层序岩相古地理编图在岩相古地理分析中的应用

THE APPLICATION OF SEQUENCE LITHOFACIES AND PALEOGEOGRAPHY MAPPING TO THE ANALYSES OF LITHOFACIES-PALEOGEOGRAPHY

岩相古地理图既是记录和说明地质作用过程中构造演化和沉积历史的重要图件 ,又是反映沉积学研究现状的标志之一。早期岩相古地理研究中 ,经典的年代地层单元编图为古地理研究奠定了基础。以板块理论为指导、以岩石地层为单元的优势相编图是第二代岩相古地理编图的标志 ,层序地层学理论的提出和发展 ,为岩相古地理编图研究提供了新的思路。作者以川滇黔桂地区泥盆系为例 ,在对中国南方部分地区泥盆系海相层序地层学研究的基础上 ,选择了层序、体系域、层序界面或相关界面为编图单元 ,进行了编制层序岩相古地理图的尝试。实践表明 ,层序岩相古地理图能够用更客观的动态变化来反映盆地的充填和演化历史 ,具有等时性、成因连续性和实用性等优点。

As a system of map representation, lithofacies paleogeographical map is one of geological data which involve rich information of basin's tectonic evolution and sedimentary history. The contents of lithofacies paleogeographical map and compilation method suggest the present situation of sedimentology. The focus of making the map is on choosing well the mapping units which belong to the composition or elements of the lithofacies paleogeographical map and display extraordinary stratigraphic units and typical stratigraphic records. Generally speaking, a sort of mapping unit means an isochronous geological body with a similar sedimentation unit . In the study history, it can be divided into 3 stages to study lithofacies and paleogeography and make the lithofacies paleogeographical map. The latter shows the notable mark. Based on paleontology and stratigraphy, chronostratigraphy is the basic mapping unit to make the first generation paleogeographical map at the beginning of sedimentological research. With the development of researching, petrostratigraphy and lithologic correlation lead to the paleolithologic map and paleogeographical map which involve the factors of mobilism. That is the second generation map. The theory of sequence stratigraphy has now brought the new thought about making the paleogeographical map which is based on sequence stratigraphy and tectonic analysis. This is the third generation map. Firstly as mapping units, sequences or system tracts are chosen to make 'time compressed' map. On the other hand, some surface boundaries, for instance, sequence boundary, maximum flooding surface, the boundary of system tracts may all be used to make the sequence lithofacies paleogeographic map. The map of 3rd generation owns some superiorities for making and using it. This paper gives some examples of the sequence lithofacies paleogeographical map from the Sichuan Yunnan Guizhou Guangxi area in China during Devonian. They show an advanced thinking and method of compiling a lithofacies paleogeographical map.