Paper No. 10-5
Presentation Time: 8:00 AM-12:00 PM
COMPARING THE PROVENANCE OF SANDSTONES IN THE MESOZOIC HARTFORD AND POMPERAUG RIFT BASINS USING DETRITAL ZIRCON GEOCHRONOLOGY
During the Late Triassic to Early Jurassic periods, the Hartford rift basin (central Connecticut) filled with over 4 km of alluvial fan, river and lake sediments with basaltic intrusive and volcanic rocks. The faults that developed along the margin of the basin were significantly more active on the eastern edge during basin fill, resulting in tilting of the strata towards the east. In conjunction with abundant conglomerate along the eastern border fault, the tilted strata suggest that the primary sediment source area was to the east of the basin. The Pomperaug basin in western Connecticut is a small outlier of sedimentary and volcanic rocks similar in age and composition to the nearby Hartford and Newark (NJ-Pa) basins, which insinuates that the Newark and Harford basins were once connected ('broad terrane’ hypothesis) and that sediment provenance may be more complex. Discontinuous outcrop and complex paleocurrent patterns pose difficulties in reconstructing the ancient river systems that transported sediment and filled the basins. In this study detrital zircon U-Pb geochronology was used to constrain sediment provenance. Two samples each from the L. Triassic South Britain Formation of the Pomperaug basin, the L. Triassic New Haven Arkose and the E. Jurassic Portland Formation (both in the Hartford basin) were analyzed using LAICP-MS at the Arizona LaserChron Center. Preliminary results indicate that the New Haven Arkose zircons are dominated by L. Ordovician ages (Taconic orogeny) with abundant ages from L. Devonian (Acadian orogeny) and L. Neoproterozoic-Cambrian ages (Avalon terrane?) and a only a few Carboniferous ages (Alleghenian orogeny). This suggests an eastern (Bronson Hill terrane) source, although a western source cannot be ruled out. The zircon ages in the Portland Formation are similar to those of the New Haven Arkose except there are more Carboniferous, no Neoproterozoic and several Mesoproterozoic (Grenville) ages. The Grenville source indicates sediment input from the west of the Hartford basin during the Early Jurassic. The zircons from the Pomperaug basin consist primarily of Acadian ages, small amounts of Alleghenian and Taconic ages, and a few Neoproterozoic and Mesoproterozoic ages. The provenance of the Triassic Pomperaug sediment appears to come from both an eastern and western source area.