Stokes M. A. - Report

Peachtree Rock - Audrey Stokes Field Trip Write-up

OVERVIEW

Peachtree Rock is a nature preserve covering a 300-acre tract, bought by The South Carolina Nature Conservancy in 1980 [1]. It received its name by an unusual sandstone formation in the vicinity that looks like a peach tree. It is located in southern Lexington County, in the Upper coastal plain of South Carolina and marks the top of the middle Eocene sediments in this area. It is noted for its unusual silicified sandstone formations, a waterfall, and abundant silicified fossil shell concentrations [2].

THE JOURNEY

Our field trip begins at the parking lot. Here we observed soil with poor sorted, well-rounded siliceous sediments. Near the top of the trail we find "Carolina" clay surrounded by long leaf pines, which is typical of upland formations and can be seen in picture one.  The clay consists of some red particles caused by iron oxidation. The presence of this clay suggests a low energy environment. As we start down the tail from the parking lot, we can see typical sand hill vegetation [1].

A bit further along the descending trail, before sighting our destination, we come across some poorly sorted rocks exposed along the north face of the valley. These rocks are composed of sand, shells, microcrystaline chert, and quartz, which are easily broken apart. Because of the shell fossils, we believe the rocks to be Claibornian in age [2]. The shells can barely be discerned in picture 2. Some people have misidentified common white layers which are rich in flakes of clay as fossiliferous.

At the end of the trail, we come to the namesake of the preserve, Peachtree Rock. Peachtree rock (picture 6) is a sandstone formation that stands out because of its more resistant substance to the environment and due to the erosion of the softer, less resistant rock and sand surrounding it. The erosion exposes laminated finer beach wash cross bedding with worm burrow intrusions (pictures 7 and 8). These tube-like borrows were most probably created by a marine animal called Calianassa when oceans washed over this area. This formation and others like it in the area originated 45-50 million years ago during the Eocene Epoch when oceans covered this region [1].

After leaving Peachtree rock, we headed toward the waterfall. Along the top of the waterfall we find calcite cross bedding, which can be seen in picture 3. The presence of this type of bedding leads us to believe this was a site of either an off shore environment or an on shore sand dune. The area around the waterfall consist of Eocene sediment silicified sequences varying from 1 to 2 meters thick. Under the ledge are unconsolidated sands that are mostly fine-grained [2]. A perched water table causes the waterfall to exist. This means that the water table supplying it is higher or perched above the water table of the surrounding area. This phenomenon is caused by water being trapped above a layer of impervious rock. In pictures 4 and 5, tube-like burrows of a marine animal called Calianassa can be seen along the waterfall outcrop [1].

After leaving the waterfall, we head to the last outcrop and stop on our trek (picture 10). Here we find Herringbone cross-stratification formed from alternating tidal currents (pictures 11 and 12). We also found some stalagmites' calcite rings under the outcrop's ledge, which Professor Kendall said was something else, but I still believe is calcite rings.

After coming from our last outcrop stop, we cross a small creek flowing east. The creek does not have much impact on the stratigraphy of the area, but it does have some neat ripple marks (picture 9).

REFERENCES

1.  Oleta Hall Beard. "The Interpretive Trail Guide for Preachtree Rock Preserve."

2. Lucille Kite, "Stratigraphy of Peachtree Rock Preserve, Southern Lexington County, South Carolina." South Carolina Geology (1985), V. 29, No.1.

Sunday, February 24, 2013
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