PASSIVE MARGIN SEDIMENTATION DURING THE EARLY DRIFT PHASE OF THE U.S. MID-ATLANTIC: PERSPECTIVES FROM U-PB DETRITAL ZIRCON GEOCHRONOLOGY

Sedimentary systems feeding passive margin depocenters respond to dynamics of tectonics and climate in the hinterland. The U.S. Atlantic margin remains understudied with respect to its long-term post-rift source-to-sink dynamics. Here, we use detrital zircon (DZ) U-Pb geochronology to assess Early Cretaceous sedimentary routing systems from the coastal plain to basin floor along the U.S. mid-Atlantic margin. We leverage DZ U-Pb age signatures to fingerprint distinct hinterland source terranes providing detritus to the onshore fluvial segment (Potomac Gp.) and the coeval offshore basin floor (Blake-Bahama Fm.). This source-to-sink approach, along with a protracted temporal record of sedimentation, yields new perspectives of the stratigraphic evolution of the early drift phase of the North Atlantic basin.

Berriasian-Hauterivian (145-133 Ma) fluvial sandstone of the Potomac Gp. exhibits a unimodal age distribution centered at ~600 Ma, consistent with a Pan-African crustal source. Time equivalent, turbiditic sandstones of the Blake-Bahama Fm. ~600 km offshore on the continental rise feature a more cosmopolitan DZ U-Pb age distribution, consistent with a wider Appalachian heritage, including a dominant Grenvillian mode (920-1300 Ma) and subsidiary Alleghenian (260-325 Ma), Taconic/Acadian (325-500 Ma) and Pan-African (510-690 Ma) modes. This Appalachian signature persists through the Albian in the Blake-Bahama turbidites and also appears in the Aptian-Albian (~125-100 Ma) Potomac Gp. The disparity between Berriasian-Hauterivian fluvial and turbidite sandstones suggests a disconnection between the onshore and offshore segments. The unimodal peak in the basal Potomac Gp. is consistent with local provenance, whereas the broad age distribution of turbidite sands suggests a larger and more integrated source area, such as the eroding central Appalachian orogen. By Aptian/Albian time both on- and offshore strata display a U-Pb age signature consistent with regional Appalachian sourcing. We interpret this similarity to represent a transition to a fully-connected onshore-offshore sediment routing system feeding the margin. These data represent the first geochronological constraints on onshore-offshore sedimentary system linkages along the U.S. mid-Atlantic passive margin.