CORRELATION AND IMPLICATION OF MARINE STRATA AROUND LIANHUA MOUNTAIN IN NORTHWEST HAINAN ISLAND

Coast of the northwestern Hainan Island, north of the Wangwu-Wenjiao Fault, has been shaped into a volcanic coast by the middle Pleistocene volcanic eruptions. The formation of the Lianhua Mountain resulted in the uplift and deformation of a set of marine deposits, which by now were the only outcrops of pre-Holocene marine strata in the coastal area of China except for Taiwan. Therefore, researches on these strata might have great implications to understand the evolution of the volcanic coast. Due to strong deformation and subsequent weathering and erosion, however, the primary sequences and conformation of the marine strata have been badly destroyed. In this paper, 5 typical outcrops around the Lianhua Mountain was studied in detail, and then, based on lithology, attitude, coastal morphology and tectonics, local correlation was made to recover the original sequences of the strata. This information about the sedimentary facies, structures, distribution, and age of the marine strata, combined with the coastal morphology, was applied to speculate the paleogeography, paleoenvironment and deformation process of the volcanic coast. Before the middle Pleistocene, study area with pre-Holocene marine deposits was the foreshore of the coast frequently affected by transgression and regression,and sediments from both the north by waves and the south by rivers mainly accumulated there. Since the middle Pleistocene, tectonic uplift induced by volcanic eruptions lifted the marine strata and, subsequently, caused them to be subjected to weathering and erosion. After the last glaciation, with the sea level ising, the coastline rapidly retreated with an average rate of 10 cm/a, and erosion of the pre-Holocene marine strata resulted in a platform of approximately 1 km wide.