广西横县六景吉维特期腕足类Rhynchospirifer和Stringocephalus的环境元素和稳定同位素生物效应

利用现代生物学研究模式，对比了吉维特期不同层位中原地埋藏的Rhynchospirifer属壳体次生层（纤维层）与其围岩之间元素和碳、氧稳定同位素变化，探讨了不同时期同属腕足类的古环境元素和稳定同位素生物效应及其变化趋势；通过对比同层位Rhynchospirifer属和Stringocephalus属化石壳体次生层及其围岩之间的元素变化，探讨了同时期、同生境不同属腕足类的古环境元素生物效应。当环境元素含量发生变化时，Rhynchospirifer因其对各元素生态幅和耐受限度的差异而并不完全对环境中各化学因子的变化产生一致性的响应，而当跨越牙形石Lower varcus和Middle varcus亚带后，其属内适应性变异造成属内特异性选择发生一定程度的变化。Stringocephalus和Rhynchospirifer对其耐受限度较小的Al，K，Sc，Co等元素保持较高的属内有效性和特异性选择；对其耐受限度和生理有效性中等、可被其他元素替代的Mn，P，Ni，Cu等元素，其特异性选择有限，并可能与有效性原则和丰度作用相叠加；对于生态幅较宽的V，Cr，Sr，Pb等元素，属内的特异性选择弱化。当与同时期生态龛比邻属种对比时，彼此的生态幅发生部分重叠，部分元素如Mg，Na，As，Pb等的含量甚至较不同时期同属生物更加接近。Rhynchospirifer壳体次生层与其围岩碳、氧同位素比值分别保持着较好的同步性和一致性，即不存在碳、氧同位素生物效应。

Life Effects of Brachiopoda Rhynchospirifer and Stringocephalus of the Givetian Period on the Environmental Elements and Stable Isotopes at Liujing Section,Guangxi,China

Taking current biological model as an example, the life-effects on environmental elements and stable isotopes and their change tendencies of different times are discussed by a comparison of element contents and isotope compositions of the second layer of in-situ-buried brachiopoda Rhynchospirifer and their host rocks from different strata of the Givetian Period,Middle Devonian, Liujing section. The coeval life-effects on the environmental elements are discussed by a comparison of element contents of the second layer of in-situ-buried brachiopoda Rhynchospirifer and Stringocephalus and their host rocks from the same life environment. Responding to the changes of environmental elements, the Rhynchospirifer had different changes for different elements. This is because that, on the one hand, it had different ecological amplitudes and endurances for different elements, on the other hand, with the time span from the Lower varcus to the Middle varcus, its in-genus evolution had some consequence to its in-genus specific selectivities. Rhynchospirifer and Stringocephalus kept a higher in-genus effective and specific selectivities on their narrow endurancing elements such as Al, K, Sc, Co. Their specific selectivities were limited or some times overlapped by effective principle and abundance effect to the moderate physiological effective and endurancing elements such as Mn, P, Ni,Cu. For the wide ecological amplitude elements such as V, Cr, Sr, Pb, the in-genus specific selectivities were weak. Parts of the ecological amplitudes were overlapped and contents of certain elements such as Mg, Na, As, Pb were even higher than those of the same genus when the two coeval genus shared the same living environment by the way of two nearby niches. The δ13C and δ18O of the second layer of Rhynchospirifer kept good consistence to their host rocks respectively, showing that there was no life effect on the δ13C and δ18O of their living environment.