Beringia as an Ice Age genetic museum     

Beth ShapiroAlan Cooper 《Quaternary Research》2003,60(1):94-100

Thousands of Late Pleistocene remains are found in sites throughout Beringia. These specimens comprise an Ice Age genetic museum, and the DNA contained within them provide a means to observe evolutionary processes within populations over geologically significant time scales. Phylogenetic analyses can identify the taxonomic positions of extinct species and provide estimates of speciation dates. Geographic and temporal divisions apparent in the genetic data can be related to ecological change, human impacts, and possible landscape mosaics in Beringia. The application of ancient DNA techniques to traditional paleontological studies provides a new perspective to long-standing questions regarding the paleoenvironment and diversity of Late Pleistocene Beringia.  相似文献   

Luminescence chronology of late pleistocene loess-paleosol and tephra sequences near Fairbanks, Alaska   总被引：1，自引：0，他引：1  

Glenn W Berger 《Quaternary Research》2003,60(1):70-83

Thermoluminescence (TL) and infrared-stimulated luminescence (IRSL) sediment-dating methods have been applied to paleosol- and tephra-bearing loess sequences younger than marine oxygen isotope stage (MIS) 7 at three important sites. TL ages indicate the development of significant paleosols ∼75,000 and ∼30,000 yr ago in the loess sequence at the Gold Hill site. Relatively minor soil development occurred ∼70,000 and ∼48,000 yr ago. Like the ∼75,000-yr-old soil, the 30,000-yr-old soil is apparently of global extent, and consistent in timing with inferred warm intervals elsewhere (e.g., Greenland, Europe, western and central China). At Birch Hill, replicate TL dating of primary loess combined with two earlier TL results from the same site, and with an earlier mean fission-track-glass-shard age of 140,000 ± 10,000 yr for the associated Old Crow tephra, yield a more precise numeric age of 142,300 ± 6600 yr for this Alaska/Yukon chronostratigraphic marker ash bed. Three of the TL ages at the Halfway House site are difficult to interpret, but combined with other evidence, they indicate: (1) the upper 5-6 m of loess from Halfway House is not part of the Gold Hill Loess (equivalent to pre-MIS 5 age) as long thought by T.L. Péwé, but rather is much younger; (2) the regionally significant variegated tephra, found in the Fairbanks and Klondike areas and previously thought to be older than MIS 5, has an age of 77,800 ± 4100 yr (late MIS 5).  相似文献   

Recurring middle Pleistocene outburst floods in east-central Alaska     

Duane G Froese  Derald G SmithJohn A Westgate  Thomas A AgerShari J Preece  Amanjit SandhuRandolph J Enkin  Florence Weber 《Quaternary Research》2003,60(1):50-62

Recurring glacial outburst floods from the Yukon-Tanana Upland are inferred from sediments exposed along the Yukon River near the mouth of Charley River in east-central Alaska. Deposits range from imbricate gravel and granules indicating flow locally extending up the Yukon valley, to more distal sediments consisting of at least 10 couplets of planar sands, granules, and climbing ripples with up-valley paleocurrent indicators overlain by massive silt. An interglacial organic silt, occurring within the sequence, indicates at least two flood events are associated with an earlier glaciation, and at least three flood events are associated with a later glaciation which postdates the organic silt. A minimum age for the floods is provided by a glass fission track age of 560,000 ± 80,000 yr on the GI tephra, which occurs 8 m above the flood beds. A maximum age of 780,000 yr for the floods is based on normal magnetic polarity of the sediments. These age constraints allow us to correlate the flood events to the early-middle Pleistocene. And further, the outburst floods indicate extensive glaciation of the Yukon-Tanana Upland during the early-middle Pleistocene, likely representing the most extensive Pleistocene glaciation of the area.  相似文献   

Climate friction and the Earth's obliquity   总被引：1，自引：0，他引：1  

B. Levrard  J. Laskar 《Geophysical Journal International》2003,154(3):970-990

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Paleomagnetism of Pleistocene widespread tephra deposits and its implication for tectonic rotation in central Japan     

Hiromi Iwaki  Akira Hayashida 《Island Arc》2003,12(1):46-60

Abstract   A single layer of widespread tephra deposits possibly can provide an instantaneous record of the past geomagnetic field and potentially can indicate even a small-scale tectonic rotation compared to a range of geomagnetic secular variations. We report paleomagnetic data of the Ebisutoge–Fukuda tephra, which is dated at approximately 1.8 Ma and is distributed in central Japan between the Osaka–Kyoto area and the Boso Peninsula. The Fukuda volcanic ash layer and its correlative ash deposits in the Osaka–Kyoto area, near Lake Biwa and in the Mie and Niigata areas yield identical site mean declinations of approximately −170° after tilt correction, whereas moderate inclination shallowing is observed in the upper unit at several localities. Anisotropy measurements both of low-field magnetic susceptibility and of anhysteretic remanent magnetization suggest that the inclination shallowing results from the biased alignment of magnetic grains, which were deposited in the fluvial environment. The source volcanic unit, Ebisutoge pyroclastic deposits in the Takayama area, yields a mean declination of approximately −155°, showing clockwise deflection from the magnetic directions of the correlative tephra deposits. These results suggest that no significant rotation occurred between the Osaka–Kyoto, Mie and Niigata areas, but that the Takayama area suffered a clockwise rotation in respect to the other areas during the Quaternary. This rotation might have been caused under an east–west stress field associated with the collision of the Okhotsk Plate with the Eurasia Plate.  相似文献   

朝鲜北部及其邻区的新构造运动和现代地形构造的形成     

李竹南 《吉林地质》1991,10(1):1-12

朝鲜北部及其邻区的第四系更新统(Q_1)由玄武岩和碎屑岩互层组成。下更新统玄武岩是在新第三纪上新世广而平坦的侵蚀面上形成的台地型玄武岩。朝鲜北部及其邻区的地形构造是通过下更新统沉积以后发生的新构造运动形成的。朝鲜下更新统和上更新统中的沉积矿产(特别是砂金矿床)普查、开发远景很大。  相似文献   

小南屯冰水堆积物的发现     

程新民 《吉林地质》1991,(2)

小南屯砂砾石层成因争论较大。通过孢粉学研究表明:该孢粉组合是以草本植物花粉为主,木本植物花粉为辅。在草本植物花粉中,又以蒿属占绝对优势,加上藜科、禾本科为特征的干燥寒冷气候带的孢粉组合,表明该砂砾石层为冰水堆积物。  相似文献   

东海西部晚更新世晚期以来地层特征的初步研究     

唐保根  昝一平 《上海国土资源》1992,(3):26-34

本文对长江三角洲沉积区、浙东近岸沉积区及陆架改造沉积区的钻孔剖面的地层进行了初步研究。根据钻孔柱状岩心的粒度、矿物、化学及生物组分的特征,本区晚更新世晚期以来的地层可划分为上更新统与全新统。  相似文献   

延庆盆地北缘断裂带蚕房营段晚更新世晚期断层作用   总被引：3，自引：5，他引：3       下载免费PDF全文

程绍平  杨桂枝 《地震地质》1994,16(4):346-354

通过１个探槽记录、３个地质学剖面、７个晚更新世沉积物表面断层崖形态学剖面和１５个放射性测年数据，论述了延庆盆地北缘断裂带蚕房营段的晚更新世晚期断层作用。这些资料显示出该时期内的两次断层作用事件：最近的一次发生在９８７０±１３０～１１８００±１１００ａＢ．Ｐ．之间，最早不超过１３２００±ｌ１００ａＢ．Ｐ．；较早一次的发生时间为１９８５０±１５５０ａＢ．Ｐ．。一次事件的位移量３．３４～３．６４ｍ，两次事件之间的重复间隔９９８０ａ。大约自２１０５０±１６００ａＢ．Ｐ．以来的垂直位移速度计算为０．３１～０．３４ｍｍ／ａ。蚕房营段的晚更新世晚期的断层作用，以较大的表面位移量和较长的重复间隔为特征。全新世没有类似的断层作用事件  相似文献   

Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean     

Ajai K. Rai  M. S. Srinivasan 《Journal of Earth System Science》1994,103(4):499-517

An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence. The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water (AABW). Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in the relative abundance ofU. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by low abundance ofU. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence ofBulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas.B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative abundance ofStilostomella lepidula occurs close to the Early/Late Pleistocene boundary.  相似文献