average content of boron may be explained by the fresh-water influence of paralic facies at that time. The low salinity of the matrix and the morphological variation of brachiopods suggest the more or less deformation of the fauna. This brachiopod fauna is distinguished by the abundance of Yanguania pingtangensis Yang and Ptychomaletoechia kinglingensis (Grabau). The discovery of Yanguania pingtangensis affords evidence for correlating the upper part of the Leigutai Formation in the Lower Yangtze Valley with the middle-upper part of the Aikuanian of southern Guizhou, SW China. Traditionally, the upper boundary of the Devonian system in the Lower Yangtze Valley has been drawn at the top of the Leigutai Formation. However, based on the brachiopod study, the present authors suggest that the Devonian-Carboniferous boundary in the Tanggeng section of Chaohu should be drawn at the level about 16.5m below the upper boundary of the Leigutai Formation, i.e., at the bottom of the brachiopod-bearing bed. DESCRIPTION OF NEW SPECIESOrthotetidae Waagen, 1884 Schuchertella Girty, 1904 Schuchertella chaohuensis Liao (sp.nov.) (P1. Ⅰ, figs. 32—40) 1987 Schuchertella sp., and Orthotetidae gen. et sp. indet., Zhang Guo-dong et al., pl. Ⅰ, figs. 6, 12. Diagnosis: Outline oval to semielliptical, shell small or tiny, holotype measuring 5.5mm long, 6.1mm wide, with the length and width approximately equal in some specimens; hinge normally forming widest part of shell, but slightly narrower than midwidth in some specimens; commissure rectimarginate. Pedicle valve moderately convex, umbonal region forming most convex part, with apex pointed or small preumbonal attachment scar; anterior broadly rounded; interarea low, normally flat or slightly convex, commonly apsacline, pseudodeltidium completely arched. Brachial valve flat or slightly concave, cardinal extremities obtuse to narrowly auriculate, brachial interarea low or absent. Costellae cover entire valves, numbering 8—9 per 1mm anteriorly, growth line weak; pedicle valve interior with small teeth, no median septum; brachial valve interior with higher socket ridges, cardinal process small. Comparison: These shell stand apart from Schuchertella species that are common in South China. They are small or tiny and less convexity than S. gueizhouensis Yang from the Kolaoho Formation of the southern Guizhou of Famenian.—Tournasian age. Trigonirhynchiidae Mclaren, 1965 Ptychomaletoechia Sartenaer, 1961 Ptychornaletoechia gaolingensisLiao (sp. nov.) (PI. Ⅰ, figs. 1—14) Diagnosis: Shell small or tiny for genus, slightly wider than long, holotype measuring 3.6mm long, 3.3mm wide, 1.7mm thick; outline subtrigonal to subpentagonal, evenly biconvex in lateral profile, commissure rectimarginate to weakly uniplicate; pedicle valve moderately convex, beak short, strongly curved, sulcus similarly shallow; brachial valve more convex than pediclevalve, and with great width anterior to midlength of most specimens, brachial umbo rounded, beak obtusely pointed, apex below beak of pedicle valve; costae distinct, simple, beginning from umbonal part, numbering three or four on fold, one fewer in sulcus, normally four on each flank, growth line weak. Comparison: Ptychomaletoechia gaolingen— sis characterized by its extremely small size for the genus, and its outline, lower convexity, and relatively few costae. It most nearly resembles P. kinglingensis (Grabau), from Kingling Limestone, but differing in its smaller size, narrower outline, and weaker sulcus and fold.
出处
《古生物学报》
CAS
CSCD
北大核心
1989年第5期562-570,690,共9页
Acta Palaeontologica Sinica
