珠江口盆地陆丰南地区文昌组沉积古环境恢复及烃源岩有机质富集主控因素研究

doi:10.13745/j.esf.sf.2023.2.74

摘要/Abstract

摘要：

文昌组为陆丰南地区主力烃源岩发育层段,为了恢复文昌期沉积古环境,探讨优质烃源岩有机质富集主控因素,选用166组文昌组泥岩样品的主、微量元素测试数据,采用元素地球化学方法,在研究区首次详尽分析文昌期不同次洼、不同层段的古盐度、古气候、古水深和古氧相的纵横向演变规律,并探讨部分钻井出现盐度异常的原因及三芳甲藻甾烷、球藻对古环境的指示意义,结合TOC、古生产力和陆源输入变化研究,明确了研究区优质烃源岩的主控因素。结果表明:陆丰南地区始新统文昌组沉积期水体以淡水环境为主,局部层段盐度微弱增加,垂向上,从文四段向文一+二段水体盐度逐渐降低,横向上,文四段沉积期,陆丰15洼水体盐度最高,文三段—文一+二段沉积期,陆丰13东洼水体盐度较高。推测陆丰南地区文昌组水体盐度变化受到海侵影响,文四段沉积期,海侵影响主要集中在陆丰15洼,文三段沉积期,海侵影响扩大至陆丰15洼和陆丰13东洼东侧,进入文一+二段沉积期,受海侵影响程度较小。球藻及三芳甲藻甾烷在研究区不能作为水体咸化或者海侵的判别指标,球藻含量变化与古气候、古生产力、古水深关系密切,受古盐度变化影响有限。陆丰南地区文四段沉积期古气候温湿,古水深最大,还原性最强,进入文三段、文一+二段,气候温湿程度、水深和还原性均有所降低;文四段沉积期陆丰13东洼水深最大,其次为陆丰15洼,还原性陆丰13东洼最强,其次为陆丰13西洼。文昌组烃源岩有机质富集主要受控于古生产力和古陆源输入,其次受古气候和古水深控制,古氧相变化对有机质富集控制作用较弱,高古生产力主导着文昌组优质烃源岩的形成及分布,主要发育生产力富集模式。

关键词: 陆丰凹陷, 文昌组, 元素地球化学, 沉积古环境, 光面球藻, 古生产力, 烃源岩

Abstract:

The Wenchang Formation is the main source rock development interval in the southern Lufeng area. In order to restore the sedimentary paleoenvironment of the Wenchang period and explore the main controlling factors of organic enrichment in high-quality source rocks, the major and trace element data of 166 mudstone samples from the Wenchang Formation are analyzed. The elemental geochemical method is used to analyze the paleosalinity, paleoclimate, paleowater depth and the vertical and horizontal evolution of the paleo-oxygen phases in different subsags and different intervals of the Wenchang period for the first time in the study area. The causes of salinity anomalies in some wells and the indicative significance of triaromatic steranes and chlorella to the paleoenvironment are discussed; combined with TOC, paleoproductivity and terrestrial input changes, the main controlling factors of high-quality hydrocarbon source rocks in the study area are clarified. The results show that the water body of the Eocene Wenchang Formation is mainly freshwater during the deposition period, with slight increase in salinity in the local layer. Vertically, the salinity of the water body gradually decreases from the 4^th to the 1^st+2^nd members of the Wenchang Formation; horizontally, water salinity is highest in the Lufeng 15 subsag during deposition of the 4^th member, and relatively high in the Lufeng 13 eastern subsag during deposition of the 3^rd to the 1^st +2^nd members. It considers the change in water salinity in the Wenchang Formation is due to transgression effect, where water transgression is mainly concentrated in the Lufeng 15 subsag during deposition of the 4^th member, and expands to the eastern Lufeng 15 subsag and Lufeng 13 eastern subsag during deposition of the 3^rd member. Granodiscus and triaromatic dinoflagellate sterane cannot be used as indicators of water salinization or transgression in the study area. The change in Granodiscus content is closely related to paleoclimate, paleoproductivity and paleowater depth, but not much affected by paleosalinity changes. During deposition of the 4^th member, the paleoclimate was warm and humid, paleowater depth the largest, and paleowater reducibility the strongest; whilst in the 3^rd and 1^st+2^nd members, all three indicators decrease in values. During the deposition of the 4^th member, the water depth in the Lufeng 13 eastern subsag is the largest, followed by Lufeng 15 subsag; in the Lufeng 13 eastern subsag paleowater reducibility is the strongest, followed by Lufeng 13 western subsag. Organic enrichment in the source rocks of the Wenchang Formation is mainly controlled by paleoproductivity and paleocontinental input, followed by paleoclimate and paleowater depth. The change in paleooxygen phase has weak impact on organic enrichment. High paleoproductivity is the dominating factor controlling the formation and distribution of high-quality source rocks in the Wenchang Formation, mainly by influencing the modes of organic enrichment.

