ALBERT

Description: Deep sea sediments contain more Cu, Ni, Ba, B etc., than transport of detrital terrigenous matter (TM) can explain. Longdistance transport in dissolved from is of no importance for many of these elements. Marine biological matter (BM) is enriched in Cu, Ni, Ba, B etc. Conservative mixing models, using BM and TM as inputs show that the compositional variations in pelagic sediments can be explained by these sources. Such mixing models have been used to estimate how the influx of BM and TM have varied with time, and to what extent different elements ares upplied by BM and TM. The results show that in Cenozoic Equatorial Pacific sediments CaCO₃, opaline silica, B, Ba, and Cu are predominantly biogenous. It is probable that also P and Ni belong to this group of elements, whereas almost all Al, Ti, Zr, V and Mn are delivered by TM or some volcanic processes. The accumulation rates (AR) for the biological constituents reached maxima during the L. Oligocene and the Miocene, and minima during the U. Oligocene and the Pleistocene; some AR from the Oligocene and the Miocene being 3-6 times higher than at present. The accumulation rate patterns for opaline silica, Ba and B co-vary, whereas the AR for CaCO₃ show another time dependance pattern. These AR-patterns are probably partly due to climatic variations. Plankton in Pacific Equatorial waters incorporate much more Cu, Ni, etc., than is required for the particulate transport of these elements to the ocean floor. This suggests that transport in particulate form of BM is an important source of Cu, Ba, B, etc. for the deep sea floor.

Description: Several tissues (e.g. kidney, blood, digestive gland) in oceanic cephalopods which do not exhibit in vivo bioluminescence, luminesce when homogenized in the presence of air or when simply exposed to air in a vial (blood). The source of the luminescence appears to be a luciferin: treatment of kidney homogenates and blood with a photophore extract presumably containing luciferase resulted in a 20-fold increase in light production. Luminescence was also found in the renal fluid, which may be the source of luminescent clouds produced by squids. The variability in luminescence found in some tissues of cephalopods appeared to be related to feeding. Luminescence was also detected in the digestive glands of midwater octopods.

Description: The means of detecting downwelling light for counterillumination in several midwater animals has been examined. Eyes and extraocular photoreceptors (drosal photosensitive vesicles in the enoploteuthid squid Abraliopsis sp. B and pineal organs in the myctophid fish Myctophum spinosum) were alternately exposed to overhead light or covered by a small opaque shield above the animal and the bioluminescent response of the animal was monitored. Covering either the eyes or the extraocular photoreceptors resulted in a reduction in the intensity of counterillumination. Preliminary experiments examining the bioluminescent feedback mechanism for monitoring intensity of bioluminescence during counterillumination in the midwater squid Abralia trigonura indicated that the ventral photosensitive vesicles are responsible for bioluminescent feedback.

Description: Infrared and Mössbauer spectroscopy show that the extent of the reduction of nontronite is dependent on the chemical composition of the nontronite and on the nature of the reducing agent. Hydrazine reversibly reduces about 10% of the iron in all of the nontronites studied irrespective of composition and it is suggested that the resulting ferrous iron occurs only in distorted octahedral sites. Similar conclusions are reached for the dithionite reduction of the nontronites containing little tetrahedral iron, but for those with more than one in eight silicons replaced by iron, changes brought about by dithionite treatment are irreversible due to dissolution of appreciable quantities of iron. Results from both spectroscopic techniques suggest that iron in tetrahedral sites is preferentially dissolved and that up to 80% of the structural iron can be reduced. Evidence is presented for the formation in these extensively reduced nontronites of a small amount of a mica-like phase resembling celadonite or glauconite, and, as dithionite is used for the pretreatment of soils, the implication of this observation is briefly discussed. The use of deuterated hydrazine as a reducing agent has enabled the nontronite absorption band near 850 cm-1 to be assigned to a Si-O (apical) stretching vibration, which is inactive in the infrared for perfect hexagonal symmetry, but which is activated by distortions in the tetrahedral layer

Description: The pollen record of three marine late Quaternary cores off Senegal shows a juxtaposition of Mediterranean, Northern Saharan, Central Saharan elements, which are considered transported by the trade winds from a winter-rainfall area, and Sahelian, Soudanese, Soudano-Guinean elements, considered transported both by winds and mostly by the Senegal River, and coming from the monsoonal, summer tropical rainfall area of southern West Africa. Littoral vegetation is either the edaphically dry and saline Chenopodiaceae from sebkhas at the time of the main regression, or the warm tropical humid mangrove with Rhizophora during the humid optimum period. Four stratigraphic zones reflect, from basis to top: Zone 4. A semi-arid period with a balanced pollen input. Zone 3. A very arid period with the disappearance of monsoonal pollen, probably from the disappearance of the Senegal River, a very saline littoral plain with Chenopodiaceae, a larger input of northern Saharan pollen from intensified trade winds. Zone 2. A quite humid period, much more so than today, very suddenly established, with a northward extension of the monsoonal areas, a rich littoral mangrove, and weakening of the trade winds. Zone 1. A slow and steady evolution toward the present semi-humid conditions with regression of the mangrove, and of the monsoonal areas toward the south. Tentative datations and correlations with the Tchad area suggested: zone 4: 22,500 to 19,000 years BP; zone 3: 19,000 to 12,500 years BP; zone 2: 12,500 to 5,500 years BP; zone l: 5,500 years BP to top of core. Dinoflagellate cysts display a tropical assemblage wwith mostly estuarine neritic elements and also a weak oceanic component, mostly in the lower slope core 47. Cosmopolitan taxa dominate the assemblage and only a few species point to more specialized environments. Quantitative variations of the assemblage are the basis of stratigraphy which is not similar to the pollen stratigraphy, and an inshore-outshore gradient has to be taken into account to correlate the three cores.

