Asymmetric, pendant cements are considered good indicators for early lithification in the vadose zone. In the present study, asymmetric cements are recorded in thin-sections of a Lower Jurassic limestone from the Traras Mountains (northwest Algeria). Geopetal fabrics, however, indicate that these seemingly “pendant cements” are, in some places, oriented upwards, i.e., they have grown in the opposite direction from that expected, or they grew from grains towards the pore centers. These observations disprove their origin as gravitational cements precipitated from pendant water droplets on the undersides of grains as in the vadose zone. In contrast, a formation in the marine phreatic zone seems more probable. Under high-energy conditions, and after an early lithification stage with isopachous cements in the subtidal zone, strong tidally driven horizontal pore-water flow allowed sufficient seawater to pass through the slightly cemented but still highly permeable rock. Those grain sides, which were oriented towards the pore center, where faster flowing water prevailed, were more exposed to CaCO3-supersaturated percolating seawater and therefore the cements precipitated here show their greatest thickness. In relatively more protected areas around the margins of the pores, asymmetric cements are rarely developed. The resulting rock exhibits an unusual, heterogeneous cementation with preferential centripetal nucleation areas.

中文翻译：

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挑战不对称胶结物作为包气成岩作用的指标：来自阿尔及利亚西北部特拉拉斯山脉下部 Pliensbachian 的“伪重力”胶结物

不对称的悬垂胶结物被认为是包气带早期岩石化的良好指标。在本研究中，在来自特拉拉斯山脉（阿尔及利亚西北部）的下侏罗统石灰岩的薄片中记录了不对称胶结物。然而，土岩织物表明这些看似“悬垂的水泥”在某些地方是向上的，即它们的生长方向与预期相反，或者它们从颗粒向孔隙中心生长。这些观察结果反驳了它们的起源，即重力胶结物是从在包气带中的颗粒下侧的悬垂水滴中沉淀出来的。相比之下，海洋潜水区的地层似乎更有可能。在高能条件下，在潮下带等厚胶结物的早期岩石化阶段之后，强大的潮汐驱动水平孔隙水流允许足够的海水通过轻微胶结但仍然具有高渗透性的岩石。那些朝向孔隙中心的颗粒面，在那里流动的水流速度更快，更多地暴露在 CaCO3 过饱和的渗透海水中，因此这里沉淀的胶结物显示出最大的厚度。在孔隙边缘周围保护区相对较多的区域，很少发育不对称胶结物。由此产生的岩石表现出不寻常的非均质胶结，具有优先向心成核区域。更多地暴露于 CaCO3 过饱和的渗透海水中，因此这里沉淀的水泥显示出最大的厚度。在孔隙边缘周围保护区相对较多的区域，很少发育不对称胶结物。由此产生的岩石表现出不寻常的非均质胶结，具有优先向心成核区域。更多地暴露于 CaCO3 过饱和的渗透海水中，因此这里沉淀的水泥显示出最大的厚度。在孔隙边缘周围保护区相对较多的区域，很少发育不对称胶结物。由此产生的岩石表现出不寻常的非均质胶结，具有优先向心成核区域。