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1.
四川茂县较场剖面厚101.1m,其中湖相沉积厚98.0m,为一套浅黄色-灰色的粉砂、粘土质粉砂和粉砂质粘土层。古地磁测试显示,除2个样品的磁偏角显示负极性外,其余样品的磁偏角全部为正,属布容正极性时,没有出现B/M界线。根据该套地层的岩性、岩相和所处的地貌部位,可以和云南金沙江谷地的龙街组对比,推测其开始沉积的时代为100~120 kaBP.另外,距顶4.0 m处光释光年龄为16.7±1.2 kaBP,推测其结束于10kaBP.湖相沉积历时约100kaBP,是岷江流域出露的末次(间)冰期以来厚度最大的剖面之一。 相似文献
2.
During the past 8000 years, large volcanic debris flows from Mount Meager, a Quaternary volcano in southwest British Columbia, have reached several tens of kilometres downstream in Lillooet River valley, with flow velocities of many metres per second and flow depths of several metres. These debris flows inundated areas that have become settled in the past 100 years and are now experiencing rapid urban growth. Notably, Pemberton, 65 km from Mount Meager, has doubled in size in the past five years. Approval of subdivision and building permits in Pemberton and adjacent areas requires assessment and mitigation of flood hazards, but large, rare debris flows from Mount Meager are not considered in the permitting process. Unlike floods, some volcanic debris flows occur without warning. We quantify the risk to residents in Lillooet River valley from non-eruption triggered volcanic debris flows based on Holocene landslide activity at Mount Meager. The calculated risk exceeds, by orders of magnitude, risk tolerance thresholds developed in Hong Kong, Australia, England, and in one jurisdiction in Canada. This finding poses a challenge for local governments responsible for public safety. 相似文献
3.
A Glacier Peak tephra has been found in the mid-Holocene sediment records of two subalpine lakes, Frozen Lake in the southern Coast Mountains and Mount Barr Cirque Lake in the North Cascade Mountains of British Columbia, Canada. The age–depth relationship for each lake suggests an age of 5000–5080 14C yr B.P. (5500–5900 cal yr B.P.) for the eruption which closely approximates the estimated age (5100–5500 14C yr B.P.) of the Dusty Creek tephra assemblage found near Glacier Peak. The tephra layer, which has not been reported previously from distal sites and was not readily visible in the sediments, was located using contiguous sampling, magnetic susceptibility measurements, wet sieving, and light microscopy. The composition of the glass in pumice fragments was determined by electron microprobe analysis and used to confirm the probable source of this mid-Holocene tephra layer. Using the same methods, the A.D. 1481–1482 Mount St. Helens We tephra layer was identified in sediments from Dog Lake in southeastern British Columbia, suggesting the plume drifted further north than previously thought. This high-resolution method for identifying tephra layers in lake sediments, which has worldwide application in tephrachronologic/paleoenvironmental studies, has furthered our knowledge of the timing and airfall distribution of Holocene tephras from two important Cascade volcanoes. 相似文献
4.
