Description of manganese deposits collected by R/V "Jean Charcot" during its EQUAMARGE II expedition in the Equatorial Atlantic

During the Equamarge II cruise (February 4 to March 21, 1988), on board the R. V. "Jean Charcot", 12.500 kms of continuous geophysical profiling have been recorded along three sectors of the Equatorial Atlantic. Two segments ofthe West African transform margin have been intensively surveyed off Guinea and off Ivory Coast and Ghana. The active Romanche fracture zone has been surveyed in details on a distance of about 100 kms. These data (multibeam bathymetry, continuous seismic profiling, magnetism and gravity) have been supplemented by 16 geological stations (dredging and coring). This report gives a synthetic review of the onboard analysis and allows to better understand the geological structures of the three surveyed areas.

(Table II, page 668-669) Distribution of elements between minerals soluble in 1M Hydroxylamine hydrochloride (Reducible); in 1m HCL (Acid-soluble) and in the insoluble residue of manganese nodules

Attempts to classify pelagic sediments have been based either on appearance and composition, or on the ultimate origin of the components. In particular it appears feasible to distinguish minerals which crystallized in sea-water from those which formed in magmas, in hydrothermal solution, or by weathering under acidic conditions. It is the case of iron and manganese oxide mineral aggregates which constitute one of the major types of rock encountered on the ocean floor; according to Menard (unpublished) about 10% of the pelagic area of the Pacific is covered by such nodules. The nodules consist of intimately intergrown crystallites of different minerals among those identified, besides detrital minerals and organic matter, are opal, goethite, rutile, anatase, barite, nontronite, and at least three manganese oxide minerals of major importance. Arrhenius and Korkisch (1959) have attempted to separate from each other the different minerals constituting the nodules, in order to establish the details of their structure and the localization of the heavy metal ions. The results demonstrate (Table II) that copper and nickel are concentrated in the manganese oxide phases concentrated in the reducible fraction. Cobalt, part of the nickel and most of the chromium are distributed between these and the acid-soluble group of the non-manganese minerals, dominated by goethite and disordered FeOOH.

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.

Geochemistry of manganese nodules from a British Columbia fjord

Concretions of iron and manganese oxides and hydrous oxidesóobjects commonly called manganese nodulesóare widely distributed not only on the deep-sea floor but also in shallow marine environments1. Such concretions were not known to occur north of Cape Mendocino in the shallow water zones bordering the North-East Pacific Ocean until the summer of 1966 when they were recovered by one of us (J. W. M.) in dredge samples from Jervis Inlet, a fjord approximately 50 miles north-west of Vancouver, British Columbia.

On the composition of oceanic and littoral manganese nodules (published online 2015)

The following analyses were made some years ago, principally with the object of ascertaining the state of oxidation of the manganese in the nodules. The nodules examined came from three different localities, two of them oceanic and the third littoral. Samples marked I., II., and III. are from nodules brought up in the trawl on board the "Challenger," on 13th March 1874, in lat. 42° 42' S., long. 134° 10' E. The depth of the water was 2600 fathoms, and the temperature of the bottom water 0·2° C. The density of the bottom water was 1·02570 at 15·56° C. Being from a high southern latitude, and therefore near the source of surface aeration, the water is highly charged with atmospheric gases, especially oxygen. It contained, per litre, 18·4 c.c. of mixed nitrogen and oxygen, of which 31·81 per cent, was oxygen, and 27·33 c.c, or 53·7 milligrammes, loosely-bound carbonic acid. The position of the station is about 400 miles south-west of the nearest part of the Australian coast, and about 500 miles west of Tasmania. It was the deepest water observed in the Antarctic voyage between the Cape of Good Hope and Melbourne. The haul was a very abundant one, and a few notes which I made at the time may be interesting: -"The water was found unexpectedly deep, the bottom being red clay, with some Foraminifera.

