Sequence-Set Scale Distribution of Carbonate Cementation: Linking Diagenesis to a Basin’S Stratigraphic Evolution
Whilst the relationship between stratigraphic development and carbonate cementation has now been documented through a number of case studies, these studies have been generally restricted to observations upon individual sequences and/or limited sub-surface data. Here, I document the distribution of carbonate cement in a sequence-set framework, on a vertical scale of 500 m over lateral distances of 200 km.
The Blackhawk Formation and Castlegate Sandstone of the Mesa Verde Group contain a minimum of seven sequences, deposited within the Western Interior Seaway foreland basin in marine and coastal plain environments. The oldest sequences were deposited under conditions of high accommodation and comprise aggradational parasequences with no sequence boundary development. Younger sequences become increasingly progradational, with more aerially extensive sequence boundary development, reflecting decreasing accommodation in the basin.
Petrographic analyses of cements in the Spring Canyon, Aberdeen, Grassy, Desert Members and the Castlegate Sandstone show that the ferroan dolomite cements are all early, relative to burial diagenesis (compaction, quartz overgrowths). Stable isotope analyses indicates that a significant meteoric component was likely present in precipitating fluids and this is consistent with the observation that cements are always present down-dip of sequence boundaries and/or leached whitecaps beneath coals. In addition, the lateral distribution of cement bodies increases consistently up-succession from less than 5 km in extent in the Spring Canyon Member, to 30 km in extent in the Castlegate Sandstone. These changes in distribution are in response to the increased progradation and sequence-boundary development in younger sequences.
The implications of these data are that spatial patterns of diagenesis, and in particular carbonate cementation, are not only controlled by the nature and presence of individual stratal surfaces, but also by the nature of larger-scale stratigraphic development and basin evolution. This evolution may be driven by eustatic shifts, or through tectonic or climatic driven base-level shifts. This, therefore, allows insights into the genuine basin-scale processes that control the macroscopic diagenetic properties of sedimentary successions and sub-surface hydrocarbon reservoirs.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009