Paleoenvironmental history of the North Atlantic region from mineralogical and geochemical data

Clay Sedimentology

“…They include chlorite, illite, irregular mixed-Iayers of illite-smectite, chlorite-smectite and rarely illite-vermiculite types, vermiculite, kaolinite, and palygorskite ( Fig. These results are confirmed by geochemical data, that do not reveal any noticeable difference in the clay mineral composition between black shales and surrounding sediments (Chamley and Debrabant 1984a;see Chapter 19). Associated non-clay minerals mainly comprise quartz, feldspars, calcite, pyrite, opal CT, clinoptilolite, and sometimes siderite, rhodochrosite or barite, diversely distributed in the sediments.…”

“…The only possible volcano-derived materials sometimes recognized consist of quartz (e.g., Jones and Fitzgerald 1984), that could also have adetrital aeolian or subaqueous origin, and could in any case hardly reflect oceanic tholeiitic volcanism. In a similar way, Albian sediments deposited elose to the North American continent contain abundant smectite, while contemporary deposits 10cated elose to the Atlantic ridge and in the volcanically active Cape Verde basin are depleted in tbis mineral (Chamley and Debrabant 1984a). The often total absence of glass is nevertheless difficult to understand, knowing that the alteration potential of volcanic material greatly differs with size, shape, porosity and composition, and that non-altered volcanic debris usually still exist in deposits rich in unquestionably volcanogenic smectite.…”

“…11.11. Autochthonous modifications clearly identified in Atlantic black shales concern minerals less stable than clays, such as pyrite, clinoptilolite, opal CT, as weIl as calcite, siderite, rhodochrosite, and are not specifically restricted to black shale facies (see Chamley 1979, Chamley andDebrabant 1984a). (After Chamley and Robert 1982) The composition of clay associations in black shales and associated sediments varies considerably according to age, but usually depends neither on the general litho logy , the abundance of organic matter, or the depth of burial (e.g., Fig.l1.11).…”

“…The increased reworking of rocky substrates compared to that of soil blankets was favored on aglobaI scale by the sea-Ievellowering, especially during late Cenozoic times, and more regionally by Chamley 1979) during Cenozoic times resulted from the development of long wet seasons with still high temperature, as well as from enhanced reworking of old lateritic soils and from the migration of the African plate across the equatorial zone. 9, 18, and discussions in Chamley 1979, Chamley and Debrabant 1984a, Stein 1985, Robert and Chamley 1987. 9, 18, and discussions in Chamley 1979, Chamley and Debrabant 1984a, Stein 1985, Robert and Chamley 1987.…”

The Cenomanian/Turonian Boundary Event (CTBE) at Hole 641A, ODP Leg 103 (Compared with the CTBE Interval at Site 398)

“…All of these form under low-temperature-low-pressure conditions, at which they are stable. Compilations of clay min eral studies of middle Cretaceous sequences of the North Atlan tic are provided by Chamley (1979), Chamley and Debrabant (1984), and Chamley and Deconinck (1985). According to these authors, on the basis on several North Atlantic sites (including Site 398), there is no appreciable sign of diagenesis with depth of burial in the clay mineral spectrum of Mesozoic deposits of the North Atlantic margins.…”