POTENTIAL MAGNETIC SUSCEPTIBILITY AND FRACTIONAL CONVERSION STUDIES OF ARCHAEOLOGICAL SOILS AND SEDIMENTS*

Potential magnetic susceptibility (χ_MAX) and, hence, fractional conversion (χ_CONV) are shown to be critical in interpreting low‐frequency mass‐specific magnetic susceptibility (χ_LF) data. Results presented from 29 sites in the UK and one in Hungary encompass six types of investigation: Quaternary sedimentary stratigraphies, archaeological contexts, surveys of old ground surfaces, topsoil surveys of lithic scatter sites, topsoil prospection surveys and ‘natural’ topsoils. The findings highlight the wide range of χ_MAX values that may be encountered; identify factors affecting χ_MAX; demonstrate that χ_CONV provides a measure of enhancement resulting from burning; and identify environments in which χ_LF analysis is likely to be problematic.     

MAGNETIC SUSCEPTIBILITY VARIATIONS AT MONS CLAUDIANUS AND IN ROMAN COLUMNS: A METHOD OF PROVENANCING TO WITHIN A SINGLE QUARRY

Mons Claudianus in the Eastern Desert of Egypt was an important source of granodiorite for Roman columns. Computer contouring of 1119 magnetic susceptibility measurements at the quarry shows systematic variations, with low readings in the west of the quarry area and higher readings in the east. One hundred and seventy measurements on 62 columns of Mons Claudianus type in Rome and its environs were compared with the quarry readings, using a t-test based procedure. Some columns with distinctively low or high magnetic susceptibility could be provenanced very precisely to areas of about 700 × 700m within the 9km² of Mons Claudianus. Columns with susceptibility in the middle of the Mons Claudianus range could not be provenanced precisely. Results indicate early (first century AD) use of both west and east parts of Mons Claudianus, and contemporaneous use of several parts of the quarry, rather than systematic or sequential opening of the area. Columns found in third-century AD monuments, provenanced to the same parts of Mons Claudianus as earlier material, may indicate reuse of columns in some monuments. Magnetic susceptibility constitutes a portable and non-destructive method capable of provenancing not only to a quarry, but to specific areas within a single quarry.     

NUCLEAR MAGNETIC RESONANCE CHARACTERIZATION OF CRETACEOUS AMBER

Carbon-13 nuclear magnetic resonance spectra have been examined under high resolution conditions for 31 samples of fossil resin that have been dated to the Cretaceous period. Samples from Alaska, Canada, parts of the United States, Greenland, France, Switzerland, Lebanon, Jordan, and Israel have very similar spectra, consistent with a common, geographically dispersed palaeobotanical source. Samples within this large group exhibit a variation in spectral linewidth that is consistent with differences in sample age or maturity. A single Triassic sample from Bavaria shows the same spectral patterns but greater linewidths, indicating that it probably had a similar palaeobotanical source.     

A COMPARISON OF INVERSE FILTERING AND MULTIPLE SOURCE WERNER DECONVOLUTION FOR MODEL ARCHAEOLOGICAL PROBLEMS

Inverse filtering and multiple source Werner deconvolution are tested on synthetic data produced by models which simulate features that occur commonly in archaeological exploration. Inverse filtering produces patterns which reflect the magnetization and lateral extent of the subterranean bodies and which are located at their centres. Multiple source Werner deconvolution locates the corners of the bodies with adequate accuracy. Both schemes can provide significant aid in interpreting magnetic data acquired for archaeological exploration.     

THE ROMANESQUE FRIEZE AT LINCOLN CATHEDRAL (ENGLAND)—PRIMARY OR SECONDARY INSERTION? MAGNETIC CONSIDERATIONS*

The current debate about the age of the Romanesque frieze of Lincoln Cathedral weighs archaeological evidence against art history. On the one hand, the panels appear to be an integral part of the original Norman structure built by the first bishop (AD 1072–92). However, on grounds of style and artistic comparisons, art historians argue for a later installation during the restoration of AD 1141–6. In order to determine when the panels were stabilized in the cathedral, we used a new method that measures their degree of remagnetization by the earth's magnetic field since they were quarried. The longer that masonry remains stabilized in a given orientation, the greater its viscous remagnetization. Viscous remanent magnetization dating has previously been successful with this particular type of limestone masonry. Our results lend support to the view that the panels were installed in the early 1140s.     

DISTINGUISHING AMBER AND COPAL CLASSES BY PROTON MAGNETIC RESONANCE SPECTROSCOPY

Fossilized resin, or amber, has been examined from 120 worldwide sources by 1D and 2D proton magnetic resonance spectroscopy in solution. These spectra fall into five categories, corresponding to the classes already established by mass spectrometry and carbon‐13 magnetic resonance spectroscopy. The wide availability of this technique provides a straightforward method to classify amber rapidly and inexpensively.     

ELECTRON SPIN RESONANCE STUDY OF PAPER SAMPLES DATING FROM THE FIFTEENTH TO THE EIGHTEENTH CENTURY

Electron paramagnetic resonance spectroscopy is used to detect paramagnetic impurities in differently degraded antique sheets of unprinted paper. Impurities consist primarily of transition metal ions (Fe³⁺, Mn²⁺, Cu²⁺) present in different environments and symmetries. Organic radicals, common in modern, wood pulp paper, are absent in these antique samples made from rags. Fe³⁺ is the largest impurity (from 300 to 700 ppm). Mn²⁺ is also present but its concentration does not exceed 50ppm. Cu²⁺ has been detected in about one-third of the samples. Coupled with nuclear magnetic resonance data, these results describe degradation as an hydrolytic process leading to a net increase of amorphous cellulose and to a decrease of bound water. Copper and rhombic iron appear to act as efficient degradation catalysts, whereas the presence of octahedral iron is almost irrelevant.     

THE PROVENANCE AND COAL RANK OF JET BY CARBON-13 NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

The carbon-13 nuclear magnetic resonance spectra of jet samples from England and Spain resemble those of carbonaceous materials from lignitic and sub-bituminous ranks. This characterization is based on the aromatic/aliphatic ratio of resonances and on the pattern of fine structure. Particularly characteristic of jet is the well-defined fine structure in the aromatic region that may be attributed to phenolic functionalities. This fine structure is found in all English and Spanish samples. Resonances from rapidly moving methyl groups are found in English but not in Spanish samples and may provide a means of distinguishing provenance.