Palaeoenyironments and human impact at Burraga Swamp in Montane rainforest,Barrington tops National Park,New South Wales,Australia     

F.K. Roberts   《The Australian geographer》1994,25(2):161-169

Palaeoecological studies have identified the broad patterns of environmental and climate change in highland south‐eastern Australia, but the detail of human impact on a variety of parameters and their interlinkages is largely missing. This study compares the erosion, productivity, fire and vegetation history in prehistoric and historical times at Burraga Swamp in montane rainforest in New South Wales. The known human impact is meagre; the major presently sustained impacts involve forestry in the surrounding sclerophyll forests and a low level of visits to the swamp by day‐walkers. While no significant changes in the largely oligotrophic conditions or in fire frequency were detected, changes in erosion rates and some vegetation change can be attributed to impacts since European settlement. There has been a small decline in eucalypts and a loss of fern cover, while grasses, Urtica and exotic species have expanded. It is clear that upland sites are sensitive to environmental change including low‐level human impact.  相似文献   

Lacustrine Sedimentary Organic Matter Records of Late Quaternary Paleoclimates   总被引：32，自引：0，他引：32  

Philip A. Meyers  Elisabeth Lallier-vergés 《Journal of Paleolimnology》1999,21(3):345-372

Identification of the sources of organic matter in sedimentary records provides important paleolimnologic information. As the types and abundances of plant life in and around lakes change, the composition and amount of organic matter delivered to lake sediments changes. Despite the extensive early diagenetic losses of organic matter in general and of some of its important biomarker compounds in particular, bulk identifiers of organic matter sources appear to undergo minimal alteration after sedimentation. Age-related changes in the elemental, isotopic, and petrographic compositions of bulk sedimentary organic matter therefore preserve evidence of past environmental changes.We review different bulk organic matter proxies of climate change in tropical and temperate sedimentary records ranging in age from 10-500 ka. Times of wetter climate result in enhanced algal productivity in lakes as a consequence of greater wash-in of soil nutrients, and these periods are recorded as elevated Rock-Eval hydrogen indices, lowered organic C/N ratios, less negative organic 13C values, and increased organic carbon mass accumulation rates. Lowering of lake water levels, which typically depresses algal productivity, can also cause an apparent increase in organic carbon mass accumulation rates through suspension of sediments from lake margins and redeposition in deeper basins. Alternations between C3 and C4 watershed plants accompany climate changes such as glacial/interglacial transitions and wet/dry cycles, and these changes in land-plant types are evident in 13C values of organic matter in lake sediments. Changes in climate-driven hydrologic balances of lakes are recorded in D values of sedimentary organic matter. Visual microscopic examination of organic matter detritus is particularly useful in identifying changes in bulk organic matter delivery to lake sediments and therefore is important as an indicator of climate changes.  相似文献   

Environmental history of the Colombian savannas of the Llanos Orientales since the Last Glacial Maximum from lake records El Pinal and Carimagua     

Hermann Behling  Henry Hooghiemstra 《Journal of Paleolimnology》1999,21(4):461-476

Late Quaternary environments have been studied by pollen analysis of lake sediments from the savannas of the Colombian Llanos Orientales at 180 m elevation. The pollen record form Laguna El Pinal (4°08N, 70°23W), dated by 6 AMS radiocarbon dates, starts at 18,290 ¹⁴C yr B.P. The record from Laguna Carimagua (4°04N, 70°14W), also dated by 6 AMS dates, starts at 8270 ¹⁴C yr B.P. Both records show a landscape dominated by grassland savanna with only few woody savanna taxa, such as Curatella and Byrsonima, frequent fires, and little occurrence of forest and/or gallery forest along the rivers. The savanna ecosystem at the studied sites was relatively stable during the last 18,000 yrs, but minor changes in floral composition, and in the proportion of savanna/forest, have been recorded. Very little gallery forest and the non permanent lake conditions of Laguna El Pinal reflect the driest period, interpreted to reflect low rainfall rates and long dry seasons during the Last Glacial Maximum until 10,690 ¹⁴ C yr B.P. During the Late Glacial, Laguna El Pinal was a permanent shallow lake, and changed into a lake with higher water levels during the Holocene, indicating wetter conditions. Expansion of regional gallery forest also started at around 10,690 ¹⁴C yr B.P. Little vegetational change observed in Laguna Carimagua at 5570 ¹⁴ C yr B.P., in combination with a simultaneous decrease of savanna observed in previously studied lakes, suggest a change to regional wetter conditions. Thus, the Holocene before 5500 ¹⁴ C yr B.P. was somewhat drier than the following period until about 3850 ¹⁴C yr B.P. In both records, Late Holocene lake deposits are incomplete. Shore vegetation of Laguna Carimagua always included a minor contribution of the palms Mauritia and Mauritiella. The marked increase of palms during the last c. 3800 yrs points to increased human impact on the vegetation under the wettest Holocene climate regime.  相似文献   

苏州A-型花岗岩性质的研究   总被引：9，自引：2，他引：9  

张兴隆  王家炳  沈波春 《岩石学报》1987,3(2)

本文从岩体地质构造、岩石结构和岩化性质,来论述苏州A-型花岗岩的非造山、无水和偏碱性特征。同时通过各种参数测定得知:本岩系中的钾长石和斜长石均为低结构态高有序度的。石英为β形。云母多为羟铁云母。副矿物有铌铁矿、磁铁矿、钛铁矿和碳硅石等四十多种。过渡性元素的Nb、Ta,Zr、REE、Y、Sn、Th、Ga和Zn丰度比其它类型花岗岩高出10倍到100倍,F的含量高得出奇,而Al、Ca、Mg则偏低。Ga/Al比值高。氧同位素值低,δ~(18)0(全岩)=7.53％。REE中Eu亏损严重。成岩时t=810℃,p=2  相似文献   

