Mg-rich Silicates Research Articles

Glaciomarine sediments and suspended particulate matter, Weddell Sea Shelf, Antarctica

Samples of glaciomarine sediments and suspended matter from the eastern and central Weddell Sea Shelf were collected during the Norwegian Antarctic Research Expedition (NARE) in 1978/79. Ice-rafted clastic materials are in general the main sediment sources. On the eastern shelf, biogenic materials are abundant (sponges and bryozoan debris), Fine-grained materials, clastic and bioclastic, are additionally supported as fecal aggregates and by currents. The composition of the bottom sediments shows only small variations laterally and within the profiles. Dissolution of the biogenic materials appears to be slight. The suspended matter is dominated by fine silt and clay particles of clastic, biogenic (mainly diatoms) and authigenic (Fe. Mg-rich silicates) origin. Metalliferous particles (Fe, Ti, Zn, Cr, Ni-rich) of possibly anthropogenic an4 or cosmic origin are observed. On the upper continental slope and the outer shelf the sedimentation rates are in the range of 2-5 cm/1OOO years, which are slightly higher than for the rest of the shelf. The bioclastic glaciomarine deposits grade southward into bioclastic free sediments, showing that glaciomarine deposits outside an ice shelf may form a sequence of alternating bioclastic-rich and bioclastic-free layers. Similarly, late Precambrian carbonate tillite sequences, especially in the case of thin carbonate layers interbedded with tillite layers, may reflect variations in glaciomarine facies rather than interglaciavglacial cycles.

Dissolved products of artificially pulverized silicate minerals and rocks, Part 1

ABSTRACT Ten grams of previously analyzed, rock-forming silicate minerals (mica, 2.5 g) were ground under 100 ml of double-distilled, and CO2-charged, waters for one hour, and the centrifuged-clear solutions analyzed for dissolved constituents. The pH's of the slurries prepared in distilled water were 8 to 9, and in CO2-charged water, 5.5 to 6.9. Total amount of dissolved ions was higher in CO2-charged water than in distilled water. Grinding in distilled water was exposed to room temperature. Highest amounts in ppm of dissolved ions in distilled and CO2-charged waters, respectively, were from minerals as follows: Si, diopside, 23.3, and enstatite, 17.4; Al, nepheline, 2.2, and microcline 1.0; Fe, biotite, 14.3, none detectible in CO2-charged water; Ca, augite, 4.5, and hornblende, 13; Mg, enstatite and olivine, 12, and olivine, 150; K, microcline, 38.8 (K dissolved from 2.5 grams of biotite in distilled water was 35.4), and microcline, 69.3; Na, nepheline, 85.9, and nepheline, 114. Olivine dissolved nearly stoichiometrically (Mg and silica); aluminous and other Mg-rich silicate minerals show relatively reduced solubility of Si, some of which apparently combines with Al and/or Mg to form clay minerals. Dissolution of Mg is singularly much higher in CO2-charged water than in distilled water. No dissolved Fe was detected in CO2-charged water, demonstrating that residual concentration of iron oxide occurs by leaching of Fe silicates by carbonic acid. Elements extraneous to mineral formulas are enriched in the solution relative to others. Minor, or trace elements, such as Mn, Ga, V, Ti, Mo, Co, Sn, Pb, Zn, are dissolved in concentrations determined spectrographically in parts per billion.