摘要
三水盆地古近系莘庄组顶部至土布心组红岗段的全岩碳酸盐稳定同位素分析结果表明其形成期间经历了多次环境变迁。根据碳酸盐氧、碳同位素比值及其相互关系的变化 ,可识别三次海水入侵期。其时δ18O值大幅度向正值漂移。而由于受有机质降解的影响 ,相应时期的δ13 C均表现为低值。在不直接受海洋影响的湖相沉积阶段 ,δ18O与δ13 C的相关程度虽然未达到典型的封闭型湖泊水平 ,但仍呈现一定的正相关变化 (r =0 .6 5 ) ,表明其湖水滞留时间较长。而频繁出现的石膏薄层沉积也指示湖盆的封闭性较好。这些均表明这一时期的三水盆地可能是一周期性封闭型湖泊。其稳定同位素组成主要受制于蒸发量 /降雨量平衡的变化。而δ13 C比值往往还受有机质活动的控制 ,更多的是反映有机质生产力。
The lacustrine environmental evolution of early Palaeogene Sanshui Basin has been established based on stable isotopic data from bulk carbonates from the Upper Xinzhuang Formation and the Honggang Member of the Buxin Formation (major oil source bed of the Basin). Three stages, when the basin had connection with the sea, have been recognized. With the transgression of sea waters and increased regional aridity, δ 18 O values showed a sharp positive shift, accompanied by the deposition of dolomites, whereas δ 13 C displayed lower values due to decomposition of organic matter that occurred at this time, which resulted in water rich in 13 C-depleted CO 2 . During the intervals without connection with the sea, the δ 18 O and δ 13 C pattern showed a positive covariance (r = 0.65). This moderately high covariance, although poorer than that reported from typical closed lakes, suggests that the basin had, like most closed lakes, relatively long residence times. Gypsum deposits that occurred frequently in the core section also indicate hydrological closure conditions. This means that the Sanshui Basin was probably a periodic hydrologically closed lake during these times. The stable isotopic compositions of carbonates were mainly influenced by variations in evaporation/precipitation balance. Higher δ 18 O values indicate overall increase in E/P ratios, low lake levels and concentrated waters.Lower δ 18 O values suggest decrease in E/P ratios and a large fluvial inflow and a subsequent high stand of water level. δ 13 C shows more variability than δ 18 O, which implies that δ 13 C was also controlled by organic activity and usually reflects the productivity, burial vs. reoxidation of organic material.
出处
《沉积学报》
CAS
CSCD
北大核心
2004年第1期36-40,共5页
Acta Sedimentologica Sinica
基金
国家自然科学基金项目 (批准号:40 2 72 0 1 1 )
广东省自然科学基金项目 (批准号:0 0 1 2 0 3)资助
关键词
氧碳同位素
碳酸盐
湖相沉积
古近系
三水盆地
stable isotopes, carbonates, lacustrine sediments Palaeogene, Sanshui Basin
