5G; Middle to Upper
Ordovician
Invertebrates
of Northwest Georgia
By:
Thomas Thurman
I want to start this page by thanking the Emory University of 1948 for funding a field camp tasked towards detailed research into an aspect of Georgia’s paleontology, Ordovician stratigraphy and invertebrates. Leading the team was Arthur T. Allen and James G. Lester, who also authored the 1957 report on this research published by the Georgia Geologic Survey as Bulletin 66. It is available below as a download.
Such strong support of Earth Science from a university, museum, municipality, or the State of Georgia would become increasingly rare in following years and is simply non-existent now. I suspect this research has been overlooked for some time and it would be a worthwhile amateur project to see how many of these localities still exist.
The Ordovician Periods spanned from 444 to 485 million years ago. At this period Georgia was completely submerged and deep in the Southern Hemisphere. The Middle toUpper Ordovician would span from 444 to 470 million years ago.
To quote the paper; (1957)
The present investigation is an outgrowth of dissatisfaction with our inability to correlate beds of known Ordovician strata with previously defined formations. Shortly after establishing the Emory Geology Camp near Ringgold in 1948, this difficulty became apparent. As a result a detailed study of Ordovician strata was begun in the summer of 1950 and has been continued during the field seasons up to the present time.
The authors have carefully collected data from all the available exposures and have measured more than 50 detailed stratigraphic sequences…
The present investigation is an outgrowth of dissatisfaction with our inability to correlate beds of known Ordovician strata with previously defined formations. Shortly after establishing the Emory Geology Camp near Ringgold in 1948, this difficulty became apparent. As a result a detailed study of Ordovician strata was begun in the summer of 1950 and has been continued during the field seasons up to the present time.
The authors have carefully collected data from all the available exposures and have measured more than 50 detailed stratigraphic sequences…
Identified Species
The team identified 182 species of invertebrates from Ordovician deposits in NW Georgia. The Ordovician Periods spanned from 444 to 485 million years ago. At this period Georgia was completely submerged beneath an ocean and deep in the Southern Hemisphere.
The species they reported included.
The author provided no images of the collected and reviewed fossils so none of the fossils imaged here are Georgia specimens.
The team identified 182 species of invertebrates from Ordovician deposits in NW Georgia. The Ordovician Periods spanned from 444 to 485 million years ago. At this period Georgia was completely submerged beneath an ocean and deep in the Southern Hemisphere.
The species they reported included.
- Algae 3 species
- Sponges 3 species
- Corals 12 species
- Worms 1 species
- Bryozoa 56 species
- Brachiopods 67 species
- Gastropods 17 species
- Bivalves (pelecypods) 2 species
- Cephalopods 11 species
- Trilobites 5 species
- Ostracods 5 species
The author provided no images of the collected and reviewed fossils so none of the fossils imaged here are Georgia specimens.
Localities
Five belts of Ordovician were mapped and measured by the Emory research team. Five general localities were explored for fossils and the finds documented, all but one represents an offshore environment. The Mill Creek fossils represent a near-shore environment.
In 1957 the various locations were mapped (crudely) and described in detail, their measured sections and thickness are reproduced here below the species list. A measured section is where a researcher measures and describes each bed occurring in an exposure. This helps later researchers identify formations and quickly locate and date fossil beds.
Five belts of Ordovician were mapped and measured by the Emory research team. Five general localities were explored for fossils and the finds documented, all but one represents an offshore environment. The Mill Creek fossils represent a near-shore environment.
- Lookout Valley (Offshore)
- Chattanooga Valley (Offshore)
- Chickamauga Valley (Offshore)
- Rabbit Valley (Offshore)
- Mill Creek Valley (Near-shore)
In 1957 the various locations were mapped (crudely) and described in detail, their measured sections and thickness are reproduced here below the species list. A measured section is where a researcher measures and describes each bed occurring in an exposure. This helps later researchers identify formations and quickly locate and date fossil beds.
General Geology of the Area (1957 paper quoted)
Within the area all rocks are of Paleozoic age and formations representing all periods from Cambrian to Pennsylvanian, with Devonian strata restricted, are exposed. Twenty-six formations with an aggregate thickness of 11,500 feet more or less are present.
Physiographically the area is classed as Valley and Ridge except for the presence of a small part of the Cumberland Plateau in the extreme northwest corner. The larger and highest mountains, Lookout and Little Sand, are capped with lower Pennsylvanian strata; the secondary ridges are monoclinal and capped by the Silurian Red Mountain Formation. Third order ridges are composed of Knox residuum. The Knox Formation forms the lower limit and the Red Mountain Formation, the upper limit of the strata included in this study, all of which crop out in the valleys and on the scarp slopes of the monoclinal ridges.
