The isotopic composition of reduced organic carbon

The subterranean estuary: a reaction zone of ground water and sea water

Present-day production of CaCO3 in tne world ocean is calculated to be about 5 billion tons (bt) per year, of which about 3 bt accumulate in sediments; the other 40% is dissolved. Nearly half of the carbonate sediment accumulates on reefs, banks, and tropical shelves, and consists largely of metastable aragonite and magnesian calcite. Deep-sea carbonates, predominantly calcitic coccoliths and planktonic foraminifera, have orders of magnitude lower productivity and accumulation rates than shallow-water carbonates, but they cover orders of magnitude larger basin area. Twice as much calcium is removed from the oceans by present-day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity (1.6 bt), suggesting that outputs have been overestimated or inputs underestimated, that one or more other inputs have not been identified, and/or that the oceans are not presently in steady state. One “missing” calcium source might be groundwater, although its present-day input is probably much smaller than that of rivers. If, as seems likely, CaCO3 accumulation presently exceeds terrestial and hydrothermal input, this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level: shallow-water accumulation decreases by an order of magnitude with a 100 m drop in sea level, while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow-water carbonates.

Production and accumulation of calcium carbonate in the ocean: Budget of a nonsteady state

The exchange of groundwater between land and sea is a major component of the hydrological cycle. This exchange, called submarine groundwater discharge (SGD), is comprised of terrestrial water mixed with sea water that has infiltrated coastal aquifers. The composition of SGD differs from that predicted by simple mixing because biogeochemical reactions in the aquifer modify its chemistry. To emphasize the importance of mixing and chemical reaction, these coastal aquifers are called subterranean estuaries. Geologists recognize this mixing zone as a site of carbonate diagenesis and dolomite formation. Biologists have recognized that terrestrial inputs of nutrients to the coastal ocean may occur through subterranean processes. Further evidence of SGD comes from the distribution of chemical tracers in the coastal ocean. These tracers originate within coastal aquifers and reach the ocean through SGD. Tracer studies reveal that SGD provides globally important fluxes of nutrients, carbon, and metals to coastal waters.

https://moritz.botany.ut.ee/~olli/eutrsem/Moore_2010.pdf

The Effect of Submarine Groundwater Discharge on the Ocean

X-ray Diffraction Procedures for Clay Mineral Identification

A metal-membrane mount for X-ray powder diffraction

A sample mount assembly for use with an X-ray diffractometer The assembly includes a holder with an opening extending therethrough, an insert to fit into the holder through its opening, a substrate filter layer, and the exposed sample layer mounted on the filter The holder's opening is larger at its lower surface than at its upper surface such, that the insert which is shaped as a four side truncated pyramid, can be placed into the holder from its lower surface but not through its upper surface opening The layer filter with its mounted sample layer is sandwiched between the insert and holder to allow the sample to be exposed to incident X-rays through the holder's upper surface Plastic tape or some other securing mechanism is used to secure the holder to the insert at the holder's lower surface The result is a mount that allows easy installation and removal with automatic sample changers for X-ray diffraction of the membranes with no vertical offset and a flat, even, sample upper surface

Sample mount for X-ray diffraction

A diffractometer mount for small samples

A group of claylike silicates from zones of vanadium mineralization in the sandstone-type deposits of the Colorado Plateau have been examined by x-ray powder diffraction methods to determine their mineralogic composition. The materials studied were separated by water elutriation, bromoform separation, or both, and oriented aggregates as well as randomly oriented powders were prepared. A comparison of the x-ray diffractometer patterns of these specimens with roscoelite from Coloma, California (AMNH 13,565) shows that most of the nine samples examined differ from roscoelite in two important ways: by interstratification of mica layers with montmorillonite, and by variation in octahedral substitution of V for A1. The mixed layering of mica-montmorillonite is revealed by distinct changes .in position and intensity of the first-order basal spacings on treatment with ethylene glycol and on heating of the samples to 400 ~ C and 500 ~ C. Variations in octahedral substitutions are inferred from variations in the intensity of the second-order basal spacings relative to the first and third orders. Low relative intensity of the second order is interpreted as indicative of high electron density in the octahedral positions caused by substitution of V for A1. One sample (ALB-34-54) from Placerville, Colorado, shows x-ray characteristics very similar to the roscoelite from California and a chemical composition which gives a sum of 1.969 for octahedrally coordinated cations, indicating that it is a dioctahedral mineral. Two samples from Rifle, Colorado, also show characteristics closely resembling roseoelite although one of these, from an oxidized zone, exhibits a relatively stronger second-order basal spacing, and the suggestion is made that the amount of vanadium substitution is less than in the Coloma, California, or the Placerville, Colorado, material. The rest of the samples show mixed layering to various degrees, with the first-order basal spacing of the untreated material ranging from 10.1 A to 10.5 A. Chlorite is present in at least seven of the samples and is the dominant mineral in at least two of them. Only in the materials from Coloma, California, and Placerville, Colorado, was chlorite absent. The chlorites in two samples show mixed layering with expanding material, although one of these--from Thompson, Utah may be more closely allied to vermiculite than to chlorite. This indeterminant sample differs considerably from the other materials examined in that the mixed-layered mica-montmorillonite as well as the vermiculitic (?) mineral do not survive heating to 500 ~ C. The nonmixed-layered chlorites are characterized by almost equal intensities of the first four basal

Mixed-Layered Structures in Vanadium Clays1

A conference on Continental Margin Mass Wasting and Pleistocene Sea-Level Changes was held in Woods Hole, Mass., August 13-15, 1980. Fortyseven participants, representing many government, academic, and industrial organizations, discussed the current state of knowledge of the features of marine mass wasting and of the interrelations of factors influencing them. These factors include sediment source, composition, textures, sedimentation rates, climatic and sea-level changes, gas and gas hydrate (clathrate) contents of sediments, geotechnical characteristics, oceanographic and morphological factors, ground-water processes, and seismic events. The part played by these factors in the processes and features of mass movement and the engineering considerations imposed by the emplacement of manmade structures on the sea floor were considered vital to the evaluation of hazards involved in offshore exploration and development. The conference concluded with a call for bold programs to establish the probability of occurrence and the quantitative importance of these factors and to devise more reliable means of measurement, particularly in place, of the characteristics of the sediment and features involved.

John C. Hathaway

Papers

A metal-membrane mount for X-ray powder diffraction

Sample mount for X-ray diffraction

A diffractometer mount for small samples

Mixed-Layered Structures in Vanadium Clays1

Conference on Continental margin mass wasting and Pleistocene sea-level changes, August 13-15, 1980