The early Miocene Wadi Waqb carbonate in the Midyan Peninsula, NE Red Sea is of great interest not only because of its importance as an archive of one of the few pre-salt synrift carbonate platforms in the world, but also as a major hydrocarbon reservoir. Despite this importance, little is known about the diagenesis and heterogeneity of this succession. This study uses petrographical, elemental chemistry, stable isotope (δ13C and δ18O) and clumped isotope (Δ47) analyses to decipher the controlling processes behind the formation of various diagenetic products, especially dolomite, from two locations (Wadi Waqb and Ad-Dubaybah) that have experienced different diagenetic histories. Petrographically, the dolomites in both locations are similar, and characterized by euhedral to subhedral crystals (50–200 µm) and fabric-preserving dolomite textures. Clumped isotope analysis suggests that slightly elevated temperatures were recorded in the Ad-Dubaybah location (up to 49°C), whereas the Wadi Waqb location shows a sea-surface temperature of c. 30°C. These temperature differences, coupled with distinct δ18OVPDB values, can be used to infer the chemistry of the fluids involved in the dolomitization processes, with fluids at the Wadi Waqb location displaying much higher δ18OSMOW values (up to +4‰) compared to those at the Ad Dubaybah location (up to −3‰). Two different dolomitization models are proposed for the two sites: a seepage reflux, evaporative seawater mechanism at the Wadi Waqb location; and a fault-controlled, modified seawater mechanism at the Ad-Dubaybah location. At Ad-Dubaybah, seawater was modified through interaction with the immature basal sandstone aquifer, the Al-Wajh Formation. The spatial distribution of the dolostone bodies formed at these two locations also supports the models proposed here: with the Wadi Waqb location exhibiting massive dolostone bodies, while the dolostone bodies in the Ad-Dubaybah location are mostly clustered along the slope and platform margin. Porosity is highest in the slope sediments due to the interplay between higher precursor porosity, the grain size of the original limestone and dolomitization. Ultimately, this study provides insights into the prediction of carbonate diagenesis in an active tectonic basin and the resultant porosity distribution of a pre-salt carbonate reservoir system.

中文翻译：

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盆地结构对断层碳酸盐平台中成岩作用和白云石化的影响：盐下碳酸盐岩储层的露头类似物，红海裂谷，沙特阿拉伯西北部

位于红海东北部 Midyan 半岛的早中新世 Wadi Waqb 碳酸盐岩具有重要意义，不仅因为它作为世界上为数不多的盐下同裂隙碳酸盐岩平台之一的重要档案，而且还是一个主要的油气藏。尽管如此重要，但对这一演替的成岩作用和异质性知之甚少。本研究使用岩相学、元素化学、稳定同位素（δ13C 和 δ18O）和成簇同位素 (Δ47) 分析来破译来自两个地点（Wadi Waqb 和 Ad-Dubaybah）的各种成岩产物，尤其是白云岩形成背后的控制过程。经历了不同的成岩历史。在岩相学上，这两个位置的白云岩相似，并以自形至半自形晶体（50-200 µm）和保留织物的白云岩质地为特征。成簇同位素分析表明，Ad-Dubaybah 位置的温度略有升高（高达 49°C），而 Wadi Waqb 位置的海面温度为 c。30°C。这些温差加上不同的 δ18OVPDB 值，可用于推断白云石化过程中涉及的流体的化学性质，与 Wadi Waqb 位置的流体相比，Wadi Waqb 位置的流体显示出高得多的 δ18OSMOW 值（高达 +4‰）。 Ad Dubaybah 位置（最高 -3‰）。针对这两个地点提出了两种不同的白云石化模型：Wadi Waqb 位置的渗流回流、蒸发海水机制；以及 Ad-Dubaybah 位置的断层控制、改进的海水机制。在 Ad-Dubaybah，海水通过与未成熟的基底砂岩含水层 Al-Wajh 地层相互作用而发生改变。这两个位置形成的白云岩体的空间分布也支持了这里提出的模型：Wadi Waqb 位置显示出巨大的白云岩体，而 Ad-Dubaybah 位置的白云岩体大多沿着斜坡和平台边缘聚集。由于较高的前体孔隙度、原始石灰岩的粒度和白云石化作用之间的相互作用，斜坡沉积物中的孔隙度最高。最终，这项研究为预测​​活动构造盆地中碳酸盐岩成岩作用以及由此产生的盐下碳酸盐岩储层系统的孔隙度分布提供了见解。而 Ad-Dubaybah 位置的白云岩体大多沿斜坡和台地边缘聚集。由于较高的前体孔隙度、原始石灰岩的粒度和白云石化作用之间的相互作用，斜坡沉积物中的孔隙度最高。最终，这项研究为预测​​活动构造盆地中碳酸盐岩成岩作用以及由此产生的盐下碳酸盐岩储层系统的孔隙度分布提供了见解。而 Ad-Dubaybah 位置的白云岩体大多沿斜坡和台地边缘聚集。由于较高的前体孔隙度、原始石灰岩的粒度和白云石化作用之间的相互作用，斜坡沉积物中的孔隙度最高。最终，这项研究为预测​​活动构造盆地中碳酸盐岩成岩作用以及由此产生的盐下碳酸盐岩储层系统的孔隙度分布提供了见解。