Sedimentary microfacies and environment of Paleogene carbonate-rich shale in Dongying Sag, Bohai Bay Basin
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摘要: 渤海湾盆地东营凹陷富碳酸盐页岩的微相特征识别、划分及其组合方式研究,是揭示相关沉积物沉积成因和空间结构的基础。基于岩心和岩石薄片资料,利用X射线衍射、扫描电镜分析等测试分析技术,通过高分辨率的岩心取样和测试,对东营凹陷斜坡带富碳酸盐页岩开展了岩石矿物学和古生物学等方面的分析。结果表明,该区富碳酸盐页岩内部可以划分出藻席微相、介壳页岩微相等10种微相类型,各类微相通过不同方式叠加构成一系列微相组合,并显示出米级尺度的页岩相变特征。对应于东营凹陷咸水湖泊演化的不同阶段,可划分出浅水蒸发岩微相组合、震荡半深水页岩微相组合和震荡深水页岩微相组合等3种岩石微相组合,这些组合通常由高频振荡背景下湖平面升降旋回控制。东营凹陷沙河街组四段上亚段自下而上,伴随气候的湿热、风化增强、湖平面上升、湖泊盐度降低,震荡深水页岩微相组合占比逐渐增加,浅水蒸发岩微相组合逐渐降低,一系列向上水体变深的沉积旋回记录了东营凹陷中始新世持续沉降和生物—环境协同演化的特点。Abstract: The identification, classification, and integration of microfacies characteristics of carbonate-rich shale in the Dongying Sag of the Bohai Bay Basin are fundamental for understanding the sedimentary origin and spatial structure of related sediments. Leveraging core and rock thin section data, along with analytical techniques such as X-ray diffraction and scanning electron microscopy, high-resolution core sampling and testing were conducted to analyze the rock mineralogy and paleontology of the carbonate-rich shale in the slope zone of the Dongying Sag. The research findings identified the presence of 10 types of microfacies within the carbonate-rich shale, including algal mat microfacies and shell shale microfacies. These microfacies combined in various ways to form a spectrum of microfacies combinations, exhibiting shale phase transition characteristics on a meter scale. Corresponding to the different stages of saline lake evolution in the Dongying Sag, three types of rock microfacies combinations emerged: shallow water evaporite microfacies combination, oscillatory semi-deep water shale microfacies combination, and oscillatory deep water shale microfacies combination. These combinations were typically controlled by the cyclical rise and fall of lake levels against a backdrop of high-frequency oscillations. In the upper submember of the fourth member of the Shahejie Formation, from bottom to top, as the climate became more humid and hot, weathering intensified, lake levels rose and lake salinity decreased, the proportion of oscillatory deep water shale microfacies combinations gradually increased, while that of shallow water evaporite microfacies combinations decreased. This series of upward-deepening depositional cycles recorded the continuous subsidence and co-evolution of biology and environment during the middle Eocene in the Dongying Sag.
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图 2 渤海湾盆地东营凹陷沙河街组四段上亚段富碳酸盐页岩沉积微相类型
a.牛斜124井,3 243.75 m,红色页岩微相;b.樊页平1井,3 470.00 m,介壳页岩微相;c.樊页1井,3 432.42 m,白云质页岩微相;d.樊页1井,3 437.30 m,生物礁滩微相;e.纯372井,2 605.90 m,颗石藻页岩微相;f.樊页1井,3 430.00 m,透镜状灰质页岩微相;g.樊页平1井,3 454.00 m,重力流水道微相;h.樊页平1井,3 468.30 m,藻席微相;i.樊页平1井,3 473.5 7 m,泥质页岩微相;j.牛55-斜4井,3 956.10 m,含盐膏页岩微相。
Figure 2. Sedimentary microfacies types of carbonate-rich shale in upper submember of fourth member of Shahejie Formation in Dongying Sag, Bohai Bay Basin
表 1 渤海湾盆地东营凹陷沙河街组四段上亚段沉积微相组合
Table 1. Sedimentary microfacies combinations of upper submember of fourth member of Shahejie Formation in Dongying Sag, Bohai Bay Basin
物源供给 微相组合 成因相 微相类型及标志 生物群落 充填方式 过补偿 震荡深水页岩微相组合 远岸生物带,风暴沉积,浊流沉积 泥质页岩微相,介壳页岩微相,重力流水道微相,含膏盐页岩微相。水平纹层 鱼类,介形虫,盘星藻,软体类 进积 平衡充填 震荡半深水页岩微相组合 泥丘,微生物席,滑塌角砾 藻席微相,透镜状灰质页岩微相,白云质页岩微相。滑塌构造,交错纹层,波状纹层,透镜状纹层,压扁纹层等 介形类,渤海藻 加积 欠补偿 浅水蒸发岩微相组合 生物礁,粒屑滩,藻席,盐沼等 颗石藻页岩微相,生物礁滩微相,白云质页岩微相,含膏盐页岩微相。鸟眼构造,干裂纹,虫孔,含植物叶片的泥晶石灰岩 有孔虫,介形类,徳弗兰藻,陆生植物化石等 退积 -
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