海南省海口地区第四纪火山盆地沉积特征

广泛分布于海南省北部的第四纪火山岩,至少有8次喷发活动。第一次发生在早更新世,沉积了凝灰岩、橄榄玄武岩,厚度为4.6～15.8m,它赋存于秀英组中,已测得热释光年龄为1999609±5988年。晚更新世道堂组有6次交替出现陆相与海相的基性火山熔岩及火山碎屑沉积岩的喷发活动,自下而上划分为四个段。其中一、三段为陆相喷发的橄榄拉斑、玄武岩、橄榄玄武岩,局部夹火山碎屑岩,厚度分别为49m和15～55m。第二、四段为海相玄武质岩屑,晶屑凝灰岩为主,含海绿石及有孔虫化石,厚度分别为129～150m、85m;第四段炭质粘上夹层测得14C年龄为16790±410年。全新世早期的石山组,主要为橄榄拉斑玄武岩,熔渣—浮岩状橄榄玄武岩,底部偶见有含集块、火山角砾橄榄玄武岩,厚度＞95m。

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.