滇黔桂盆地早二叠世亚丁斯克期的沉积环境分异与䗴有孔虫响应     

黄明立  田坤烜  史宇坤 《地学前缘》2020,27(6):313-328

亚丁斯克期华南滇黔桂地区沉积环境分异明显,主要发育局限或半局限海台地沉积区、开阔海台地沉积区和台地边缘沉积区,不同沉积区䗴有孔虫动物群面貌也有所区别。本文详细研究了黔南地区的猴场打望剖面和惠水竹子冲剖面阿瑟尔期—亚丁斯克期的地层,在打望剖面识别出4个䗴类化石带,由老至新为Pseudoschwagerina beedei-Sphaeroschwagerina constans共存延限带、Staffella xiushuiensis-Eoparafusulina contracta富集带、Pseudofusulina ellipsoidalis富集带和Misellina subcycloidea间隔带。竹子冲剖面识别出3个化石带,由老至新为Pseudoschwagerina uddeni-Sphaeroschwagerina sphaerica组合带、Eoparafusulina certa富集带和Staffella discoides延限带。对滇黔桂地区不同沉积相区剖面䗴类动物群以及沉积相特征的综合研究显示:开阔台地或台地边缘环境的䗴动物群以Pamirina为特征分子,同时还产出丰富的希瓦格䗴亚科(Schwagerininae)分子;局限或半局限台地环境的䗴类以史塔夫䗴亚科分子(Staffellininae)为主。沉积环境对䗴有孔虫的影响可能主要来自水动力、光照和氧气含量。个体较大、隔壁褶皱强烈的纺锤形希瓦格䗴亚科分子更适应水动力强、透光性好、氧气充足的水体;小个体、结构简单的史塔夫䗴亚科分子可在透光性差、含氧量较低的水体中生存。  相似文献   

东海和黄海表层沉积物生物标志物的分布特征及古生态重建潜力   总被引：6，自引：0，他引：6  

张海龙  邢磊  赵美训  孙耀  唐启升 《中国海洋大学学报(自然科学版)》2008,38(6)

多参数生物标志物法已被广泛用于重建浮游植物生产力和种群结构.但目前还缺乏这一应用的现代证据,尤其是西太平洋边缘海地区.文中作者对东/黄海的表层沉积物中的浮游植物生物标志物的分布进行研究,发现东海表层沉积物中菜子甾醇、甲藻甾醇、长链烯酮的总含量变化范围为357～3 115 ng/g,黄海的总含量变化范围为2 898 ～6 714 ng/g,硅藻、甲藻和颗石藻生物标志物总量基本具有近岸高、离岸低的趋势,与现场调查资料所得到的趋势基本一致.生物标志物比例结果显示在东海的长江口方向离岸越远硅藻相对比例下降,而在长江口以南则是离岸越远硅藻比例升高.在东海和黄海颗石藻所占比例都很低,但是有离岸越远比例升高的趋势.用生物标志物所重建的种群结构的变化趋势与现场调查资料相符,但其绝对值却与现场资料存在差异.本研究为生物标志物重建种群结构提供了现代数据,但是此方法的定量应用还需做进一步的研究.  相似文献   

Fossil midge associations and the historical status of fish in acidified lakes     

M. G. Johnson  J. R. M. Kelso  O. C. McNeil  W. B. Morton 《Journal of Paleolimnology》1990,3(2):113-127

Chaoborid and chironomid (Diptera) fossils were examined in sediment cores form nine Ontario Precambrian Shield lakes that were fishless in 1979. An abundance of Chaoborus americamus (intolerant of predation by fish) throughout cores from four lakes indicated that they were fishless historically. Occurrence of Chaoborus punctipennis and C. flavicans and absence of C. americanus in cores, except near the surface in two cases, indicated that four other lakes were inhabited by fish historically. One of these was probably periodically fishless as suggested by fluctuations among these Chaoborus species. The ninth lake was not suitable for Chaoborus; only one specimen of C. trivittatus was found in this core. Chironomid fossil associations were substantially different in historically fishless and inhabited lakes. Fishless lakes had chironomids typical of eutrophic conditions indicating that seasonal oxygen depletion likely was inimical to fish. Chironomid associations of oligotrophic waters occurred in lakes historically inhabited by fish. Both good water quality and accessibility were required for long-term habitation by fish. Partial recovery of alkalinity and rise in pH were accompanied by substantial re-invasion by fish in two lakes which had been inhabited historically by fish. Diptera associations provide valuable information on the historical suitability of lakes for fish and the presence/absence of fish in regions where acidification of surface waters has occurred.  相似文献   

