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.

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Neogene ocean history is dominated by the theme of stepwise global cooling (with occasional reversals); the main trends of carbonate sedimentation on the Ontong Java Plateau show the regional response of productivity, dissolution, winnowing, and redeposition to this overall climatic change. The relative importance of these processes in controlling accumulation rates and carbonate content is difficult to assess for any given place and time. Thus, the outstanding feature of the carbonate record, the Tortonian-Messinian accumulation rate peak centered in the latest Miocene (maximum sedimentation rate >60 m/m.y.), is the product of a complex interplay of a general late Miocene to early Pliocene productivity maximum combined with increased mechanical and chemical erosion before and after the peak. The mix of erosional factors depends on the depth level considered and changes with time. Increased productivity apparently derives from high nutrient content in Pacific deep waters, caused by increased production of North Atlantic Deep Water (NADW) in the latest Miocene and basin-basin fractionation. Enhancement of the thermocline strength is indicated at that time from an increase in planktonic foraminifers living at intermediate depths. A fundamental change in the mode of productivity (toward pulsed productivity?) is indicated by changes in the coccolith flora.The main focus of this study is the definition of major patterns of sedimentation and associated open questions, as follows:1. Carbonate records are parallel over a wide depth range. Does this mean that dissolution is also important on the upper plateau? Or is there a "conspiracy" of separate factors acting in concert?2. Dissolution of carbonate cannot explain both carbonate and sedimentation rate patterns. The "loss paradox*' arises from the fact that carbonate percentages at different depths are so similar that the differences in carbonate are insufficient to account for differences in sedimentation rate, assuming that dissolution produces these differences.3. Equatorial crossings have little or no effect on carbonate content or sedimentation rate. "Equatorial insensitivity" indicates that equatorial upwelling is of subordinate importance in biogenic sedimentation on the plateau in the late Neogene (as is the case today).4. There is evidence for a general insensitivity of both carbonate and sedimentation rate records with regard to global changes in conditions, as seen in commonly used proxies. Changes in δ 18 θ of benthic foraminifers, for example, and sea-level changes (as mapped by sequence stratigraphy) are not clearly correlated with the main parameters of Neogene carbonate sedimentation on the plateau. Correspondence to the δ 3 C record is somewhat better, however. Proxies may be ill defined, or the regional overprint may obscure global relationships.The issues listed above are of a very general nature. Without a successful attack on these questions, the major patterns of carbonate sedimentation on the plateau will remain enigmatic, as will many phe...

Differential dissolution affects the isotopic composition of different species of planktonic foraminifera in different ways. In the two species studied here in cores from Ontong 3ava Plateau, the less resistant species, Globigerinoides sacculifer, is more readily affected at a shallower depth than the more resistant species, Pulleniatina obliquiloculata (2.9 versus 3.4 km), but shows a smaller and less predictable response to partial dissolution (0.2 to 0.3 per mil versus 0.6 to 0.7 per mil). Comparison of isotopic values from the last glacial period with those from the late Holocene indicates that the apparent dissolution effect is considerably reduced during the last glacial, presumably due to reduced dissolution intensity during glacial time. A change in the level of the lysocline of about 400 m is suggested. In the published isotope records from Pacific cores V28-238 and V28-239, the dissolution-generated difference in 6180 (noted previously by Shackleton and Opdyke [1976]) is seen to describe a mid-Brunhes dissolution maximum, between 300 and 500 thousand years ago. This mid-

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Thirteen sites were occupied during Ocean Drilling Program Leg 175 along southwestern Africa, starting with the Congo Fan in the north and ending off the Cape of Good Hope. North of the Walvis Ridge, penetration was limited because of safety concerns. Sediments from the Congo Fan are rich in opal. Maximum rates of sedimentation were found at holes drilled off Lobito (Angola), with rates as high as 60 cm/k.y. because of high terrigenous influx from a rising coast. On the Walvis Ridge and in the Walvis Bay, organic matter-rich calcareous clays were recovered. The highest organic content, the most vigorous development of methane and carbon dioxide, and abundant noxious gases were found at Site 1084, located off Lüderitz, Namibia. The sites occupied off the Cape of Good Hope are characterized by calcareous oozes. Organic matter abundance, diatom accumulation, and composition of benthic faunas, among other indicators, are the most important tools for the reconstruction of the productivity history of the Angola-Benguela upwelling system. Problems arising include (1) the origin of the Matuyama Opal Maximum, centered near 2.2 Ma, (2) the question of phase relationships between diatom productivity and organic matter supply, and (3) the role of precessional effects in the modulation of productivity as a function of latitude. Regarding the first problem, it emerged that the maximum supply of diatoms is linked to incursions of both warm pelagic water and Antarctic water during the early Matuyama, presumably resulting in the formation of chaotic frontal zones. Coastal upwelling dominates after the maximum. Thus, opal deposition goes through an optimum situation within the latest Pliocene. We hypothesize that increased silicate concentrations in subsurface waters made this optimum possible. As the Benguela Current became stronger in the Quaternary, a more vigorous flow of underlying Antarctic Intermediate Water increased ventilation of the thermocline off southwestern Africa, thereby helping to decrease the silicate content of subsurface waters. Observations during Leg 75 regarding glacial/interglacial cycles on the Walvis Ridge (that warming is accompanied by