Hongshan residential zones were investigated by magnetometer survey
and stratigraphic testing in three areas within the Upper Daling survey region: Erbuchi, Dongshanzui, and Sanjia.
Magnetometry is a well established archaeological prospection method, and has been used successfully in a range of environments around the world. Magnetometers measure subtle variations in the earth’s magnetic field caused by the varying content of weakly-magnetic iron minerals found naturally in the soil. Buried archaeological remains, such as post holes, pits, ditches, burned features, and other activities that have disturbed soil horizons, alter the natural situation and may produce detectable anomalies (Aspinall et al. 2008; Clark 1990: 64-98; Gaffney & Gater 2003: 36-39; Linford 2006; Scollar et al.:422-519).
A Bartington Grad601-2 dual fluxgate gradiometer was employed. In an effort to increase the likelihood of detecting smaller features and improve anomaly interpretation, data were collected at 0.125 m intervals along traverses spaced 0.5 m apart. This relatively high resolution has been adopted by Horsley elsewhere in China and in North America (e.g. Horsley 2009; Flad et al. forthcoming), and found to be particularly beneficial on prehistoric occupation sites. Within each 30 by 30 m grid square, spatial accuracy was achieved by maintaining a constant walking pace along marked survey ropes. Calibration of the instrument was checked and, if necessary, adjusted every two to three grid squares. Following data collection, data were downloaded from the onboard data logger to a field laptop for treatment and display using ArcheoSurveyor, a dedicated processing package. Minimal data treatment was applied, consisting of sensor destriping to correct for variations between the two fluxgate pairs (see Horsley and Wilbourn 2009). Finally the data were interpolated once in the Y direction, resulting in a resolution of 0.25 m x 0.125 m; this has the effect of smoothing the overall appearance of the data to aid anomaly identification. Images of the data were then exported at appropriate display ranges for georeferencing and integration with other project data.
Aspinall, Arnold, Chris Gaffney, and Armin Schmidt (2008). Magnetometry for Archaeologists. Lanham, MD: Altamira Press.
Clark, Anthony J. (1990). Seeing Beneath the Soil: Prospecting Methods in Archaeology. London: B.T. Batsford.
Flad, Rowan K., Timothy J. Horsley, Jade D’alpoim Guedes, He Kunyu, Gwen Bennett, Chen Pochan, Li Shuicheng, Jiang, Zhanghua (forthcoming). Survey, Excavation and Geophysics at Songjiaheba—A Small Bronze Age Site in the Chengdu Plain. Asian Perspectives.
Gaffney, Chris, and John Gater (2003). Revealing the Buried Past: Geophysics for Archaeologists. Stroud: Tempus Publishing Ltd.
Horsley, Timothy J. (2009). Diqiu wuli jishu zai Zhongguo Sichuan Chengdu Pingyuan kaogu gongzuo zhong de yingyong 2006 nian 12 yue - 2007 nian 1 yue 地球物理技术在中国四川成都平原考古工作 中的应用 2006年12月-2007年1月 [The Utility of Geophysical Techniques in China Based on Archaeological Research in the Chengdu Plain, Sichuan, Dec. 2006–Jan. 2007]. Nanfang minzu kaogu 南方民族考古 [Southern Ethnoarchaeology] 2009(6):279-294.
Horsley, Timothy J., and D. Wilbourn (2009). Destriping Linears: A New Approach to an Old Problem. ISAP News: The Newsletter of the International Society for Archaeological Prospection 21:3–5.
Scollar, Irwin, A. Tabbagh, A. Hesse, and I. Herzog (1990). Archaeological Prospecting and Remote Sensing. Cambridge: Cambridge University Press.