Marine and non-marine shales from two sedimentary basins were analyzed chemically and mineralogically. Ion-exchange characteristics of marine and non-marine surface samples were investigated for possible use as environmental indicators. Exchangeable calcium and magnesium, and water-leachable copper content can be used to differentiate the marine and non-marine shales studied.

The ion-exchange characteristics of subsurface shale samples were compared to surface samples to determine the effects of weathering and the restrictions imposed on the use of ion-exchange data by surface leaching. The effects of leaching are important for chlorine, sodium, and potassium. Calcium, zinc, iron, magnesium, manganese, lithium, and rubidium are not significantly affected by surface weathering conditions. Subsurface samples would be more suitable for ion-exchange studies.

The exchange capacity is not greatly affected by age; however, the lower Paleozoic shales have a low exchange capacity for iron, potassium, chlorine, and magnesium. The low exchange capacity is attributed to the movement of ions from exchange sites to lattice sites.

A detailed investigation of the clay mineralogy of the shales from two separate sedimentary basins indicates that the clay mineralogy is independent of environment. Source is the major factor controlling the clay mineralogy. The ion-exchange data for rubidium and lithium indicate that the clay minerals are relatively unaltered in the marine environment. The clay mineralogy largely controls the exchange characteristics of the shales investigated. Organic matter appears to have some effect on the ion-exchange characteristics; however, the extent of this control is unknown.

The possible application of a chloride specific electrode to chloride-ion determinations in natural geologic systems was investigated. Bromide and iodide are the only ions which interfere. The coefficient of variation is 18.4 with a range of detectability from 0.1 ppm to 10,000 ppm.

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