The Geology of Columbia, South Carolina

Introduction to the Geologic History of Columbia

Columbia is located in the Atlantic Coastal Plain physiographic province, which has a rich geologic history spanning over 100 million years. The bedrock underneath Columbia consists of sedimentary rocks from the Upper Cretaceous and Lower Tertiary periods which were deposited as sediments in ancient seas, rivers, and swamps.

Over time, geological processes like erosion, deposition, subsidence, and sea level fluctuations have shaped the landscape of the Columbia area into a gently rolling plain. Understanding the local geology gives insights into how the land has changed over time and why the region has certain mineral resources, soil types, and terrain.

Bedrock Geology

Sedimentary Rock Units Under Columbia

The sedimentary bedrock underlying the Columbia area consists of layers of sand, clay, limestone, and marl. These sedimentary rocks range in age from the Late Cretaceous to Early Eocene epochs (100-50 million years old).

The main bedrock units under Columbia are:

  • Black Mingo Formation – Dark gray sandy clay and clayey sand from the Paleocene Epoch. Up to 50 feet thick under Columbia.
  • Peedee Formation – Calcareous and silty clay from the Late Cretaceous. Up to 200 feet thick locally.
  • Tuscahoma Formation – Glauconitic sand and sandy limestone from the Late Cretaceous. Up to 350 feet thick in the region.

These bedrock units have major implications for groundwater availability, mineral resources, and engineering properties in the Columbia area.

Black Mingo Formation

The Black Mingo Formation consists of dark gray, micaceous, quartz sandy clay and clayey sand. It was deposited in fluvial-deltaic environments around 60 million years ago in the Paleocene Epoch.

The clay layers in this unit provide confinement for groundwater aquifers in underlying units. The Black Mingo Formation is also an important source of common clay and kaolin clay resources.

Peedee Formation

Underlying the Black Mingo Formation is the Late Cretaceous Peedee Formation, consisting of calcareous and silty clay with occasional limestone beds. It formed in marine shelf environments about 80-70 million years ago.

The Peedee Formation is up to 200 feet thick in the Columbia area. Its clay and limestone composition make it a useful construction material for cement and brick manufacturing.

Tuscahoma Formation

The oldest bedrock unit under Columbia is the Tuscahoma Formation, made up of fine to coarse glauconitic quartz sand along with sandy fossiliferous limestone. It was deposited in shallow marine environments during the Late Cretaceous Period.

Groundwater is extracted from aquifers within the permeable Tuscahoma sand beds. This unit also yields aggregate sand, limestone, and glauconite mineral resources.

Structural Geology Features

The sedimentary strata underlying Columbia have a gentle regional dip of 30-60 feet per mile toward the southeast. There are a few faults in the area, but little tectonic deformation.

This produces a relatively simple structural geology setting, with flat-lying to gently dipping sedimentary rock layers stacking up like pancakes. The lack of major faults and folds makes the lithology and thickness of rock units quite predictable across the region.

Economic Mineral Resources

Various mineral commodities are extracted from the Columbia area bedrock and sediments, supporting local industries. Economic minerals found in the region include:

Clays – Common clays mined from the Black Mingo Formation are used to manufacture bricks, Portland cement, and lightweight aggregate. Kaolin clays are also mined for paper coating and filling.

Sand – Silica/quartz sands from the Tuscaloosa Formation are a source of construction aggregate and industrial sand. The sand is high purity (>99% SiO2).

Limestone – Limestone layers in the Tuscahoma Formation are mined for aggregate road metal, cement manufacturing, and agricultural lime.

Glauconite – The glauconitic greensand zones of the Tuscahoma Formation are mined for use as a soil conditioner and fertilizer mineral.

Surficial Geology and Soils

Surficial Sediments Overview

The bedrock geology of Columbia is largely obscured by surficial sediments up to 25 meters thick deposited in the past 40 million years as seas retreated and the land surface was exposed. These younger loose sediments include:

Pleistocene Sediments

  • Fluvial terrace deposits – Sand and gravel along old river channels and terraces.
  • Alluvium – Modern channel and floodplain deposits along rivers and streams.

