“陆相层型”建立的认识与思考

从总结陆相侏罗-白垩纪地层界线的研究成果和工作方法,结合国际地层委员会“修订准则”和国际地层指南的规定,论述了建立“陆相层型”的紧迫性、理论和方法。我国陆相地层极为发育,但研究明显滞后于海相地层,主要问题是缺乏划分对比标准。目前以海相地层研究建立的层型尚不能应用于陆相地层,况且一些地质断代还未建立层型。陆相地层研究要先建立自己的标准。与海相地层比较,陆相地层在同位素测年、磁性地层划分和事件地层学研究方面具备建立层型的优势,同样可以找到分布广泛和利于大范围地层对比的化石门类。建立陆相层型的关键是找到沉积连续、化石丰富和暴露完全的剖面。陆相层型可以“单位层型”与“界线层型”建立并举,有条件的地质断代还是要重视建立“界线层型”。生物地层学研究一定要以恢复演化谱系或发生序列为基础,界线化石标志应该选在其“首现”层位。“陆相层型”的建立应强调多学科、多门类、多方法的综合研究。

Knowledge and ideas about establishment of "Terrestrial Stratotype"

Theory, methods and urgency of establishing the terrestrial stratotype are discussed based on the study of the stratotype candidate of terrestrial Jurassic-Cretaceous boundary, Luanping, northern Hebei Province, compared with "Revised Guidelines" of the ICS and stipulation of the International Stratigraphic Guide. The standard of terrestrial stratotype is necessary to be established alone. Terrestrial strata are especially developed in China and the studies are urgent to be deepened, but stratotypes established now by studies on marine strata can not be applied to terrestrial strata. Terrestrial strata can meet requirements of stratotype establishment, and have distinctively superiorities as contrast to marine strata. They contain rich volcanic rocks and minerals by which reliable iso-chronic data can be got, possess successive sandstone and mudstone by which accurate magneto-stratigraphic columns can be set up and distinguish geological events, and also contain a large number of wide-spread fossils which can be used to correlate strata in a large scope. Key of the terrestrial stratotype establishment is to discover a sediment-successive section with rich fossils and complete exposure. Both "unit stratotype" and "boundary stratotype" can be carried out equally, but it is better firstly to set up "boundary stratotype" if a suitable section could be found. Biostratigraphic zonation and mark-fossil erection should be based on restoring evolutionary pedigrees or occurrence sequences, and the boundary should be confirmed at the horizon of their "first appearence". Moreover, it should be stressed that establishment of the terrestrial stratotype should be based on comprehensive studies including multi-disciplines, multi-methods and multi-classes of fossils.