摘要
以非海相介形类为依据而建立的侏罗纪末至白垩纪的生物地层学,尤其是欧洲所谓"Purbeck-Wealden层段"(提塘阶顶部至巴列姆阶/阿普特阶底部)和全球同期沉积层的生物地层学建立已久,但这一生物地层学存有很多问题与局限性。本文对中生代晚期(聚焦于早白垩世)的非海相介形类生物地层学的基本原理、历史、目前进展、存在问题和前景进行了综述。因为介形类的繁殖、扩散与成种机制已有比较成熟的研究,所以介形类的生物地层学的应用潜力被认识已久。然而,全球不同地区中生代晚期的非海相介形类众多的研究积累已构成了一个丰富但常常混乱和矛盾的文献库。这些问题不仅存在于介形类的分类鉴定中,也见于关于古环境和系统发育的解释中。虽然地区性的盆地内的介形类生物地层学研究已产生了好结果,并可能能够用于局部地区的高精度对比。但是在进行地区间(盆地间至全球)的对比时,其实用性广遭怀疑。在过去的二十年间,许多学者采用了将今论古的古生物学研究方法,努力修订和更新中生代晚期的非海相介形类的生物地层学与古环境意义,从而促进了地区间生物地层学研究和对比的发展。古生物学家认识到,对于许多非海相介形类动物来讲,它们的分布和扩散不仅仅局限于单个的水系或较小的地理区域,而是和现生的非海相介形类一样,晚侏罗世至白垩纪的非海相介形类动物和它们的卵可被较大的动物或风长距离搬运,跨越迁移的屏障,进行扩散。鉴于以上事实,地区间的对比必须涉及两大内容:分类学的应用与古环境背景。缺乏适用于地区—全球的稳定和一致的分类学系统是进行正确对比的重要障碍。由于大量地方性分类命名、地方性特有动物的假设、与壳体特征相关的分类和生态型认识的混乱,以及对种内变异尺度的统一认识的缺乏,导致了对生物分异度的过高或过低的估量。非海相白垩纪介形类的地层记录受到诸多因素的影响:分类单元的演化与灭绝、扩散事件、当地的环境变化和地区性至全球的气候变迁。在生物地层学的应用中,我们可以通过不同手段去把握同时代的Cytheroidea,特别是Cypridoidea中具重要地层意义的Cypridea属及其亲近者(即CypridoideaMartin,1940)的分类单元的形态变异度。解释种内变异时需要格外谨慎。区分生物自生(内因)导致的变异(遗传的和形态的变异)和环境(外因)导致的变异(生态表型)是一大难题。比较保守的分类学观念(分类单元很少,但变异极大(分类单元中包含了多种生态表型))有助于不同古环境间的(生物地层)对比。另一方法是运用随着时间的古环境变化及其对介形类组合的组成的影响来进行(生物地层)对比。古生物工作者已在利用受环境控制的周期性介形类组合变化建立对比关系方面进行了大量有意义的尝试,但这些工作仍处在争议中。建立全球生物地层学方法,建立统一而持久的分类概念这一目标可以达到,但不可能在短期内实现。用现代的思想(概念)理解和研究非海相介形类的古生物学和古生物地理学及新资料将有助于修订工作的进展。尽管我们对中生代的非海相介形类的演化和分布的认识还很不全面,但目前我们已取得了可喜的进展。盆地间至大陆间的对比是否可行,早已不是问题。目前和未来的指导原则无疑是发展以介形类为基础,并与其他的年代地层学和地质年代学资料及方案相结合的从地区至全球范围的地层对比系统。因为我们正在迈向一个非海相晚中生代介形类生物地层学的重新解释和应用的新时代,我们必须承认我们还有许多东西需要学习。
Latest Jurassic-Cretaceous biostratigraphy based on non-marine ostracods has a long tradition, particularly with respect to the so-called ＂Purbeck-Wealden interval＂ （uppermost Tithonian to Barremian/lowermost Aptian） in Europe and contemporaneous deposits worldwide, but has, at the same time, always been affiliated with considerable problems and limitations. We review the fundamentals, history, recent progress, problems and perspectives of late Mesozoic non-marine ostracod biostratigraphy with a focus on the Lower Cretaceous. The application potential of these ostracods has long been known, as have been the considerations of reproductive, dispersal and speciation mechanisms. However, the accumulation of numerous studies of late Mesozoic non-marine ostracods in different parts of the world has produced a rich literature that is often confusing and contradictory. This not only applies to the taxonomical identities of the ostracods but also to their interpretation with respect to palaeoenviron- ments and phylogeny. While regional, intra-basinal ostracod biostratigraphy has produced good results and has potential for local high-resolution correlations, their utility for supraregional （inter-basinal to global） correlations has widely been doubted. By adoption of a uniformitarian, palaeobiological approach, attempts made by various authors to revise and rejuvenate the biostratigraphical and palaeoenvironmental applications of late Mesozoic non-marine ostracods over the past two decades have promoted the supraregional biostratigraphical approach. Essential to this is an appreciation of the fact that many non-marine ostracod groups are not restricted to individual waterbodies or smaller geographical regions in their distribution and dispersal. As today, whole living specimens or eggs of Late Jurassic and Early