Fossil bioerosion traces at a new site of Les Bez (Jura Department) and those already known from Verrières-de-Joux (Doubs Department) in the central French Jura record an ancient Miocene cliffed shoreline cut into Lower Cretaceous limestones. Both localities are at about 900 m above the present sea level. Caulostrepsis, Gastrochaenolites and Circolites are the ichnogenera identified at Les Bez, whereas only Gastrochaenolites is present at Verrières-de-Joux. This ichnoassociation identifies the Entobia ichnofacies, which corresponds to the upper infralittoral marine environment, biologically associated with the biocenosis of photophilic algae. By means of digital analysis of high-resolution field images, the percentage of the surface affected by the erosive activity of polychaete worms, bivalves and echinoids has been calculated. This information permits a better evaluation of their biological activity, thus complementing the data on the number of specimens per surface area. The cliff preserved at Les Bez was more affected, showing Gastrochaenolites with diameters smaller than those at Verrières. The Circolites–Caulostrepsis association is well developed at Les Bez, where polychaete borings are located within echinoid bowl-shaped pits with particular patterns, suggesting an ecological relationship between involved organisms. Moreover, the distribution of the borings along this outcrop is not uniform and digital analysis at three sections (A, B and C) suggests a lower and an upper zone developed on the outcrop under slightly different environmental conditions within the upper infralittoral. The exceptional preservation of the Les Bez fossil cliff-site demands protection in order to ensure its future existence and accessibility.

中文翻译：

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法国侏罗山早中新世（布尔迪加尔）海相岩石海岸：古生态和古环境分析

在 Les Bez（侏罗省）新地点的化石生物侵蚀痕迹和在法国侏罗中部的 Verrières-de-Joux（Doubs 省）已知的化石生物侵蚀痕迹记录了一条古老的中新世悬崖海岸线切割成下白垩纪石灰岩。这两个地方都在目前海平面以上约 900 m 处。Caulostrepsis、Gastrochaenolites 和 Circolites 是在 Les Bez 鉴定的 ichnogenera，而 Verrières-de-Joux 仅存在 Gastrochaenolites。这种 Ichnoassociation 确定了 Entobia Ichnofacies，它对应于上沿海海洋环境，在生物学上与嗜光藻类的生物群落有关。通过高分辨率现场图像的数字分析，计算了受多毛类蠕虫、双壳类动物和海胆类侵蚀活动影响的表面百分比。该信息允许更好地评估它们的生物活性，从而补充关于每个表面积样本数量的数据。保存在 Les Bez 的悬崖受到的影响更大，显示出直径小于 Verrières 的 Gastrochaenolite。Circolites - Caulostrepsis 协会在 Les Bez 得到了很好的发展，其中多毛类钻孔位于具有特定图案的海胆碗形坑内，表明所涉及的生物之间存在生态关系。此外，沿该露头的钻孔分布并不均匀，三个剖面（A、B 和 C）的数字分析表明，在浅海上部环境条件略有不同的情况下，在露头上发育了一个下部和一个上部区域。