Key words: Lufeng Sag, Wenchang Formation, element geochemistry, sedimentary palaeoenvironment, Granodiscus, paleoproductivity, source rocks

中图分类号:

何雁兵, 雷永昌, 邱欣卫, 肖张波, 郑仰帝, 刘冬青. 珠江口盆地陆丰南地区文昌组沉积古环境恢复及烃源岩有机质富集主控因素研究[J]. 地学前缘, 2024, 31(2): 359-376.

HE Yanbing, LEI Yongchang, QIU Xinwei, XIAO Zhangbo, ZHENG Yangdi, LIU Dongqing. Sedimentary paleoenvironment and main controlling factors of organic enrichment in source rocks of the Wenchang Formation in southern Lufeng, Pearl River Mouth Basin[J]. Earth Science Frontiers, 2024, 31(2): 359-376.

图/表 13

图1 珠江口盆地纲要图(a)、陆丰凹陷构造单元划分(b)和古近系地层综合柱状图(c)

Fig.1 Outline map of the Pearl River Mouth Basin (a), structural unit division of Lufeng Sag (b) and comprehensive column chart of Paleogene stratum (c)

图2 珠江口盆地陆丰南地区文昌组Couch法计算古盐度值

Fig.2 Calculation of paleosalinity by Couch Method in Wenchang Formation in South Lufeng Depression, Pearl River Mouth Basin

图3 珠江口盆地陆丰南地区不同次洼文昌组文四段—文一+二段古盐度指标

Fig.3 Paleosalinity index of 4th-1st members of Wenchang Formation in the southern Lufeng area, Pearl River Mouth Basin

图4 珠江口盆地陆丰南地区各次洼古气候指标

Fig.4 Paleoclimate indexes of each subsag in the southern Lufeng area, Pearl River Mouth Basin

图5 珠江口盆地陆丰南地区文昌组文四段—文一+二段古水深指标

Fig.5 Paleodepth index of 4th-1st members of Wenchang Formation in the southern Lufeng area, Pearl River Mouth Basin

图6 珠江口盆地陆丰南地区文昌组文四段—文一+二段古氧相判别指标

Fig.6 Paleo oxygen facies discrimination index of 4th-1st members of Wenchang Formation in the southern Lufeng area, Pearl River Mouth Basin

图7 珠江口盆地陆丰南地区文昌组烃源岩甾类化合物质量色谱图

Fig.7 Mass chromatogram of steroids in source rocks of Wenchang Formation in the southern Lufeng area, Pearl River Mouth Basin

图8 珠江口盆地陆丰凹陷陆丰13东洼LF13E-6、LF13E-8和LF13E-9井文昌组地球化学指标及古生物变化图

Fig.8 Geochemical indexes and paleontological changes of Wenchang Formation of Wells LF13E-6, LF13E-8 and LF13E-9 in Lufeng 13 East subsag, Lufeng Sag, Pearl River Mouth Basin

图9 珠江口盆地陆丰南地区文昌组古盐度与古气候、古水深相关性

Fig.9 Correlation of paleosalinity with paleoclimate and paleowater depth in the southern Lufeng area, Pearl River Mouth Basin

图10 珠江口盆地陆丰南地区文五段—文一+二段古生产力指标

Fig.10 Paleoproductivity index of 5th-1st members of Wenchang Formation in the southern Lufeng area, Pearl River Mouth Basin

图11 珠江口盆地陆丰南地区文四段—文一+二段古陆源输入

Fig.11 Paleo terrigenous input of 4th-1st members of Wenchang Formation in the southern Lufeng area, Pearl River Mouth Basin

图12 珠江口盆地陆丰南地区文昌组泥岩有机碳(TOC)含量与古环境、古生产力、陆源碎屑输入指标相关性图

Fig.12 Correlation between organic carbon (TOC) content of Wenchang Formation mudstone and paleoenvironment, paleoproductivity, and input indexes of terrigenous clastic rocks in the southern Lufeng area, Pearl River Mouth Basin

图13 珠江口盆地陆丰南地区LF13E-10井和LF15-2井文昌组元素地球化学指标及有机质丰度变化图

Fig.13 Variation diagram of element geochemical discrimination index and organic matter abundance in Wenchang Formation of Well LF13E-10 and Well LF15-2 in the southern Lufeng area, Pearl River Mouth Basin

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