地层学的几个基本问题及中国地层学可能的发展趋势

对地层学的几个基本问题,包括地层分类、国际地层表的建立、全球地层标准剖面及剖面点进行了讨论。在各种地层分类体系中,年代地层学和岩石地层学是分类中的主体,其他系统都居于补充或从属的地位。国际地层表是地质学的基本文件和地学研究的主要参照,其建立的基础应是地史上关键性地质事件的记录,其方法应是多学科的综合研究。前寒武纪与显生宙划分的建立标准应是一致的。国际地层委员会制订的GSSP做出了重大贡献,但所定点位不够稳定,点位以外无法对比,在实践上和认知上都有不足。可考虑用多学科综合研究,寻觅接近等时的物理界面取代剖面点作为地层界面。在中国地层研究方面,以三次全国地层会议为准,分阶段概括论述了半世纪以来做出的主要成果。对今后中国地层研究的可能趋势提出了一些看法。主要是:应从系统论、整体观和复杂性观点的高度开展多学科的融合,共同解决地层的时空关系和划分对比等复杂问题;应当扩大服务面和扩展研究面,着重开展以古环境和古气候为中心的地层研究,协助解决与经济建设中的资源与环境两大主题有关的地质课题;制订2008年后的中、长期规划,改进GSSP程序,持续完善《国际地层表》这一永恒任务;开展高分辨率、高精度地层学研究,建立融合及协调多种分支学科的综合地层学;扩大地层学对整个地球科学的服务,使中国地层学研究进入一个新的阶段。

SOME FUNDAMENTAL PROBLEMS OF STRATIGRAPHY AND THE POSSIBLE TENDENCY OF DEVELOPMENT OF STRATIGRAPHY IN CHINA

This paper attempts to briefly review some fundamental problems in stratigraphy, to summarize the main achievements of stratigraphical studies in China, and to suggest possible developmental tendency in stratigraphy of China. The essential points are as follows:1 Among the various classification categories of stratigraphy, chronostratigraphy and lithostratigraphy are characterized by a hierarchcal systematic and they cover the entire rock strata on earth surface. They represent respectively the temporal and the spatial aspects of the stratigraphic science. All other categories are supplementary or merely methodological.2 In recent years, the improvement of the International Stratigraphic Chart (World Chronostratigraphic Scale) seems to have laid more emphasis on multidisciplinary stratigraphic research and on geological events that mark the critical interals in earth history. The dual principles used in stratigraphic subdivision——GSSP in phanerozoic subdivision and GSSP in Precambrian subdivision——may not be adequate. Precambrian geologists have made continual effort to subdivide the Precambrian using geological events, as is well demonstrated in the recently proposed Geologic Time Scale 2004. 3 The GSSP procedures proposed by ICS and widely practiced in recent decades have made numerous contributions to the International Stratigraphic Chart, but have their own deficiency. This is mainly related to the difficulties in the recognition and lateral correlation of the point in the field, and to the uncertainty of lower boundary of the biozones owing to incomplete sampling. The possibility that GSSP boundary surfaces may not be recognizable beyond the GSSP point and the fact that the International Stratigraphic Chart is merely a conventional frame work indicate that the GSSP principles, may not be adequate. The alternative seems to select and use an approximately isochronous physical surface, such as the first flooding surface in a depositional sequence, immediately below the base of the biozone of choice rather than the base of biozone itself as the chronostratigraphic boundary.4 The main achievements of stratigraphic research in China after 1949 may be summarized in accordance with the three All-China Stratigraphic Conferences held in 1959, 1979 and 2000. On the whole, the serial stratigraphic monographs published after the conferences were of international standard, among which the Precambrian and Quaternary parts were even more systematic than their contemporaneous counterparts in the western world. The 15-volume "Stratigraphic Code of China" published in the 1990s is outstanding, and the recent contributions to GSSP studies on the lower Palaeozoic and Permian-Triassic boundary are also significant. 5 With regard to the developmental tendency in stratigraphy of China, several points can be suggested. First, stratigraphic research, as a branch of the earth system science in the new era, should try to proceed with the modern views of systems science, holism and complexity, and adopt an integrative method with close coordination and mutual interaction of concerned disciplines. Second, stratigraphy needs to broaden its scope and aspects of service, with special emphasis on its application in geological mapping and studies of palaeoenvironment, such as the significant anoxic black shale and oxic oceanic red beds, so as to be of some help to resolve the two main themes, resources and environment, in the economic development of the country. Third, to cope with the program of ICS, further efforts should be made to improve the GSSP procedures and to establish higher standard GSSPs in China before 2008. In the same time, studies should also be concentrated on the development of high-precision integrative stratigraphy, and bringing the stratigraphical research in China to a new level.