The depositional environment of the Antalo Limestone was previously interpreted from regional field-based studies and microfacies. However, stable oxygen and carbon isotopes are also invaluable proxies of paleo-environmental conditions, depositional, and diagenetic environments. Hence, the analyses of stable oxygen and carbon isotopic composition of this unit were examined from bulk limestone samples and integrated with a detailed petrographic study to interpret depositional environments and diagenetic evolution. The samples were collected from three outcrop sections, which together represent the full thickness of the unit. The microfacies identified from these samples indicate shallow–deep marine depositional as well as meteoric phreatic, marine phreatic, and deep burial diagenetic environments. The limits of variations of the oxygen isotopic ratios range from − 10.46 to − 3.56‰, with − 6.07‰ mean value. The limits of variations of the carbon isotopic ratios range from − 0.02 to 2.56‰, with 1.4‰ mean value. The calculated z values range from 123.08 to129.7 and the paleo-temperatures are estimated to be 32.4–73.52 °C, with an average temperature of 46.5 °C. The carbon isotope ratios indicate marine-water sources. This was confirmed from z values (> 120), indicating that the samples are marine carbonates. The depleted oxygen isotope ratios and high-temperature values, on the other hand, represent deep-burial diagenesis, which indicates the isotopic composition and the temperature conditions of the cement precipitating diagenetic fluids. The compositional fields of the δ18O–δ13C cross plots, also indicate marine carbonates subjected to mixing zone–deep-burial diagenesis. Therefore, both the petrographic and stable oxygen and carbon isotopic evidences are mutually in agreement, indicating related depositional and diagenetic environments.

中文翻译：

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埃塞俄比亚北部 Mekelle 盆地 Antalo 石灰岩的岩相学和稳定的氧和碳同位素组成：对海洋环境和深埋成岩作用的影响

Antalo 石灰岩的沉积环境以前是通过区域实地研究和微相来解释的。然而，稳定的氧和碳同位素也是古环境条件、沉积和成岩环境的宝贵代表。因此，该单元的稳定氧和碳同位素组成分析是从大块石灰岩样品中检查出来的，并与详细的岩石学研究相结合，以解释沉积环境和成岩演化。样品是从三个露头部分收集的，它们一起代表了单元的整个厚度。从这些样品中确定的微相表明浅-深海相沉积以及大气潜水、海洋潜水和深埋成岩环境。氧同位素比值的变化范围为- 10.46 到- 3.56‰，平均值为- 6.07‰。碳同位素比值变化范围为−0.02～2.56‰，平均值为1.4‰。计算的z值范围为123.08～129.7，古温度估计为32.4～73.52℃，平均温度为46.5℃。碳同位素比率表示海洋-水源。这从 z 值 (> 120) 得到证实，表明样品是海洋碳酸盐。另一方面，贫氧同位素比值和高温值代表深埋成岩作用，表明了水泥沉淀成岩流体的同位素组成和温度条件。δ18O–δ13C 交会图的组成场，还表明受混合带-深埋成岩作用的海相碳酸盐岩。因此，岩石学证据和稳定氧碳同位素证据相互吻合，表明相关的沉积和成岩环境。