Quartz cementation history of sandstones revealed by high-resolution sims oxygen isotope analysis

摘要

Evaluating the timing and origin of quartz cement is central to understanding how porosity is lost in sandstones during burial. Kinetic models of quartz cementation have been calibrated using large-scale datasets but have never been tested at the microscopic level at which cement forms. Here, we use high-precision, in situ oxygen isotope analyses on sandstone from the Jurassic Ness Formation from the North Sea to reveal the growth history of single quartz overgrowths to a resolution of 2 μm. Measured δ~(18)O (cement) range from +28 to +20% V-SMOW in early to late cement and are consistent with quartz cementation models that propose the bulk of quartz precipitates as a continuous process beginning at 60-70 °C. Quantitative X-ray Diffraction analyses and clay mineralogical analysis of interbedded shales are inconsistent with a silica source from shale, implying that silica for the cement is sourced internally to the sand. These isotope data are broadly consistent with predictive, conceptual quartz cementation models and provide a critical link from micron-scale measurements to basin-scale predictions and observations.