三峡库区二级阶地发现的东方剑齿象化石及其环境与考古学意义

Some Stegodon orientalis Fossils Discovered in the Second Terrace of the Three Gorges,Yangtze River

本文记述的象化石产自三峡库区长江右岸二级阶地。该二级阶地沉积物可分为两个沉积单元:由下部含化石的砂砾层和上部具乌木的土状堆积组成。显然,这些沉积物反映不同的古环境。据铀系法测定,下部沉积的年代约为距今6.4万年前,而上部堆积层的14C测年值为距今约8 000年。依二级阶地上、下层间呈不整合接触和测年数据,下部沉积之后曾有较长时间的沉积间断。下部埋藏阶地的砂砾石层被钙质胶结的现象表明,该地区在二级阶地形成后有一段气候干燥而寒冷的时期。迄今三峡库区已发现了55处旧石器地点,大多数位于二级阶地中,但缺乏化石和测年的可靠证据。这次埋藏阶地象化石的发现为三峡地区二级阶地的旧石器遗址提供了可资对比的地层和时代依据,对古人类在该地区生存行为演变的阐释及旧石器分期提供了重要参照。

Three pieces of molar of Stegodon orientalis were unearthed in a gravel layer of second terrace of the Yangtze River, near the village of Pujiacun, Wanxian county, Chongqi. The deposits of second terrace are composed of three layers, namely a clay layer on the top, a thin calcified layer in the middle and a gravel layer at the bottom. The molar of Stegodon orientalis from the gravel layer is dated by U-series method back to 64 000 ± 5 000 years BP. In addition, some ebony materials obtained from the clay layer are dated by Carbon 14 method back to 7 930 ± 90 years BP. Through analyzing the relationships of these layers, we draw a conclusion that the sandy gravel layer is actually the second terrace deposit covered by the clay deposit of the first terrace. In addition, the gravel layer partially cemented by calcium carbonate shows that there existed a period of cold and dry climate between the Late Pleistocene and the Early Holocene. These discoveries provide important information for the study of the formation and age of the lower terrace, the effect of the Neotectonic Movements, the Paleoclimate, etc.