摘要
前言我国是石炭-二叠纪地层极为发育的国家之一。在华北,石炭-二叠纪地层是一套海陆交互相沉积;在华南的许多地区则为一套连续的、代表不同沉积环境的海相沉积。这为研究石炭-二叠纪牙形刺及石炭-二叠系界线提供了极为良好的条件。我国石炭-二叠纪牙形刺的研究虽起步较晚,但已取得了不少成果。1981年,王成源、王志浩在“
The conodonts described here were collected from six main sections across the CarboniferousPermian boundary in Guizhou, Guangxi, Henan and Shanxi, including 33 species belonging to 10 genera.In most areas of southern Guizhou, the strata across the Carboniferous-Permian boundary are continuous and consist of marine sediments. The conodont sequence in the Nashui (Luosu) section, Luodian of this region was reported by Xiong and Zhai (1985) in ascending order as: Streptognathodus elegantulus Zone; S. wabaunsensis Zone; S. elongatus Zone; Gondolella bisselli Zone and Sweetognathus whitei Zone. Later, the conodont sequence in the same section was changed by Xiong et al. (1987) to Streptognathodus elegantulus-S, oppletus Assemblage; S. elongatus-S, gracilis-S, wabaunsensis Assemblage; Sweetognathus whitei-Gondolella bisselli Assemblage and Sweetognathus whiteiGondolella sp. A-G. sp. B Assemblage. In cooperation with his collegues the present writer made a field trip to the above section, with the conodont sequence reported in ascending order as: Streptognathodus elegantulus Zone; S. elongatus Zone; Neogondolella dentiseparata Zone; N. bisselli Zone and Sweetognathus whitei Zone (Wang and Rui, 1987). After more conodont samples have been collected and processed from the same section, the refined conodont sequence can be recognized as: Streptognathodus elegantulus Zone; S. elongatus Zone; S. wabaunsensis Zone; S. barskovi Zone; Neogondolella dentiseparata Zone; N. bisselli Zone; Sweetognathus inornatus Zone and S. whitei Zone. The course change and development of conodont zonation across the CarboniferousPermian boundary in this section are given in Table I. The relationship between facies and distribution of conodonts is also discussed in this paper. Ⅰ. Conodont ZonesThe conodont zonation across the Carboniferous-Permian boundary has been described by Xiong and Zhai (1985), Xiong el al., (t987), Wang and Rui (1987). Here described is the refined conodont zonation from the Luosu section, Luodian, Guizhou.8. Sweetognathus whitei Zone, extending from 316 m up to 332m of the section represented by Samples N 167—N 171, with base and top marked by the first occurrences of Sweetognathus whitei and Neostreptognathodus pequopensis respectively.7. Sweetognathus inornatus Zone, represented by Samples N 152—N 166, occupying a 17-m interval from 299 m to 316 m at the base of the section, and containing Sweetognathus inornatus and Neogondolella bisselli, with the upper and lower limits marked by the first occurrences of Sweetognathus whitei and S. inornatus respectively.6. Neogondolella hisselli Zone, occupying a 10-m interval represented by Samples N 147—N 151, with base and top marked by the first occnrrences of Neogondolella bisselli and Sweetognathus inornatus respectively.5. Neogondolella dentiseparata Zone, represented by Samples N 132—N 146, occupying a 26-m interval in the section, with base and top marked by the first occurrences of Neogondolella dentiseparata and N. bisselli respectively.4. Streptognathodus barskovi Zone, occupying a 17-m interval in the section, and represented by Samples N 125—N 131, with the upper and lower limits marked by the first occurrences of Neogondolella dentiseparata and Streptognathodus harskovi respectively.3. Streptognathodus wabaunsensis Zone, extending for 6m in the section, and represented by Samples N 123—N 124, with top and base recognized by the first occurrences of Streptognathodus barskovi and S. wabaunsensis respectively.2. Streptognathodus elongatus Zone, occupying a 10-m interval in the section, and represented by Samples N 116—N 122, with the upper and lower limits marked by the first occurrences of Streptognathodus barskovi and S. elongatus respectively.1. Streptognathodus elegantulus Zone, occupying an 11-m interval in the section, and represented by Samples N 111—N 115, with base and top marked by the first occurrences of Streptognathodus elegantulus and S. elongatus respectively.Correlations of the conodont and fusulinacean zones between South China and USSR are given in Table Ⅲ.Ⅱ. Pbylogeny of Some Zonal Species across the Carboniferous-Permian boundaryBased on detailed study of the conodonts at the Carboniferous-Permian boundary in several sections, especially the Luosu section of Luodian, Guizhou, the phylogenetic changes of some zonal species can be shown in Text-fig. 5.Streptognathodus simplexThis species is very similar in shape to S. elegantulus, but the latter is not so slender, with the surface of its oral trough in U-shape rather than V-shape in transverse section. It has descended from S. elegantulus through narrowing the base of the oral trough at the beginning of the S elongatus Zone. Many specimens which seem to be transitional forms from S. elegantulus to S. simplex have been found in the present sections.Streptognathodus wabaunsensisThis species is very similar to S. gracilis in shape, but differs from the latter in