Mineralogy of ODP Leg 104 holes

The mineralogical and geochemical study of samples from Sites 642, 643, and 644 enabled us to reconstruct several aspects of the Cenozoic paleoenvironmental evolution (namely volcanism, climate, hydrology) south of the Norwegian Sea and correlate it with evolution trends in the northeast Atlantic. Weathering products of early Paleogene volcanic material at Rockall Plateau, over the Faeroe-Iceland Ridge and the Voring Plateau indicate a hot and moist climate (lateritic environment) existed then. From Eocene to Oligocene, mineralogical assemblages of terrigenous sediments suggest the existence of a warm but somewhat less moist climate at that time than during the early Paleogene. At the beginning of early Miocene, climatic conditions were warm and damp. The large amounts of amorphous silica in Miocene sediment could indicate an important flux of silica from the continent then, or suggest the formation of upwelling. Uppermost lower Miocene and middle to upper Miocene clay assemblages suggest progressive cooling of the climate from warm to temperate at that time. At the end of early Miocene, hydrological exchanges between the North Atlantic and the Norwegian Sea became intense and gave rise to an important change in the mineralogy of deposits. From Pliocene to Pleistocene, the variable mineralogy of deposits reflects alternating glacial/interglacial climatic episodes, a phenomenon observed throughout the North Atlantic.

对642、643、644站位样品开展的矿物学与地球化学研究，使我们得以重建挪威海南部新生代古环境演化的多个维度（即火山作用、气候与水文过程），并将其与北大西洋东北部的演化趋势进行对比。罗卡尔海台、法罗-冰岛海脊及沃林海台处早古近纪火山物质的风化产物，指示当时存在炎热湿润的气候（红土型环境）。从始新世至渐新世，陆源沉积物的矿物组合表明，当时的气候温暖但较早古近纪略显干燥。早中新世初期，气候条件温暖湿润。中新统沉积物中大量产出的非晶质二氧化硅，可能指示当时存在来自大陆的重要硅质通量，或是反映了上升流的形成。最顶部下中新统及中-上中新统的黏土矿物组合表明，当时气候逐步降温，从温暖转为温带。早中新世末期，北大西洋与挪威海之间的水文交换变得强烈，引发了沉积物矿物学的重大变化。从上新世至更新世，沉积物多变的矿物学特征反映了交替出现的冰期/间冰期气候旋回，这一现象在整个北大西洋区域均有观测记录。