多方法约束的复杂物源示踪——以渤海湾盆地东营凹陷古近系孔店组-沙河街组四段下亚段为例

Multi-method-constrained tracing of complex provenance： A case study of the sequence from the Paleogene Kongdian Formation to the lower submember of the 4th member of the Shahejie Formation in the Dongying Sag

张倩

Qian ZHANG

物源分析对于追溯源-汇过程、明确有利储层展布规律具有重要意义。渤海湾盆地东营凹陷孔店组-沙河街组四段（沙四）下亚段是盆地裂陷初期充填的一套红色沉积，受多个物源共同控制，但其物源方向仍存在争议。为明确该时期物源发育特征，系统开展了砂岩碎屑组分统计、重矿物分析、泥岩全岩主量和微量元素地球化学测试以及碎屑锆石U-Pb同位素年龄研究。结果显示：①东营凹陷孔店组-沙四下亚段砂岩主要为岩屑质长石砂岩，成分成熟度较低，岩屑成分以变质岩和岩浆岩为主。②重矿物类型主要有锆石、石榴石、钛铁矿和磷灰石等。③泥岩全岩主量元素具有高硅、高铝和富碱的特征，微量元素中Li，Cr和Cs元素相对富集，稀土元素表现为轻稀土富集和Eu元素负异常的特点。④碎屑锆石U-Pb年龄范围为2 817 ~ 75 Ma，呈现多峰特征，主要年龄区间有175 ~ 130，315 ~ 250，1 900 ~ 1 855 Ma和大约2 500 Ma。研究表明，东营凹陷孔店组-沙四下亚段沉积时期具有强烈构造活动背景下的复杂母岩供源条件，母岩主要有太古宇中-酸性岩浆岩和变质岩、古元古界中-基性岩浆岩、下古生界碳酸盐岩以及中生界中-基性岩浆岩，中生界和古生界碎屑岩的再旋回对孔店组-沙四下亚段物源也具有重要贡献。结合区域构造背景和凸起区母岩性质，认为研究区在孔店组-沙四下亚段沉积时期以发育近源沉积体系为特征，主要有滨县-陈家庄体系、广饶体系和鲁西-青城体系等3大物源体系。

Provenance studiy holds great significance for tracing the source-to-sink process and clarifying the distribution patterns of favorable reservoirs. The sequence from the Kongdian Formation to the lower submember of the 4th member of the Shahejie Formation （also referred to as the Sequence） in the Dongying Sag represents a suite of red deposits filled in the initial rifting stage of the Bohai Bay Basin under the joint control of multiple provenance. However， there is still controversy regarding their directions. To reveal its provenance characteristics at this stage， we systematically analyze the detrital composition and heavy minerals of sandstones， as well as conduct geochemical tests ofmajor and trace elements of mudstones and detrital zircon U-Pb dating. The results indicate that the sandstones in the Sequence primarily consist of lithic feldspar sandstones， exhibiting low compositional maturity with lithic fragments dominated by metamorphic and igneous rocks. The main heavy minerals in the sandstones include zircon， garnet， ilmenite， and apatite. The whole-rock major element analysis of mudstones in the Sequence reveals high silicon and aluminum contents and rich alkali. The trace element data show that the mudstones are relatively enriched in Li， Cr， and Cs. Regarding rare earth elements （REEs）， the mudstones feature enrichment of light REEs （LREEs） and negative Eu anomalies. The U-Pb isotope ages of detrital zircons in the Sequence range from 2 817 Ma to 75 Ma， concentrated in 175 ~ 130 Ma， 315 ~ 250 Ma， 1 900 ~ 1 855 Ma， and around 2 500 Ma. The Sequence is deposited under complex provenance conditions against the background of intense tectonic activities， with primary parental rocks encompassing the Archean intermediate-acid igneous rocks and metamorphic rocks， the Paleoproterozoic intermediate-mafic igneous rocks， the Lower Paleozoic carbonate rocks， and the Mesozoic intermediate-mafic igneous rocks， along with significant contribution from recycled clastics of the Mesozoic and Paleozoic. In all， it is indicative of proximal depositional systems during the Sequence formation， mainly consisting of Binxian-Chenjiazhuang， Guangrao， and Luxi-Qingcheng systems.

10.11743/ogg20250218