Changtou Fm

No. 764 Party of the Guangdong Bureau of Geology erected the Changtou Group in 1959, but no naming section was indicated when the name was coined. The reference section is located in well ZK0802, ~500 m south of Changtou Village in the Changchang coal mine, Qiongshan County, Hainan.

Changtou formation refers to 1.84 ~ 431 m section of well CK106 in Changchang basin. It consists of red clastic rocks and oil shale. Two members are distinguished: Lower member is called the red member, marked by brownish red conglomerate, sandy conglomerate, feldspathic quartz sandstone, calcareous very fine sandstone and calcareous mudstone with grayish white fine sandstone, 124 m thick; Upper member is called the oil shale member, represented by gray, grayish green and brownish red calcareous feldspathic quartz fine sandstone, siltstone and mudstone with oil shale in the lower part and alternating beds of gray feldspathic quartz sandstone, calcareous mudstone and oil shale in the upper part, ~249 m thick. Its lower member is uniform, while its upper member varies relatively greatly in lithology and thickness. In the southern part of the Changchang basin there occurs shale and mudstone with fine sandstone, 250 m thick, which change facially into alternating beds of mudstone and fine sandstone with gypsum bands in the northern part, where the thickness is 96 m. The total thickness is 365.1 m in well ZK0802 of the Changchang basin.

The upper member of the Changtou Formation yields ostracods, sporopollen and plants. Ostracods are Sinocypris excelsa, Eucypris serrata, E. stagnalis, Limnocythere hubeiensis and Cypris Formosa; sporopollen is represented by the Subtriporopollenites-Ulmipollenites minor-Pentapollenites assemblage; plants include Osmunda lignitum, Nelumbo protospeciosa, Cinnamomum larteti and Citrus niger etc. According to the above-mentioned fossils, the age of the formation may be Paleocene-early Eocene.

This formation is composed of endorheic fluvio-lacustrine deposits.