Geological History of Oaky Woods

Taken from "Geologic History of Georgia", edited for Save Oaky Woods by Ocmulgee Archaeological Society members Stephen Hammack and John Trussell

Cretaceous Period and Paleogene Period

Oaky Woods Wildlife Management area is covered with ancient paleontology fossils like sand dollars and whale bones. Where did they come from?  For background,During the Cretaceous period (145 to 65.5 million years ago), the climate was much warmer than it is today, and tropical conditions existed in Georgia. No glaciers existed at the poles, and as a result, sea level was much higher than it is at present. The Atlantic Ocean covered southeastern Georgia inland as far as present-day Macon, Columbus, and Augusta, and left marine sediments containing mollusk shells, sharks' teeth, bits of turtle shell, and the occasional dinosaur bone. Dinosaurs roamed Georgia during the Cretaceous and sometimes floated out to sea after they died. The remains of such dinosaurs as the duck-billed hadrosaurs and the ferocious carnivore Albertosaurus, a close relative of Tyrannosaurus rex, are found in Late Cretaceous rocks (65 to 100 million years old) These fossils have been found near Columbus and Rome , Georgia , but not here. The Cretaceous ended with the extinction of the dinosaurs, possibly as a result of an asteroid impact or a combination of natural causes.

Stephen Hammack, Archaeologist, holds two sand dollars from an exposed limestone ridge along Big Grocery Creek in Oaky Woods WMA in Houston County. The sand dollars are between 65 to 145 million years old. If Oaky Woods is developed this ancient treasure will be buried once again, this time by a large man-made lake. (photo by John Trussell)

From the Late Cretaceous period to the Middle Eocene epoch of the Paleogene period (about 40 to 100 million years ago), large quantities of kaolinite, a white alumino-silicate clay resembling chalk, were deposited in middle Georgia. (Kaolin is mined for use in the manufacture of glossy paper, plastic, rubber, paints, ceramics, and other products. Georgia is the world's leading producer of kaolin.) This clay derives from the weathering of feldspar, a mineral found in Piedmont rocks. The clay was transported by streams and deposited in deltas, estuaries, and coastal marshes.

Marine deposits associated with kaolin, including abundant limestone, indicate that the Coastal Plain was flooded by a warm, shallow sea. This sea was inhabited by mollusks, sand dollars, foraminifera, bryozoans, and an early whale with hind legs (38 to 41 million years ago), an evolutionary remnant from an ancestor that walked on land. This is the period from which our Oaky Woods sand dollars come into being.

A dramatic event occurred about 35 million years ago during the Eocene era, when an asteroid or comet struck the Chesapeake Bay region of Virginia. The impact shattered and melted the rocks at the point of impact, forming a crater 90 kilometers in diameter and ejecting droplets of molten rock, which flew through the air for hundreds of kilometers. The molten rock cooled to form coin-sized, translucent, green glassy stones known as tektites, some of which landed in the sea covering east-central Georgia.

The climate cooled dramatically near the end of the Eocene, and during the remainder of the Cenozoic era, glaciers began to grow and the worldwide sea level dropped. The seas receded from Georgia, and sediments derived from the erosion of the Appalachian Mountains and the Piedmont built eastward. Sediments were deposited at a thickness of more than 5,000 meters, or 5 kilometers, in the Coastal Plain area and thickened toward the southeast.

Neogene Period

This small waterfall in Oaky Woods and the rocky terrain is very unusaul in Houston County and helps to make Oaky Woods a special place! (photo by John Trussell)

Glaciers periodically covered much of northern North America during the Pleistocene epoch (1.8 million years ago to the present), although Georgia remained ice-free. The seas alternately flooded and retreated from the land along the coast as the glaciers advanced and receded. During peak glacial episodes, sea level was about 100 to 120 meters lower than at present, and the coast was out near the edge of the continental shelf. Between glaciations, sea level stood as much as 50 meters above present levels. Sea-level high stands are marked by beach ridges. Beaches were dominated by white quartz sand, but during times of rising sea level or higher wave energy, concentrations of black sands, rich in such heavy minerals as ilmenite, zircon, rutile, epidote, sillimanite, staurolite, magnetite, tourmaline, and kyanite, formed on the beaches. Some of these heavy mineral sands are present in Pleistocene beach ridges near the Okefenokee Swamp and contain valuable economic deposits of titanium.

