Estimating magnitudes of relative sea level fluctuations from the sedimentary record is challenging, but illuminates possible mechanisms of sea-level change. Here, we provide a new approach to calculate magnitudes of relative sea-level change using reconstructed depositional slopes and downdip-to-updip extents of transgression across those slopes. Magnitudes of rise on transgressive surfaces within lower to middle Atokan (upper Bashkirian to middle Moscovian) fan-delta strata of the Fountain Formation (Colorado) range from minimums of ∼8–15 m to maximums of ∼13–20 m. These estimates are low relative to other intervals of the Permian–Pennsylvanian, but approach estimates from coeval deposits elsewhere. Each cycle shows evidence for the rise and fall of sea level that, coupled with the magnitude, and coincidence with inferred glacioeustatic cyclothems elsewhere, suggests a glacioeustatic origin.

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