THE SEARCH FOR THE ORIGIN OF BITUMEN EXCAVATED FROM ARCHAEOLOGICAL SITES IN THE NORTHERNMOST ISLAND IN JAPAN BY MEANS OF STATISTICAL ANALYSIS OF FI–MS DATA*

Abstract

The origin of bitumen excavated from archaeological sites in Hokkaido, the northernmost island in Japan, was sought by means of field‐ionization mass spectrometry (FI–MS) and gas chromatography – mass spectrometry (GC–MS) of the hydrocarbon components. The field‐ionization mass spectra were decomposed by Z‐numbers into several components, where the Z‐number refers to z in the formula C n H 2n+z . This is equivalent to the deficit number of H atoms, when compared to the corresponding saturated hydrocarbon, which is related to the number of saturated hydrocarbon rings in alkanes. By use of the spectral intensities of the seven alkane components in each sample, multiple discriminant analysis was employed for the data of raw bitumen samples and excavated samples from archaeological sites. Based on this method and the gas chromatogram type, the following bitumen trade in the prehistoric age of Japan was elucidated: bitumen from Niigata, one of the main sources on the main island of Japan, spread to the north in 2000 bc, probably via the coastal zone, and reached a small island near the north end of Hokkaido. Bitumen from Sakhalin reached the central lowland in Hokkaido, but it went no further. Bitumen from Akita, another main source on the main island, spread over northern Honshu much earlier and reached the Oshima peninsula, the southwestern part of Hokkaido. The Akita bitumen scattered into the central lowland after the Niigata and Sakhalin bitumen. This area is believed to be the place where people from the south and the north met in those periods.