珠江口盆地白云凹陷恩平组泥岩元素地球化学特征及环境指示意义

Element geochemistry of the Enping Formation in the Baiyun Sag of Pearl River Mouth Basin and their environmental implications

泥岩的元素特征对沉积环境变化有较高的灵敏度,能够较好地保存原始沉积记录。为了明确白云凹陷恩平组烃源岩发育环境,选取凹陷内5口钻井泥岩样品进行元素测试。利用元素地球化学方法,系统分析白云凹陷各洼陷恩平期古水深、古氧相、古气候、古盐度和埋藏效率等古环境指标,结果表明:白云西洼处于水深较深、气候偏冷潮湿、还原性弱的淡水环境,埋藏效率相对最低;白云东洼处于水深较浅、气候湿热、亚还原半咸水环境,埋藏效率高;白云主洼处于水深相对最深、暖湿气候、亚还原—还原的淡水环境,埋藏效率相对中等;白云南洼处于水深总体较浅、暖湿气候、亚还原环境,咸水—半咸水—淡水均有分布,埋藏效率总体趋好。环境恢复结果显示白云主洼、白云东洼和白云南洼恩平期烃源岩的形成和保存条件较好,白云西洼相对较差。

The element composition of mudstone may well preserve the original sedimentary information and is highly sensitive to the changes of sedimentary environment.In order to define the depositional environment of source rocks of the Enping Formation in the Baiyun Sag,mudstone samples from 5 drilling holes were selected for analysis of element composition.Studied are such paleoenvironmental parameters as paleo-water depth,paleo-oxygenation facies,paleoclimate,paleosalinity and burial efficiency during the Enping period in the Baiyun Sag.The results indicate that the West Baiyun Sub-sag was then a deep fresh water environment under cold-wet climate,weak reducibility,and lowest burial efficiency;the East Baiyun Sub-sag was located in the partly salted water environment under shallow water depth,wet-hot climate,weak reducibility and high burial efficiency;the Main Baiyun Sub-sag is located in a fresh water environment with deep water depth,warm-wet alternative climate,weak reducibility-reducibility and moderate burial efficiency,while the South Baiyun Sub-sag was located in an environment with generally shallow water depth,warm-wet climate and sub reducing environment,where salt water,semi salt water and fresh water are all observed,and fluctuated relatively high burial efficiency.The above environmental parameters reveal that the genetic and preservative conditions of source rocks in the Main Baiyun Sub-sag,East Baiyun Sub-sag and South Baiyun Sub-sag are highly qualified and much better than those in the West Baiyun Sub-sag.