High-precision U-series dating of Locality 1 at Zhoukoudian, China

Thermal ionization mass spectrometric(230)Th/(234)U dating has been carried out on intercalated speleothem samples from the limestone cave occupied by Homo erectus at Zhoukoudian, China. The samples were recently collected in proper stratigraphic context after detailed field examinations. The results show that the age of the No. 5 Skull from Layer 3 is >400 ka, possibly in the range of about 400-500 ka, and that the hominid fossils from the lower strata are at least 600 ka and possibly >800 ka, much older than previously thought. The near-equilibrium(230)Th/(234)U ratios and internal consistency of the dates and stratigraphy lend credence to the results and allow us to comment on their important implications for human evolution.     

Evolutional process and depositional cycles of Peking Man Cave in relation to the living environments and cultural development of Peking Man

Evolutional process of the Peking Man Cave, from funnel and vertical channel development in the Early Pliocene to the cave close in the late Middle Pleistocene, may be divided into six stages. Cave deposits in filling process of the cave from Layer 13 to Layer 1 can be divided into seven depositional cycles. These cycles allow a correspond with the loess sequences S7-L2 in China and oxygen isotope stages 19-6 of climatic cycles I-C of deep sea records. The living environments and cultural development of Peking Man in closely related to the cave environments of each stage in evolutional process and each cycle in depositional process of the cave are researched in this paper. The cave evolutional process has gone through about 4 Ma. The Peking Man start entered into the cave and made stone implements before 580 ka B.P. The cultural development of Peking Man may be divided into the early, middle and late three stages about in 580–420 ka, 420–340 ka and 340–250 ka, respectively. Peking Man's first used fire is about 530 ka B.P. Habitation of Peking Man concetrated in the western part of the cave after 340 ka B.P. when eastern cave roof was collapsed. Peking Man left the cave after 250 ka B.P. during the cave was continuous collapsed and almost filled up.     

Optical dating of dune sands in the northeastern deserts of China

Optical dating has been used to obtain the ages of fossil-stabilized sand dunes from four sections in the northeastern deserts of China. Our results indicate that the optically stimulated luminescence ages of the four sections correlate well, even though the samples were collected from different deserts about 600 km apart. Our results also indicate that active dune formation in this region lasted from the Last Glacial Maximum to about 10 ka, and that the warm climate of the Holocene was interrupted by a cold/dry dune formation episode about 3.5-1.7 ka. The Holocene Optimum in this region is between 10 and 3.6 ka, and a later warm/humid dune stabilization phase lasted from at least 1.6 to 1.0 ka. The youngest age on the uppermost sand unit yielded an age of only 40 yr, supporting the previous argument that the existence of modern active eolian sands in the regions with a mean annual precipitation of up to 450 mm is not mainly due to drought, but to extensive land cultivation over historic time. From the luminescence properties of the quartz grains, it is hypothesized that the sands in most of the sections are probably derived from more than one source, with a minor source of quartz having a different thermal history before deposition.     

Uranium-series ages of marine terraces,La Paz Peninsula,Baja California Sur,Mexico

Uranium-series dating of coral samples from raised marine terrace deposits between 1.5 and 10 m above sea level in the La Paz Peninsula area, Baja California Sur, yielded ages between 123 ka and 138 ka that are in agreement with previously reported results. The stratigraphy and ages of marine units near the El Coyote Arroyo indicate the presence of two high stands of the sea during the last interglacial or oxygen isotope substage 5e at about 140 ka and 123 ka. Accepting 5 m for the sea level during the last interglacial transgression, we calculate average uplift rates for the marine terraces of about 70 mm/ka and 40 mm/ka. These slow rates of uplift indicate a relative stability of the La Paz peninsula area for the past 140 000 years. In contrast, areas of Baja California affected by major faultf experienced higher rates of uplift. Rockwell et al. (1987) reported vertical uplift rates of 180 to 300 mm/ka at Punta Banda within the Aqua Blanea fault zone in northern Baja California.     

New High Resolution Pollen Records from Two Lakes in Xizang (Tibet)

Studies on the pollen from cores of Lake Hidden (29~48.77' N, 92~22.37' E) and Ren Co (30%3.97'N, 96~40.97'E) in Southeast Xizang (Tibet) showed climatic changes and the evolution of vegetation since the last Glacial Maximum (LGM). Before 16 ka BP pollen assemblages were dominated by Chenopodiaceae (20% -50% ) and Artemidis (10% ~ 30% ) and pollen influx values were very low from Lake Ren Co in Basu county. The vegetation around the lake was probably a desert-steppe during the LGM. The data also suggest that the climate in the Basu area was cold and dry during the LGM and the last glacial time. The mean annual temperature was probably 4 ~ 6 ℃ colder than the present, and the mean annual precipitation was only 250 mm, about 40% of the present. The Southwest monsoon became stronger from 12 ka BP to 6 ka BP reaching its acme by 7 ka BP, but weakened gradually from 5 ka BP to the present. The paleovegetation was dominantly forest or forest-meadow around Lake Hidden and Ren Co during the 9.2 ~ 5 ka BP. The mean temperature in January was probably 2 ~ 3 ℃ higher than the present, and the mean annual precipitation was 100 mm more than the present. The timing of vegetational and climatic changes based on pollen records generally supports the results of global climatic-model experiments that predict a strengthened monsoon system during the early to middle Holocene followed by a weakened monsoon system.     

