Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek tephra, northwestern North America

Pollen analysis at two sites, correlated by the presence of the 190,000 yr-old Sheep Creek tephra, documents fluctuations in vegetation and climate consistent with this date and indicates that the records span marine oxygen isotope stage 7 and the stage 6/7 transition. Dawson Cut, near Fairbanks, Alaska, provides a 5.2-m-long pollen record of interglacial boreal forest succeeded by shrub tundra and then forest/tundra. Ash Bend, Stewart River, central Yukon, provides a 9.5-m-long record of interglacial boreal forest succeeded by forest/tundra, shrub tundra, and herbaceous tundra. The replacement of forest at both sites by more open or tundra vegetation indicates warm interglacial conditions giving way to cold and arid climate. It is not clear whether stage 7 was warmer than the present. The warm-cool-warm climate oscillation evident at both sites may correlate to Lake Baikal substages 7a, 7b, and 7c. Sheep Creek tephra fell on forest/tundra vegetation.     

Decoupling of stalagmite-derived Asian summer monsoon records from North Atlantic temperature change during marine oxygen isotope stage 5d

The Asian monsoon is an important component of the global climate system. Seasonal variations in wind, rainfall, and temperature associated with the Asian monsoon systems affect a vast expanse of tropical and subtropical Asia. Speleothem-derived summer monsoon variation in East Asia was previously found to be closely associated with millennial-scale change in temperature in the North Atlantic region between 75 and 10 ka. New evidence recovered from East Asia, however, suggests that the teleconnection between summer monsoon in East Asia and temperature change in the North Atlantic region may have significantly reduced during 120 to ~ 110 ka, a period directly after the full last interglaciation and corresponding roughly to marine oxygen isotope stage 5d. This reduction may be due to the low ice volume in the North Hemisphere at that time, which makes the millennial-scale change in temperature in the North Atlantic region less effective in influencing the Asian summer monsoon. This is important for investigating the mechanisms controlling the Asian summer monsoon and the paleoclimatic teleconnection between East Asia and the North Atlantic region, and for predicting monsoon-associated precipitation in East Asia under a global-warming trend.     

Norwegian sea‐surface palaeoenvironments of marine oxygen‐isotope stage 3: the paradoxical response of dinoflagellate cysts

High‐resolution marine palynological data have been obtained from two very long sediment cores (MD952009 and MD952010) retrieved from the southern Norwegian Sea. The dinoflagellate cyst assemblages show pronounced fluctuations in composition, which correlate strongly with magnetic susceptibility records and also mimic the δ¹⁸O signal of the GISP2 Greenland ice‐core. If focusing on the period from 48 to 30 cal. kyr BP, this correlation suggests a paradoxical response of the sea‐surface environments to the atmospheric conditions over Greenland: when the Greenland δ¹⁸O signal reflects warm interstadial conditions, the Norwegian Sea depicts cold sea‐surface temperatures with quasi‐perennial sea‐ice cover (based on dinoflagellate cysts). In contrast, when the Greenland δ¹⁸O records cold stadial periods, the Norwegian Sea‐surface temperatures are warm (based on dinoflagellate cysts), probably linked to inflow of the North Atlantic Drift. These results, similar in both cores, are contrary to those of previous studies and shed light on a possible decoupling of Norwegian sea surface‐water conditions and atmospheric conditions over Greenland. This decoupling could be linked to an atmosphere–ocean system behaving similar to that which the Northern Hemisphere is experiencing at present, i.e. strongly variable owing to the North Atlantic Oscillation. Copyright © 2002 John Wiley & Sons, Ltd.     

