13H: Fossils of Oaky Woods
Houston County, Georgia
An Amateur Field Research Project
Attention:
For Observation and Photography Only
No Collecting in Oaky Woods
Excavations and/or removing of artifacts
is illegal.
For Observation and Photography Only
No Collecting in Oaky Woods
Excavations and/or removing of artifacts
is illegal.
Collection by photography only please!
Oaky Woods is actively hunted.
Be thoughtful of other users and dress accordingly.
Orange vests are strongly recommended.
Oaky Woods is actively hunted.
Be thoughtful of other users and dress accordingly.
Orange vests are strongly recommended.
Location 1:
Oligocene Undifferentiated Residuum
Oligocene Epoch; 33.9 to 23.03 million years old
Approximate elevation 435 to 475 ft, variable. (Google Earth)
The name Oligocene Undifferentiated Residuum is a mouthful, it simply means that these are mixed Oligocene aged fossils which formed both during the Early & Late Oligocene Epoch.
There were two high stands of sea levels during the Oligocene. Limestone reefs formed in Georgia both times. When sea levels fell again ground water inundated these limestone reefs and in many cases the silica in the groundwater turned the limestone into hard, enduring chert.
The limestone which wasn't turned to chert was slowly dissolved by acids in the groundwater (think how caves are formed) and was weathered away; leaving behind the harden chert which is immune to acid.
All that remains of of those fertile Early & Late Oligocene seas is loose boulders and dornicks scattered across many central Georgia counties.
Early Oligocene fossils occur but Late Oligocene fossils dominate; boulders and dornicks can be packed with fossils; populations were high, but diversity was low due to the extinction event which had just occurred.
There were two high stands of sea levels during the Oligocene. Limestone reefs formed in Georgia both times. When sea levels fell again ground water inundated these limestone reefs and in many cases the silica in the groundwater turned the limestone into hard, enduring chert.
The limestone which wasn't turned to chert was slowly dissolved by acids in the groundwater (think how caves are formed) and was weathered away; leaving behind the harden chert which is immune to acid.
All that remains of of those fertile Early & Late Oligocene seas is loose boulders and dornicks scattered across many central Georgia counties.
Early Oligocene fossils occur but Late Oligocene fossils dominate; boulders and dornicks can be packed with fossils; populations were high, but diversity was low due to the extinction event which had just occurred.
Oaky Woods Oligocene Fossils
Throughout most of the Oaky Woods highlands sea shells, of various descriptions, occur abundantly in chert boulders & dornicks (dornicks are hand samples). These boulders and dornicks are abundant and diverse in coloration and content.
Frequently the boulders and dornicks are seen clustered or piled on top of each other. These have been relocated either during road building or by farmers over the last two centuries, clearing their land.
These fossils occur 150 miles inland from the nearest modern coastline. It is not uncommon to see a single boulder containing many thousands of shell fossils. Small, fingernail sized cavities created by the shells are often geodes, containing small calcite or quartz crystals.
This is the sedimentary rock chert, often as jasper and agate; typically in hues of red but other colors are present. It was the preferred tool making material of Native Americans which once lived and hunted in this area. It is also popular material for modern lapidary work. This is fully silicified limestone, no reaction to weak acid.
Both early and late Oligocene material is present, representing two distinct high stands of sea levels.
To the author’s knowledge these fossils have never been studied in detail to determine contemporary marine conditions. The general distribution and occurrence of this material was researched and reported in 1993 by Paul F. Huddlestun; who also confirmed its age by its fossil content.
For more information on fossils of this type see; Public Fossil Locations, South Houston County, of this website.
Throughout most of the Oaky Woods highlands sea shells, of various descriptions, occur abundantly in chert boulders & dornicks (dornicks are hand samples). These boulders and dornicks are abundant and diverse in coloration and content.
Frequently the boulders and dornicks are seen clustered or piled on top of each other. These have been relocated either during road building or by farmers over the last two centuries, clearing their land.
These fossils occur 150 miles inland from the nearest modern coastline. It is not uncommon to see a single boulder containing many thousands of shell fossils. Small, fingernail sized cavities created by the shells are often geodes, containing small calcite or quartz crystals.
This is the sedimentary rock chert, often as jasper and agate; typically in hues of red but other colors are present. It was the preferred tool making material of Native Americans which once lived and hunted in this area. It is also popular material for modern lapidary work. This is fully silicified limestone, no reaction to weak acid.
Both early and late Oligocene material is present, representing two distinct high stands of sea levels.
To the author’s knowledge these fossils have never been studied in detail to determine contemporary marine conditions. The general distribution and occurrence of this material was researched and reported in 1993 by Paul F. Huddlestun; who also confirmed its age by its fossil content.
For more information on fossils of this type see; Public Fossil Locations, South Houston County, of this website.
Oligocene/Eocene Transition
An Explanation
33.9 million years ago
Globally, there was a serious extinction event at about 33.9 million years ago separating the Oligocene Epoch and the Eocene Epoch.
This was a major glacial event and retreat in coastlines lasting 2 million years which ended the hot-house Eocene Epoch and introduced the cooler Oligocene Epoch.
