Search

Several gentle hills close to the crest of the East Pacific Rise are covered with extensive Fe-Mn-rich deposists. The setting of the sediments precludes the possibility that turbidite flows, slumping or downhill winnowing of material can have been responsible for the accumulation of these sediments, as is also indicated by the lack of reworked faunas or crushed shells. Palaeontological dating and the magnetic anomalies of the crustal substratum show that the sediments must be very young, that is, the sedimentation rates are very high; thus, 8–10-m-thick sediments were formed in 600,000 yeas. The accumulation rates on these hills for several elements, such as Fe, Mn, Cu and Ba, are much higher than in ordinary pelagic regions. The element deposition is best described as an exhalative-sedimentary process. The areal extent of these sediments is considerably larger than that of any other currently forming analogous deposits. The results have far-reaching implications for the discussion of how sedimen...

Unaltered hausmannite ores from Langban, Sweden, contain two rhombohedral carbonate phases, namely calcite and a carbonate with a disordered calcite structure; the latter with the approximate composition Ca0.4Ba0.4(Pb, Mg)0.2CO3 and cell dimensions (hexagonal setting) a = 5.12 and c = 18.12A. The carbonate phases were emplaced together with the ore minerals before the metamorphic events, which in their turn preceded the late vein and vug forming period in Langban. It appears likely that such carbonates are much more common than was previously realized, and that they were the source of most of the Pb, Ba and Ca present in the native lead-pyrochroite veins.

An 8.5 m long apparently undisturbed core from a hilltop on the crest of the East Pacific Rise has uranium and thorium isotope distributions that are very unusual. The core is very poor in 232Th, and very rich in U, particularly at the 500-cm level, where a value of about 150 ppm is reached. At the same depth the 230Thxs reaches very large negative values. These facts could be accounted for if one assumes that solutions rich in U and poor in Th had been postdepositionally injected into the sediments about 90,000–110,000 years ago. The top of the sediment received much of its U from seawater, judging from the 234 U 238 U ratio. Possibly carbonate rich solutions were the carriers of the injected uranium.

A spectrochemical method for the determination of major constituents in rocks, minerals, and related materials is described The samples are fused with lithium or sodium borate and burned with a Stallwood jet in carbon dioxide Cobalt is used as the internal standard Comparisons with chemically analysed samples show good accuracy and reproducibility.

Neutron activation and spectrographic data on 58 ultramafic rocks, representative of diverse geographic and geologic settings, indicate considerable differences in abundances of Al, Si, Ti, Co, Cr, Fe, Sc, Mn, Cu, V, and Ni. These wide differences in composition vitiate any calculation of mean elemental abundances for ultramafic rocks taken as a single homogeneous group and indicate gross chemical differentiations either within the mantle or between the mantle and the ultramafic rocks.

High concentrations and accumulation rates of Ba occur on active (spreading) ridges, and in some areas of high biological productivity. These patterns show that Ba is deposited on the deep sea floor by both volcanic and biological processes.

Galenas from the Upper Mississippi Valley district, the Picher field, and the southwestern United States were analyzed for a number of trace elements by emission spectroscopy. Quantitative determinations of Ag, Bi, Cu, and Sb are reported here for most of the 31 samples. The samples varied in crystal habit from simple cubes through mixed forms to octahedrons. The concentrations were found to vary widely from one mineralized area to another; but within a given district, crystals of cubic habit are systematically enriched in Sb compared to those of octahedral habit. No progressive change in either the Ag or the Bi content with crystal habit was observed. Particularly large concentrations of some of the trace elements, however, did occur in some of the deposits in which octahedral faces were especially prominent. Both the trace element content and the crystal habit appear to be symptomatic of other factors involved in the formation of galena. Temperature is probably one of the most important factors; the cubic form seems to predominate at the lowest temperatures.

