新疆尼勒克上石炭统下部的头足类

LOWER UPPER CARBONIFEROUS CEPHALOPODS OF NILKA, WESTERN XINJIANG

尼勒克陶坎-伊宁水泥厂石炭系剖面位于新疆维吾尔自治区伊宁地区尼勒克县城北东。1984年夏和1985年夏,中国科学院北疆队在该剖面采集化石;1986年夏,该队承担“七五”攻关项目--加速查明新疆矿产资源综合研究项目的子课题“新疆北部石炭系及其含矿性研究”,再次前往该剖面补采化石。以上3次所采的头足类化石交笔者研究,经鉴定计13属18种,含8新种。其中,鹦鹉螺类有4属6种,含5新种;菊石类9属12种,含3新种。尼勒克陶坎-伊宁水泥厂石炭系剖面(插图1)含菊石地层层序自上而下为:

Here described are the cephalopods collected from Bed 8 of the D ontujinh Formation at the Taokan-Yining Cement Plant section, NE of Nilka, western Xinjing, containing 18 species in 13 genera, namely, Celox gyrata sp. nov., Valhallites quadratus sp. nov., V. elliptious sp. nov, Rineceras tricarinatum sp. nov., R. sp., Epistroboceras xinjiangense sp. nov., Prolecanites nilkaensis sp. nov., Glyphiolobus subglobosus Sheng, Proshurnardites karpinskii Rauser-Tschernoussawa, Syngastrioceras supinum Ruzhencev et Bogoslovskaya, S. parasupinum Ruzhencev et Bogoslovskaya, S. oblatum (Miller et Moore), Schartymites chumazensis Rizhencev et Bogoslovskaya, Physematites sp., Homoceratoides acutus sp. nov., Surenites cf. artilectus Ruzhencev et Bogoslovskaya, S. laxilectus Ruzhencev et Bogoslovskaya, and Tectiretites nilkanus sp. nov.Of the above taxa, the ammonoids bear a strong resemblance to those from the Soviet Urals and Kazakhstan, such as Surenites artilectus, S. laxilectus, Syngastrioceras supinum, S. parasupinum and Schartymites chumazensis first described by Ruzhencev and Bogoslovskaya (1978) together with Proshumardites karpinski and representatives of Physematites, Tectiretites and Glyphiolobus from the lower Baschkirian stage of USSR. This cephalopod fauna is comparable with the Reticuloceras alpharhipaeum zone (Nm_2b_a bed) of the Reticuloceras-Bashkortoceras zone i.e., the middle of the Reticuloceras zone in USSR. However, noteworthy is the presence of Prolecanites nilkaensis sp. nov. Up to now, the genus Prolecanites, and also the family Prolecanitidae, occurs in the beds below the Homoceras zone, indicating that Pr. nilkaensis may be known as the youngest member of the genus Prolecanites.This cephalopod fauna may be compared with those recorded as equivalents of the Reticuloceras zone in China. It is equivalent to the ammonoids from the Huanglong Formation in Nandan of northern Guangxi (Ruan Yi-ping, 1981b) and from the basal Weining Formation in Panxian of western Guizhou (Zhao ain-ke and Liang Xi-luo, 1974; Yang Feng-qing, 1978; Ruan Yi-Ping and Zhou Zu-ren, 1987), which are represented by the occurrences of Tectiretites carinatus, T. nandanensis, T. kueichowensis, Bogdanoceras subglobosus and Isohomoceras striatum It is slightly lower than the cephalopods from the upper Tsingyuan Formation at Xiaoyuchuan in Zhongwei of Ningxia (Ruan Yi-ping and Zhou Zu-ren, 1987), including Reticuloceras reticulatum, Retites ortivus, R. obscurus and Domatoceras sp. However, the ammonoids from the Hongtuwa Formation in Jingyuan of eastern Gansu, which were referred by Sheng Huai-bin (1987) to the Bilinguites-Phillipsoceras assemblage consisting of Phillipsoceras alpharhipaeum, Ph. cf. remessum and Ph. yushuliangense, really belong to the Bilinguites-Cancelloceras zone, without any index fossil for Reticuloceras having been found therdn. The specimen from the Shaquanzi Formation in Zhaosu of western Xinjiang, which was illustrated by Liang Xi-luo and Wang Ming-qian (1988) as Reticuloceras sp. and known as the representative of the Reticuloceras zone in Xinjiang, should not be referred to Reticuloceras, either. Thus, the cephalopods described here should be regarded as indicating the first discovery of the Reticuloceras zone in Xinjiang.Description of new species Celox gyrata sp. nov. (Pl. Ⅰ, fig. 7; Text-figs. 2, 3)Shell relatively small-sized, discoidal and evolute, with a maximum diameter of less than 20 mm. Whorl growing fast in both and width. Impressed zone shallow. Whorl at width of 7.2mm showing broadly elliptical cross section with rounded renter and narrowly rounded flanks; that at width of 10.7 mm possessing a narrowly helmeted cross section with rounded venter gradually passing into the same rounded flanks. Umbilicus relatively small, occupying about 1/2 of shell diameter. Umbilical shoulder subangular; umbilical wall steep.Ribs occurring only on the flanks, highly projecting and thick at the ventrolateral shoulder with a row of nodules on it, extending prorsiradiately to the outer part of flank where they become thickened to form another row of nodules, and then rapidly become feeble and ended at the umbilical shoulder.Suture bearing quite shallow ventral and lateral lobes and a moderately deep and rounded dorsal lobe. Siphuncle situated at the center of shell.Comparison: The new species is similar to 'Temnocheilus' waageni Loczy in the shape of shell andsculpture, but in the latter the ribs only occur on the inner whorls. C. erratica Shimansky differs from this species in its broadly reniform whorl cross section at maturity.ValhaUites quadratus sp. nov. (Pl. Ⅰ, figs. 1, 9; Text-figs. 4, 5)Shell relatively small-sized, discoidal and evolute with a maximum diameter of less than 30 mm. Impressed zone shallow. Whorl expanding faster in width than in