Carbon, nitrogen, and sulfur variation in the Bishop tuff, California.

Vitric pumice from the airfall deposit and the basal non-welded ashflow tuff show similar concentrations of carbon (250 + or - 125 p.p.m.), nitrogen (85 + or - 20 p.p.m.), and sulphur (70 + or - 40 p.p.m.). Whole rock samples from a vertical section through the sheet have concentrations similar to the vitric pumice, regardless of the degree of secondary crystallization. Glassy pumice from the upper non-welded part of the sheet and samples of tuff collected at the surface have a much higher abundance of C and S, apparently due to rising gases during cooling or to later meteoric water. Samples from fumarolic pipes have a significant enrichment in C and S deposited from rising gases. -G.R.