Arch Lake Woman: Physical Anthropology and Geoarchaeology

Geoarchaeology

Microprobe Analysis, Iron-bearing Sediment 15 Geoarchaeology ✦ T he exact location of the burial in the north wall of the road cut has been obliterated due to attrition during the past thirty-three years (fig. 2). However, the stratigraphy in the north and south walls remains intact. Stratigraphic profiles were exposed and described on both walls of the road cut (figs. 11a, 11b, and 12), and sediment samples were collected (fig. 13, color plate). Additional geological testing at the site was undertaken to determine whether additional skeletal remains were present. The results were negative, as described later. The south wall reveals a column of three reddish brown dune sand strata (figs. 11a, 12, and 13; strata Z2, Z1, and y) that overlie a light brown to white eolian sand (stratum x) into which the burial pit had been excavated (fig. 11b). Both Z1 and Z2 are weakly consolidated fine- to medium-grained eolian sands bearing uneven, irregular light and dark laminations and weakly developedpedogenesis (table1).StratumZ1isabsentfromthenorthsidecolumn. Figure 11A. geologic cross sections through road cuts at the Arch Lake burial site. 15 Study of the Arch Lake Site 16 Except for transition y/x, the basal contacts are sharp with little disruption by bioturbation. Stratum y is a darker reddish brown eolian sand with a grayish brown desert A horizon over a weakly prismatic B horizon. The basal contact is very irregular, with the top of stratum x having numerous filled rodent burrows (bioturbation). Stratum y was sampled from the south wall section (figs. 12a and 13; samples 3, 4, 5, and 6). Radiocarbon measurements on sample 3AL99 from stratum y were 190 ± 40 RC yr. (AA-34602) on bulk sediment and 425 ± 40 RC yr. (AA-34603) on humic acids. These dates provide a minimum age of 400 RC yr. for pedogenesis following the deposition of stratum y. It is apparent that nuclear-age carbon has contaminated this paleosol, making it appear anomalously young for the degree of pedogenesis. A weaker soil occurs at the top of stratum Z1. On the north wall of the road cut, the oldest dune deposit, Stratum x, is subdivided into three parts (fig. 12b). The lowest part, stratum x1, is laminated medium- to coarse-grained light brown sand without visible CaCO3 . This is transitional upward over 3 cm to stratum x2, a very light brown (white), firm, calcareous, laminated medium- to coarse-grained sand with thin (1–2 mm) CaCO3 laminae and mottles. Stratum x2 is gradational upward over 5 cm to stratum x3, which is composed of light brownish white firm, massive Figure 11B. generalized profile of the north bank of the road cut. 17 medium- to coarse-grained sand with lighter and darker mottles due to bioturbation. It is clear from Green’s 1967 stratigraphic sketch and photographs (figs. 3a and 3b) that the burial pit was excavated from the y/x contact and penetrated strata x3 and x2, ending in the top of x1. Several small lumps of dispersed charcoal (sample 1AL99) collected from the heavily bioturbated irregular contact between strata x and y could be from a buried hearth, but the intense bioturbation by rodents makes the stratigraphic provenance questionable. Thus dating this charcoal was not attempted. An in situ radiocarbon sample (2AL99) was collected from a distinct hearth feature exposed in the road bed about 40 m east of the burial site (fig. 2). The hearth pit was reportedly thicker in the past, but the top of the fire pit has been lost through road grading and deflation. The surface from which the fire pit was excavated cannot be determined with certainty (fig. 11b). The hearth appears to have been within stratum y because artifacts have been eroding out of this stratum. An AMS radiocarbon date of 3010 ± 45 RC yr. BP (AA-34294) Figure 12. Stratigraphic columns for the south and north banks of the road. Geoarchaeology Study of the Arch Lake Site 18 indicates a Late Archaic age for the hearth. Whether stratum y deposition was complete before the fire pit was dug is unknown. However, it does provide a minimum age for the beginning of y deposition. On the basis of color, calcification, and stratigraphic as well as geomorphic TABLe 1. SeDiMeNTAry CHArACTeriSTiCS OF STrATA expOSeD By THe rOAD CuT AT THe ArCH LAke BuriAL LOCALiTy. DeSCripTiONS By HAyNeS. Stratum Description Thickness (cm) Z2b Sand Light brown (10 yr 4 /3 ) soft, massive, fine...