ALBERT

Description: Analyses by atomic absorption spectrophotometry and spark-source mass spectrography of 25 basal metalliferous sediment units from widely spaced locations on the western flank of the East Pacific Rise show that the deposits are enriched relative to normal pelagic sediment in Fe, Mn, Ni, Cu, Pb, Zn, and many trace elements. The elements are partitioned differently between the various mineralogic constituents of the sediment, with Fe and Mn largely in separate phases and many of the remaining elements primarily associated with reducible ferromanganese oxide minerals but also with iron minerals and other phases. Most of the iron in the deposits is probably of volcanic origin, and much of the manganese and minor elements is derived from sea water. The bulk composition of the deposits varies with age; this is thought to be due to variations in the incidence of volcanic activity at the East Pacific Rise crest where the deposits were formed.

Description: Pliocene and Pleistocene planktonic foraminiferal biogeography and paleoceanography have been examined in Deep Sea Drilling Project (DSDP) sites of the Panama Basin (Pacific Ocean) and Colombian and Venezuelan Basins (Atlantic Ocean) to determine the timing of the isolation of Atlantic and Pacific tropical planktonic faunas resulting from the development of the Central American isthmus. Previous studies have suggested a late Miocene to middle Pliocene occurrence of this event. The Panama Basin (DSDP site 157) and the Colombian Basin (DSDP site 154A) share two early Pliocene biogeographic events: (1) great abundance of sinistral coiling Neogloboquadrina pachyderma at 4.3 m.y. ago at site 157 and 0.7 m.y. later at site 154A, and (2) a sinistral-to-dextral change in the coiling-direction preference in Pulleniatina 3.5 m.y. ago at both locations. Identification of these events farther to the east in the Venezuelan Basin (DSDP site 148) is complicated by insufficient lower Pliocene core recovery, but abundant sinistral N. pachydcrma appear to have extended far to the east in the Caribbean 3.6 m.y. ago; perhaps the early Pliocene abundance of this form is not indicative of cool water. The coiling-direction history and stratigraphic ranges of Pulleniatina became different in the Atlantic and Pacific Oceans during the early Pliocene; this is inferred to result from geographic isolation of the assemblages. Saito (1976) used the temporary disappearance of this genus from Atlantic waters at 3.5 m.y. ago to mark the closure of the Isthmus of Panama, but I show that in the Colombian Basin (site 154A) its disappearance was closer to 3.1 m.y. ago. This suggests the possibility of surface-water communication between the Atlantic and Pacific until that time.

Description: The uranium content of glass from chilled margins of oceanic tholeiitic basalt flows is generally 〈0.1 ppm, even for old samples with highly altered crystalline interiors. Such low values represent the original whole rock concentrations, although subsequent to eruption low-temperature weathering has added uranium, and other elements, to the crystalline portions of these basalts. Consideration of the K/U ratios of altered samples suggests that basalt weathering may provide the major oceanic sink for these two elements.

Description: Accumulation rates of Mg, Al, Si, Mn, Fe, Ni, Cu, Zn, opal, and calcium carbonate have been calculated from their concentrations in samples from equatorial Deep Sea Drilling Project sites. Maps of element accumulation rates and of Q-mode factors derived from raw data indicate that the flux of trace metals to equatorial Pacific sediments has varied markedly through time and space in response to changes in the relative and absolute influence of several depositional influences: biogenic, detrital, authigenic, and hydrothermal sedimentation. Biologically derived material dominates the sediment of the equatorial Pacific. The distributions of Cu and Zn are most influenced by surface-water biological activity, but Ni, Al, Fe, and Mn are also incorporated into biological material. All of these elements have equatorial accumulation maxima similar to those of opal and calcium carbonate at times during the past 50 m.y. Detritus distributed by trade winds and equatorial surface circulation contributes Al, non-biogenic Si, Fe, and Mg to the region. Detrital sediment is most important in areas with a small supply of biogenic debris and low bulk-accumulation rates. Al accumulation generally increases toward the north and east, indicating its continental source and distribution by the northeast trade winds. Maxima in biological productivity during middle Eocene and latest Miocene to early Pliocene time and concomitant well-developed surface circulation contributed toward temporal maxima in the accumulation rates of Cu, Zn, Ni, and Al in sediments of those ages. Authigenic material is also important only where bulk-sediment accumulation rates are low. Ni, Cu, Zn, and sometimes Mn are associated with this sediment. Fe is almost entirely of hydrothermal origin. Mn is primarily hydrothermal, but some is probably scavenged from sea water by amorphous iron hydroxide floes along with other elements concentrated in hydrothermal sediments, Ni, Cu, and Zn. During the past 50 m.y. all of these elements accumulated over the East Pacific Rise at rates nearly an order of magnitude higher than those at non-rise-crest sites. In addition, factor analysis indicates that some of this material is carried substantial distances to the west of the rise crest. Accumulation rates of Fe in basal metalliferous sediments indicate that the hydrothermal activity that supplied amorphous Fe oxides to the East Pacific Rise areas was most intense during middle Eocene and late Miocene to early Pliocene time.

