ALBERT

Description: DSDP Leg 26, is the fifth cruise of D/V Glomar Challenger in the Indian Ocean, and the first cruise of Phase III of the Deep Sea Drilling Project. The Indian Ocean is the smallest of the three major ocean basins but appears to be geologically the most complex. The sites drilled on Leg 26 were selected to try to elucidate a number of specific problems of both local and broad regional significance, as well as to add to the general knowledge of the area. In particular: a) To locate the oldest sediment in the Indian Ocean and thus possibly the date of the initial breakup of Gondwanaland (Sites 250, 256, 257); b) To determine the effects of the initiation of the Circumpolar Current on southern Indian Ocean sedimentation (Sites 250, 252, 256, 257, 258); c) To determine the history of spreading of the Southwest Branch of the Indian Ocean Ridge and the history of the crust and oceanic sedimentation in that general region (Sites 250, 251, 252).

Description: Cruise MN-74-01 of the R/V Moana Wave was the first part of the field work of the NSF-IDOE Inter-University Ferromanganese Research Program in 1974. This program was designed to investigate the origin, growth, and distribution of copper/nickel-rich manganese nodules in the Pacific Ocean. The field effort was designed to satisfy sample requirements of the 15 principal investigators, while increasing general knowledge of the copper/nickel-rich nodule deposits of the equatorial Pacific. This report is the first of a series of cruise reports designed to assist sample requests for documented nodules, sediment, and water samples so the laboratory results can be realistically compared and related to the environment of nodule growth.

Description: Site 76 was selected in order to core a thick sequence of sediments north of the Tuamotu ridge that had been crossed by Glomar Challenger justprior to the termination of Leg 8 in Tahiti. Two holes at this site continuously cored 27 meters of lower Pliocene to Recent phillipsitic clay and calcareous nannofossil ooze interbedded with calcareous turbidites. The drill bit was stopped by a silicified calcareous turbidite of Early Pliocene age.

Description: Site 79 is located on the crest of the equatorial Pacific sediment belt (Ewing and others, 1968) and is the westernmost of a series of sites (79, 81, 82 and 83) that follow the crest of this belt eastward to and across the crest of the oceanic ridge, locally known as the East Pacific Rise. The purpose of these sites is two-fold: 1) to study variations in biostratigraphy and sediment type from west to east across the Pacific and 2) to paleontologically date basement and determine the rate of spreading of the Pacific plate since the time of deposition of the oldest sediments at Site 77.

Description: Because of its position between the North Atlantic and the Arctic oceans, its young age, small size, and diversity of geological structures, the Norwegian-Greenland Sea provided a unique target for deep drilling on Leg 38 of the Glomar Challenger. From studies of the sediments and basement rocks it was expected to gain insight particularly as to the following: 1) The tectonic framework and evolution of this area with special emphasis on the continental margins and on questions concerned with shifts of spreading axis and existence of foundered continental areas. 2) The youngest times of existence of land bridges between Eurasia and North America and the effect these land bridges had on water circulation and paleoclimates. 3) The date of the initiation of glaciation and dates of glacial advances and retreats. 4) Description of the Tertiary marine microfauna and microflora of the Norwegian-Greenland Sea, which are essentially unknown at present, and investigation of their similarity with microfauna and microflora from other areas.

Description: Unlike many cruises of the Deep Sea Drilling Project, Leg 48 was scientifically planned to drill a number of sites to systematically address the problems of passive margin evolution. Site 400 was drilled at the foot of the Meriadzek Escarpment of North Biscay in 4399 meters depth. The site was located in a half-graben forming part of a succession of tilted and rotated fault blocks near the continent/ocean boundary. Site 401 was situated on the planated edge of a tilted fault-block underlying the southern edge of the Meriadzek Terrace on the north Biscay margin. Site 402 was located on the upper slope of the northern continental margin of the Bay of Biscay. The main objectives were to establish the presence or absence of shallow water Upper Cretaceous beds, and to penetrate pre-Aptian synrift sediments and the upslope equivalent of the deep water Albian-Aptian carbonaceous mudstones penetrated at Hole 400A.

Description: IPOD Leg 49 recovered basalts from 9 holes at 7 sites along 3 transects across the Mid-Atlantic Ridge: 63°N (Reykjanes), 45°N and 36°N (FAMOUS area). This has provided further information on the nature of mantle heterogeneity in the North Atlantic by enabling studies to be made of the variation of basalt composition with depth and with time near critical areas (Iceland and the Azores) where deep mantle plumes are thought to exist. Over 150 samples have been analysed for up to 40 major and trace elements and the results used to place constraints on the petrogenesis of the erupted basalts and hence on the geochemical nature of their source regions. It is apparent that few of the recovered basalts have the geochemical characteristics of typical "depleted" midocean ridge basalts (MORB). An unusually wide range of basalt compositions may be erupted at a single site: the range of rare earth patterns within the short section cored at Site 413, for instance, encompasses the total variation of REE patterns previously reported from the FAMOUS area. Nevertheless it is possible to account for most of the compositional variation at a single site by partial melting processes (including dynamic melting) and fractional crystallization. Partial melting mechanisms seem to be the dominant processes relating basalt compositions, particularly at 36°N and 45°N, suggesting that long-lived sub-axial magma chambers may not be a consistent feature of the slow-spreading Mid-Atlantic Ridge. Comparisons of basalts erupted at the same ridge segment for periods of the order of 35 m.y. (now lying along the same mantle flow line) do show some significant inter-site differences in Rb/Sr, Ce/Yb, 87Sr/86Sr, etc., which cannot be accounted for by fractionation mechanisms and which must reflect heterogeneities in the mantle source. However when hygromagmatophile (HYG) trace element levels and ratios are considered, it is the constancy or consistency of these HYG ratios which is the more remarkable, implying that the mantle source feeding a particular ridge segment was uniform with respect to these elements for periods of the order of 35 m.y. and probably since the opening of the Atlantic. Yet these HYG element ratios at 63°N are very different from those at 45°N and 36°N and significantly different from the values at 22°N and in "MORB". The observed variations are difficult to reconcile with current concepts of mantle plumes and binary mixing models. The mantle is certainly heterogeneous, but there is not simply an "enriched" and a "depleted" source, but rather a range of sources heterogeneous on different scales for different elements - to an extent and volume depending on previous depletion/enrichment events. HYG element ratios offer the best method of defining compositionally different mantle segments since they are little modified by the fractionation processes associated with basalt generation.

