准南四棵树凹陷沉积古环境与物源研究——来自侏罗系—下白垩统元素地球化学的指示

准噶尔盆地西南缘四棵树凹陷下组合油气勘探程度较低，并在侏罗纪—早白垩世沉积古环境演化的认识上还存在分歧，影响了对层序和沉积演化的理解，制约了勘探进程。利用便携式XRF元素仪大量、快速、无损地测试了北天山山前塞力克提沟和扎伊尔山前吐孜阿克内沟侏罗系—下白垩统野外露头细粒沉积物的元素地球化学数据，结合钻井岩心的重矿物分析，重建了凹陷侏罗纪—早白垩世的古气候、古盐度、古氧化—还原条件和古物源的演化历史。研究结果表明:从J₁b至K₁q时期，古气候表现为从温湿向干热变化的趋势，早侏罗世温度相对偏高、湿度偏低，中—晚侏罗世温度下降至最低、湿度增至最大，而K₁q时期以干热气候为主。沉积水体总体为淡水，盐度受古气候的影响较大，早侏罗世相对偏高，中—晚侏罗世相对最低，K₁q时期沉积水体盐度达到弱咸化程度。J₁s古水体相对最深、还原性最强，J₁b平均古水深相对较浅，处于弱氧化—弱还原状态，中侏罗世至K₁q时期平均古水深逐渐减小，从弱还原向氧化环境递变。凹陷在侏罗纪主要受南部北天山物源区的影响，K₁q时期北部的扎伊尔山物源区供源作用逐渐变强；J/K之交，北天山物源区母岩混入部分凝灰岩，而扎伊尔山物源区变质岩类型母岩组分升高较明显。

Palaeoenvironment and Provenance of the Sikeshu Sag in the Junggar Basin: Indications from element geochemical records

There is still some disagreement on understanding the evolution of the sedimentary palaeoenvironment from the Jurassic to the early Cretaceous within the Sikeshu sag， southwestern Junggar Basin. The low exploration level in the lower hydrocarbon accumulation system influences the comprehension of the sequence stratigraphy， sedimentation， and reservoirs， seriously restricting the process of further exploration. This paper attempts to obtain the evolution of the climate， salinity， redox condition， and provenance by applying the portable XRF element instrument and heavy mineral analysis. The instrument was used to quickly and nondestructively test a great amount of fine-grained rock samples from the two J?K₁q outcrops， which are the Sailiketigou Formation， located at the southern sag and in front of the North Tianshan Mountain， and the Tuziakeneigou Formation， located at the southwestern basin and near the Zaire Mountain. Our results indicate a total climatic trend from humid （J） to semiarid （K₁q）. The temperature reduced from J₁， reached minimum at J₃q， and increased rapidly during K₁q. The salinity， which is influenced by the climate， obviously grew in K₁q despite the sedimentary water always remaining fresh. The lacustrine deposit was the deepest and anoxic in J₁s and the shallowest and oxic in early K₁q， which demonstrates that the lacustrine depth and Eh are governed more by tectonic subsidence than climate. The supply of terrigenous detrital to the sag was mainly governed by the North Tianshan provenance during the Jurassic， and the Zaire provenance obviously supplied the sediment during K₁q. The tuffs were mixed into the source rocks of the North Tianshan provenance， and the metamorphic rocks were added into the source rocks of the Zaire provenance during the J/K periods.