At Cap Blanc Nez (Channel coast, France), the chalk of the Lower Cenomanian is very rich in glauconite. Glauconite is of authigenic origin and requires the mobilization of chemical elements for its growth: Si, Fe and K. If we already know thanks to elementary geochemistry (Ge/Si ratio) that the silica of the flint present in the chalk originates from the dissolution of sponges, is it the same for glauconite? This question only makes sense if glauconite is proved to be autochthonous and synsedimentary, and not reworked during the Cenomanian transgression. In addition, we wanted to know whether the study of the content of trace elements in glauconite could provide information on the conditions of authigenesis in glauconious chalk.

The clay content of the chalk from the Lower Cenomanian has been examined and the green minerals were extracted from the rock to study their morphology, mineralogy, geochemistry (major & trace elements) and grain size. The chalk consists of calcium carbonate, smectite and true glauconite, in the form of pellets, sometimes with rare traces of quartz and some centimeter-scale phosphate gravel. The grain-size distribution of the glauconites varies from one sample to another and is always poorly sorted, which militates in favor of an autochthonous (not reworked) origin of these minerals. This origin is also suggested by the virtual absence of terrigenous minerals, except for smectite known for its potential for wide distribution in the marine environment. The geochemistry of the samples shows a very homogeneous composition of major and trace elements, with a K₂O content greater than 8%. This characterizes these glauconites as being very evolved, which indicates a long authigenic formation time (> 100 ky) and therefore an extremely reduced or irregular sedimentation rate. Here, glauconites are very rich in germanium, which makes it impossible to identify a source of silica (unlike what is possible with flints). It cannot therefore be said that the silica results from the dissolution of sponges but this enrichment in Ge, coupled with that in vanadium and the absence of enrichment in molybdenum, indicates a slightly reducing deposition milieu (suboxic). Such conditions usually favor organic matter accumulation, but not here, due to protracted sedimentation hiatuses. Lastly, glauconite trapped relatively large amounts of Ge due to reducing conditions and long exposure time to seawater, which makes it a potential chronometer assessing the duration of authigenesis, and a possible compartment of the marine cycle of germanium.

在Cap Blanc Nez（法国海峡沿岸），下塞诺曼尼亚的白垩含有非常丰富的海绿石。海绿石是自生来源，需要化学元素的动员才能生长：Si、Fe 和 K。如果我们已经知道，由于基本地球化学（Ge/Si 比），存在于白垩中的燧石的二氧化硅源自溶解海绵，海绿石也一样吗？只有证明海绿石是本土的和同沉积的，并且在森诺曼尼亚海侵期间没有重新加工，这个问题才有意义。此外，我们想知道对海绿石中微量元素含量的研究是否可以提供有关海绿石自生条件的信息。

已经检查了下森诺曼阶白垩的粘土含量，并从岩石中提取了绿色矿物，以研究它们的形态、矿物学、地球化学（主要和微量元素）和粒度。白垩由碳酸钙、蒙脱石和真正的海绿石组成，呈颗粒状，有时带有稀有的石英痕迹和一些厘米级的磷酸盐砾石。海绿石的粒度分布因样品而异，并且总是分类不佳，这有利于这些矿物的本土（未再加工）来源。除了以在海洋环境中广泛分布的潜力而闻名的绿土之外，几乎没有陆源矿物也表明了这一起源。₂O含量大于8%。这表明这些海绿石非常进化，这表明自生形成时间很长（> 100 ky），因此沉积速率极低或不规则。在这里，海绿石中的锗含量非常丰富，因此无法确定二氧化硅的来源（与使用燧石可能做到的不同）。因此，不能说二氧化硅是由海绵溶解产生的，但这种富含 Ge 的物质，再加上钒的富集和钼的缺乏，表明沉积环境略有减少（亚氧）。这种条件通常有利于有机物质的积累，但由于长期的沉积间断，这里不适合。最后，由于减少条件和长时间暴露在海水中，海绿石捕获了相对大量的锗，