Drainage migration and out of sequence thrusting in Bhalukpong,Western Arunachal Himalaya,India

In the foreland regions of the Western Arunachal Himalaya (WAH), geological studies along the Kameng river (between Tipi village and the Himalayan Frontal Thrust (HFT)) reveal four levels of unpaired terraces and a paired terrace. In WAH, wrench deformation of HFT zone resulted in a SE propagation of the Balipara anticline and it is suggested that the Mikir high basement controls its orientation. Ages of terrace surfaces from Siwaliks suggest that since the Late Pleistocene, Kameng River migrated at a rate varying between ∼7.5 cm/yr in upper reaches and ∼13.5 cm/yr towards northeast due to HFT related uplift. In the Brahmaputra plains, luminescence ages of abandoned paleochannel deposits suggest eastward shifting of the Kameng river at an average rate of ∼1 m/yr. Field evidences between Bhalukpong and Tipi villages show Pliocene strath and Quaternary terrace surfaces, displaced by faults that do not correspond to the mapped faults in the foreland region. We interpret them as out-of-sequence thrusts (OOSTs). This is the first such report of OOST in the NE Himalaya. Presence of active OOST is inferred by similar age (∼1 ka) and differing incision rates of the surface of same terrace (T_2b) in adjacent locations. This suggests that OOSTs in the western Arunachal Siwalik are <1 ka. Average slip rate and horizontal shortening rate on OOST during the Holocene, are calculated as ∼12 mm/yr and 7 mm/yr respectively. Thus any estimation of Holocene shortening in the Siwalik therefore, needs to incorporate slip along the OOSTs given that it accommodates a significant amount of N-S compression of the Himalayan fold-and-thrust belt. The reason for OOST in the WAH Siwalik foreland is discussed in terms of the critical wedge dynamics arising from erosion via tectonics-climate interaction. We estimate a minimum slip rate of Siwalik as ∼27 mm/yr during the Holocene and suggest acceleration in shortening rates east of Bhutan.     

Lavini di Marco (Trentino,Italy): 36Cl exposure dating of a polyphase rock avalanche

The Lavini di Marco rock avalanche deposit (“Marocca di Marco”) is located along the left side of the middle Adige Valley, south of the town of Rovereto (NE Italy). The deposit is estimated to have a volume of ∼2 × 10⁸ m³ and cover an area of ∼6.8 km². It comprises Jurassic Calcari Grigi limestones that detached from the western slope of Mt. Zugna Torta. The Lavini di Marco is composed of at least two different rock avalanche bodies, the main deposit known as Lavini di Marco (the principal) and the much smaller Costa Stenda deposit. Costa Stenda deposits overlie Lavini di Marco deposits. Samples for ³⁶Cl exposure dating were collected from boulders within the deposits, from sliding plane bedrock and from the bedrock wall at the head scarp. Exposure ages range from 800 ± 210 to 21310 ± 1000 years. The latter age stands as a notable outlier suggesting that that Costa Stenda boulder was exposed for a considerable amount of time in the pre-slide bedrock. Lavini di Marco and Costa Stenda boulder ages are 2600 ± 200, 2700 ± 200, 3100 ± 300, 3300 ± 300, 3400 ± 300, 4400 ± 290, 5300 ± 300, and 5400 ± 300 years. The latter three are Costa Stenda boulders which we also interpret to contain inherited nuclide concentrations. The five remaining boulder ages cluster around 3000 years. We calculate a mean age for the Lavini di Marco and Costa Stenda rockslides of 3000 ± 400 years. Within the uncertainties of our data the two slides were simultaneous. For the bedrock sliding plane we obtained significantly younger ages, 1600 ± 100 and 1400 ± 100 years, and for the head scarp 800 ± 200 years. The sliding plane ages record small-scale reactivation which seems to overlap in time with a catastrophic flood event of the Adige River in Verona, as reported in the Fulda Annales, in 883 AD. Only the single age of 800 ± 210 years suggests activity at Lavini di Marco coincident with the well-known Verona earthquake (1117 AD).     

浙江瓶窑BHQ孔全新统孢粉组合特征与气候变化

利用浙江省瓶窑北湖BHQ孔长约14m的岩心,以4个AMS¹⁴C数据为年代依据,对49块样品进行孢粉分析。分析结果发现,样品中孢粉浓度差异较大,植物种类繁多,总计103个科/属。通过对孢粉组合特征的分析,结合岩性特征,划分出3个孢粉带和9个亚带,重建了研究区早—中全新世植被演替和气候冷暖波动的环境序列。19～8.9m沉积时段,对应于早全新世气候回暖期,研究区植被主要是以落叶栎、松、阿丁枫和枫杨为主,混有少量常绿栎和榆等的针叶—落叶阔叶混交林,常绿乔木花粉含量较低,说明研究区经历晚更新世晚期新仙女木事件后进入全新世,气候迅速转暖;8.9～6.7m沉积时段,对应于全新世最适宜期,为研究区水热条件配置最佳阶段,主要发育由落叶栎、常绿栎、松、阿丁枫、枫杨和榆等组成的常绿—落叶阔叶混交林,常绿乔木的种类和含量要远远高于前一阶段,指示气候变化的最适宜阶段;6.7～4.775m沉积时段,对应于中全新世气候波动期,孢粉组合发生明显波动,研究区植被主要以落叶栎、枫香、松、枫杨等落叶阔叶乔木为主,常绿栎花粉的含量急剧萎缩,表明研究区植被类型演替为落叶阔叶林,反映经历了较为剧烈的气候恶化事件,而本段高含量的稻属花粉(≥35μm)可能指示该时段研究区存在一定规模的古人类活动。     

