Geology topics

S. Bloch

Publications and source records attributed to S. Bloch.

3 recordsLinked to original sources

USGS1983

The mobility and distribution of heavy metals during the formation of first cycle red beds

Holocene-Pliocene sequence sampled in northern Baja California. Geochemical data supported by petrographic, X-ray, and SEM observations of mineralogical transformations, fission-track radiography, and uranium decay series measurements. Results indicate that metal content of the studied samples is inherited from constituent detrital minerals and that reddening of whole-rock samples does not promote major open-system migration of heavy metals. The amount of secondary iron oxides and the fraction of whole-rock metals associated with the oxides increase during red-bed development. Results suggest that developed red beds which are well flushed by suitable pore fluids may be sources of significant quantities of heavy metals.

Economic Geology↗

USGS1981

Antipathetic magnesium-manganese relationship in basal metalliferous sediments

Basal metalliferous sediments from sites 77B, 80 and 81 of the Deep Sea Drilling Project represent mixtures of pelagic clay, biogenic ooze, and a metalliferous component of hydrothermal origin. The metalliferous end-member of the sediments displays a strong inverse relationship (r = -0.88) between Mg and Mn. Mg is most likely tied up in an X-ray amorphous Mg-silicate ("sepiolite"), whereas Mn occurs almost exclusively in an oxide phase. Precipitation of the Mg-rich phase is favored by high flow rates and limited mixing of the hydrothermal end-member (source of silica) with seawater (source of Mg). Under those conditions much of the hydrothermal Mn2+, with its slow oxidation kinetics, may escape to the free water column. In contrast, in highly-diluted hydrothermal fluids, which provide a source solution for Mn-rich sediments, dissolved silica is diluted below saturation with respect to "sepiolite". The separation of the Mn and Mg phases may be further compounded by hydraulic fractionation. ?? 1981.

Chemical Geology↗

USGS1980

Some factors controlling the concentration of uranium in the world ocean

Low-temperature alteration of the oceanic crust is a major sink for the U supplied to the oceans and may account for about 50% of the estimated present-day input of this element. Uranium uptake by organic-rich sediments and coexisting phosphorites on continental margins is also important and may remove in excess of 10% of the total supply. High-temperature alteration of oceanic basalts, metalliferous sediments, carbonate sediments, and sediments in anoxic basins deeper than 200 m play a relatively minor role in the removal of U. Each of these sinks is responsible for the uptake of less than 5% of the overall input.

Geochimica et Cosmochimica Acta↗