Cementation Below Marine Flooding Surfaces: Examples from the Blackhawk and Castlegate Formations, Book Cliffs, Utah

Kevin G. Taylor, Robert L. Gawthorpe, Charles D. Curtis

The excellent exposure of the Campanian sediments in the Book Cliffs, Utah allows the relationships between carbonate cementation and stratigraphic development to be investigated. Within the Blackhawk and Castlegate formations carbonate-cemented horizons occur beneath major marine flooding surfaces. The predominant mineralogy of these cements is ferroan dolomite, although calcite occurs. The presence of firmgrounds, compactional features around many concretions, preservation of high minus-cement-porosity (c. 40%), and a pre-quartz overgrowth origin for the carbonate suggest an early timing for this cementation.

In proximal areas cementation is rare and restricted to a thin zone immediately beneath marine flooding surfaces. When traced down-dip the cement volume increases, initially forming isolated concretions. Eventually the concretions coalesce to form laterally continuous zones decimetres to metres in thickness. However, the volume of cement and its continuity decline when traced further down-dip into shelf mudstones.

The localisation of early diagenetic cements beneath major flooding surfaces is interpreted to relate to the non depositional hiatus associated with the development of the marine flooding surface. The lowered sediment accumulation rates during the non-depositional hiatus result in the sediment having long residence times within early diagenetic zones and the intensification of early diagenetic reactions. The relative rates of relative sealevel rise and sediment supply are thus major controls on cementation. However, the intrinsic properties of the host sediment (e.g. bedding style, permeability) exert a control on the cement geometry and continuity.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995