摘要
一、前言对于奥陶纪和志留纪的生物地层学和年代地层学,笔石的生物带至今仍不失其标准性。但是就生态地层学而言,笔石的深度分带则研究甚少。近20年来,由于各国笔石研究工作者注意研究笔石的孤立标本和立体标本,恢复笔石的微细结构和超微构造,使笔石的个体古生态(autecology)研究大大地前进了一步,但是笔石的群体古生态(synecology)仍是薄弱环节。这主要是因为笔石虽生活在不同水层中,但所保存者均为死亡后沉落于海底的状态,况且笔石在石炭纪以后已经绝灭,无现生的笔石可以借鉴。
Graptolite biozones are generally recognized as the standard zonal scheme for correlation in Ordovician and Silurian biostratigraphy and chronostratigraphy. However, graptolite depth zonation has been considered only rarely as tool of ecostratigraphy. The reconstruction of graptolite fine structure and ultrastructure based on isolated and three-dimensioned specimens in the past twenty years has made great progress possible in graptolite autecology. However, graptolite synecology is still a virgin field for the graptolite workers due to the absence of significant evidence for the graptolite living environment and especially the absence of living graptolite for comparison. All explanations of graptolite ecology are based upon functional morphology and the structure of the rhabdosome.
Many authors assume that graptolite lived in different water layers during the Ordovician and Silurian (Berry, 1962; Bulman, 1964; Rickards, 1975; Kaljo, 1978; Mu En-zhi, 1983; Bates and Kirk, 1984), but they all found it difficult to work out the relative depth positions of various graptolite based only on implications of morphology.
In a study of Telychian brachiopods in Wales, Ziegler (1965) demonstrated that 5 brachiopod communities paralleled the shoreline and indicated a differential depth zonation. His study strongly encourages paleontologists to examine benthic communities. Boucot (1975) critically summarized 5 Benthic Assemblage zones, and tried to determine the depth significance of the benthic assemblages. Ziegler's communities or benthic assemblages may thus be interpreted as reflecting an increasing depth along the bathymetric gradient. Graptolites associated or buried with shelly faunas are also indicative of the same depth. Based on data from Europe, North Africa and North America showing the occurrences of graptolites with shelly faunas from Telychian deposits, Berry and Boucot (1972a) and then Boucot (1975) proposed a model for the depth distribution of Silurian graptolites (Text-fig. 1). Subsequently Rong (1986) proposed that BA1 laid in the intertidal zone, and Chen (1986) also suggested that GA2—5 should be used for graptolite assemblages instead of graptolite 'BA2—5' which was used by Mu, Boucot et al. (1986). Unfortunately, the basic data which supported Berry and Boucot's model were insufficient to emphasize the major aspects since the shallow water platforms, both in Britain and in the Baltic, were narrow during the Silurian, and the graptolites associated with the shelly faunas are present only in a few localities both in North America and in North Africa. The Chinese material in the present paper represents about 13 localities at different horizons where the graptolites are associated with the studied brachiopod communities or benthic assemblages (Text-fig. 2). Most of the data come from the Yangtze Platform (about 9×10~5 km^2), the major part of the South China Paleoplate, which was occupied by a widespread epicontinental sea during the Early Paleozoic; these data provide abundant support and a reasonable revision for this model.
出处
《古生物学报》
CAS
CSCD
北大核心
1990年第5期507-526,共20页
Acta Palaeontologica Sinica
基金
国家自然科学基金4870090项目资助
为中英志留系研究项目的阶段成果之六
