Where in Georgia do you find Sediments & Sedimentary

Rocks?

Coastal Plain Province

Valley & Ridge Province*

In all provinces, young sediments are associated with rivers and streams. These are “Quaternary alluvium” - Qal

Sediments & Sedimentary Rocks in Georgia and adjacent states

(Modified from Hatcher et al. (1990), Steltenpohl et al. (1995), and Hooper & Hatcher (1988).)

Map on left Adapted from Ga. Geologic Survey

state geologic map, 1977

Valley & Ridge Province is composed of Paleozoic Sedimentary rocks

Valley & Ridge*

Sandstones Shales Limestones Coal Conglomerate

Rocks deposited in a variety of sedimentary environments, shallow marine passive margins, shallow inland sea, delta and tidal flat deposits.

Origin of these sedimentary rocks.

Part I - Late Precambrian (700 to 600 m.y.) – Rifting of supercontinent Rodinia, opening of Iapetus Ocean.

Passive margins

Low-grade Metamorphosed sedimentary rocks are exposed in the western Blue Ridge Province.

These were deposited as rift-related sandstones, conglomerates, and shales.

The shoreline of the Iapetus Ocean might have looked like this – w/o the vegetation

Part II – Periodic coverage of the continent by shallow, inland seas.

Tropical to sub-Tropical conditions

Sedimentary rocks of passive margin and shallow inlands seas include sandstone, shale, and limestone.

Silurian limestone from Chattanooga area

Common Paleozoic fossils (photos from Univ. of Calif. Berkeley Museum of Paleontology website) in Ga. include:

Trilobites Crinoids

Brachiopods

With each of the 3 periods of Appalachian uplift, there was erosion of the rising mountain chain and the deposition of large river delta systems to the NW, draining into the shallow inland sea that covered the continental interior. After the Ordovician Period, most of the Ga. sedimentary rocks were deposited in delta/tidal flat conditions with some incursions of marine conditions during the Mississippian Period.

The first Clastic wedge developed NW of Taconic Highlands, includes Red Mountain Fm. in NW Ga. and Birmingham, AL.

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When the uplands were eroded and less clastics were reaching the inland seas, marine conditions resumed. The last deposition of Paleozoic limestones in NW Georgia occurred during the Mississippian Period. Fossils include blastoids and horn corals.

The Mississippian St. Genevieve Limestone hosts many of the caverns in TN, AL, and KY.

Typical Pennsylvanian river delta (clastic wedge) related sedimentary rocks.

A close-up of typical fluvial sandstones

The Pottsville Sandstone is one of the clastic wedge units.

Tidal flat deposits, e.g., the Red Mountain Fm., include red sandstones, shales, and siltstones.

Photo by P. Bouker

Passive margin

Coastal Plain Province

With the Triassic and Jurassic rifting of Pangea, a passive

margin (continental shelf) developed on the Gulf and

Atlantic Coasts

Geologic Time Scale

As the continent eroded, the land rose (remember Isostacy?), exposing the Late Cretaceous through Miocene Continental Shelf sediments. The remainder of the Coastal Plain is alluvial and fluvial, except for the coastal barrier islands.

The rising of the SE portion of North America produced an “Emergent Shoreline”

Fall Line – separates crystalline rocks of Piedmont from softer sediments of Coastal Plain.

Fall Line Cities – Columbus, Macon, Augusta

Marked by waterfalls and rapids.

Coastal Plain

PiedmontFall Line

Coastal Plain Province –Late Cretaceous to Holocene (Recent) deposits at shoreline. Age – 100 m.y. - >10,000 yr.Layered sediments, sands, clays, limestones.Late Cretaceous sediments – mostly deltaic, including Providence Sand.Paleocene – Oligocene sediments – mostly marine.Miocene – Holocene – mostly continental deltaic, fluvial and alluvial sediments, except near coast.Aquifers – uniform sediments, a few karst wells.

Aerial view of a Meandering River System on the Gulf Coastal Plain

Eocene Epoch – warm temperatures, high sea level, widespread deposition of shallow-water limestones and much fossil biodiversity. This particular sand dollar (echinoid) is from SE of Perry, Ga..

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Residuum of Paleocene Clayton Fm. over deltaic Cretaceous Providence Sand

Excess sand from Providence Canyons erosion produces braided streams in canyon bottom, i.e., too much sand.

Sinkholes can form wherever limestone or marble is at the surface – Coastal Plain, Valley & Ridge, or Blue Ridge – Murphy Marble Belt.

On the Piedmont (and maybe parts of the Blue Ridge), we can find more modern river sediments on flood plains and abandoned channels.

An example of Qal, sand and gravels in a small Piedmont creek.