琼东南盆地北部新近系三亚组遗迹组构特征及其沉积环境^*

Ichnofabric characteristics and sedimentary environment of the Neogene Sanya Formation in northern Qiongdongnan Basin

摘要

琼东南盆地北部新近系地层厚度巨大,遗迹化石非常发育。在对7口取心井岩心详细观测的基础上,综合利用薄片分析、成像测井与相关实验等资料,对琼东南盆地北部新近系三亚组遗迹组构特征及其沉积环境进行了研究。结果表明: (1)琼东南盆地北部新近系三亚组共识别出遗迹化石14属,根据遗迹化石的类型、产状、丰度和分异度、扰动程度、生物潜穴之间的共生关系等,可划分出5种遗迹组构, 其中Ophiomorpha-Thalassinoides遗迹组构主要发育在临滨上部沉积环境中, Palaeophycus遗迹组构主要发育在临滨中部沉积环境中, Planolites-Thalassinoides遗迹组构主要发育在临滨下部沉积环境中, Phycosiphon-Planolites遗迹组构主要发育在浅海上部沉积环境中, Phycosiphon-Chondrites遗迹组构主要发育在浅海下部沉积环境中;(2)根据遗迹组构和测井相分析认为琼东南盆地北部新近系三亚组沉积环境为滨-浅海, 三亚组一段的沉积环境为由滨岸向浅海过渡,而三亚组二段的沉积环境为浅海;(3)综合岩相、生物化石、遗迹组构、测井相和沉积微相分析结果,建立了琼东南盆地北部新近系三亚组的沉积模式。本项研究对指导南海北部新近系的油气勘探具有重要的借鉴意义。

Abstract

The trace fossils are well developed in the Neogene strata with the huge thickness in northern Qiongdongnan Basin. Based on detailed observation of the cores from seven drilling wells,combining with the thin section analysis,imaging logging and related experiments,the ichnofabric characteristics and sedimentary environment of the Neogene Sanya Formation were studied in detail. The results show that a total of 14 genera of trace fossils have been identified in the Neogene Sanya Formation in northern part of the Qiongdongnan Basin. Based on the types,occurrence,abundance and diversity of trace fossils,biodisturbance degree,and symbiotic relationship between biological burrows,five ichnofabrics can be classified. Among them,the Ophiomorpha-Thalassinoides ichnofabric was mainly developed in the upper shoreface,the Palaeophycus ichnofabric was mainly developed in the middle shoreface,the Planolites-Talassionides ichnofabric was mainly developed in the lower shoreface,the Phycosiphon-Planolites ichnofabric is mainly developed in the upper shallow sea,and the Phycosiphon-Chondrites ichnofabric was mainly developed in the lower shallow sea. Based on analysis of the ichnofabrics and logging facies,it is believed that the coastal and offshore sedimentary environment was mainly dominated in the Neogene Sanya Formation in the study area. The first section of Sanya Formation transited from coast to shallow marine,while the second section of Sanya Formation was mainly dominated by shallow sea deposition. Based on the analysis of lithofacies,fossils,ichnofabric characteristics,logging facies and sedimentary microfacies of Sanya Formation,the sedimentary model of Neogene Sanya Formation in the northern part of the Qiongdongnan Basin has been established. It has an important guidance for the hydrocarbon exploration of the Neogene in the northern South China Sea.

关键词

遗迹组构 / 沉积环境 / 三亚组 / 新近系 / 琼东南盆地

Key words

ichnofabric / sedimentary environment / Sanya Formation / Neogene / Qiongdongnan Basin

基金资助

*国家自然科学基金项目(编号: 41472104,42272178)、河南省高校科技创新团队项目(编号: 21IRTSTHN007)和河南理工大学科技创新团队项目(编号: T2020-4)联合资助