Thorough study of the mineralogy of clay matter retrieved from DSDP drill sites is important in understanding the geological development of the sea floor. This report deals with: (1) the stratigraphic age distribution of clay minerals in sections of the Leg 48 holes; (2) bonds of clay mineral associations with lithological types of rocks and volcanism; and (3) features of formation of clay mineral associations.The mineralogical composition of the clay fraction of sediments and rocks of Leg 48 was studied on Sites 403,404, 405, and 406 in the vicinity of Rockall Plateau, and on Sites 401 and 402 of the Bay of Biscay. The 18Å (Reynolds, 1968).The identification of mixed-layer minerals was carried out on the basis of works by Brindley
During Leg 48 of the IPOD phase of the Deep Sea Drilling Project, seven holes were drilled on the margins of the Bay of Biscay and Rockall Plateau to compare the evolution of passive margins of contrasting age and structural development. The geological setting and principal results of the drilling are outlined for each margin. We discuss the history of rifting and subsidence on these margins in relation to the sea floor spreading history of the adjacent ocean basins. Implications of the results for the nature of unconformities at passive margins and anoxic episodes during the Lower Cretaceous are discussed briefly.
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