Holocone paleovegetation and paleohydrology of a prairie pothold in southern Saskatchewan, Canada     

Catherine H. Yansa 《Journal of Paleolimnology》1998,19(4):429-441

The Andrews site represents one of countless prairie potholes found in areas of hummocky moraine on the northern Great Plains. Sediments from a depth of 5.8 to 3.1 m at this 'kettle-fill' site in the Missouri Coteau upland of southern Saskatchewan, Canada, provides a record of vegetation, climate, and hydrologic changes within a small, ca 30 m diameter, closed-drainage basin from ca 10.2 to 5.8 ka. Plant macrofossil analyses of 67 samples, 6 ¹⁴C ages, and stratigraphy were used to identify 5 zones, representing the paleohydrological changes that followed deglaciation in southern Saskatchewan.Results of this study indicate that with the melting of residual stagnant ice a pond (>2 m deep) with abundant aquatic, emergent, and shoreline plants developed in the basin at ca 10.2 ka and persisted until at least ca 8.8 ka. During this time there was a shift in upland vegetation from a white spruce forest (Zone II) to a deciduous parkland at ca 10 ka (Zone III). As climate warmed, brackish and alkaline conditions developed coincident with shallowing of the pond at the end of Zone III. The perennial water phase ended at ca 8.8 ka and was followed by a low-water stand lasting ca 1100 years. Prairie fires and slopewash from unstable slopes were dominant sedimentological processes until ca 7.7 ka (Zone IV). Water levels began to rise and between ca 7.7 and 5.8 ka a semi-permanent pond was established in a grassland setting (Zone V). After ca 5.8 ka this prairie pothole wetland became ephemeral, to the point that plant macrofossils could not be preserved, a situation continuing today. Interactions between climate change, variability in local groundwater supply, and sedimentological processes likely account for the paleohydrologic events reconstructed at the Andrews site.  相似文献   

High-resolution paleoecological analysis of recent disturbance in a southern Chilean Nothofagus forest     

Julian M. Szeicz  Barbara A. Zeeb  K.D. Bennett  John P. Smol 《Journal of Paleolimnology》1998,20(3):235-252

A 1600 year paleoecological record of environmental change is developed from a small lake in the Nothofagus forest of southern Chile (45.5°S, 72°W). High resolution fossil pollen, charcoal, sedimentological, and chrysophycean stomatocyst analyses are used to investigate the impacts of natural and anthropogenic disturbances on terrestrial and lacustrine environments. Chronological control is based on a combination of ²¹⁰Pb and ¹⁴C dating. Temporal resolution during the past 150–200 yr is ca. 8 yr/sample. The macroscopic charcoal record correlates very closely with historical and dendroecological records of 20th century anthropogenic burning in this region. The chrysophyte stratigraphy indicates that this burning had immediate impacts on the lake itself, while the pollen record provides evidence for a succession of vegetation changes lagging slightly behind the disturbance. These palynological changes are very similar to the pollen signal of European disturbance in northeastern North America. Pre-European shifts in chrysophyte assemblages may be due to the influence of earthquake activity on the lake, though there is no corroborative evidence in the pollen or charcoal records. This study demonstrates that high resolution paleoecological methods can be used to help bridge the temporal gap between traditional ecological and paleoecological studies of environmental change in the temperate forests of southern South America.  相似文献   

渤海湾盆地沙河街组钙质超微化石古生态及沉积环境   总被引：3，自引：0，他引：3  

唐祥华 《海洋地质与第四纪地质》1993,13(1):41-45

渤海湾盆地沙河街组中钙质超微化石的发现,表明这一时期渤海湾盆地与海水有过联系。对钙质超微化石古生态及沉积环境研究表明,化石主要产出时代为始新世晚期至渐新世早中期,属“间冰期”亚热带气候型。这一问题的深入研究,对于渤海湾盆地的石油勘探有重要意义。  相似文献   