湖光岩玛珥湖晚全新世人类活动的叶蜡烷烃及其碳同位素沉积记录

通过对广东省湛江市湖光岩玛珥湖晚全新世沉积物中叶蜡烷烃（n-C₂₉,n-C₃₁,n-C₃₃）及其碳同位素（δ^{13C）进行分析,探讨该湖区约3.5 ka BP以来的植被变化历史,重点讨论了人类活动对该区域植被变化可能带来的影响。叶蜡烷烃δ13区C₃植物占绝对优势,表现为典型的C在1.7 ka BP以前偏轻,例如长链烷烃碳同位素在1.78 ka BP为-33.27 ‰,表明湖C₃型生态系统;在1.7 ka BP之后碳同位素明显快速偏重,在1.63 ka BP为-28.26‰,指示了C₄植物出现和C₄比例上升的过程。C₄植物的出现通常指示气候的干旱化,但是烷烃P_aq和ACL指数（平均链长）则显示湖区气候可能在1.7 ka BP后变湿润。通过与研究区甘蔗的同位素和ACL指数的比较分析,推测这一矛盾现象可能与湖区开始有一定规模的甘蔗种植活动有关。}     

青藏高原东北缘冬给错纳湖全新世湖面波动

青藏高原处于东亚季风、印度季风和西风环流交互作用区.末次冰消期以来,太阳辐射对该地区的古气候环境产生了重要影响,湖泊随着季风系统的变化发生了明显的水位升降,对湖岸阶地的形成起到了直接作用.本项研究重建了青藏高原东北缘冬给错纳湖湖岸阶地记录的湖面波动历史,试图了解青藏高原季风系统演变过程.通过湖泊北岸265 cm厚湖岸阶地沉积物粒度、碳酸盐、矿物、元素和介形虫古环境指标,结合OSL年代模式,分析表明在约10. 2 ka B. P.之前水体较浅;约10. 2~9. 0 ka B. P.湖面开始上升,气候凉湿;9. 0~8. 5 ka B. P.为印度季风强盛期,湖面明显上升,降雨量增高、温度上升;8. 5~7. 9 ka B. P.湖面降低与气候变冷有关;7. 9~7. 0 ka B. P.印度季风开始减弱,气温、降雨下降,但有效湿度较大,湖面降低;7. 0~6. 1 ka B. P.湖面上升可能与低蒸发作用有关,印度季风仍然影响该地区;6. 1~5. 2 ka B. P.,印度季风衰退,气候逐渐变冷、降雨量减小、水体变浅;5. 2~4. 6 ka B. P.气候冷干,有效湿度减小,湖面进一步下降;4. 6 ka B. P.至今气候干冷,东亚季风衰退,湖面下降,期间也可能受西风环流影响而有短暂的降雨增加时期.     

全新世中期相对稳定的长江水位造成约3000年的湖泊沉积缺失

长江中下游地区浅水湖泊密布,全新世该区湖泊沉积的模式还不清晰。本研究在长江中下游的南漪湖、升金湖和菜子湖这3个湖泊开展了多钻孔AMS^14C测年工作,测年结果显示这些湖泊沉积地层中广泛出现长时间尺度的沉积物缺失。南漪湖湖泊钻孔的沉积物14C年龄介于5668~7828cal.aB.P.,菜子湖湖泊钻孔的沉积物^14C年龄介于6221~7929cal.aB.P.,升金湖围垦区钻孔14C年龄介于6302~7049cal.aB.P.。结合该地区以往湖泊钻孔研究资料,发现全新世长江中下游两岸洼地湖泊存在较广泛的6~3ka的沉积间断。结合长江水位重建资料,笔者提出关于全新世湖泊沉积存有长期间断的新认识:即6~3ka,长江水位相对平稳,湖泊沉积物虽有堆积,但易于被侵蚀搬运造成沉积间断;与此对应的是,在约8~7ka,海面上升造成长江水位较快上升,由于顶托作用,湖泊沉积物持续堆积;在约3ka以来,由于人类活动的影响,以及长江水位的进一步上升,湖泊沉积物也易于堆积,但在一些湖区沉积物也会被侵蚀。在6~3ka之间湖泊沉积物易于被侵蚀的一个可能原因是该时段长江上游来沙来水减少,自然堤易被破坏,对两岸湖泊洼地的封堵作用减少,使得湖泊泥沙易被侵蚀入江。     

