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Reworked marine sandstone concretions: A record of high-frequency shallow burial to exhumation cycles

机译：返工的海洋砂岩固结物：高频浅埋至掘尸循环的记录

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Concretions, with abundant calcite-dolomite cement-replacement textures originally hosted in shallow-marine sandstones, were reworked into Lower Cretaceous fluvio-deltaic conglomerates and shoreface sandstones (External Zones, Betic Cordillera). A cycle of host sand deposition, early diagenetic concretion formation and concretion reworking is documented: (1) Well-sorted shoreface sandstone deposited. (2) Spherical to ovoid, non-ferroan calcite-cemented concretions formed below flooding surfaces at shallow-burial depths during early eodiagenesis. Non-ferroan calcite cements were precipitated from the bicarbonate derived from seawater and from dissolution of marine bioclasts, as shown by isotope analyses. (3) Concretions were reworked and exposed on the seafloor in a high-energy setting as indicated by the presence of numerous bivalve borings (Entobia ichnofacies), laminated micritic microbial crusts around the concretions, and epilithobionts (oysters, barnacles and corals) on the concretion surface. Concretions also appear as erosional remnants on the floor of channels which were incised into the shoreline sandstone when sea-level fell. (4) The fluvio-deltaic channels were filled with sediment during flooding in the late lowstand of sea-level. (5) The concretions are partly dolomitized, and the presence of siderite, pyrite and barite in the outer part of the concretions precipitated before the dolomite, suggests that the latter formed during shallow burial.
机译：最初在浅海砂岩中堆积的方解石-白云石水泥置换质地丰富的凝结物被重新加工成下白垩统河流-三角洲砾岩和海岸面砂岩（外部区域，贝蒂科迪勒拉）。记录了宿主砂沉积，早期成岩固结形成和固结返工的循环：（1）沉积良好的海岸面砂岩。 （2）在早期成岩过程中，在浅埋深度的淹没面之下形成了球形至卵形，非铁型方解石水泥胶结物。如同位素分析所示，非铁方解石水泥是从海水和海洋生物碎屑的溶解产生的碳酸氢盐中沉淀出来的。 （3）在高能量的环境中对凝结物进行了改造并暴露在海底，这表明存在大量的双壳虫钻孔（Entobia ichnofacies），在结石周围的层状微生微生物壳以及在表层上的表生石类（牡蛎，藤壶和珊瑚）。固结面。在海平面下降时切入海岸线砂岩的河道底部残留着侵蚀物，也形成了凝结物。 （4）在海平面低位后期洪水期间，河流三角洲河道充满了沉积物。 （5）胶结物是部分白云石化的，在胶结物的外部沉淀出菱铁矿，黄铁矿和重晶石，这是在白云岩浅埋之前形成的。

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