204 Paleozoic Tectonics of SW Laurentia Without Borders: Final Amalgamation of Pangea in the USA, Mexico, and South America

We invite contributions that explore the Paleozoic tectonic evolution of southwestern Laurentia during the final assembly of western Pangea. Research on Paleozoic tectonic belts in Gondwana, particularly from Mexico and South America, is especially welcome.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 217B

Continental Levering Explains up to ~30% Variation in Magnitude of Pennsylvanian Sea Level Cycles Observed in Cyclic Stratigraphy

Paper number: 204-8
Program: Technical Sessions
Time: 3:25 PM – 3:45 PM

Authors

  • Ryan Leary Presenting Author
    New Mexico Institute of Mining and Technology, Socorro, NM
  • Sophie Coulson
    University of New Hampshire, Durham, NH

Abstract

Pennsylvanian and Permian cyclic strata, especially those exposed across the North American midcontinent, have been interpreted to record cyclic sea level change resulting from the waxing and waning of Late Paleozoic ice sheets. These strata also serve as primary archives of the tectonic evolution of the Ancestral Rocky Mountains, Ouachita-Marathon, and to some extent Appalachian orogenies. Pennsylvanian-Permian cyclic strata have been used as the basis for interpretations of the magnitude of glacially-driven sea level fluctuation; correlations of otherwise poorly temporally constrained strata in basins 1000’s of kilometers apart; and interpretations of the tectonic drivers of Late Paleozoic basin subsidence. However, the magnitudes of sea level fluctuation have been controversial, and estimates range from 0 m to >120 m. Additionally complicating these estimates as well as long-distance stratigraphic correlations, previous work on Late Paleozoic cyclic strata has assumed a “bathtub” sea level model that does not account for the complex spatial-temporal patterns of sea level fluctuation that result from glacio-isostatic adjustment (GIA) in response to ice sheet growth and retreat. 

Here, we explore the extent to which GIA contributes to the stratigraphically reconstructed patterns of sea level fluctuation using GIA modelling of latest Pennsylvanian global paleogeography. Our model predictions show that up to ~30% of sea level cycle magnitude in far-field locations (with respect to ice sheets) is correlated to the distance from the paleo marine shoreline, with sea level cycle magnitude increasing oceanward. Stratigraphic data generally support these results, although model results cannot explain the entire range of stratigraphic estimates. The oceanward increase in sea level cycle magnitude is interpreted to reflect continental levering processes, in which increased water loading of ocean basins during interglacial periods produces uplift of emergent areas. Additionally, we show that except in ice sheet proximal areas, sea level cycles are in-phase such that transgression-regression cycles should correlate across long paleo distances.   

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413898

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