Title

Investigation of Surficial Sandy Strata Near Middleground in Bulloch County, Georgia

Document Type

Presentation

Publication Date

3-24-2011

Abstract

The area of investigation lies within the Inner Coastal Plain, ~ 14 km north of Statesboro, Georgia. A road cut west of the Middleground community exposes a tan sand < 1 meter thick overlying maroon clayey sandstones and sand-clay couplets of the Meigs Member of the Miocene Coosawhatchie Formation. The tan sand rests disconformably upon the Meigs Formation truncating cross-bedded strata in the Meigs. Contacts with underlying Meigs strata vary from sharp to gradational within an exposure, depending on the local extent of bioturbation. The surficial position of the tan sand suggests Holocene deposition, but the age has not been verified. The most likely origins for the surficial sand include eolian or fluvial deposition. The elevation is well above local floodplains favoring eolian deposition; however, the sand is very poorly sorted with a clast size range from pebbles, granules, coarse to fine sand to silt and clay. These field observations are being tested in the lab with sieving and grain-size analyses. Initial sieving results show an increase in the coarse size fraction with depth in the sections sampled to date. A fluvial origin for the sands as possible terrace deposits of the Ogeechee River or its tributaries is a possibility. Ground Penetrating Radar (GPR) profiles were conducted at the field site using a MALA system with a cart-mounted 250MHz shielded antenna. The GPR profile showed mostly planar reflection elements of the surficial sand overlying and filling an irregular surface but did not reveal distinctive internal structures within the sand. Additional GPR profiling will be conducted at selected sites with an 800 MHz antenna in an attempt to resolve fine bed forms. The study area and methods will expand to include GPS data for elevation and location control of the sand-Meigs contact to test the stream terrace origin. Charcoal fragments are common in the sand and have been collected for age determination by radiocarbon methods. These methods should allow determination of the origin and age of the sand.

Sponsorship/Conference/Institution

Geological Society of American Southeastern Section Annual Meeting (GSA)

Location

Wilmington, NC