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Taphonomic Reworking and Stratal Organization of Tempestite Deposition
Carl Drummond, Hope Sheets
Tempestite beds of the Ordovician Kope Formation of northern Kentucky provide an interesting subject for numerical simulation and stratigraphic analysis. Taphonomic characteristics of these shell-rich beds suggest that they were formed by multiple reworking and amalgamation events. If so, then storm-driven redepositional processes could have led to temporal condensation within the tempestite beds. Numerical simulation of tempestite formation indicates that storm-bed abundance is maximized by frequent, weak storm events, whereas shell degradation is increased by frequent, strong storms. Conversely, these stratigraphic and taphonomic parameters are insensitive to changes in storm intensity when such events are relatively uncommon. Additionally, the stratigraphic and taphonomic characteristics of tempestite formation are found to be largely insensitive to the abundance of shell material in the undisturbed shale.
Lacunarity analysis of the vertical spacing of Kope Formation tempestite beds (grainstones and packstones) demonstrates stratal clustering. Such clustering was caused by either absolute or relative changes in storm intensity or frequency. Given the temporal scale of tempestite clustering within the Kope, changes in water depth across the shallow shelf--driven either by changes in sea level or sedimentation rate--is a likely mechanism by which such relative changes in storm processes occurred. Conversely, climatologic variability at the scale of tens to hundreds of thousands of years could drive absolute changes in storm intensity leading to stratigraphic clustering of tempestite beds.
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