EVOLUTION OF SEDIMENT DISPERSAL SYSTEMS DURING THE EARLY DRIFT PHASE OF U.S. ATLANTIC MARGIN DEVELOPMENT: INSIGHTS FROM DETRITAL ZIRCON U-PB GEOCHRONOLOGY

Passive margins serve as vital bookkeepers of geologic history, chronicling hinterland tectonics and landscape evolution in their extensive, continuous stratigraphic records. Though many passive margins worldwide are well understood, the U.S. Atlantic margin remains relatively understudied. We present detrital zircon (DZ) U-Pb ages from Early Cretaceous fluvial and deep marine sandstones to assess sediment provenance and routing systems operating during early development of the mid-Atlantic margin. These results test previous hypotheses of Early Cretaceous sediment dispersal systems and provide new insight into potential linkages between onshore and offshore depositional segments. Sandstones from the onshore, fluvial Potomac Gp (subsurface Maryland) are compared to offshore, turbidite sands of the Hatteras Fan (~600 km offshore mid-Atlantic).

The basal Potomac Gp (Waste Gate Fm.), of Berriasian age, exhibits a unimodal age distribution, with a peak centered on ~600 Ma, attributable to the proximal, Pan-African (500-710 Ma) Carolina Terrane. In contrast, coeval turbidite sandstones feature a cosmopolitan age distribution consistent with an Appalachian hinterland heritage, including a dominant Grenvillian (920-1300 Ma) age peak with secondary modes attributable to Alleghenian (260-325 Ma), Taconic/Acadian (325-500 Ma), and Pan-African source terranes. The de-coupled nature of onshore and offshore age spectra suggests multiple independent systems operating along the margin during lowermost Cretaceous time (Berriasian-Hauterivian). By Aptian-Albian time, however, age spectra of the onshore strata of the Patuxent Fm and the offshore fan correlate, each exhibiting the widespread age distribution featured in the lower fan strata. These results suggest that Early Cretaceous sediment routing systems along the margin were dynamic, with onshore systems evolving from small catchments to regional drainage networks linked to distal offshore segments. These data represent the first geochronologic constraints on offshore Mesozoic strata from the U.S. mid-Atlantic, and provide new insights into the evolution of sediment routing during early drift of the U.S. passive margin.