渤海湾盆地古近纪沙三、四段沉积期古盐度不均衡性研究

渤海湾盆地不同凹陷区钻井岩芯资料显示,古近纪沙三、沙四段沉积的泥岩、灰岩、云岩、膏岩多呈现相互间隔的韵律层分布。但在不同凹陷及各洼陷内,其发育的厚度、缺失程度以及韵律的完整性却是不尽一致的。通过对孢粉资料的分析发现,当时的古气候在全盆地基本趋于稳定,干、湿程度的微弱变化不足以引发沉积剖面上如此大的岩性差异。对比下辽河、东营、沾化和东濮凹陷的沉积记录和古盐度数据,发现各地岩性组合的不一致性主要是由于各地湖盆古盐度差异所致。综合各项数据分析推断,沉积时期盆地东北部隆-堑夹持区下辽河凹陷(上游)的动态淡水不断向盆内注入,最终在西南部低洼区东濮凹陷(下游)汇集,造成了盆内咸化环境产生了较大的不均衡性。上游区咸化环境被淡水稀释,盐岩类型单一、厚度小;下游区则由于较稳定的高盐度环境,在遇干旱气候时,盐、膏层大量析出,而位处中游的东营、沾化凹陷则呈现由淡趋咸的过渡状态。高盐度咸化环境有利于有机质的保存,能够促成烃类的早生早排,对规模油气资源量的形成极为有利。

The Imbalance Property of Ancient Salinity in Bohaiwan Basin during Es3-Es4 Stage in the Paleogene

From the drilling core data in different sags within Bohaiwan Basin, the rhythmic layered mudstone, limestone, dolomite, gypsum which had deposited at the Paleogene Es₃-Es₄ stage, was inter-layer distribution for each other. The rock thickness, whether or not the missing one, or the prosodic integrity, is inconsistent in the different sags or dips. Through the analysis of pollen data, the weak degree change between drought and wetting can't result in the huge difference of the deposition profile under a condition of the stable ancient climate. According to the deposition record and ancient salinity period of Xialiaohe, Dongying, Zhanhua and Dongpu sags, the result was founded that the different lithological combination is due to the different ancient salinity from each basin. Comprehensive analysis and inference, during the deposition of the Es₃-Es₄ stage, dynamic fresh water is injected into the basin, from Northeast Xialiaohe sag which is upstream region clamped by uplift and rift valley. Finally, water is collected in the southwest of the low-lying areas, the downstream region, Dongpu sag. The salty environment in the basin is not balanced. In the upstream region, salty environment is diluted by fresh water, single rock type and low thickness. In the downstream region, the high salinity environment is stable, and salt rock and gypsum rock strata are well developed when it comes to a dry climate. In the middle reaches of Dongying and Zhanhua sags, water is sometimes too fresh, sometimes too salty, and sometimes in transient state. Salty environment of high salinity is favorable for the preservation of organic matter, and it is capable of contributing to the early discharge of hydrocarbons. The salty environment is favorable for the formation of the oil and gas resources.