【摘要】 测试了西藏南部岗巴剖面上白垩统宗山组上段地层中厚壳蛤不同壳层的Sr、Mn、A l、S i含量,以及碳、氧、锶同位素组成,测试结果表明:1)厚壳蛤的不同壳层(包括柱状层、珍珠层和二者间的过渡层)的碳酸盐矿物均已新生变形为成岩低镁方解石(DLMC),各种原始碳酸盐矿物(沉积低镁方解石或文石)都已不同程度地发生重结晶;2)从壳的外层(柱状层)向内层(珍珠层)方向,碳酸盐矿物重结晶作用有逐渐增强的趋势,柱状层仍具有很好的柱状结构,其平均阴极发光强度明显弱于内部的珍珠层;3)厚壳蛤不同壳层的Sr含量和δ18O值都呈现有规律的变化,从靠外部的柱状层到内部的珍珠层,Sr含量和δ18O值都逐渐降低,同样说明内部的珍珠层丢掉的海水信息相对较多;4)厚壳蛤不同壳层和体腔充填物的1δ8O值都显著低于前人报道的同期海水值,说明在新生变形过程中,厚壳蛤不同壳层和体腔充填物的氧同位素都与大气水或其它成岩流体发生了交换,但柱状层的氧同位素与大气水(或其它成岩流体)的交换相对较少;5)厚壳蛤不同壳层和体腔充填物的锶、碳同位素组成与同期海水值接近,不同壳层之间也没有表现出有规律性的变化,因而在矿物的新生变形过程中,厚壳蛤的锶、碳同位素与成岩流体间的交换相对较少,同时也说明,在氧、碳、锶三种同位素中,氧很容易与成岩流体发生同位素交换,而碳、锶同位素则更多地代表了海水信息。更多还原

【Abstract】 The concentrations ofMn,Sr,SiO₂, Al₂O₃,and values ofδ¹³C,δ¹⁸Oand ⁸⁷Sr/⁸⁶Srhave been measured for different shell layers of rudist bivalvefrom a Late Cretaceoussection in the south of Tibet.The study results are as follows: 1) The constitutionminerals,inthe pillar,pearl and transitionlayers for the shell of rudist bivalvehave totally transposedto diagenetic low magnesiumcalcite（DLMC） by neomorphism and all the original carbonates are recrystallized to a certain extent. 2) The recrystallization ofinner shell layers（pearl or transitionlayer）is much stronger than that of outer shell layer.The outer shelllayer,with duller catholuminescence,has pillar texture. 3) The concentration of Srand value of δ¹⁸Odisplays a regular varietyfrom the outer shelllayer（pillar layer） to inner shell layer（pearl layer）.The concentration of Srand value of δ¹⁸Ofor outershell layer are lower than those of innershell layer,suggesting that the innershell layerlost more information of sea water during neomorphism. 4) The δ¹⁸Ovalues of all the shell layers and the celom filling are much lower than those of original sea water reportedby the published papers,so the exchange withmeteoric water（or other diagenetic fluid） in oxygen isotope shouldhave happened during neomorphism of precursoryminerals in the shell,but relatively less exchange happenedin outer shell layer. 5) The carbon and strontium isotope composition of different shell layers is close to the values of coeval sea water,and no regular variation among different shell layers,indicating less exchange with diagenetic fluid in carbon and strontium isotope.The reason is that diagenetic recrystallization of carbonates is accomplished in a system with a low water/ rock ratio for carbon（also for strontium）,buta high ratio for oxygen,and thereforethe isotope compositions ofcarbonand strontium contains more information for originalsea water.更多还原