Fig. 5
δ18O vs δD diagram showing the isotopic compositions of 15 secondary silica samples extracted from Kaibab Formation rubble breccia lag deposits. The oxygen and hydrogen isotope ratio data of secondary silica separates form domains elongated away from Line A. Line A (actually more of a band) is the inferred locus of isotopic compositions of cherts in equilibrium with modern sea water at various temperatures [45]. Silica data elongated away from Line A indicate that meteoric (fresh) waters were involved in the crystallization history of the silica. Silica data are interpreted in terms of palaeotemperatures by comparing them with temperature lines drawn approximately parallel to the meteoric water line [45]. Palaeotemperature estimates for the secondary silica separates range from ~ 17 to 22 °C. The most 18O- and D-depleted samples are likely those with the purest amount of authigenic silica. These are represented on the diagram by four samples which plot farthest from Line A and closer to the warmest palaeotemperture estimates of ~ 21–22 °C