季风与西风对青藏高原全新世气候变化的影响:同位素证据

青藏高原气候变化在冰期-间冰期、千年、十年际和季节尺度上受亚洲季风和西风环流的交互影响,表现出显著的区域性特征。然而全新世以来青藏高原气候变化的机制还不甚清楚,主要原因之一是缺少指示意义明确的古气候代用指标。课题组近年来利用叶蜡氢同位素(δDwax)重建了高原东北部的青海湖、中北部的令戈错、中部的达则错、西部的班公错和阿翁错不同时间尺度的大气降水同位素记录,本文对上述工作进行总结,并结合青藏高原全新世以来已发表的其他地点的同位素和古水文记录,揭示全新世以来季风与西风对青藏高原不同区域气候变化的影响。结果表明:1)早全新世青海湖、令戈错、班公错和阿翁错4个湖泊均主要受夏季风影响,夏季风可以影响到青藏高原的大部分地区,此时夏季风在青藏高原的最北界限可能位于青海湖以北、克鲁克湖以南。2)中全新世青海湖、班公错和阿翁错受夏季风影响逐渐减弱;然而令戈错在7.0~4.5 ka水汽主要来源于西风环流。3)晚全新世青海湖和班公错受季风的影响进一步减弱;西风在3.5~1.7 ka和2.0~1.0 ka分别影响到高原中部的令戈错和达则错;晚全新世阿翁错受冰川融水补给影响降水同位素异常偏负。4)本研究表明在中晚全新世季风较弱的时期,西风能够深入到青藏高原内部地区,给高原内部地区带来冷湿的水汽。     

High‐Precision Barium Isotope Measurements of Carbonates by MC‐ICP‐MS

This study presents a high‐precision method to measure barium (Ba) isotope compositions of international carbonate reference materials and natural carbonates. Barium was purified using chromatographic columns filled with cation exchange resin (AG50W‐X12, 200–400 mesh). Barium isotopes were measured by MC‐ICP‐MS, using a ¹³⁵Ba–¹³⁶Ba double‐spike to correct mass‐dependent fractionation during purification and instrumental measurement. The precision and accuracy were monitored by measuring Ba isotope compositions of the reference material JCp‐1 (coral) and a synthetic solution obtained by mixing NIST SRM 3104a with other matrix elements. The mean δ^137/134Ba values of JCp‐1 and the synthetic solution relative to NIST SRM 3104a were 0.21 ± 0.03‰ (2s, n = 16) and 0.02 ± 0.03‰ (2s, n = 6), respectively. Replicate measurements of NIST SRM 915b, COQ‐1, natural coral and stalagmite samples gave average δ^137/134Ba values of 0.10 ± 0.04‰ (2s, n = 18), 0.08 ± 0.04‰ (2s, n = 20), 0.27 ± 0.04‰ (2s, n = 16) and 0.04 ± 0.03‰ (2s, n = 20), respectively. Barium mass fractions and Ba isotopes of subsamples drilled from one stalagmite profile were also measured. Although Ba mass fractions varied significantly along the profile, Ba isotope signatures were homogeneous, indicating that Ba isotope compositions of stalagmites could be a potential tool (in addition to Ba mass fractions) to constrain the source of Ba in carbonate rocks and minerals.     

北京石花洞石笋微层层面有机物质的形成时间及机理初探

通过对北京石花洞滴水水溶性有机碳(DOC)近一个水文年的观测,发现不同点滴水DOC浓度均表现出明显的季节性变化,7月中旬均有一个大的主峰出现。初步说明中国北方石笋微层的层面物质沉积于7月雨季,主要来源于大的雨量对土壤中有机质的淋溶;洞穴顶板较薄的滴水点在5月和8月有明显的DOC次峰,可能与石笋亚年层形成有关。     

11.5kaBP以来尕海沉积物氧化物地球化学特征及其环境意义

通过对柴达木盆地尕海DG03孔沉积序列的年代学测定和沉积物分析,选取对气候环境较为敏感的SiO2,Al2O3,TiO2,Fe2O3,MgO,ＣaO,K2O,Na2O等作为环境代用指标,分析了尕海地区11.5 kaBP以来的气候环境变化。研究表明尕海地区在11.5 kaBP以来存在4个明显的气候变化期:晚冰期晚期（11.5～10.16 kaBP）的气候波动较大,其中11.5～11.16 kaBP是暖干气候;11.16～10.16 kaBP,气候冷干,可能是新仙女木事件的反映;全新世早期（10.16～7.83 kaBP）气候转暖,有短期极干冷事件的发生;中全新世适宜期（7.83～4.73 kaBP）,气候温暖湿润;4.73 kaBP以来的全新世晚期,气候环境明显恶化,期间出现气候暖湿与干冷的多次波动变化。