NEAREST NEIGHBOR ANALYSIS OF COMPACTION IN BASIN MARGIN SEDIMENTS OF THE CAPITAN DEPOSITIONAL SYSTEM

Prograding carbonate shelf margins are capable of exerting high levels of overburden pressure upon underlying sediments that may induce processes of physical and chemical compaction in facies with different compaction potentials. During the Guadalupian time of the Upper Permian Period, the Capitan shelf margin prograded over compactable wackestones, packstones, and mudstones of the basin margin. A number of workers studying the Capitan depositional system have adopted the model of differential compaction to explain the tilting and thickening of outer shelf strata. Although workers have observed synsedimentary features on the upper platform that have likely formed as a result of differential compaction induced subsidence, little is known about the significance of compaction in the underlying basin margin. The inability of traditional methods to circumvent uncertainties of burial depth and initial porosity has created a high demand for a new method that can be used to quantify compaction within these sediments.

In this study, we develop a new method that can be used to quantify compaction in basin margin facies of the Capitan depositional system. Our methods involve the use of nearest neighbor techniques that quantify compaction based upon the index of grain repackaging. Although our methods are affected by material heterogeneities, they consistently provide a minimum estimate for compaction in fossiliferous limestones that can be used to broaden the understanding of carbonate diagenesis and reef bathymetry. We apply our methods to samples of the Lamar Limestone Member and demonstrate that the compaction of basin margin sediments has likely contributed to the subsidence of outer shelf strata on the Capitan Shelf Margin.