IGNEOUS ERRATICS IN THE KITTATINNY MOUNTAIN AREA OF SUSSEX COUNTY, NEW JERSEY: CLUES TO GLACIAL FLOW AND EROSION

Provenance of distinct glacier erratic boulders can be used to trace erosion and glacier flow. This is the case for nepheline syenite erratics found near Kittatinny Mountain, in Sussex County, Northwest New Jersey, USA. In this study, we verify the provenance of the nepheline syenite boulders found in late Wisconsinan moraine deposits west of Kittatinny Mountain, and hypothesize the glacial erosion and transport mechanisms involved. Quaternary ice sheets overrode the highest terrain in northwest New Jersey, the Kittatinny Mountain ridge. Existing geomorphic maps indicate a north-south ice sheet flow, modifying in late glaciation to northeast-southwest flow parallel to the topography.

A local intrusion of alkaline igneous rocks, the Beemerville Intrusive Suite (Ordivician/Silurian), occupies a small (~3km) area within Ordivician and Silurian sedimentary rocks on the southeast flank of Kittatinny Mountain. Beemerville igneous rocks are entrained into the till on the eastern side of Kittatinny Mountain. Nepheline syenite, presumed from the Beemerville intrusion, is rare but found in moraines on the western side of Kittatinny Mountain. One small boulder is located on the Tinsley/Geology Trail of Stokes State Forest. Another cobble-sized clast of similar appearance was excavated during a soil survey, about 1.5km to the northwest. This cobble provided material for a chemical composition analysis with ICP-OES, to compare to samples of Beemerville nepheline syenite retrieved from the type locality. Both the Geology Trail boulder and the soil survey cobble were within the Wisconsinan recessional Ogdensburg-Culvers Gap Moraine. If these samples were indeed eroded out of the Beemerville intrusion, the unique erratics appear to have been moved 30° to as much as 90° west from the presumed glacial flow direction, over the intervening ridge with >200m of topographic relief (subtracting glacial sediment fill). We draw two hypotheses based on these observations: 1) glacier flow over Kittatinny Mountain fanned out to the west, possible with a thicker ice sheet, but the evidence since erased by late-Wisconsinan erosion; or 2) Beemerville intrusive rocks were more extensive (to the northeast) or higher in elevation, in a position to be better transported over the ridge but now greatly eroded.