In Georgia sea levels fell to, or near, the continental shelf, far below modern levels. So there is a gap, a discontinuity, in the Oaky Woods fossil record.
The Oligocene begins with a warming of the Earth and a return of high sea levels. Though the Oligocene would never be as warm as the Eocene, at least twice in the 10 million year span of the Oligocene Epoch sea levels rose far enough to submerge Oaky Woods.
Upper Eocene Sediments
Ocmulgee Formation
&
Tobacco Road Sand
Interfingering.
Uppermost Eocene Epoch;
33.75 to 33.90 million years old
Foram Zone P17
Central Georgia's Upper Eocene sediments are complex.
In 1986 Paul F. Huddlestun & John H. Hetrick published Bulletin 95 of the Georgia Geologic Survey (3);
Upper Eocene Stratigraphy of Central & Eastern Georgia.
This work has not been officially revised since that time.
There are errors in it, but it is still widely used by researchers.
At left is the chart developed for this paper showing, at the top, how the Ocmulgee Formation and Tobacco Roads Sand Formation are of the same age and interfinger.
Ocmulgee Formation
&
Tobacco Road Sand
Interfingering.
Uppermost Eocene Epoch;
33.75 to 33.90 million years old
Foram Zone P17
Central Georgia's Upper Eocene sediments are complex.
In 1986 Paul F. Huddlestun & John H. Hetrick published Bulletin 95 of the Georgia Geologic Survey (3);
Upper Eocene Stratigraphy of Central & Eastern Georgia.
This work has not been officially revised since that time.
There are errors in it, but it is still widely used by researchers.
At left is the chart developed for this paper showing, at the top, how the Ocmulgee Formation and Tobacco Roads Sand Formation are of the same age and interfinger.
Location 2:
Tobacco Road Sand Ravine
Tobacco Road Sand
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Foram Zone P17
Approximate elevation 385-395 ft above sea level
(Google Earth records it as 415 ft)
Tobacco Road Sand Ravine
Tobacco Road Sand
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Foram Zone P17
Approximate elevation 385-395 ft above sea level
(Google Earth records it as 415 ft)
The Tobacco Road Sand is a member of the Barnwell Group; sediments which are terrestrial in origin, dominated by sands, but clays are also common.
In Oaky Woods locations, the Tobacco Road Sand overlies the Ocmulgee Formation but this isn't true everywhere. As Paul F. Huddlestun reported the two formations are the same age and interfinger (1); which occurs as uppermost changes geographically. The Tobacco Road Sand is terrestrial and tends to be landward, the Ocmulgee Formation is marine, seaward.
The Tobacco Road Sand outcrops in only one currently confirmed Oaky Woods location; an erosion feature; a “Y” shaped ravine just beyond the southern border of the Wildlife Management Area and just off the road. (See crude map below.)
Overall the Tobacco Road Sand is sparsely fossiliferous; however, in this ravine three well-defined beds of fossils occur, one atop the other.
Huddlestun & Hetrick (1) reported that each of the three beds contained distinct, extinct, species of the genus Periarchus of sand dollars (echinoids).
Gastropods also occur commonly as shells, not molds.
The brick red, fossil bearing rock in these beds is silicified, stratified sandstone, no reaction to weak acid, it's chert.
Being chert it has no reaction to acid.
The fossil beds are separated by non-fossil-bearing compacted, fine grained sand where individual grains are coated with cohesive very fine gained red clay.
The deep brick red coloration of the Tobacco Road Sand is not continuous, if you break open the rock; the coloration of the interior is much lighter.
Silicification and oxidized iron staining occurred post-deposition through exposure to groundwater.
This outcrop is actively eroding due to drainage run-off from access road.
In 1978 Huddlestun & Hetrick (7) reported that Periarchus quinquefarius occurred in the uppermost bed and Periarchus pileussinensis occurred in the lowermost bed. a potential new intermediate species of Periarchus sand dollar occupied the center bed.
There are no known follow-up reports on this and the only known occurrence of the possible intermediate species is in Oaky Woods.
On 22/Nov/2015 Paul F. Huddletsun, Dr. Don M. Thieme (Valdosta State University) and myself investigated the outcrop but could not locate a specimen sufficiently complete to confirm or deny such a transition species. The outcrop had significantly weathered since Huddlestun's last visit in 1978.
Subsequent investigations by the author (Thurman) have failed to produced a complete enough specimen suggesting an intermediate species between Periarchus quinquefarius and Periarchus pileussinensis.
On 22/Nov/2015 Paul F. Huddletsun, Dr. Don M. Thieme (Valdosta State University) and myself investigated the outcrop but could not locate a specimen sufficiently complete to confirm or deny such a transition species. The outcrop had significantly weathered since Huddlestun's last visit in 1978.
Subsequent investigations by the author (Thurman) have failed to produced a complete enough specimen suggesting an intermediate species between Periarchus quinquefarius and Periarchus pileussinensis.
