PROVENANCE OF FERRUGINOUS SANDSTONE AT MENOKIN ON THE NORTHERN NECK PENINSULA, VIRGINIA

Menokin is a Georgian-style plantation house built in 1769 on Virginia’s Northern Neck in Richmond County near the Rappahannock River. The house was built by John Tayloe II for his daughter, Rebecca, and her husband, Francis Lightfoot Lee, one of the signers of the Declaration of Independence. Menokin was built not using brick, but instead using locally-sourced ferruginous sandstone. The house is located on a low-relief upland (elevation ~40 m) on the Atlantic Coastal Plain. The purpose of our study is to determine the provenance of the sandstone, and to better understand the geochemical and physical processes that produced this rock.

The sandstone is reddish-brown, medium- to coarse-grained, and poorly sorted with rounded to angular clasts of predominantly quartz with minor feldspar and lithic fragments of fine-grained metavolcanic rock. Based on the clast assemblage the sandstone ranges from a quartz arenite to a sublitharenite. The sandstone a porous clast-supported rock with 20 to 40% matrix composed of massive orange/reddish brown goethite with lesser amounts of limonite and hematite. Sedimentary structures include cross-bedding and graded bedding, indicative of a moderate-energy fluvial environment. The poorly cemented sandstone is a relatively friable and a generally poor building material.

We interpret this sandstone to be a ferricrete formed at the base of the 1.6-1.8 Ma Bacons Castle Formation, which is typically a moderately to poorly sorted sand and laminated sand. Shallow Fe-bearing groundwater flowed along the boundary between the Bacons Castle Formation and the underlying impermeable strata of the Pliocene Eastover Formation, as these waters reached the surface along steep hillslopes, iron oxidized and cementation occurred. The precipitation and cementation process cracked and dilated clasts, and produced more angular fragments in the sandstone. Ferricrete formation is an ongoing process near the Earth’s surface.

The sandstone used to construct Menokin was likely quarried from a hillslope ~150 m from the house. Similar ferruginous sandstone was used to construct other notable buildings 18^th century buildings on the Northern Neck.