122 From the Cosmos and Back: Quantifying Processes and Rates of Landscape Change

This session explores how methods such as cosmogenic nuclides, apatite (U-Th)/He thermochronometry, U-series geochemistry, luminescence, and chemical mass balances quantify relationships between climate, tectonics, and erosion.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 212AB

QGG Denton, Andrews, Porter Glacial Geology Award: Quaternary base level history, valley bottom wetland formation, and carbon storage across tectonic and climatic gradients for the Appalachian Piedmont

Paper number: 122-8
Program: Technical Sessions
Time: 3:35 PM – 3:50 PM

Authors

Abstract

Typically considered a stable landscape, the Appalachian Piedmont harbors deposits and landforms suggestive of dynamic adjustment to tectonic and climatic forces that influence carbon storage in the critical zone. We leverage a south-to-north gradient in climate, crustal deformation, and glacial isostatic adjustment (GIA) from repeated Laurentide ice sheet advances and retreats to investigate base level changes encoded in the longitudinal profiles of Piedmont rivers. Using the stream power rule that assumes a linear relationship among stream steepness, rock erodibility, and erosion rate, we invert the fluvial topography to estimate accommodation space generation over Neogene-Quaternary time scales (<10 Ma) in valley bottoms where wetlands capable of storing carbon may have formed. The Conestoga, Catawba, and Broad watersheds coincide with published constraints on incision (geomorphic markers), erosion rates (terrestrial cosmogenic nuclides), and buried wetland stratigraphy (mid-Pleistocene-Holocene). The Southern Piedmont is distal to the glacial boundary, characterized by a humid subtropical interglacial/boreal glacial climate, minimal crustal uplift, and a muted GIA signal. Here, inverted profiles reveal steady uplift (~7m/Ma) until ~10Ma, a transient increase around 8-10Ma (~20m/Ma), and renewed steady uplift (~5m/Ma) to present. The Catawba watershed, perched above neighboring basins, shows evidence of stream piracy and drainage divide adjustments as transient knickpoints propagate upstream. Knickpoints here are co-located with 35+ sites where inverted topography preserves Pleistocene-aged wetland deposits at watershed divides, and a late Miocene response time (τ), which constrains the timing of accommodation space generation. In contrast, the Northern Piedmont near the glacial margin--characterized by a humid-temperate continental interglacial/arctic tundra glacial climate, relatively high crustal uplift, and strong GIA-- exhibits increased uplift around 8-10Ma (~11m/Ma), followed by a steady rise from ~5-1Ma, and a Pleistocene spike in uplift. Despite evidence of Pleistocene fluvial gravels in the context of time-transgressive terraces, wetland deposits older than Holocene millpond sediments are unknown; however, inversion modeling predicts areas of the Conestoga basin that could preserve mid-Pleistocene aged deposits. These results support a framework in which mid- and late-Miocene dynamic topography and Pleistocene GIA create transient knickpoints and modulated accommodation space. Ongoing work documents the presence of pre-Holocene valley bottom wetlands south of the glacial boundary, model the fluvial processes responsible for their formation, and evaluate carbon storage potential in the Piedmont critical zone.

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

doi: 10.1130/abs/2025AM-413411

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