Coupled effects of diagenesis and deformation on fracture evolution in deeply buried sandstones

摘要

Using examples fromCretaceous Frontier Formation, we document quartzvolumes deposited during and after opening in fractures formed at shallow (<2 km), intermediate (>4 km) and deep (>6 km) conditions. Inconspicuous rinds >0.02 mm thick predominate at shallow depths. At intermediate depths, rinds and porosity are interspersed with narrow ~0.04-mm wide spanning bridges that thicken with time. At >6 km, spanning bridges are thicker and more pervasive (>50%), but retainedporosity is extensive. Quartz volumes are governed by spanning potential, which reflects temperature, thermal exposure, opening rate, and rock composition. Fluid inclusionassemblages trapped during fracture growth record porosity creation andpersistence at depths of>4-6 km for >5 to 40 m.y. Results show that open fractures persist at high temperatures despite gradual cement accumulation. Where amounts of quartz deposited during propagation is high, fracture clustering is more pronounced, suggesting interaction between cement accumulation and fracture affects spatial arrangement.