The Drop Before the Drop: Identification and Impact of an Underappreciated Early Carboniferous Sea-Level Fall

Early Carboniferous (Mississippian) mixed carbonate-siliciclastic strata accumulated during the Late Paleozoic Ice Age (LPIA) prior to a glacial maximum representing the Mississippian–Pennsylvanian boundary. Exposure and subsequent truncation at this boundary complicate the late Mississippian stratigraphy. Concurrently, in North America, regional inconsistencies in formation names along with the use of time designations as formation identifiers lead to miscorrelation of Mississippian strata.

Re-assessment of mid to late Mississippian strata across the North American craton linking biostratigraphically constrained subsurface core description and correlation, outcrop interpretations, and existing studies highlights a significant sea-level drop during the middle Visean (Meramecian–Chesterian) throughout the North America, predating the well-defined glacial maximum. New correlations indicate a sea-level fall of at least 80 meters with prolonged platform exposure. The sea-level drop resulted in development of siliciclastic trunk systems that delivered terrigenous material across the craton, accumulation of an extensive mixed carbonate-siliciclastic lowstand wedge across much of the southern Laurentian margin, restriction and evaporite deposition in intracratonic basins, and variable local sediment starvation resulting in organic-rich mudrock deposition.

This sea-level drop and the resulting depositional trends are poorly recognized on global and regional sea-level curves and paleogeographic reconstructions. Accurate identification of this boundary and subsequent sedimentation patterns should aid in understanding broad basin-scale shifts in sedimentation patterns, facies architecture, stratal geometries, and sequence stratigraphic implications for this interval across the North American craton, as well as provide insight into the initiation of the LPIA.