经过在若尔盖盆地进行全面野外考察,在黄河第一弯岸边发现了沉积序列清晰的、具有代表性的完整沉积地层剖面。通过沉积学和地层学特征和沉积相的观测分析,结合实验室粒度分析、数据处理和测年断代,其结果表明：该剖面底部蓝灰色古湖相沉积层反映出盆地内部在OSL年龄35 ka之前为较深的湖泊。其上覆盖的风沙与泥炭互层,反映出在该区域湖水消失之后,在30 ka之前古湖底出现泥炭沼泽,同时风沙作用盛行。而浊黄橙色古洪水沉积层（OFD1）则反映出在30~27 ka之间,曾经有来自于黄河源区流域的规模巨大的洪水进入若尔盖盆地,在古湖底泛滥并且将其携带的分选良好的细沙与粉沙质泥沙堆积下来。该剖面中部厚度达5~7 m的河漫滩-风沙层,沿着河岸追索,则可见其表现为高低起伏的古沙丘。这表明在末次冰期盛期和冰消期,气候干旱寒冷,黄河已经下切形成其河槽,其河漫滩沉积物被强劲的风力吹扬,形成连绵起伏的沙丘。该层之上所覆盖的浊黄橙色古洪水沉积层（OFD2）,则反映出在全新世初期9.86~8.28 ka之间,来自于黄河源区流域的大洪水再次进入盆地,在黄河第一湾两岸的古湖底沉积了分选良好的细沙质与粉沙质的泥沙。到了全新世中期后,若尔盖盆地风沙作用依然盛行,黄河河槽深切,第一湾两岸接受沙尘暴沉积。在全新世中期的相对温暖湿润气候条件之下,沙尘暴沉积物被改造为亚高山草甸黑土类土壤,成熟度极高。到了全新世晚期以来,风沙作用与沙尘暴沉积过程持续,沙尘暴沉积物也被改造为亚高山草甸黑土层。本文研究对于深入理解黄河源区末次冰期以来环境变化与地表过程演变,以及晚更新世以来的气候水文变化规律具有重要的科学意义。 相似文献
5.
Sedimentation processes in a short residence-time intermontane lake, Kamloops Lake, British Columbia 总被引：1，自引：0，他引：1
Kamloops Lake in central British Columbia is a deep, intermontane lake fed by the strong and seasonally variable flows of the Thompson River. Considerations of lake-river interaction, supported by physical and geological evidence, suggest that sediment transport and deposition within the lake is controlled by three interdependent but distinct processes: delta progradation at the lake-river confluence which results in delta topset and foresee bedding; sediment density surges originating along the delta face which result in turbidite sequences lakeward from the base of the delta; and dispersal by the interflowing river plume which, due to Coriolis effects, results in a higher sedimentation rate and greater fraction of coarser material along the right-hand side (Northern Hemisphere) of the lake in the direction of flow. 相似文献
6.
Baotian Pan Qingyu Guan Hongshan Gao Dongsheng Guan Fenliang Liu Zongmeng Li Huai Su 《Boreas: An International Journal of Quaternary Research》2014,43(1):121-131
The grain size of the loess‐like sediment in the Jinsha River Valley is essentially similar to that of typical loess, and it differs from that of the fluvial sediment in the Jinsha River area. We conclude that the loess‐like sediment is of aeolian origin, as is the loess of the Chinese Loess Plateau. The geochemical characteristics of the loess‐like sediment are similar to those of dammed lake and fluvial sediments in the same area, which is significantly different from those of the typical loess in NW China. The geochemical characteristics show that the loess‐like sediment originated from proximal materials. Combined with the grain‐size distribution pattern of the aeolian deposits, we suggest that the loess‐like sediment of the Jinsha River Valley originated from the dammed lake and fluvial sediments that accumulated in the valley. The local mountain‐valley wind circulation (especially the valley wind in winter and spring) provided the transport force for the loess‐like sediment. The presentation of the loess‐like sediment may indicate the appearance of the grassland and forest steppe and the beginning of the dry‐hot valley phenomenon. 相似文献
7.
Hans-Joachim Pachur Bernd Wünnemann Linyuan Zhang Hucai Zhang Yuzheng Ma 《GeoJournal》1994,34(1):97-106
At Lingfeng, (34°17'N, 104°08'E) on the northern slopes of the Qinling Mountains, a stratigraphic survey was made of a 21-m-profile of floodplain sediments on the watershed between the Chang Jiang (Yangtze River) and Huang He (Yellow River) at 2500 m above sea level. The sediments contain <2 m thick layers of peat and detritical plant matter that had been deposited on the floodplain of the Langouhe. If the radiometric dates are reliable, the chronology of the site spans some 80,000 years, covering an accumulation process from the terminal Last Interglacial up to <24 ka BP. The phase >73 ka BP had cool and wet conditions with a coniferous forest vegetation. Between 73 ka and > 40 ka colder and drier conditions were likely. The vegetation changed from aPicea-Pinus forest to aPicea-Abies-Larix forest with a later increase of non-arboreal pollen. Around 40 ka the climate was warm and moist. The accumulation of silt and organic matter as well as the development of a mixed coniferous forest with high rates of thermophilous trees(Quercus, Castanea) characterize the interstadial conditions at this time. Later on, the climate changed to cool and moist conditions, evidenced by silt and peat accumulation and a coniferous forest vegetation up to <24 ka BP. The loess in this area was deposited after 24 ka and erosion by the tributaries of Chang Jiang and Huang He to a depth of at least 40 m created the watershed between the two river systems. 相似文献
8.
