北京斋堂东胡林全新世早期遗址的黄土剖面

The Early Holocene Loess Section in the Donghulin Site near Zhaitang in Beijing

门头沟斋堂东胡林遗址是目前北京地区发现的最早且内涵最丰富的新石器早期遗址(9281±120～8270±60 a BP)。该遗址的黄土剖面清晰,包含了晚更新世及早全新世的黄土堆积、全新世早期的沉积间断及埋藏古土壤。在相对精确的^(14)C年龄时间框架下,本文对保存该遗址的黄土剖面的分层、黄土的粒度特征、矿物成分、化学成分、孢粉图谱及蜗牛的相对丰度进行了研究。分析表明本地区晚更新世气候比较干冷,气候的明显转暖应在全新世早期(早于9281±120 a BP),在约8500 a BP华北地区的年均温度可能已达到比现在高约2～3℃左右的状况。正是在这样的环境背景下,山顶洞人的后裔们,在清水河畔的阶地上开始了全新的生活。

The Donghulin site near Zhaitang in Mentougou District is the oldest of the early Neolithic age (9281 ± 120 to 8270 ± 60 a BP) ever discovered in Beijing, where very diverse cultural relics have been found. The loess sec- tion in this site is well exposed at the Fenpo gully west of the village. The whole section is 788 cm in thickness, and makes up the second-order terrace. It contains strata ranging from the late Pleistocene to the early Holocene, which are embedded by several layers of buried soil. Within an accurate 14C timing framework, this paper presents a study and analysis of the stratigraphic divisions of the section, as well as the grain size, mineral and chemical compositions, spore and pollen spectrum, and terrestrial snail abundance and diversity. The sec-tion may be divided by the Pleistocene/Holocene unconformity into two parts. The lower part is made up of late Pleistocene loess-like accumulation of talus-flowing water origin, with angular and poorly sorted gravels and lithic clasts. The upper part consists of Holocene loess accumulation, with a brownish red buried soil layer. Ne-olithic materials have been found below the soil layer. There are fluvial conglomerates between the late Pleis-tocene and the Holocene seen toward the gully mouth. Lithologically, the grain size of all the samples is charac-terized by a unimodal distribution pattern, with the peak at 5-6φ, which is identical with that in most Loess Plateau regions, i. e. , coarse silts are the dominant component. Mineralogically, quartz and feldspar contents are higher in the lower part than in the upper part, whereas clay mineral contents are higher in the upper part than in the lower part. Calcium carbonates are mainly of secondary origin, and their abundance is characterized by a distinctive alteration pattern in the Holocene. Similarly, the Fe2O3/FeO ratios in the late Pleistocene and early Holocene change in a pattern of low-high values, suggesting alternating cool-warm environmental condi-tions.Three sporopollen assemblages have been recognized from bottom to top in the section. (1) The late Pleis-tocene is characterized by high contents of herbaceous pollen of the Chenopodiaceae and Artemisia; ( 2 ) Pollen of woody plants becomes more abundant in the early Holocene, with high contents of Pinus and Quercus pollen; (3) Pollen contents of woody plants decrease and herbaceous pollen contents increase, with Gramineae and the Leguminosae becoming predominant. The three assemblages indicate a trend from temperate-cool to warm-wet, and to dry conditions. The gastropod fauna in the Donghulin Holocene interval is characterized by eurytopic snails of the North China taxa, including Cochlicopa lubrica, Cathaica pulreraticula, Pupilla cryptodon grandis etc. The abundance and diversity of snails indicate that the early Holocene was characterized by warm and wet conditions, with intermittent dry and cool climates. It may be deduced from the above lithologic, sporopollen, and snail data that it was relatively dry and cold in the late Pleistocene in the study area. The time interval when the climate became distinctly warmer should be the early Holocene (earlier than 9281 ± 120 a BP). In ad-dition , the gastropod Neritina violacea shells have been found being used as shell beads of the Donghulin neck-lace associated with a woman skeleton around 8540 a BP. The gastropod is at present distributed only in the subtropical to tropical regions, e. g. , the Zhejiang coast and the Philippines. This suggests that the climate around 8540 a BP was probably much warmer than that today in the North China region, with an average an-nual temperature about 2~3℃ higher, and also suggests a strong summer monsoon influence. It is in such en-vironmental conditions that the descendants of the ' Upper Cave Man' began a new life on the terrace along the Qingshui River.