Sedimentology of surface sediments from the continental shelf and slope off West Africa (Table 1)

Samples from sutface sediments of the shell, continental slope, and adjacent deep sea regions off West Africa between 27° N and 15° N were investigated with respect to grain size distribution of the total samples, sand contents of the acid insoluble residues, carbonate content of the total samples, and the separate grain size fractions, specific surfaces, colours and mineralogical composition of the clay fractions.
The grain size distributions of the total samples of the sediments of the shelf and the continental slope off Spanish-Sahara are controlled mainly by biogenic components. The supply of terrigeneous material in this area is very low. At deeper parts of the continental slope and in the deep sea areas, the relative amounts of carbonate minerals in the sediments are considerably reduced. The prevailing sand contents of the upper slope changes into clay dominance.
On the shelf of Mauritania - represented by profiles extending down to 200 m water depth - the grain size is also controlled mainly by biogenic carbonates. Nevertheless, the admixture of fossil silicate components is important, too.
The southern parts of the area is investigated are located in a region influenced by sediments of the Senegal River, which especially control the contents of silt and clay. The silicate sands, predominately of quartz, are fossil and form a mixed sediment with younger deposits.
The carbonate contents of the different grain size fractions are formed either by sedimentation of carbonate and silicate particles of the respective grain size or by autochtonous disintegration of coarser sediment particles, as shown by the occurence of Mg-rich calcite and especially aragonite in the clay sized fraction.
In the northern parts of the area investigated, which have very minute terrigeneous supply, the latter mechanism is the dominant factor, controlling the carbonate contents of the fine grain sized fractions. In the vicinity of the mouth of the Senegal the carbonate contents are influenced by extremely high dilution with terrigencous silicates.
Mg-rich calcite and aragonite are produced preferentially in shallow slope and shelf areas up to 500 m of water depth.
The specific surfaces of the carbonate-free clay fractions indicate that the clay fractions of the shelfareas with little terrigenous supply consits of relatively coarser particles. Very fine particles are removed and transported towards the deep sea. Lateral differentiation of this kind was not observed in the area off Senegal. The high surface areas, characterizing the clay fractions of this region, are thought to be due to high montmorillonite contents as was found for deep seas sediments. The mineralogical composition of the clay fraction from the southern parts of the area is characterized by high kaolinite and montmorillonite contents, while in the northern illite is predominating. At least two types of montmorillionites are present: in areas influenced by the Senegal mostly one type was found, which could swell to 17; on the shelves and slopes of the other regions the montmorillonite-group is represented by a montmorillonite-mica-type mixed-layer mineral. A "glauconite", found in the sand fraction, which had very similar properties to those of the montmorillonite-mica mixed-layer, is believed to be the source of this mixed-layer-type mineral.
Palygorskite is present in all samples out of range of the Senegal supply. It may be an indicator of eolian transported material. The occurence of rich palygorskit deposits in the arid hinterlands emphasizes the terrestrial origin.

对西非北纬27°至15°海域沿岸贝壳、陆架、大陆坡及邻近深海区域的表层沉积物（surface sediments）样品开展了研究，分析内容涵盖全样粒度分布（grain size distribution）、酸不溶残渣的砂含量、全样碳酸盐含量（carbonate content）及单独粒级组分、比表面积（specific surfaces）、颜色以及黏土组分（clay fractions）的矿物组成（mineralogical composition）。
西属撒哈拉沿岸陆架与大陆坡沉积物的全样粒度分布主要受生物成因组分控制，该区域陆源物质（terrigenous material）供给量极低。在大陆坡较深区域及深海区域，沉积物中碳酸盐矿物的相对占比显著降低，上斜坡普遍发育的砂质组分逐渐转变为黏土主导的沉积特征。
在水深可达200m的毛里塔尼亚陆架区，沉积物粒度同样主要受生物成因碳酸盐控制，但古硅酸盐组分的混入同样具有重要意义。
研究区南部区域受塞内加尔河（Senegal River）沉积物影响显著，该区域的粉砂与黏土含量主要受此控制。以石英（quartz）为主的古硅酸盐砂体与年轻沉积层形成混合沉积。
不同粒级组分的碳酸盐含量，要么由对应粒级的碳酸盐与硅酸盐颗粒沉积作用形成，要么由较粗沉积物颗粒的原地解离（autochtonous disintegration）作用生成，这一点可从黏土级组分中富镁方解石（Mg-rich calcite）尤其是文石（aragonite）的产出得到佐证。
在陆源供给极少的研究区北部，上述原地解离作用是控制细粒级组分碳酸盐含量的主导因素。而在塞内加尔河口附近区域，碳酸盐含量则受陆源硅酸盐的极强稀释作用影响。
富镁方解石与文石优先形成于水深500m以浅的陆坡与陆架区域。
不含碳酸盐的黏土组分的比表面积数据显示，陆源供给稀少的陆架区黏土组分由相对较粗的颗粒组成，极细颗粒被搬运至深海区域。这种横向分异特征在塞内加尔沿岸海域并未观测到。该区域黏土组分具有高比表面积特征，这被认为与深海沉积物中常见的高蒙脱石（montmorillonite）含量有关。研究区南部黏土组分的矿物组成以高含量高岭石（kaolinite）与蒙脱石为特征，而北部则以伊利石（illite）为主。研究区至少存在两类蒙脱石：受塞内加尔河影响的区域多产出一类可膨胀至17层的蒙脱石；其余区域陆架与陆坡的蒙脱石族矿物则以蒙脱石-云母型混层矿物（mixed-layer mineral）为代表。在砂组分中发现的一种与蒙脱石-云母混层矿物性质极为相似的“海绿石（glauconite）”，被认为是该混层型矿物的来源。
不受塞内加尔河沉积物供给影响的所有样品中均产出坡缕石（palygorskite，又称凹凸棒石），其可作为风成搬运物质（eolian transported material）的指示物。干旱内陆区（arid hinterlands）产出的富坡缕石沉积进一步证实了其陆源成因。