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Leg 14 of the Deep Sea Drilling Project completed 9 holes; 7 were located off NW Africa, 1 in Ceara Abyssal Plain, and 1 on Demerara Rise. Quaternary and Pliocene sediments consist of nanno chalk oozes and brown clay. The facies boundary (CCD) is near 5000 meters. Sedimentation rates are between 10 and 30 meters/million years (m/My) for chalk ooze and 2 to 4 m/My for pelagic clay. Redeposition off the Amazon produces terrigenous and bioclastic turbidite sequences with rates increasing, on the average, from 50 to 150 m/My. During the Miocene the CCD is shallow, with restricted calcareous ooze and extended brown clay domain. Terrigenous and siliceous deposits are abundant off NW Africa. The Oligocene is characterized by a major hiatus; where present (Demerara Rise, foot of continental rise), it appears similar to the Miocene. Off NW Africa, Eocene sediments consist of brown clays, in part zeolitic, and greenish clays which, though rich in quartz and siliceous fossils, are less rich than Miocene sediments. Chert is rare. On Demerara Rise, the Eocene is represented by siliceous foram-nanno chalk. The Paleocene rests unconformably on Maestrichtian at Site 144, where the Cretaceous-Tertiary boundary was cored. Off NW Africa, brown and green pelagic clay and dolomite-clay (chert) cycles apparently belong to this period. The major sediment types of the Post-Cenomanian Cretaceous are zeolitic radiolarian, brown clay, black shale, limestone beds and chert layers. Redeposition is thought to play a major role in the origin of ümestones and cherts. Cenomanian carbonates consist mainly of nanno marl ooze, presumably deposited on an ancestral Mid-Atlantic Ridge. Calcareous carbonaceous sediments intercalated with limestone beds occur on Demerara Rise. Below the CCD, black shales, limestones and chert accumulated off NW Africa. Near the presumed boundary of ancestral ridge flank and continental rise, cyclic sequences of black shale and dolomite silts (in part ankerite) were deposited. Aptian and Albian sediments consist of black nanno marl off NW Africa and of shelly and quartzose calcarenite, and carbonaceous clay on Demerara Rise. The changing sediment patterns are related to changes in topography (continental drift, sea-floor spreading, sea-floor subsidence, orogenic activity including compressional buckling at the Gibraltar Fracture Zone) and changes in deep-sea circulation (carbonate under-saturation, oxygenation, nutrient concentration, bottom current strength), upper water circulation (from transAtlantic to intra-Atlantic currents, variations in upwelling, fertility), and redeposition processes.

The upper Holocene marine section from a kasten core taken from the oxygen minimum zone off Karachi (Pakistan) at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1.2 mm/yr and a unique record of monsoonal climatic variability covering the past 5000 years. Our chronostratigraphy is based on varve counts verified by conventional and AMS14C dating. Individual hemipelagic varve couplets are about 0.8–1.5 mm thick, with light-colored terrigenous laminae (A) deposited mainly during the winter monsoon alternating with dark-colored laminae (B) rich in marine organic matter, coccoliths, and fish debris that reflect deposition during the high-productivity season of the late summer monsoon (August–October). Precipitation and river runoff appear to control varve thickness and turbidite frequency. We infer that precipitation decreased in the river watershed (indicated by thinning varves) after 3500–4000 yr B.P. This is about the time of increasing aridification in the Near East and Middle East, as documented by decreasing Nile River runoff data and lake-level lowstands between Turkey and northwestern India. This precipitation pattern continued until today with precipitation minima about 2200–1900 yr B.P., 1000 yr B.P., and in the late Middle Ages (700–400 yr B.P.), and precipitation maxima in the intervening periods. As documented by spectral analysis, the thickness of varve couplets responds to the average length of a 250-yr cycle, a 125-yr cycle, the Gleissberg cycle of solar activity (95 yr), and a 56-yr cycle of unknown origin. Higher frequency cycles are also present at 45, 39, 29–31, and 14 yr. The sedimentary gray-value also shows strong variability in the 55-yr band plus a 31-yr cycle. Because high-frequency cyclicity in the ENSO band (ca. 3.5 and 5 yr) is only weakly expressed, our data do not support a straightforward interaction of the Pacific ENSO with the monsoon-driven climate system of the Arabian Sea.

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