加拿大育空西南部冻土区一条孢粉剖面及其古环境意义     

王夏成 《冰川冻土》1989,11(2):99-112

  相似文献   

冻胀作用对孢粉聚集速率测定的影响     

王夏成  葛梓 《冰川冻土》1989,(3)

孢粉聚集速率是描述孢粉产量的一个定量指标。多年冻土区孢粉聚集速率的确定受到冻胀作用的强烈影响。主要体现在两个方面:首先,野外测得的沉积物厚度是冻胀后的数值,显然偏大,因而影响到沉积物沉积速率的计算。其次,样品中分凝冰透镜体的存在,影响到孢粉样品体积的测定。由于孢粉聚集速率是一个包含沉积物沉积速率及孢粉样品体积的多变量函数,因而冻胀作用对孢粉聚集速率的测定产生显著影响。加拿大育空西南部一条冻土钻孔剖面的孢粉资料表明,冰分凝引起的冻胀作用是导致孢粉聚集速率误差的主要因素。  相似文献   

蛇绿岩研究之检讨与反思:以“双沟蛇绿岩”为例     

张旗 《岩石学报》2021,37(4):957-973

"双沟蛇绿岩"是笔者最早研究的蛇绿岩之一,位于云南哀牢山带。双沟出露的岩石有二辉橄榄岩、辉长岩、辉绿岩、斜长花岗岩、玄武岩、硅质岩等。辉长岩亏损LREE,锆石U-Pb年龄为362～328Ma。玄武岩具N-MORB和E-MORB的特征,锆石U-Pb年龄为249Ma。研究认为,"双沟蛇绿岩"可能产于陆间小洋盆或裂谷或裂陷槽背景。但是,双沟没有可信的深海沉积和混杂堆积的记录,虽然岩石组合类似蛇绿岩,地球化学也具有MORB的特征,暗示双沟可能不是一个典型的蛇绿岩。如果双沟不是蛇绿岩,则晚古生代的哀牢山带就不存在一个有一定规模的洋盆,也不可能存在大陆碰撞的记录。双沟不是蛇绿岩是什么?可能是造山橄榄岩(Orogenic peridotite)。造山橄榄岩与蛇绿岩的岩石组合类似,蛇绿岩的橄榄岩产于洋壳之下;造山橄榄岩产于陆壳之下。检讨双沟蛇绿岩的研究,反思蛇绿岩的概念。笔者认为,斯泰因曼的"三位一体"概念是合适的,1972年彭罗斯会议的决议是正确的,1996年怀柔会议构造学家对蛇绿岩概念的理解是对的。考虑到混杂堆积对于蛇绿岩的重要性,建议将混杂堆积也作为与蛇绿岩相伴的一个重要指标加进来。如果这个想法合适,则一个完整的蛇绿岩组合将由三个要素组成:1)岩浆岩(包括地幔岩、堆晶岩、侵入岩和火山岩,代表大洋岩石圈的物质组成); 2)深海沉积(代表洋盆顶部的物质组成); 3)混杂堆积(代表洋盆消失、陆块碰撞的构造产物)。蛇绿岩不同于其他岩浆岩,其研究需要特殊的方法和思路,明白这一点,蛇绿岩研究才能走上正轨。双沟蛇绿岩研究遇到危机,中国其他一些蛇绿岩也可能需要重新审视。因此,检讨双沟蛇绿岩,对反思蛇绿岩的研究具有一定的意义。  相似文献   

甘肃武都龙家沟三趾马动物群化石的聚集特点   总被引：1，自引：0，他引：1  

张云翔  薛祥煦 《沉积学报》1996,14(3):122-128

龙家沟三趾马动物群中不同类型、不同大小动物的保存量及保存部位相差很大，实际保存量仅为理论保存量的６%左右，其化石材料明显经过水流的搬运作用。搬运过程中的分选作用是造成材料流失的主要原因，其中小型动物的流失最为明显。这是古生态恢复及古环境再造值得注意的问题。  相似文献   

昆仑山口第四纪化石组合的生态环境分析及其对昆仑山隆升的意义   总被引：13，自引：0，他引：13       下载免费PDF全文

阴家润  崔之久  葛道凯  刘耕年  伍永秋 《地球科学》1996,5(3)

最近从昆仑山口地区的羌塘组、三岔河组及格尔木河阶地采集了一些第四纪生物化石样品，这些生物化石包括一些哺乳类动物的牙齿、昆虫类、植物苇、藁类茎干化石以及大量双壳类和腹足类化石．化石生态组合的比较研究和埋藏学研究提供了有意义的沉积环境变迁的古气候的信息，据此推断昆仑山在上新世－早更新世的海拔高度估计在７００～１５００ｍ；早、中更新世之交昆仑山迅速地大幅度抬升至３０００～３５００ｍ左右，此后昆仑山相对缓慢地持续上升至目前高度  相似文献   

一个海底基性火山喷流成因的银锑矿床地质特征   总被引：8，自引：3，他引：8  

郑庆年 《矿床地质》1996,15(3):238-248

广东梅县嵩溪宝山是个产于具裂谷性质的永－梅裂陷槽南段翼部裂陷火山－沉积盆地内的一个海底基性火山喷流成因的银锑组合大型银矿。文中阐述以下问题：容矿层位岩性组合、建造和相及层位地球化学特征、矿区地质构造；海底基性熔岩玄武岩的地质、地球化学、稀土元素特征及其构造环境与成矿意义；矿体（层）形态、产状、矿石结构构造、矿物共生组合、地球化学、稀土元素、同位素、包裹体等  相似文献