Palaeotemperature reconstructions of the European permafrost zone during marine oxygen isotope Stage 3 compared with climate model results

A palaeotemperature reconstruction based on periglacial phenomena in Europe north of approximately 51 °N, is compared with high‐resolution regional climate model simulations of the marine oxygen isotope Stage 3 (Stage 3) palaeoclimate. The experiments represent Stage 3 warm (interstadial), Stage 3 cold (stadial) and Last Glacial Maximum climatic conditions. The palaeotemperature reconstruction deviates considerably for the Stage 3 cold climate experiments, with mismatches up to 11 °C for the mean annual air temperature and up to 15 °C for the winter temperature. However, in this reconstruction various factors linking climate and permafrost have not been taken into account. In particular a relatively thin snow cover and high climatic variability of the glacial climate could have influenced temperature limits for ice‐wedge growth. Based on modelling the 0 °C mean annual ground temperature proves to be an appropriate upper temperature limit. Using this limit, mismatches with the Stage 3 cold climate experiments have been reduced but still remain. We therefore assume that the Stage 3 ice wedges were generated during short (decadal time‐scale) intervals of extreme cold climate, below the mean temperatures indicated by the Stage 3 cold climate model simulations. Copyright © 2003 John Wiley & Sons, Ltd.     

Late Cretaceous marine reptiles (Elasmosauridae and Mosasauridae) of the Chatham Islands, New Zealand

A new marine reptile record for the Upper Cretaceous of the Chatham Islands is described from the Takatika Grit. Incomplete mosasaur and plesiosaur remains represent the first record of marine reptiles from the Chatham Islands and wider New Zealand. Present among the myriad bones are elasmosaurid plesiosaurs and mosasaurine mosasaurs. This assemblage is comparable to the New Zealand marine reptile record and represents apex predators that flourished in a zone of upwelling in a Late Cretaceous southern high-latitude ecosystem.     

Oxygen isotope stage 3 fluvial and eolian successions in Europe compared with climate model results

Fluvial and eolian successions of oxygen isotope stage 3 are compared with global (GCM) and regional climate (RCM) modeling experiments of the stage 3 and last glacial maximum climate in Europe. Differences in precipitation between stage-3 stades and interstades were minor, which is confirmed by the fluvial successions. The fluvial response to climate variation is non-uniform, and in southern Europe more pronounced than in northern Europe. The model simulations indicate a strong western winter circulation over Europe during stage 3, which is supported by the eolian deposits data. Wind speeds in the last glacial maximum simulation appear modest compared with those of stage 3, which contrasts with the abundance of eolian deposits. This suggests that during glacial climates the stabilizing effect of vegetation determines eolian sedimentation rates, rather than wind speed. Stage 3 can be divided into an older part (>45,000 cal yr B.P.) with a relatively stable landscape and moist climate and a younger part with more frequent climate change and decreasing landscape stability.     

大别山中生代中酸性岩浆岩锆石U-Pb定年、元素和氧同位素地球化学研究

对大别山中生代主簿源、天柱山和团岭中酸性岩浆岩进行了锆石U-Pb定年、全岩主量和微量元素分析以及全岩和单矿物的氧同位素分析。结果表明,这些富钾的中酸性侵入岩表现出明显的轻稀土富集和高场强元素(Nb、P和Ti)负异常,与围岩片麻岩之间具有类似的微量元素分布特征和初始Sr-Nd-Ph同位素组成。锆石U-Pb年龄指示了早白垩世(121～131Ma)的岩浆结晶年龄。通过CL照相和SHRIMP定年在某些锆石颗粒中发现了老的继承核,年龄分别为742～815Ma和222Ma。这些新元古代和三叠纪核年龄分别与大别-苏鲁造山带超高压变火成岩原岩年龄和超高压变质年龄一致。尽管石英和锆石具有较小的δ~(18)O值变化范围(石英:6.30‰～8.66‰,锆石:4.14‰～6.11‰),全岩和其它单矿物氧同位素比值变化较大(全岩:0.07‰～7.13‰,钾长石:0.55‰～7.40‰,斜长石:-4.88‰～6.96‰),大多数锆石具有与正常地幔锆石(5.3±0.3‰)一致的δ~(18)O值。大多数样品的石英-锆石之间保存了氧同位素平衡分馏,而其它矿物(如,钾长石、斜长石、黑云母和角闪石)与锆石之间则大多表现出明显的氧同位素不平衡分馏,指示它们受到了岩浆期后亚固相水-岩相互作用的扰动。元素和同位素特征表明,大别山中生代中性岩起源于加厚基性下地壳的脱水部分熔融,在岩浆侵位过程中伴随有结晶分异作用;而花岗岩则起源于与北大别TTG正片麻岩具有相似化学组成的中性地壳的部分熔融。因此,大别山中生代中酸性岩岩浆源区是三叠纪扬子陆块俯冲产生的加厚地壳,形成机制可能与早白垩世地幔超柱事件热扰动所引起的部分熔融有关。     

