HRTEM of microcrystalline opal in chert and porcelanite from the Monterey Formation, California

摘要: Microcrystalline opal was investigated using low-dose transmission electron microscopy (TEM) methods to identify microstructural characteristics and possible phase-transformation mechanisms that accommodate silica diagenesis. High-resolution TEM (HRTEM) revealed microcrystalline in opal-CT chert (>90 wt% silica) porcelanite (50-90 from the Miocene Monterey Formation of California displays various amounts structural disorder coherent incoherent lamellar intergrowths. Species microfibrous identified by HRTEM early-formed include length-slow opal-C unidimensionally disordered ({open_quotes}lussatite{close_quotes}). These fibers often display a microstructure characterized an aperiodic distribution highly strained domains separate ordered located at discrete positions along direction fiber axes. Microfibrous occurs as several types fiber-aggregation forms. siliceous matrix later-formed consists equidimensional, nanometer-size crystallites lussatite fibers. Pseudo-orthorhombic tridymite (PO-2) one sample porcelanite. Burial diagenesis results precipitation epitaxial growth on substrates. Diagenetic maturation banded opal-CT-quartz occur result solid-state ordering. The primary diagenetic phase transformationsmore » between noncrystalline opal, quartz predominantly series dissolution-precipitation reactions. However, showed chert, enhances rate diagenesis.« less