Abstract

A petrographic, mineralogical, and geochemical investigation reveals evidence for selective preservation of microfacies in siliceous sinters. Plio-Pleistocene sinters from Steamboat Springs, Nevada, contain identical but fewer petrographic textures than Pleistocene sinters from Artist Point, Yellowstone National Park, Wyoming. The latter are preserved in altered sediments of unknown origin. A sequence of pore-filling and mineralogical changes explains the excellent preservation of nine microfacies and two petrographic textures. Plio-Pleistocene Steamboat Springs sinters are preserved in successions of andesitic basalt flows and were likely subjected to a more extreme thermal and a different hydrological environment than those from Yellowstone National Park. Most microfacies were obliterated during postdepositional heating of Steamboat Spring sinters. Differences in diagenetic histories related to depositional environment, water chemistry, and/or subsequent burial must account for the loss of textural evidence between the diagenetic stage represented by Artist Point sinters and that of Steamboat Springs sinters. Hence, early postdepositional history affects both the likelihood and quality of microfossil preservation.