EAST TENNESSEE GEOLOGICAL SOCIETY

April 2026 Virtual Meeting

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Monday, May 11, 2026
6:00 - 7:30 pm

Note: ETGS members will receive an email with info for logging into the meeting.
 

May Presentation

Preliminary observations from USGS mapping in the eastern Piedmont of central Georgia

By

Mark Carter, PG, CPG and Ryan Deasy, USGS Florence Bascom Geoscience Center

The USGS has started detailed geologic mapping on the USF&W Piedmont National Wildlife Refuge (PNWR) in the eastern Piedmont of central Georgia for natural resource management and critical mineral studies. Our study area comprises the southernmost end of the Charlotte terrane, northeast of the Pine Mountain window. We recognize several upper amphibolite facies metaigneous and metasedimentary units. Multiple generations of granitoids are present in the northern and southern parts of the field area, whereas migmatitic biotite gneiss and amphibolite are the dominant lithodemes in the central portion of the PNWR. Biotite gneiss and interlayered amphibolite are the oldest rocks and occur as outcrop- to map-scale xenoliths within granitoids. Younger amphibolitized mafic dikes crosscut igneous contacts and older metamorphic fabrics and are variably transposed into the penetrative regional foliation. These rocks may be feeder dikes to olivine gabbros of the Silurian-Devonian Concord-Salisbury Plutonic Suite in the northern part of the field area. Strain is highly partitioned. Sigmoidal megalithons, 10s to 100s of m thick, of relatively low strain but still dextrally sheared rocks are bound by zones of northeast-southwest-striking, steeply dipping migmatitic mylonites. Lower amphibolite- to greenschist overprint is sparsely localized and consists of white mica forming in foliation planes in some rocks and static replacement of metagabbro by chlorite-talc-tremolite.

All units host pegmatites with mineralogy varying by host rock. Pegmatites in metagabbro have feldspathic margins and quartz-muscovite cores; these have been mined for feldspar. Pegmatites in amphibolite commonly contain nonmagnetic metallic minerals. Granitoids tend to be deeply saprolitized, with variably thick overlying pedogenic regolith. Contacts between regolith, saprolite and fresh rock may be sharp or gradational over several to 10s of meters; where discernible, saprolite fronts are commonly vertical.
 

Biography

Mark Carter is a professional geologist with three decades of experience in bedrock mapping and applied geoscience across the southern Appalachian region and Atlantic Coastal Plain. He earned his B.S. from Old Dominion University and his M.S. from the University of Tennessee, Knoxville.

Mark began his career in 1996 with the North Carolina Geological Survey in Asheville, where he mapped the Blue Ridge and parts of the Chauga belt in western North Carolina. In 2004, he joined the Virginia Division of Mineral Resources, expanding his fieldwork to the eastern Piedmont, upper Coastal Plain near Richmond, and the Virginia Blue Ridge.

In 2009, Mark joined the U.S. Geological Survey as part of the Eastern Geology and Paleoclimate Science Center's Appalachian Blue Ridge Project, conducting detailed geologic mapping along the Blue Ridge Parkway. He later served as the local USGS coordinator for the agency's response to the 2011 Mineral, Virginia earthquake.

Mark has led multiple National Cooperative Geologic Mapping Program projects, including major efforts focused on seismic hazards, Fall Zone geology, and regional Piedmont and Blue Ridge framework studies. He currently serves as Project Chief for the NCGMP "Eastern Piedmont and Upper Coastal Plain, Virginia to Georgia" project, with ongoing mapping in southeastern Virginia, northeastern North Carolina, and central Georgia - including work on the Piedmont National Wildlife Refuge, Bond Swamp National Wildlife Refuge, and portions of Oconee National Forest.

His research integrates geochemical, geophysical, LiDAR, and diverse geochronologic techniques to better understand the evolution of the southern Appalachian orogen and its overlying Coastal Plain sediments, with particular emphasis on critical mineral resources and geologic hazards.

 

 

Greetings, and welcome to the May 11, 2026 ETGS virtual meeting.
 

This meeting will be attended via Zoom and as a courtesy please mute your cell phone or the microphone in your laptop/tablet to minimize background noise and feedback echos. We will also make an effort to mute all participants - at least until the presentation is finished. Please use the chat feature to type any comments or questions you may have. We recommend that you send questions for the speaker to "everyone" so all participants can see the question. In the interest of time, we may hold the Q&A at the end of the presentation.

We will create a virtual attendance list. It is not always possible to tell who is participating on-line, especially for those joining by phone, so please email etgs@live.com to be listed on the attendance sheet. Let us know exactly how your name should appear on the list. We will add a note explaining the lack of signatures due to remote participation and have an ETGS officer sign as usual.

Thank you for your patience and understanding as we continue with this online format. As always, we welcome and appreciate your feedback and suggestions for improvement.

 

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President
Tony McClain

Vice President
David Carlone

Secretary
J. Brad Stephenson

Treasurer
Seaira Stephenson

Webmaster/Social Media Coordinator
Bob Gelinas

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Page updated May 03, 2026