石家庄地区早全新世冷湿气候的牙齿微磨痕和同位素证据

COLD AND/OR WET EARLY HOLOCENE IN SHIJIAZHUANG DISTRICT: EVIDENCES FROM TOOTH MICROWEAR AND STABLE ISOTOPE ANALYSES

早全新世11~8kaB.P.是末次盛冰期之后全球经历的第一个温暖期,研究表明该时期华北气候温暖湿润,但在8.2kaB.P.华北对全球冷事件的响应没有相关报道。本文通过^(14)C测年和冲刷事件对比手段确定石家庄河床沉积中的诺氏古菱齿象(Palaeoloxodon naumanni)-披毛犀(Coelodonta antiquitatis)动物群生活在8.2kaB.P.时期。对来源于石家庄市郊区砂砾石层中的5件成年古菱齿象牙釉质样品进行了XRD粉末衍射、碳氧同位素和牙齿微磨痕分析。结果表明,牙齿XRD粉末衍射模式与现生大象相似,说明未受到地下水的影响;碳同位素分析表明早全新世华北东部为森林草原环境;极低的氧同位素值说明当时气候寒冷或湿润,地层中的针叶林茎杆和披毛犀化石也说明气候的寒冷;石家庄地区古菱齿象的凹坑痕出现频率极低,长条痕缺乏纤细类型。这种模式说明石家庄地区的古菱齿象以木质茎秆(55%)和草(45%)为食,而湿润季节以草为食是大象的特点,当时的石家庄是气候寒冷或湿润的针叶林草原环境。

A Palaeoloxodon naumanni-Coelodonta antiquitatis fauna and many fossil conifers were unearthed in sandstones from an alluvial deposit in Shijiazhuang,the capital city of Hebei Province, North China. The sequence （38°08＇N, 114°29＇E） can be divided into three layers：The lower one（ Q4^al1） ,with a depth varying between 1.5m and 6.0m, is mainly composed of pebble, sand and coal silt, which could be removed from coal strata （a coal erosion） and refilled in the pebble gap. A possible correlation is equivalent to a loess erosion event, which took place during 9000 - 8800aB. P. in Nanguanzhuang （34°27＇N, 107°46＇E） , about 120km in the northwest of Xi＇an ; The middle layer（Q1^al2）,with a depth varying between 5m and 17m,is composed of 7 cycles of sequence with particles from pebble size to sand,and the fossil mammals located at the second cycle, and are 30cm depth below the fossil conifers, a 814C age date from the conifers is 8150＋120aB. P., and the age of the sequence containing Palaeoloxodon-Coelodonta fauna can be deduced as about 8200aB. P. ; The upper layer（ Q4^p13 ） as pluvial sediments, with a depth varying between 2m and 30m,is composed of fine sand and silt. X-ray diffraction, isotopes＇ composition, and microwear analyses of 5 molars from various individuals （P. naurnanni）were used to reconstruct the climate event during 8.2kaB. P. There is a good agreement between the XRD pattern of the dental enamel of P. naumanni and that of extant Elephas maximus, suggesting that no underground water influenced the fossil dental enamel. Lower values of the oxygen（813OpDB = （--7. 730±0. 314）%0, n = 5） suggest a cold and/or wet condition,and the existence of fossil conifer and Coelodonta in the same sequence also shows a cold climate. The carbon values（ with a mean 813CpoB = （ -5. 760±0. 4459） %o, n = 5, varying between -5. 358%0 and -6.463%0）suggest a forest steppe zone in the Northeast China during the global cold period of 8.2kaB. P. The pit frequencies of P. naumanni from Shijiazhuang is lower than those of extant ungulates and proboscideans, and the scratch frequencies of P. naumanni is equal to those of extant mixed ungulates, and farther lower than those of proboscideans. Hypercoarse scratches on enamel surface wiped the earlier pits and coarse scraches,and lowered the earlier scraches frequencies. This pattern suggests that the P. naumanni feeds on hard objects such as bark and grass. Grasses eaten may increase during more humid periods. So it is a cold and/or wet forest steppe in Early Holocene in Shijiazhuang.