DETRITAL ZIRCON CONSTRAINTS ON PROVENANCE AND WATERSHED INTEGRATION: IMPLICATIONS FOR US EAST COAST ATLANTIC CONTINENTAL DRAINAGE DIVIDE DEVELOPMENT

A geologic paradox exists in the evolution of a continental drainage divide formed during continental rifting. Namely, landscape evolution models and thermochronologic data provide conflicting stories on how these divides migrate into the foreland: either by rapid retreat only in the early post-rift stages, or by a more gradual progression over time. This applies to the Atlantic US East Coast continental drainage divide, where a long-term thermochronologic retreat rate contrasts with a recent rate of retreat determined by cosmogenics. Based on recent landscape evolution modeling of divide retreat and a low modern retreat rate, I tested the hypothesis that the Atlantic divide migrated rapidly after rifting to its current location (‘western foreland’) followed by relative stability. Foreland source units in Pennsylvania have unique detrital zircon (DZ) age spectra, and the Coastal Plain sink records the eroded equivalents of these units. I conducted a DZ provenance study of these sink units from the Early Cretaceous to the Miocene because migration of this divide has implications for the foreland units depositing sediment to the sink. The goal of these analyses was to determine when the divide began integrating western foreland units in western Pennsylvania. Support of the hypothesis would include all sampled DZ age spectra displaying similar age populations that include signals of the western foreland (i.e., Taconic ages). This would mean the divide migrated rapidly following rifting, remaining relatively stable since the Early Cretaceous. If the older age spectra don’t show western foreland signals, this would falsify the hypothesis and point to a more gradual retreat of the divide. Three preliminary Coastal Plain samples from Early and Late Cretaceous, and Miocene fluvial units all show similar peaks including western foreland age signals. These results indicate that the divide had already migrated and was integrating western foreland units by the Early Cretaceous. Future DZ analysis of Late Triassic units in the Newark Basin will provide greater resolution on the timing of drainage divide arrival to the western foreland in Pennsylvania. These findings have implications for how sediment routing systems develop following rifting, and support the early rapid retreat thermochronologic and modeling data.