Lastly, in the 1978 & 1993 (1 & 4) Huddlestun & Hetrick reported Shellstone Creek Bed Formation (Oligocene) overlay the Tobacco Road Sand in direct contact in Oaky Woods at this location.
After a Nov. 2015 field trip Paul F. Huddlestun confirms that this is an error and the Shellstone Creek Bed Formation is absent at this location. (Dr. Burt Carter, Hank Josey & myself were also present.)
In 1978 Huddlestun & Hetrick (1) also reported the Twiggs Clay as underlying the Tobacco Road Sand at this location in Oaky Woods. By texture, coloration, purity and lack of reaction to acid the Twiggs Clay is confirmed in the ravine bed.
This outcrop of the Twiggs Clay represents an interesting as the elevation is approximately 385 feet above sea level at the ravine floor and less than a mile away the Ocmulgee Formation, which also overlies the Twiggs Clay, occurs at both 330 and 365 feet above sea level (Location 3 & 4 of this report).
The Tobacco Road Sand found in the ravine is overlain by the Oligocene Undifferentiated Residuum and underlain by the Tiwggs Clay.
After a Nov. 2015 field trip Paul F. Huddlestun confirms that this is an error and the Shellstone Creek Bed Formation is absent at this location. (Dr. Burt Carter, Hank Josey & myself were also present.)
In 1978 Huddlestun & Hetrick (1) also reported the Twiggs Clay as underlying the Tobacco Road Sand at this location in Oaky Woods. By texture, coloration, purity and lack of reaction to acid the Twiggs Clay is confirmed in the ravine bed.
This outcrop of the Twiggs Clay represents an interesting as the elevation is approximately 385 feet above sea level at the ravine floor and less than a mile away the Ocmulgee Formation, which also overlies the Twiggs Clay, occurs at both 330 and 365 feet above sea level (Location 3 & 4 of this report).
The Tobacco Road Sand found in the ravine is overlain by the Oligocene Undifferentiated Residuum and underlain by the Tiwggs Clay.
On 14/Oct/2016 Dr. Burt Carter, Paul F. Huddletun, Hank Josey and myself (Thurman) revisited this location.
Burt Carter (Georgia Southwestern) is an expert on Southeastern echinoid fossils and their evolution.
He found ample fragmentary Periarchus pileussinensis in the uppermost bed of the western branch of the Tobacco Road Sand ravine.
This finding further supports that while the genus Pericarchus occurs in numbers in all three beds of the Tobacco Road Sand ravine exposure, and both P quinquefarius & P pileussinensis are present, they are not limited to upper & lower beds but distributed throughout the three beds.
Carter & Huddlestun concur that the 1978 observations of an intermediate species likely represents individual & perhaps localized variations in existing Periarchus species.
Burt Carter (Georgia Southwestern) is an expert on Southeastern echinoid fossils and their evolution.
He found ample fragmentary Periarchus pileussinensis in the uppermost bed of the western branch of the Tobacco Road Sand ravine.
This finding further supports that while the genus Pericarchus occurs in numbers in all three beds of the Tobacco Road Sand ravine exposure, and both P quinquefarius & P pileussinensis are present, they are not limited to upper & lower beds but distributed throughout the three beds.
Carter & Huddlestun concur that the 1978 observations of an intermediate species likely represents individual & perhaps localized variations in existing Periarchus species.
Ocmulgee Formation
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Foram Zone P17
Formerly known as the Cooper Marl
Of the central Georgia sediments the Ocmulgee Formation is the most variable in character.
The type locality is Taylor's bluff only accessible by boat just north of Hawkinsville along the Ocmulgee River.
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Foram Zone P17
Formerly known as the Cooper Marl
Of the central Georgia sediments the Ocmulgee Formation is the most variable in character.
The type locality is Taylor's bluff only accessible by boat just north of Hawkinsville along the Ocmulgee River.
Location 3:
Ocmulgee Formation
Low Cliffs on the Oaky Woods Flood Plain
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Foram Zone P17
Approximate elevation 330ft (Google Earth)
The Ocmulgee Formation is a highly variable Ocala Group limestone & clay deposit formed in a near-shore environment. Being limestone it always reacts vigorously to acid, even the clays react strongly to acid.
At this location the Ocmulgee Formation is exposed as a series of low limestone cliffs, no more than 20 feet high, which are highly fossiliferous and form “toes” at the base of a forested ridge rising 80 to 100 feet above the floodplain of Oaky Woods.
These cliffs match Bed #4 in Huddlestun & Hetrick's 1986 description of the type locality at Taylor's Bluff. On 13/Nov/2016 Hank Josey & I hiked the base of the ridge and counted at least 6 individual cliffs separated by weathered slump.
The limestone cliffs stand on the floodplain, the floor, of Oaky Woods at the NE base of the ridge. It is the same ridge where the Tobacco Road Sand occurs in a SW ravine, so the two formations inter-finger within the ridge.
The cliffs are underlain by the Twiggs Clay.
Big Grocery Creek flows across the basin plain of Oaky Woods at this location, about 100 to 200 meters NE from the cliffs. The bed of the creek reveals spotty occurrences of the Twiggs Clay frequently covered by weathered, transported sediments; predominantly sand.
