武蔵野-多摩-鶴見地域における縄文時代錘具の分布評価 : GISで考古遺物の性格を読み解く

縄文遺跡から出土する石錘・土錘は,多くの場合漁網錘として解釈されるが,他にも釣り用の錘や独木舟の碇,編物用の錘など,さまざまな用途が提案されており,決着をみていない。このような問題をふまえ,本稿では,武蔵野台地・下末吉台地および多摩丘陵において縄文時代錘具および錘具出土遺跡の全数調査を実施した結果に基づいて,地理情報システム(GIS)を用いて報告点数・器種・コンテクスト・重量など錘具の諸属性をマッピングし,錘具の出土した「空間」の特性を人間活動の「場所」として評価することによって,その「場所」で用いられた錘具という考古遺物の性格ならびに用途を再検討する。分析の結果,(1)錘具は古東京湾岸と多摩川下流左岸・野川一帯に集中しつつ,武蔵野台地や多摩丘陵にスポット状に分布する傾向があることと,(2)縄文中期中葉の勝坂II式期より中期後葉の加曽利EIII式期にかけて土器片錘が爆発的に普及すること,(3)海岸ゾーンに近づくほど土器片錘の比率が増し,遠ざかるほど石錘の比率が増すこと,(4)中期中葉には東京湾に近づくほど阿玉台式土器片錘の比率が高まること,(5)後期に切目石錘の比率が高まり,晩期には切目石錘・有溝石錘・有溝土錘を主体とした器種構成になること,(6)石錘の方が土錘よりも重い資料が多いが全体としては両器種ともよく似た重量分布を示すこと,そして(7)土錘・石錘ともに包含層・住居趾からの出土を基本としながら低湿地の水成堆積層からも出土することなどが明らかになった。これらの現象を総合的に考察すると,縄文時代の錘具は,打欠石錘も含めて,一般的には漁網の沈子として用いられ,300gを超える大型石錘も水域での活動に用いられた可能性が高いと結論することができる。Stone/clay sinkers are recovered from a number of Jomon (the Japanese Neolithic hunter-gatherer culture) sites. These objects have been usually interpreted as fishing net sinkers. However, this issue is still under debate because other purposes, such as angling sinker, kayak anchor, or weaving weight, are also suggested. Using the Geographical Information System (GIS), this paper aims at identifying the applications of Jomon sinkers by a series of spatial analyses of the dataset from certain areas in East Japan, namely, the Musashino Upland and Tama Hills, located in Tokyo Metropolis and the northeast part of Kanagawa Prefecture (Fig.2). This research project consists of several methodological steps. First, a large dataset of approximately 4, 100 Jomon sites and 3, 800 stone/clay sinkers in the study area are integrated into the GIS-compatible database (Fig.1, Tables 1-3; see also Appendix). Second, some important archaeological attributes of sinkers-number yielded, assemblage, spatial and temporal context, and weight-are displayed as a variety of dot maps, pie charts, or histograms on the GIS interface. By interpreting the spatial patterns from these maps, the nature of the "space" in which sinkers are discovered is evaluated as a "place" of human activity. As a result of the GIS-based spatial analysis, the following patterns are pointed out : (1) High-density clusters of sinker sites are identified in the Paleo-Tokyo Bay area, the left bank of the Tama River Valley, and its tributary, Nogawa (Fig.4); (2) ceramic sinkers become predominant from the middle (Katsusaka II) to later (Kasori-E III) phase of the Middle Jomon period (Figs.5-12; Tables 4 and 5); (3) the percentage of ceramic sinkers in the assemblage per site is higher in the coastal zone (Fig. 13); (4) in the middle phase of the Middle Jomon period, the percentage of Atamadai type ceramic sinkers is more significant in the bay area (Fig. 14); (5) in the Late Jomon period, the percentage of incised stone sinker increases, and in the Final stage, the assemblage includes a wide variety of sinker repertoire such as incised stone, grooved stone, and grooved clay type (Tables 4 and 5); (6) the comparative weight statistics of stone and clay sinkers indicate that stone sinkers are heavier than their clay counterparts with regard to their mean and median values (Figs. 15-17; Table 6); (7) although these sinkers are mainly recovered from fill deposits and house fills/floors, a significant number of them are also found in the alluvial deposits in the low wetland sites (Fig. 18 and Table 7). The holistic interpretation of these archaeological patterns enables us to conclude that Jomon sinkers including both stone and clay subtypes are highly likely to be used as fishing net sinkers, with the except ion of the heavy (300 g and more) tools from several sites, which should be used for other purposes related to fishing. This study also demonstrates that the GIS is a rather effective toolkit for analyzing spatial patterns of archaeological objects