DEPOSITIONAL ENVIRONMENTS AND TIMING OF FORMATION OF THE ‘LILESVILLE GRAVELS’, ANSON COUNTY, NC

Near Lilesville, NC, on the western margin of the Fall Zone, there occur upland gravels containing unusually coarse-grained, imbricated cobbles. These upland ‘Lilesville Gravels’ form an extensive plateau capping the hilltops at an elevation of ~135 meters ASL (~100 meters above the current Pee Dee River), and they lie unconformably on the deeply weathered Lilesville granite. The ‘Lilesville Gravels’ contain the following facies: 1) clast-supported quartz pebble conglomerates with a medium sand matrix; 2) cross-bedded medium-coarse sands containing lenses of pebbly gravels and plant fragments; 3) thinly bedded silts, sands, and pebble-rich conglomerates locally occurring as channel fills; 4) a white marker-bed consisting of leached fine-medium sand; 5) cross-bedded, medium to fine sands with well developed, tubular, vertical mottling; and 6) clay-rich lignite with abundant plant fragments. The ‘Lilesville Gravels’ are assigned to the mid-to-late Miocene (7-10 ma), based on pollen derived from the lignite facies and their elevation above the current position of the Pee Dee River. A ground penetrating radar transect is consistent with a facies 3 channel form observed in an adjacent quarry high wall. Iron activity ratios (Fe_H /Fe_D) of soil profiles from quarry high walls suggest multiple periods of soil formation, indicating times of stable conditions interspersed with periods of deposition by the ancient Pee Dee River. Three buried paleosols have been identified and one soil is currently forming at the land surface. Lithofacies analysis suggests that the ‘Lilesville Gravels’ are the product of a braided stream system and record an interval of aggradation by the southerly-flowing ancestral Pee Dee River system as it migrated back and forth across the landscape. The ‘Lilesville Gravels’ may record a time of epeirogenic uplift in the source area and/or a transition to a wetter paleoclimate, creating the conditions to mobilize large quantities of coarse-grained sediment.