CAJ | 학술논문

碳、氧同位素作为反映古沉积环境、成矿物源和水–岩反应等良好的稳定同位素指标,被广泛应用。通过对老挝龙湖钾盐矿区ZK309、ZK301、ZK311和ZK004四个钻孔农波组盐岩上覆泥岩碳、氧同位素组成的分析,讨论了盐岩上覆泥岩沉积的碳、氧同位素组成变化特征及其指示的沉积环境。经分析,所测碳、氧同位素基本代表了碳酸盐碳、氧同位素组成,初步推测这些碳酸盐均为当地自生,受后期改变很少，δ13C 和δ18O 平均值分别为-5.1‰和-4.6‰,其中δ13C值略高于一般陆相碳酸盐碳同位素最大值–5.69‰,δ18O值介于–2.71‰~–10.8‰之间, ZK309和ZK301钻孔碳、氧同位素相关系数均小于0.7,初步指示盐岩沉积之后沉积环境为陆相。δ13C值略高于–5.69‰,推测是后期盐岩层被淋滤,泥岩层受淋滤后的残余卤水影响的结果,这也解释了蒸发岩沉积层序异常(钾石盐覆盖于光卤石之上)的沉积特征。因此,在本研究中,大气水在泥岩碳、氧同位素的变化中扮演了重要角色。
탄、양동위소작위반영고침적배경、성광물원화수–암반응등량호적은정동위소지표,피엄범응용。통과대로과룡호갑염광구ZK309、ZK301、ZK311화ZK004사개찬공농파조염암상복니암탄、양동위소조성적분석,토론료염암상복니암침적적탄、양동위소조성변화특정급기지시적침적배경。경분석,소측탄、양동위소기본대표료탄산염탄、양동위소조성,초보추측저사탄산염균위당지자생,수후기개변흔소，δ13C 화δ18O 평균치분별위-5.1‰화-4.6‰,기중δ13C치략고우일반륙상탄산염탄동위소최대치–5.69‰,δ18O치개우–2.71‰~–10.8‰지간, ZK309화ZK301찬공탄、양동위소상관계수균소우0.7,초보지시염암침적지후침적배경위륙상。δ13C치략고우–5.69‰,추측시후기염암층피림려,니암층수림려후적잔여서수영향적결과,저야해석료증발암침적층서이상(갑석염복개우광서석지상)적침적특정。인차,재본연구중,대기수재니암탄、양동위소적변화중분연료중요각색。
Carbon and oxygen isotopes have been used widely to indicate ancient sedimentary environment, sources of ore deposits and water-rock reactions. In this paper, characteristics of carbon and oxygen isotopic composition of carbonates in the mudstone from the borehole ZK309, ZK301, ZK311 and ZK004 were studied to discuss the geological evolution and sedimentary environment of the Nong Bok Formation in Laos. It is concluded that the carbonates are primarily authigenic according to analysis of mineral composition and carbon and oxygen isotopic composition of the mudstones. The result shows that the stable carbon isotope composition (δ13C) slightly higher than –5.69‰ and the stable oxygen isotope composition (δ18O) varying between–2.71‰and–10.8‰, and the average value ofδ13C andδ18O of the carbonates are–5.1‰ and–4.6‰respectively in the mudstone. The multiple correlation coefficients R betweenδ13C and δ18O values for samples from the borehole ZK309 and ZK301 are lower than 0.7. Based on the carbon and oxygen isotopic compositions and correlations of δ13C and δ18O value, we conclude that the Nong Bok Formation is terrestrial facies. The average value of δ13C are slightly higher than the threshold value of terrestrial carbonates (–5.69‰), it may due to the mudstones were reformed by brine after deposited. The brine might be generated from dissolution of the underlying salt rocks by meteoric water. This could decipher the abnormal sequence of salt rock deposition (sylvite overlies carnallite). Therefore the meteoric water played an important role in the changes of oxygen and carbon isotopic compositions of the carbonates in mudstones in the study area.