大兴安岭北部比利亚谷铅锌矿黄铁矿Re-Os同位素年龄及He-Ar同位素地球化学特征

比利亚谷铅锌矿位于海拉尔-根河中生代火山盆地北西缘的得尔布干成矿带.该矿床赋存于上侏罗统满克头鄂博组酸性火山岩中,受NW向断裂构造控制,主矿体呈脉状产出.由于缺少适合传统放射性同位素定年的矿物,其成矿时代未得到很好的限定,制约了对矿床成因的认识.本文采用矿床中与矿石矿物密切共生的黄铁矿Re-Os同位素定年技术对比利亚谷...     

Dawson tephra,a widespread 29-ka marker bed,in a marine core from Patton Seamount off the Alaska Peninsula and its potential marine–terrestrial correlation

A tephra layer with normal grading in the sub-bottom depth interval 119–122 cm in marine core SO202-27-6 was collected on Patton Seamount in the northeast North Pacific Ocean. Based on the geochemistry of volcanic glass shards determined by a wavelength dispersive electron probe micro-analyser and an X-ray fluorescence analyser, this layer is correlated to the Dawson tephra, a widespread late Pleistocene time marker tephra in Alaska and the Yukon. The age of the Dawson tephra in the core is 29.03 ± 0.178 ka (1 sigma) based on a published age model. The Dawson tephra is revealed to have been deposited in the transition from marine isotope stage 3 to 2, i.e. the last stage of Heinrich Stadial 3 derived from the ice-rafted debris signal. According to the correlation between Greenland (NGRIP ice core) and this core, the Dawson tephra occupies the record immediately before inter stadial 4 in the δ¹⁸O stratigraphy of NGRIP. The Dawson tephra on Patton Seamount includes lithic fragments, which suggests that it was deposited not only by fall-out but also in part via another mechanism, such as icebergs from the Cordilleran ice sheet or seasonal sea ice.     

The lower marine to lower freshwater Molasse transition in the northern Alpine foreland basin (Oligocene; central Switzerland–south Germany): age and geodynamic implications

The Wilhelmine Alpe section near Immenstadt (Allgäu, south Germany), which represents one of the best continuously exposed outcrops within the northern Alpine foreland basin, has been analyzed for magnetostratigraphic and palynostratigraphic signals. The section comprises the marine-to-terrestrial transition from Lower Marine (UMM) to Lower Freshwater Molasse (USM) sediments. Based on the correlation of the local magnetic pattern with the geomagnetic polarity timescale (GPTS) and palynostratigraphic data, an age of about 31 Ma is suggested for the UMM–USM transition in the Wilhelmine Alpe section. A comparison with coeval magnetostratigraphic sections from central and eastern Switzerland indicates that the regression of the UMM sea along the southern margin of the Molasse basin occurred strongly heterochronously between 31.5 and 30 Ma. The heterochroneity is attributed to the deposition of fan-delta and alluvial fan sediments which document that the overall marine conditions during the UMM were accompanied by strong clastic input derived from the rising Alps. This clastic contribution had a much stronger influence on the depositional pattern than previously thought.     

