Abstract: Immature carbonates with sapropelic organic matter of the Lower Triassic were first discovered at the central uplift of Jurong Basin, and afterwardsthe same carbonates containing sapropelic-humic organic matter(mixed type)were drilled through at Ningzhen rise, southern Jiangsu. These discoveries not only indicate that immature or under-matured carbonates source rocks are distributed widely in this area, but also modify the traditional idea that only gas can be found in the Pz-Mz marine carbonates which have undergone many tectonic movements. In fact, the prospect of oil exploration in this area is quite positive. This paper gives the organic geochemical features of the immature source rock from a wildcat well at Ningzhen rise. Analysis data show that the immaturity of the carbonate source rocks is controlled by the different degree of maturation of the mixed type organic matter under the given geological setting. Compared with mud source rocks containing the same organic matter from the same well, the rocess of maturation of the carbonate organic matter is much slower than that of the mudstone. This is theoretically helpful to find oil pool in the Pz-Mz marine carbonate in southern Jiangsu.