As a follow-up to this story on the Wichita Mountains as an "Exhumed Permian Landscape" is my own smaller-scaled "Exhumed post-Miocene Landscape" on the Georgia Coastal Plain (see "Youngest Formations" in this link).
It was about 20 years ago, while I was working on the Georgia Geologic Survey STATEMAP Project, east of the Flint River, I was mapping a portion of Turkey Creek (with the permission of the Turkey Creek Hunting Club) on the Drayton USGS 7.5 minute quadrangle (Summerour, 1999).
In an area with an "Asymmetrical" creek valley (bluff on the south side, flood plain on the north) at this particular location, the bluff was on the "outside" of a meander. Per this link's definition, looking downstream (southwest), this area had a local "Positive Asymmetry", i.e., bluff on the left, gentle slope (flood plain) on the right.
At the base of the bluff, at creek's waterline (and just above) was a Middle Eocene Lisbon Formation "marl" (a sandy, calcareous, glauconitic clay), with numerous interesting small marine fossils.
The matrix disaggregated easily in water revealing a mix of tiny Comatulid Crinoid centrodorsals (and other "pieces) (Microcrinus conoideus), small Brachiopods (Terebratulina sp.), small Echinoids (Echinocyamus parvus, Protoscutella conradi.), as well as other small fossils and microfossils (Summerour, 1999), some of which facilitated paleontological research (Oyen and Summerour, 2002) and 32 of which were donated to the Florida Museum of Natural History Invertebrate Paleontology collection.
On the bluff, above the "marl" was interpreted to be Late Eocene Clinchfield Formation marine sands, all the way to the top of the bluff (perhaps 30 feet (+/-)). I don't recall if there was any thin or discontinuous Miocene Altamaha Formation at the very top of the bluff or not.
The Altamaha Formation is composed of clays, gravels, sands, all of which are interpreted to be fluvial. The Altamaha Formation commonly comprises the surficial deposits of the Inner Coastal Plain.
During my solo mapping sessions and field-checking by colleagues, it was generally agreed that the north side (inside) of the meander was eroded Altamaha Formation, though it was significantly lower than the top of the bluff.
This led to some time spent in deep contemplation sitting on the bluff, both alone and other times with a colleague, wondering "What the hell happened here?"
I had dealt with smaller asymmetrical valleys in the area, including Turkey Creek, upstream and east of the town of Byromville. In that and the other local cases, the side opposite the bluff was usually covered with terrace alluvial deposits and the topographic contrast was not as prominent.
It had been about 22 years since my Geomorphology course and I hadn't given much recent thought to "exhumed landscapes", though I had consulted Thornbury (1968) to make my case for isolated low "sand ridges" adjacent to some creeks being "non-paired, non-cyclical terraces in an asymmetrical valley" elsewhere in the study area.
Anyway, as I sat on the Late Eocene in the upper part of the bluff, I looked across Turkey Creek AND DOWN at the Miocene on the other side. Though the proper word "exhumed" didn't jump out at me, I sensed that "something old was being uncovered", i.e., something from a previous cycle of erosion and deposition was exposed across the creek, rather than the "normal" flood plain deposits.
References:
Oyen, C. W. and Summerour, J. H., 2002 New records of comatulid crinoids from the Eocene of Southwestern Georgia; (abs.) Geological Society of America Abstracts with Programs, vol. 34, #2, p. A117.
It had been about 22 years since my Geomorphology course and I hadn't given much recent thought to "exhumed landscapes", though I had consulted Thornbury (1968) to make my case for isolated low "sand ridges" adjacent to some creeks being "non-paired, non-cyclical terraces in an asymmetrical valley" elsewhere in the study area.
Anyway, as I sat on the Late Eocene in the upper part of the bluff, I looked across Turkey Creek AND DOWN at the Miocene on the other side. Though the proper word "exhumed" didn't jump out at me, I sensed that "something old was being uncovered", i.e., something from a previous cycle of erosion and deposition was exposed across the creek, rather than the "normal" flood plain deposits.
As I couldn't properly articulate what I had seen (and I was on a schedule to finish and move elsewhere), I chose not to include that in my report.
References:
Oyen, C. W. and Summerour, J. H., 2002 New records of comatulid crinoids from the Eocene of Southwestern Georgia; (abs.) Geological Society of America Abstracts with Programs, vol. 34, #2, p. A117.
Summerour, J. H., 1999 Geologic Atlas of the Byromville, Drayton, and Leslie, Georgia 7.5 minute quadrangles; Georgia Geologic Survey Digital Open-File Report 99-1, 42 pp., 4 pl.
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