Speleothem evidence of warm episodes in northeast France during Marine Oxygen Isotope Stage 3 and implications for permafrost distribution in northern Europe

U-Th ages have been obtained by TIMS on the growth periods of a stalagmite from the “Grotte des Puits de Pierre-la-Treiche” (northeastern France), during the middle part of the “Weichselian glaciation” (Marine Isotope Stage 3), between 55.36 ± 0.95 and 53.34 ± 0.49 ka and around 45.85 ± 0.49 ka. These episodes are contemporaneous with abrupt climatic variations recorded in Greenland ice cores (Greenland interstadials 12, 14 and 15) that have been previously recognized in European speleothems. They also coincide with two interstadials, known as “Goulotte” and “Pile” in the Grande Pile pollen sequence (eastern France), which have been correlated with the Moershoofd complex in the Netherlands. Such evidence of speleothem deposition related to temperate episodes gives a strong indication of the absence of continuous shallow permafrost during the middle part of MIS 3 in northeastern France.     

Identification of the Fugloyarbanki tephra in the NGRIP ice core: a key tie‐point for marine and ice‐core sequences during the last glacial period

A visible tephra horizon in the NGRIP ice core has been identified by geochemical analysis as the Fugloyarbanki Tephra, a widespread marker horizon in marine cores from the Faroe Islands area and the northern North Atlantic. An age of 26 740 ± 390 yr b2k (1σ uncertainty) is derived for this tephra according to the new Greenland Ice Core Chronology (GICC05) based on multi‐parameter counting of annual layers. Detection of this tephra for the first time within the NGRIP ice core provides a key tie‐point between marine and ice‐core records during the transition between MIS 3 and 2. Identification of this volcanic event within the Greenland records demonstrates the future potential of using tephrochronology to precisely correlate palaeoarchives in widely separated localities that span the last glacial period, as well as providing a potential method for examining the extent of the radiocarbon marine reservoir effect at this time. Copyright © 2008 John Wiley & Sons, Ltd.     

A prolonged warm and humid interval during marine isotope stage 13–15 as revealed by hydrographic reconstructions from the South China Sea (IMAGES MD972142)

Variations of orbital-driven insolation, ice volume, and greenhouse gas effects have been proposed as major controlling factors in determining the timing and amplitude of Quaternary cyclic climate changes. However, it remains to be determined how the internal feedback in the tropical atmosphere and ocean and the coupling between the low- and high-latitude systems may have produced instability or non-cyclic changes in the long-term climate evolution. Such “abnormalities” have been reported increasingly from paleoclimatic reconstructions in East Asia and the western Pacific for a prolonged warm and humid climate interval during marine isotope stage (MIS) 13–15, ～475–610 kya. To better address the climate abnormality in MIS 13–15 that has been observed in the western Pacific, here we report high-resolution late Quaternary planktic foraminifer faunal abundance and faunal sea surface temperature (SST) records from the International Marine Past Global Change (IMAGES) program core MD972142, which was retrieved from the southeastern South China Sea (SCS). Our results indicate that the faunal assemblages and SSTs in the southeastern SCS express a substantially prolonged, unusual warm interglacial-type climate condition in MIS 13–15. The climate was abnormally warm during the cold MIS 14. Our study also suggests a lowering of sea surface salinity (SSS) during MIS 13–15. While the western Pacific climate experienced a persistently warm and humid period at MIS 14, a “normal” cooling (～2 °C) condition on the surface of the eastern equatorial Pacific existed concomitantly. While assessing possible interpretations of this “abnormal” climate interval in MIS 13–15, our study indicates that an enhanced interhemispheric and/or longitudinal temperature gradient across the basin-wide Pacific cannot be ruled out. A change in the sensitivity of the East Asian Monsoon (EAM) that controlled temperature and precipitation patterns in East Asia and the western Pacific is probably also important or responsible for this climate abnormality. Based on our evidence, we suggest that the tropical dynamics would have played a role in the climate abnormality in MIS 13–15, through maintaining or even increasing the longitudinal SST gradient in the equatorial Pacific, which may have intensified the low-latitude trade winds in the eastern component of the Walker Circulation that drove a longer duration and/or stronger intensity of the summer vs. winter EAM.     

