Exploring the Georgia Cambrian

[EMP]

Most people are familiar with the Conasauga Formation when they think of Georgia's Cambrian record, but the Peach State has a paleontological history dating back several million years before the Conasauga was deposited. Indeed, the oldest fossils in Georgia date back to the early Cambrian, and consist of a diverse form of worms, brachiopods, trilobites, and other creatures such as hyoliths and archaeocyathids. This early Cambrian record is largely divided into three formations, from oldest to youngest the Weisner Formation (part of the Chilhowee Group), the Shady Dolomite, and the Rome Formation. All of these formations, as well as the overlying middle Cambrian rocks of the Conasauga Formation, are well exposed in the Rome and Cartersville areas.

 

Cartersville is a mid-sized town in North Georgia with a rich interconnection between history and geology. Situated near the confluence of three major geological provinces (the Valley and Ridge, the Blue Ridge, and the Piedmont), the Cartersville area was uniquely positioned for the discovery and future development of a variety of mineral resources. Wide scale mining began in the mid-19th century with the establishment of the Etowah Iron Works along the Etowah River. Although the bulk of the works were destroyed by Union forces during the Civil War, mining not only continued in and around Cartersville but actually expanded in the post-war period. Iron was the principal product for a while owing to the region's rich limonite deposits, but by the turn of the century ochre and barite production also became prominent, if not more so. Mining operations peaked by the middle of the 20th century, but some active mines remain in the area, and they continue to be a favorite with mineral and fossil collectors. 

 

Thankfully, this past history of mining, combined with the recent construction due to Atlanta's explosive growth, has exposed rocks typically left buried under the thick clay and vegetation of North Georgia. 

 

 

 

The Shady Dolomite was, and still is, the focus of the brunt of the ochre mining around Cartersville. A carbonate unit, the Shady is easily weathered in North Georgia's humid and rainy climate, dissolving much of the rock and underlaying the ground in a thick, reddish clay. Due to the nature of the weathering, however, distinct beds can sometimes be seen in cuts made into the Shady, as shown in the above photo from a construction site in Cartersville. 

 

 

Another exposure of the red clay residuum made out of weathered material from the Shady Dolomite.

 

Although the carbonates of the Shady are frequently weathered into a thick, red muck, this weathering process typically uncovers a wide variety of rock types that are more resistant to chemical attack, and which would have otherwise been locked into the dolomite. At exposures like the one above, pieces of shale, iron oxides, and chert are common. Alongside the chert are fossils from some of the oldest reef communities in Georgia. 

 

 

This small piece of rock contains fragments of archaeocyathids, ancient sponge-like organisms that once established reefs in the early Cambrian sea. Alongside archaeocyathids, other fossils like trilobites and brachiopods are sometimes found in the Shady, but I didn't find any personally. 

 

Aside from iron and ochre, Cartersville was an important center for barite mining around the turn of the century. Most barite mines were located east of town, near the contact between the Valley and Ridge and the Blue Ridge provinces. Although most have been filled in or flooded, one pit that is still left can be seen at Pine Mountain east of town. A few pieces of barite ore line the trail leading up the mountain. 

 

 

A small piece of barite ore from near Cartersville. 

 

 

The walls of a former mining operation near the base of Pine Mountain contrasted with an image of a similar mine when in operation.

 

Leading up the trail at Pine Mountain, one travels across geologic provinces. The valley floor is underlain by rocks of the Shady Dolomite and Rome Formation, part of the Valley and Ridge province, while Pine Mountain itself lies within the Blue Ridge. Climbing up Pine Mountain, you begin to sense that change reflected in the rocks underneath you. The red clay and chert residuum of the Valley and Ridge gives way to brown and white dirt, and the chert and dolomite boulders give way for quartzose sandstones, quartzites, and schists. Along the trail, numerous pieces of quartz sandstone from the Weisner Formation are exposed, and in these boulders you can sometimes catch glimpses of the earliest recorded life in Georgia! 

 

 

The picture here shows a sandstone boulder with a couple of well-worn Skolithos linearis worm burrows. Whereas the Shady Dolomite was deposited in a shallow, tropical sea, the upper Chilhowee Group was deposited in a near-shore environment as indicated by the coarse sediment. That means that 530-550 million years ago, during the early Cambrian, what is now a mountain would have been a warm, sandy beach! And, although they may not seem like much, the humble tubes in the rock illustrate a time when life was not everywhere abundant, and the diverse lifeforms we find at beaches today had yet to appear. 

 

Climbing the rocky trail to the summit, one is well-rewarded with a view of the entire Cartersville area, including a view across much of the Piedmont to Kennesaw Mountain beyond, and across much of the Great Valley to the Armuchee Ridges. One can also get a sense of the legacy of intense mining that took place around Cartersville from the many red-colored pits scoured into the nearby hillsides, ghosts of operations past and present. On top of all of that, one can also visualize the impact geology has on the topography of an area. Being the intersection of so many geologic provinces, the Cartersville area is marked by numerous faults, folds, and other complex structural geology that has left pockets of one formation nearly surrounded by pockets of another. This has contributed to the hilly nature around Cartersville, as the comparatively resistant rocks of the Rome Formation and Chilhowee Group forms island-hills in the sea-valleys of the Shady Dolomite.

 

 

The view from Pine Mountain. The red areas are current and past mines around Emerson, Georgia, just south of Cartersville (which includes the buildings in white). The hills here, which make up part of the Allatoona Mountains, are held up by resistant units like the Chilhowee and Rome while the valleys are underlain by softer carbonates like the Shady. On a clearer day you could make out the Armuchee Ridges lying at the western edge of the Great Valley, a synclinorium of Cambro-Ordovician rocks that stretches from here all of the way to Quebec. 

 

I hope you enjoyed the report! 

[digit]

Very nice! Thanks for the geologic travelogue.

 

 

Cheers.

 

-Ken

[Andúril Flame of the West]

Thank you for taking us along with you! It is always quite surprising when one realizes the impact geology can have on the history of a place. 

[bockryan]

Great report! Was just looking at some Shady outcrop locations in VA that I may try to check out soon, if they're still around. Glad you had success