having a shallow oral trough and an accessory lobe, which is situated more anteriorly than in the latter. S. gracilis gave rise to S. wabaunsensfs through the shallowing of the oral trough and the move of the accessory lobe toward the anterior at the base of the S. wabaunsensis Zone. Many transitional forms have been found, which show the shallowed oral trough and the anteriorly moved accessory lobe. Streptognathodus barskoviThis species is very similar in shape to S. wabaunsensis, but it differs from the latter in lacking the accessory lobe. It probably has originated from the latter through reducing and losing the accessory lobe at the base of the S. barskovi Zone. It is observed that some exemplars of S. wabaunsensis have a tendency towards reducing and losing the accessory lobe on the platform.Neogondolella dentiseparataThe origin of this species is not yet known. There is a gap in the phylogenetic lineage of Neogondolella in the present section, in which no specimens of this genus have been found between the N. clarki and N. dentiseparata Zones, while the N. bisselli group (N. dentiseparata) occurs near the base of the N. dentiseparata Zone.Neogondolella bisselliAt the base of the N. bisselli Zone, this species has evolved from N. dentiseparata through an increase in the denticles of the carina.Sweetognathus whiteiIt is supposed that this species has descended from S- inornatus through expanding the nodes of the carina laterally at the base of the S. whitei Zone.Ⅲ. Comments on the Carboniferous-Permian Boundaryso far as we know, among the many proposals for this boundary, four of them are acceptable by most geologists and palaeontologists, which separately place the boundary (a) at the base of the Neogondoldla bisselli Zone, corresponding to that of the Sakmarian in Ural of USSR; (b) at the base of the Neogondolella dentfseparata Zone, corresponding to that of the Streptognathodus constrictus-N, dentiseparata Zone of the Asselian in Ural of USSR; (c) at the base of the Streptognathodus barskovi Zone, corresponding to that of the Sphaeroschwagerina vulgaris-S, fusiformis Zone of the Asselian in USSR; and (d) at the base of the Streptognathodus wabaunsensis Zone, equivalent to that of the Asselian in Ural of USSR.In the Luosu section four horizons can be considered as the standard for the CarboniferousPermian boundary.The first (uppermost) horizon is the base of the Neogondolella bisselli Zone. The level marked by the first occurrence of N. bisselli can be considered as available for the boundary in South China because it is: 1) equivalent to the base of the Sakmarian in Ural of USSR; 2) corresponding to the evolutionary change from Neogondolella dentiseparata to N. bisselli; 3) corresponding to the base of the N. bisselli Zone; and 4) close to the top of the fusulinacean Pseudoschwagerina Zone. Although N. bisselli is a worldwide-distributed species, it is still restricted to the basinal or outer shelf facies.The second horizon is the base of the Neogondollella dentiseparata Zone- The level marked by the first occurrence of N. dentiseparata can be considered as available for the boundary in South China because it is roughly close to the base of the fusulinacean Sphaeroschwagerina-Robustoschwagerina Zone and corresponding to the base of the Schwagerina moelleri-Ps, fecunda or Streptognathodus constrictus Zones in Ural of USSR. The third horizon is the base of the Streptognathodus barskovi Zone. The level marked by the first occurrence of S. barskovi is considered as available for standardizing the Carboniferous-Permian boundary in South China because it is 1) corresponding to the major evolutionary change from Streptognathodus wabaunsensis to S. barskovi; 2) equivalent to the base of the Streptognathodus barskovi Zone; 3) corresponding to the base of the fusulinacean Schwagerina vulgaris-S. fusiformis Zone in USSR; 4) approximately corresponding to the first occurrences of Pseudoschwagerina uddeni, P. beedei, and P. texana in the Luosu and Ziyun sections; 5) approximately equivalent to the base of the arnmonoid Svetlanoceras-Juresanites Zone in Ural of USSR; in addition, Streptognathodus barskovi is widely distributed in the deep and shallow water facies. Based on the first occurrence of S. barskovi, the boundary in North China also can be recognized.The fourth (lowermost) horizon is the base of the Streptognathodus wabaunsensis Zone, corresponding to that of Asselian (the fusulinacean Daixina bosbytauensis-D, robusta Zone) in Ural of USSR and to the evolutionary change from Streptognathodus gracilis to S. wabaunsensis. The above two proposals are based on the evolutionary changes from Streptognathodus gracilis to S. barskovi, while that from S. wabaunsensis to S. barskovi is more eventful.By careful comparison of the above proposals, the present writer considers the third one as more reasonable.The following is my recommendation of this boundary to the Carboniferous-Permian Working Group for reference:1. That an international Car
出处
《古生物学报》
CAS
CSCD
北大核心
1991年第1期6-41,141-144,共36页
Acta Palaeontologica Sinica
基金
国家自然科学基金
