///Natural gamma ray measurement was applied to the Saergan shale and Yingan shale from the Middle-Upper Ordovician system in the Dawangou section of the Keping area. In this paper, variation curves of high-frequency sea-level changes for these two suites of shales were established. Meanwhile, analyses of pyrolysis, organic carbon content, X-diffraction of clay minerals and contents, and mudstone density were performed on 54 mud shales sampled from the Saergan and Yingan formations. The results indicated that: 1)  the Saergan shale with a thickness of 13.4 m remained with a third-order sequence of sea-level changes; 2) both the Saergan and Yingan shales showed an increasing content of clay minerals as sea level rising; 3) clay minerals in the Saergan shale and Yingan shale were composed mainly of a mixture of illite and smectite; and 4) both the Saergan and Yingan shales were characterized by an increase of organic matter abundance and a decrease of mudstone density as sea level rising, but a decrease of organic matter abundance and an increase of mudstone density as sea level falling.