元素地球化学在新区古环境重建中的应用——以珠江口盆地韩江15洼为例

Application of element geochemistry in paleoenvironment reconstruction in new area: A case study of Hanjiang 15 Subsag in Pearl River Mouth Basin

应用元素地球化学方法对珠江口盆地珠一坳陷东北部韩江凹陷新钻井H4开展了系统分析研究,在其元素地球化学分析结果的基础上,重点对韩江15洼沉积古环境进行了详细分析,初步探讨和阐明了韩江15洼始新世沉积环境及其纵向演化过程,并获得了以下重要成果与认识:(1)重建了韩江15洼始新统古水深、氧化还原条件、古气候、古盐度的演化历史;(2)韩江15洼始新统沉积期主要以浅水环境为主,水体富氧,但文昌组三段水体加深,以弱氧化环境为主;(3)文昌组沉积期气候偏干,进入恩平期气候向湿润转变;(4)韩江15洼文昌期受东南方向海侵影响,水体盐度增高,但恩平期未受海侵影响,以淡水环境为主;(5)根据元素地球化学判别结果、测井相及岩性特征,综合判识韩江15洼始新统文昌组上段(H4探井附近区域)主要为浅水三角洲沉积。上述研究成果及认识,对于深化韩江凹陷始新世沉积环境的认识及海侵影响分析等均具有一定的指导及参考意义。

In this paper, the elemental geochemistry method is used to systematically analyze and study the new drilled H4 in Hanjiang Sag,northeastern Pearl River Mouth Basin. Based on the results of elemental geochemistry analysis, the sedimentary paleoenvironment of Hanjiang15 subsag is analyzed in detail. The Eocene sedimentary environment and its vertical evolution process of Hanjiang 15 Subsag are preliminarily discussed and clarified. The following important achievements and understandings are obtained :(1) The evolution history of Eocene water depth, oxidation-reduction conditions, paleoclimate and paleosalinity in Hanjiang 15 Subsag is reconstructed.(2) The sedimentary period of Eocene in Hanjiang 15 Subsag is mainly shallow water environment, and the water body is rich in oxygen. However, the water body of the third member of Wenchang Formation is deepened, and the weak oxidation environment is the main environment.(3) The climate of Wenchang Formation was dry during the sedimentary period and changed to humid during Enping period.(4) The Wenchang Formation in Hanjiang 15subsag was affected by the southeast transgression during the sedimentary period, and the salinity of water increased. However, the sedimentary period of Enping Formation was not affected by the transgression, and the freshwater environment was dominated.(5)According to the results of element geochemical discrimination, logging facies and lithologic characteristics, the upper member of Wenchang Formation( near H4exploration well) of Eocene in Hanjiang 15 Subsag is mainly shallow water delta deposits. The above research results and understandings have certain guidance and reference significance for deepening the understanding of the Eocene sedimentary environment and the analysis of transgression influence in Hanjiang Subsag.