Cretaceous non-marine ostracods are considered to have been able to be transported passively by larger animals or wind over long distances, crossing migration barriers. Acknowledging these facts, attempts at supraregional correlation have to deal with two major issues： the applica- tion of taxonomy and the palaeoenvironmental context. A major obstacle to success is the absence of a stable, consistent taxonomical scheme that is applicable on regional to global scales. This has resulted in both over- and under-estimations of diversity, resulting from an abundance of largely local taxon names, assumptions of endemicity, confusion of taxo- nomically and ecophenotypically relevant carapace features, and the lack of a consensus on how much morphological variation to allow in one species. Evolution and extinction of taxa, dispersal events and varying influences of local en- vironmental factors as well as regional to global climatic factors have all contributed to the very complex stratigraphic records of Cretaceous non-marine ostracods. In biostratigraphical applications, there are several ways of handling the morphological variability exhibited by contemporaneous taxa of the Cytheroidea and particularly of the Cypridoidea, namely those of the stratigraphically important genus Cypridea and its close relatives （i.e., the extinct Family Cyprideidae Martin, 1940）. Great caution is advisable when interpreting the morphological variation within species. One big problem is the separation of biologically induced variation （genetical and morphological variation） and environ- mentally induced variation （ecophenotypy）. A more conservative taxonomical concept （fewer taxa with strong true variation including a high proportion of ecophenotypes） facilitates correlations between different palaeoenvironments. Another issue is the handling of palaeoenvironmental changes and their influences on ostracod assemblage compositions over time. Significant efforts have been made to establish correlations using environmentally-influenced, cyclic changes in ostracod assemblages, but remain the subject of debate. Heading towards a global biostratigraphical approach, the goal of global taxonomical concepts and stability appears achievable but is not expected to be reached quickly. Modern insights into non-marine ostracod palaeobiology and pa- laeobiogeography and as well as new data can assist the process of revision, and in spite of considerable gaps in our knowledge of the Mesozoic evolution and distribution of non-marine ostracods, we presently make good progress. It is no longer a question of whether inter-basinal to inter-continental correlations are possible; the recent and future guiding principle is rather to take this fact for granted and to develop an ostracod-based network of stratigraphic ties on a re- gional to global scale and to integrate this with other chronostratigraphical and geochronological data and schemes. As we approach a new era of fundamental reinterpretation and application of late Mesozoic non-marine ostracod biostrati- graphy, we must accept that we still have much to learn.
出处
《地层学杂志》
CSCD
北大核心
2012年第2期266-288,共23页
Journal of Stratigraphy
基金
国家自然科学基金(No.91114201)
国家重点基础研究发展计划(2012CB821906)资助出版