Determination of sulfite and manganese in sediments from the K/T boundary

The solid-state-physics technique of electron spin resonance (ESR) has been employed in an exploratory study of marine limestones and impact-related deposits from Cretaceous-Tertiary (KT) boundary sites including Spain (Sopelana and Caravaca), New Jersey (Bass River), the U.S. Atlantic continental margin (Blake Nose, ODP Leg 171B/1049/A), and several locations in Belize and southern Mexico within -600 km of the Chicxulub crater. The ESR spectra of SO3(1-) (a radiation-induced point defect involving a sulfite ion substitutional for CO3(2-) which has trapped a positive charge) and Mn(2+) in calcite were singled out for analysis because they are unambiguously interpretable and relatively easy to record. ESR signal strengths of calcite-related SO3(1-) and Mn(2+) have been studied as functions of stratigraphic position in whole-rock samples across the KT boundary at Sopelana, Caravaca, and Blake Nose. At all three of these sites, anomalies in SO3(1-) and/or Mn(2+) intensities are noted at the KT boundary relative to the corresponding background levels in the rocks above and below. At Caravaca, the SO3(1-) background itself is found to be lower by a factor of 2.7 in the first 30,000 years of the Tertiary relative to its steady-state value in the last 15,000 years of the Cretaceous, indicating either an abrupt and quasi-permanent change in ocean chemistry (or temperature) or extinction of the marine biota primarily responsible for fixing sulfite in the late Cretaceous limestones. An exponential decrease in the Mn(2+) concentration per unit mass calcite, [Mn(2+)], as the KT boundary at Caravaca is approached from below (1/e characteristic length =1.4 cm) is interpreted as a result of post-impact leaching of the seafloor. Absolute ESR quantitative analyses of proximal impact deposits from Belize and southern Mexico group naturally into three distinct fields in a twodimensional [SO3(1-)]-versus-[Mn(2+)] scatter plot. These fields contain (I) limestone ejecta clasts, (II) accretionary lapilli, and (III) a variety of SO3(1-) -depleted/Mn(2+) enriched impact deposits. Data for the investigated non-impact-related Cretaceous and Tertiary marine limestones (Spain and Blake Nose) fall outside of these three fields. With reference to thes enon-impact deposits, fields I, II, and III can be respectively characterized as Mn(2+) -depleted, SO3(1-) -enhanced, and SO3(1-) -depleted. It is proposed that (1) field I represents calcites from the Yucatin Platform, and that the Mn(2+) -depleted signature can be used as an indicator of primary Chicxulub ejecta in deep marine environments and (2) field II represents calcites that include a component formed in the vapor plume, either from condensation in the presence of CO2/SO3(1-) -rich vapors, or reactions between CaO and CO2/SO3 rich vapors, and that this SO3(1-) -enhanced signature can be used as an indicator of impact vapor plume deposits. Given these two propositions, the ESR data for the Blake Nose deposits are ascribed to the presence of basal coarse calcitic Chicxulub ejecta clasts, while the finer components that are increasingly represented toward the top are interpreted to contain high- SO3(1-) calcite from the vapor plume. The apparently-undisturbed Bass River deposit may contain even higher concentrations of vapor-plume calcite. None of the three components included in field III appear to be represented at distal, deep marine KT-boundary sites; this field may include several types of impact-related deposits of diverse origins and diagenetic histories.

Iron and manganese in bottom sediments and interstitial waters sampled in the White Sea on August 21-30, 2003

