西沙石岛生物礁的矿物组成及其环境指示意义
Mineral Compositions and Their Environmental Implications in Reef of Shidao Island, Xisha

通过对西科1井岩心碳酸盐岩样品进行矿物组成分析,来研究礁体的发育过程和古海洋环境的变化.初步研究结果表 明:西科1井岩心碳酸盐岩的矿物由低镁方解石、高镁方解石、文石和白云石组成.矿物组成特征表明,井深35.4m 处为一重 要的地层界面或环境变化界面.在岩心(井深0~748m)中共识别出5个白云岩层,其中上新统莺歌海组一层(井深:289.3~ 312.3m,厚约23m),上中新统黄流组三层(分别位于井深:373.3~412.7m,厚约39.4m;424.7~450.6m,厚约26.1m; 469.70~564.96m,厚约95.2m),中中新统梅山组一层(井深:615.20~636.96m,厚约21.7m).各层的白云岩化程度不尽相同, 5层白云岩中白云石矿物含量的最大值在79.3%~100%之间.生物礁的发育主要受控于古海洋环境的变化,与古气候变化有 关的海平面升降间接地控制了岛礁碳酸盐岩的白云岩化作用.石岛西科1井中的5层白云岩应该是在较长时间稳定环境条件 下发育而成,主要应该是蒸发泻湖渗透回流作用下早期形成的方解石类碳酸岩白云岩化的结果,但并不排除混合水白云岩化 作用的可能性.
The reef carbonate rocks of we11 Xike-1 are analyzed for minera1 compositions to exp1ore the deve1opment process of reef and paleo-ocean environrnenta1 changes. It is found that carbonate minerals in the core of we11 Xike-1 are rnainly composed of calcite(1ow-Mg and high-Mg), aragonite and do1omite. Minera1 characteristics suggest that there is an important strati- graghic or environmenta1 change interface at the core depth of 35.4 m. Five do1omitelayers have been identified in the core(0- 748 m)including onelayer(289.3-312.3 m core depth) in the Yinggehai Formation of Pliocene, threelayers(373.3-412.7 m, 424.7-450.6 m and469.70-564.96 m respectively) in Huangliu Formation of Upper Miocene, and onelayer(615.20- 636.96 m) in the Meishan Formation of Middle Miocene. The biggest value of do1omite contents varies from79.3% to100%, indicating do1omitization difference in different do1omitelayers. The deve1opment of the reef is mainly contro11ed by paleo-ocean environment changes and do1omitization of island reef is associated with sea-1eve1 changes contro11ed by paleoclimate events, such as the formation of ice sheet in Arctic in Pliocene, Messinian event in Late Miocene and expansion of ice sheet in Antarctic in Middle Miocene. The five do1omitelayers should have been deve1oped during a1ong-term stable environment mainly by the 1agoon seepage-refluction mode1 and possibly by mixed-water mode1