Holocene vegetation history of Bundjalung National Park and Bungawalbin Creek,north‐eastern New South Wales     

R. McGrath 《The Australian geographer》1998,29(2):205-221

Few studies have been conducted into the environmental history of the North Coast region of New South Wales (NSW). To address this, two sedimentary sequences located in the coastal Bundjalung National Park and at Bungawalbin Creek, just north of the Park (both near Evans Head, NSW) have been investigated. Palynological and geochemical analyses were used to reconstruct the history of the sites. Fossil pollen evidence representing much of the Holocene period — basal radiocarbon dates of 8700 ± 60 years BP and 6600 ± 60 years BP are available from the Bundjalung National Park and Bungawalbin Creek sites, respectively — indicates a dynamic past environment, with an overall tendency towards drier conditions. This evidence is supported, in part, by charcoal analyses indicating an increase in the occurrence of fire over time. Chemical analyses of the sediments indicate that the Bungawalbin site was strongly influenced by estuarine conditions, whereas the Bundjalung National Park site was only influenced indirectly by estuarine conditions.  相似文献   

Geomorphology and late Holocene climatic change in Northeastern Spain     

M. Gutirrez-Elorza  J. L. Pea-Monn 《Geomorphology》1998,23(2-4)

During the late Holocene, accumulation and downcutting stages affected the slopes and infilled valleys in the semiarid areas in NE Spain. The presence of archaeological remains, charcoal and ashes within slope deposits and valley fills makes it possible to carry out accurate datings. In the case of infilled valleys, the different accumulations may be diachronous at a regional level. These diachronisms among different infilled valleys may be caused by both human activity and complex responses of the system. On the slopes, one can distinguish between two accumulation periods separated by an incision period. The older accumulation stage has a widespread distribution and developed from the Bronze Age to the Iberian–Roman Epoch. The following accumulation period was formed in the Post-Medieval period and is spatially more restricted. Because of the widespread synchronism shown by these accumulations, a climatic cause is put forward as the possible triggering factor for the accumulation–incision stages in the slopes. The datings obtained indicate that the first accumulation corresponds to the Iron Age Cold Epoch (900–300 years B.C.) and the second to the Little Ice Age. Between both accumulation periods, a downcutting stage took place (approximately from 300 B.C. to 1450 A.D.). This downcutting interval can be related to the warm stages of the Subatlantic Period, during which there was a relatively lower percentage of vegetation cover. Finally, the last incision period, which is still taking place, has affected previous accumulations.  相似文献   

The dune systems of the Konya Plain (Turkey): their relation to environmental changes in Central Anatolia during the Late Pleistocene and Holocene     

C. Kuzucuoglu  R. Parish  M. Karabiyikoglu 《Geomorphology》1998,23(2-4)

Several sand flats located on the northern shores of the Late Pleistocene palaeolake of the Konya plain (inner Anatolia, Turkey), are related to changes in lake levels. In this paper, the two main dune systems are mapped according to their geomorphological, sedimentological and dynamic characteristics, and their significance is discussed with regard to the environmental changes since the Late Pleistocene, both at time of the former lake and during the drier periods of the Holocene. Cross-sections show the relationship of the dunes to the topography of the basement. Analyses of the sand fraction show distinct characteristics in size distribution, quartz and shell contents, wind erosion effects on the quartz grains and petrographic composition. Interpretation of the results, coupled with information provided by the geomorphology of the dune systems studied in the field and from aerial photographs and satellite images, highlights the importance and variations in time of local factors such as prevailing winds, sand sources, changes in lake levels and vegetation. A chronology of the main sand fields is proposed, based on the evidence of three main droughts during the Upper Pleistocene. The older one, much eroded (maximum height=3 m), covers a limestone surface at +50 m above the bottom of the dried lake. An Optical Scanning Luminescence (OSL) date shows a last period of accumulation at 14,328±3220 years. The younger one (maximum height=12 m) has moved over the emerged Late Pleistocene lacustrine marls. An OSL date gives an age of 5674±988 years for the last accumulation period. Evidence of very recent activation of this younger dune system is apparent as a result of overgrazing and excessive land reclamation. A third period of dominant wind action and dune construction is responsible for the installation of a younger and thin dune field over the Mid-Holocene lacustrine deposits of the Karapinar lake. The success of the stabilization programme of the dunes over the last 30 years shows that the last period of dune movement is not related to climate change but to overpressure on the land due to the needs and activities of an increasing population.  相似文献   

