Acta Petrolei Sinica ›› 2025, Vol. 46 ›› Issue (2): 355-371.DOI: 10.7623/syxb202502005

• PETROLEUM EXPIORATION • Previous Articles     Next Articles

Eocene palynoflora and paleoclimate reconstruction in Weixi’nan sag,Beibuwan Basin

Liu Zixuan1,2,3, Yan Detian2,3, Yu Jianxin4, Deng Yong5, Ding Yan2,3   

  1. 1. Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process, Ministry of Education(China University of Mining and Technology), Jiangsu Xuzhou 221116, China;
    2. Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Hubei Wuhan 430074, China;
    3. Hubei Provincial Key Laboratory of Oil and Gas Exploration and Development Theory and Technology, Hubei Wuhan 430074, China;
    4. School of Earth Sciences, China University of Geosciences, Hubei Wuhan 430074, China;
    5. Zhanjiang Branch, CNOOC China Limited, Guangdong Zhanjiang 524057, China
  • Received:2024-08-07 Revised:2024-10-24 Online:2025-03-13 Published:2025-03-13

北部湾盆地涠西南凹陷始新世孢粉植物群与古气候重建

刘紫璇1,2,3, 严德天2,3, 喻建新4, 邓勇5, 丁延2,3   

  1. 1. 中国矿业大学煤层气资源与成藏过程教育部重点实验室 江苏徐州 221116;
    2. 中国地质大学(武汉)构造与油气资源教育部重点实验室 湖北武汉 430074;
    3. 油气勘探开发理论与技术湖北省重点实验室 湖北武汉 430074 ;
    4. 中国地质大学(武汉)地球科学学院 湖北武汉 430074;
    5. 中海石油(中国)有限公司湛江分公司 广东湛江 524057
  • 通讯作者: 严德天,男,1977年12月生,2008年获中国科学院地质与地球物理研究所博士学位,现为中国地质大学(武汉)资源学院教授、博士生导师,主要从事沉积学、沉积地球化学和盆地分析工作。Email:yandetian@cug.edu.cn
  • 作者简介:刘紫璇,女,1996年7月生,2024年获中国地质大学(武汉)博士学位,现为中国矿业大学博士后,主要从事富有机质页岩形成机理方面的研究。Email:tbh493@cumt.edu.cn
  • 基金资助:
    中海石油(中国)有限公司湛江分公司项目"涠西南凹陷流沙港组古湖泊、古环境及沉积体系研究"(CCL2023ZJFN0420)资助。

Abstract: Sporopollen fossils play an important role in stratigraphy division and correlation, vegetation succession, and paleoclimate reconstruction. This study focuses on Liushagang Formation in the Weixi’nan sag of Beibuwan Basin, where palynological analysis was conducted to quantitively reconstruct the paleoclimate during its depositional period. The research results are as follows. (1) The sporopollen assemblage is mainly dominated by angiosperm pollen, with notable abundances of Quercoidites and Cupuliferoipollenites. Besides, the gymnosperm pollen is primarily represented by Abietineaepollenites and Piceaepollenites, while the fern spores are dominated by Polypodiaceaesporites. (2) Based on variations in sporopollen content and species composition, three sporopollen assemblages have been identified in Liushagang Formation, including Assemblage Ⅰ (Polypodiaceaesporites-Cupuliferoipollenites-Osmundacidites) in the middle-lower part of the third Member of Liushagang Formation, Assemblage Ⅱ (Quercoidites-Ulmipollenites-Pentapollenites) in the upper part of the third Member of Liushagang Formation to the upper part of the second Member of Liushagang Formation, and Assemblage Ⅲ (Leiosphaeridia-Granodiscus) in the top of the second Member of Liushagang Formation to the lower part of the first Member of Liushagang Formation. (3) Through analyzing the vegetation, humidity, and climate types of the nearest living relatives of sporopollen fossils, the vegetation and paleoclimate for each assemblage were quantitatively reconstructed. During the development of Assemblage Ⅰ, vegetation was dominated by deciduous and evergreen broad-leaved trees, with well-developed herbaceous plants. The content of mesophytic sporopollen was the lowest among the three assemblages, while that of helophytic and hygrophytic sporopollen is the highest, indicating a semi-humid subtropical climate. During the development of Assemblage Ⅱ, herbaceous plants declined, conifers and evergreen broad-leaved trees increased, mesophytic sporopollen rose, and helophytic types decreased, reflecting a semi-humid to semi-arid central subtropical climate. During the development of Assemblage Ⅲ, the evergreen broad-leaved trees continued to develop, and the content of mesophytic sporopollen further increased, indicating a sustained semi-humid to semi-arid subtropical climate. (4) Quantitative paleoclimate reconstruction using the coexistence approach reveals that during the deposition of Liushagang Formation, the mean annual temperature (MAT) ranged from 13.3 ℃ to 19.8 ℃, the warmest month mean temperature from 25.8 ℃ to 27.5 ℃, and the coldest month mean temperature from 1.9 ℃ to 11.9 ℃. Moreover, the mean annual precipitation (MAP) ranged between 797.5 mm and 1 113.2 mm, and the average maximum and minimum monthly precipitation ranged from 179 4 mm to 239.1 mm and from 10.2 mm to 11.3 mm, respectively. Climatic fluctuations occurred within the depositional period, with an overall trend of decreasing MAT and MAP from the third Member to the first Member of Liushagang Formation.

