汉水上游汉中盆地新发现的旧石器及其年代

2009~2012年,在秦岭南麓汉水上游汉中盆地梁山周围新发现何家梁和窑厂湾2处旷野类型旧石器地点,采集石制品252件。早期人类加工石制品的原料来自于河流堆积物中的石英、火山岩、石英岩、硅质灰岩和砂岩等砾石,采取硬锤直接打击法和砸击法剥片。石制品种类包含石锤、石核、石片、修理的工具和断块。工具类型以砍砸器、石球、重型刮削器、手斧和手镐等重型器物为主。汉中盆地梁山周围以龙岗寺等地点为代表的旧石器地点群是含阿舍利(Acheulian)类型器物的石器工业。何家梁和窑厂湾地点分别位于汉江右岸第二和第三级阶地上,通过对窑厂湾地点黄土地层剖面进行回授光释光(TTOSL)方法测年,结合古地磁测试和对比黄土高原标准黄土地层序列测年结果,证实汉中盆地古人类活动的时代最晚在60万年前就已经开始,而何家梁地点的地层测年数据则表明距今7、8万年左右存在另外一个古人类活动繁盛的阶段,早期人类在汉中盆地活动有较长的时间跨度。以前汉中盆地发现的旧石器地点没有独立的年代数据,极大地限制了学术界对其石器工业技术和人类行为的深入研究,这是首次获得的汉中盆地埋藏旧石器地点地层的独立年代数据,是对汉中盆地旧石器遗址年代学认识上的一大突破。本研究结合可靠的测年数据,分析石器组合及加工技术,对建立中更新世以来秦岭山区的旧石器文化序列,理解我国南北方旧石器工业的发展演化以及东西方旧石器工业技术比较具有重要的参考价值。

Newly Discovered Paleolithic Open-air Sites in Hanzhong Basin in Upper Valley of Hanjiang River and Their Ages

Two Paleolithic open-air sites were identified in the Hanzhong Basin and 252 stone artifacts were collected during 2009-2012 in the upper valley of Hanjiang River in the southern piedmont of the Qinling Mountains, central China. Fieldwork at the Hejialiang site and the Yaochangwan site was carried out in August 2010 and May 2011, with three additional visits in 2009 and 2012. The catchment of Hanjiang River is regarded as one of the most important place for hominin living in the recent geological time. The newly discovered stone artifacts distributed on the second and third terraces of the south bank of Hanjiang River at the piedmont of the Liangshan Mountain. The lithic assemblage analysis suggests that the stone artifacts were made of local raw materials of pebbles/cobbles which derived from the riverbank alluvial deposits of the Hanjiang River. The lithic samples from the Hejialiang site frequently made of quartz, Graywacke, and igneous rock, but infrequently made of quartzite and silicon limestone. The lithics of the Yaochangwan site more frequently made of quartz, quartzite and igneous rock, but infrequently made of sandstone and silicon limestone. The main percussion techniques used are direct hard hammer percussion and bi-polar techniques. The core and flake platforms are dominated by cortical surfaces. The lithic artifacts consist of hammer stones, cores, flakes, retouched tools and flaking debris. The retouched tools include choppers, spheroids, Hand-axes, picks, heavy-duty scrapers, small scrapers and point. Composition and technology of the lithic artifacts in the two sites share some common characteristics with Paleolithic open-air sites in the Ankang Basin, the Danjiang Reservoir areas in the lower valley of the Hanjiang River, and the Luonan Basin in the South Luo River, and the Bose Basin in south China. The Hejialiang section on the second terrace and the Yaochangwan section on the third terrace were sampled in detail. In the Hejialiang site, there is a thin eolian deposit with thickness of 5.2m covering on the fluvial sand, pebbles, and cobbles. An in situ flake was just found at the lower part of the unique paleosol layer in the Hejialiang section. In the Yaochangwan site, distinct loess and paleosol alternations are present on the third river terrace with a thickness of more than 15m. From this loess-paleosol sequence, five loess units and five paleosol complexes can be identified. Two in situ flakes were found in the fifth paleosol layer at a depth of 14m. Two samples at Hejialiang section and five samples at the Yaochangwan section were collected for TT-OSL (Thermally transferred optically stimulated luminescence) dating. The TT-OSL is a newly developed dating technique which probably extends the dating range of quartz samples to middle and early Pleistocene. The TT-OSL signal has a saturation limit at least an order of magnitude higher than the fast component of the conventional OSL signal. The TT-OSL signal is measured after the depletion of the conventional OSL signal and a subsequent pre-heat, which is applied to induce the thermal transfer of charge. All of these measurements are carried out in the OSL Laboratory of Nanjing University. The results suggest that the buried lithic artifacts layer at the Hejialiang site is approximately correlated with the last interglacial paleosol S1 in Chinese Loess Plateau, it is dated from 80ka to 70ka BP. The Yaochangwan site spans approximate from 600ka to 100ka and correlates with S5-S1 in the typical Chinese loess paleosol sequences, respectively. These ages suggest that hominin already occupied the Hanzhong Basin from approximately 600ka BP, and during from 80ka to 70ka BP was another time for hominin occupied this basin.