Core from Eastern Inner Piedmont - Cat Square Terrane, Iredell County, NC

Photo mosaic of portion of rock core from Core Hole 2, Allison Woods research station, Iredell County (Photograph from NCDENR-DWQ). 


According to the geologic core descriptions in (Huffman and Abraham, 2010) of Core Hole 2 (CH-2), Regolith is present from 0 – 55 feet, Transition zone is present from 55 – 70 feet and Bedrock is present from 70 feet to bottom of boring at 185 feet depth.


Dominant rock types present in core include: schist, biotite gneiss and amphibolites gneiss.  These are typical lithologies for the Inner Piedmont.  Note compositional banding and foliation almost perpendicular to core length.  Low lying (shallow dipping) foliation and compositional banding is characteristic of rock types in the Inner Piedmont.

The Allison Woods research station was established to determine the hydrogeologic characteristics of the regolith-bedrock aquifer system in the Inner Piedmont litho-tectonic terrane of the North Carolina Piedmont.  The site was established as a multiyear cooperative study between the North Carolina Department of Environment and Natural Resources (NCDENR), Division of Water Quality (DWQ) and the U.S. Geological Survey (USGS) (Huffman and Abraham, 2010)

Huffman, B.A., and Abraham, Joju, 2010, Compilation of water-resources data and hydrogeologic setting for the Allison Woods research station in Iredell County, North Carolina, 2005–2008: U.S. Geological Survey Open-File Report 2010–1015, 56 p. Link to Report

Gneiss - Inner Piedmont

Select section of core from Core Hole 2, Allison Woods research station, Iredell County (Photograph from NCDENR-DWQ).  Core has been sprayed with water to show rock texture. 

Rock types include interlayered biotite and hornblende gneiss of varying textures.  Note compositional banding and foliation almost perpendicular to core length.  Low lying (shallow dipping) foliation and compositional banding is characteristic of rock types in the Inner Piedmont.

According to Goldsmith et al. (1988), the research site is located in unit CZbga near the contact with unit CZbg.  The site may be underlain by lithologies of both unit.

 
CZbga: Biotite gneiss and amphibolites – Interlayered biotite gneiss, hornblende gneiss, amphibolites, metagabbro(?), and subordinate mica schist.  Locally contains much granitoid rock, forms migmatite resembling migmatitic granitoid gneiss (OCgm).


CZbg: Biotite gneiss – Gray to dark-gray, thin- to thick-layered biotite-quartz-feldspar gneiss, in part garnetiferous, locally inequigranular and porphyroblastic.  Interlayered with calc-silicate rock, sillimanite-mica schist, mica schist, and amphibolites. Locally contains small masses of granite.  Gradationaly into and interlayered with white-mica schist (CZs) and sillimanite-mica schist (CZss).

Rock Type: Gneisses and schists

Terrane: Cat Square terrane (Hatcher, 2002) of the Inner

Piedmont (Eastern Inner Piedmont)

Gneiss - Inner Piedmont

Select section of core from Core Hole 2, Allison Woods research station, Iredell County (Photograph from NCDENR-DWQ).  Core has been sprayed with water to show rock texture. 

Rock types include interlayered biotite and hornblende gneiss of varying textures.  Note compositional banding and foliation almost perpendicular to core length.  Low lying (shallow dipping) foliation and compositional banding is characteristic of rock types in the Inner Piedmont.

Gneiss - Inner Piedmont
Enlargement of portion of above photograph to show texture and compostional banding and foliation. Gneiss - Inner Piedmont

Select section of core from Core Hole 4, Allison Woods research station, Iredell County (Photograph from NCDENR-DWQ).

Arrow points to coarse-grained granitic textured interlayer.

Gneiss - Inner Piedmont