Daniel R Muhs Thomas A AgerJosh Been J.Platt BradburyWalter E Dean 《Quaternary Research》2003,60(1):110-122
Recent stratigraphic studies in central Alaska have yielded the unexpected finding that there is little evidence for full-glacial (late Wisconsin) loess deposition. Because the loess record of western Alaska is poorly exposed and not well known, we analyzed a core from Zagoskin Lake, a maar lake on St. Michael Island, to determine if a full-glacial eolian record could be found in that region. Particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian. Silt deposition took place from at least the latter part of the mid-Wisconsin interstadial period through the Holocene, based on radiocarbon dating. Based on the locations of likely loess sources, eolian silt in western Alaska was probably deflated by northeasterly winds from glaciofluvial sediments. If last-glacial winds that deposited loess were indeed from the northeast, this reconstruction is in conflict with a model-derived reconstruction of paleowinds in Alaska. Mass accumulation rates in Zagoskin Lake were higher during the Pleistocene than during the Holocene. In addition, more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape. The thinner loess record on land may be due to the sparse, herb tundra vegetation that dominated the landscape in full-glacial time. Herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height. The lack of abundant, full-glacial, eolian silt deposition in the loess stratigraphic record of central Alaska may be due, therefore, to a mimimal ability of the landscape to trap loess, rather than a lack of available eolian sediment. 相似文献
9.
Four stratigraphic sections in the southern part of the Columbia Basin preserve a sequence of aeolian and non-aeolian sediments ranging in age from 9·43 to >47·0 14 C ka based on accelerator mass spectrometry radiocarbon dating of fossil molluscs, geochemistry of Cascade Mountain-sourced tephra and association with formally recognized pedostratigraphic units (the Washtucna and Old Maid Coulee soils). Study sections are interpreted as representing concurrent deposition of loess and distal Missoula Flood rhythmites in valleys tributary to main drainages backflooded during the Missoula Floods, and formation of carbonate and iron-rich soils. Sediments belong to the formally recognized L-1 and L-2 loess units established for the Palouse loess, which were deposited in the Columbia Basin subsequent to events of glacial outburst flooding. Sediments associated with the Mount Saint Helens set S and set C tephras in the study sections preserve a fauna of five species of gastropod mollusc which have not been reported previously from sediments of late Pleistocene age in the Palouse region. The fossils comprise two distinct faunules stratigraphically separated by the Mount Saint Helens So tephra. Accelerator mass spectrometry radiocarbon dating of the fossils collected above the tephra in two of the sections yielded ages of 12·48 ± 0·06 and 9·43 ± 0·05 14 C kyr. These ages suggest that independent determinations of the 13·35 14 C kyr age of the So tephra in other areas where Missoula Flood sediments are preserved are probably accurate, and help to refine the age of the latest events in the most recent sequence of catastrophic glacial outburst flooding. 相似文献
10.
