从历史大地构造学和地层学论岩相、古地理的研究

前言 根据近三十年来从事历史大地构造学及地层学的教学与研究工作所得到的启示,深感两者对于岩相、古地理的研究工作密切相关。利用历史大地构造学有关原则进行岩相、古地理的研究,应当认为是当前岩相、古地理研究中的一个方面。其基础则建立在新全球构造观点上。即运用地史期间古板块的离散与聚敛或漂移以及古地磁极移动和古气候带的变迁等基本特征来进行岩相、古地理研究,并了解有关沉积矿产的分布规律。看来与根据以岩石学、地球化学和沉积学为基础的岩相、古地理研究矛盾并不大,而且将起到互为补充、相辅相成的作用。实际上,两者经历着殊途同归的过程。

ON THE STUDY LITHOFACIES AND PALEOGEOGRAPHY IN THE LIGHT OF THE HISTORICAL GEOTECTONIC GEOLOGY AND STRATIGRAPHY

The theory of historical geotectonic geology, stratigraphy and sedimentology are complementary with one another and should be intimately combined. Thus, the development of these theories must have exerted a strong influence on much of the study of geologic history events. No matter how many new discoveries have been made, the progress in the study of plate tectonics will by all means exert a great influence on the sedimentology studies. In the past two decades or so, the sediments and rock samples obtained from beneath the oceans and continents have provided decisive data that have served to revolutionize the earth science. Unexpected features and event courses revealed and comprehensive data built up, the geologic history of the continents and the oceans may be said to have been mastered. Based upon the study of great qualities of data (stratigraphy, lithology, radioactive istope age and paleogeography, etc.) collected and accumulated over so many years, historical geotectonic geology is concerned with the forms and history of the deformation of the earth's crust. To put it briefly, stratigraphy is to study the character, sequence relationship, distribution and origin of sedimentary rocks. Seen from this point of view, every sediment is wholly determined by geotectonic events; but in general, we accept the environmental circumstances which determine the lithofacies of a sediment and palaeogeography and determine its geotectonic control as the variations imposed on it by the ever-changing geotectonic conditions. Much of the lithofacies evidence that is useful in deciphering geotectonic geology-and development is the same as that employed in the reconstruction of palaeogeography. It is mainly distribution and characters of lithofacies and palaeogeogragy phy that is derived from the stratigraphy. It is evident that the primary tectonic environment of Cryptozoic and Phanero-zoic should be related partly with a eugeosyncline or trench, and partly with miog- geosyncline and land block (Craton). They contain a wide variety of rocks. For example,the flysch deposits are widely distributed over the miogeosyncline and eu-geosyncline. Precisely speaking, in the eugeosyncline volcanic rocks may be found underlying the flysch deposits -which in turn were overlain by synorogenic volcanic-rocks. Evidences have been found and have proved the existence of turbiditesin the flysch deposits. It has also become clear that the turbidites consist of material that originated from the land blocks around these geosyclines, and these turbidites were controlled by deep fratures. It is well known that after the Variscian erogenic cycle came the subduction of the Pacific plate that sank lower than the Asia-Europe plate; the collision of the Indian plate with the Asia-Europe plate gave rise to the Tethys-Himalayan geo-synclinal foldbelts, forming such a great variety of rocks. Lithofacies can be reorganized and traced in the subsurface on the basis of drilling records. Among the diagnostic features utilized are: 1. lithologic characters) 2. metamorphic alteration) 3. fossil assembledge) 4. stratigraphic relations) 5 . temporal sequence) 6. structural form) 7. environmental influences) 8. tectonic control) 9. genetic interpretation) 10. geographic occurrence.