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川西南阿什及尔期地层中的全岩REE分配模式显示 ,含有浮游笔石和小型无铰纲腕足类的黑色页岩具有较低的Ce异常值 (0 .6 2～ 0 .74) ,而含有底栖三叶虫、有铰纲腕足类和藻类的非黑色页岩则具有较高的Ce异常值 (0 .92～ 1.30 )。Ce与其他元素的相关分析进一步揭示 ,Ce与Fe的相关性最好 (r =0 .85 ) ,与P的相关性次之 (r =0 .6 1) ,与Al的相关性较差 (r =0 .2 9) ,而与Mn和Ca几乎不相关 (r =0 .14,r =- 0 .0 2 )。实际观察可能表明 ,研究区底层水体在氧化和碱性条件下 ,Ce氧化为Ce4 + 并进入Fe的氢氧化物和磷酸盐的晶格中 ,或者被吸附到它们的表面 ,造成Ce在氧化水体中呈现负异常而在同期氧化沉积物中呈现正异常或负异常不明显 ;相反 ,在还原和酸性条件下 ,Ce在水体中以 +3价状态富集 ,引起Ce在同期缺氧沉积物中呈现明显负异常。作为古海水氧化还原指示的全岩Ce异常 ,通常限定于解释远洋细粒沉积物的沉积环境。我们的研究结果说明 ,移去化石骨骼 (通常是磷酸盐化石骨骼 )的浅海细粒沉积物同样可以用于全岩REE分析 ,以获得可靠的能够指示古海水氧化还原条件变化的Ce异常
The whole-rock REE distribution pattern in the Ashe-Erh stratigraphy in the southwestern Sichuan Basin shows that the black shale with buoyant penoliths and small-sized non-hinged brachiopods has a lower Ce anomaly value (0.626-0.74) Non-black shales with benthic trilobites, hinge brachiopods, and algae have high Ce anomalies (0.92-1.30). The correlation analysis between Ce and other elements further revealed that the correlation between Ce and Fe was the best (r = 0.85), followed by P (r = 0.61), and the correlation with Ce was poor r = 0.29), but little correlation with Mn and Ca (r = 0.14, r = -0.02). The actual observations may indicate that under the oxidation and alkaline conditions, Ce is oxidized to Ce4 + and enters the crystal lattice of Fe hydroxide and phosphate, or adsorbed to their surface, resulting in the formation of Ce in the oxidation of water In the same period of oxidation sediments showed positive or negative anomalies is not obvious; the contrary, in the reduction and acidic conditions, Ce in the water state +3 valence state, causing Ce in the same period of anoxic sediments Showing a significant negative anomaly. The whole-rock Ce anomaly, which is indicative of ancient seawater redox-reduction, is usually limited to interpreting sedimentary environments of oceanic fine-grained sediments. Our results suggest that shallow-sea fine-grained sediments removed from fossil bones (usually phosphate fossil bones) can also be used for whole-rock REE analysis to obtain reliable Ce anomalies that can indicate changes in redox conditions in paleo-seawater