Key words: Beibuwan Basin, Weixi’nan sag, Liushagang Formation, sporopollen analysis, paleoclimate, coexistence approach

摘要: 孢粉在地层划分对比、植被演替和古气候恢复等方面具有重要意义。以北部湾盆地涠西南凹陷始新统流沙港组为研究对象,通过孢粉分析对流沙港组沉积期的古气候进行了定量恢复。研究结果表明:①流沙港组的孢粉类型以被子植物花粉为主,栎粉属和栗粉属含量较突出。裸子植物花粉以单束松粉属和云杉粉属为主,蕨类孢子以水龙骨单缝孢属为主。②根据孢粉含量及种属变化,将流沙港组划分为3个孢粉组合,其中,流沙港组三段中—下部为孢粉组合Ⅰ(Polypodiaceaesporites-Cupuliferoipollenites-Osmundacidites组合),流沙港组三段上部—流沙港组二段上部为孢粉组合Ⅱ(Quercoidites-Ulmipollenites-Pentapollenites组合),流沙港组二段顶部—流沙港组一段下部为孢粉组合Ⅲ(Leiosphaeridia-Granodiscus组合)。③根据孢粉对应的最近亲缘关系类群的生态、干湿度及气候条件,对不同孢粉组合的植被面貌和古气候进行了恢复。孢粉组合Ⅰ发育期,植被面貌以落叶阔叶树和常绿阔叶树为主,草本植物较发育,中生类孢粉含量在3个孢粉组合中最低,而沼生类和湿生类孢粉含量在3个孢粉组合中最高,指示该时期整体为半湿润的南亚热带气候;孢粉组合Ⅱ发育期,草本植物减少,针叶树和常绿阔叶树增多,中生类孢粉含量升高而沼生类孢粉含量降低,指示该时期整体为半湿润—半干旱的中亚热带气候;孢粉组合Ⅲ发育期,常绿阔叶树进一步扩张,中生类孢粉含量进一步升高,指示该时期整体为半湿润—半干旱的中亚热带气候。④共存因子分析法对流沙港组沉积期古气候进行定量恢复的结果认为,流沙港组沉积期的年平均温度为13.3~19.8 ℃,最热月平均温度为25.8~27.5 ℃,最冷月平均温度为1.9~11.9 ℃,年平均降水量为797.5~1113.2 mm,平均最大月降水量为179.4~239.1 mm,平均最小月降水量为10.2~11.3 mm,且流沙港组沉积期内部存在气候波动,从流沙港组三段沉积期到流沙港组一段沉积期整体表现为年平均温度和年平均降水量降低的趋势。

关键词: 北部湾盆地, 涠西南凹陷, 流沙港组, 孢粉分析, 古气候, 共存因子分析法

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