Subsurface Stone Lines, Stone Zones, Artifact-Manuport Layers, and Biomantles Produced by Bioturbation via Pocket Gophers (Thomomys Bottae)

Abstract

A prominent subsurface zone (layer) of large stones with diameters greater than 6-7 cm occurs in gravelly soil on colluvial aprons in the Lompoc area of California. The soil is mounded and churned by botta pocket gophers (Thomomys bottae). Sedimentological analyses show that the soil within and above the stone zone—and within the gopher mounds—is relatively homogeneous in fine fraction and forms a biomantle. None of the mounds contained stones with long-axis diameters greater than the maximum diameter of gopher burrows, about 6-7 cm. Larger stones gradually subside and form a stone zone. Both field observations and laboratory tests confirm that gopher bioturbation produces stone zones in coarse gravelly soil. This finding, and similar findings in two other recent studies, have important implications for interpreting archaeological site formation, and for interpreting geologic-pedologic processes inasmuch as artifact layers (and nonartifact layers) in some sites entirely may be due to nonanthropic, nongeologic, postdepositional biological agents.

Buried artifacts in stable upland sites and the role of bioturbation: A review

“…To this point, Bocek (1986Bocek ( , 1992, Erlandson (1984), and Johnson (1989) warn that observable cultural stratigraphy may actually represent faunal-related horizons and not separate cultural components because the distribution of artifacts may be completely unrelated to prehistoric human behavior. Erlandson found a bimodal vertical distribution of artifacts associated with a small, single component campsite in southern California that he related to gopher activity.…”

“…Generally, artifacts (stones) whose diameters are less than the diameter of the burrows of soil fauna may be translocated upward and deposited in mounds. For example, studies indicate that crayfish (Robertson and Johnson, 2001), pocket gophers (Johnson, 1989), and mole-rats (Mbenza et al, 1989) will shift rock fractions smaller than the diameter of the burrows to the surface. I have observed concentrations of fist-sized cobbles in back-dirt piles formed outside the mouths of burrows of unidentified large mammals.…”

“…He concluded that the objects began as a layer on the surface and were buried and moved downward as a layer. Upland sites in Illinois (Van Nest, 1997), Missouri (Kreisa, 1995), and California (Johnson, 1989) are known to retain vertical stratigraphic relationships in which buried artifacts of older cultures underlie buried artifacts of younger cultures. Michie (1990) found that while temporally-distinct cultural horizons in upland sites on the coastal plain of South Carolina generally retained their vertical stratigraphic relationships, there was some mixing of artifacts from different periods.…”

Biomantle formation and artifact translocation in upland sandy soils: An example from the Holly Springs National Forest, north‐central Mississippi, U.S.A.

“…4. If artifacts or other clasts of sufficient size are present, they may occur as a "stone line," a discrete layer of artifacts located at the base of the upper, wormdeposited stratum (Johnson, 1989(Johnson, , 1990Johnson and Watson-Stegner, 1990;. Given the generally homogeneous texture of soils in the study area, a simple rather than a two-layered or other complex biomantle (Johnson, 1990) is expected; the biomantle thus produced would be considered a faunalmantle (Johnson, 1990).…”

The good earthworm: How natural processes preserve upland Archaic archaeological sites of western Illinois, U.S.A.

“…Activities of pocket gophers, which excavate burrows about 6 cm in diameter, have received perhaps the most attention recently (Erlandson, 1984;Bocek, 1986;Johnson, 1989Johnson, , 1990Johnson and Watson-Stegner, 1990). Western North American gophers concentrate large artifacts (Ͼ6 cm) but mix up smaller materials throughout the upper biomantle.…”