During the Pleistocene, Georgia was inhabited by mammals not seen today, including mastodons, mammoths, elephants, camels, bison, tapirs, and giant ground sloths up to 6 meters tall. The climate was arid at times during the Pleistocene. About 20,000 years ago, rivers dried up and strong winds from the west blew the river sand into large dunes. Pleistocene sand-dune fields remain along the east side of several rivers, including the Flint, Ohoopee, and Canoochee. Oaky Woods Geology & Paleontology


 How do we judge the value of Oaky Woods geologically? Is a place worth preserving just because of its rocks? Most people would answer “no”.  However, given the current concerns over climate & environmental change, you have to ask, what is the value of a record which reveals Central Georgia through more than 25 different environments over 50 million years? That record is in Oaky Woods.
 The Shellstone Creek Bed formation is one concern. This formation is 36 million years old and it shows that Oaky Woods was then part of a chain of barrier islands, often lagoonal in nature according to the fossils. Most of Middle Georgia was submerged with just the hilltops as islands. The hills would probably have been higher then.
 Globally, the Shellstone Creek Bed formation has been positively identified in three places, two of which are in Oaky Woods. The third near is the intersection of Red Dog Farm Road & Magnolia Road, in the Shellstone Creek valley wall of Bleckley County. All three exposures are subtly different and the reason for this difference isn’t understood. More research needs to be done. Of course, developing Oaky Woods will mean that we’ll only have one exposure to study, maybe none depending on how the developer does the infrastructure.
 The Shellstone Creek Beds formed at the beginning of the Oligocene Epoch, this was a time of transition. The Earth was ending a period of relative long-term climate stability and entering one of repeated climate change. In the twelve million year length of the Oligocene Epoch, Georgia saw at least 10 major sea level changes, probably several more. The Shellstone Creek Beds tell jus one story of many.
 It is important that these sediments not be undisturbed. There are layers of rock in Oaky Woods, like a cake’s layers. Some of these layers (or more properly formations) are many feet thick and some are just a few inches. Each tells something about the environment which created it. They occur in order, typically, with the most recent on top and deeper layers being older. It’s very much like a book, you start at page one and continue to the end. However, nothing is simple,  sometimes sea levels were too low to leave a record and sometimes heavy currents erased or moved existing rocks and confused the record, especially during the repeated change of the Oligocene. So some pages of our book are already missing or have been displaced naturally, this complicates things, so the remainder has to be studied all the more carefully. Development, since it also cuts and moves the earth, further upsets the order and it becomes even more difficult to understand the story.
    The oldest rocks in Oaky Woods represent global sea levels at their maximum, there was no ice at the poles and Houston County was the bottom of a tropical sea 200 feet deep. The Georgia coastline was well north of Macon, north of Columbus & north of Augusta. All this was 50 million years ago. Fifteen million years after the dinosaurs.
 In the long view of geologic time Georgia is usually the bottom of a sea, it has been so many times in the past and will be so again, but probably not in our lifetimes or the lifetimes of our grandchildren.  However, sea-levels will measurably rise and seas will be measurably warmer in our lifetimes. At the very least this will affect the distribution of  modern coastal marine life and impact fishing in Georgia. Remember, we’re at the tail-end of the ice ages, the world is colder and dryer than its geologic average. Global warming moves us closer to that warm-world average. Studying the rock formations of Oaky Woods will tell us what Middle Georgia is like in a warm-world environment. Few other things will.
 There is also the paleontology which needs to be done, fossils to study before they’re lost to development.

