老挝他曲地区石盐流体包裹体特征、氢氧同位素组成及成盐物质补给方式

对老挝他曲地区钻孔中石盐流体包裹体特征、类型以及氢氧同位素组成进行了研究,用以重塑盆地成盐过程中的古环境,并在此基础上对盆地成盐物质的补给方式进行了探讨。结果显示,钻孔中塔贡组下盐段原生石盐岩主要包括人字形和漏斗形晶体两种类型。其中人字形石盐晶体在下盐段中广泛发育,漏斗形晶体数量较少,但通常与人字形石盐晶体产于同一层位,指示了下盐段沉积时盆地处于一种极浅水环境。石盐原生流体包裹体氢氧同位素组成明显偏离全球大气降水线,集中分布于其右下方,反映盆地成盐过程中处于强烈蒸发条件之下。氢氧同位素组成在纵向上的变化,可能揭示了在盐湖演化至钾盐沉积阶段大气温度具有升高趋势。白垩纪中期全球海平面达到极大值,而在呵叻盆地内部,持续的坳陷和强烈的蒸发作用将导致湖平面快速下降。这样,外海与盐盆之间则会产生水位差,由此产生的水力梯度将为外海海水通过障壁向盆地方向进行渗透提供潜在的动力。此外,早白垩世呵叻高原广泛发育的沙漠沉积,则为外海海水大规模的侧向渗透进入盐盆提供了可能的通道。因此,结合现有的资料,本文提出,除海侵补给外,外海通过障壁侧向渗透补给对老挝钾盐盆地成盐物质的供给也具有重要作用。

Characteristics and Hydrogen Oxygen Isotopic Compositions of Halite Fluid Inclusions in the Thakhek Area, Laos, and the Way of Salt Material Supplies

Characteristics, classification and hydrogen oxygen compositions of halite fluid inclusion of core sample were used to reconstruct paleo environments during salt deposition of the Thakhek area, Laos, and based on which the way of supply of salt materials was explored. The results show that, primary halite in the Lower Member of the Tagon Formation mainly includes two types, the chevron halite and the cumulate halite. The chevron halite crystals largely occur in the Lower Member of the Tagon Formation, and the cumulate halite crystals is relatively few but usually coexisted with chevron halite crystals in the same layers, indicating an extremely shallow water environment during halite formation. Hydrogen oxygen isotopic compositions of halite fluid inclusion obviously deviated from the global mean meteoric line and mainly concentrated at the bottom right of the line, suggesting a strong evaporative condition during halite deposi tion. The vertical variability of hydrogen oxygen isotope probably implies an increasing trend of air temperature from halite to potash salt deposition. The sea level peaked at the middle Cretaceous. However, water level of salt basin dropped significantly due to continuous subsidence of salt basin and strong evaporation concentration of salt lake, When this occurred, the difference in water level between the sea and salt basin created a horizontal hydrostatic head gradient that had the potential to drive water through the barrier. Moreover, desert sediments occurred widely in Khorat Plateau during the early Cretaceous, providing a necessary passageway for the large scale sea water. Therefore, combining with the existing data, we proposed that, in addition to marine intrusion, seepage of seawater through barrier played a significant role in supplying of salt materials of basin in Laos.