Hardground discontinuities within carbonate platforms form important stratigraphic surfaces which can be used at basin scale to correlate sequence boundaries. Although these surfaces are commonly used in sequence strati-graphy, the timing and duration of hardground lithification and the crystallization of early cements remain unexplored. Here, early calcite cements were dated by U-Pb geochronology for five Jurassic hardgrounds, interpreted as third-order sequence boundaries, situated within a well-constrained petrographic, sedimentological and stratigraphic framework. The consistency or the slight deviation between the age of the cements and the stratigraphic age of deposition of the formations illustrate that cementation occurred early in the diagenetic history. The ages obtained on dogtooth cements, replacing aragonite in gastropod shells and pendant cements in intergranular spaces, match those of the standard Jurassic biostratigraphic ammonite Zones, making calcite U-Pb geochronology a promising method for dating third-order sequence boundaries of depositional sequences and refining the Jurassic time scale in the future.

中文翻译：

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方解石铀铅地质年代学应用于硬地岩化和层序边界测年

碳酸盐平台内的硬地不连续性形成了重要的地层表面，可在盆地尺度上用于关联层序边界。尽管这些表面通常用于层序地层学，但硬地岩化的时间和持续时间以及早期胶结物的结晶仍未得到探索。在这里，早期方解石胶结物通过 U-Pb 年代学测定了五个侏罗纪硬地的年代，解释为三级层序边界，位于约束良好的岩石学、沉积学和地层框架内。胶结物年龄与地层沉积地层年龄之间的一致性或轻微偏差说明胶结作用发生在成岩历史的早期。在狗牙水泥上获得的年龄，