The Lower Ordovician succession, consisting of the Yingshan and Penglaiba formations, encompasses significant petroleum reservoirs in Yubei area, southwest Tarim Basin. Mesogenetic dissolution and dolomitization strongly contributed to the increase in rock porosities here. Wells YB 7, YB 5, and YB 1-2X drilled in eastern Yubei area met the deposits of Yingshan and Penglaiba formations, providing abundant data for the mesogenetic diagenesis analysis. Among them, Well YB 5 encountered the thickest Penglaiba Formation and was chosen for detailed analysis. Eight diagenetic elements (i.e., micrite encrust, radial fibrous calcite cement, stylolites, poikilotopic calcite cement, dolomite, fracture, bladed quartz, and equant quartz) are identified and ascribed to seven paragenetic events. Their Paragenetic sequence evidences Yingshan and Penglaiba Formations experienced severe deep burial diagenesis. The presence of green luminescent fluorite, non-luminescent and zoned quartz, and violet to orange luminescent saddle dolomite with sweeping extinctions, together with the positive Eu 2+ anomalies shown in the rare earth element (REE) patterns all help to ascribe the buried dissolution and dolomitization to the incorporation of hydrothermal fluids. The inconsistency between the REE patterns of the Yingshan and Penglaiba formations and that of the organic-rich source rocks of Lianglitage and Bachu Formations exclude the assumption that hydrocarbon influx caused the mesogenetic dissolution. High-angle fractures, generated by the Middle Caledonian–Early Hercynian tectonic movements, acted as conduits for hydrothermal fluid migration and promoted the mesogenetic dissolution to form dolomite reservoirs. The coincidence that samples with positive Eu 2+ anomalies all fall in the basalt province, while samples lacking positive Eu 2+ anomalies from Tahe fall out, backs up that the main source of the hydrothermal fluid promoting the mesogenetic dissolution was probably derived from the Permian magma. Strata possessing similar geochemical and petrological characteristics as Yingshan and Penglaiba formations in eastern Yubei area, and experiencing subsequent tectonic and magmatic activities could be potential exploration targets in further exploration practice in Tarim Basin and in the other basins in the world.

中文翻译：

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塔里木盆地渝北地区奥陶系灰岩中生成岩作用

下奥陶统由鹰山组和蓬莱坝组组成，在塔里木盆地西南部的渝北地区拥有重要的油藏。中生溶解和白云石化强烈地促成了这里岩石孔隙度的增加。在渝北地区东部钻探的YB 7、YB 5和YB 1-2X井遇到了鹰山组和蓬莱坝组的沉积，为中生成岩分析提供了丰富的数据。其中，YB 5 井遇到了最厚的蓬莱坝组，被选中进行详细分析。八种成岩元素（即泥晶壳、径向纤维状方解石胶结物、针柱石、异质方解石胶结物、白云石、裂缝、叶片石英和等长石英）被确定并归因于七个共生事件。他们的共生层序表明鹰山组和蓬莱坝组经历了严重的深埋成岩作用。绿色发光萤石、不发光和分带石英、紫罗兰色到橙色发光的鞍状白云岩的存在，以及在稀土元素 (REE) 模式中显示的正 Eu 2+ 异常都有助于归因于埋藏溶解和白云石化以掺入热液流体。鹰山组、蓬莱坝组与良里塔格组、巴楚组富有机质烃源岩的稀土元素格局不一致，排除了油气流入引起中生溶蚀的假设。由中加里东-早海西构造运动产生的大角度裂缝，作为热液运移的管道，促进中生溶蚀形成白云岩储层。Eu 2+ 正异常的样品全部落入玄武岩省，而塔河Eu 2+ 正异常的样品均落入玄武岩省的巧合，支持了促进中生溶解作用的热液流体的主要来源可能来自二叠纪岩浆。与渝北地区东部鹰山组和蓬莱坝组具有相似地球化学和岩石学特征的地层，并经历了随后的构造和岩浆活动，可以成为塔里木盆地和世界其他盆地进一步勘探实践的潜在勘探目标。Eu 2+ 正异常的样品全部落入玄武岩省，而塔河Eu 2+ 正异常的样品均落入玄武岩省的巧合，支持了促进中生溶解作用的热液流体的主要来源可能来自二叠纪岩浆。与渝北地区东部鹰山组和蓬莱坝组具有相似地球化学和岩石学特征的地层，并经历了随后的构造和岩浆活动，可以成为塔里木盆地和世界其他盆地进一步勘探实践的潜在勘探目标。Eu 2+ 正异常的样品全部落入玄武岩省，而塔河Eu 2+ 正异常的样品均落入玄武岩省的巧合，支持了促进中生溶解作用的热液流体的主要来源可能来自二叠纪岩浆。与渝北地区东部鹰山组和蓬莱坝组具有相似地球化学和岩石学特征的地层，并经历了随后的构造和岩浆活动，可以成为塔里木盆地和世界其他盆地进一步勘探实践的潜在勘探目标。