Karst bauxite deposits represent 11% of the global quantity of bauxite (Bardossy and Aleva, 1990). Karst Bauxite is defined as bauxite deposits overlying carbonate rocks above a more or less karstified surface. Allochtonous karst bauxites result from two successive processes: (1) intense weathering and formation of a lateritic profile, involving the development of bauxitic and duricrust horizons; and (2) erosion of the lateritic profile and deposition above a carbonate unit located downstream. In the Villeveyrac basin (southern France), Lower to Mid-Albian allochtonous karstic bauxites are deposited on a Jurassic karstified bedrock, and are overlain by a Late Albian marine siliciclastic cover. A drillcore, sampling the substratum, the bauxites and their cover, is analyzed and offers the opportunity to investigate the depositional conditions and interactions of climate and tectonic during the mid- to late Cretaceous, through the analysis of mechanical and chemical weathering evidence. Sedimentological study allowed the definition of four bauxite facies and three siliciclastic cover facies, overprinted by four different pedofacies. Mineralogical and geochemical analyses allowed the distinction of four mineralogical units controlled by climate-related weathering processes. The bauxite deposits emplaced by mud-flow/debris-flow gravity currents are composed by boehmite-hematite and goethite. The top of the bauxite presents a progressive upward decrease in Al2O3 and TiO2 associated with the occurrence of kaolinite. The base of the cover that overlies the bauxite interval corresponds to a paralic environment, dominated by kaolinite, with a sub-ferricrete paleosol. The following paralic sequence presents a clay-rich suite dominated by smectite, associated with mica/illite and quartz, which suggests aridification of climate around the latest Albian. We interpret this sedimentary succession as the result of erosion of an autochthonous laterite cover, induced by major tectonic uplift in the upstream drainage area, which led to a significant increase in slope gradient, under a wet tropical climate. Mechanical erosion of autochthonous laterite bauxite in the upstream drainage led to a reverse stacking of the reworked autochthonous lateritic profile in the depositional basin. A continuous transgressive trend was responsible for trapping of the allochtonous karst bauxite. This was followed by stacking of siliciclastic paralic sequences, which record progressive erosion of the bedrock in the upstream drainage area, under dry tropical conditions. Our results thus suggest that dismantling of the autochthonous laterite cover was initiated by Albian uplift and this ended with a change towards drier and more seasonal climate at the Albian-Cenomanian transition.

中文翻译：

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外来铝土矿沉积的构造和气候控制。来自法国南部中白垩世 Villeveyrac 盆地的例子

岩溶铝土矿矿床占全球铝土矿数量的 11%（Bardossy 和 Aleva，1990 年）。岩溶铝土矿被定义为覆盖在或多或少岩溶表面上方的碳酸盐岩上的铝土矿沉积物。外来岩溶铝土矿由两个连续过程产生：（1）强烈风化和红土剖面的形成，包括铝土岩和硬壳层的发育；(2) 位于下游的碳酸盐单元上方红土剖面的侵蚀和沉积。在 Villeveyrac 盆地（法国南部），下至中阿尔比斯异地岩溶铝土矿沉积在侏罗纪岩溶基岩上，并被晚阿尔比安海相硅质碎屑覆盖层覆盖。一个钻芯，对基质、铝土矿及其覆盖层进行取样，通过对机械和化学风化证据的分析，对白垩纪中晚期的沉积条件和气候与构造的相互作用进行了分析并提供了机会。沉积学研究允许定义四个铝土矿相和三个硅质碎屑覆盖相，由四个不同的土壤相叠加。矿物学和地球化学分析允许区分受气候相关风化过程控制的四个矿物学单元。被泥流/碎屑流重力流侵位的铝土矿矿床由勃姆石-赤铁矿和针铁矿组成。随着高岭石的出现，铝土矿顶部的 Al2O3 和 TiO2 逐渐向上减少。覆盖铝土矿层的盖子底部对应于一个偏远的环境，以高岭石为主，亚铁质古土壤。下面的平行层序展示了以蒙脱石为主的富含粘土的岩层，与云母/伊利石和石英有关，这表明最近阿尔比斯附近气候干旱化。我们将这种沉积序列解释为，在潮湿的热带气候下，上游流域的主要构造抬升引起了本土红土覆盖层的侵蚀，导致坡度梯度显着增加。上游排水系统中原生红土铝土矿的机械侵蚀导致沉积盆地中重新加工的原生红土剖面反向堆积。连续的海侵趋势是捕获外来岩溶铝土矿的原因。随后是硅质碎屑平行层序的堆积，记录了在干燥的热带条件下上游流域基岩的逐渐侵蚀。因此，我们的研究结果表明，本土红土覆盖层的拆除是由阿尔布隆起引发的，最终在阿尔布-塞诺曼阶过渡期气候变得更加干燥和更具季节性。