Authigenic minerals: Locality 80, Bed I Tuffs, Olduvai Gorge, Tanzania.

摘要

Understanding climatic and water-mineral chemistry affecting hominin habitats during the period 1.92 to 1.80 Ma in Paleolake Olduvai basin, Tanzania is of social and scientific interest. Previous Olduvai research reported climate cycles in bulk sample mineral analyses. X-ray diffraction, X-ray fluorescence, and color analyses of Locality 80 Tuff Bed I samples tested the null hypothesis: Alteration mineralogy of Central Basin volcanic Tuffs IA through IF reflect salinity/alkalinity cycles. Such cyclicity was not found. Several primary authigenic minerals were confirmed, but not as previously reported. Tuffs are thoroughly altered, mostly to potassium-feldspars, zeolites, and carbonates, plus other feldspars and clay minerals (clays not in this study). Nevertheless, other findings reveal there is more to be learned. Results imply a major geochemical shift around 1.869-1.857 Ma, from non-zeolite forming environments to zeolite forming environments. A newly developed age model could aid re-analysis of past work and assist future research.