豫西南早志留世的笔石群

本文详细介绍了河南省淅川县后垇—岭上的一条志留系下统的生物地层剖面,并首次系统描述了该剖面上目前所发现的一个早志留世笔石群,共计9属22种。根据这些笔石在剖面上的分布情况,自下而上初步建立了四个笔石带:1.Coronograptus Leei带,2.Demira-strites triangulatus带,3.Demirastrites convolutus带,4.Monograptus sedgwickii带。

EARLY SILURIAN GRAPTOLITES FROM SOUTHWESTERN HENAN

The Early Silurian strata, belonging to "mixed" (gratolites and shelly) facies, is exposed in Xichuan county of southwestern Henan. Based on the study of graptolites which were collected from Hou'ao-Lingshang section of Xichuan county by a Paleozoic research group in 1983-1984 organized by the Regional Geological Survey Party of Henan Province, the following four zones can be recognized: 4. Monograptus sedgwickii zone 3. Demirastrites convolutus zone? 2. Demirastrites triangulatus zone 1. Coronograpttts leei zoneThe C. Let zone is easy to be correlated with the zone of the same name from western Hubei (Wang, 1978; Ni, 1978), Qijiang, Sichuan (Jin et al, 1982) and Guizhou (Mu et al, 1974) of China, and is likely to be equivalent to the L. acinaces and C, cyphus zones from Great Britain in age (Rickards, 1976). Since no graptolites are found in the undrelying strata except a few shelly fossils, it is worth further finding out whether the earliest Silurian graptolites zones are present in this area and where is the lowerest limit of the C. leei zone. The D. triangulatus zone is characterized by the presence of a lot of D. triangulatus, along with D. denticulatus, O. cf. communis, S. lobiferus. Its age is probably longer than that of the D. triangulatus zone defined in Great Briatin, Northern Cordillera (Lenz, 1982) and equivalent to that of the D. triangulatus, D. magnus and P. argenteus zones there, and also correlated with that of the C. gregarius zone from USSR (Koren, 1973), Alaska, North American (Churkin et Cartev, 1970) and Bornkolm, Denmark (Bjereskov, 1975). It is indicated that a stratigraphic interval with graptolites D. denticulatus, D, decipiens, M. cf. undelatus, Pr. jaculum and a few trilobites, Encrenuroides, Leonaspis situated between the D. trian gulatus and M. sedgwickii zones is likely to be correlative with the D. convolutus zone elsewhere in the world, although the typical species of this zone have not been found yet in the present area. The M. sedgwickii zone is recognized by 'the appearence of M. sedgwickii associated with O. involutus, Pr. regularis. It can be correlated, at least in part with the homoymous zone of Great Briatin, Canada, USSSR and Alasks, USA. Whether the uppermost part of the section, consisting of yellow mudstone and purplish red mudstone with gravel, 11. 41m in thickness is correlative with the R. maximus zone or belongs to the upper M, sedgwickii zone is still uncertain, because the graptolites are absent there, and instead some trilobites with long range in age are present. In this paper 22 species, belonging to 9 genera, arc described, of Which, one species is new.