Description and chemical composition of ferromanganese nodules from Station 123, Oneida Lake, New York

226Ra is used to document the growth histories of six manganese nodules from Oneida Lake, New York. Detailed sectioning and analysis reveal that there are discontinuous gradients in 226Ra content in these samples. These gradients result from periods of rapid growth (>1 mm/100 years) separated by periods of no growth of erosion. Although the 226Ra 'age' of the nodules approximates the age of Oneida Lake, the nodules are not sediment-covered because they occur only in areas of the lake where fine-grained sediments are not accumulating.

Description and chemical composition of ferromanganese deposits from Oneida Lake, New York

Saucer-shaped iron-manganese crusts occur adjacent to gravel shoal areas in Oneida lake in central New York. The crusts usually have a crude concentric banding owing to an alternation of orange, iron-rich layers and black, iron-poor layers. Materials from both types of layers are x-ray amorphous. The Oneida lake crusts, like most other freshwater manganese nodules, contain about the same Mn concentration as marine manganese nodules, but are usually higher in Fe and lower in trace metals than their marine equivalents. Although Fe and Mn may be precipitating directly from the lake water, it is more likely that the oxidate crusts are the result of precipitation of Fe and Mn when reduced sediment pore water comes in contact with well oxygenated bottom waters. Organisms, particularly bacteria, may play a role in the formation of the crusts, but to date no evidence of this has been found.

Description and chemical composition of ferromanganese encrustations and deposits in the Atlantic Ocean from R/V Atlantis II cruises 20, 42, 60, 85; R/V Chain cruise 35; R/V Knorr cruise 61 and RRS Shackleton cruise 75/1 stations

Chemical and mineralogical compositions of ferromanganese oxide coatings on rocks dredged from the New England Seamounts, the Sierra Leone Rise and the Mid-Atlantic Ridge near the Equator have been determined in an investigation of regional differences in Atlantic ferromanganese deposits. Most encrustations are clearly of hydrogenous origin, consisting mainly of todorokite and delta MnO2, but several recovered from the equatorial fracture zones may be hydrothermal accumulations. Differences in the chemistry of the water column and in growth rates of the ferromanganese coatings may be important in producing this regional contrast in composition. Fine-scale changes in element abundances within the encrustations indicate that the nature of the substrate has little influence on compositional variations.

TECHNO encrustation description and analysis

The distribution of radioactivities in a large polymetallic encrustation (TECHNO) sampled from the Pacific sea floor has been studied in great detail. The study includes measurements of the long-lived U and Th decay series isotopes, alpha-particle tracks and SUP-10 Be and SUP-26 Al (Results on the latter two cosmonuclides have been reported by Guichard, Reyss and Yokoyama, 1978). The data are discussed in terms of their implication on age dating of the sample. Two interpretations of the data are presented leading to vastly different time scales for the formation of the sample. Here the opinion is divided among the authorship. One group, as well as Guichard et al (1978), favours the million-years scale and the other favors scale measured in thousands of years. The principal pros-and-cons aspects of the two views are mentioned.

Description and iron and manganese content of ferromanganese nodules from Oneida Lake, NY

Ferromanganese nodules in the deep-sea and in freshwater lakes usually accrete layers rich in manganese oxides alternating with layers rich in iron oxides. The mechanism producing these alternating layers is unknown; indeed, the mechanism producing the nodules themselves is unknown. In Oneida Lake, New York, precipitants from the lake water and the surfaces of nodules at the sediment-water interface are enriched in Mn, whereas nodules buried in lake sediments have surface layers enriched in Fe. It is hypothesized here, using field and laboratory evidence, that reduction and mobilization of Mn from the nodule surface during periods of anoxic sediment cover produce the high Fe layers observed in the nodules.

Calcium carbonate, organic carbon, sediment description and hydrogen and oxygen index at DSDP Sites 93-603, 93-605, 93-604 and 95-603

The organic matter contents of sediments and rocks sampled during DSDP Leg 93 have been characterized by CHN and Rock-Eval analyses. Most samples from Sites 604 and 605 on the New Jersey continental slope and from Site 603 on the Hatteras outer continental rise contained less than 0.5% organic carbon. Some Neogene samples from the slope contained 1 to 2% organic carbon, and Cretaceous samples from the outer rise were as rich as 13.6% organic carbon by weight. Thin layers of black claystones of Santonian, Cenomanian, and Albian age were found interbedded in organiccarbon- lean, bioturbated, turbiditic claystones. Similar layers of turbiditic black marlstones were interspersed among Neocomian limestones and sandstones. Although the organic matter in many of the samples appeared to be detrital continental material, according to Rock-Eval and C/N values, Cenomanian black shales, in particular, contained substantial proportions of marine-derived organic matter.

Description and analyses of manganese nodules from the South-Western Pacific

Manganese nodules from the Campbell Plateau and Macquarie Ridge have been chemically analysed and their compositions compared with other Pacific nodules. No significant differences in composition are apparent. Foraminifera from nodule nucleii are late Tertiary or Quaternary, indicating the late geological formation of manganese nodules in this region. Nodule formation may be related to late Tertiary or Quaternary submarine volcanism.