“Tiger Dirt” What is it and what does it mean? Prepared by: Roger Leab, NRCS Soil Scientist April, 2009
Definition: Tiger Dirt A
general term applied to soil horizons that have patterned mottling
Patterned Mottling The
most typical is reticulate or netlike mottling
Two Examples
Patterned Mottling The
horizontal component of the mottling is usually the more pronounced giving a striped appearance (Hence “Tiger Dirt”)
Strong Horizontal Component
However, the Vertical Component can be Stronger
What Causes It? It
is caused by extended saturation It is usually the result of a perched water table, but it can be an apparent water table
Where Does It Occur? It
most often occurs in soils developed in sedimentary deposits Occasionally occurs in residual soils
What Type Sedimentary Deposits? Old
colluvial/alluvial capping on high parts of the landscape Old stream terraces Marine, fluvial-marine, and eolian deposits of the Sandhills Marine deposits of the Upper Coastal-plain
In What Type Residual Soils Does it Occur? (Examples) Cataula
series (thermic)* Helena series (thermic) Vance series (thermic) Hard Labor series (thermic) Casville series (mesic) Halifax series (mesic)
“Tiger Dirt” Development Mottling
is generally much more strongly expressed in the soils formed in sediments than in the soils formed in residuum
“Tiger Dirt” in Old Colluvial/Alluvial Capping (Examples) Hiwassee
series (thermic) Mattaponi series (thermic) Appomattox series (mesic)* Yadkin series (mesic)
Appomattox Series
Tiger Dirt” in Old Stream Terrace (Examples) Masada
series (thermic) Dorian series (thermic) Danripple series (mesic) Banister series (mesic)*
Banister Series
Marine, fluvial-marine, and eolian deposits of the Sandhills Ailey
series* Fuquay series*
Ailey Series
Fuquay Series
Fuquay Series: Platy Structure
Marine Deposits of Upper Coastalplain Dothan
series*
Dothan series
Mottling in Residual Soils Cataula
series (thermic) is a good example
Cataula series (two examples)
Why Does the Mottling Pattern Develop? Water
stands in the larger pores between soil peds and frequently in old root channels above a layer that does not have the large pores and acts as an aquatard causing the formation of redoximorphic features
Residual Aquatard The
aquatard is generally a thin layer with platy structure just above the C horizon or it is a C horizon where most or all of the old rock fractures are filled and sealed with clay
Sedimentary Aquatard The
aquatard layer is generally a 2C horizon in the sedimentary deposits or occasionally a 2B horizon
What is a 2C Horizon? It is a layer of different source material than that of the soil horizon above it. Example 1—the soil formed in old alluvium, but the 2C horizon material underneath it is residuum Example 2—the soil formed in fluvialmarine sediments, but the 2C or 2B horizon is a much older paleosol (a very old soil) which has been truncated and buried under the sediments in which the new soil formed.
Example of “Tiger Dirt” at Leesburg, here in Wake County
Site is Near John Kelley’s Home John
stopped at construction site and thought soil was a unique residual soil John asked me to help describe and classify the soil profile. After a careful review of the site and soil We determined that it was old alluvial capping and that the Appomattox series fit best
Appomattox Series at Leesburg Site
Appomattox Series Living roots and old root channels are all in the gray, iron depleted zones The redox mottling extends down to the contact with the underlying residuum (over 200 inches)
Appomattox series
What Does It Take To Form Redox Features? Organic
matter for microbes to feed on in the saturated zone Continuous saturation for 15 or more days such that available oxygen is depleted in that zone by the feeding microbes
Redox Features
So! What Does “Tiger Dirt” Mean for Interpretations? That
is a tricky one!
Interps In
many cases it means there is a water table (perched or apparent) during significantly wet periods
Interps In
other cases the redox features are relict and pose no present limitation
What is the Answer for Onsite Use? I don’t think we can be sure in many cases without a piezometer or water well study. If the water table was perched and the aquatard is still present and not too deep, why would we think the wetness condition no longer exist? If the water table was apparent and the hydrology of the area has changed such that the present water table is much lower or no long exist, then we should assume the redox features to be relict.