Holocene Sediments

  • Eolian deposits – Wind blown dune sands.
  • Wetland deposits – Swamp and marsh sediments.
  • Anthropogenic deposits – Manmade fill materials.

This mix of surficial sediments influences soil types, land use, hydrology, and geo-environmental aspects across the Columbia area.

Soils and Land Use

The main soil orders present in Columbia based on the surficial geology are:

  • Ultisols – Red and yellow, clay-rich, acidic soils in uplands. Dominant soil order.
  • Entisols – Younger floodplain soils high in sand/silt. Common along major rivers.
  • Histosols – Organic wetland soils in swamps/marshes. Poorly drained.

These soil types along with the terrain largely dictate land use patterns in the region:

  • Well drained ultisols in gently rolling uplands are utilized for forestry/agriculture.
  • Entisols along floodplains are often used for pasture/grassland.
  • Poorly drained histosols in flat, low-lying wetlands are undeveloped.

Hydrogeology

The interactions between groundwater and geology influence water supplies in the Columbia area. Important hydrogeologic factors include:

Aquifers

The Tuscaloosa-Tuscahoma aquifer system provides most municipal and industrial water supply. Other minor aquifers exist in shallower Pleistocene and Holocene sediments.

Confining Units

Clay layers in the Black Mingo Formation inhibit downward groundwater flow, allowing high pressure artesian conditions to occur in underlying aquifers.

Recharge Areas

The sandy upland soils and fluvial terrace deposits facilitate rapid groundwater recharge to aquifers. Development of these areas can impact water availability.

Careful management of recharge areas and deeper confined aquifers is crucial to maintain ample groundwater reserves serving the growing Columbia population.

Geologic Hazards

While geology provides essential natural resources, it also poses hazards including:

Seismicity

  • Low earthquake hazard – Small intraplate quakes possible but rare major shaking.

Land Subsidence

  • Minor risk where excessive groundwater pumping depresses potentiometric surfaces in aquifer systems.

Sinkholes and Karst

  • Very low sinkhole/karst hazard in Columbia area. No soluble carbonate bedrock near surface.

Other Hazards

  • Flooding major issue during heavy rains due to low relief and frequent tropical storm impacts.
  • Issues also arise from slope failuresoil erosionexpansive clay soils, etc.

Proper identification and management of geologic conditions is key to mitigating environmental hazards affecting Columbia. Ongoing geological and hydrogeological research will provide an improved scientific basis for sustainable planning decisions.

Interesting Geological Points in Columbia Area

Lake Murray Meteorite Crater

A 1.2 kilometer wide meteorite impact structure lies underneath Lake Murray, northwest of Columbia. The Mid-Tertiary age crater eroded and was buried prior to the creation of Lake Murray in the 1920s. Gravity and magnetic surveys have delineated the circular subsurface crater.

Congaree River Blue Granite Outcrops

Outcrops of Proterozoic age Winnsboro blue granite bedrock occur along the Congaree River within Congaree National Park. The granitic gneiss contains blue quartz, visible near the Bates Old River diversion tunnel. These represent the oldest rock exposures in Columbia’s vicinity.

Fossil Collecting Sites

Late Cretaceous through Paleogene age mollusk fossils can often be found weathering out of local exposures of the Black Mingo and Tuscahoma Formations. Large scallop and oyster fossils are common finds eroding from road cuts and quarries mining the glauconite-bearing layers. These allow collectors to recreate environments from over 65 million years ago.

Conclusions

  • Columbia developed atop 100+ million year old coastal plain sedimentary bedrock units.
  • Mineral resource extraction and aquifers rely on local geology.
  • Surficial sediments and soils strongly influence land use.
  • Geology affects hazards from flooding to clay shrink-swell issues.

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