Stability of phytoliths in the archaeological record: a dissolution study of modern and fossil phytoliths

Opaline phytoliths are important microfossils used in archaeological and ecological research. Relatively little is known about the stability of phytoliths after burial. Under alkaline pH conditions they can dissolve, and mechanical disturbances can cause a loss of their more delicate appendages. Here we present an experimental study of phytolith stability (combination of solubility and abrasion). Modern and fossil phytoliths were extracted from wheat using new methods to minimize dissolution, and by burning in an oven. These assemblages were placed in a solution buffered to pH 10 and maintained under constant temperature and shaking conditions. The silicon concentrations in the solution were monitored once a week for 5 weeks. The phytolith morphologies in each assemblage were determined at the outset of the experiment and after 5 weeks. The results show that there are differences in stability between various assemblages. Modern inflorescence wheat phytolith assemblages are more unstable than those from leaves/stems. Burnt assemblages are less stable than unburnt assemblages, and a fossil phytolith assemblage about 3000 years old is more stable than the modern wheat assemblages. The results also show that individual phytolith morphotypes have different stabilities, and as a result of dissolution and abrasion, some morphotypes may resemble others. This study further shows that archaeological and/or paleo-environmental interpretation of phytolith assemblages may change with the assemblage’s state of preservation.     

Use of space in a Neolithic village in Greece (Makri): phytolith analysis and comparison of phytolith assemblages from an ethnographic setting in the same area

Phytolith analyses were conducted in a Pottery Neolithic village (Makri) of Northern Greece in order to reconstruct aspects of past human activities as a function of both space and time. The analyses of phytolith assemblages were based on a reference collection of modern plant phytoliths (Tsartsidou et al., 2007), as well as an ethnographic study in an agropastoral community (Sarakini) in the same area that showed that many phytolith assemblages are characteristic of the activities carried out in different locations within and around the village (Tsartsidou et al., 2008). The same approach was used for studying the phytolith assemblages in the Neolithic village of Makri, namely measuring phytolith concentrations, diversities of phytolith assemblages relative to control samples collected from samples outside the village and detailed analysis of various phytolith morphotypes. At Makri samples from floors and various constructions (i.e. pit, platforms) were analysed, as well as sediments from an open area inside the village. The results show that Neolithic Makri was a society with a mixed agricultural and pastoral economy. Wheat and barley were cultivated for food and fodder and free-range animals were raised in a village inhabited year round. Indoor areas were not clearly differentiated from outdoor areas inside the village. The phytolith assemblages in only one series of floors produced at a specific location over an extended period of time reflected the use of that space for cereal storage or food processing. The phytolith assemblages from all the other floors examined did not reflect the local activities, but rather the constructional materials used for producing the floors.     

Late Holocene human impact on the vegetation around Mizorogaike Pond in northern Kyoto Basin,Japan: a comparison of pollen and charcoal records with archaeological and historical data

Pollen and macroscopic charcoal analyses of AMS radiocarbon-dated sediment from Mizorogaike Pond, located near Japan’s ancient capital established in AD 794, were used along with archaeological and historical data to reconstruct vegetation change in the northern Kyoto Basin since 7300 cal yr B.P. Between ca. 7300 and 3400 cal yr B.P. (Early to Late Jomon period), the site was surrounded by warm-temperate forest composed of Quercus subgenus Lepidobalanus and Q. subgenus Cyclobalanopsis with Celtis/Aphananthe trees. With the occurrence of fire disturbance, Q. subgenus Lepidobalanus increased from ca. 3400 to 1400 cal yr B.P. (Late Jomon to Kofun periods). In the early seventh century (Asuka period), Pinus started to increase, coinciding with a significant charcoal peak, probably related to the operation of roof tile kilns near the site. Pinus continued to increase and Q. subgenus Cyclobalanopsis decreased through the seventh to tenth centuries (Asuka to Heian periods). Further increase of Pinus occurred in the eleventh century, possibly reflecting the establishment of the manor of Kamigamo Shrine. From the eleventh to seventeenth centuries (Heian to medieval periods), no significant vegetational change or fire disturbance took place. In the eighteenth century, the landscape became totally open, with poor vegetation and sparse Pinus woodland. The medieval and early modern landscapes reconstructed from the palaeoecological record are rather similar to those described from studies of ancient artwork and historical documents. This study demonstrates that late Holocene vegetation change in the northern Kyoto Basin was closely tied to anthropogenic activities, such as the pottery industry and fuel wood collection.