Description: Surface sediments from 5 profiles between 30 and 3000 m water depth off W Africa (12-19° N) have been studied for their sand fraction composition and their total calcium carbonate and organic matter contents to evaluate the effect of climatic and hydrographic factors on actual sedimentation. On the shelf and upper slope (〈 500 m), currents prevent the deposition of significant amounts of finegrained material. The sediments forming here are characterized by high sand contents (〉 60 % ; in most samples 〉 80 %), low organic carbon contents (in most samples 〈 0.8 %), high median diameters of the sand fraction (120-500 μm), and by a predominance of quartz and biogenic relict shells (most abundant: molluscs and bryozoans) in the sand fraction. Median diameters of total sand fraction and of major biogenic sand fraction components (biogenic relict material, benthonic molluscs, benthonic and planktonic foraminifers) co-vary to some extent and show maximum values in 100-300 m water depth, reflecting the sorting effect of currents (perhaps the northward flowing undercurrent; MITTELSTAEDT 1976). In this water depth, biogenic relict material is considerably enriched relative to quartz, the second dominating sand fraction component on the shelf and upper slope, resulting in distinct calcium carbonate maxima of the bulk sediments. The influence of the undercurrent is also reflected in a northward transport of finegrained river load and perhaps in the distribution of the red stained, coarse silt and sand-sized clay aggregates, which show maxima in 300-500 m water depth. They probably originate from tropical soils. Abundant coarse red-stained quartz on the shelf off Cape Roxo (12-13° N) suggests a southward extension of last glacial dune fields to this latitude. Below about 500 m water depth, current influence becomes negligible - as indicated by a strong decrease in sand content, a concomitant increase in sedimentary organic carbon contents (up to 2.5-3.5 %), and the occurrence of high mica/quartz ratios in the sand fraction. Downslope transport, presumably due to the bioturbation mechanism proposed by BEIN & FüTTERER (1977), is indicated by the presence of coarse shelfborne particles (glauconite, relict shells) down to about 1000 m water depth. The fine/coarse ratio (clay + silt/sand) of the sediments from water depths 〉 500 m never exceeds a value of 11 in northern latitudes (19°-26° N), but shows distinct maxima, ranging from 50 to 120, at latitudes 18°, 17°, 15° 30', and 14° N in about 2000 m water depth. This distribution is attributed to the deposition of fine-grained river load at the continental slope between 18° and 14° N, brought into the sea by the Senegal and southern rivers and transported northward by the undercurrent. Strang calcium carbonate dissolution is indicated by the complete disappearance of pteropods (aragonite) and high fragmentation of planktonic foraminifers (calcite) in sediments from water depths 〉 300-600 m. Fragmentation ratios of planktonic foraminifers were found to depend on the organic carbon/carbonate ratio of the sediment suggesting that calcite dissolution at the sea bottom may also be significant in shelf and continental slope water depths if the organic matter/carbonate ratio of the surface sediment is high and the tests remain long enough within the oxidizing layer on top of the sulfate reduction zone. The fact that in the region under study intensity and annual duration of upwelling decrease from north to south is neither reflected in the composition of the sand fraction (i. e. radiolarian and fish debris contents, radiolarian/planktonic foraminiferal ratios, benthos/plankton ratios of foraminifers), nor in the sedimentary organic carbon distribution. On the contrary, these parameters even show in comparable water depths a tendency for highest values in the south, partly because primaty production rates remain high in the whole region, particularly on the shelf, due to the nutrient input by rivers in the south (SCHEMAINDA et al. 1975). In addition, several hydrographic, sedimentological and climatic factors severely affect their distribution - for example currents, dissolution, grain size composition, deposition of river load, and bulk sedimentation rates.