Structurally it is a region of northeast trending synclinal mountains and anticlinal valleys. High. angle overthrust faults, both simple and bifurcating are common and trend in directions essentially paralleling the ridges and valleys. No attempt is made to present the structural detail of the area and the study has been restricted to the sedimentary and the stratigraphic relations.
Within the area all rocks are of Paleozoic age and formations representing all periods from Cambrian to Pennsylvanian, with Devonian strata restricted, are exposed. Twenty-six formations with an aggregate thickness of 11,500 feet more or less are present.
Physiographically the area is classed as Valley and Ridge except for the presence of a small part of the Cumberland Plateau in the extreme northwest corner. The larger and highest mountains, Lookout and Little Sand, are capped with lower Pennsylvanian strata; the secondary ridges are monoclinal and capped by the Silurian Red Mountain Formation. Third order ridges are composed of Knox residuum. The Knox Formation forms the lower limit and the Red Mountain Formation, the upper limit of the strata included in this study, all of which crop out in the valleys and on the scarp slopes of the monoclinal ridges.
Structurally it is a region of northeast trending synclinal mountains and anticlinal valleys. High. angle overthrust faults, both simple and bifurcating are common and trend in directions essentially paralleling the ridges and valleys. No attempt is made to present the structural detail of the area and the study has been restricted to the sedimentary and the stratigraphic relations.
Fossils Reported by Allen & Lester in 1957
Algae
- Cryptozoon (mats of filamentous calcareous algae?)
- Lookout Valley
- Solenoporo sp. (red algae)
- Lookout Valley
- Chickamauga Valley
- Rabbit Valley
- Mill Creek Valley
- Solenoporo compacto (red algae)
- Lookout Valley
- Chattanooga Valley
Sponges
- Cryptophragmus antiquatus
- Lookout Valley
- Chattanooga Valley,
- Stromatocerium sp.
- Chickamauga Valley
- Stromatocerium rugosum
- Lookout Valley
- Chattanooga Valley
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Corals
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Worms
- Cornulites flexus
- Lookout Valley
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Bryozoa
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Brachiopods
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Gastropods
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Pelecypods (Bivalves)
- Byssonchia sp.
- Chattanooga Valley
- Chickamauga Valley
- Rabbit Valley
- Byssonchia intermedia
- Lookout Valley
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Cephalopods
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Ostracods
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Trilobites
- Bathyurus sp.
- Chickamauga Valley
- Rabbit Valley
- Calyptaulax callicephala (Formerly; Callops callicephala)
- Rabbit Valley
- Dipleura dekayi
- Rabbit Valley
- Flexicalymene sp.
- Chickamauga Valley
- Isotelus sp.
- Chattanooga Valley
Note: I posted the below pic of Dipleura dekayi in Georgia’s Fossils Group and Cam Muskelly, who is very familiar with trilobites and NW GA sediments commented. “I'm pretty sure this species of trilobite is only known from Middle Devonian rocks.” He wondered if it might be mislabeled. A few others agreed with Cam.
The Upper to Mid Ordovician sediments are 44 to 470 million years old. Mid Devonian sediments would be 382 to 393 million years old.
So, this is a significant discrepancy.
There is no mention of where, or if, the collected fossils were housed. I know that most samples held by the Georgia Geologic Survey were discarded or lost before it was “abolished” in 2004. I emailed the Emory’s Environmental Sciences Program, but I would be very surprised if they’re still holding a fossil after so many decades. My experience with universities shows that few, if any, maintain research fossil collections after the collecting professor retires. In some cases specimens are turned over to museums, either in the university or an external institution. As of this writing there’s been no reply from Emory.
The simplest explanation is that the fossil was misidentified, if the fossil is not available for review, then we can only proceed with the information at hand and see what future finds reveal.
The Upper to Mid Ordovician sediments are 44 to 470 million years old. Mid Devonian sediments would be 382 to 393 million years old.
So, this is a significant discrepancy.
There is no mention of where, or if, the collected fossils were housed. I know that most samples held by the Georgia Geologic Survey were discarded or lost before it was “abolished” in 2004. I emailed the Emory’s Environmental Sciences Program, but I would be very surprised if they’re still holding a fossil after so many decades. My experience with universities shows that few, if any, maintain research fossil collections after the collecting professor retires. In some cases specimens are turned over to museums, either in the university or an external institution. As of this writing there’s been no reply from Emory.
The simplest explanation is that the fossil was misidentified, if the fossil is not available for review, then we can only proceed with the information at hand and see what future finds reveal.
