北戴河红色风化壳地球化学特征及气候环境意义

Geochemical characteristics and climatic-environmental significance of the red weathering crusts in the Beidaihe coast, North China

风化壳地球化学特征具有环境指示意义。用X射线荧光光谱法（XRF）和X射线衍射法（XRD）分别测试了秦皇岛北戴河燕山大学北侧红色风化壳（简称燕大风化壳）主量元素和粘粒粘土矿物。结果表明：除Ca外，Si、Al、Fe、Na、K的含量在风化壳上均有不同程度的波动，其中Si、Na、K波动轨迹基本一致，Al、Fe则与其相反，相关性分析显示SiO2与Al2O3、TFe、Fe2O3，Al2O4与TFe、Fe2O3，Na2O与CaO具有较好相关性；粘土矿物组合为1．4nm过渡矿物（25％～45％）＋伊利石（10％～20％）＋伊蒙混层矿物（20％～35％）＋高岭石（15％～30％），矿物演化系列是长石、黑云母→（蛭石→1．4nm过渡矿物）→（伊利石）→高岭石。与粘土矿物以1：1型高岭石为主的富铝化南方红色风化壳相比，燕大风化壳Si淋失度，Fe、Al富集度，矿物演化程度都较低，属硅铝化风化壳。燕大风化壳是上新世暖温带到北亚热带过渡型气候的风化产物，与现代秦皇岛暖温带半湿润型气候不同，这反映第四纪以来该区气候干旱因子增多。CIA、S／A等指示的风化强度异常表明，燕大风化壳形成后至少遭受过两次构造抬升，为剥蚀型风化壳，反映该区新构造运动间歇式上升的特点。

The geochemical characteristics of the weathering crusts are used to monitor environmental changes. We have measured the major elements and identified clay minerals of the red weathering crusts to the northern part of Yanshan University, Beidaihe coast, Qinhuangdao, North China, by means of X-ray fluorescence and X-ray diffraction analysis. These studies show that the red weathering crusts exhibit fluctuations in the contents of Si, Al, Fe, Na and K with the exception of Ca The fluctuation patterns of Si, Na and K are basically consistent, whereas those of Al and Fe are negatively correlated with Si, Na and K. Correlation analysis suggests that there are relatively closer correlations between SiO2 and Al2O3-TFe-Fe2O3, Al2O3 and TFe-Fe2O3, and Na2O and CaO, respectively. Clay mineral assemblages include 1.4 nm transitional minerals（25%-45% ） ＋ Illite（ 10 %-20% ） ＋ Illite-Smectite layer-mixed minerals（20%- 35% ） ＋ Kaolinite（15%-30 %）, wit h a mineral paragenetic sequence of. Feldspar, Biotite→ （Vermiculites1.4 nm transitional minerals）→（Illite）→Kaolinite. Compared with red weathering crusts in the south China, where the clay mineral is mainly represented by 1：1 type Kaolinite, the red weathering crusts in the Beidaihe coast have relatively lower levels of mineral evolution, deficient in Si and enrichment in Fe and Al. It is suggested that the red weathering crusts in the Beidaihe coast belong to a sialic weathering crust. The red weathering crusts in the Beidaibe coast, a product of transitional climate between a warm temperate zone and a North subtropical zone during the Pliocene, is incompatible with modern subhumid climate in Qinhuangdao, which reflects the increase of arid climatic factors since the Quaternary. The analysis of CIA and S/A shows that there were at least two tectonic uplifts after the red weathering crusts were formed, which changed it into a denuded weathering crust, reflecting the characteristics of the neotectonic movement.