A palaeolimnological study of Tugulnuit Lake, British Columbia, Canada, with special emphasis on river influence as recorded by chironomids in the lake's sediment     

Andrea Rück  Ian R. Walker  Richard Hebda 《Journal of Paleolimnology》1998,19(1):63-75

Sediments from Tugulnuit Lake in the Okanagan Valley of British Columbia, Canada, were examined for chironomid assemblages. The chironomid stratigraphy obtained encompasses the last 4000 to 5000 years and suggests a warm and fairly stable climate typical for a temperate lake at low- to mid-elevation. This is indicated by the even distribution of warm-water taxa, such as Cladopelma, Dicrotendipes, Polypedilum, Pentaneurini, Stempellina, Stempellinella/Zavrelia and Pseudochironomus throughout the core. Very few cold-water taxa occurred in the sediments. However, stream inputs have had a major impact on Tugulnuit Lake. Sandy sediments and the appearance of Simuliidae and stream-inhabiting chironomid taxa (e.g., Brillia/Euryhapsis, Eukiefferiella/Tvetenia, Rheocricotopus) indicate that a stream intruded into the current lake's basin ca. 3800 yr Before Present (BP). Sediments deposited prior to, and after, the stream's intrusion show a distinctly different chironomid assemblage exhibiting chironomid taxa more typical for lentic habitats. This result indicates that chironomids can serve to detect past stream influences on lake environments. Thus, rheophilic chironomids preserved in lake cores provide a new alternative for reconstructing stream palaeoenvironmental records.  相似文献   

A high-resolution Holocene ostracod record from the Sahel zone of Northeastern Nigeria     

Jonathan A. Holmes  Patrick A. Fothergill  F. Alayne Street-Perrott  R. Alan Perrott 《Journal of Paleolimnology》1998,20(4):369-380

The ostracod record from Kajemarum Oasis in the Sahel zone of Northeastern Nigeria covers the last c. 4000 cal. years of a 5500 cal. year lake-sediment sequence. The first appearance of ostracods, around 4000 cal. yr BP, reflects the switch from a very dilute lake during the mid-Holocene, to slightly oligosaline conditions that favoured the occurrence and preservation of ostracods. Between 3800 and 3100 cal. yr BP, the lake remained permanent and fresh or slightly oligosaline, with a Ca-Mg-HCO3 composition. A rise in salinity c. 3100 cal. yr BP, accompanied by a change to more variable conditions on a seasonal to interannual timescale, led to the influx of more-euryhaline taxa. Oligosaline conditions continued between 3100 and 1500 cal. yr BP. Around 1500 cal. yr BP, there was a sharp rise in salinity, probably accompanied by a shift to Na-CO3-type water, with marked seasonal and interannual variability. Salinity decreased after 900 cal. yr BP, although short-term variations were marked between 900 cal. yr BP and the top of the sequence, 95 cal. yr BP. Changes in the species assemblages and ostracod abundance were a response to climate-driven variations in the seasonal and interannual stability of the lake, together with changes in its salinity and solute composition, but there is no simple relationship between ostracod faunas and salinity. Within Kajemarum, there is no evidence of ostracod assemblages typical of deep, fresh water, nor of hypersaline Na-Cl waters. The sediments associated with the freshest waters at Kajemarum did not favour ostracod preservation, and the driest climatic conditions were associated with oligosaline to mesosaline water of Na-CO3-type. The species-poor assemblages reflect the short-term instability of the lake, coupled with the limited opportunities for the colonisation of this isolated basin.  相似文献   

海滩岩在连云港的发现   总被引：1，自引：1，他引：0  

李春生 《地理科学》1998,18(3):288-292

作者在江苏连云港海滨首次发现的全新世海滩岩。经岩石样品及簿片、扫描电镜、＾１４Ｃ同位素等分析测定,海滩岩主要由陆源碎屑和生物碎屑组成,胶结物为文石和高镁方解石。该地海滩岩主要形成于全新世早期,当时气温高于现在８￣１０℃,据此对连云港市全新世早期古气候、水动力条件、海岸线的发展变化及古地理环境等作了初步探讨。  相似文献   

