Distribution of diagenetic alterations in relationship to depositional facies and sequence stratigraphy of a wave- and tide-dominated siliciclastic shoreline complex: Upper Cretaceous Chimney Rock Sandstones, Wyoming and Utah, USA

This study constrains the distribution of diagenetic alterations and their impact on reservoir-quality evolution in relation to depositional environments (wave-dominated delta and tide and mixed-energy estuaries) and sequence stratigraphy (systems tracts and key sequence stratigraphic surfaces) of Campanian sandstones from Wyoming- Utah, USA. The diagenetic alterations include cementation by calcite, dolomite, pyrite, micro-quartz and iron oxides, dissolution of carbonate cement and detrital dolomite, dissolution and kaolinitization of framework silicates, mechanical compaction of argillaceous grains and infiltration of grain coating clays. Calcite, the dominant cement, is most abundant in the wave-dominated deltaic of the highstand (HST) and forced regressive (FRST) systems tracts. Oxygen and strontium isotope values (δ18O = -15:9 to -3.7% and ⁸⁷Sr=⁸⁶Sr = 0:7095 - 0:7112) suggest that calcite cements precipitated from dominantly meteoric waters. Diagenetic dolomite is more abundant in HST than in the FRST, lowstand (LST) and transgressive (TST) systems tract sandstones which is attributed to the precipitation of dolomite under marine-meteoric mixing conditions. These conditions were achieved through progradation and concomitant meteoric water incursion to the deltaic sands during highstand times. Kaolinite ismost abundant in distributarychannels ofHSTandFRSTandin upper delta front sandstones below the sequence boundary. Kaolinite formation is attributed to the flux of meteoric water in the paralic sediments during relative sea-level fall and in outer-estuarine tidal bars belowcoal layers (TST) aided by the generation of organic acids and CO2 during percolation of meteoric waters in the peat deposits. Iron oxide cement occurs in all systems tracts but particularly in TST and HST. Pyrite occurs below coal layers and sequence boundaries. Infiltration of grain coating clays is restricted to the TST marginal tidal-flat and marsh sandstones. Micro-quartz occurs in trace amounts in all systems tracts. The findings of this work can help predicting the distribution of diagenetic alterations and their of impact on reservoir properties of sandstones.