Mangos shale‐associated alluvium

Abstract

Inquiry into the dissolution kinetics of naturally occurring geologic materials, rather than indiviual minerr. species, has been relatively neglected. This is especially true of surface processes, the realm of surface water hydrology and geomorphology. This paper focuses attention at a laboratory study of the rate of such complex reactions.Functions defining the dissolution rates of saline (0.1-20 per cent salt content) Mancos Shale-associated alluvium in distilled water follow varying patterns. Dissolution is characterized by an initial (4 min) high rate constant, by a following phase (20 min-57 h) where rates are reduced drastically, and by a final period of encroachment to equilibrium. Initial dissolution rates increase with increase in salt content and sediment : water ratio. The time necessary to approach equilibrium is, however, found to be directly proportional to the sediment :water ratio. The concentration of Na', Mg2', Ca2*, SO:-and HCO;, and the relative abundance of Ca2' and HCO; increase continuously with contact time, indicating that the hydrated sodium and magnesium sulphate minerals provide most of the initial solutes, though not necessarily most of the total solute bulk.The results obtained in this study indicate that the high initial dissolution rate of soluble minerals from alluvium, and particularly from shales in contact with aqueous solutions, is too short-lived to account for most of the solutes occurring in heavily sediment-laden surface flow. Excluding input from slower, usually supersaturated subsurface flow, dissolution from sediment in transport should be a major source of solutes in originally undersaturated and kinetically unequilibrated surface water in semiarid and arid regions.

Badland Morphology and Evolution: Interpretation Using a Simulation Model

“…Underlying this is a looser granular sublayer of partially weathered shale shards grading gradually to dense, unweathered shale at a depth of 10 to 25 cm. When unweathered Mancos Shale is saturated with water, it decomposes within a few tens of hours into loose flaky chips with a modest net swelling (<25 per cent volume increase), yielding a yellowish liquor of dissolved salts (mostly sodium and calcium sulphates (Laronne, 1981(Laronne, , 1982). If these salts are not leached, further disintegration of the shale is inhibited.…”

Mineralogical, chemical, organic and microbial properties of subsurface soil cores from Mars Desert Research Station (Utah, USA): Phyllosilicate and sulfate analogues to Mars mission landing sites

“…The MS is the major source of solutes and suspended load in the Colorado River and numerous sulfate minerals have been reported (Whittig et al 1982;Larrone 1981) SO 4 ). The predominance of sodium sulfate species is particularly noteworthy.…”