大别造山带天柱山燕山期中酸性岩浆岩元素和同位素地球化学研究

大别-苏鲁造山带中生代岩浆岩的物质来源和成因机制,是大陆碰撞造山带研究的热点和前沿问题之一。本文通过对大别造山带天柱山燕山期中酸性岩进行全岩主量和微量元素以及放射成因同位素、单矿物氧同位素分析,指示这些碰撞后岩浆岩是俯冲陆壳物质再循环的产物。研究发现,这些中酸性岩表现出明显的轻稀土富集、高场强元素Nb、Ta和Ti负异常以及Pb正异常。它们都具有较高的Sr同位素初始比值(0．7062-0．7083)和较低的εNd(t)值(-17．1--19．7),与北大别杂岩的变化范围一致。单矿物氧同位素变化范围较大(石英:7．48-9．16‰,钾长石:3．76-7．80‰,斜长石:2．06- 6．96‰,锆石:4．16-5．83‰),大多数样品锆石具有与正常地慢锆石(5．3±0．3‰)一致的δ18O值。大多数样品的石英-锆石之间达到并保存了岩浆结晶时的氧同位素平衡分馏,而其它矿物(如钾长石、斜长石、黑云母和角闪石)与锆石之间大多表现为明显的氧同位素不平衡分馏,表明它们受到了岩浆期后亚固相水-岩相互作用的扰动。元素、Sr-Nd同位素和锆石氧同位素特征表明,大别山中生代中性岩可能是由加厚的扬子板块基性下地壳脱水部分熔融并经结晶分异形成的,花岗岩是由化学组成类似于北大别TTG片麻岩的中性下地壳脱水部分熔融形成的。     

赣北石门寺花岗斑岩锆石U-Pb年龄、岩石地球化学、Hf同位素特征及其对成矿的制约

大湖塘钨矿田石门寺矿段钨多金属矿成矿作用与燕山期花岗质岩浆活动密切相关。其中燕山期花岗斑岩与热液隐爆角砾岩关系密切,是重要的成矿地质体。为研究该岩体成岩时代、岩石成因与演化、形成背景,探讨岩体与成矿的关系,对石门寺花岗斑岩开展了系统的岩相学、岩石化学、锆石U-Pb年龄及Hf同位素研究。结果表明,花岗斑岩形成年龄为154.36±0.83 Ma;花岗斑岩为高硅（SiO2含量为71.90%~76.53%）、过铝质（Al2O3含量为12.76%~14.76%,A/CNK值为1.25~1.39）、高钾钙碱性系列（K2O含量为2.58%~5.42%）岩石;富集大离子亲石元素,亏损高场强元素,稀土元素含量（49.38×10-6~72.36×10-6）较低、LREE/HREE（9.83~16.76）和（La/Yb）N值（16.43~39.45）较高,呈明显负Eu（δEu=0.27~0.65）异常;岩石类型为S型花岗岩。锆石的εHf（t）值为-23.6~-2.9,二阶段模式年龄为1.39~2.70 Ga,表明石门寺花岗斑岩可能为古老地壳部分熔融的产物。岩浆源岩主要为富粘土物质;岩浆演化过程中经历了镁铁质矿物、钛铁矿、斜长石的分离结晶,磷灰石没有发生显著分离结晶作用。结合区内中生代成矿地球动力学背景分析,九岭-鄣公山隆起带存在2期重要的成矿作用：①约150 Ma,由于太平洋板块俯冲汇聚而产生的挤压构造背景下的成岩成矿作用;②约135 Ma以来,处于区域岩石圈伸展减薄背景下的钨多金属成矿作用。     

