(Tables 1-3) Silicon dioxide, Corg and trace element concentrations in sediments of the outer Eckernfoerder Bay, Western Baltic Sea

The main question, posed in the work scheme before laboratory analysis was started, was expressed as follows: Do marked seasonal fluctuations occur in trace element content of the sediment surface, and what are the probable influences of factors such as changing hydrographical parameters, plankton sequence etc. ? Special attention was paid to elements known as pollutants, for example mercury. Within this framework samples have been analysed for their contents of manganese, iron, zinc, lead, and mercury. The amounts of silica and organically-bound carbon serve in most cases as reference values for the trace element content. On sand temporary conditions of increased C org content raise the concentrations of all determined elements. Especially the values reached for mercury in July are worth nothing. It is concluded that Zn, Pb, and Hg tend to enrich with respect to C org as the decomposition of organic matter progresses. On mud-sand flocculation and precipitation of Mn/Fe-hydroxides probably represent an additional concentrating factor for the other elements as the relationship of the results for zinc and manganese shows. Manganese may indicate a seasonally related concentrating cycle at the sediment surface.

(Table 3, page 264), Composition of a manganese micronodule found in a fossil red clay bed from Western Timor

Chemical analyses are presented for two Cretaceous clays from Noil Tobee, Timor. Mineralogical examination has shown that they consist principally of quartz, feldspar, illite and chlorite, together with minor amounts of montmorillonite. Both chemically and mineralogically the clays are very similar to the recent argillaceous deep-sea sediments of the Pacific and Indian Oceans, which confirms Molengraaff's theory (1921) that they are of deep-sea origin. Further confirmation of this theory is provided by comparison of the composition of micromanganese nodules, separated from one of these clays, with that of manganese nodules from the Pacific Ocean.

(Table 2, page 1182) Partial composition of manganese encrustations from Gulf of Aden

Manganese encrustations from two adjacent sampling sites in the Gulf of Aden display markedly different compositional characteristics. The enrichment of manganese, and consequent depletion of iron and a series of trace elements, in the manganiferous crusts from Sta. 6243 is attributed to the diagenetic remobilisation of manganese within the sediment column and the resultant enrichment of this element in the encrustations from this station. Molybdenum, and possibly nickel, appear to show similar migration characteristics. Submarine vulcanism does not appear to play any significant role in controlling nodule composition within the area.

Annotated record and chemical analyses of a polygenetic manganese nodule (slab) from the Scott Plateau, Indian Ocean (core VA-16-13KD)

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.

(Table 1, page 376), Composition of manganese deposits from the Gulf of Aden and the Carlsberg Ridge

Iron-manganese nodules from the ocean floor have been extensively studied. But, because of the fine grain size of the particles of the nodules, structural identification by X-ray and electron diffraction techniques is difficult and the mineralogy of the iron oxide phase has not been well characterized. The observation of the Mössbauer spectrum-in which each nucleus absorbs gamma-rays independently-is not limited by particle size in the same way as is the observation of Bragg peaks in diffraction measurements, in which radiation must be scattered coherently from a large number of atoms. The magnetic hyperfine splitting in the Mössbauer spectrum of magnetic materials is affected, however, when the particles are so small that they become superparamagnetic. We describe here an investigation using the 57Fe Mössbauer effect of two iron-manganese nodules in which the iron oxide phase could not be detected by X-ray or electron diffraction.

Geochemistry of bulk samples and various minerals of sediment core CRP-1 from the Ross Sea, Antarctica

Thirty-nine medium and fine grained sandstones from between 19,26 and 147,23 mbsf in the Cape Roberts-l core (CRP-1) were analysed for 10 major and 16 trace elements. Using whole-lock compositions, 9 samples were selected for analyses of mineral and glass grains by energy dispersive electron microscope. Laser-Ablation Mass-Spectrometry was used to determine rare earth elements and 14 additional trace elements in glass shards, pyroxenes and feldspars in order to examine their contribution to the bulk rock chemistry. Geochemical data reveal the major contribution played by the Granite Harbour Intrusives to the whole rock composition, even if a significant input is supplied by McMurdo volcanics and Ferrar dolerite pyroxenes McMurdo volcanics were studied in detail; they appeal to derive from a variety of litologies, and a dominant role of wind transpoitation from exposures of volcanic rocks may be inferred from the contemporary occurrence of different compositions at all depths. Only at 116.55 mbsf was a thin layer of tephra found, linked to an explosive eruption McMurdo volcanic rocks exhibit larger abundances at depths above 62 mbsf, in correspondence with the onset of volcanic activity in the McMurdo Sound area. From 62 mbsf to the bottom of the core, McMurdo volcanics are less abundant and probably issued from some centres in the McMurdo Sound region. However, available data do not allow the exclusion of wind transport from some eruptive centres active in north Victoria Land at the beginning of the Miocene Epoch.

Chemistry of minerals from amphibole-chlorite veins of ODP Site 209-1270

We examined small-scale shear zones in drillcore samples of abyssal peridotites from the Mid-Atlantic Ridge. These shear zones are associated with veins consisting of chlorite + actinolite/tremolite assemblages, with accessory phases zircon and apatite, and they are interpreted as altered plagiogranite melt impregnations, which originate from hydrous partial melting of gabbroic intrusion in an oceanic detachment fault. Ti-in-zircon thermometry yields temperatures around 820°C for the crystallization of the evolved melt. Reaction path modeling indicates that the alteration assemblage includes serpentine of the adjacent altered peridotites. Based on the model results, we propose that formation of chlorite occurred at higher temperatures than serpentinization, thus leading to strain localization around former plagiogranites during alteration. The detachment fault represents a major pathway for fluids through the oceanic crust, as evidenced by extremely low d18O of altered plagiogranite veins (+3.0-4.2 per mil) and adjacent serpentinites (+ 2.6-3.7 per mil). The uniform oxygen isotope data indicate that fluid flow in the detachment fault system affected veins and adjacent host serpentinites likewise.