Kevin G. Taylor¹, Rob L. Gawthorpe²

(1) Manchester Metropolitan University, Manchester, United Kingdom
(2) University of Manchester, Manchester, United Kingdom

ABSTRACT: Meteoric Fluids and Carbonate Cementation in Marine Sandstones Beneath High Frequency Sequence Boundaries; Upper Cretaceous Blackhawk Formation, Utah

Meteoric fluids have commonly been invoked as playing a major role in carbonate cementation in sandstone successions, acting as both a source and a transport mechanism for internally or externally derived carbonate. The origin, timing and pathways of these fluids, however, is often poorly constrained. We present data showing the clear spatial and temporal relationship of authigenic dolomite cement bodies to high frequency sequence boundaries in the Desert Member of the Blackhawk Formation, Utah.

Dolomite cement bodies in the Desert Member take the form of large concretions, up to 50m long and 10m thick, and can occupy up to 20 volume% of reservoir facies. Detailed field and stratigraphic mapping of these cement bodies reveals that they are present within sandstone units downdip from high frequency sequence boundaries. The size and abundance of these cement bodies decreases distally away from the sequence boundaries, but are still present tens of kilometers into the basin. The concretions are composed of early diagenetic ferroan dolomite cement, with carbon and oxygen stable isotope values indicative of carbonate derivation from detrital dolomite, with precipitation from fluids with a strong meteoric component.

We propose that meteoric fluids ingressed into marine sandstones as a result of sub-aerial exposure during the formation of high frequency sequence boundaries. These fluids mixed with marine pore-fluids, precipitating dolomite cements in these mixing zones. Kinetic barriers to dolomite precipitation were probably overcome by the presence of detrital dolomite acting as nucleation sites.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado