Mineralogical and Geochemical Investigations of Sediments on the Mazagan Plateau, Northwestern African Margin (Leg 79, Deep Sea Drilling Project)

Abstract

Detailed mineralogical and geochemical studies were performed on samples from selected time intervals recovered during Leg 79 on the Mazagan Plateau. The uppermost Albian and Cenomanian sediments of Sites 545 and 547 can be correlated on the basis of mineralogy and geochemistry; these sediments illustrate differential settling processes and the existence of hot climates with alternating humid and dry seasons in the African coastal zone. The upper Aptian to Albian black shales of Site 545 point to an irregular alternation of tectonic activity and relaxation stages, allowing different behaviors in the reworking of soils, crystalline rocks, and sediments born in peri-marine basins. The barren lower Mesozoic reddish sediments and evaporitic series of Sites 546 and 547 are characterized by a strong physical erosion of sialic landscapes, without clear evidence of post-depositional metamorphic events. At Site 546 strong early diagenetic processes in a confined evaporitic environment affect both the mineralogy and the geochemistry of pre-Miocene rocks.

Clay Mineralogy of Neogene Sediments of the Western Arabian Sea: Mineral Abundances and Paleoenvironmental Implications

“…Samples were pretreated with 5 N HC1 to remove carbonates, and the <2µm fraction was extracted by settling and decantation. The < 2 µm materials were then prepared as oriented mounts on glass slides, and each was scanned three times: from 2.5° to 28.5° 20 on unexpanded and unheated samples, from 2.5° to 14.5° 20 on glycolated samples, and from 2.5° to 14.5° 20 on samples heated for 2 hr at 490° C. The analytical techniques and the methods of quantitatively interpreting the diffractograms are described in detail in Chamley and Debrabant (1984) and Holtzapffel (1985). Analytical uncertainties in the clay mineral relative abundances are estimated to be ± 5% (absolute) for abundances above 20%, ± 3% (absolute) for abundances between 5% and 20%, and ± 2% (absolute) for abundances less than 5°7o.…”

Mineralogical and Geochemical Investigations on Latest Miocene Deposits in the Tyrrhenian Sea (ODP Leg 107)

“…A similar transition has been reported in the Atlan tic domain during Mesozoic times, when tectonic instability of continental margins resulting from rifting (or acceleration of spreading) was followed by the relaxation of continental borders and the development of pedogenesis (e.g., Chamley and Debrabant, 1984a). The lower series of Hole 654A, that contains abundant and fresh illite, chlorite, and feldspars, and fairly abundant quartz, points to the direct supply of terrigenous ma terial from the tilted blocks of the Sardinia margin that were submitted to very active erosion during the early stages of the basin formation.…”

“…3). This morpho logic character is not usually encountered in buried sediments, except near some evaporative sediments, like early Mesozoic de posits of Mazagan Plateau, Northeast Atlantic (Chamley and Debrabant, 1984b). The preferential development of chlorite could be favored by the magnesian diagenetic environments linked to Messinian evaporitic conditions.…”

The Clay-Mineralogical Record of the Last 10 Million Years off Northeastern Australia

“…Oriented mounts were prepared on glass slides and were scanned three times (Cu, K a radiation): from 2.5° to 28.5° 2θ on untreated samples, from 2.5° to 14.5° 2θ on glycolated samples, and from 2.5° to 14.5° 2θ on samples heated for 2 hr at 490°C. Analytical techniques, determination, and quantitative estimation of clay minerals are detailed in Chamley and Debrabant (1984) and Holtzapffel (1985). Analytical uncertainties in the clay-mineral abundances are 5% (absolute) for abundances above 20%, 3% (absolute) for abundances between 5% and 20%, and 2% (absolute) for abundances below 5%.…”