According to Huddlestun & Hetrick (3) this Twiggs Clay is number 3 on the chart above and is calcareous clay, meaning it should contain calcium carbonate and react to acid. Samples tested had no reaction to acid. Lack of reaction to acid is typical of the Twiggs Clay in other occurances.
The cliffs reveal scallops, a great wealth of bryozoan debris, forams, Periarchus pileussinensis & Periarchus quinquefarius; typically in living positions. Gastropods are present as molds, with shells dissolved.
Huddlestun & Hetrick described variability in the fossil content of Bed #4 and that was observed in the cliffs. Some levels of the cliffs are sand rich and bryozoan poor, while others are almost entirely made up of bryozoan debris.
Between the low cliffs there are often shallow, rain-weathered slump with seams in the hillside where loose fossils can be seen in decomposing limestine. Often whole, pristine, Periarchus sand dollars (echinoids) can be found; sizes vary from large to small individuals. These will typically have superb preservation.
The genus Periarchus is a Late Eocene (Jacksonian & Bartonian) guide fossil where it proliferated in Southeastern sediments. It emerged in older Claibornian sediments. It did not survive the Eocene/Oligocene extinction event.
Basilosaurid in Oaky Woods
(See Section 11 of this website for description of basilosaurus)
In May 2008 Warner Robins Cub Scout Pack Leader Amanda Rhonemus found an end-of-tail vertebra from a Basilosaurus in Oaky Woods Wildlife Management Area, Houston County, Georgia. (Known age & coloration of the fossil show that the source matrix was the Ocmulgee Formation)
John Trussell, a Middle Georgia hunter and author, was guiding the scouts on a tour when the specimen was discovered. The Macon Telegraph covered the story with pictures by John Trussell on Sunday, May 11, 2008.
It was John Trussell who first showed me the northern most cliff back in 2008. I tentatively ID'd the outcrop as Ocmulgee Formation at that time but it wasn't until 22/Nov/2015 that this was confirmed when I guided Paul Huddlestun & Don Thieme to the same northernmost cliff face (see pics above).
No other vertebrate material has been observed any other among these cliffs though it is undoubtedly present. A shark tooth, see Location 4, was recently found on an Ocmulgee Formation hilltop in Oaky Woods.
At this location the Ocmulgee Formation is exposed as a series of low limestone cliffs, no more than 20 feet high, which are highly fossiliferous and form “toes” at the base of a forested ridge rising 80 to 100 feet above the floodplain of Oaky Woods.
These cliffs match Bed #4 in Huddlestun & Hetrick's 1986 description of the type locality at Taylor's Bluff. On 13/Nov/2016 Hank Josey & I hiked the base of the ridge and counted at least 6 individual cliffs separated by weathered slump.
The limestone cliffs stand on the floodplain, the floor, of Oaky Woods at the NE base of the ridge. It is the same ridge where the Tobacco Road Sand occurs in a SW ravine, so the two formations inter-finger within the ridge.
The cliffs are underlain by the Twiggs Clay.
Big Grocery Creek flows across the basin plain of Oaky Woods at this location, about 100 to 200 meters NE from the cliffs. The bed of the creek reveals spotty occurrences of the Twiggs Clay frequently covered by weathered, transported sediments; predominantly sand.
According to Huddlestun & Hetrick (3) this Twiggs Clay is number 3 on the chart above and is calcareous clay, meaning it should contain calcium carbonate and react to acid. Samples tested had no reaction to acid. Lack of reaction to acid is typical of the Twiggs Clay in other occurances.
The cliffs reveal scallops, a great wealth of bryozoan debris, forams, Periarchus pileussinensis & Periarchus quinquefarius; typically in living positions. Gastropods are present as molds, with shells dissolved.
Huddlestun & Hetrick described variability in the fossil content of Bed #4 and that was observed in the cliffs. Some levels of the cliffs are sand rich and bryozoan poor, while others are almost entirely made up of bryozoan debris.
Between the low cliffs there are often shallow, rain-weathered slump with seams in the hillside where loose fossils can be seen in decomposing limestine. Often whole, pristine, Periarchus sand dollars (echinoids) can be found; sizes vary from large to small individuals. These will typically have superb preservation.
The genus Periarchus is a Late Eocene (Jacksonian & Bartonian) guide fossil where it proliferated in Southeastern sediments. It emerged in older Claibornian sediments. It did not survive the Eocene/Oligocene extinction event.
Basilosaurid in Oaky Woods
(See Section 11 of this website for description of basilosaurus)
In May 2008 Warner Robins Cub Scout Pack Leader Amanda Rhonemus found an end-of-tail vertebra from a Basilosaurus in Oaky Woods Wildlife Management Area, Houston County, Georgia. (Known age & coloration of the fossil show that the source matrix was the Ocmulgee Formation)
John Trussell, a Middle Georgia hunter and author, was guiding the scouts on a tour when the specimen was discovered. The Macon Telegraph covered the story with pictures by John Trussell on Sunday, May 11, 2008.
