Geoarchaeology of the Brook Run site (44CU122): an Early Archaic jasper quarry in Virginia, USA

Abstract

Abstract The Brook Run site (44CU122) is an Early Archaic jasper quarry situated near the eastern margin of the Triassic-age Culpeper Basin in Virginia, USA. It occupies the upland margin of a relatively broad and shallow, first-order tributary valley of the Rapidan River. Archaeological and geological investigations focused on site stratigraphy, chronology, and formation processes as well as attributes of the quarried jasper. The Brook Run jasper occurs as large blocks of red-to-yellow brecciated masses of microcrystalline quartz that are cemented together by minor amounts of black chert. These jasper blocks, which were the targets for prehistoric quarrying, occur only within a ca. 1-m-wide Triassic-age fault zone and appear to “float” in a matrix of very weathered, fine-grained fault gouge. 14C age estimates indicate that aboriginal quarrying began by 10 kyBP and proceeded by excavating a ca. 4 m deep pit to remove jasper blocks from the fault. Quarrying ceased by 9.4 kyBP, and the site was abandoned soon after. Petrological and geochemical analyses show that the jasper and black chert formed in stages from hydrothermal fluids injected into the fault zone during Triassic–Jurassic volcanic activity. Unique characteristics of the jasper were also identified that may aid in sourcing artifacts derived from the quarry.