广东三水盆地古近系心组生油层的元素地球化学特征

沉积物的元素地球化学特征是对沉积盆地水体环境以及古气候条件变化的响应。本文根据元素（Al、Fe、Mg、Ca、K、Na、P、V、Ni、Co、Cr、Cu、Zn、Sr、Ba、Cd、Li、Mn、Pb、Ti）的含量及其比值（Al/Ti、Fe/Mn、Sr/Ba、Mg/Ca、Sr/Ca、Na/Ca、V/Cr、Ni/Co、Ni/V）的变化，对三水盆地古近系心组红岗段生油层的沉积条件进行了系统分析。心组红岗段下部（亚段A）表现为较稳定的地球化学特征。各元素丰度及其比值指示这一时期陆源输入持续较高、且物源组成变化不大。由于海水入侵的影响，湖盆水体盐度相对较高，底部水体以弱氧化条件为主，O₂-H₂S界面位于水/沉积物界面附近。红岗段中上部（亚段B、C）的元素地球化学特征变化较为频繁且幅度很大，反映古气候和湖盆沉积条件的迅速变迁。在潮湿气候条件下，沉积物的地球化学特征表现为以Al、Ti为代表的外源元素含量及其比值较高，而Mg、Ca等盆内化学沉积元素含量较低。古氧气指标指示底部水体为还原环境，有利于有机质保存。因而，相应于较高的有机碳含量。在间歇性干旱时期，陆源输入减少，外源元素含量及其比值显著降低。随着蒸发作用的加强，水体盐度加大，内源元素丰度以及Mg/Ca、Sr/Ba、Sr/Ca和Na/Ca比值大幅度上升。底部水体为氧化环境，O₂-H₂S界面多位于水/沉积物界面或沉积物中。上述两种气候条件在红岗段中上部沉积时期交替出现。红岗段沉积后期由于淡水的长期输入，湖水出现逐渐淡化趋势。

Elemental geochemistry and sedimentary environments of soure rocks of the Buxin Formation of Eocene in Sanshui Basin,Guangdong Province

The main source rocks in the Sanshui Basin are developed in the Honggang Member of the Buxin Formation of Eocene.This work aims at assessing the sedimentary environments of these source rocks based on elemental geochemical data.The distributions of elements (Al,Fe,Mg,Ca,K,Na,P,V,Ni,Co,Cr,Cu,Zn,Sr,Ba,Cd,Li,Mn,Pb and Ti) and elemental ratios (Al/Ti,Fe/Mn,Sr/Ba,Mg/Ca,Sr/Ca,Na/Ca,V/Cr,Ni/Co and Ni/V) serve as proxies for palaeoenvironmental conditions.Elemental concentration and ratios in submember A indicate higher terrigenous fluxes with relatively constant chemical composition and low-oxygen bottom waters with higher salinity than the other lithozones.Highly saline bottom waters were probably the consequence of intermittent sea water incursions.Submembers B and C are characterized by large variations in geochemical features,which reflect rapid fluctuations in palaeoclimate and sedimentary conditions.During humid intervals,elements that are usually enriched in terrestrial detrital minerals,such as Al and Ti,and Al/Ti ratios show high values,while endogenic elements,represented by Mg and Ca,have low concentrations.Palaeo-oxygenation indices suggest anoxic conditions developed in bottom waters,which were favourable for organic matter preservation.Consequently,a higher organic carbon content is observed.During intervals of dry climatic conditions,characterized by reduced terrestrial input,the concentration of terrigenous elements and Al/Ti ratios decreased.Increasing evaporation and salinity resulted in high values of endogenic elements and high Mg/Ca and Sr/Ba ratios.Palaeoredox proxies indicate prevailing oxidative environments developed in bottom waters.Salinity indices for the uppermost part of the Honggang Member show lower values,suggesting that an increasing input of fresh waters caused freshening of the lake waters.