Tiger Dirt. What is it and what does it mean? Prepared by: Roger Leab, NRCS Soil Scientist April, 2009

“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 appl...
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“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


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. ‹