 Because of so much environmental change over so many years Georgia’s fossil record is rich. Going back 50 million years to the early Eocene Epoch we find some of the earliest ocean going whales and Georgiacetus vogtlensis, (Casually called the Vogtle Whale) which is arguably Georgia’s most important marine fossil. Georgia-cetus means Georgia whale. The first specimen of this whale was discovered in Burke County, near Augusta, during the construction of nuclear Plant Vogtle.  This was the first protocetid (early whale) found outside the Pakistan / India area which leads to the question of  how did it get here? Were these early whales ocean going or did they follow prey-fish migrations around the coastal edges of the Atlantic?
  We know it belongs to the whale family because of its ear structure, even the earliest semi-aquatic whales share an unusual ear structure also found in modern whales. No other line of animals has this structure. Georgiacetus does have this ear structure. It had well developed hind legs but its hip bone was not fused to its spine so its hind legs could not support its weight on land. It’s believed that Georgiacetus was about 16 feet long in life. One of the most interesting things about the Vogtle Whale was the location of its blowhole, not at the crown of the head like modern toothed whales but halfway between the crown and the tip of its snout. It is an evolutionary transitional whale. You can see Georgiacetus at Georgia Southern University and there are several entries about it on the web.
 A few other specimens have been found since the Plant Vogtle discovery and more could easily be preserved somewhere in Oaky Woods, the time and environment is about right.
  Houston County has also produced several Basilosaurus fossils over the years, this was a later whale which reached nearly 70 feet in length and was both numerous & widespread in the southeastern seas. It’s the State Fossil of both Alabama and Mississippi.
 Zygorhiza is another ancient whale fossil often found in Georgia, one is on display at Macon’s Museum of Arts & Sciences, this fossil was found in Twiggs County.
 These are the rock stars of Georgia’s whale fossils, many more later whales and porpoises have been found as well as many more vertebrate marine animals. Our State Fossil is the shark’s tooth, you can find specimens in Okay Woods from many different time frames & many different species including the some of the largest shark’s teeth known. Manatee fossils have been found in Houston County as well as the fossils from sea going crocodiles up to 30 feet long. Any of these could easily be in Oaky Woods.
 Since Georgia’s rivers are very old and sea levels have changed so frequently you may also find fossils from many different land animals. Elephants once roamed Georgia and it’s not impossible that you’ll find their fossils in Oaky Woods. The Columbia Elephant was once common in Georgia and Florida. Mastodons were in Georgia as well, a forest dweller whose fossils have been found in Houston County.  You might even find fossils from some unusual four tusked mastodons, they are also known to occur in Georgia.
 Giant ground sloth fossils are known to occur in Georgia. Glyptodons too, which is a giant member of the armadillo family with a club tail and solid carapace, like a turtle’s, reaching five feet in length.
 Several types of wild pigs are thought to have occurred in Georgia’s, some of which grew to nearly six feet high at the shoulders. They were widespread along the Atlantic seaboard so certainly in Georgia too. There are boar hunters who will dream tonight of seeing something like that.
 Camels & llamas are known to appear in Georgia though they are uncommon in areas that were heavily forested.  Giant beavers liked water and forests, they are also in our fossil record, as big as a modern black bear. Ancient deer fossils are known, many of which are very similar to today’s deer but one small species had no antlers, instead it had long, thin, curved upper canine tusks. There are also many species of the horse ancestor fossils found in Georgia including small forest dwellers.
 With all these prey animals populating our forests there were many predators.  Black bears have been in the area far longer than any humans, basically unchanged, though I hate to call them predators. They are indeed omnivores and eat meat. The short faced bear also appears in our fossil record, it was widespread in North America and is believed to be the largest bear that ever lived standing more than five feet at the shoulders on all four legs. A very big bear. It was more closely related to the grizzly, which is indeed a predator.
 Two species of wolf appear, the dire wolf  vanished 11,000 years ago, and the second about  200 years ago, it was known by the Native Americans and European settlers. Bobcats, lion-like cats, and saber tooth tigers all hunted Georgia. Even Smilodon, the spectacular lion-sized saber toothed cat was here.
 Since most of these mammals were at least partially forest dwellers, and there was a major water source nearby, it’s not impossible that their fossils may be found in Oaky Woods. You just can’t know until something is found. So help preserve these woods, anyway you can, then put on your boots and go see what fossils you can find.

 “Stratigraphy, Paleontology, & Economic Geology of Portions Of Perry & Cochran Quadrangles, Georgia” by Sam Pickering, 1970, Publications of the Georgia Geology Survey, Bulletin 81.
 “The Oligocene” by Paul F. Huddlestun, 1993, Publications of the Georgia Geologic Survey, Bulletin 105

 “Prehistoric Vertebrates of the Georgia Coastal Plain” by Vernon J. Hurst, Reprinted from the Georgia Mineral Newsletter, Vol X, No. 3, Autumn 1957. Available from Publications of the Georgia Geologic Survey.