Mixed Carbonate-Siliciclastic Sequences

The study of carbonate-siliciclastic mixed sequences has seen an increase in the number of investigations that focus on mixed settings as part of the continuum between the carbonate and clastic end members. Cyclic deposition in mixed basins by reciprocal sedimentation has become one of the foundation blocks for sequence stratigraphy. In addition, these mixed sequences have a variety of distinctive petroleum reservoir characteristics, important for both exploration and development programs. The emphasis now is on reevaluating ancient sequences in the light of a more dynamic understanding of spatial and temporal variations and controls on these sequences. Examples in this volume are subdivided under the following headings: Shelf Wide, Coastal and Inner Shelf, Middle to Outer Shelf, Slope to Basin and Paleokarst. Many mixed sequences have been described in the literature, but understanding the controls of these sequences from a process approach in now in an adolescent stage.
Depositional Environments and Facies Analysis of the Cherokee Group in West-Central Kansas Available to Purchase
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Published:January 01, 1991
Abstract
In west-central Kansas the Cherokee Group of early Desmoinesian, Pennsylvanian age is a mixed siliciclastic and carbonate sequence. It was deposited in environments that were transitional from continental to marginal marine as the sea transgressed over the Mississippian unconformity out of the Hugoton Embayment and onto the Central Kansas Uplift. Sandstones of the Cherokee Group are important oil reservoirs in west-central Kansas, but they are highly variable in properties and in aerial distribution; therefore, they are difficult to predict. Core studies and subsurface analysis using wireline logs reveal two persistent and widespread limestone beds that form useful stratigraphic markers within the Cherokee. They provide a framework for facies analysis and regional mapping that may be useful as a predictive tool for oil exploration. Six basic lithofacies are interpreted from lithologies and sedimentary structures observed in cores obtained from four wells in eastern Ness County: (1) basal Pennsylvanian conglomerate, (2) fluvial sands, (3) fine-grained tidal-flat deposits, (4) shallow marine limestones and shales, (5) shoreline sands and tidal-channel sands, and (6) braided-stream sandy conglomerates. Successions of these facies are equivalent to components commonly observed in Kansas cyclothems. Two transgressive-regressive cycles are identified in the Cherokee, and maximum transgression is correlated with the basal portion of the two widespread limestone beds.
Following burial of the Mississippian karstic surface, deposition of peritidal sediments occurred on a uniformly shallow platform. Sedimentation was punctuated by episodes of subaerial exposure and weathering. Clastics derived from the eroding Central Kansas Uplift were probably supplied episodically to the coastal plain by braided streams that were reworked by coastal processes.