Ball, Stephen (Glenn A. Black Laboratory of Archaeology, Indiana University,
Bloomington)
EFFECTIVENESS OF GEOPHYSICAL TECHNIQUES IN DETECTING CERTAIN
CLASSES OF ARCHAEOLOGICAL MATERIAL
The relative effectiveness of magnetic surveys in detecting different classes
of cultural material was evaluated with the excavation results from the Clampitt
site (12 Lr 329). The Clampitt site, a late prehistoric Oliver phase village located
on the East Fork of the White River in Lawrence county, Indiana, was excavated
in 1991 and 1992 with support from the Indiana Historical Society, the Glenn A.
Black Laboratory of Archaeology, and the Department of Anthropology, Indiana University.
A 20 meter by 160 meter magnetic survey was conducted over the site in the spring
of 1991 with a Geoscan FM36 gradiometer prior to the 1991 excavation. Information
from that survey was incorporated into the excavation strategy used in 1991. The
gradiometer successfully detected sub-surface pits rich in cultural materials,
but was unsuccessful in the detection of a stockade trench that surrounded the
village and pits that contained low densities of cultural material.
A SAS regression analysis was performed to determine what material or combination
of materials were primarily responsible for the strength of the magnetic signal
emanating from the detected features. Cultural materials recovered from these
features, and included in the analysis, were pottery, fire- cracked rock, chert
(much of which was heat-treated), and limestone. The results of the analysis are
summarized in Table 1.
The regression analysis indicated that pottery was the only significant source
of a feature's magnetic field strength. This agreed with a direct comparison of
pottery weights between those features detected by the magnetic survey and those
that were overlooked (see Table 2). Feature 3 was problematical; it had less of
all classes of cultural materials than did its neighbor, Feature 6, which was
not detected by the magnetic survey (see Figure
11). The only unique material recovered from Feature 3 was an intact geode
found in the northern half of the pit. The geode was analyzed and found to have
iron oxide inclusions located in cracks in its crust, which were the source of
its higher magnetic susceptibility. The low amount of iron oxides in the other
local rocks appears to explain their lack of significance in a feature's magnetic
field strength. These results have implications for the future use of magnetic
surveys on aceramic sites in south-central Indiana.
TABLE 1: ANALYSIS OF VARIANCE
Sum of Mean
Source DF Squares Square FValue Prob>F
-------------------------------------------------------------------
Model 4 8704.93154 2176.23288 7.817 0.0614
Error 3 835.19721 278.39907
C Total 7 9540.12875
Root MSE 16.68530 R-square 0.9125
Dep Mean 42.91250 Adj R-sq 0.7957
C.V. 38.88213
Parameter Estimates
Parameter Standard T for H0:
Variable DF Estimate Error Parameter=0 Prob > |T|
---------------------------------------------------------------------------
INTERCEP 1 14.743221 11.90202399 1.239 0.3035
POT 1 0.025794 0.00691353 3.731 0.0336
CHERT 1 0.001579 0.02316588 0.068 0.9499
FCR 1 -0.012625 0.04229773 -0.298 0.7848
LIME 1 0.023262 0.05225092 0.445 0.6863
Variable DF Tolerance
----------------------------------
INTERCEP 1 -
POT 1 0.43930128
CHERT 1 0.66423466
FCR 1 0.09238805
LIME 1 0.11318376
TABLE 2: AMOUNT OF POTTERY RECOVERED IN EACH FEATURE
UNDETECTED FEATURES DETECTED FEATURES
GRAMS FEATURE NUMBER GRAMS FEATURE NUMBER
------- ---------------- ------- ---------------
0 33,36,42,43,44,46,58 17 3
1 35,42 159 31
4 34 400 2
23 56 473 49
85 6 499 1
544 32
1992 30
4083 27
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