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Details of Localities
- Lookout Valley
- Chattanooga Valley
- Chickamauga Valley
- Rabbit Valley
- Mill Creek Valley
Below are locations of recorded Sections (Details of sections given in original paper)
#1 Lookout Valley Exposures
- Morganville
- Secondary road south of Morganville across Slygo Ridge, west of US Hwy 11
- 256.2’ Thick
- Trenton
- West of Hwy 11 in Trenton City Limits, north of GA Hwy
- 141.9’ Thick
- Union
- East of US Hwy 11 & .75 mile north of Union
- 274.7’ Thick
- East of US Hwy 11 & .75 mile north of Union
- U.S. highway 11
- Along Tadpole Branch across US Hwy 11
- 321.7’ Thick
- Along Tadpole Branch across US Hwy 11
#2 Chattanooga Valley Exposures
- Mill Branch
- Along Mill Branch west of Chattanooga Valley Road
- 358.7’ Thick
- Along Mill Branch west of Chattanooga Valley Road
- Cooper Heights Quarry
- One and one-half miles north of Cooper Heights and 1000 feet
- west of Georgia Highway 193.
- 332.5’ Thick
- One and one-half miles north of Cooper Heights and 1000 feet
- Cooper Heights No.2
- .25 mile north of Cooper Heights, east-west across Georgia Highway 193
- 652.9’ Thick
- .25 mile north of Cooper Heights, east-west across Georgia Highway 193
#3 Chickamauga Valley
- Bethel Church
- East of Old Bethel Church approximately two miles east McLemore Cove Road.
- 222.1’ thick
- East of Old Bethel Church approximately two miles east McLemore Cove Road.
- Telephone Line
- One and one-half miles southeast of McLemore Cove Road along secondary road
- 57.2’ Thick
- One and one-half miles southeast of McLemore Cove Road along secondary road
- Pigeon Mountain
- East from Chickamauga Creek along Scenic Highway to west flank of Pigeon Mountain
- 1047.6’ Thick
- East from Chickamauga Creek along Scenic Highway to west flank of Pigeon Mountain
- T.A.G. Railroad
- Along Tennessee, Alabama, and Georgia Railroad, one-half mile north of Davis Crossroad
- 739.0’ Thick
- Along Tennessee, Alabama, and Georgia Railroad, one-half mile north of Davis Crossroad
- Voiles Creek
- Along Voiles Creek one-half mile northeast of Hermon Church
- 613.2’ Thick
- Along Voiles Creek one-half mile northeast of Hermon Church
- Hog Jowl Creek
- Along Hog Jowl Creek, one-half mile southwest of McLemore Cove Road
- 310.6’ Thick
- Along Hog Jowl Creek, one-half mile southwest of McLemore Cove Road
#4 Rabbit Valley
- Friendship Church
- East and west of Georgia Highway 151, 4 miles north of Ringgold
- 973.7’ Thick
- East and west of Georgia Highway 151, 4 miles north of Ringgold
- Pleasant Valley
- West from Georgia Highway 151, three miles north of Ringgold
- 372.5’ Thick
- West from Georgia Highway 151, three miles north of Ringgold
- Benchmark
- East-west across Georgia Highway 151 just north of Benchmark 120
- 1236.6’ Thick
- East-west across Georgia Highway 151 just north of Benchmark 120
- Chickamauga Creek
- 1 mile north of Ringgold, eastward from meander in Chickamauga Creek
- 649.3’ Thick
- 1 mile north of Ringgold, eastward from meander in Chickamauga Creek
- Maddox Gap
- Along Lookout Scenic Highway across Taylor Ridge at Maddox Gap
- 1455.9’ Thick
- Along Lookout Scenic Highway across Taylor Ridge at Maddox Gap
- Smith Gap
- Along secondary road one-half mile north of Goodram Cemetery off of old Alabama Road
- 479.9’ Thick
- Along secondary road one-half mile north of Goodram Cemetery off of old Alabama Road
#5 Mill Creek Valley
- New Hope Church,
- 10 miles northeast of Tunnel Hill on Varnell Road, 1000 feet east of New Hope Church.
- 211.5’ thick
- 10 miles northeast of Tunnel Hill on Varnell Road, 1000 feet east of New Hope Church.