安徽南部地区奥陶纪海相红层的分布及时代

在充分收集前人奥陶系地层学、古生物学和沉积学等资料的基础上, 对安徽南部地区奥陶系进行了系统梳理, 开展皖东地1井和贵池冯村剖面奥陶纪海相红层系统研究, 为地层对比、古气候和古地理恢复提供重要的科学依据。研究表明: 奥陶纪海相红层主要分布于紫台组、牯牛潭组、大田坝组、宝塔组、汤头组和胡乐组, 时代为早奥陶世弗洛晚期至晚奥陶世凯迪中期; 主要岩石类型为碳酸盐岩(瘤状泥质灰岩、网纹状灰岩、含生物碎屑灰岩和泥微晶灰岩等), 少量碎屑岩(泥岩、含粉砂质泥岩、含粉砂质页岩); 大多数属半深水海相红层, 局部为浅水和深水海相红层; 自北西向南东呈现一层式→二层式→三层式→二层式→一层式→零层式的横向变化, 出现时代凯迪期→达瑞威尔期→弗洛期的纵向变化, 海相红层的分布与沉积环境、古水温和不同地区构造性质密切相关; 研究区海相红层不仅具有区域性(与湖北宜昌奥陶系具有对比性), 而且具有全球性(中国主要块体), 在地层划分与对比上具有重要的研究价值。

     

柴北缘平台地区下干柴沟组下段碳酸盐胶结物特征及意义

综合运用岩石学、矿物学和地球化学等方法,对柴达木盆地北缘中段平台地区古近系下干柴沟组下段储集岩中碳酸盐胶结物的成岩温度、形成环境和物质来源等进行了系统研究。结果表明,平台地区储集砂岩中主要发育方解石和白云石两种碳酸盐胶结物。自生黏土矿物主要以伊利石、绿泥石和伊-蒙混层为主,测定其碳同位素(δ~(13)C)值分布范围在-7.5‰~-1.4‰之间,平均为-4.0‰;氧同位素(δ~(18)O)值分布范围在-14.4‰~-10.1‰之间,平均为-11.6‰,推算古盐度(Z)值分布范围为106.38~119.23,平均值为113.24。平台地区古近系下干柴沟组下段储集岩在成岩阶段早期有少量有机碳加入,成岩流体以淡水环境为主。碳酸盐胶结物的形成温度在71.49~101.01℃之间,平均值为81.32℃。根据成岩特征及形成温度,揭示平台地区古近系下干柴沟组下段储集岩主要处于早成岩阶段晚期。     

再论塔里木北缘阿克苏蓝片岩的时代和成因环境:来自锆石U-Pb年龄、Hf同位素的新证据

阿克苏蓝片岩和基性岩墙形成时代和构造背景对认识塔里木地块前寒武纪构造演化以及新元古代超大陆重建具有重要意义.本文通过对含蓝片岩的阿克苏群中变质碎屑岩和侵入阿克苏群的基性岩墙的锆石U-Pb定年及Hf同位素分析表明,(长石)石英片岩中碎屑锆石出现2个明显的统计峰值,较老一组锆石²⁰⁷Pb/²⁰⁶Pb的表面年龄集中在~1.9Ga,并有少量太古代的年龄信息;另一组较年轻锆石²⁰⁶Pb/²³⁸U表面年龄峰值为~820Ma,代表阿克苏群的最大沉积年龄.侵入阿克苏群的基性岩墙锆石U-Pb年龄为~760Ma.阿克苏蓝片岩相变质的时间被严格限定在820~760Ma区间内.碎屑锆石Hf同位素地壳模式年龄峰值出现在2.2~2.3Ga,2.6Ga和3.2~3.3Ga.综合本次工作及前人研究成果,表明阿克苏蓝片岩地体是塔里木早前寒武纪基底之上发育起来的大陆边缘岩浆弧.     

碳酸钙同质多象转变过程中氧同位素分馏的实验研究

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