Description: The Baie du Lévrier (some 800 km2, 〈 20 m deep) lies at about 21° N. The climate is arid. Hydrographie conditions are controlled by (1) Trade winds, which largely determine wave base, (2) tidal currents, and (3) upwelling on the shelf nearby. Sediments range from carbonate-poor silty muds to carbonate-rich sands. Below wa ve base sediments characteristically have 〈 30% sand, sand medians 〈 125 μm and 55-80% silt, whereas wave-washed sediments have 〉 70% sand with medians 〉 400 μm. Other dynamic factors, notably tidal currents, may blur the distinction between these two populations. Sources for the terrigenous components are (1) modern aeolian dunes whose sands enter the sea to form a prograding coastal sediment wedge; (2) wind dust deposited as silty muds below wave base; (3) sub-Recent relict material on the seafloor; ( 4) cliff and bank erosion (local); (5) sea bed-load, significant in current-washed areas. Non-terrigenous components include pellets, ooids and skeletal debris. Pellets, incompletely indurated and mainly faecal, form up to 2/3 of the sand fraction in muds below wave base. Relict pellets are rare. Superficial ooids occur in trace quantities in some beach and nearshore samples. Skeletal debris accounts for most of the carbonate sand and also contributes significant quantities of biogenic opal and phosphatic material. Relict and mineralized (goethite and Fe-silicates) skeletal grains are locally important. Like the modern skeletals they are of foramol type. In the modern skeletal sand molluscan material is ubiquitous ( 〈 20% to 〉 90% of skeletal sand) but, as little can be identified further, molluscs as a whole have little interpretative value. Other skeletals form two groups: ( 1) typical of the banks and flanks of the bay, includes barnacles, worm tubes, calcareous red algae, bryozoans and alcyonarian spicules (the two lattcr tend to occur close to rather than on the banks and to lie below wave base rather than in the wave zone as the others do); (2) found in "basinal" sediments below wave base, includes calcarcous, opalinc and phosphatic forms: foraminifers (benthonic and planktonic), echinoderms, ostracodes, sponge spicules, diatoms (planktonic and benthonic) and fish remains. From the relationships between the bank and "basinal" groups five skeletal grain assemblages are recognized and shown to be related to sedimentary facies (ranging from carbonate-poor, silty mud facies with foraminifers, sponge spicules, diatoms and fish remains, to carbonate-rich sand facies characterized by bank group skeletals, particularly barnacles). Within some of the assemblages there are marked and systematic lateral shifts in relative importance of skeletal components. All these features can be interpreted in terms of source and transportability of the grains, some (e.g. barnacle) being moved principally as bed load, while others are carried in suspension. Laterally graded suspensions are proposed to explain the distribution of the components of the "basinal" group and also, near banks (or flanks), of alcyonarian spicules and bryozoans. Proximity to oceanic influences is expressed particularly in fine-grained "basinal" sediments by relative increase of echinoderms, ostracodes and molluscs (particularly Pinna needles) as well as of planktonic foraminifers and diatoms relative to benthonic ones. Significant regional environmental features are expressed in the sediments as follows: Aridity limits terrigenous sediments to a coastal wedge of dune-derived sands, aeolian dust in silty muds below wave base, and products of local cliff erosion. By precluding freshwater "dilution" it allows evaporation to increase salinity and a few ooids form. Combination of offshore upwelling and the Canary Current accounts for the presence of the foramol skeletal association in the tropics, and for the unusually high percentage of biogenic opal (up to 〉 12% of total sample), (cool-water) planktonic foraminifers (up to 〉 25% of total foraminifers), fish debris, and perhaps also of ostracodes. The general water temperature and salinity regime is such that the Baie du Lévrier lies in a critical position on or near the boundaries between major provinces of carbonate sedimentation both for skeletal (foramol, but chloralgal known 150 km to south) and non-skeletal components (normally pellet, but oolithaggregate locally reached).

Description: Geophysical and geological surveys by R.V. "Meteor" (1967, 1975, 1977) and R.V. "Vema" (1973) revealed new information on the seismic stratigraphy and geological evolution of the Mazagan Marginal Plateau. Fragments of a light-colored, mylonitic granite were recovered from the base of the escarpment and interpreted as slivers of foundered continental basement, pushed upwards along landward dipping thrust faults. The upbuilding of a 〉 2 km thick carbonate platform during (? pre-)Oxfordian to middle Cretaceous times kept pace with its fast subsidence (up to 80 m/m.y.). At the foot of the 27-38° steep escarpment we dredged an Oxfordian well sorted algal and foraminiferal limestone which is devoid of any terrigenous components and full of shallow-water organisms; it indicates an euphotic, sublittoral, perireefal environment. Upslope on the escarpment, we infer outcrops of middle Aptian to early Albian quartzose, calcareous and siliceous nanno claystones which reflect an outer shelf setting. Below the outer Mazagan Plateau, seismic evidence suggests that individual reefal bioherms continued to grow above a mid-Cretaceous unconformity, while the underlying carbonate platform subsided below wave base and was covered by Late Cretaceous pelagic sediments. A Paleogene (? Paleocene) and an Oligocene unconformity can be distinguished on seismic records and correlated to Cretaceous and Tertiary outcrops on the shelf off EI Jadida. Paleogene glauconitic marls and thin Neogene hemipelagic sediments top the plateau and represent a slope environment of deposition.