ARSENIC IN THE NEWARK AND GETTYSBURG BASINS: DOES DISTANCE FROM SEDIMENT SOURCE MATTER?

Arsenic is a ubiquitous element throughout the Earth’s crust, but has been found heterogeneously distributed at concentrations above the crustal average of 1.7 mg/kg in crystalline environments such as the Northern Appalachian Mountains (Peters, 2008) and in sedimentary environments such as the Newark rift basin. In addition, groundwater in both environments has arsenic concentrations above the maximum contaminant level of 10 μg/L. Little research has been done on the relationship between arsenic in crystalline environments of the ancient Appalachian Mountains and arsenic in the Newark and Gettysburg rift basins of New Jersey and Pennsylvania, USA. The provenance of the sediments in these basins is predominantly from the southeast and therefore likely from accreted terranes along the ancient active margin. 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. If groundwater comes into contact with high arsenic sedimentary rocks, arsenic will desorb and travel in the aqueous phase in the groundwater.

To test this model for arsenic occurrence, we present data from the Newark and Gettysburg basins, the accreted terranes and areas in between. The Gettysburg Basin is located southwest of the Newark Basin and further west from the accreted terrane. We expect to see arsenic concentrations in surface and groundwater to be lower than 10μg/L and rock concentrations near the crustal average of 1.7 mg/kg, possibly due to the greater distance from the source terrane.