TIMOTHY F. JOHNSEN TRACY A. BRENNAND 《Boreas: An International Journal of Quaternary Research》2006,35(1):106-125
During decay of the Cordilleran Ice Sheet, ˜13 000–10000 cal. yr BP, numerous ice-dammed, ribbon-shaped lakes developed within the moderately deep valleys of the Interior Plateau of British Columbia. We describe the pattern and characteristics of lake sediments within the Thompson Valley, propose a palaeoenvironmental model for glacial lakes Thompson and Deadman and explore their implications for the palaeogeography of Cordilleran Ice Sheet decay. Seventeen glaciolacustrine lithofacies are identified within deltas, subaqueous fans and lake-bottom beds. Sediments accumulated at high rates and by a diversity of sediment dispersal and depositional processes: hyperpycnal and surge-type turbidity currents, grain flows and debris flows. Megascale subaqueous failures (tens of metres thick) were facilitated by high sedimentation rates. The palaeoenvironmental model highlights: (i) high rates of basin infilling; (ii) the dominant role of tributary rivers, rather than valley-occupying ice, in delivering water and sediment to lakes; and (iii) the role of melt cycles, jökulhlaups and hyperpycnal flows in sediment delivery. These conditions, in combination with a lack of organics and a fining upward sequence in lake sediments, suggest that glacial lakes Thompson and Deadman were coeval with dwindling plateau ice. 相似文献
11.
通过对若尔盖盆地进行野外考察,在盆地中部黄河唐克段右岸发现了包含深湖相的河岸沉积物,进行了细致的地层观测和系统年代学样品采集。在实验室利用光释光和AMS14C测年技术建立了年代框架,并结合各个层次的地层沉积相宏观特征和理化性质,分析探讨了若尔盖盆地内部从末次冰期古湖消亡以来的环境和地表过程变化规律。研究结果表明：古黄河在37 ka沿着玛曲断陷谷地溯源侵蚀,沟通了若尔盖古湖水系,盆地内部在30.9 ka之前为深湖环境,稳定地沉积了蓝灰色湖相淤泥层。30.9 ka之后,黄河贯穿若尔盖湖盆内部,古湖水外泄消失,原有的古湖水系转变成为黄河源水系。黄河从湖盆上游远距离搬运携带来的浊黄橙色泥沙大量沉积,覆盖了古湖相沉积层,湖盆内部风沙作用盛行。在末次冰盛期（Last Glacial Maximum, LGM）,盆地内部松散沉积物普遍地受到冰缘冻融作用的改造,形成了冻融褶皱现象。到了14.6~12.5 ka,响应B/A（B?lling-Aller?d）时期的温暖气候,盆地周边山地冰川消融,冰融水汇入盆地,古湖盆底部各种浅洼地形成了大小不等的浅湖,沉积了滨浅湖相的沙层。在12.5~11.7 ka,对应于全球性新仙女木（Younger Dryas,YD）事件,盆地气候再次变冷,转变为冰缘冻土环境,盆地内部滨浅湖相的沙层受到冻融作用和古地震扰动,形成复式褶皱现象。进入全新世,在11.7~4.8 ka气候逐渐变得温暖湿润,古湖盆底部浅洼地积水成为淤泥质沼泽环境,在全新世中后期4.8~1.8 ka则转变成为沼泽草甸环境,在1.8 ka之后,盆地内沼泽面积收缩,风沙活动盛行,河岸台地的近源沙尘暴沉积物经过成壤改造形成亚高山草甸黑土类现代土壤。 相似文献
12.
We present textural and thickness data on loess from 125 upland sites in west-central Wisconsin, which confirm that most of this loess was derived from the sandy outwash surfaces of the Chippewa River and its tributaries, which drained the Chippewa Lobe of the Laurentide front during the Wisconsin glaciation (MIS 2). On bedrock uplands southeast of the widest outwash surfaces in the Chippewa River valley, this loess attains thicknesses > 5 m. OSL ages on this loess constrain the advance of the Laurentide ice from the Lake Superior basin and into west-central Wisconsin, at which time its meltwater started flowing down the Chippewa drainage. The oldest MAR OSL age, 23.8 ka, from basal loess on bedrock, agrees with the established, but otherwise weakly constrained, regional glacial chronology. Basal ages from four other sites range from 13.2 to 18.5 ka, pointing to the likelihood that these sites remained geomorphically unstable and did not accumulate loess until considerably later in the loess depositional interval. Other OSL ages from this loess, taken higher in the stratigraphic column but below the depth of pedoturbation, range to nearly 13 ka, suggesting that the Chippewa River valley may have remained a loess source for several millennia. 相似文献
13.
Subglacial landsystems in and around Okanagan Valley, British Columbia, Canada are investigated in order to evaluate landscape development, subglacial hydrology and Cordilleran Ice Sheet dynamics along its southern margin. Major landscape elements include drumlin swarms and tunnel valleys. Drumlins are composed of bedrock, diamicton and glaciofluvial sediments; their form truncates the substrate. Tunnel valleys of various scales (km to 100s km length), incised into bedrock and sediment, exhibit convex longitudinal profiles, and truncate drumlin swarms. Okanagan Valley is the largest tunnel valley in the area and is eroded >300 m below sea level. Over 600 m of Late Wisconsin-age sediments, consisting of a fining-up sequence of cobble gravel, sand and silt fill Okanagan Valley. Landform–substrate relationships, landform associations, and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds. They are best explained by meltwater erosion and deposition during ice sheet underbursts.During the Late-Wisconsin glaciation, Okanagan Valley functioned as part of a subglacial lake spanning multiple connected valleys (few 100s km) of southern British Columbia. Subglacial lake development started either as glaciers advanced over a pre-existing sub-aerial lake (catch lake) or by incremental production and storage of basal meltwater. High geothermal heat flux, geothermal springs and/or subglacial volcanic eruptions contributed to ice melt, and may have triggered, along with priming from supraglacial lakes, subglacial lake drainage. During the underburst(s), sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys. Progressive flow channelization focused flows toward major bedrock valleys. In Okanagan Valley, most of the pre-glacial and early-glacial sediment fill was removed. A fining-up sequence of boulder gravel and sand was deposited during waning stages of the underburst(s) and bedrock drumlins in Okanagan Valley were enhanced or wholly formed by this underburst(s).Subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes. The prevailing conceptual model for growth and decay of the CIS suggests significantly thicker ice in valleys compared to plateaus. Subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner (due to melting and enhanced sliding, with significant transfer of ice toward the ice sheet margin). Subglacial lake drainage may have hastened deglaciation by melting ice, lowering ice-surface elevations, and causing lid fracture. This paper highlights the importance of ice sheet hydrology: its control on ice flow dynamics, distribution and volume in continental ice masses. 相似文献
14.
对郧县—白河段汉江Ⅰ级河流阶地上风成黄土的沉积学、理化性质、地球化学和年代学进行了系统研究。结果表明,汉江Ⅰ河流阶的形成不晚于25 ka BP;黄土具有马兰黄土(L1)→过渡黄土(Lt)→古土壤(S0)→全新世黄土(L0)→表土(TS)的地层序列,与渭河谷地的黄土地层序列完全可比;25~11.5 ka BP,冬季风强盛,气候冷干,从11.5 ka BP开始,冬季风逐渐减弱,气候开始向暖湿方向逐步转化,从8.5 ka BP开始,夏季风达到了末次冰期结束后的鼎盛时期,3.1 ka BP前后,东亚季风格局发生变化,夏季风减弱,重新进入一个相对干冷的时期,而人类活动对地表的影响形成了表土;汉江上游谷地黄土记录的末次冰期后季风逐渐加强、中全新世季风强盛、随后季风衰退和气候变干的夏季风演变模式与渭河谷地黄土的记录高度一致,与邻区石笋和泥炭记录的季风变化趋势也有良好的可比性,但与石笋/泥炭记录的夏季风强盛期的起始时间(9.3~4.2 ka BP)并不完全一致。 相似文献
15.
郧县前坊村剖面黄土-古土壤序列风化成壤及古气候研究 总被引：2，自引：0，他引：2
秦岭作为我国南方和北方地理、气候、自然环境的天然分界线,并当作是黄土高原的南屏障。汉江上游谷地地区位于秦岭南侧,属于北亚热带气候区域,受季风气候活动影响强烈。为了探讨该地区在亚热带气候背景下,风成黄土成壤改造对气候变化的响应机制,通过对汉江上游谷地前坊村（QFC）剖面磁化率、烧失量、粒度、Rb/Sr等理化性质进行研究。结果表明:①末次冰期以来沙尘暴很有可能越过秦岭在其南侧堆积,黄土-古土壤剖面地层序列从上到下依次为:MS-L0-S0-Lt-L1-AD;这些沉积物完整记录了一级阶地上晚更新世气候变化信息,地层单元受到各个时期不同程度成壤强度的改造。②前坊村剖面中,理化性质在不同地层单元有显著差异。例如磁化率、烧失量、Rb/Sr指标平均含量的高值出现在古土壤层中,低值出现在黄土层;而Zr/Rb含量变化正好相反;这些理化性质表明,在古土壤发育期,水热条件进入最适宜期,沉积物的风化成壤作用显著;在黄土堆积期,气候寒冷干燥,主要以粉尘堆积为主,沉积物的风化成壤作用较弱。③秦岭南侧北亚热带汉江上游前坊村一级阶地剖面化学风化强度变化揭示了黄土-古土壤环境气候变化的规律:末次冰期以来（大约18.0～11.5 ka B.P.）,气候干冷,沙尘暴频繁出现,沉积物以黄土堆积为主,成壤作用微弱,形成马兰黄土（L1）;全新世早期（约11.5～8.5 ka B.P.）,气候由干冷向暖湿方向转变,但主要以干冷为主,形成过渡层（Lt）;在全新世大暖期（8.5～3.1 ka B.P.）,气候条件达到最优阶段,水热配合较好,生物活动活跃,成壤作用十分显著,发育了古土壤S0;到了全新世晚期以来（3.1 ka B.P.）气候又由暖湿向干冷方向转变,成壤作用明显减弱,沙尘暴出现较为频繁,形成了以黄土堆积为主的全新世黄土（L0）。现代表土层（MS）是在（1.5 ka B.P.）以来气候转暖,加之人类长期农业耕作扰动,在全新世黄土L0顶部叠加而形成的。 相似文献
16.
The Quaternary fills of the buried valleys of southern Alberta and Saskatchewan have provided a wealth of information for the reconstruction of the glacial-interglacial record of the western plains of Canada, and this paper reports on the previously unstudied stratigraphy of the buried Calgary Valley and its former tributaries in the lower Red Deer River area. We attempt to differentiate Empress Group sediments, which potentially relate to pre-glacial, interglacial/ interstadial and post-glacial lake and river deposition, using sedimentology, stratigraphy and palaeoecology. Twenty-nine stratigraphical logs indicate that Empress Group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the Calgary Valley, located 15 km to the north of Dinosaur Provincial Park. Radiocarbon dates of 52.4 ka, 27.4 ka and > 42.4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid-Wisconsinan in age. However, outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials/interstadials and that older (even pre-glacial) sediments could have survived. Subglacial channels, recognisable on air photographs, largely coincide with buried valley positions due to the preferential excavation of the Quaternary sediment by meltwater and are filled with post-glacial lake sediment from which a radiocarbon date of 16 ka BP was obtained. Pre-glacial and glacial/post-glacial Empress Group sediments are lithologically indistinct but cover a large time span in southern Alberta. 相似文献
17.