Description: Twenty-four manganese nodules from the surface of the sea floor and fifteen buried nodules were studied. With three exceptions, the nodules were collected from the area covered by Valdivia Cruise VA 04 some 1200 nautical miles southeast of Hawaii. Age determinations were made using the ionium method. In order to get a true reproduction of the activity distribution in the nodules, they were cut in half and placed for one month on nuclear emulsion plates to determine the alpha-activity of the ionium and its daughter products. Special methods of counting the alpha-tracks resolution to depth intervals of 0.125 mm. For the first time it was possible to resolve zones of rapid growth (impulse growth) with growth rates, s 〉 50 mm/106 yr and interruptions in growth. With few exceptions the average rate of growth of all nodules was surprisingly uniform at 4-9 mm/10 yr. No growth could be recognized radioactively in the buried nodules. One exceptional nodule has had recent impulse growth and, in the material formed, the ionium is not yet in equilibrium with its daughter products. Individual layers in one nodule from the Indian Ocean could be dated and an average time interval of t = 2600±400 yr was necessary to form one layer. The alternation between iron and manganese-rich parts of the nodules was made visible by colour differences resulting from special treatment of cut surfaces with HCl vapour. The zones of slow growth of one nodule are relatively enriched in iron. Earlier attempts to find paleomagnetic reversals in manganese nodules have been continued. Despite considerable improvement in areal resolution, reversals were not detected in the nodules studied. Comparisons of the surface structure, microstructure in section and the radiometric dating show that there are erosion surfaces and growth surfaces on the outer surfaces of the manganese nodules. The formation of cracks in the nodules was studied in particular. The model of age-dependent nodule shrinkage and cracking surprisingly indicates that the nodules break after exceeding a certain age and/or size. Consequently, the breaking apart of manganese nodules is a continuous process not of catastrophic or discontinuous origin. The microstructure of the nodules exhibits differences in the mechanism of accretion and accretion rate of material, shortly referred to as accretion form. Thus non-directional growth inside the nodules as well as a directional growth may be observed. Those nodules with large accretion forms have grown faster than smaller ones. Consequently, parallel layers indicate slow growth. The upper surfaces of the nodules, protruding into the bottom water appear to be more prone to growth disturbances than the lower surfaces, immersed in the sediment. Features of some nodules show, that as they develop, they neither turned nor rolled. Yet unknown is the mechanism that keeps the nodules at the surface during continuous sedimentation. All in all, the nodules remain the objects of their own distinctive problems. The hope of using them as a kind of history book still seems to be very remote.

Description: Phosphatized bioclastic limestones of Early Tertiary age have been dredged from the crest of a seamount in the equatorial Atlantic near 9°N, 21°W. The samples were recovered from water depths of 700 to 970 m but clearly were deposited in a high-energy reefal environment, thus indicating significant Tertiary subsidence. The vertical movement is beleived to reflect reactivation of an old structural line, the Guinée Fracture Zone, which may have had important effects on the transfer of bottom waters of polar origin between the Sierra Leone and Gambia basins. Examination of foraminiferal limestone coating the shallow water material suggests that deep-water conditions were established on the seamount by Middle Miocene time. All phosphatized samples are covered with a layer of ferromanganese oxides which, from textural and faunal evidence, is Palaeocene or Eocene in age and of shallow water origin. Pervasive phosphatization of the bioclastic limestones appears to have been accomplished before the end of the Eocene while the crest of the seamount was near sea level, because Upper Eocene limestone of shallow water facies is unaffected by such radical diagenesis. Phosphatization probably was associated with vigorous upwelling near the seamount and has been taken to an unusually advanced stage, resulting in a phosphoritesof high economic grade. P2O5 contents are in the range of 37 to 41%. The purity of the phosphorites may be related to the intensity of upwelling during the Early Tertiary, but other factors such as the paucity of terrigenous detritus, frequent reworking of the sedimentary capping of the seamount, and a high primary porosity of the limestones may have been important in their information. The Early Tertiary period of phosphorite deposition on the seamount and in northwest Africa ended before the close of Eocene time in both areas, while shallow water conditions prevailed. It is argued that the cessation of phosphorite formation reflects major changes in the surface circulation of the Atlantic during the Eocene.

Description: This chapter discusses the formation and distribution of some metals in ocean-floor manganese nodules in the light of the observed data in the literature and thermodynamic and kinetic considerations of the oxidation of metal ions in the oceanic environment. There are, in general, two major schools of thought on the mechanism of incorporation of the minor elements such as nickel, copper, and cobalt with the major elements such as manganese and iron. One is the lattice substitution mechanism and the other the adsorption mechanism. If the mechanism is lattice substitution, extraction of the metal ions is not possible unless the lattice of the major elements is first broken and exchanged with other ions from the bulk solution. Consequently, the leaching behavior of minor elements should display a very close relationship with that of major elements.