Geophysical Investigations at Archaeological Sites 38SU45, 38SU147, 38SU215, AND 38SU232, Poinsett Electronic Combat Range, Sumter County, South Carolina

A series of large area high data sample density geophysical surveys have been performed to discover and map historic and prehistoric archaeological components at the Poinsett Electronic Combat Range. Three prehistoric sites and one historic site totaling 14,000 square meters were surveyed. Resistivity, magnetic field gradient and ground penetrating radar surveys were performed. More than ten data samples per square meter were collected, processed and mapped. A number of historic and prehistoric features have been discovered and located for test excavation. The absence of well defined hearth and pit features in the data from the prehistoric sites as well as the unambiguous but spatially diffuse data from the historic site both suggest that the archaeological record at these sites has very low geophysical contrast with respect to the surrounding soil matrix. This may be due to a poor state of preservation of the archaeological record and/or an ephemeral (e.g. transient) initial occupation. A poor state of preservation is likely. The resistivity contrast (associated with pits) will be low due to the presence of high acidity well leached soils, a combination which conspires to remove the low resistivity components typically found in pits. The magnetic contrast will be low due to the absence of iron oxides in these soils. Both these processes are further aggravated by the unconsolidated nature of the sands, bioturbation and the disturbance associated with plantation pine agriculture. Test excavation can confirm or correct these conclusions.为在波因塞特电子作战靶场（Poinsett Electronic Combat Range）发现并标注历史与史前时期的考古遗存分布，科研团队已开展一系列大面积高数据采样密度的地球物理勘探工作。本次勘探覆盖3处史前遗址与1处历史时期遗址，总面积达14000平方米。勘探采用电阻率（Resistivity）法、磁场梯度（Magnetic Field Gradient）法与探地雷达（Ground Penetrating Radar）三种技术手段，每平方米采集、处理并绘制了十余组数据样本的成果分布图。目前已发现并定位多处历史与史前考古遗迹，可开展试掘验证。史前遗址的勘探数据中未发现轮廓清晰的炉灶遗迹与坑穴遗迹特征，而历史遗址的勘探数据虽特征明确却呈空间弥散状，二者均表明：上述遗址的考古遗存与周边土壤基质之间的地球物理物性反差极低。该现象或源于考古遗存保存状况不佳，亦或因初始居住活动具有临时性（如短暂定居）。结合区域实际情况，考古遗存保存状况不佳的可能性更高。与坑穴相关的电阻率物性反差较低，原因在于该区域存在高酸度且淋溶程度较高的土壤——这类土壤会移除坑穴中通常存在的低电阻率组分，进而削弱物性反差。该区域土壤不含铁氧化物，导致磁物性反差同样偏低。砂层疏松、生物扰动（Bioturbation）以及人工松林农业活动带来的干扰，进一步加剧了上述两种物性反差弱化的过程。试掘工作可验证或修正上述结论。