摘要
本文测试了采自湖南花垣中、上寒武统的11个碳酸盐岩样品的δ^(18)O值和δ^(13)C值。采样地层所含牙形石的CAI指标均为1。影响CAI值的主要因素和成岩改造作用对δ^(18)O的主要影响因素是相同的。据此可以推断出,这11个样品所在层位的成岩改造作用是大体相同的,也就是说,同原始沉积时的δ^(18)O值相比,测出的δ^(18)O值的变化幅度也大致相同,因而,可以用来指示古水温的相对值。作图结果表明,温度越高,牙形石分异度越大;反之,牙形石分异度越小.
δ^(18)O and δ^(13)C values were measured upon eleven carbonate samples collectedin the Middle--Upper Cambrian in Huayuan, Hunan. Because of the secular influ-ence of diagenesis, the measured δ^(18)O values can not be applied to the calculationof the absolute values of palaeotemperature. The main factors for the influence of diagenesis on δ(18)O are as follows: time(effect), depth of bulial, and the participation of atmosphereic air and fresh waterin diagenesis. The main factors for affecting CAI are depth and duration of burial. On thesegrounds, the main factors for affecting CAI are generally the same in many as-pects as those for affecting δ^(18)O. The horizons of the analysed isotopic samples yield conodonts which all havea CAI of only 1. In view of the above, It may be inferred that the horizons ofthe analysed eleven samples should have undergone approximatelly identical dia-gensis. In other words, the measured δ^(18)O values have changed within nearly thesame range, as compared with the primary δ^(18)O values. Consequently, they maybe applied to the indication of the relative values of palaeotemperature. As isshown in Fig. 1, the warmer the marine water was, the higher the conodont diver-sity was, and the cooler, the lower. At present, the new technique of oxygen--isotope measurements of conodontscan not be applied to Cambrian conodonts, because it is impossible to recover1000--6000 conodont specimens to meet the reqiurement of such measurements inper conodont sample (average 3 kg) in Cambrian strata. It is suggested that asuitable biogenic phosphate lock material be used in place of Cambrian conodontspecimens in the future resarch.
出处
《地质论评》
CAS
CSCD
北大核心
1992年第4期368-371,共4页
Geological Review
关键词
δ^O
古水温
相对值
牙形石
δ^(18)O
palaeotemperature
conodont diversity