It was John Trussell who first showed me the northern most cliff back in 2008. I tentatively ID'd the outcrop as Ocmulgee Formation at that time but it wasn't until 22/Nov/2015 that this was confirmed when I guided Paul Huddlestun & Don Thieme to the same northernmost cliff face (see pics above).
No other vertebrate material has been observed any other among these cliffs though it is undoubtedly present. A shark tooth, see Location 4, was recently found on an Ocmulgee Formation hilltop in Oaky Woods.
Location 4:
Ocmulgee Formation
Hilltop Bryozoan Colonies & loose fossils
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Approximate elevation 365ft (Google Earth)
Ocmulgee Formation
Hilltop Bryozoan Colonies & loose fossils
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Approximate elevation 365ft (Google Earth)
Bryozoan colonies occur in the loose soil about .25 miles SE along Bait Barrell Road, on the north side of Oaky Woods. These are bryozoan colonies, as golf-ball sized and smaller specimens.
The first known shark's tooth was also observed at this location a single, small, Carcharias cuspidata or sand tiger. This species is well documented in the Ocmulgee Formation literature.
The location for the bryozoan colonies & shark tooth is a weathered, recently logged, crest of a gentle hill.
The bryozoa colonies occur as loose specimens in the loose dove-grey, sandy clay. Specimens were observed in the road bed.
The first known shark's tooth was also observed at this location a single, small, Carcharias cuspidata or sand tiger. This species is well documented in the Ocmulgee Formation literature.
The location for the bryozoan colonies & shark tooth is a weathered, recently logged, crest of a gentle hill.
The bryozoa colonies occur as loose specimens in the loose dove-grey, sandy clay. Specimens were observed in the road bed.
Some specimens show extensive, even complete clogging and fill of structures and apertures from post-mortem (?) sedimentation. Some have apertures recrystallized with calcite. Others are nearly free of secondary sedimentation and the structures and apertures are free, or nearly free, of recrystallization and sediments.
Specimens actively react to acid.
All show a small degree of probably post-mortem transportation with rounded edges, but none show extensive wear. Due to the very fragile nature of the branching structure it seems unlikely that this material was transported very far or violently. Likely the specimens only show "in place" movement wear due to tidal action.
Specimens actively react to acid.
All show a small degree of probably post-mortem transportation with rounded edges, but none show extensive wear. Due to the very fragile nature of the branching structure it seems unlikely that this material was transported very far or violently. Likely the specimens only show "in place" movement wear due to tidal action.
Some colonies are entombed in their source matrix limestone dornicks loose in the soil.
One excellent specimen, nearly golf-ball in size, was almost pristine. It had originally formed on a gastropod shell, but that shell has long ago dissolved away.
These bryozoan colonies were recently identified to the level of genus with the assistance of George Phillips, Curator of Paleontology, Mississippi Museum of Natural Science and Dr. Paul Taylor, Department of Paleontology at The Natural History Museum in London, England.
One excellent specimen, nearly golf-ball in size, was almost pristine. It had originally formed on a gastropod shell, but that shell has long ago dissolved away.
These bryozoan colonies were recently identified to the level of genus with the assistance of George Phillips, Curator of Paleontology, Mississippi Museum of Natural Science and Dr. Paul Taylor, Department of Paleontology at The Natural History Museum in London, England.
Phillips saw good quality images of our best sample on Facebook's Georgia's Fossils Group during a debate over whether these were bryozoans or rhodoliths. He forwarded the pics to Paul Taylor, the leading bryozoan expert.
Taylor commented; "Yes, those... images are definitely cyclostome bryozoans, provisionally identifiable as (genus) Idmidronea. Such cyclostomes do occasionally grow as ball shaped colonies accentuated by rolling..."
The species can only be identified by scanning electron microscope. Samples will soon be provided to Mississippi Museum of Natural History (George Phillips), the Florida Museum of Natural History (Roger Portell) and Valdosta State University (Don Thieme) for specimen storage and proper identification.
My best specimen will go to Roger Portell at Florida Natural History Museum to be kept for research purposes.
This outcrop could represent levels 7, 6, or 5 in the 1986 Huddlestun & Hetrick Type Section of the type locaality at Taylor's Bluff (as see above).
Taylor commented; "Yes, those... images are definitely cyclostome bryozoans, provisionally identifiable as (genus) Idmidronea. Such cyclostomes do occasionally grow as ball shaped colonies accentuated by rolling..."
The species can only be identified by scanning electron microscope. Samples will soon be provided to Mississippi Museum of Natural History (George Phillips), the Florida Museum of Natural History (Roger Portell) and Valdosta State University (Don Thieme) for specimen storage and proper identification.
My best specimen will go to Roger Portell at Florida Natural History Museum to be kept for research purposes.
This outcrop could represent levels 7, 6, or 5 in the 1986 Huddlestun & Hetrick Type Section of the type locaality at Taylor's Bluff (as see above).
Location 5:
An erosional rain fed stream & ravine.
The Tobacco Road Sand
seen as overlying
the Ocmulgee Formation
Uppermost Eocene
First report of exposure.
