Late Glacial to Early Holocene environmental adjustment in the Mediterranean semi-arid zone of the Salines playa-lake (Alacant, Spain)     

S. Giralt  F. Burjachs  J.R. Roca  R. Julia 《Journal of Paleolimnology》1999,21(4):449-460

The transition from the Late Glacial to the Early Holocene in the endorheic Salines sequence, which is characterized cyclical sedimentation, occurs between 5.50 and 2.85 m depth. From 5.50-3.50 m depth the cycles are composed of a centimetre alternation of layers of dolomitic marls and gypsarenites and from 3.50-2.85 m depth by the alternation of calcitic marls and calcarenites.Pollen, biotic assemblages and geochemistry provide evidence of a gap with respect to the new hydrological conditions that characterized the beginning of the Holocene. Mesic pollen taxa increased their percentages at the beginning of the Holocene, indicating climate improvement, which coincides with the 14C radiocarbon age of 10,000 years BP. The first biotic remains (gastropods, ostracods and foraminifers) found in this sequence appeared later, at 3.80 m depth, which corresponds to 9,500 years BP, whereas the mineralogical change occurred at 3.50 m depth, which corresponds to 9,000 years BP. The advanced adaptation of the vegetation and biotic aquatic assemblages with respect to the mineralogical response corresponds to a process of a gradual increase in water availability into the lacustrine system. During the Boreal, the calcitic cycles reached their maximum thickness, suggesting a more continuous water input. This assumption has also been corroborated by the expansion of the mesic pollen taxa and the occurrence of biota taxa which depend on a permanent water body for their development.The multiproxy approach in paleoclimate scenarios is an essential tool for understanding the ecosystem adjustment during climate changes. Our results demonstrate an interval of 1000 years between the vegetal and the mineralogical reaction.  相似文献   

关于东亚早期人类生态环境的重建   总被引：4，自引：0，他引：4       下载免费PDF全文

黄慰文  侯亚梅 《第四纪研究》1999,19(2):155-164

在东亚早期人类生态环境重建中流行的“莫氏线”理论将东亚(包括东南亚)视为第四纪全球环境频繁、激烈和迅速变化的例外。这个主要建立在化石哺乳动物群基础上的假说存在明显的局限性,不符合近二三十年来中国黄土、西太平洋边缘海等领域研究所揭示的东亚第四纪环境变化的性质和特点。东亚早期人类生态环境重建工作的滞后不仅妨碍了考古学家对旧大陆早期人类和文化发展格局的研究,也不利于整个第四纪研究的发展。加强考古学与第四纪研究其它领域的沟通、配合和合作,是整个第四纪研究的共同任务。  相似文献   

Depositional history of the Fire Clay coal bed (Late Duckmantian), Eastern Kentucky, USA     

S. F. Greb  C. F. Eble  J. C. Hower 《International Journal of Coal Geology》1999,40(4):629

More than 3800 coal thickness measurements, proximate analyses from 97 localities, and stratigraphic and sedimentological analyses from more than 300 outcrops and cores were used in conjunction with previously reported palynological and petrographic studies to map individual benches of the coal and document bench-scale variability in the Fire Clay (Hazard No. 4) coal bed across a 1860 km² area of the Eastern Kentucky Coal Field. The bench architecture of the Fire Clay coal bed consists of uncommon leader benches, a persistent but variable lower bench, a widespread, and generally thick upper bench, and local, variable rider benches. Rheotrophic conditions are inferred for the leader benches and lower bench based on sedimentological associations, mixed palynomorph assemblages, locally common cannel coal layers, and generally high ash yields. The lower bench consistently exhibits vertical variability in petrography and palynology that reflects changing trophic conditions as topographic depressions infilled. Infilling also led to unconfined flooding and ultimately the drowning of the lower bench mire. The drowned mire was covered by an air-fall volcanic-ash deposit, which produced the characteristic flint clay parting. The extent and uniform thickness of the parting suggests that the ash layer was deposited in water on a relatively flat surface without a thick canopy or extensive standing vegetation across most of the study area. Ash deposits led to regional ponding and establishment of a second planar mire. Because the topography had become a broadly uniform, nutrient-rich surface, upper-bench peats became widespread with large areas of the mire distant to clastic sources. Vertical sections of thick (>70 cm), low-ash yield, upper coal bench show a common palynomorph change from arborescent lycopod dominance upward to fern and densospore-producing, small lycopod dominance, inferred as a shift from planar to ombrotrophic mire phases. Domed mires appear to have been surrounded by wide areas of planar mires, where the coal was thinner (<70 cm), higher in ash yield, and dominated by arborescent lycopods. Rectangular thickness trends suggest that syndepositional faulting influenced peat accumulation, and possibly the position of the domed mire phase. Faulting also influenced post-depositional clastic environments of deposition, resulting in sandstone channels with angular changes in orientation. Channnels and lateral facies were locally draped by high-ash-yield rider coal benches, which sometimes merged with the upper coal bench. These arborescent-lycopod dominant rider coal benches were profoundly controlled by paleotopography, much like the leader coal benches. Each of the benches of coal documented here represent distinctly different mires that came together to form the Fire Clay coal bed, rather than a single mire periodically split by clastic influx. This is significant as each bench of the coal has its own characteristics, which contribute to the total coal characteristics. The large data set allows interpretation of both vertical and lateral limits to postulated domed phases in the upper coal bench, and to the delineation of subtle tectonic structures that allow for meaningful thickness projections beyond the limits of present mining.  相似文献   

