Abstract: The Carboniferous is a new petroliferous system in Santanghu basin, in which volcanic rocks are favorable oil-gas reservoirs. However, the long-term unclear recognition of internal structure of the Carboniferous and distribution of volcanic rocks in it influences the cause for petroleum exploration here, because it is hard to get effective seismic reflectance information from the deep sequences. The application of high-accuracy gravity-magnetic-depth sounding technology allows the previous seismic prospecting deficiency to be made up for, by the fact that the remained trough distribution and the sequence structures as well as the vertical and lateral distribution of volcanic rocks of the Carboniferous in Malang sag are basically recognized. The study shows that the remained trough of Carboniferous in southeastern Malang sag is a favorable target or direction for petroleum exploration. The Harjiawu formation of Upper Carboniferous belonging to low-resistivity bed with argillaceous clastic rock could be as a source rock, while the Kalagang formation and the Batamayineishan formation belonging to high-resistivity bed with volcanic rocks could be favorable reservoirs. The field-constructive sounding profile can be applied to vertically recognize the multi-set sequences and their volcanic bodies; the high-accuracy gravity and magnetic prospecting technology can be used for studying the lateral distribution of geologic bodies like volcanic rocks. It is suggested that the integration of these two technologies should be effective means for study of the geologic structure and volcanic rocks of the Carboniferous in this area.

Key words: Santanghu basin, gravity-magnetic prospecting, field sounding, Carboniferous, volcanic rock