Land-use change for rice and foxtail millet cultivation in the Chengtoushan site,central China,reconstructed from weed seed assemblages

Archaeobotanical analysis of moat sediments from the Neolithic site of Chengtoushan, Hunan, China, provides evidence of the land-use change for rice and foxtail millet cultivation around the site. Rice constantly appeared through the three phases of Daxi culture with high percentages, while accompanying wetland species of paddy field weeds gradually decreased. In contrast, foxtail millet increased together with upland field and ruderal weeds through the time. These changes suggest that foxtail millet cultivation was established with the expansion of dry farming in region of the site, while rice cultivation was continuously practiced on the alluvial plain surrounding the site. This diversification of land-use through the addition of foxtail millet cultivation may be attributed to population increase or as a buffer to natural disasters such as flooding. In addition, gathering of wild nuts and fruits continued alongside cultivation. These multiple strategies for food procurement provided sustainable food supply for the population of Chengtoushan for 1,800 years.     

Thermoluminescence age of quartz xenocrysts in basaltic lava from Oninomi monogenetic volcano, northern Kyushu, Japan

We determined the eruption age of basaltic rocks by application of thermoluminescence (TL) method, which is often used for TL dating, to quartz. Mafic magma only rarely includes quartz because of their mutual disequilibration. The basaltic lavas reported herein include quartz as xenocrysts, as corroborated by their rounded or anhedral shape. The basaltic lava used for this study is from the Oninomi monogenetic volcano in northern Kyushu, Japan. The volcano eruption was estimated as occurring 7.3–29 ka because the lava exists between two widespread tephras: Aira-Tanzawa ash (26–29 ka) and Kikai-Akahoya ash (7.3 ka). We succeed-ed in collecting ca. 200 mg of quartz by decomposition of 30 kg of the lava samples. TL measurements for the lava indicate the eruption age as 15.8 ± 2.5 ka, which is fairly consistent with the stratigraphical estimation. Although the TL method has played a considerable part in constraining the timescale of Quaternary events, its application has been limited to silicic samples. The present result demonstrates the availability of quartz for dating even of mafic rock.