1. A brief, incomplete, and surprising history of the Dougherty Plain
Burt Carter

2. GA Geological Society Physiographic Map of Georgia

3. Poorly marked boundary
Sharp, distinct boundary
at the Pelham Escarpment
Poorly marked boundary
at outcrop of older,
non-carbonate rocks.
GA Geological Society Physiographic Map of Georgia

5. Ichawaynochaway Cr
Flint River
Aycocks Creek
Flint River
Big Slough
Fishpond Drain
Spring Creek
Chattahoochee River
Surface Drainage to
Ochlocknee River

6. The Florida Straits connect the Gulf of Mexico to the Atlantic
The Florida Straits connect the Gulf of Mexico to the Atlantic. The northern branch of the Florida Straits carry the main body of the Gulf Stream out of the Gulf and into the Atlantic.
Gulf Stream
FLORIDA STRAITS

7. Florida Straits ? ? ? ? Florida Bay – Lime Mud Lower Keys Marathon
Hawk Channel – Lime Mud
Key
West
White Banks – Lime Sand ? ?
Rhodolith Gravel
Florida Straits
Reef
Tract ? ?

8. Ocala Limestone (Eocene)? ?
Ocala Limestone (Eocene)

9. ?
(Manker and Carter, 1987)

10. Florida Straits Suwannee Strait
Cuba Disneyland
Florida Straits Suwannee Strait
Reef Tract Reef Tract
(~Flint R.)
White Banks Dougherty Plain
Hawk Channel Dougherty Plain
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
U. Cretaceous
L. Cretaceous
Jurassic
Triassic
“basement”

11. 100’
GA Geological Society Physiographic Map of Georgia
From Beck and Arden, 1983

13. (~160’)
(~130’)
(Bridgeboro, actually)
From Beck and Arden, 1983

14. Other facies equivalents to the
Dougherty Plain
Pelham Escarpment
Tifton Upland
Miocene Altamaha Formation
Oligocene Bridgeboro Limestone
(locally with Chattahoochee or Suwannee
Limestone at the top)
Eocene Ocala Limestone (uppermost part missing)
Other facies equivalents to the
Bridgeboro

15. Beck and Arden proposed the mechanism shown here for the origin of the Rockhouse Cave system, and by extension, for the Pelham Escarpment overall. I have modified it slightly because the original doesn’t show the escarpment well, and actually implies that there is a separate escarpment facing the wrong way.
At the time the Bridgeboro Limestone was not recognized, so while there is a thin Suwannee Limestone above it, the bulk of cave development here is in the Bridgeboro.
Between the middle and lower pictures the land, of course, doesn’t shift to the left (west), the escarpment retreats to the right (east). PE PE PE
From Beck and Arden, 1983

16. Beck and Arden suggested that the retreat process might be expected to be fairly continuous, but that if the retreat stalled at a particular location or along a particular line, then an overdeveloped solution valley would form there. This possibility is schematically shown in the lower image here.
They applied that model to the formation of an important geomorphic feature farther south called “Big Slough”, which Jake Sanders has been studying this year.
Time 2
Valley formed by excessive cave and sinkhole development during stalled retreat.
Time 1
Steady Retreat
Time 3
Steady Retreat PE
From Beck and Arden, 1983

17. Normal stream profile with a local base level.70 80 90
100
110
120
130
140
150
160
170
180 5 10 15 20 25 30 35 40
Big and Little Rock Sink
Normal stream profile with a local base level.
Karst surface across which water obviously could not flow permanently.
Elevation above Sea Level (feet)
Miles Below Starting Point at Camilla

19. TRACING THE LONG AXES OF SINKHOLES (up to 2 miles long by less than half a mile wide) SUGGESTS THAT THEY WERE FORMED IN SOME RELATIONSHIP TO STREAMS WITH DENDRITIC DRAINAGE.
Branchville

21. LIMESTONE WITH SLOW DIFFUSE GROUNDWATER FLOW THROUGHOUT
INTEGRATED SURFACE DRAINAGE INITIATED ON RELATIVELY IMPERMEABLE CLASTICS
LIMESTONE WITH SLOW DIFFUSE GROUNDWATER FLOW THROUGHOUT
TIME 1
DOWNCUTTING AND REMOVAL OF SURFICIAL CLASTICS BY SURFACE DRAINAGE SYSTEM.
POSSIBLE INITIAL INFILTRATION TO LIMESTONE FROM TRUNK STREAMS
TIME 2
MOST VALLEY FLOORS APPRAOCH OR INTERSECT TOP OF LIMESTONE. HIGH RECHARGE RATE THROUGH THEM ENHANCES SOLUTION RATE ALONG THEIR COURSES.
CAVERNOUS POROSITY DEVELOPS BELOW DEEPLY INCISED CHANNELS. GROUNDWATER FLOW AWAY FROM CHANNELS STILL DIFFUSE.
TIME 3
DERANGED KARST DRAINAGE ON DENUDED SURFACE WITH VESTIGIAL CLASTICS
TIME 4
LIMESTONE WITH SINKHOLES AND DOMINANT GROUNDWATER FLOW BENEATH FORMER CHANNELS. SINKHOLES BEGIN TO DEVELOP MORE BROADLY.