Abstract

During the last glacial period, when sea level was low, meltwater discharge drove incision of the lower Mississippi valley, with valley filling and delta construction during Holocene sea-level rise. Isostatic modeling shows that sediment volumes removed and replaced were sufficient to induce uplift of >9 m along valley margins followed by subsidence of the same magnitude, with effects dissipating only over distances of >100–150 km along the Gulf of Mexico coast. Recognition of cyclical uplift and subsidence refutes recent interpretations of delta stability, and suggests that late Holocene relative sea-level curves from the delta region are instead a record of subsidence of the pre-Holocene depocenter. More broadly, incised valley cutting and filling is a common fluvial response to glacioeustasy, and cyclical uplift and subsidence should be common to large alluvial-deltaic systems elsewhere.

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