Subcontinuously cored early(?)-middle Miocene to recently deposited sediments from ODP Site 645 were studied texturally, mineralogically, and geochemically. The entire sequence contains minerals and associated chemical elements that are chiefly of detrital origin. In particular, the clay minerals, which include smectite, kaolinite, chlorite, and illite, are detrital. No obvious evidence of diagenesis with depth, of burial, of volcanism, or of hydrothermal alteration was observed. The sedimentary textures, clay mineralogy, and <2-/«n fraction geochemistry of the early middle Miocene sediments (630 to 1147 mbsf) suggest the pronounced but variable influence of a southward bottom current. Two clay facies are defined. The lower one, Cj (780 to 1147 mbsf), is characterized by the great abundance of discrete smectite (with less than 15% illite interlayers), probably detrital in origin, and reworked older, discrete, smectite-rich sediments. The upper clay facies, C 2 (630 to 780 mbsf), shows a net decrease of the fully expandable clay abundances, with a great abundance of mixed-layer, illite-smectite clays (60 to 80% of illite interlayers). Such clay assemblages can be inherited from paleosoils or older sedimentary rocks. An important change occurs at 630 mbsf (clay fraction) or 600 mbsf (sedimentary texture), which may be explained by the beginning of continental glaciation (630 mbsf, ~ 9 Ma) and the onset of ice rafting in Baffin Bay (600 mbsf, ~ 8 Ma). Above this level, the characteristics and modifications of the clay assemblages are controlled climatically and can be explained by the fluctuations of (1) ice-rafting, (2) speed of weak bottom currents, and (3) some supply by mud turbiditic currents. Three clay facies (C 3 , C 4 , and C 5) can be defined by the abrupt increases of the inherited chlorite and illite clays.

Mineralogical and geochemical investigations carried out on Callovian to upper Cenozoic basalt and sediments of Hole 534A are the bases for paleoenvironmental interpretations. The clay mineralogy primarily reflects events that occurred on the American continent (tectonics, morphology, alteration and pedogenesis, climate), except in the basalt and at the precise basalt/sediment contact where in situ alteration and local metamorphic effects exist. The inorganic and organic geochemistry mainly reflects the influence of and increasing distance from the spreading center during the first stages of sedimentation, the terrigenous influence from the Valanginian upward, and the bottom reducing or oxidizing conditions linked to the widening and deepening of the ocean affected by global tectonics.

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One hundred and thirty samples of various Cretaceous to Pleistocene sediments from DSDP Sites 399 and 400 (north Biscay Bay) and 403 to 406 (south Rockall Plateau) were studied for their clay mineralogy and bulk geochemistry. Both geographical areas were compared with each other, then compared with the area south of Biscay Bay (Site 398, DSDP Leg 47). In Aptian to Paleogene sediments the clay fraction is dominated by smectite. In Biscay Bay the mineral is rich in Al-Fe and chiefly expresses the erosion of soils formed under arid-warm climatic conditions with contrasted wet and dry seasons. Two stages with fibrous clays occur in Albian (attapulgite, palygorskite) and Paleocene/Eocene (attapulgite, sepiolite) sediments, suggesting the existence of wet and warm periods and of nearly closed marginal basins. In the south part of the Iceland Sea the smectite is of a Fe-Mg type and mainly results from the transformation of volcanic material, probably in subaerial conditions. In post-Paleogene sediments the primary minerals (illite, chlorite, quartz, feldspars) and mixed-layers increase irregularly, expressing both periodic continental cooling, the major stages of which occurred in late Miocene and Pleistocene times, an increase in the intensity of the north/south oceanic current. In general, kaolinite and fibrous clays are less abundant, smectite more abundant, and coolings appear to have been stronger in Pleistocene time in the more northern drill sites. The diagenetic changes are unusual. There is no modification with depth of burial and no basic chemical sedimentation. An in situ evolution in volcanic environment appears locally in Rockall sites only. The "black shales" facies does not induce any argillaceous modification in north Biscay Bay and affects only some chemical elements such as Ca, Fe, and Mn. Ionic removing and trapping can locally induce the autochthonous crystallization of cristobalite-tridymite and of some zeolites. Site 402 of Biscay Bay, not as deep as Sites 398, 399, 400, and 401, seems to be aside from open sea circulations, which might affect especially the distribution of Mn in Albian to lower Miocene sediments and, perhaps, as well, that of fibrous clays. The chemical and mineralogical sequence observed from Site 402 to Sites 399 and 400 in Upper Cretaceous sediments suggests a deltaic paleoenvironment, which, seaward is marked by a geochemical homogenization, a decrease of the carbonaceous phase, and an increase of small-sized, highly buoyant minerals (smectite, fibrous clays). The sudden arrival of detrital primary minerals in the Campanian/Maestrichtian suggests the establishment of a deep-sea circulation perhaps related to the opening of the western North Atlantic, or to a tectonic event or a marine regression. South of Rockall Plateau during early Cenozoic time, the chemical and mineralogical environment was more pelagic than in Biscay Bay, especially at Sites 405 and 406 where the volcaniclastic influence was not as strong as at Sites 403 and 404. The ending of the major volcanic activity ...

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