The middle Proterozoic mescal paleokarst, central Arizona, USA: Karst development, silicification, and cave deposits

摘要

A regionally extensive paleokarst developed on the Mescal Limestone of the middle Proterozoic Apache Group in central Arizona prior to deposition of the overlying middle Proterozoic Troy Quartzite and before intrusion of 1.1 Ga diabase sills. Intense weathering of middle Proterozoic basalt lavas overlying the Mescal released abundant silica that led to widespread silicification of the underlying paleokarst. Dissolution of the host carbonate allowed insoluble early diagenetic cherts of the Mescal to accumulate in their original stratigraphy while the remaining carbonate underwent nearly complete replacement by secondary silica phases. Silicified collapse breccias, cave-filling sandstone lenses, thinly laminated cave-floor siltstone, and newly discovered flowstone indicate extensive development of caves and cave deposits during the karst event. The geographic distribution of silicification was controlled by adjacent uplift caused by movement along Precambrian monoclines cutting across the Sierra Ancha. The Mescal paleokarst is one of the best preserved silicified karsts on Earth and hosts some of the best preserved cave flowstone from the Precambrian.