Deep sea hemipelagic sediments from the east Pacific show an oxidized upper zone of variable thickness and a reduced zone below. The geochemistry of a core from this region was studied in detail. The Eh of the upper zone is close to + 100 mV, while in the lower zone it reaches about −400 mV. Reducing conditions in the lower section of the core are related to the oxidation of organic matter in the sediment, as indicated by the gradual decrease with depth of the concentration of nitrogen in the upper part of the core. Various elements, such as Mn, Ni, Co, P and La, are enriched in the upper oxidized zone, while Cr, V, U and S are enriched in the lower reduced zone. Postdepositional mobility of the elements in question, mainly by diffusion in the interstitial solutions, can explain their distribution in the core. Redox reactions can account directly for the mobilization of Mn, Ni, Co, Cr, V and U, indirectly for that of P and La. Fe and Cu do not migrate significantly, since they are immobilized as sulfides in the reduced zone. Th appears not to be affected by diagenetical mobility. Some of the consequences of the Postdepositional mobility of elements in deep sea sediments are: 1. (1) The average elemental content of deep sea sediment, generally estimated from measurements of samples from the upper part of the sediment column, may be affected by errors; namely, an overestimation in the case of Mn, Ni, Co, P and La; an underestimation in the case of V, Cr and U. 2. (2) Postdepositional redistribution of U may introduce errors in age determinations of sediments by the Th 230 Th 232 and Th 230 Pa 231 methods. 3. (3) Some geographical variations in the composition of Fe-Mn nodules can be explained by postdepositional mobility of Mn, Ni and Co.

The results of 399 new analyses and 144 analyses from the literature indicate that the carbonate-free fraction of sediments from active oceanic ridges is characterized by very low aluminum and titanium content and high iron and manganese content compared with sediments from other volcanic regions and from inactive ridges. These active ridge sediments appear to originate by volcanic processes associated with ocean-floor spreading and high heat flow. The total mass of these sediments is probably only a few per cent of all deep-sea sediments.

Samples from a sediment core taken during the Swedish Deep-Sea Expedition 1947–1948 have been analyzed for their content of some minor constituents. The core, No. 69, Sta. 102, in the collection of the Expedition, was obtained from 13° 25′ S, 149° 30′ W. It had been analyzed earlier for the major constituents, the ferrides and boron. These results are published elsewhere. The lower part of the core (565-340 cm from the top) is a manganiferous marl ooze, and the upper part (336-6 cm) is a manganiferous-ferruginous clay (“red clay”). The decrease in the carbonate content during sedimentation is rather sudden at about the 340-cm level; the corresponding increase in the phosphorus concentration is more gradual. The average relative concentration of silicate-oxide (sil), phosphorus (ap) and CaCO3 (car) and the concentrations of the constituents studied are given in Tables 1–4. The excess and deficiency in the concentrations, in comparison with the averages, are discussed and also the probable sources of elements. Four chief sources are responsible for the distribution pattern of the minor constituents studied: the fine fractions of weathering material from basic igneous rocks, authigenic mineral forming processes in the sea, biological processes, and precipitation of metal ions on the surface of colloidal particles.

Along with specimens of manganese oxides and basalt, rocks containing more than 30 percent iron by weight and consisting mainly of poorly crystallized goethite have been dredged from the flanks of a seamount located on the East Pacific Rise. The Fe-Mn ratio varies widely among the various oxide rocks deposited at this locality and at another seamount in the same area. The deposit was probably formed by fractional precipitation of iron and manganese which had been introduced locally into the bottom water by hydrothermal solutions of volcanic origin, and by leaching from deep-sea basaltic lavas.

A simple and inexpensive accessory to an atomic-absorption spectrometer can be built which permits one to determine 1–300-ng quantities of mercury in various types of samples without any prior chemical treatment. The detector has been used with samples of sediments, rocks, coals, tissues, and waters, and is especially suited for mercury pollution studies.

The upper limit of the quantity of mercury released by weathering processes is approximately 230 metric tons per year. The quantity of mercury released by burning of coal is estimated to be of the order of 3000 tons per year, a quantity comparable to that emitted as waste from industrial processes.

Potassium-argon determinations of age from whole-rock samples of tholeiitic basalts, dredged from the crest of the East Pacific Rise and from the flanks of three seamounts at varying distances from the crest, show that the crest is younger than 1 million years and that age does not correlate with distance from the crest. Our data, however, do not necessarily oppose the general concept of spreading of the ocean floor.

Macusanite, originally believed to be a type of tektite because of its sculpture, is shown to be related to sillar of the Macusani region, Peru. K-Ar measurements establish identical Pliocene ages (4.2 m.y.) for macusanite and sillar and relate these deposits to the extensive ash flows of the southern Andes. These rocks are unique for glassy rocks in that lithium, boron, and arsenic contents are very high; cesium, rubidium, tellurium, fluorine, and tin are higher than normal; zinc, copper, chromium, and zirconium are lower than normal; and high-alumina minerals such as andalusite are present.