库车盆地古新世-始新世极端干热气候事件及其成钾效应研究

The Paleocene-Eocene Evaporites with great thickness and occurrence of multiple potassium minerals indicate the Kuqa Basin have good potential for further potash exploration. The Kuqa Basin was situated in the north margin of the Tethys domain during the Cenozoic and thus the formation and development of evaporites in the basin are closely related to the environmental changes caused by the transgression-regression of Tethys. However, the paleo-environmental change during the transgression-regression and its coupled relationship with salt/ potash formation is still poorly understood. Our team previously conducted a drilling project for potash research in Kuqa Basin and obtained well-preserved and continuous Paleocene-Eocene core samples, providing unique opportunity for answering the above questions. In this study, firstly, we will use the vertical distribution of salt minerals and evaporitic rhythm/cycle to interpret the phase of Tethys transgression-regression. Secondly, clay mineral climate proxy and halite fluid inclusion homogenization temperature will be utilized to distinguish the extreme hot and arid event during the regression. Combining with the chronology of extreme arid/hot event constrained by Ar-Ar isotope of illite, the coupling between extreme arid/hot event and potash formation will be explored to provide evidence and inference for the further prediction of potential potassium-rich beds.

库车盆地古新统-始新统发育巨厚蒸发岩沉积，且发现多种钾盐矿物，指示盆地具有广阔的找钾前景。盆地新生代位于特提斯北缘，蒸发岩形成演化与特提斯海侵-海退密切相关。但目前关于特提斯海侵-海退过程中的古环境变化及其与成盐成钾的关系研究仍较为薄弱。申请人所在团队前期在库车盆地实施了第一口钾盐科探钻井工程，获取了大量保存完好、连续的古新统-始新统岩心，为回答上述问题提供了难得的机会。据此，本项目拟首先运用钻孔中盐类矿物纵向分布特征，结合蒸发岩沉积韵律、旋回划分，确定海侵-海退期次；同时利用粘土矿物气候指标、石盐流体包裹体均一温度,获得古新世-始新世古干旱度、古大气温度记录，确定海退过程中的极端干热气候事件。在此基础上，运用Ar-Ar同位素年代学方法，对极端干热气候进行时代约束，探讨盆地极热极旱事件与盆地成钾的关系，以期为下一步有利成钾层位的预测提供理论依据。

库车盆地新生代位于特提斯北缘，古新世—始新世发育巨厚蒸发岩沉积，且发现有多种钾盐矿物，指示盆地有广阔的找钾前景。目前，关于特提斯海侵—海退过程中古环境变化及其与成盐成钾关系的研究仍较为薄弱。本项目以库车盆地第一口钾盐科学钻探工程为主要研究对象，结合盆地已有钻孔资料分析和野外露头调查，开展分析测试，取得了一定成果。将库车坳陷古近系-新近系蒸发岩系划分为五个I级沉积旋回；利用S同位素地球化学，揭示库车盆地古新世—始新世海侵—海退期次，库车盆地古新世早期为海相沉积，以后海水的影响逐渐减弱，变为陆相环境，突然始新世早期又出现短暂海侵事件，随后转变为陆相环境。对库车盆地温宿盐场以及 KL4、DZK01 井等含盐系蒸发岩矿物进行了鉴定和识别，发现了钾石盐、钾石膏以及含钾钙芒硝等含钾矿物，并建立了含钾矿物演化序列；利用石盐包裹体均一温度首次对库车盆地始新世古海水温度进行了定量重建，结果显示，始新世时期库车盆地大气温度范围为12.8℃~37.3℃，平均值分别为22.4℃和23.3℃。最高均一温度37.3℃代表了当时库车盆地成盐水体最高温度，这与前人基于模拟得出的当时海水最高温度34℃相近，但显著高于现代同纬度海水温度，这种现象可能与中始新世气候极值事件相关。该研究是库车盆地新生代首次获得的定量古气候记录，为重建和评估这一时期整个特提斯东段古大气状况提供了重要数据支撑。综合项目分析数据，结合已有工作成果，初步认为库姆格列木群上部具有找钾前景，为盆地下一步钾盐勘查明确了目标层位，同时基于包裹体均一温度、成分、钻井岩芯元素地球化学及盐类矿物组合等指标，进一步揭示古盐湖过程中极端干热气候事件尽管持续事件较短，但仍有利于钾盐富集。