A Comparison of Sediment Varves (1950–2003 AD) in Two Adjacent Lakes in Northern Sweden     

V. Gälman  G. Petterson  I. Renberg 《Journal of Paleolimnology》2006,35(4):837-853

Koltjärnen and Nylandssjön are two closely situated lakes (<2 km apart) in northern Sweden. During the past century, distinct varved sediments have formed in these lakes. Nylandssjön has two varved, deep basins. Since lake and catchment characteristics superficially appear very similar for the two lakes and they are exposed to the same climate, one would expect the sediment varves to be similar. This investigation compares the varves in the two deep basins of Nylandssjön, and in the two lakes. The comparison of basins of Nylandssjön shows that varve thickness, water content and annual accumulation rates of organic matter and nitrogen are correlated for the period (1970–2003). The grey-scale curves are only clearly similar in about 50% of the varves. In the between-lake comparison varve thickness, water content and annual accumulation rates of organic matter and nitrogen are correlated for the period (1950–1996). However, the annual accumulation rates of dry mass, minerogenic matter and biogenic silica differ between the lakes, as well as within-varve successions in grey-scale. A general explanation to the differences is that the prerequisites for varve formation are not totally similar because of differences in catchment size, catchment- to-lake material fluxes, lake productivity and land-use influence. This study illustrates the complex relationships that exist between a lake, its catchment, in-lake productivity and formation of sediment varves. As a consequence, we must not apply a too simplistic view of the potential of varves as past climatic indicators, especially if the lakes are affected by land-use.  相似文献   

Lake Sediment Core Records of Sulphur Accumulation and Sulphur Isotopic Composition in Central Ontario, Canada Lakes     

M. Catherine Eimers  Andrew M. Paterson  Peter J. Dillon  Sherry L. Schiff  Brian F. Cumming  Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109

Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~ 20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ ³⁴S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment were relatively low (1.9–5 mg S g⁻¹ dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in δ ³⁴S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally reciprocal depth pattern between total S concentration and δ ³⁴S ratios. While initial shifts in total S and δ ³⁴S were likely due to enhanced SO₄ reduction of newly available anthropogenic SO₄, both the magnitude and pattern of up-core S enrichment and shifts in δ ³⁴S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and δ ³⁴S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S deposition in this region, likely due to redox-related mobility of S in upper sediment.  相似文献   

Seasonal Diatom Variability and Paleolimnological Inferences – A Case Study     

Dörte Köster  Reinhard Pienitz 《Journal of Paleolimnology》2006,35(2):395-416

The seasonality of physical, chemical, and biological water variables is a major characteristic of temperate, dimictic lakes. Yet, few investigations have considered the potential information that is encoded in seasonal dynamics with respect to the paleolimnological record. We used a one-year sequence of diatoms obtained from sediment traps and water samples, as well as the sedimentary diatom record covering the past ca. 1000 years in Bates Pond, Connecticut (USA), to investigate which variables influence the seasonal distribution of diatoms and how this can be used for the interpretation of the fossil record. The seasonal patterns in diatom assemblages were related to stratification and, to a lesser extent, to nitrate, silica, and phosphorus. During mixing periods in spring and autumn, both planktonic and benthic species were collected in the traps, while few lightly silicified, spindle-shaped planktonic diatoms dominated during thermal stratification in summer. Changes in fossil diatom assemblages reflected human activity in the watershed after European settlement and subsequent recovery in the 20th century. A long-term trend in diatom assemblage change initiated before European settlement was probably related to increased length of mixing periods during the Little Ice Age, indicated by the increase of taxa that presently grow during mixing periods and by application of a preliminary seasonal temperature model. We argue that the analysis of seasonal diatom dynamics in temperate lakes may provide important information for the refinement of paleolimnological interpretations. However, investigations of several lakes and years would be desirable in order to establish a more robust seasonal data set for the enhancement of paleolimnological interpretations.  相似文献   

A chronological assessment of Lake Okeechobee (Florida) sediments using multiple dating markers     

Shawn P. Schottler  Daniel R. Engstrom 《Journal of Paleolimnology》2006,36(1):19-36

Reconstructing recent limnological history often relies on lead-210 dating to accurately ascribe a chronology to a sediment profile. In Lake Okeechobee, Florida, a large, shallow subtropical lake that may experience severe mixing, multiple dating methods are required to confirm that conformable sedimentation has been preserved and that the assumptions of the ²¹⁰Pb method are satisfied. This study uses stratigraphic profiles of heavy metals, ¹³⁷Cs, PCBs and pollen as independent dating markers to validate the sediment chronology as determined by ²¹⁰Pb for three cores from the central mud zone of the lake. Unsupported ²¹⁰Pb and most dating markers show distinct concentration/depth profiles, suggesting that the sediments have not been severely mixed for at least the last 75 years. Onset and maximum activity of the radioisotope ¹³⁷Cs in the cores coincides with the ²¹⁰Pb-dated interval of 1945–1970. This agrees well with the known timing of atmospheric deposition of ¹³⁷Cs that resulted from above-ground nuclear testing during late 1940s until 1963. Sediment core profiles of atmospherically deposited metals such as Zn and Pb, which reflect regional increases during industrialization and decreases after regulation in the 1970s, exhibit expected concentration increases and peaks coinciding within 5–15 years of the predicted ²¹⁰Pb dates. Uranium, a contaminant in some phosphate fertilizers, shows large concentration increases at core depths dated to be about 1950 by ²¹⁰Pb, matching the intensification of agriculture after WWII. PCBs, which are expected to peak in the early 1970s, were measured in one core, and the observed peak corresponds to a ²¹⁰Pb date of about 1960. Pollen makers were unable to verify specific events, but increases in disturbance taxa and declines in native types correspond generally with the expected dates assigned by ²¹⁰Pb dating. Conformity between the ²¹⁰Pb defined dates and independent markers of < ±15 years confirm that Lake Okeechobee sediments do preserve a sequential and reliable stratigraphic history of the lake, useful for reconstructing past limnological conditions.  相似文献   

Environmental Changes at the Desert Margin: An Assessment of Recent Paleolimnological Records in Lake Qarun, Middle Egypt   总被引：1，自引：0，他引：1  

R. J. Flower  C Stickley  N. L. Rose  S Peglar  A. A. Fathi  P. G. Appleby 《Journal of Paleolimnology》2006,35(1):1-24

Lake Qarun has been profoundly affected by a combination of human activities and climatic changes during the past 5000 years. Instrumental records available for the 20th century show that during most of this period both lake water level and salinity increased and that by the late 1980s lake water salinity was approximately that of seawater. Sediment cores (c. 1 m long) were collected from this shallow (Z_max 8.4 m) saline lake in 1998 and the master core (QARU1) was used to examine the potential of paleolimnology for reconstructing the recent environmental history of the site. According to ¹³⁷Cs and ²¹⁰Pb radio-assay, the recent sediment accumulation rate in QARU1 was around 5 mm year⁻¹ during the latter half of the 20th century but radionuclide levels were low. Spheroidal carbonaceous particles (SCPs) were present in the upper c. 30 cm of QARU1 and indicates contamination by low level particulate pollution, probably beginning around 1950. The record of exotic pollen (Casuarina) indicated that sediment at 51–52 cm depth dated to around 1930. Otherwise the pollen spectra indicated a strongly disturbed landscape with high ruderals and increased tree planting particularly since c. 1950. Diatom records were strongly affected by taphonomic processes including reworking and differential preservation but typical marine diatoms increased after the 1920s. Instrumental records show that the lake became more saline at this time. Freshwater taxa were present at approximately similar abundances throughout the core. This distribution probably reflected a combination of processes. Reworking of ancient freshwater diatomites is one likely source for freshwater diatoms in QARU1 but some taxa must also be contributed via the freshwater inflows. Overall, the diatom stratigraphy indicated increasingly salinity since the 1920s but provided no firm evidence of lake eutrophication. Diatom inferred salinity reconstructions were in only partial agreement with instrumental records but inferred for the lower section of the core (pre 20th century to the 1960s) accord with measured water salinity values. Surficial sediments of Lake Qarun contain environmental change records for the 20th century period but high sediment accumulation rate and pollen reflect the high degree of human disturbance in the region. Because of poor preservation and evidence of reworking, the relationships between diatom records and past water quality changes require careful interpretation, especially in the upper section of the core. Nevertheless, early to mid 20th century measurements of increasing lake water salinity are well supported by sediment records, a change that is probably linked to ingress of saline ground water  相似文献   

Ammonium regeneration in intertidal sediments of the Yangtze estuary during air-exposure     

L.J. Hou  M. Liu  J.J. Lu  S.Y. Xu  D.N. Ou  Y. Yang  D.G. Zheng 《Environmental Geology》2006,49(7):937-945

The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification rate (˜500 nmol N cm⁻³ day⁻¹), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×10⁵ t N year⁻¹ in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to the estuarine ecosystem.  相似文献   

马朗凹陷马1井储层长石中有机包裹体研究          下载免费PDF全文

张小青  伊海生  危国亮  张小芹 《沉积与特提斯地质》2005,25(4):83-86

根据对马朗凹陷马1井储层长石中有机包裹体的基本特征、均一温度、荧光及荧光光谱分析，得出有机包裹体均一温度为60～90℃．120～140℃，其对应的荧光颜色分别为黄色和蓝绿色。认为储层的油气运移经历了两期，第一期为烃类的主要运移、聚集期，油气为低成熟油；第二期为少量的烃类聚集，并判断出二叠系条湖组该段储层为油气产层。  相似文献   

油气成藏机理研究进展和前沿研究领域   总被引：23，自引：7，他引：23  

郝芳  邹华耀  王敏芳  杨旭升 《地质科技情报》2002,21(4):7-14

随着地质工作者刻划和认识地下地质体构成、结构的能力及研究和预测沉积盆地能量场（温度场、压力场和应力场）及其演化能力的不断提高，以流体流动和油气运移为核心的油气成藏机理研究取得了重要进展：（1）证实了油气的优势通道运移并妆步提示了优势运移通道的微观和宏观控制机制，从而使基于油气运移路径三维预测的油气藏定位预测成为可能；（2）证实了幕式快速成藏过程并初步揭示了幕式成藏的驱动机制、有利场所和地球化学识别标志，突破了油气成藏是一个缓慢渗流过程的传统模式；（3）深盆气勘探和成藏机理研究取得了进展，从而突破了背斜成藏的传统观念，使“向斜”（盆地凹陷区）成为一些盆地寻找大型天然气藏的重要场所。沉积盆地深层油气成藏过程和保存条件、活动构造背景下油气晚期快速成藏过程是油气成藏机理研究的重要前沿研究领域。  相似文献   

平落坝储层有机包裹体特征与气藏形成过程研究   总被引：4，自引：0，他引：4  

高岗  黄志龙 《沉积学报》2002,20(1):156-159

通过储集层成岩作用与有机包裹体的研究认为,研究区储集层有机包裹体主要通过交代和重结晶作用而形成,有各种相态形式,主要分布在石英颗粒内溶蚀缝或孔隙中,构造裂缝中基本未见有机包裹体。上三叠统储集层包裹体丰度明显高于侏罗系沙溪庙组。香二气藏砂岩有机包裹体均一温度主峰在 10 0～ 110℃;沙溪庙气藏砂岩有机包裹体均一温度主峰在 90～ 10 0℃。香二气藏形成时间早,经历了印支期少量注入到印支期末-喜山早期大量注入,再到喜山晚期调整、部分注入的过程。沙溪庙气藏天然气注入则主要发生于喜山运动期。  相似文献   

济阳坳陷孤南洼陷低熟油成藏特征   总被引：8，自引：0，他引：8  

陈建渝  田波等 《地球科学》2002,27(4):435-440

孤南洼陷具有丰富的低熟油资源，低熟油中的生物标志物以高伽玛蜡烷含量，植烷优势，低成熟度为特征。下第三系沙一段是低熟油的源岩，其岩性为富含藻类有机质的油页岩，油泥岩，低熟油在平面上环生烃洼陷分布，剖面上层位集中在沙二－沙一段，断层控制了低熟油的运移距离和聚集层位，低熟油的成藏模式有3种，即自源侧向运移聚集成藏，自源断层垂向运聚成茂混合运取成藏模式。孤南洼陷低熟油盆地内部以侧向运移，侧向充注入岩性－断块圈闭为主，形成单源油藏。在断藏带原油是以垂向运移及垂向充注断块圈闭为主，形成混源油藏。  相似文献