内蒙古中西部地区全新世大暖期气候与环境初步研究   总被引：17，自引：1，他引：16  

杨志荣 《地理科学》1998,18(5):479-485

以大青山调角海子剖面的孢粉和地球化学分析资料为依据,结合邻区古土壤序列,湖泊演化及考古研究资料,阐明内蒙古中西部地区全新世气候最适宜期始于９２５０ａＢ．Ｐ．左右,结束于４０００ａ,Ｂ．Ｐ．前后,６３３０ａＢ．Ｐ．前后出现大暖期植被与气候变化的重要转折;  相似文献   

A high-resolution climatic change since the Late Glacial Age inferred from multi-proxy of sediments in Qinghai Lake   总被引：12，自引：3，他引：9  

Ryo Matsumoto 《中国科学D辑(英文版)》2005,48(6):742-751

The study of climatic changes since the Late Glacial Age has become one of the hotspots of the PAGES in recent years.Deep-sea cores from the high-latitude area show that the climate was very unstable during the transitional period from the Late Glacial Age to the Holocene[1,2],which has also been testified by the geological records from ocean sediments,ice cores and terrestrial sections in different latitudes of the earth[3—8].What’s more,climatic instability also ex-isted in the Holoce…  相似文献   

Holocene development of aquatic vegetation in shallow Lake Njargajavri,Finnish Lapland,with evidence of water-level fluctuations and drying   总被引：1，自引：0，他引：1  

Minna?V?lirantaEmail author  Seija?Kultti  Marjut?Nyman  Kaarina?Sarmaja-Korjonen 《Journal of Paleolimnology》2005,34(2):203-215

Holocene development of aquatic plant communities in subarctic Lake Njargajavri, Finnish Lapland, was studied using plant macrofossil analysis. Sediment lithology, grain size, and C/N ratios showed distinct lithological phases, indicating past water-level fluctuations. The colonization of limnophytes took place right after the formation of the lake (after ca. 11,500 cal. BP). The earliest plant macrofossil assemblages indicate nutrient-rich conditions and a warmer climate than at present. After this primary succession phase, aquatic vascular plants were replaced by aquatic bryophytes (before ca. 10,200 cal. BP). Together with lithological evidence, we interpret this as being related to the lowering water table. According to palynological, chronological, and sedimentological evidence, Njargajavri underwent a very shallow phase between ca. 10,000 and 9500 cal. BP and dried out for an unknown period of time between ca. 8000 and 5000 cal. BP. After the dry phase, the water level started to rise and sedimentation at the coring point began again. Despite re-establishment of the lacustrine habitat, late-Holocene plant macrofossil data show no marked recolonization of either vascular limnophytes or bryophytes. The reason for all limnophytes being presently absent from the lake remains speculative. The lack of nutrients and/or the cooling climate (especially shortening of the open-water season) during the latter part of the Holocene may explain why limnophytes failed to recolonize the lake.  相似文献   

Diatom paleoecology of Laguna Zoncho,Costa Rica     

Kurt?A.?HaberyanEmail author  Sally?P.?Horn 《Journal of Paleolimnology》2005,33(3):361-369

We analyzed diatoms in a sediment profile from Laguna Zoncho in southern Pacific Costa Rica (lake elevation 1190 m asl, depth 2.6 m, area 0.75 ha) spanning some 3240 cal yr. Diatoms are common in the profile, which we subdivide into three zones. Zone C (3240–1020 cal yr B.P.) is dominated by Staurosira construens var. venter and Aulacoseira spp.; during this time, the lake was dilute and circumneutral. Benthic and acidophilous taxa increase gradually in the upper section of this zone. Zone B (1020–460 cal yr B.P.) almost totally lacks Aulacoseira, and instead is dominated by combinations of Eunotia minor, Encyonema lunatum, Gomphonema gracile, and Pinnularia braunii. Previous pollen and charcoal analysis indicates that this zone falls within the peak of prehistoric agricultural activity at the lake, but diatoms may also reflect climate change. During this period, the lake was likely shallower and more acidic, but not eutrophic. Finally, Zone A (460 cal yr B.P. to AD 1997) begins near a 1.5-cm tephra layer from nearby Volcán Barú; diatom assemblages are dominated by Aulacoseira spp., and suggest deepening of the lake and return to conditions similar to Zone C. This was a time of indigenous population decline and forest recovery in the Zoncho region, probably reflecting the impact of European diseases on the native population, although climate change and impacts of the tephra deposition cannot be wholly discounted.  相似文献