Diagenetic style in the Upper Cretaceous Blackhawk and Castlegate Formations of Utah is strongly linked to basin-scale processes which control stratigraphic and sequence development. Characteristic facies- and stratigraphic-related diagenesis is present in proximal (fluvial and coastal plain), mid-proximal (shoreface) and distal (offshore) environments. In proximal environments, early leaching beneath coals removed detrital carbonate and felspar, giving rise to prominent white caps. Importantly, whilst this leaching commonly occurs in lowstands, the leaching is not restricted to the presence of sequence boundaries as coal horizons are also common within coastal plain sediments in highstand systems tracts. In mid-proximal environments, shoreface sandstones are characterised by the presence of large concretionary carbonate cements, formed by the mobilisation and reprecipitation of detrital dolomite from beneath coal horizons updip. The location of these cements is controlled by both lithofacies (with cement geometries commonly constrained by lithofacies boundaries) and the presence of high frequency sequence boundaries (with sandstones capped by such a surface updip forming preferential sites for cement precipitation). In distal environments, a range of cementation styles are associated with stratal surfaces. Concretionary carbonates, with meteoric d¹⁸O signatures, are present beneath the correlative equivalents of sequence boundaries. Locally, ooidal ironstones overlay sequence boundaries, developed as a result of sediment reworking and slow net sediment accumulation during sediment bypass. Laterally extensive cements are present beneath major marine flooding surfaces, formed as a result of breaks in sediment accumulation during marine flooding.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah