甘肃秦安崖湾剖面新近纪哺乳动物化石及其生态环境特征

MAMMAL FOSSILS AND ECOLOGICAL ENVIRONMENT FEATURES OF THE NEOGENE FROM QIN'AN AREA,GANSU PROVINCE

甘肃东南部的天水盆地新近纪沉积十分发育,其中富含哺乳动物化石,自20世纪六、七十年代发现铲齿象等哺乳动物化石后,一直鲜有关于这一地区化石发现的报道。近几年,在对天水盆地北部秦安一带的新生代地层研究过程中。经过野外考察和测量,确认秦安县城西北部约15.5km郭嘉镇附近的崖湾剖面属于新近系沉积,其沉积地层大致可以划分为3段(共37层),并于第二段的23层(褐红色砂质泥岩层)和28层(褐红色粉砂质泥岩层)中发现了丰富的哺乳动物化石,经有关专家鉴定属于三趾马动物群,共包含有5目10科11属13种。其中上化石层(第28层)三趾马动物群主要代表性属种有Hipparion chiai,H.weihoense,H.fossatum,H.plocodus,Acerorhinus fuguensis,Chilotherium wimani,Ch.habereri,Chleuastochoerus stehlini,Palaeotragus microdon等,其化石组合时代大致与府谷喇嘛沟动物群和临夏盆地大深沟动物群相当,时代可能为保德期早期,相当于欧洲MN11。下化石层(第23层)哺乳类可能为晚中新世灞河期晚期,相当于欧洲MN10。由下本地区正好位于我国东部季风区向青藏高原区的过渡区,因此,崖湾剖面上化石层动物群代表了晚中新世华北三趾马动物群与青藏高原三趾马动物群之间过渡区域的三趾马动物群面貌,其化石组合特征反映出当时该区可能属于亚热带稀树草原的生态环境特征,气候相对较为适宜,是比较适合大型哺乳动物生存的。该区具有过渡性质三趾马动物群的发现,对于研究三趾马动物群在我国境内的分异与东西演化、确定该区地层年代以及古生态环境都具有重要的意义。

The Tianshui Basin at southeast Gansu preserved well developed Neogene strata,in which enclose rich mammal fossils. However,there are few reports on these fossils after the Platybelodon fauna were discovered during the 1960s and 1970s. For the last decades, we have carried out detailed investigation on the Neogene sequence around the Tianshui region and found that ~the Neogene deposits at Yanwan（ 105~34＇E,34~58＇N）, 15.5km northwestern to Qin＇an county in Tianshui Basin, contain abundant mammal fossils. The Yanwan section can be divided into three segments, including 37 layers according to sedimentary characteristics. Mammal fossils were excavated from layer 23rd and 28th,which is composed by red-brown sandy mudstone and silty mudstone respectively. Altogether, 13 species,belonging to 11 genera,10 families and 5 orders were identified,they all belong to the Hipparion fauna in Late Miocene. Thereinto, the upper fossils layer（ layer 28th）includes typical elements of that, such as Hipparion chiai, H. weihoense, H. fossatum, H. plocodus, Acerorhinus fuguensis, Chilotherium wimani, Ch. Habereri, Chleuastochoerus stehlini, Palaeotragus microdon,etc. The upper fossil assemblage of the Yanwan section is similar to that of the Lamagou fauna in Fugu, North China and Dashengou fauna in Linxia, suggesting a synchronous development of these three sites. The biozone of the upper assemblage can be correlated to early Baodean stage, corresponding to MN （European Neogene mammal zones）11, similarly,the lower（ layer 23rd）to Late Miocene upper Bahean stage,corresponding to the MN 10 in biochronology. Fossil assemblage features of Yanwan site suggest that the Tianshui region was dominated by subtropical savanna environment quite suitable for the inhabitation of large mammals. Situated at the transitional region from eastern monsoon region to Qinghai-Xizang Plateau region, the Yanwan fauna from upper fossil layer might be a representative Hipparion fauna site between North China and Qinghai-Xizang Plateau. Thus the fauna has important implications on the study of differentiation of Hipparion fauna in China continent,on regional stratigraphic correlation and paleoecological reconstruction as well.