- Hamilton Mountain
- East-west road from Georgia Highway 71 five miles north of Dalton
- 1304.0” thick
- East-west road from Georgia Highway 71 five miles north of Dalton
- Rocky Face
- East of village of Rocky Face, north of U. S. Highway 41
- 932.9’ Thick
- East of village of Rocky Face, north of U. S. Highway 41
- Mill Creek
- Along U. S. Highway 41 through Mill Creek Gap
- 1045.8’ Thick
- Along U. S. Highway 41 through Mill Creek Gap
- Dug Gap
- Along Dug Gap Road across Rocky Face Mountain
- 1360.9’ Thick
- Along Dug Gap Road across Rocky Face Mountain
- Master’s Pasture
- 200 yards south of Mill Creek Cemetery and west of Forest Boundary Road
- 153.6’ Thick
- 200 yards south of Mill Creek Cemetery and west of Forest Boundary Road
- Furnace Creek
- Along east-west road 3 miles southeast of Villanow and one-quarter mile north of Furnace Creek
- 813.0’ Thick
- Along east-west road 3 miles southeast of Villanow and one-quarter mile north of Furnace Creek
- Horn Mountain
- East-west road across Horn Mountain from Sugar Valley
- 132.0’ Thick
- East-west road across Horn Mountain from Sugar Valley
- Johns Mountain
- Along Dunaway Gap Road across Johns Mountain
- 288.5’ Thick
- Along Dunaway Gap Road across Johns Mountain
Research Conclusions, 1957
My readers, especially collectors, are strongly encouraged to download the original paper and become familiar with it, There is a great deal of additional information, especially the recorded sections, which will be useful in the field.
Here I have reproduced, in part, their findings, the complete passage is an even more interesting read.
Conclusions
Late in the Ordovician the seas again became shallow and the limestones grade transitionally into the sandstones and siltstones of the lower Silurian.
During the middle Ordovician transgression and regression occurred with first the Near-Shore sediments extending throughout the area and then again restricted to the Mill Creek Belt.
During upper Ordovician the line of separation between the Near-Shore and Offshore Facies lay along the western boundary of the Tunnel Hill Quadrangle and swung to the west of Taylor Ridge south of Maddox Gap.
It is inferred that during the entire Ordovician a trough roughly paralleling the shoreline existed in the area of the easternmost exposures. This trough (Mill Creek Valley) was filled with the clastic sediments and only a small amount of calcium was precipitated. At the same time limestones were being deposited in the outer portion of the trough (Rabbit Valley) and thinning westward over the barrier (Chickamauga and Chattanooga Valley) and thickening again in Lookout Valley. Apparently since the seas were relatively clear as a result of the settling of most of the clastics in the trough, the strata are comprised largely of impure limestones. Only during relatively short durations of time were conditions such as to allow the silts and muds to spill over outside the trough area.
Although a few scattered fossil horizons are present in the Near-Shore Facies, the organic life was greatly more abundant outside the area of heavy clastic deposition.
In some horizons of the Offshore Facies, the fossils are completely preserved indicating conditions of quiescence; in others the fossils are present only as fragments and indicate rigorous current action. Fossils are almost completely absent from the red and limy siltstones and silty limestones.
My readers, especially collectors, are strongly encouraged to download the original paper and become familiar with it, There is a great deal of additional information, especially the recorded sections, which will be useful in the field.
Here I have reproduced, in part, their findings, the complete passage is an even more interesting read.
Conclusions
Late in the Ordovician the seas again became shallow and the limestones grade transitionally into the sandstones and siltstones of the lower Silurian.
During the middle Ordovician transgression and regression occurred with first the Near-Shore sediments extending throughout the area and then again restricted to the Mill Creek Belt.
During upper Ordovician the line of separation between the Near-Shore and Offshore Facies lay along the western boundary of the Tunnel Hill Quadrangle and swung to the west of Taylor Ridge south of Maddox Gap.
It is inferred that during the entire Ordovician a trough roughly paralleling the shoreline existed in the area of the easternmost exposures. This trough (Mill Creek Valley) was filled with the clastic sediments and only a small amount of calcium was precipitated. At the same time limestones were being deposited in the outer portion of the trough (Rabbit Valley) and thinning westward over the barrier (Chickamauga and Chattanooga Valley) and thickening again in Lookout Valley. Apparently since the seas were relatively clear as a result of the settling of most of the clastics in the trough, the strata are comprised largely of impure limestones. Only during relatively short durations of time were conditions such as to allow the silts and muds to spill over outside the trough area.
Although a few scattered fossil horizons are present in the Near-Shore Facies, the organic life was greatly more abundant outside the area of heavy clastic deposition.
In some horizons of the Offshore Facies, the fossils are completely preserved indicating conditions of quiescence; in others the fossils are present only as fragments and indicate rigorous current action. Fossils are almost completely absent from the red and limy siltstones and silty limestones.
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The 1957 paper is available as a download to the right.
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References
- Allen, Arthur T.; Lester, James G. (Emory University); Zonation of the Middle and Upper Ordovician Strata in Northwestern Georgia; Bulletin 66, Georgia Geologic Survey, 1957
