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Abstract

As part of a larger intercollegiate effort to reconstruct late Triassic, presalt sediment provenance and routing environments for the Gulf of Mexico sedimentary basin, an integrated geochronologic approach leveraging more traditional biostratigraphic, sedimentologic, and sequence stratigraphic provenance constraints from geologic cores, cuttings, and geophysical well logs was initiated. This paper presents the initial results of this ongoing study and details detrital zircon U-Pb extraction methodologies while Inductively Coupled Plasma Mass Spectrometry analyses are pending. Eagle Mills Formation sandstone samples were collected from well core and cuttings, at five sub-crop locations extending from Texas to South Carolina to the West Florida shelf, in preparation for U-Pb detrital zircon provenance analysis. Prior to separation of detrital zircon grains, a sedimentologic-stratigraphic analysis was conducted including detailed core description, well log evaluation, and thin-section petrography assessment. These findings confirm a hypothesis that late Triassic Eagle Mills siliciclastics were derived from the erosion of an active horst-graben rift block topography with associated igneous intrusives. Specifically, preliminary results reveal pervasive very finegrained mottled gray to red bed sandstone lithology confirming synrift continental alluvium having little or no marine component, and probable deposition in a warm, humid environment but with increasing aridity. Classic fluvial facies features are highlighted including depositional cross strata typifying dynamic braided to meandering channel belts and alluvial floodplain deposits. Less common siltstone and shale lithologies were likely deposited amidst lower energy subfacies including potential shallow lakes, marshes, and/or ephemeral ponds. Bioturbated trace fossils were only rarely preserved, and there was no evidence of marine or eolian facies incursion. Igneous magmatism was prevalent in most subsurface Eagle Mills Formation samples including intrusive diabase, basalt flows, and volcanic ash.

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