Description: Stable isotopic analyses of Middle Miocene to Quaternary foraminiferal calcite from east equatorial and central north Pacific DSDP cores have provided much new informatlon on the paleoceanography of the Pacific Neogene The history of delta18O change in planktonic foraminifera reflects the changing Isotopic composition and temperature of seawater at the time of test formation. Changes in the isotopic composition of benthonic foraminifera largely reflect changes m the volume of continental ice. Isotopic data from these cores indicates the following sequence of events related to continental glaciation (1) A permanent Antarctic ice sheet developed late in the Middle Miocene (about 13 to 11.5 m.y. ago) (2) The Late Miocene (about 11.5 to 5 m.y. ago) is marked by significant variation in delta18O of about 0.5‰ throughout, indicating instability of Antarctic ice cap size or bottom-water temperatures (3) The early Pliocene (5 to about 3 m.y. ago) was a time of relative stability in ice volume and bottom-water temperature (4) Growth of permanent Northern Hemisphere ice sheets is referred to have begun about 3 m.y. ago (5) The late Pliocene (3 to about 1.8 m.y. ago) is marked by one major glaciation or bottom-water cooling dated between about 2.1 to 2.3 m.y. (6) There is some evidence that the frequency of glacial-interglacial cycles increased at about 0.9 m.y. There is significant variation in delta13C at these sites but no geochemical interpretation is offered in this paper. The most outstanding feature of delta13C results is a permanent shift of about -0.8‰ found at about 6.5 m.y. in east equatorial and central north Pacific benthonic foraminifera. This benthonic carbon shift may form a useful marker in deep-sea cores recovering Late Miocene carbonates.

Description: Seventy four samples of DSDP recovered cherts of Jurassic to Miocene age from varying locations, and 27 samples of on-land exposed cherts were analyzed for the isotopic composition of their oxygen and hydrogen. These studies were accompanied by mineralogical analyses and some isotopic analyses of the coexisting carbonates. d18O of chert ranges between 27 and 39%. relative to SMOW, d18O of porcellanite - between 30 and 42%. The consistent enrichment of opal-CT in porcellanites in 18O with respect to coexisting microcrystalline quartz in chert is probably a reflection of a different temperature (depth) of diagenesis of the two phases. d18O of deep sea cherts generally decrease with increasing age, indicating an overall cpoling of the ocean bottom during the last 150 m.y. A comparison of this trend with that recorded by benthonic foraminifera (Douglas and Savin, 1975; http://www.deepseadrilling.org/32/volume/dsdp32_15.pdf) indicates the possibility of d18O in deep sea cherts not being frozen in until several tens of millions of years after deposition. Cherts of any Age show a spread of d18O values, increasing diagenesis being reflected in a lowering of d18O. Drusy quartz has the lowest d18O values. On-land exposed cherts are consistently depleted in 18O in comparison to their deep sea time equivalent cherts. Water extracted from deep sea cherts ranges between 0.5 and 1.4 wt %. dD of this water ranges between -78 and -95%. and is not a function of d18O of the cherts (or the temperature of their formation).

Description: A large manganese nodule (manganese slab) was dredged from 2100 m on the Scott Plateau by R.V. Valdivia in 1977. It is an irregular ellipsoid, with a maximum dimension of 28 cm, parallel to the sea floor. Chemical analyses show that Mn and Fe proportions are comparable, and total Ni + Cu + Co content averages 0.7%. The nodule has a complex growth history which started with radial upward growth leading to coalescing into a continuous crust. The crust was coated with horizontal layers. After fracturing and infilling of cracks with calcareous sediment, further layers encased the nodule.

Description: Basalt underlying early Campanian chalk at Deep Sea Drilling Project (DSDP) Site 163 is divided into seven extrusive cooling units bounded by glassy margins. The margins have dips of 15° to 70°, suggestive of pillow flows rather than tabular flows. The margins are fresh sideromelane (glass) grading inward to opaque and reddish-brown globules containing microcrystalline material with radial, undulose extinction. Relative to adjacent sideromelane, the reddish-brown globules are enriched in sodium and calcium, whereas the opaque globules are depleted in these elements and enriched in iron and magnesium. It appears that basalt just inside the pillow margins has differentiated in place into globules of two distinct compositions. This globule zone grades inward to less rapidly cooled pyroxene varioles and intergrowths of plagioclase and opaque minerals. In the center of the thicker cooling units, the texture is diabasic. Alteration and calcite vein abundance are greatest at pillow margins and decrease inward; the interior of the thickest cooling unit is only slightly altered, and calcite veins are absent. Chemical analysis of whole rock by atomic absorption spectrophotometry, and of sideromelane by electron microprobe, indicates that the rock is a slightly weathered tholeiite. The atomic absorption analyses, except the one nearest the top of the basalt, are relatively uniform and similar to the sideromelane microprobe analyses, including those near the top of the basalt. This suggests that deep penetration is not necessary to get through the severely altered layer at the basalt surface, and that within this altered layer, analyses of sideromelane may be more representative of crustal composition than analyses of whole rock.

Description: The cores described in this report were taken on the SEVENTOW Expedition in February-September 1970 by the Scripps Institution of Oceanography from the R/V Thomas Washington. A total of 193 cores and dredges were recovered and are available at Scripps for sampling and study.

Description: This site was accidentally spudded on a small basement pinnacle and was abandoned when hard rock was reached within a few meters from the surface. The section penetrated consisted of coarse winnowed calcareous sand over thin chalk ooze resting on a hard crust of ferromanganese oxide presumably covering basalt.