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Geologic applications - Geoarcheology

Updated September 2005

This geoarcheology project was conducted to assist the Division of Cultural Resources to determine the type and possible origin of foundation stones located at the James Coffield House, 209 East King Street, Edenton, North Carolina.

The original house was built around 1764. None of the original structure remains visible today. Through the 19th and 20th centuries, there have been numerous modifications to this house. During restoration in 1973 it was discovered that the oldest foundation consisted of blocks of limestone. One of these blocks was recovered and serves as the basis of this study.

The foundation stones are limestone and it was concluded that the stones origin was possibly the Bahamas. They were most likely transported to North Carolina by trading ships circa 1700's.

Foundation rocks were identified using a hand lens followed by petrographic thin section examination to confirm the rock type. This page summarizes the findings of the study and presents a series of photomicrographs of these rocks. This brief study was done in 2004 by Kenny Gay, staff geologist with the North Carolina Geological Survey. E-mail Kenny Here


James Coffield House, 209 East King Street, Edenton, North Carolina.
Bedded and cross-bedded, biosparite or biograinstone in foundation underneath house
Good general photomicrograph showing characteristics of the foundation stones. These features include micritized, skeletal, carbonate sand grains, bioclasts, grain-contacts, and meniscus calcite cement. Other features include isopachous bladed calcite cement partly surround some bioclasts, a micrite envelope is filled with blocky calcite, and some of the internal porosity in the bioclasts is filled with blocky calcite. Magnified 10x
Bryozoan bioclast, zooecia, are partly filled with bladed calcite cement. The right side of photo shows grain-contacts, meniscus calcite cement, and isopachous bladed calcite cement. Magnified 10x
Coral bioclast, the intergranular porosity is partly filled with blocky calcite cement. Magnified 10x
Benthonic foram. The intergranular porosity is partly and completely filled with blocky calcite cement. Magnified 10x
Isopachous bladed calcite cement surrounding an oolith.  Also, bioclasts, are showing grain-contacts, meniscus calcite cement, and some intergranular porosity is partly and completely filled with blocky calcite cement. Magnified 10x
Rounded, micritized, bioclast showing grain-contacts, meniscus calcite cement. Also, isopachous bladed calcite cement partly surrounding some of the bioclasts. The boring in the  upper left is partly filled with bladed calcite cement. Magnified 20x
Micrite envelope. A micrite envelope is formed when the original clast has been removed by solution leaving the outer-most rim of the clast behind. Magnified 10x
An oolith showing grain-contact, meniscus calcite cement. Magnified 10x

An intraclast of micritized oolites or pellets. The intergranular porosity is partly filled with blocky calcite cement. Magnified 10x

 

Bioclasts of red algae, a worm tube, and other micritized clasts are cemented by grain-contact, meniscus calcite cement. Also, the intergranular porosity is partly to completely filled with blocky calcite cement. Magnified 10x

Contact information

Kenny Gay
North Carolina Geological Survey
1620 Mail Service Center
Raleigh, NC 27699-1620
919-733-7353, ext. 28
kenny.gay@ncmail.net.

Additional information about the James Coffield House is located in, "Edenton — An Architectural Portrait," by Thomas R. Butchko, 1992, pages 201-202. The report was published by the Edenton Woman's Club and Chowan County Government, Edenton, North Carolina. The Library of Congress Catalog Card Number is 92-90186.