Approximate elevation;
From 410ft to 310ft over about .50 mile (Google Earth)
An erosional rain fed stream & ravine.
The Tobacco Road Sand
seen as overlying
the Ocmulgee Formation
Uppermost Eocene
First report of exposure.
Approximate elevation;
From 410ft to 310ft over about .50 mile (Google Earth)
Well above the Oaky Woods floodplain there is a shallow, narrow, rainwater fed stream between two weathered hills along a weathered ridge.
It descends the hillsides like a long, gentle, natural staircase seeking the floodplain. There’s a series of low falls, the highest being maybe 10 feet with several others being a foot high or less. The stream bed is fascinating, and often dense with Eocene fossils.
After a rain the stream gurgles and burbles happily. But tread carefully… much of the stream runs over dense clay and the bed is magnificently slick.
The highest point on this ridge is a hill standing 515ft above sea level which is highish for Oaky Woods.
The stream has cut into the Ocmulgee Formation which is typically resistant to weathering and highly variable in character.
This same ridge also hosts the Tobacco Road Sand exposure described in Location 2 of this report and Section 13E of this website.
On a map, the ravine is about half a mile east-northeast of Ocmulgee Formation stream bed described here.
Why this is interesting;
In the narrow stream bed debris from Ocmulgee Formation limestone is intermingled with Tobacco Road Sand chert.
Over a distance of approximately .25 to .75 mile the stream descends from approximately 410ft to 310ft.
To date I haven’t explored the full length of this ravine.
It descends the hillsides like a long, gentle, natural staircase seeking the floodplain. There’s a series of low falls, the highest being maybe 10 feet with several others being a foot high or less. The stream bed is fascinating, and often dense with Eocene fossils.
After a rain the stream gurgles and burbles happily. But tread carefully… much of the stream runs over dense clay and the bed is magnificently slick.
The highest point on this ridge is a hill standing 515ft above sea level which is highish for Oaky Woods.
The stream has cut into the Ocmulgee Formation which is typically resistant to weathering and highly variable in character.
This same ridge also hosts the Tobacco Road Sand exposure described in Location 2 of this report and Section 13E of this website.
On a map, the ravine is about half a mile east-northeast of Ocmulgee Formation stream bed described here.
Why this is interesting;
- The Tobacco Road Sand is primarily a terrestrial sourced formation, sands and clays.
- Ocmulgee Formation is primarily marine sourced limestone and clay.
- The Tobacco Road Sand is deeply stained red from iron oxidation.
- The Ocmulgee Formation is only mildly and discontinuously stained with iron oxidation
- The Tobacco Road Sand is cherty, silicified limestone weak acid has no effect on it. (As explained in the Location 2 text of this report.)
- The Ocmulgee Formation Limestone reacts actively to weak acid, it has never been silicified.
In the narrow stream bed debris from Ocmulgee Formation limestone is intermingled with Tobacco Road Sand chert.
Over a distance of approximately .25 to .75 mile the stream descends from approximately 410ft to 310ft.
To date I haven’t explored the full length of this ravine.
Uppermost observed large fall (Location 5):
The largest fall yet explored is on the upgrade end of the stream, maybe 10 feet high and supported by a bed dense, seemingly pure tan colored clay. The fall has created a semi-circular hollow on the forest floor, 20 to 25 feet wide, whose walls are pure clay.
Both topping and flooring the fall are flat ledges of hardened limestone. The fall itself is actually a retreat between two ledges. The beds of clay forming the retreat wall are thicker at the base, maybe a foot thick for the lowest three beds, but much thinner at the top, many less than an inch thick. Casual observation suggests 30 to 50 beds overall.
Macrofossils (easily visible) weren’t observed in the clay beds, no sample was taken for microscope observation. Close inspection was not performed as the stream bed has dangerous footing. The hike to this site is in relatively rugged terrain, I was alone, no one knew exactly where I was and I had no cell service.
This was not a place to get injured.
It is worthwhile to note that in 1970 Sam Pickering reported that such clay beds in other Houston County locations contained calcite lenses which were often dense with echinoid (sand dollar & sea urchin) fossils.
The upper and lower hardened limestone ledges were inspected for macrofossils as well, they were very sparsely fossiliferous, rare & random clam or scallop molds were observed in the ledges.
Weak acid field tests were performed on top and bottom ledges and the clay itself, all three reacted actively. The ledges are just hard limestone, they aren’t silicified.
The largest fall yet explored is on the upgrade end of the stream, maybe 10 feet high and supported by a bed dense, seemingly pure tan colored clay. The fall has created a semi-circular hollow on the forest floor, 20 to 25 feet wide, whose walls are pure clay.
Both topping and flooring the fall are flat ledges of hardened limestone. The fall itself is actually a retreat between two ledges. The beds of clay forming the retreat wall are thicker at the base, maybe a foot thick for the lowest three beds, but much thinner at the top, many less than an inch thick. Casual observation suggests 30 to 50 beds overall.
