Abstract:

The Dushan Devonian section in south Guizhou, which belongs to carbonate platform facies, is one of typical Devonian sections in China. A small knoll reef built by stromatoporoids and corals is found in the lower Jiwozhai (Chiwochai) Formation of the Middle Devonian at Jiwozhai village, Dushan. The small knoll reef is composed of bafflestones, bindstones, framestones, and conglomeratic limestones. In addition, some deformed structures, including small-sized folds and faults are found in the reef. The small-sized folds are mainly recumbent and compact folds with angular and arcual hinge zone. The small-sized faults are mainly dominated by reverse fault together with some tensile faults near the hinge zone of the small-size fold. Nevertheless, the reef base and cap are normal sedimentary calcareous mudstone and limestone, respectively, no deformed structures. The characteristics of the deformed structures in the small knoll reef and the normal reef base and cap imply that the reef slumped between post-deposition and pre-diagenesis. The contemporaneous slump structure is possibly related with volcanic activity in the Guangxi-Guizhou Sea during the Givetian of Middle Devonian.