Nodule Field Research Articles

Nodules of Hydrothermal Birnessite in the Caldera of a Young Seamount

Manganese nodules made of radiating rods of well crystallized birnessite were sampled at 8° 481.2'N, 103° 53.8'W, 1875 m below sea level by a dredge that also collected hyaloclastite and basaltic talus. The nodule field is on the floor of a caldera within a young tholeiitic seamount and was discovered and photographed during a deep-two survey. It is interpreted as a brecciated hydrothermal deposit, crystallized from an amorphous manganese oxide precipitate that formed when seawater-based hydrothermal fluids mixed with oxidized seawater. The nodules and surrounding igneous rocks have subsequently been encrusted with hydrogenous ferromanganese oxides.

Distribution of Si, Mn, Fe, Ni, Cu, Co, Zn, Pb, Mg, and Ca in reain-size fractions of sediment samples from a manganese nodule field in the Central Pacific Ocean

Deep-sea sediment samples from a manganese nodule field of the Central Pacific were separated into eight grain-size fractions. From these fractions chemical analyses were made for the elements Si, Mm, Fe, Ni, Cu, Co, Zn, Pb, Mg, and Ca. Mn, Cu, Ni, and, less significantly, Co and Zn are enriched in the 10–20 μm fraction. Fe and Mg show a continuous increase with decreasing grain size, whereas SiO 2 is characterized by diminution. Pb does not show any correlation with the other elements. More than 50% of each of Mg, Fe, Cu, Zn, and Pb is bound in the < 2 μm fraction. The metals Mn-Ni-Cu-Co on the one hand, and Mg-Fe on the other, show good positive correlations. In the finer fractions clay minerals and colloidal particles are important carrier matters for metals as are micronodules and opaline silica skeletons in coarser grain-size classes. Assuming that all the Mn in samples is fixed to micronodules, our calculations (based on chemical analyses of micronodules) prove that the following proportions of metal are not fixed to micronodules: Ni: 25%, Cu: 63%, Co: 85%, Zn: 82%, Pb: 88%. About 30% of the non-nodular metal amounts are fixed to the > 4 μm fraction. The significance of these results and implications for the metal supply during the growth of macronodules are discussed.

Significance of Unstained and Stained Gravel on the Newfoundland Continental Slope and Rise

ABSTRACT The continental slope and rise, east of Newfoundland, accommodates two distinct gravel populations. The upper slope (300-700 m depth) population is characterized by unstained, granules to boulders of predominantly granitic and terrigenous sedimentary composition that show affinity to Paleozoic and Proterozoic rocks of Newfoundland and areas further north. The rise (2,500->3,000 m depth) population consists of iron- and ferromanganese-stained granules to cobbles composed mainly of carbonate that presumably has been derived from the high Canadian Arctic. The rise clasts are further distinguished in that they are finer grained, slightly more rounded and more altered by solution and/or boring organisms than their shallower water counterparts. The upper slope gravel has been reworked from underlying sediments, and deposited from ice rafts, and both processes are probably continuing today. Gravel on the rise has been concentrated through winnowing of middle Holocene sediments by the Western Boundary Undercurrent which appears to have been operative as a winnowing agent since about 4,000 to 5,000 y BP. The undercurrent has also affected the distribution of stained gravel which is most common and most intensely stained beneath a fast-flowing undercurrent core where environmental conditions resemble those documented for deep-sea, ferromanganese nodule fields.

Erosion of deep-sea sediments in the Southern Ocean between longitudes 70°E and 190°E and contrasts in manganese nodule development

Using our previously published results, we present trend surface maps of surface sediment age, and the thickness of sediment deposited during the last 0.7 m.y. for the area between the Kerguelen Plateau, Broken Ridge, Australia, New Zealand, and Antarctica. Four separate centers of widespread deep-sea sediment erosion have developed in response to high bottom-water velocities. Two of these, centered on the South Tasman Basin and the western end of the South Australian Basin, respectively, areassociated with extensive manganese nodule development. The manganese nodule fields are almost entirely developed on sediment which averages at least 0.5 m.y. in age. In contrast, the southern and eastern flanks of the Kerguelen Plateau, the Ross Sea and the Campbell Plateau have very limited manganese nodule deposits, despite abundant evidence of widespread active erosion. It is concluded that sediment erosion is a necessary but insufficient requirement for extensive manganese nodule development in the area, and that an important role is also played by submarine volcanism.

