ASSESSING THE RELATIONSHIP BETWEEN ACCRETED TERRANES AND ARSENIC IN THE NEWARK SUPERGROUP OF THE GETTYSBURG BASIN

Groundwater obtained from wells in the Passaic and Lockatong Formations of the Newark Supergroup in the Newark Basin have arsenic concentrations above10μg/L, the maximum contaminant limit for drinking water. These formations are predominantly fine-grained containing organic matter and/or iron oxides and have the highest arsenic concentrations of the lithologies in the basin. The provenance of the sediments was predominantly from the southeast and therefore likely from accreted terranes along the ancient active margin. Evidence from New England shows that accreted terranes carried deposits of arsenic, but little has been done to assess the relationship between accreted terranes and arsenic in the Newark Supergroup. If the accreted terranes that formed the ancient Appalachian Mountains contained arsenic minerals, then sediments deposited from these terranes into Mesozoic rift basins along the East Coast of North America will have elevated arsenic compared to deposits from the west.

To test this model for arsenic deposition, we present data from the Gettysburg Basin, which has similar strata to the Newark Basin. The Gettysburg Basin is located southwest of the Newark Basin and further west from the accreted terrane. We expect to see arsenic concentrations in both the rocks and surface and groundwater to be lower than 10μg/L, possibly due to the greater distance from the source terrane.