Recent environmental changes inferred from the sediments of small lakes in Yellowstone's northern range     

D. R. Engstrom  C. Whitlock  S. C. Fritz  H. E. Wright Jr. 《Journal of Paleolimnology》1991,5(2):139-174

Recent sediments of eight small lakes in the northern winter range of Yellowstone National Park were cored to examine stratigraphic records of past changes in limnology and local environment that might be attributed to grazing and other activities of elk, bison, and other large ungulates. Cores of undisturbed sediment were analyzed at close intervals to depths covering the last 100–150 years according to chronologies established by lead-210 dating. Pollen analyses were made to show change in regional vegetation, and diatom and geochemical analyses were made to reveal possible limnological changes resulting from soil erosion and nutrient input from the lake catchments.Variations in sedimentary components prior to establishment of the Park in 1872 indicate some natural variability in environmental factors e.g., erosional inputs in landslide areas west of Gardiner. All lakes had abundant nutrient inputs.After the Park was founded, fire suppression may have been responsible for small increases in pollen percentages of various conifers and Artemisia tridentata (big sagebrush) at different times in different lakes. Perceptible decreases in pollen of willow, aspen, alder, and birch at different times may reflect local ungulate browsing, although drier climatic conditions may have been a factor as well.The most striking manifestation of accelerated erosion in a catchment was found at a lake located beside a road constructed in the 1930s. In contrast to changes at this site, the record of erosion at other lakes is hardly perceptible. Changes in sediment-accumulation rates seen at most sites result from redistribution of sediment within the lake after initial deposition.In the century following Park establishment, the abundance of planktonic diatoms relative to benthic taxa varies among lakes and may reflect differential nutrient inputs or changes in lake level. Four of the five lakes analyzed for diatoms show in the last few decades an increase in planktonic relative to benthic species, implying elevated nutrient inputs. The recent flora, however, is similar to that in pre-Park levels which suggests that these lakes have not been perturbed outside their normal range. Increased nutrient supply in recent decades for at least two of the lakes is supported by the geochemical data, which show an increase in biogenic silica and in organic matter.As a whole, our investigation of the sedimentary record does not support the hypothesis that ungulate grazing has had a strong direct or indirect effect on the vegetation and soil stability in the lake catchments or on the water quality of the lakes.  相似文献   

Foraminiferal associations of the Mid-Tertiary Edegem Sands at Terhagen, Belgium     

F. Symons  F. De Meuter 《Mathematical Geology》1974,6(1):1-15

A factor-analytic approach (varimax rotated factors) was used in studying the benthonic foraminiferal associations of the Mid-Tertiary Edegem Sands at Terhagen (near Antwerpen) Belgium. The fauna can be described by two groups. The lower and upper part of the stratigraphic section are characterized by one group and the middle transitional part by a second group. The results can be correlated with the number of the planktonic forms and with the fossil richness of the sediment.  相似文献   

General equations for volume and surface area of a logarithmically coiled shell     

David M. Raup  Richard R. Graus 《Mathematical Geology》1972,4(4):307-316

The equations of Moseley for the volume and surface area of a coiled shell have been rewritten in their most general forms. The general volume equation has been tested with 15 gastropods and found to give satisfactory results wherever there are no significant ontogenetic changes in the shell geometry. The equations provide a means for calculating the carbonate efficiency of a coiled shell. With this parameter analyzed into its component parts, it has been possible to understand the relationships between aspects of shell calcification and environmental factors that affect calcium carbonate availability. Preliminary studies indicate that it also may be possible to discriminate morphologically between terrestrial and aquatic gastropods, the various gastropod modes of life, and higher taxonomic categories. These equations offer possibilities for other studies concerned with the ecology, paleoecology, and evolution of coiled shells.  相似文献   

皖南休宁地区恐龙脚印等化石的产出特征   总被引：5，自引：0，他引：5  

余心起 《安徽地质》1999,(2)

皖南休宁地区发现“三位一体”的恐龙骨骼化石、恐龙蛋化石、恐龙足迹和尾迹化石。本文着重描述这批化石的形态大小和结构特点,并从古生态学方面对化石进行了探讨分析;按化石产出层位,对应的各类恐龙活动时间总计约为40Ma。  相似文献