Changes in forest cover in China during the Holocene

Pollen map data at 2000-year intervals are used to reconstruct changes in Holocene forest cover in China north of the Yangtze River. In almost all regions, the early Holocene from 10 ka b.p. to 6 ka b.p. is characterised by an increase in forest cover although there was a reversal to lower forest cover at 8 ka b.p. in the eastern monsoon regions. A maximum of forest cover was reached at 6 ka b.p. in all regions except for Northeast China where forest cover peaked in the late Holocene. All regions except for Northeast China experienced a marked decline in forest cover after 6 ka b.p. Since 6 ka b.p., forest cover has decreased by about 92% in the middle and lower reaches of the Yellow River, 64% in the easternmost part of the Qinghai-Tibet Plateau and 37% between the Yangtze River and the Huaihe River. In contrast, forest cover in Northeast China increased significantly from 6 ka b.p., but has declined between 2 ka b.p. and the present. Changes in forest cover prior to 6 ka b.p. were probably caused by climate, but the evident drop in forest cover since that time in most regions may have been induced predominantly by human activities.     

Direct ESR dating of a Pliocene hominin from Swartkrans

Two fragments of a hominin tooth (Australopithecus robustus) and two bovid teeth from the Hanging Remnant of the Swartkrans Formation were analysed with ESR. Research was complicated by the fact that the samples came from a curated collection and their precise provenance is unknown. The environmental dose rate was reconstructed by a series of in situ gamma spectrometric measurements and elemental analyses of a range of sediment samples. U-series isotopic analyses indicated that each of the teeth had a significantly different uranium uptake history, rendering the assumptive early U-uptake and linear U-uptake models ineffective. ESR and U-series data were combined to calculate open system ages, resulting in a best estimate of 1630+/-160 ka for the Hanging Remnant. An open-system model which provides the maximum age for given U-series and ESR measurements yielded an estimate of about 2100 ka.Two bovid teeth from Member 2, previously estimated to be between 1.0 and 2.0 Ma, yielded age estimates of between about 100 and 200 ka. No known geochemical processes are likely to explain this severe age underestimation. We conclude that these samples are of Middle to Upper Pleistocene age and their presence in Member 2 was either due to reworking or inadequate stratigraphical discrimination of these deposits.     

Postglacial environmental change of the Pacific Ocean off the coasts of central Japan

Downcore changes in microfossil assemblages and oxygen isotope ratios in three piston cores recovered from the Northwestern Pacific, off central Japan, show that the subtropical Kuroshio front was located to the south of C-4 core site (Lat. 33° N) during the last glacial. The front then advanced northward, passing over the C-4 site and the C-6 site (34.6° N) at about 13 ka and 10 ka, respectively, and reached the C-1 core site (36° N) at about 7 ka. After 5.5 ka it retreated to the area between the C-1 and C-6 sites. A brief but significant cold event, the readvance of the cold Oyashio Current, is recognized between 11 and 10 ka in the two northern cores, but the current did not reach the southern C-4 site. A contemporaneous cold event is known in the North Atlantic, and the cooling was probably a global phenomenon likely to be associated with lowering of sea level. Contamination of isotopically light water is apparent between 14 and 11 ka in the marked change in isotopic composition of benthic foraminifers. Oxygen isotope ratios of planktonic foraminifers show that prior to the advance of the Kuroshio front, the surface water at these core sites was isotopically lighter than the Kuroshio water at that time.     

天山乌鲁木齐河源区3．6ka BP以来的植被变化和环境变迁：以大西沟剖面为例

天山乌鲁木齐河源区大西沟剖面孢粉鉴定结果表明：在3．6～3．2ka BP,该区气候较今温暖湿润;在3.2～2．0ka BP,气候变为寒冷干燥,这一时期乌鲁木齐河源地区曾出现一次冰进;在2．0～1．4ka BP,气候又转为暖湿;在1．4～0．5ka BP,出现了3．6ka BP以来气候最适宜的时期。整个剖面自下而上都有一定量的淡水水生植物出现,这反映了该剖面3ka BP以来一直处于淡水沼泽的环境中。通过对云杉属生态习性、传播特性等综合分析,认为剖面中的云杉丰值可能与林线上移、山谷风搬运以及冰川退缩等有一定的相关性。通过对孢粉样品中炭屑浓度统计以及磁化率测试结果的综合研究,提出在0．5ka BP左右,该地区可能出现过多次火灾;炭屑的峰值可能与人类活动有关。     

天山乌鲁木齐河源区3.6 ka BP以来的植被变化和环境变迁:以大西沟剖面为例

天山乌鲁木齐河源区大西沟剖面孢粉鉴定结果表明:在3.6～3.2 ka BP,该区气候较今温暖湿润;在3.2～2.0 ka BP,气候变为寒冷干燥,这一时期乌鲁木齐河源地区曾出现一次冰进;在2.0～1.4 ka BP,气候又转为暖湿;在1.4～0.5 ka BP,出现了3.6 ka BP以来气候最适宜的时期.整个剖面自下而上都有一定量的淡水水生植物出现,这反映了该剖面3 ka BP以来一直处于淡水沼泽的环境中.通过对云杉属生态习性、传播特性等综合分析,认为剖面中的云杉丰值可能与林线上移、山谷风搬运以及冰川退缩等有一定的相关性.通过对孢粉样品中炭屑浓度统计以及磁化率测试结果的综合研究,提出在0.5 ka BP左右,该地区可能出现过多次火灾;炭屑的峰值可能与人类活动有关.