Underwater photographs of manganese nodules from the Southwestern Pacific Basin

Abstract Underwater photographs have revealed an extensive field of manganese nodules in the Southwestern Pacific Basin, south-west of Rarotonga. The nodules almost completely cover the sea floor and are comparable in surface density with those from the siliceous ooze province south of Hawaii.

Deep-Sea Erosion and Manganese Nodule Development in the Southeast Indian Ocean

Features exhibited by a large number of sea floor photographs together with the dating of 187 sediment cores from the southeast Indian Ocean have revealed extensive manganese nodule development and sediment erosion in deep basinal areas. The most extensive nodule field, with an area of 10(6) square kilometers, occurs in the northwestern sector of the South Australian Basin and is named the Southeast Indian Ocean Manganese Pavement. The crests and flanks of the adjacent mid-ocean ridge are, in contrast, free of nodules and marked by much less dynamic bottom water conditions.

Experimental erosion of North Pacific red clay

Threshold erosion velocities for plane beds of pelagic red clay were established by ten experimental runs in a recirculating salt-water flume. Even with water content as high as 82%, observable erosion of the sediment required a velocity equivalent to a bottom current of about 30 cm/sec. Sediment beds to which manganese nodules were added, simulating an abyssal nodule field, were eroded by much slower flows (e.g., by the equivalent of a 12 cm/sec current at 84% water content). These experimentally derived values may be useful approximations of critical current speeds on the deep-sea floor, though very slow erosion may well occur there at lower speeds, especially in the presence of benthic fauna.

Nickel- and Copper-Rich Nodules of Equatorial North Pacific: ABSTRACT

The authors compiled a map of all available data on the distribution and metal content of ferromanganese deposits throughout the oceans which revealed only one geographic area where nodules were abundant and consistently rich in copper and nickel. It was an east-west band in the equatorial North Pacific between coordinates 8°00^primeN to 10°00^primeN and 125°00^primeW to 154°00^primeW. Nodular deposits were most abundant at the eastern and western ends of this rectangular province. Inspection of analytical data reveals that they are at least twice as rich in copper and nickel than the world average for nodules. Moreover, metal values suggest east-west axes of maximum values of both copper and nickel (2.5 to 3.0% dry weight of the nodules) at the northe n and southern limits of the province. In order to explain this unusually rich province, the east-west trends of maximum metal values, and variations in abundance of the nodules, a comprehensive study is underway. In order to quantify the data, many sea-floor parameters were established and each inserted as a viable controlling influence on the distribution and metal content of the deposits. They include gradient of sea-floor, water depth, submarine physiography, topographic grain of seabed, distribution of seamounts, distance from major fracture zones, substrate type, porosity and moisture content of substrate, and age of surficial sediment. Characteristics of the nodules, including average and range of size, percent of sea-floor covered and their concentration, were combined with the preceding measures. Our study has led to the following conclusions: (1) the geographic limits of nodules rich in copper and nickel reflect the distribution of exposures of Tertiary sediments on the ocean floor. (2) The east-west trend of the province is a function of exposures of Miocene, Oligocene, and strata. (3) Copper and nickel content of nodules appear to increase with increasing age of substrate, i.e., strata, and presumably Eocene nodules, are characterized by maximum values of these metals (3%). Miocene strata and associated nodules have lower copper and nickel values (2.5%), but contain greater amounts of these metals than other nodular deposits. (4) The regional patterns of major nodule fields are directly related to locations of seamounts and fracture zones. Presumably subsea eathering and explosive submarine volcanism release and disperse seed grains of basalt. Nodules are most abundant in the eastern and western thirds of the enriched zone where submarine volcanoes are common, and along a narrow band which follows the Clarion fracture zone. The central section has appreciably fewer nodules because of a limited number of volcanoes and the Clipperton fracture is a site of rapid sedimentation. (5) Eocene nodules represent potential mineable deposits. (6) Further evaluation of this resource should be directed toward definition of Eocene, Oligocene, and Miocene exposures close to sources of basaltic seed grains. (7) Porosity and moisture content of radiolarian deposits are higher than any other ocean sediment and may play a role in upward diffusion of metals w thin the substrate and into nodules. (8) Differential erosion and deposition within the area of Tertiary exposures during the past 55 m.y. may have imposed a secondary pattern of nodular concentration over crests of abyssal hills and dilution by burial in adjacent valleys. End_of_Article - Last_Page 1441------------