《Russian Geology and Geophysics》2016,57(6):933-943
Several sections have been studied to understand the distribution and interrelation of basic genetic types of Quaternary deposits in the Uimon basin and adjacent area. The OSL date of 101 ± 10 ka from the glaciolacustrine terrace on the northeastern rim of the basin corresponds to the cool substage of MIS 5. The glaciolacustrine sediments of the northern rim are covered with widespread diamictic flows of the outburst draining of the ice-dammed lake. The diamicts are overlain by a subaerial complex of loesses and three fossil soils. From the OSL loess dates in the range of 43 to 49 ka we infer that the complex formed from the early MIS 3 through the Holocene. This is also supported by radiocarbon dates from alluvial deposits incised into the glaciolacustrine terrace and into megaflood sediments of the final draining of the last paleolake. The OSL dates in the range of 77 to 89 ka from alluvial sediments indicate that postglacial downcutting of the present-day Katun’ valley probably started just after MIS 5. The discrepancy between the beryllium dates from dropstones and Holocene TL-dates of the Katun’ valley floods ranging from 23 to 6 ka can be explained if the younger floods are related to the draining of moraine- and rock slide dammed rather than ice-dammed lakes. The younger floods, though being less voluminous than the glacial megafloods, were capable of producing giant ripple marks. 相似文献
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金沙江中游云南龙街粉砂层沉积环境演化特征 总被引：2，自引：0，他引：2
沿金沙江攀枝花三堆子至武定县白马口段河谷两岸分布一套以灰黑色、灰黄色、灰白色粉砂、粘土质粉砂和粘土为主的湖相地层,尤以云南省元谋县龙街盆地内最为发育,被称为龙街粉砂层。通过龙街YA钻孔和龙街、白泥湾剖面的磁性地层学和光释光年代学的研究,探讨龙街粉砂层的时代与归属。龙街YA钻孔地层厚度101.18m,其中龙街粉砂层厚92.96m,上覆7.5m的红棕色细砂和砂砾石层,下伏厚度大于0.72m的灰绿色含角砾粗砂。综合分析YA钻孔的磁性地层学和光释光年龄,认为获取龙街粉砂层的沉积时代为150~30ka BP,属于晚更新世。通过地层沉积特征变化,反演晚更新世以来湖泊的形成及沉积环境变化,探讨晚更新世以来区域新构造的活动阶段及其对河流演化过程的控制作用。 相似文献
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J.Grunert C.Stolz N.Hempelmann A.Hilgers D.Hulle F.Lehmkuhl T.Felauer D.Dasch 《第四纪研究》2009,29(4):678-686
In order to investigate pluvial lakes in the Gobi two places were selected for field studies: Khongoryn Els in South and Mongol Els in WestMongolia. In the eastern and central parts of Khongoryn Els two small endorheic basins,Bayan Tukhem and Khongoryn Gol depressions were studied. Pluvial lake deposits and beach ridges both supposedly midHolocene in age give evidence of a 9m and a 15m deep freshwater lake,respectively. Today both depressions are nearly dried out and exposed to wind deflation. A different situation was found at Uujin Sair river valley which cuts through the dune field at its lowest and narrowest(3km)part. Here,a 22.5m thick fossil accumulation of at least 20 layers of fine sand(dune sand)alternating with silt(fluvial playa sediment)was exposed and OSL dated. 12 dates ranging between 14ka and 17ka reveal the accumulation as Late Glacial which correlates well with the aridity at that time reported for Central Asia by several authors. Interpreting the dates it seems obvious that the whole sediment was quickly deposited in a period of about 16ka,and shortly after dissected by the Uujin Sair during a similar short time due to increasing humidity of the climate. Another situation was found at the eastern rim of Mongol Els. Two rivers,Shurgiyn Gol and Zavran Gol are impinging here on the high dunes which have damed both rivers in the past. A younger,shallow lake existed during midHolocene(14Cdated to some 5.5ka)and a large,17m deep lake(14C－dated to some 39ka)probably during stage 4.Expected OSL dates will hopefully support this hypothesis. Anyhow,the palaeogeography of the dune field was different from today; it moved eastward daming the large river Shurgiyn Gol. 相似文献