FAR-FIELD TECTONIC CONTROLS ON THE SPATIAL DISTRIBUTION OF CRITICAL MINERAL-ENRICHED DEVONIAN BLACK SHALES IN THE CENTRAL US

Devonian metalliferous black shales in the U.S. contain multiple high-potential critical minerals (CM) resources. Previous USGS-led research showed some Devonian phosphorites in this interval have rare earth concentrations exceeding 200 times background levels. New Earth MRI research in the central U.S. shows CM enrichment in Devonian black shales is stratigraphically and spatially complex.

Integration of chemostratigraphy, facies analysis, and detrital zircon geochronology was used to characterize Devonian CM enrichment and explore the oceanographic and tectonic drivers implicit in the “marine chemocline” mineral systems model. Portable X-ray fluorescence, utilizing USGS check materials, was used to generate over 7000 new analyses to characterize Devonian critical minerals trends in the New Albany Shale and associated units. Our chronostratigraphic results demonstrate the presence of angular unconformities truncating hundreds of meters of Silurian and Ordovician strata that are onlapped by late Givetian to early Mississippian CM-enriched black shales and associated strata. These unconformities cross-cut preexisting deep-water facies belts suggesting partial basin inversion. Detrital zircon geochronology of sandstones in this interval from across the eastern U.S. show the reappearance of distinct provenance signatures absent from much of the underlying lower Paleozoic strata.

Our preliminary results suggest that Devonian CM distributions in the central U.S. are influenced by both oceanographic and tectonic events. The enrichment of critical minerals near the Frasnian-Famennian and Devonian-Mississippian boundaries appears to be linked to geochemical processes associated with the Kellwasser and Hangenberg oceanic anoxic events. Additionally, these enriched successions are significantly impacted by far-field tectonism related to the Acadian orogeny. Evidence for basin inversion and reemergence of heterogeneous provenance signatures indicates that basement block uplifts, extending deep into the continental interior, played a key role in shaping the basin architecture. This architecture controlled the spatial extent of the chemocline, mixing of water masses between basins, and preservation of CM-enriched sediments.