Sedimentology of the Rio Grande Rise area

Surface sediment samples and three gravity cores from the eastern terrace of the Vema Channel, the western flank of the Rio Grande Rise, and the Brazilian continental slope were investigated for physical properties, grain size, and clay mineral composition. Discharge of the Rio Doce is responsible for kaolinite enrichments on the slope south of 20° and at intermediate depths of the Rio Grande Rise. The long-distance advection of kaolinite with North Atlantic Deep Water from lower latitudes is of minor importance as evidenced by low kaolinite/chlorite ratios on the Mid-Atlantic Ridge. Cyclic variations of kaolinite/chlorite ratios in all our cores, with maxima in interglacials, are attributed to low-and high-latitude forcing of paleoclimate on the Brazilian mainland and the related discharge of the Rio Doce. A long-term trend toward more arid and 'glacial' conditions from 1500 ka to present is superimposed on the glacial-interglacial cyclicity.本研究针对取自韦马海峡（Vema Channel）东部阶地、里奥格兰德海隆（Rio Grande Rise）西翼以及巴西大陆坡的表层沉积物样品与3根重力岩心，开展了物理性质、沉积物粒度以及黏土矿物组成的分析测试。多西河（Rio Doce）的径流作用是造成20°S以南陆坡与里奥格兰德海隆中等深度区域高岭石富集的主要原因。大西洋中脊（Mid-Atlantic Ridge）处较低的高岭石/绿泥石比值表明，来自低纬度区域、随北大西洋深层水（North Atlantic Deep Water）进行长距离平流输送的高岭石，其对研究区的影响相对有限。所有岩心的高岭石/绿泥石比值均呈现周期性波动，且在间冰期达到峰值，该现象可归因于巴西陆域古气候受到的高低纬度气候强迫，以及由此驱动的多西河径流变化。在冰期-间冰期旋回之上，还叠加了自1500 ka（150万年）至今，气候向更干旱、更具冰期特征方向发展的长期演化趋势。