Dr. Kevin G. Taylor1,
Rob L. Gawthorpe2
(1) Manchester Metropolitan University, Manchester, United Kingdom
(2) University of Manchester, Manchester, United Kingdom
Abstract: Large-scale patterns of carbonate cementation: Insights into early diagenetic fluid pathways and stratigraphic development
Carbonate cement is a major diagenetic feature in siliciclastic successions, leading to reservoir degradation and the formation of permeability baffles. Extensive outcrops of the Upper Cretaceous Blackhawk Formation and Castlegate Sandstone in Book Cliffs, Utah allow the geometry, form, and stratigraphic distribution of diagenetic carbonate cements to be determined. Such a data set allows for a better appreciation of the interplay between early diagenetic fluid transport, stratigraphic development and carbonate cementation in siliciclastic reservoirs, and illustrates the importance of large-scale outcrop diagenetic studies.
Large (up to 10m) dolomite cement bodies formed through early diagenetic remobilization of detrital carbonate by meteoric water, which entered shallow marine sediments at times of relative sea-level fall. Systematic changes in form of these cement bodies can be traced distally away from updip exposure surfaces. The carbonate cements thereby act as tracers of meteoric water input and mixing with marine waters at times of relative sea-level fall. Field mapping of dolomite cement bodies indicates that for minor sea-level falls meteoric ingress was up to 30km, whilst during major sea level falls meteoric fluids migrated over 100km into the basin.
The presence of meteorically-derived cement bodies within distal ‘detached’ sand-bodies presently encased in Mancos Shale, suggests that these units were at one time hydrologically connected to the foreshore. This diagenetic evidence suggests that these sandbodies became detached through later sedimentological processes (possibly transgressive erosion) rather than through primary deposition as detached sandbodies, with implications for the interpretation of such distal sandbodies.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana