Mid-Holocene evolution and paleoenvironments of the shoreface–offshore transition, north-eastern Argentina: New evidence based on benthic microfauna

A sedimentary record spanning 5792–5511 cal yr BP and 3188–2854 cal yr BP was recovered at 36° 45′ 43″ S–56 ° 37′ 13″ W, south-west South Atlantic. The sedimentological features and micropaleontological (benthic foraminifera and ostracoda) content were analyzed in order to reconstruct paleoenvironmental conditions. Considerable environmental fluctuations are indicated by all these proxies. Five different stages were distinguished: Stage 1 (ca. 5800–5000 cal yr BP) consists of muddy sand with abundant microfossils. In this interval, species typical for inner marine shelf environments maintained a high abundance. Stage 2 consists of plastic light greenish grey clays barren of microfossils, and probably represents fluvial input from the de la Plata River to the shelf contemporaneous of a lowering of sea level. Stage 3 is composed of brownish yellow sandy silts, and represents increasing marine conditions in the area as reflected by higher faunal diversity and typical foraminifera of inner shelf environments. Stage 4 is made of homogeneous mud, barren of microfossil, which represents a new pulse of fluvial input to the shelf in consequence of a new fall in sea level. The final part of the core (Stage 5) is a coarsening upward sequence, grading from greeny brown clayey sandy silts to coarse shelly sands and represents the modern sedimentation in the area. This interpretation strengthens the stepped model of late-Holocene sea-level fall between 5511–5792 cal yr BP and 2854–3188 cal yr BP in Buenos Aires coast, and agrees with the relative sea-level history previously proposed by some authors from western South Atlantic coasts.     

华南沿海地区全新世海平面变化特征

１海平面变化特征１．１全新世中期海侵根据地层中所含硅藻属种雷州半岛海康南田乡一１５ｍ钻孔岩芯，含有丰富的硅藻，主要属种是①：具槽直链藻（Ｍｅｌｏｓｉｒａ　ｓｕｌｃａｔａ（Ｅｈｒ）Ｋｕｔｚ）、范氏回箱藻（Ｐｙｘｉｃｌｉｃｕｌａ　ｗｅｙｐｒｅｃｈｔｉｉＧｒｕｎ）、条纹小环藻（Ｃｙｃｌｏｔｅｌｌａｓｔｒｉａｔａ（Ｋｕｔｚ）Ｇｒｕｎ）、流水双菱藻（ＳｕｒｉｒｅｌｌａｆｌｕｍｉｎｅｎｓｉｓＧｒｕｎ）。上述硅藻主要是海相生活属种，今日南田乡已距离海岸线５ｋｍ。徐闻海安西侧一１８．５ｍ钻孔岩芯中的硅藻除上述属…     

“3S”技术在四川生态环境动态监测中的应用研究

为有效实现四川省生态环境的动态监测,运用RS、GIS和GPS技术,以2004年中巴资源卫星(CBERS-02)遥感影像数据为信息源,2000年TM遥感影像解译的数据为基础,对2004年遥感影像进行解译,修改2000年数据库;手持GPS接收机,在野外对解译成果进行验证,更新数据库;利用GIS技术的空间分析功能,提取出2000～2004年期间土地利用/覆被变化信息,得到2000～2004年期间四川省高精度的土地利用/覆被变化数据库。最后对四川省土地利用/覆被变化信息进行分析,对四川省生态环境的下一步研究指名了方向。     

青藏高原甜水海盆地MIS 3阶段湖泊沉积与环境变化

青藏高原西北部甜水海盆地地处内陆干旱区和喀喇昆仑山的东侧雨影区,气候环境极端干旱。但多次考察结果揭示晚更新世时期存在着大湖和高湖面的地质证据。为了探讨该地区过去气候与环境的演变历史,在甜水海盆地(海拔4840m)进行钻探采得沉积岩芯56.32m(TS95),通过对沉积岩芯其中一段的粒度、生物、同位素及地球化学多指标综合分析,探讨了MIS3时期甜水海地区气候环境演化过程。沉积岩芯显示沉积物岩性变化频繁,记录着湖面多次波动、沉积环境多变的演化过程,分别在59～56kaB.P.,49～47kaB.P.,45～41kaB.P.,35.5～34.0kaB.P.和28～25kaB.P.期间存在高湖面和湖水稀释。在其多环境指标的记录中,Heinrich事件和D-O旋回均有反映,揭示了全球变化信号在研究区的响应。同时,不同高湖面阶段内部环境波动也较明显,差别较大,其产生原因也各有不同,归结为3种情况:1)由于气候变暖导致冰雪融水补给增加而产生的高湖面;2)由于冷湿气候导致的高湖面;和3)由于暖湿气候导致的高湖面。本研究揭示出了MIS3时期气候频繁波动的特征和气候的不稳定性。     

黑河流域水环境演变及其驱动机制研究进展

基于近几十年来诸多学者对西北干旱区典型内陆河流域——黑河流域水环境演变诸方面研究成果,综述了上游山区成水环境、中游绿洲用水环境和下游荒漠天然绿洲水成环境在不同时间尺度上的演变过程及其驱动机制。通过对各种古环境代用指标的对比研究表明：在大尺度上,流域上下游表现出阶段性的一致性水环境演变趋势;在小尺度上,则表现水环境演变的时空异质性。驱动机制方面,在空间上,流域上、中、下游水环境演变的气候变化和人类活动影响驱动作用各有侧重;在时间上,表现为不同尺度上气候变化与流域人类活动耦合作用的驱动机制。     

Effect of volatiles erupted from Mesozoic and Cenozoic volcanic activities on paleo-environmental changes in China

Based on the determination of composition of volcanic volatiles and petrologic estimation of the total mass of volatiles erupted, we showed important advances in the study of the impact of Mesozoic and Cenozoic volcanic activities on paleo-environmental changes in China. The volcanic activities include western Liaoning and Zhangjiakou Mesozoic intermediate-acidic explosive eruptions, southern Tibet and Shanwang Cenozoic volcanism, and Mt. Changbai volcanic eruption around one thousand years ago. The paper predominantly discusses the earth’s surface temperature changes, ozone depletion, acidic rain formation and mass mortalities of vertebrate induced by the Mesozoic and Cenozoic volcanism in China. __________ Translated from Bulletin of Mineralogy, Petrology and Geochemistry, 2007, 26(4): 319–322 [译自: 矿物岩石地球化学通报]     

Sea level and diagenesis: a case study on Pleistocene beaches,Whalebone Bay,Bermuda

Pleistocene fluctuations of sea level have left marine and aeolian limestones intercalated with glacial red soils on the Bermuda Carbonate Platform (Atlantic, 64°50W, 32°20N). Successive eustatic highstands of similar amplitude drowned the tectonically stable platform and piled up similar sets of sediments. Up to three Pleistocene beaches are stacked in shorelines sections. Post-depositional diagenetic histories of these beaches can be linked to repeated changes in sea level and pore waters.This paper presents field evidence and petrographic results (microscope, X-ray, cathodoluminescence, SEMEDAX) for the diagenetic histories of two superimposed Pleistocene beaches in Whalebone Bay, Bermuda North Shore. The younger beach was deposited during isotopic stage 5e, about 120 ka ago. The age of the older beach may be isotopic stage 9 or older.Diagenesis drastically altered the older beach before the stage 5e transgression. Primary high-Mg calcite (HMC) and aragonite were no longer present. Marine skeletal grains were instead leached or recrystallized to low-Mg calcite (LMC). Primary and secondary pore space were largely reduced by LMC cement. Lines of needle relics reminiscent of marine aragonite cement occur as inclusions within syntaxial rim cements around echinoderm grains, indicating that a marine influence had at least once interrupted this period of freshwater alteration. Finally, before the rocks became buried by the sediments of the younger beach, a crust of marine, bladed HMC cement was precipitated throughout the pore space.The younger beach consists of skeletal grains that are, apart from the effects of non-selective dissolution, essentially unaltered. The sediments are only weakly lithified by cryptocrystalline LMC showing an alveolar texture, tangential fibres and other features characteristic of calichification. A younger post-depositional marine influence is not recorded.These results suggest that, under favourable conditions, diagenetic processes can document sea-level fluctuations. The recorded fluctuations, however, are difficult to assess because even major sea-level highstands may not produce a diagenetic imprint. Correspondence to: R. Vollbrecht     

Tripartite climate reversal in Central Europe 5600-5300 years ago

The history of variations in water level of Lake Constance, as reconstructed from sediment and pollen analysis of a sediment sequence from the archaeological site of Arbon-Bleiche 3, shows an abrupt rise in lake level dendrochronologically dated to 5375 yr ago (5320 yr relative to AD 1950). This event, paralleled by the destruction of the Neolithic village by fire, provoked the abandonment of this prehistoric lake-shore location established in the former shallow bay of Arbon-Bleiche, and was the last of a series of three episodes of successively higher lake level, the first occurring at 5600-5500 cal yr B.P. The dendrochronologically dated rise event was synchronous with an abrupt increase in atmospheric ¹⁴C. This supports the hypothesis of an abrupt climate change forced by varying solar activity. Moreover, the three successive episodes of higher lake level between 5600 and 5300 cal yr B.P. at Arbon-Bleiche 3 coincided with climatic cooling and/or changes in moisture conditions in various regions of both hemispheres. This period corresponds to the mid-Holocene climate transition (onset of the Neoglaciation) and suggests inter-hemispheric linkages for the climate variations recorded at Arbon-Bleiche 3. This mid-Holocene climate reversal may have resulted from complex interactions between changes in orbital forcing, ocean circulation and solar activity. Finally, despite different seasonal hydrological regimes, the similarities between lake-level records from Lake Constance and from Jurassian lakes over the mid-Holocene period point to time scale as a crucial factor in considering the possible impact of climate change on environments.     

Climate variability in the Spanish Pyrenees during the last 30,000 yr revealed by the El Portalet sequence

Palynological, sedimentological and stable isotopic analyses of carbonates and organic matter performed on the El Portalet sequence (1802 m a.s.l., 42°48′00?N, 0°23′52?W) reflect the paleoclimatic evolution and vegetation history in the central-western Spanish Pyrenees over the last 30,000 yr, and provide a high-resolution record for the late glacial period. Our results confirm previous observations that deglaciation occurred earlier in the Pyrenees than in northern European and Alpine sites and point to a glacial readvance from 22,500 to 18,000 cal yr BP, coinciding with the global last glacial maximum. The patterns shown by the new, high-resolution pollen data from this continental sequence, chronologically constrained by 13 AMS ¹⁴C dates, seem to correlate with the rapid climate changes recorded in Greenland ice cores during the last glacial-interglacial transition. Abrupt events observed in northern latitudes (Heinrich events 3 to 1, Oldest and Older Dryas stades, Intra-Allerød Cold Period, and 8200 cal yr BP event) were also identified for the first time in a lacustrine sequence from the central-western Pyrenees as cold and arid periods. The coherent response of the vegetation and the lake system to abrupt climate changes implies an efficient translation of climate variability from the North Atlantic to mid latitudes.     

Benthic foraminifers in upper Quaternary sediments of the southern Bering Sea: Distribution and paleoceanographic interpretations

Composition and distribution of benthic foraminifers, being coupled with isotopic-geochemical data on Upper Pleistocene and Holocene sediments from the southern Bering Sea (Core GC-11; 53°31′ N, 178°51′E, water depth 3060 m), demonstrate variations in bottom water properties during the last 54 kyr. Their abundance increased to some extent during short periods corresponding to warm Dansgaard-Oeshger interstadials 14, 12, 8, and 2 of marine isotopic stages (MIS) 3 and 2. The first and second deglaciation phases separated by the Younger Dryas cooling episode are marked by significant abundance peaks of benthic foraminifers (an order magnitude higher than in the glacial period), although their share in community of benthic and planktonic foraminifers taken together decreases. Species typical of stable high-productivity areas gain the dominant position. A significant proportion of agglutinated species in the Holocene sediments is indicative of Ca ions deficiency that accelerates dissolution of carbonate tests up to their disappearance approximately 2.5–3 ka ago.