Marine resurge sequences at Flynn Creek impact structure, Tennessee, USA

Abstract

The Flynn Creek crater is a 3.8-km impact structure located in the Eastern Highland Rim geological province of Jackson County, Tennessee (36°17’ N; 85°40’ W), which displays a central uplift, breccia-filled crater moat, and terraced crater rim. The impact occurred during Late Devonian in an epicontinental shelf setting wherein the target Upper Ordovician bedrock carbonates were just beginning to be overlain by thin, basal beds of the transgressive Upper Devonian Chattanooga Shale. Granulometric (line-logging) and statistical studies of two drill cores, FC77-3 and FC67-3, shows that the crater-filling deposits containing four distinct parts. The lower part is interpreted as fall back sediments, which are followed by slump deposits from the crater rim. The middle part is a mixing zone between slump from the collapsing central peak and initial marine resurge flow. This is capped by a normally graded breccia unit formed by marine resurge water. Petrographic study of thin sections including microprobe analyses reveals that the crater moat-filling breccia contain two types of melt: a previously known grey silica melt, that shows a cryptocrystalline texture and commonly containing euhedral dolomitic inclusions, and a previously unknown phosphatic amber-colored melt, that occurs in association with elements from the base of the Chattanooga Shale supporting the idea that the shale was already being deposited at the time of the impact. Uneven distribution of petrographic components throughout the drill cores on opposite sides of the central uplift may suggest possible ejecta asymmetry.