Abstract:

 In the study of sequence lithopalaeogeography, the quantitative analysis, precise calculation and detailed comparison of tremendous geological data, such as field profiles, logging records and seismic curves from different areas, are the basic requirements. In order to obtain a more reliable and precise result, we have developed a method, by using the spatial database to manage effectively the data that cannot be treated by traditional ways. Various attributes of the basic stratigraphic units and their characteristics, such as sequence thickness, penecontemporaneous dolostone content, shallow water plaster content, and terrigenous material content, can be fully utilized statistically in facies analysis and in mapping. Based on this analysis, we have exerted singlefactor isopachous mapping quantitatively for each of the Ordovician sequences in the basin, and we used a single factor formula to delineate the borders of facies units. Finally synthesis multiple factors have to be used to reconstruct the lithopalaeogeography for each of the sequence intervals. The study shows that the proposed method is quite effective and has a much higher resolution in recognizing lithopaleogeographic subunits than traditional ways. For example, in one of the Middle Ordovician sequence interval (444446 Ma) of the Ordos Basin, we have successfully mapped the precise distribution of various facies units, such as old land, submarine uplift, up tidal flat, middle tidal flat and down tidal flat.

Key words: Key words: spatial database; singlefactor analysis; Ordos Basin; Ordovician; sequence stratigraphy; lithopalaeogeography