Application of spatial database and single-factor analysis in litho-palaeogeographic reconstruction of the Ordos basin

In the study of sequence stratigraphy and litho-palaeogeography,quantitative analysis,precise calculation and detailed comparison of tremendous geological data,such as field profiles,logging records and artificial seismic curves from different areas,are the basic requirements.In order to obtain more reliable and precise result,we have developed a method,by combining the spatial database analysis and the single-factor mapping technology,to establish sequence stratigraphical succession and to map the Ordovician litho-paleogeography of the Ordos basin-one of the largest oil-gas bearing basin in North China Platform.By using the method,all of the related basic geological data can be quantitatively analyzed and scientifically managed.Various attributes of the basic stratigraphic units and their characters,such as the overall color,sequence and parasequence thickness,pene-contemporaneous dolostone content,shallow water plaster content,terrigenous material content,carbonate grain ratio,parasequence number,and the relative thickness of the lower and upper units in a parasequence,can be fully utilized statistically in facie 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 finally synthezed multiple factors to construct the litho-palaeogeographical maps for each of the sequence intervals.The study shows that the proposed method is quite effective and has much higher resolution in recognizing litho-paleogeographic units than traditional ways.For example,in one of the Middle Ordovician sequence interval(the SQ17 in Lower Majiagou Formaton) of the Ordos basin,we have successfully mapped the precise distribution of various facie units.