Integrated high-resolution stratigraphy of the Devonian-Carboniferous Boundary and lower Mississippian Interval of the U.S. Midcontinent
Creators: name: Braun, Matthew Gregory
Publisher: name: University of Iowa
Year: 2023
Subjects: subject: public abstract
subject: Geochemistry
subject: FOS: Earth and related environmental sciences

description: The tri-state area of Iowa, Illinois, and Missouri contains some of the best exposed Mississippian strata in the world, including the type area for the Mississippian subsystem. Strata here was deposited across a broad carbonate shelf and are thinnest along the central middle shelf, thickening both up-ramp and down-ramp, forming a complex dumbbell-like stratigraphic pattern rather than a simple clinoform geometry of thinning into the basin. Significant hiatuses mark the Devonian-Carboniferous Boundary (DCB) and Kinderhookian-Osagean Boundary (KOB) and as a result the precise temporal relationship between strata deposited across the region remain uncertain. Our new data demonstrate a complex relationship of complementary stratigraphic thicknesses where the DCB interval is thin or absent in the up-ramp inner-shelf setting and preserved in a significantly expanded interval in the central to distal middle shelf deposits of southeast Iowa and northeast Missouri. However, the overlying KOB interval is not preserved in this down-ramp setting but is preserved in significantly expanded strata in the up-ramp inner-shelf setting of central Iowa.
description: New high-resolution, major- and trace-element geochemistry from the Devonian-Carboniferous Boundary interval of southeast Iowa was produced from an expanded record of the Hangenberg Crisis. Similar to the classical European successions, elevated abundances of metals such as Cu, Co, Ni, and Pb occur within this stratigraphic interval in Iowa. Immobile/incompatible lithophile elements (Zr, Ti, Hf, W, U, and Th) show strong co-variation and increased abundance during this interval, suggesting they are likely associated with heavy minerals and a progressive increase of detrital input through the Hangenberg Crisis interval. Other redox-sensitive indicators such as Pb, Mo, P, and TOC demonstrate that patterns of redox change and TOC preservation are likely driven by enhanced primary productivity. Overall, our data suggest that enhanced delivery of continental materials increased primary productivity near the onset of the Hangenberg Excursion in Iowa, and that a complex feedback between sea level, volcanism, weathering, productivity, and anoxia may have played a significant role in the initiation of the Hangenberg Crisis.
description: The Black Hills, South Dakota, USA, expose thick packages of Mississippian carbonates and represent a shallow-water succession on the NW margin of the Transcontinental Arch. These carbonates are the up-ramp facies of the well-studied Devonian-Carboniferous Boundary succession in the Williston Basin, and are critical to the development of a detailed sequence stratigraphic history within the Williston Basin itself, and the early Mississippian of the U.S. Midcontinent in general. Conodont yields were generally poor, but the Mickelson Member of the Englewood Formation and lowermost two beds of Pahasapa Formation contain conodonts of the S. sandbergi Zone and the remaining lower portion of the Pahasapa contained S. crenulata Zone fauna. The Kinderhookian-Osagean boundary could not be placed precisely at the outcrop, however, there is no evidence that the Pahasapa Formation in the studied succession extends higher than within the global Tournaisian Stage.