41-19 Structural control on the origin of the Upper Ordovician Strodes Creek Member of the Lexington Limestone, central Kentucky, U.S.A.

Session: Paleontology, Stratigraphy, Sediments, and Soils (Posters)

Presenting Author:

Authors:

Abstract:

     The Strodes Creek Member of the Lexington Limestone is one of the most unusual members of the Lexington Limestone and is largely known for its fragmented and overturned stromatoporoid beds and is bound on its western margin by extant faults that probably reflect basement precursors. The Strodes Creek Member is wholly encompassed by the Millersburg Member of the Lexington, which represents a shallow, open-marine, mixed-clastic-carbonate platform, characterized by thin-bedded to nodular, fossiliferous calcarenites and calcirudites interbedded with shale. The Millersburg Member is also known for its local stromatoporoid biostromes. In contrast, the Strodes Creek exhibits background sedimentation of dark, organic-rich, calcareous shales with a westward-thickening section of very irregularly bedded, stromatoporoid-rich, fossiliferous calcisiltites (packstones and wackestones), which are commonly associated with hummocky crossbedding and gutter casts. The fragmented stromatoporoid beds are thicker and more abundant near the western, fault-bounded margins of the unit. More distal to the faults in eastern parts of the unit, Strodes Creek beds become thinner, more even-bedded, and contain fewer stromatoporoids.

     We interpret Strodes Creek background sedimentation to represent deeper-water, dysaerobic, lagoonal conditions associated with the downdropped fault blocks. The beds of fragmented, overturned stromatoporoids, in contrast, represent lobes of storm debris transported from Millersburg platform environments and dumped into the lagoonal setting. Most of the stromatoporoids were too fragmented to regrow again, but in a few cases, they were able to regenerate new colonies in the Strodes Creek lagoons. Although time-equivalent based on fossils, the sharp differences in lithologies between the Millersburg and Strodes Creek members clearly reflect changes in water depth that are most likely related to synsedimentary movement on the western bounding faults. Hence, the unique nature of the Strodes Creek Member apparently represents the interface between storm sedimentation and synsedimentary structural control on deposition.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

doi: 10.1130/abs/2026SE-13817

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