THE APPLICATIONS OF MAGNETIC METHOD IN ARCHAEOLOGICAL INVESTIGATIONS OF LEJJA PREHISTORIC SITE IN ENUGU STATE, SOUTH- EASTERN NIGERIA
THE APPLICATIONS OF MAGNETIC METHOD IN ARCHAEOLOGICAL INVESTIGATIONS OF LEJJA PREHISTORIC SITE IN ENUGU STATE, SOUTH- EASTERN NIGERIA
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Date
2013-01
Authors
OGAH, AREWA JAMES
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Abstract
The search for historic evidence in Lejja has been conducted using data acquired from
sites measuring 2,160m2, 2,030m2 and 2,400m2 in Uwani, Ugbelenabo and Ejuona
villages respectively. The total magnetic field data and the vertical gradient of the total
field data were acquired simultaneously on a regular 1 m x 1 m grid using proton
precession magnetometer (Geometrics model G-856AX). The measured fields were
stored in the machine’s internal memory and directly downloaded into a digital
computer thereby avoiding transcription errors. The total field data were reduced using
polynomial fitting method for diurnal correction while regional-residual separation was
done using the golden software, surfer. This method of diurnal correction is one out of
the two modifications made (in the course of this study) to the existing method of land
magnetic data reduction. Integrated method of interpretation was deployed using Euler
deconvolution and analytic signal methods which were validated using synthetic fields.
The synthetic data were generated using Rao and Babu Algorithm. Both methods of
interpretation gave error margin of about ±5% with the synthetic data. Analysis of the
field data from the three sites revealed that some of the artefacts still remain in situ
while others have been displaced as revealed by the orientations of their anomalies. The
artefacts which include furnaces, slag blocks, blooms, tuyères, fired pits, etc., are
mostly found in Ejuona and Uwani villages located in south-eastern and the central
parts of the community respectively. Two types of smelting furnace are suspected.
These include a small type with diameter of about 1.0 metre or less mapped in Uwani,
and a large one with diameter between 1.2 and 1.5 metres also mapped in Ejuona. A
large mound of an estimated area of about 70 m2 has also been mapped in Ejuona
village. The spatial locations of the above ancient relics at the three sites have been
obtained. A few of the relics including fired pits and fired stones suspected at the
Ugbelenabo village can be found at shallow depths of between 0.62 m and 0.86 m. On
the other hand, the depth of burial of the artefacts at Uwani and Ejuona villages are
relatively greater than those of Ugbelenabo. The ranges are from 1.07 m to 2.09 m, and
from 1.08 m to 1.82 m in Uwani and Ejuona villages respectively. Due to small sizes of
the survey sites, longitude-latitude coordinates of only the origin of each site has been
indicated with surface locations of the artefacts measured from this point. Excavation
plans which can serve as bases for further studies have been drawn up for the three
locations surveyed. It is expected that successful execution of the latter will serve as an
encouragement for the practice of archaeological geophysics in the Lejja site and
beyond. In addition to the polynomial fitting method mentioned earlier, single step
approach of magnetic data reduction tagged, “Automatic Reduction of Magnetic Data
(ARMAD)”, was also introduced in the course of this study. The latter method bypasses
the conventional multi-stage method of magnetic data reduction
Description
Dissertation submitted to the School of Post Graduate Studies,
Ahmadu Bello University, Zaria
In partial fulfillment of the requirements for the Award of Degree of
Doctor of Philosophy in Applied Geophysics
Department of Physics, Faculty of Science
Ahmadu Bello University, Zaria, Nigeria
January, 2013
Keywords
APPLICATIONS,, MAGNETIC,, METHOD,, ARCHAEOLOGICAL,, INVESTIGATIONS,, LEJJA PREHISTORIC SITE,, ENUGU STATE,,, SOUTH- EASTERN NIGERIA