Macrofossils (easily visible) weren’t observed in the clay beds, no sample was taken for microscope observation. Close inspection was not performed as the stream bed has dangerous footing. The hike to this site is in relatively rugged terrain, I was alone, no one knew exactly where I was and I had no cell service.
This was not a place to get injured.
It is worthwhile to note that in 1970 Sam Pickering reported that such clay beds in other Houston County locations contained calcite lenses which were often dense with echinoid (sand dollar & sea urchin) fossils.
The upper and lower hardened limestone ledges were inspected for macrofossils as well, they were very sparsely fossiliferous, rare & random clam or scallop molds were observed in the ledges.
Weak acid field tests were performed on top and bottom ledges and the clay itself, all three reacted actively. The ledges are just hard limestone, they aren’t silicified.
Fossil littered stream bed (Location 5):
Moving downstream from the fall is a gentle incline of perhaps 15 yards where the rainwater wanders over an area maybe 10 yards wide. This area was littered with cobbles, dornicks and small boulders, abundant leaf litter and natural forest debris. Small macro fossils were everywhere.
A complete, adult Periarchus quinquefarius (imaged) was observed on the stream bed floor. It was undamaged and preservation was superb. Coloration shows that it was iron-oxide stained and no reaction to an acid test confirms that it’s silicified, this sand dollar weathered out of the Tobacco Road Sand and was transported to this location.
In the debris nearby were fossil rich cobbles of Ocmulgee Formation limestone which did react actively to acid. This stream bed contains a mixture of Ocmulgee Formation and Tobacco Road Sand fossils.
Moving downstream from the fall is a gentle incline of perhaps 15 yards where the rainwater wanders over an area maybe 10 yards wide. This area was littered with cobbles, dornicks and small boulders, abundant leaf litter and natural forest debris. Small macro fossils were everywhere.
A complete, adult Periarchus quinquefarius (imaged) was observed on the stream bed floor. It was undamaged and preservation was superb. Coloration shows that it was iron-oxide stained and no reaction to an acid test confirms that it’s silicified, this sand dollar weathered out of the Tobacco Road Sand and was transported to this location.
In the debris nearby were fossil rich cobbles of Ocmulgee Formation limestone which did react actively to acid. This stream bed contains a mixture of Ocmulgee Formation and Tobacco Road Sand fossils.
Four foot fall (Location 5):
Another fall is encountered after the stream runs over a very rough, softer portion of the Ocmulgee Limestone just a couple of feet wide and maybe a dozen feet long.
At the time this soft, rough span was visited, the day after a heavy rain, the thread of water was only a few inches wide but fast moving. There was obvious wear and smoothing on the rough limestone from water.
The rough limestone is underlain by another dense clay bed, creating a fall and another hollow about four feet high but much wider, maybe 20 to 30 feet. But there are actually two falls at this location, the four foot fall seems to be excess run-off. There is a lower, steady, but apparently restricted flow to one side maybe a 6” high which seems to be water cutting down through the rock.
At the time of visit the lower flow was active at maybe a few gallons a minute but the higher fall was minimally active, just a trickle of water.
This hollow is problematical; none of the sediments exposed show the typical Tobacco Road Sand stratigraphy of alternating clay rich sand beds and fossil bearing chert. Rather, the walls of the hollow are fossiliferous limestone. However, as seen in the pictures, much of it is stained light brownish-red with iron oxide and much of it is the pale beige-grey which is more typical of the Ocmulgee Formation. The presence of both, overlapping, suggests transitional conditions.
The clay rich sand of the Tobacco Road as seen at Location 2 of this report would be highly vulnerable to active water flow, quickly weathering out the fossil bearing chert. Which explains isolated Tobacco Road Sand chert nodules found in the stream bed.
One beige-grey Ocmulgee Formation boulder, maybe a couple of feet long and ten inches wide and imaged here with my Estwing Burpee pick, was extremely dense with mollusk fossils, mostly as bivalves (clam shells) but gastropods (snails) were also present. The boulder was limestone, reacting to weak acid.
Such densely fossiliferous chert boulders are common in the younger Oligocene chert (impervious to weak acid) material of the forested hilltops of Oaky Woods, as described in Location 1 of this report. To find such a boulder in late Eocene limestone (reacting to acid) is very unusual, the limestone is much softer than the chert and heavily fossiliferous boulders are easily broken up during natural transportation by water or simple erosion.
As seen in the pics, this boulder rests directly below lightly iron oxide stained Ocmulgee Formation limestone walls of the hollow.
Abundant mollusk fossils occur in the walls and as debris on the hollow’s floor.
Another fall is encountered after the stream runs over a very rough, softer portion of the Ocmulgee Limestone just a couple of feet wide and maybe a dozen feet long.
At the time this soft, rough span was visited, the day after a heavy rain, the thread of water was only a few inches wide but fast moving. There was obvious wear and smoothing on the rough limestone from water.
The rough limestone is underlain by another dense clay bed, creating a fall and another hollow about four feet high but much wider, maybe 20 to 30 feet. But there are actually two falls at this location, the four foot fall seems to be excess run-off. There is a lower, steady, but apparently restricted flow to one side maybe a 6” high which seems to be water cutting down through the rock.