height, causing the development of the whorl cross section from nearly circular at the whorl width of 3.7 mm, through subtrapezoidal upside down at the whorl width of 5.2 mm and broadly subrectangular with the slightly rounded bottom at the whorl width of 9.2mm, to subsquare with the rounded bottom at the whorl width of 14.5 mm. Umbilicus wide, about 2/5 to 1/2 of shell diameter. Umbilical shoulder rounded; umbilical wall low and convex.Longitudinal lirae distributed on the whole surface, coarse and sparse on the flanks and slightly finer across the renter, amounting to 60 on the surface. Growth lines quite dense and fine, with broadly rounded ventral and lateral sinuses. Ribs occurring only on the flanks, prorsiradiate in course, most robust at the middle of the flanks.All lobes shallowly rounded and all saddles narrowly rounded. Siphuncle subcentral by renter.Comparison: The new species is distinguished from other species by the diagnostic development of whorl cross section in ontogeny, the moderately wide umbilicus and the marked ribs.Valhallites ellipticus sp. nov. (Pl. Ⅰ, figs. 3, 10; Text-figs. 6, 7)Shell small-sized, discoidal and evolute with a maximum diameter of less than 35 mm. Development of the whorl cross section during immaturity similar to that of V. quadratus. At maturity, whorl depressed, with an elliptical cross section; narrowly rounded ventrolateral shoulder separating the arched venter from the rounded flanks. Impressed zone moderately deep. Umbilicus wide, less than 1/2 of shell diameter. Umbilical shoulder rounded; umbilical wall convex.Longitudinal lirae thick and sparse, amounting to 50 on the surface, most marked at the umbi lical shoulder, then weakening ventrally and dorsally. Growth lines fine and dense, with shallowly rounded ventral and lateral sinuses and narrow dorsal sinus. Sparse ribs occurring only on the flanks, rather faint at the umbilical shoulder, then extending and thickening prorsiradiately, most prominent at the ventrolateral shoulder.Suture with a wide and shallow ventral lobe, a pair of rounded lateral lobes and a short, lingual dorsal lobe.Comparison: The new species is very close to V. quadratus sp. nov., but different from the latter in its broadly elliptical whorl cross section at maturity, the narrowly rounded ventrolateral shoulder and sparse ribs.Rineceras tricarinatum sp. nov. (Pl. Ⅰ. fig. 4; Text-fig. 8, 9)Shell relatively small-sized, discoidal and serpenticonic, with a maximum diameter of less than 20 mm. Impressed zone rather shallow. Inner whorl at width of 3.5 mm with a circular cross section. Outer whorl possessing a depressed and lenticular cross section with arched venter and narrowly convex flanks. Umbilicus moderately wide, a little less than 1/3 of shell diameter.Three pairs of longitudinal keels visible on the surface, with one pair at the ventrolateral shoulder, and the other two pairs on the flanks. Growth lines fine and dense.Suture almost straight, except for the quite shallow ventral lobe.Comparison: This species is distinguished from other species by the diagnostic features of three pairs of longitudinal keels.Epistroboceras xinjiangense sp. nov. (Pl. Ⅰ, figs, 2, 8; Text-figs. 11, 12)Five fragments available. Shell obviously discoidal and evolute. Impressed zone shallow. Venter narrow and slightly concave, delimited by the subangular ventrolateral shoulder. Flanks broad, slightly converging ventrally. Whorl higher than wide, with a subtrapezoidal cross section, with the greatest width at the subangular umbilical shoulder.Longitudinal keels prominent, bearing sharp crest, amounting to 4 pairs on the surface, with first pair on the venter, second pair at the ventrolateral shoulder, while third and fourth pairs on the inner part of flank and the umbilical shoulder respectively.Suture consisting of a rounded ventral lobe, a pair of widely rounded lateral lobes and a narrow dorsal lobe.Comparison: E. chancharense Shimansky i similar to this species in the shape of shell, but it has three pairs of longitudinal keels instead of four pairs. E. ventrosiphonatum Lai et Wang also approximates to this species in sculpture, but differs from the latter in its broad flanks without any longitudinal keels on them.Prolecanites nilkaensis sp. nov. (Pl. Ⅱ, figs. 2, 5; Text-fig. 13)Shell small-sized and serpenticonic, with a maximum diameter of less than 20 mm. Venter narrowly rounded; flanks arched. Whorl higher than wide, narrowly elliptical in cross section, with the greatest width at the middle of flanks. Impressed zone shallow. Umbilicus wide, attaining about 2/5 of shell diameter. Umbilical shoulder narrowly rounded; umbilical wall low and oblique.No ornaments visible. Ventral lobe with subparallel sides; medium prong rather long. Lateral lobe inflated in the lower part, slightly wider than the ventral lobe. U_2 lobe wide and long with obtuse tip; U_1 lobe with obtusely pointed tip, while U_4 lobe short and cuneiform.Comparison: The new species is similar to Pr. librovitchi (Ruzhencev), but in the latter the ventral lobe is a little narrower, the lateral lobe is shorter but wider than the U_2 lobe, and t