SEDIMENTARY FEATURES OF THE QUATERNARY VOLCANIC BASIN IN THE HAIKOU AREA,HAINAN PROVINCE

At least 8 volcanic eruptions are recognizable in Quaternary volcanic rocks distributed in the Haikou area, Hainan Province. The first eruption occurred in the early Pleistocene. The rocks consist mainly of tuff and olivine basalt, 4.6-15.8 m thick, and occur in the Xiuying Formation. They were measured to have a thermoluminescent age of 1999.609±5.988 Ka. Six terrestrial and marine eruptions that occurred alternately have been recognized in the late Pleistocene Daotang Formation. The erupted rocks include basic lavas and volcani-clastic sedimentary rocks. From below upwards they can be divided into four divisions. The first and third divisions are of marine origin;lithologically represented by olivine tholeiite and olivine basalt locally With pyroclastic rocks, being 49 m and 15-58 m respectively. The second and fourth divisions are of marine origin dominated by basaltic lithie and crystal turfs, containing glauconite and foraminiferal fossils, being 129-150 m and 85 m thick respectively. The carbonaceous clay interbed of the fourth division was measured to have a C¹⁴ age of 16. 790±0.41Ka. The early Holoeene Shishan Formation consists mainly of olivine tholeiite and scoriaceous-pumiceous olivine basalt with occasional block-and angular fragment-bearing olivine basalt at the base, greater than 95 m in thickness.