Geological Perspectives on Upstate Soils

William A. RansonDepartment of Earth & Environmental Sciences

Furman University

In Reality a Closed System 4.6 Ga After Formation!

[From Press et al., 2004, Understanding Earth, 4th Edition]

Implications of a Closed System Earth

•Finite resources

•No “away” to throw things - all waste remains on Earth

•A change in one part of the Earth System eventually affects all parts of the Earth system

Atmosphere

Hydrosphere

Geosphere Biosphere

Global Commons = Natural Capital

Global Commons

•Clean Air•Clean Water•Energy Resources•Mineral Resources•Fertile Soil•Biological Diversity

Soil A complex medium of:• Clay minerals•Al-Fe-hydroxides•Bedrock fragments•Humus•Microorganisms•Air•Water

Pangaea at 290 Ma

Appalachian cross section

Rocks and Minerals of the Upstate: The Raw Materials for Soil

FelsicGneiss - feldspar, quartz, mica (biotite & muscovite),

hornblende

Schist - muscovite, biotite with minor feldspar and quartz

MaficAmphibolite - hornblende, feldspar

Diabase - feldspar and pyroxene

Weathering of Rock

Mechanical•Ice wedging/frost action•Exfoliation•Vegetation

Chemical•Dissolution•Hydrolysis•Oxidation

Hydrolysis

Feldspar+water+carbonic acid=>Clay+dissolved ions

OxidationIron silicates+Oxygen=>Iron oxides/hydroxides

Lack of glaciation means a thick accumulation of clay minerals and saprolite.

Climate - temperature, rainfall

Bedrock Mineralogy

Bedrock Structure/Faults/Fractures

Topography

Influences on Weathering & Soil Production

Products of Weathering

Saprolite - in situ, chemically weathered bedrock; retains the structural features of the rock

Soil - a complex medium of clay minerals+Al-Fe-hydroxides+bedrock fragments+humus+microorganisms+air+water

Photo of saprolite

Saprolite!

Rock and Mineral Chemistry

Gneiss - K, Na, Al, Si minor Fe, Mg

Schist - K, Al, Si, minor Na, Fe, Mg

Amphibolite - Ca, Fe, Mg, Al, Si, minor Na, K

Diabase - Ca, Na, Fe, Mg, Si

Soil Horizons

Soil pH and Plant DiversityFelsic Rocks with Rich A-Horizon•Acidic Soils with pH~5.0-5.3•Lower Plant Diversity

Mafic Rocks with Rich A-Horizon•Circum Neutral Soils with pH~6.7-6.8•Greater Plant Diversity

Mafic Rocks with Depleted A-Horizon•Acidic Soils with pH~5.6-5.8•Lower Plant Diversity

Threats to Soil

Erosion - physical removal by:•Running water•Wind•Ice•Bulldozer

Degradation - physical or chemical changes to the soil that render it unviable

•Increased salinity•Heavy application of fertilizers/pesticides/herbicides•Removal of vegetation and exposure to sun

Influences on Erosion in the Upstate

•Naturally steep slopes and hillsides•Hard, relatively impermeable silicate bedrock•Temperate, humid climate=>abundant water & clay ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~•Urbanization=reduced permeable surface area•Considerable agriculture•Lack of riparian buffers•Improper logging practices•Road construction•Less than optimal land-clearing practices

About 5.6 tons/acre/yearor

~4 cm/100 years

Average Rate of Soil Production in the US

~0.6 cm/100 years

Average Loss of Soil in the US

[US Soil and Water Conservation Service, 2002]

Along the Blue Ridge Escarpment steep slopes combined with hard, relatively impermeable gneisses result in a thin soil profile that is susceptible to mass movement. Mass movement is the slow to rapid down slope movement of soil and/or rock debris under the influence of gravity.

Glassy Mountain Development

1984

Mature Piedmont landscape

Average Annual Transport of Rock & Soil

•Wind erosion 1.0•Glaciers 4.3•Mountain building 14•Oceanic volcanism 30•Humankind 42•Water 53

Billion Tons

[Source: Hooke, 1994]

• a physical contaminant• a chemical contaminant if laden

with pesticide, herbicide, or fertilizer residue

Eroded Soil

•Careful land-use planning•Better construction practices•Better logging practices•Riparian buffers for agriculture/grazing•Terracing•Strip cropping•Alley cropping or agroforestry•Windbreaks or shelterbelts•Gully reclamation•Conservation-tillage farming•More soil/water conservation education and enforcement

Some Obvious Solutions