The Stratum, Age And Geographical Environment Of Houjiayao Relic Site

Houjiayao Relic Site is one of the most important Paleolithic sites both in local and international, which plays a significant role on human evolution in North China. Since the Houjiayao Site has been excavated in 1974, archaeologists have founded a lot of stoneworks, bone ware, ancient human and mammal fossils, which significantly distinguish the site from other sites. Currently, the Houjiayao Site has become one of the Paleolithic sites with a high comprehensive research level in China. How long did the ancient Houjiayao man live in Nihewan Basin? How did they adapt the changing natural environment? And how did the changing natural affect the living situation and culture of the ancient Houjiayao man? To study and solve these problems would be significant to investigating the origin of oriental human, to the origin, dispersal and evolution of modern Homo sapiens.In this study, we presented a comprehensive research of a 15 meter thickness profile in the Houjiayao Relic Site(Point 74093). Based on the analysis of 11 OSL dating, 294 pollen, 323 grain-size and 323 magnetic susceptibility samples, we have determined the stratum genesis, geological age, quantitatively reconstructd the history of temperature and precipitation changes of the Houjiayao Site by using MAT method(Modern Analogue Technique, MAT) on the basis of East Asian Pollen Dataset, revealed the history of vegetation evolution by using BIOME method, and restored the living conditions of ancient Houjiayao man.The results and conclusions obtained are as follows:(1) Field observation and grain size analysis results suggested that the bottom Houjiayao cultural layer were main consisted of silty clay, black peat and gray silty lenticel, indicated a stagnant, reducing sedimentary environment. Combined with the development and distribution evidence of ancient rivers, we speculate that the lower cultural layer of Houjiayao Relic Site belongs to oxbow lake deposition which was formed by a water-cannel appeared during the ancient Nihewan lake shrinking and disappearing, and clogged by a NNW-SSE ancient river.(2) Paleontological evidence showed that the ancient Houjiayao man was strongly characterized by the transition from the Homo erectus to early Homo sapiens, and a kind of transitional type from Homo erectus pekinensis to Homo sapiens neanderthalensis. The lithic culture of Houjiayao man belongs to “Small Tool Tradition” in North China, which is an important link of Peking Culture to Shiyu Culture. Mammal assemblages and pollen assemblages indicated that the upper cultural layer of Houjiayao Relic Site was formed between middle Pleistocene to late Pleistocene. OSL dating results suggested that the Houjiayao Relic Site was formed during 240 ka B.P. to 130 ka B.P.: the lower cultural layer formed from 240 ka B.P. to 190 ka B.P., corresponding to marine isotope stage(MIS) 7; the upper cultural layer was formed from 190 to 130 ka B.P., corresponding to MIS 6; the fluvial layers were deposited by rivers’ filler, which were formed from 130 ka B.P. to 80 ka B.P., corresponding to MIS 5.(3) Pollen data revealed that the study area has experienced twice warming and cooling cycles: the climate was extreme cold in Nihewan layer, the mean annual temperature(TANN), the mean temperature of the warmest month(MTWA) and the mean temperature of the coldest month(MTCO) was 2 ℃, 16 ℃ and 14 ℃, respectively; The annual precipitation(PANN) is about 400 mm to 600 mm; the surrounding vegetation was mainly cold coniferous trees(mainly spruces and pines). In the lower cultural layer(240 ka B.P. to 190 ka B.P.), the climate was temperate, TANN, MTWA and MTCO were all showed an evident increasing trend, each of them reached 4℃ to 6℃, 19 to 22℃ and-14℃ to-10℃, respectively; The PANN was maintained at around 400 mm to 500 mm; The zonal vegetation was forest and steppe. In the upper cultural layer(190 ka B.P. to 130 ka B.P.), the PANN increased dramatically; TANN and MTCO had dropped 2℃ and-16℃, respectively, whereas MTWA was relative steady, indicated a cold and wet climatic condition; And a mixed coniferous and broad-leaved forest dominated by pines and spruces might have developed around the site. In the fluvial layers(130 ka B.P. to 80 ka B.P.), the study area showed a warming trend; During the early stages, PANN was about 400 mm, and then it increased, which indicated a warm and wet climatic condition; The vegetation landscape was mixed warm coniferous and broad-leaved forest and steppe. The result of BIOME analysis was similar to vegetation typed that analyzed by pollen assemblage and each result can be validated with the others.(4) The climate change history of Houjiayao Relic Site was accordant with mid-low latitude regions in North Hemisphere. And we speculated that earth’s orbit forced insolation was the dominant contributor to climate change in study area.(5) Favorable geomorphology conditions, abundantanimal resources and stone materials protected the continuation of Houjiayao Culture in cold MIS 6 stage, it suggested that cold climate conditions didn’t lead to the extinction of Houjiayao Human, but promoted the progress of Houjiayao culture to a certain extent.