Iron and manganese in bottom sediments studied along the sublatitudinal transect from Kandalaksha to Arkhangelsk are characterized by various contents and speciations depending on sedimentation environment, grain size of sediments, and diagenetic processes. The latter include redistribution of reactive forms leading to enrichment in Fe and Mn of surface sediments, formation of films, incrustations, and ferromanganese nodules. Variations in total Fe content (2-8%) are accompanied by changes in concentration of its reactive forms (acid extraction) and concentration of dissolved Fe in interstitial waters (1-14 µM). Variations in Mn content in bottom sediments (0.03-3.7%) and interstitial waters (up to 500 µM) correspond to high diagenetic mobility of this element. Changes in oxidation degree of chemical elements result in redox stratification of sediment strata with maximum concentrations of Fe, Mn, and sulfides. Organic matter of bottom sediments with considerable terrestrial constituent is oxidized by bottom water oxygen mainly at the sediment surface or in anaerobic conditions within the sediment strata. The role of inorganic components in organic matter oxidation changes from surface layer bottom sediments (where manganese oxyhydroxide dominates among oxidants) to deeper layers (where sulfate of interstitial water serves as the main oxidant). Differences in river runoff and hydrodynamics are responsible for geochemical asymmetry of the transect. The deep Kandalaksha Bay serves as a sediment trap for manganese (Mn content in sediments varies within 0.5-0.7%), whereas the sedimentary environment in the Dvina Bay promotes its removal from bottom sediments (Mn 0.05%).

Geochemistry and isotopic ratios of samples from the Tiger gabbroic complex, Northern Victoria Land, Antarctica

Subduction related mafic/ultramafic complexes marking the suture between the Wilson Terrane and the Bowers Terrane in northern Victoria Land (Antarctica) are well-suited for evaluating the magmatic and structural evolu- tion at the Palaeo-Pacific continental margin of Gondwana. One of these intru- sions is the "Tiger Gabbro Complex" (TGC), which is located at the southern end of the island-arc type Bowers Terrane. The TGC is an early Palaeozoic island-arc related layered igneous complex characterized by extraordinarly fresh sequences of ultramafic, mafic and evolved lithologies and extensive development of high-temperature high-strain zones. The goal of the present study is to establish the kinematic, petrogenetic and temporal development of the TGC in order to evaluate the magmatic and structural evolution of the deep crustal roots of this Cambrian-aged island-arc. Fieldwork during GANOVEX X was carried out to provide insight into: (i) the spatial relations between the different igneous lithologies of the TGC, (ii) the nature of the contact between the TGC and Bowers Terrane, and (iii) the high-temperature shear zones exposed in parts of the TGC. Here, we report the results of detailed field and petrological observations combined with new geochronological data. Based on these new data, we tentatively propose a petrogenetic-kinematic model for the TGC, which involves a two-phase evolution during the Ross orogeny. These phases can be summarized as: (i) an early phase (maximum age c. 530 Ma) involving tectono-magmatic processes that were active at the deep crustal level represented by the TGC within the Bowers island arc and within a general NE-SW directed contractional regime and (ii) a late phase (maximum age c. 490 Ma) attributed to the late Ross orogenic intrusion of the TGC into the higher-crustal metasedimentary country rocks of the Bowers Terrane under NE-SW directed horizontal maximum stress and subsequent cooling.

Documentation of manganese nodules form the northwest Indian Ocean

Microscopic and electron probe examination of some manganese nodules show that they consist of segregations of manganese-iron oxides in an interstitial material almost free of manganese but rich in iron and silicates. The segregations are widely spaced in the volcanic cores of the nodules but become more abundant towards their outer crusts where they form the centres of linked polygons of interstitial materials. Most of the minor elements are concentrated in the segregations compared to the interstitial materials. It is suggested that the structures observed result partly from solution and reprecipitation of elements in the original volcanic cores of the nodules and partly from the replacement and coating of these cores by manganese-iron oxides precipitated from sea water.

Description and chemical composition of manganese nodules sampled during the R/V "Vityaz" Expedition Vityaz-35

This paper presents data on the chemical composition of iron-manganese nodules and associated sediments collected during the 35th voyage of the R/V "Vityaz" in 1962. The samples were made available to the author by Prof, P. L. Bezrukov. Data on the general distribution of manganese nodules at the bottom of the Indian Ocean were already given by P. L. Bezrukov (1962, 1963). Here the author analyzed the geochemistry of nodules samples from seven stations and four samples from the associated sediments. The analysis separates the outer layer of nodules from their apparent internal core.