Trace and rare earth elements (REEs) are considered to be reliable indicators of chemical processes for the evolution of carbonate systems. One of the best examples of ancient carbonate successions (Berdiga Formation) is widely exposed in NE Turkey. The Lower Cretaceous limestone succession of Berdiga Formation may provide a case study that reveals the effect of ocean paleoredox conditions on diagenetic alteration. Measurement of major, trace and REEs was carried out on the Lower Cretaceous limestones of the Berdiga Formation, to reveal proxies for paleoredox conditions and early diagenetic controls on their geochemistry. Studied micritic limestone microfacies (MF-1 to MF-3) indicate deposition in the inner platform to a deep shelf or continental slope paleoenvironment during the Hauterivian-Albian. The studied limestone samples mainly exhibit low Mg-calcite characteristics with the general chemical formula of Ca_{98.35–99.34}Mg_0.66–1.65(CO₃). They are mostly represented by a diagnostic REE seawater signature including (1) slight LREE depletion relative to the HREEs (ave. 0.72 of Nd/Yb_N and ave. 0.73 of Pr/Yb_N), (2) negative Ce anomalies (Ce/Ce* = 0.38–0.81; ave. 0.57), (3) positive La anomaly (La/La* = 0.21–3.02; ave. 1.75) and (4) superchondritic Y/Ho (ave. 46.26). Studied micritic limestones have predominantly low Hf (bdl to 0.5 µg/g), Sc (bdl to 2 µg/g) Th (bdl to 0.9 µg/g) contents suggesting negligible to minor shale contamination. These findings imply that micritic limestones faithfully record chemical signals of their parental and diagenetic fluids. The succession also exhibits high ratios of Eu/Eu* (1.01–1.65; ave. 1.29 corresponding to the positive Eu anomalies), Sm/Yb (1.26–2.74; ave. 1.68) and La/Yb ratios (0.68–1.35; ave. 0.9) compared to modern seawater and wide range of Y/Ho ratios (29.33–70.00; ave. 46.26) which are between seawater and hydrogenetic Fe-Mn crusts. Several lines of geochemical evidence suggest water-rock interaction between parental seawater and basaltic rocks at elevated temperatures triggered by hydrothermal activity associated with Early Cretaceous basaltic magma generation. The range of Ce/Ce* values is suggestive of mostly oxic to dysoxic paleoceanographic conditions, with a sudden change to dysoxic conditions (Ce/Ce* = 0.71–0.81), in the uppermost part of the MF-1. This is followed by an abrupt deepening paleoenvironment with a relative increase in the oxic state of the seawater and deposition of deeper water sediments (MF-2 and MF-3) above a sharp transition. The differences in microfacies characteristics and foraminifera assemblage between MF-1 and overlying facies (MF-2 and MF-3) may also confirm the change in paleoceanographic conditions. Therefore, REEs data obtained from studied limestones have the potential to contribute important information as to regional paleoceanographic conditions of Tethys during an important period in Earth history.

中文翻译：

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土耳其东北部古米什哈内白垩纪下白垩统石灰岩演替的稀土元素特征：对海洋古氧化还原条件和成岩作用的影响

痕量和稀土元素（REEs）被认为是碳酸盐系统演化过程中化学过程的可靠指标。土耳其东北部广泛暴露了古代碳酸盐岩演替的最佳实例之一（贝尔迪加组）。Berdiga组的下白垩统灰岩演替可能提供了一个案例研究，揭示了海洋古陆条件对成岩作用的影响。在Berdiga组的下白垩统石灰石上进行了主要，痕量和REE的测量，以揭示古近氧条件的代用物及其早期成岩控制的地球化学特征。研究的微影石灰岩微相（MF-1至MF-3）表明，在上特勒期-阿尔布期期间，内部平台沉积到深层架或大陆斜坡古环境。_{98.35–99.34} Mg _0.66–1.65（CO ₃）。它们主要由诊断性的REE海水特征表示，包括（1）相对于HREE的轻度LREE损耗（Nd / Yb _N的平均0.72和Pr / Yb _N的平均0.73）。），（2）负Ce异常（Ce / Ce * = 0.38–0.81;平均0.57），（3）正La异常（La / La * = 0.21–3.02;平均1.75）和（4）超软骨质Y /何（平均46.26）。研究的微影石灰岩的Hf（bdl至0.5 µg / g），Sc（bdl至2 µg / g），Th（bdl至0.9 µg / g）含量低，表明对少量页岩的污染可以忽略不计。这些发现表明，微晶灰岩忠实地记录了其母体和成岩流体的化学信号。演替过程还显示出较高的Eu / Eu *（1.01–1.65;平均值1.29，对应于正Eu异常），Sm / Yb（1.26–2.74;平均值1.68）和La / Yb比率（0.68–1.35; ave）高比率。 0.9）与现代海水相比，在海水和富氢Fe-Mn地壳之间的Y / Ho比范围很广（29.33–70.00；平均46.26）。几条地球化学证据表明，在高温下母体海水与玄武岩之间的水-岩相互作用是由与白垩纪玄武质岩浆生成有关的热液活动引发的。Ce / Ce *值的范围表明大多数是有氧的到低氧的古海洋学条件，并且在MF-1的最上部突然转变为低氧的条件（Ce / Ce * = 0.71-0.81）。随之而来的是突然的加深古环境，海水的含氧量相对增加，并且在急剧转变以上沉积了较深的水沉积物（MF-2和MF-3）。MF-1和上覆相（MF-2和MF-3）之间的微相特征和有孔虫组合的差异也可能证实了古海洋学条件的变化。因此，