At the time of visit the lower flow was active at maybe a few gallons a minute but the higher fall was minimally active, just a trickle of water.
This hollow is problematical; none of the sediments exposed show the typical Tobacco Road Sand stratigraphy of alternating clay rich sand beds and fossil bearing chert. Rather, the walls of the hollow are fossiliferous limestone. However, as seen in the pictures, much of it is stained light brownish-red with iron oxide and much of it is the pale beige-grey which is more typical of the Ocmulgee Formation. The presence of both, overlapping, suggests transitional conditions.
The clay rich sand of the Tobacco Road as seen at Location 2 of this report would be highly vulnerable to active water flow, quickly weathering out the fossil bearing chert. Which explains isolated Tobacco Road Sand chert nodules found in the stream bed.
One beige-grey Ocmulgee Formation boulder, maybe a couple of feet long and ten inches wide and imaged here with my Estwing Burpee pick, was extremely dense with mollusk fossils, mostly as bivalves (clam shells) but gastropods (snails) were also present. The boulder was limestone, reacting to weak acid.
Such densely fossiliferous chert boulders are common in the younger Oligocene chert (impervious to weak acid) material of the forested hilltops of Oaky Woods, as described in Location 1 of this report. To find such a boulder in late Eocene limestone (reacting to acid) is very unusual, the limestone is much softer than the chert and heavily fossiliferous boulders are easily broken up during natural transportation by water or simple erosion.
As seen in the pics, this boulder rests directly below lightly iron oxide stained Ocmulgee Formation limestone walls of the hollow.
Abundant mollusk fossils occur in the walls and as debris on the hollow’s floor.
Limestone Steps & Smallest Observed Fall (Location 5):
Moving further downstream a series of low falls or steps are encountered (See images). Overall these are maybe twenty feet long with each step “falling” a couple of inches. The steps are individual hardened limestone ledges.
The lovely little flight of steps terminates downstream with a small hollow and perhaps two foot high fall. The hollow is maybe a couple of feet wide and four feet long. The fall is formed, once again, by bedded, dense clay. There is a tree growing diagonally across the fall.
Continuing downstream, the flow is across clay and the streambed is littered with eroded limestone and hard clay dornicks as well as assorted cobbles containing fossils.
The stream has yet to be explored further downstream; but as described in Location 3 of this report, the Ocmulgee Formation has been confirmed on the Oaky Woods floodplain at the foot of this same ridge. (See section 13E of this website for details.) It is expected that the Ocmulgee Formation continues to host the rainwater runoff of the stream until it reaches the base of the ridge.
Location 6:
Suspected Tobacco Road Sand surface outcrop
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Approximate elevation 435ft (Google Earth)
Suspected Tobacco Road Sand surface outcrop
Uppermost Eocene Epoch; 33.75 to 33.90 million years old
Approximate elevation 435ft (Google Earth)
Just as this access road crests a ridge, along the eastern road bank, a small outcrop of what appears to be Tobacco Road Sand occurs. A complete gastropod shell was observed loose on the surface, as well as matrix, at the edge of the tree line.
While not pristine, the shell was whole and detail was preserved. The specimen was silicified and did not react to acid.
Coloration and texture most resembles the Tobacco Road Sand as seen in Location 2.
While not pristine, the shell was whole and detail was preserved. The specimen was silicified and did not react to acid.
Coloration and texture most resembles the Tobacco Road Sand as seen in Location 2.
Location 7: Big Grocery Creek bed find
Pleistocene (Ice age)
Approximate elevation 303ft (Google Earth)
While hiking Big Grocery Creek some years ago a metatarsal (toe bone) from a deer (genus; Odocoileus) was found in the stream bed just a few dozen or yards, or so, down- stream from where the access road dead ends at the creek.
No source matrix is known, but it is very likely that other Pleistocene fossils occur in the lowlands of Oaky Woods.
Pleistocene (Ice age)
Approximate elevation 303ft (Google Earth)
While hiking Big Grocery Creek some years ago a metatarsal (toe bone) from a deer (genus; Odocoileus) was found in the stream bed just a few dozen or yards, or so, down- stream from where the access road dead ends at the creek.
No source matrix is known, but it is very likely that other Pleistocene fossils occur in the lowlands of Oaky Woods.
References:
- Stratigraphy of the Tobacco Road Sand – A New Formation; Paul F. Huddlestun, John H. Hetrick, Short Contributions to the Geology of Georgia, Bulletin 93, Georgia Geologic Survey, 1978
- Stratigraphy, Paleontology and Economic Geology of Portions of Perry and Cochran Quadrangles, Georgia. Sam M. Pickering Jr. Bulletin 81. Georgia Geological Survey. 1970
- Upper Eocene Stratigraphy of Central and Eastern Georgia. Paul F. Huddlestun and John H. Hetrick. Bulletin 95. Georgia Geologic Survey. 1986
- The Oligocene, A Revision of the Lithostratigraphic Units of the Coastal Plain of Georgia; Paul F. Huddlestun, Bulletin 105, Georgia geologic Survey, 1993