(Tab. XIII.1) TOC content, carbonate content, carbonate mineralogy, percentage of total carbonate, aragonite, low magnesium calcium, and high magnesium calcium, and grain-size contents from samples from the Golfe d'Arguin and from the Western Sahara

Modern carbonate sedimentation takes place on the northern Mauritanian shelf (20°N), where typical tropical components (e.g. hermatypic reefs, calcareous green algae) are absent. Such deposits are reminiscent of extratropical sediment in the geological record. The tropical open shelf of Mauritania is influenced by large siliciclastic dust input and upwelling, highly fertilizing the ocean, as well as strongly
limiting the light penetration. In this context, temperature does not appear to be the steering factor of carbonate production. This thesis describes the depositional system of the Golfe d'Arguin off Mauritania and focuses on environmental conditions that control the depositional pattern, in particular carbonate production. The description of this modern analogue provides a tool for paleoenvironmental interpretation
of ancient counterparts.
The Golfe d'Arguin is a broad shallow shelf comprising extensive shoals (<10 m water depth; i.e. the Banc d'Arguin) on the inner shelf where waters warm up. The sediments collected in water depths between 4 and 600 m are characterized by mixed carbonate and siliciclastic (dust) deposits. They vary from clean coarse-grained, almost pure carbonate loose sediments to siliciclastic-dominated fine-grained sediments. The carbonate content and sediment grain size show a north-south decreasing pattern through the Golfe d'Arguin and are controlled by the hydraulic regime influenced by wind-driven surface currents, swell, and tidal currents.
The carbonate grain association is heterozoan. Components include abundant molluscs, foraminifers, and worm tubes, as well as barnacles and echinoderms, elements that are also abundant in extratropical sediments. The spatial distribution of the sedimentary facies of the Golfe d'Arguin does not display a depth zonation but rather a mosaic (i.e. patchy distribution). The depth and climatic signatures of the different sedimentary facies are determined by taxonomic and ecological investigations of the carbonate-secreting biota (molluscs and foraminifers). While certain planktonic foraminifers and molluscs represent upwelling elements, other components (e.g. mollusc and benthic foraminifer taxa) demonstrate the tropical origin of the sediment. The nutrient-rich (and thus also low light-penetration) conditions are reflected in the fact that symbiotic and photosynthetic carbonate-producing organisms (e.g. hermatypic corals) are absent.
The Mauritanian deposits represent an environment that is rare in the modern world but might have been more common in the geological past when global temperatures were higher. Taxonomic and ecological studies allow for distinguishing carbonate sediments formed under either tropical high-nutrient or extratropical conditions, thus improving paleoclimate reconstruction.

现代碳酸盐沉积作用发生在毛里塔尼亚北部陆架（北纬20°），该区域缺失典型的热带沉积组分，例如造礁珊瑚（hermatypic reefs）、钙化绿藻（calcareous green algae）。这类沉积与地质记录中的温带沉积物特征高度相似。

毛里塔尼亚热带开阔陆架受大量硅质碎屑（siliciclastic）粉尘输入与上升流影响，既为海洋提供了充足养分，也极大限制了光线穿透深度。在此背景下，温度似乎并非控制碳酸盐沉积作用的主导因素。

本论文阐述了毛里塔尼亚外海阿尔金湾（Golfe d'Arguin）的沉积体系，重点探讨控制沉积格局（尤其是碳酸盐沉积作用）的环境条件。对这一现代沉积类比体系的研究，可为古沉积的古环境重建提供分析工具。

阿尔金湾是一片宽阔的浅海陆架，其内陆架分布有大面积浅滩（水深小于10米，即阿尔金浅滩（Banc d'Arguin）），该区域水体温度较高。水深4至600米范围内采集的沉积物以碳酸盐与硅质碎屑（粉尘）混合沉积为特征，沉积物类型跨度较大，从纯净的粗粒近乎纯碳酸盐松散沉积物，到以硅质碎屑为主的细粒沉积物均有分布。阿尔金湾内的碳酸盐含量与沉积物粒径均呈现自北向南递减的分布规律，其受控于风驱表层流、涌浪与潮流共同影响的水动力条件。

碳酸盐颗粒组合属于异养型（heterozoan），其组分包括丰富的软体动物（molluscs）、有孔虫（foraminifers）、虫管，以及藤壶（barnacles）与棘皮动物（echinoderms），这些组分在温带沉积物中也大量存在。阿尔金湾沉积相的空间分布并未呈现深度分带特征，而是呈现镶嵌状（即斑块状）分布。不同沉积相的深度与气候标识，可通过对分泌碳酸盐的生物群落（软体动物与有孔虫）的分类学与生态学研究来确定。部分浮游有孔虫（planktonic foraminifers）与软体动物属于上升流指示生物，而其他组分（如软体动物与底栖有孔虫（benthic foraminifer）类群）则表明沉积物具有热带起源属性。养分富集（同时伴随光线穿透度极低）的环境特征，可通过区域缺失共生光合型碳酸盐沉积生物（如造礁珊瑚（hermatypic corals））得到体现。

毛里塔尼亚的这类沉积环境在现代全球范围内较为罕见，但在全球温度更高的地质历史时期可能更为普遍。通过分类学与生态学研究，可以区分热带高养分环境与温带环境下形成的碳酸盐沉积物，从而助力古气候重建工作的完善。