Postglacial vegetation community change over an elevational gradient on the western Kenai Peninsula,Alaska: pollen records from Sunken Island and Choquette Lakes     

R. Scott Anderson  Edward Berg  Chris Williams  Tami Clark 《第四纪科学杂志》2019,34(4-5):309-322

The Kenai Peninsula of south‐central Alaska is a region of high topographic diversity with a complex glacial history. The sedimentary record of two small lakes [Sunken Island (SIL; 76 m a.s.l.) in the Kenai Lowlands; Choquette (CL; 527 m a.s.l.) in the Caribou Hills upland] exemplifies the postglacial development of the conifer–hardwood forest over an elevational range there. A herb–shrub tundra was established at both sites after deglaciation. By ~10.7 ka, poplar (Populus sp.) and alder (Alnus) dominated the lowland forest, while alder with minor poplar occurred at the upland site. Lake levels lower than today occurred during the early Holocene until ~8 ka. Subsequently at SIL, the near‐modern Kenai birch (Betula kenaica) – white spruce (Picea glauca) forest maintained prominence throughout the Holocene. However, at CL, alder dominated with dwarf birch and other subshrubs; small amounts of white spruce arrived ~5.2 ka. Black spruce (Picea mariana) grew around SIL by ~4 ka, but never gained prominence at CL. Fire, a prominent agent of disturbance in the Kenai Lowlands since ~8 ka, was essentially absent at the hardwood‐dominated upland site before ~6 ka, and rare thereafter. This suggests an important link between fire and spruce in Kenai forests.  相似文献   

Coniferization of the mixed‐wood boreal forests under warm climate     

Ccile C. Remy  Dominic Senici  Han Y. H. Chen  Yves Bergeron  Martin Lavoie  Laure Paradis  Adam A. Ali 《第四纪科学杂志》2019,34(7):509-518

Mixed‐wood boreal forests are characterized by a heterogeneous landscape dominated by coniferous or deciduous species depending on stand moisture and fire activity. Our study highlights the long‐term drivers of these differences between landscapes across mixed‐wood boreal forests to improve simulated vegetation dynamics under predicted climate changes. We investigate the effects of main climate trends and wildfire activities on the vegetation dynamics of two areas characterized by different stand moisture regimes during the last 9000 years. We performed paleofire and pollen analyses in the mixed‐wood boreal forest of north‐western Ontario, derived from lacustrine sediment deposits, to reconstruct historical vegetation dynamics, which encompassed both the Holocene climatic optimum (ca. 8000–4000 a bp ) and the Neoglacial period (ca. 4000 a bp ). The past warm and dry period (Holocene climatic optimum) promoted higher fire activity that resulted in an increase in coniferous species abundance in the xeric area. The predicted warmer climate and an increase in drought events should lead to a coniferization of the xeric areas affected by high fire activity while the mesic areas may retain a higher broadleaf abundance, as these areas are not prone to an increase in fire activity. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

渤海湾盆地东部中新世馆陶组古植物群及其古气候分析     

汪舒  尹太举 《地质与资源》1992,28(6):503

通过孢粉图谱的绘制及孢粉数据的统计分析，得出渤东地区馆陶组植物孢粉在地层上的组合特征及气候演化特点.主要表现为：乔木层的演化分为两个阶段，馆陶组早期（孢粉组合带Ⅲ、Ⅳ）——针叶树为主的混交林；馆陶组晚期（孢粉组合带Ⅰ、Ⅱ）——落叶林含有许多亚热带成分.统计发现馆陶组湿生植物明显多于旱生植物，喜热植物明显多于喜温植物，具有典型的亚热带季风气候特点.挑选典型孢粉计算得到S/A、E-T两个参数，详细地刻画了样品点间的气候变化，证明馆陶组气候波动频繁，气候以湿热为主.  相似文献   

Paleoecology of Late Carboniferous Phylloid Algae in Southern Guizhou, SW China   总被引：4，自引：0，他引：4  

GONG Enpu ZHANG Yonglil GUAN Changqing Elias SAMANKASSOU SUN Baoliang 《《地质学报》英文版》2007,81(4):566-572

Phylloid algae arc important rcef-builders in the late Carboniferous. This paper focuses on the paleoecology of phylloid algae in the Late Carboniferous on well-exposed reefs in Ziyun County, Guizhou Province. Phylloid algae growing closely packed arc attached via holdfast or similar structure to substrate. They were growing in environments such as shallow water, photic zone and below the wave base with medium energy currents. They have a variety of morphological forms, such as single cup-shaped, cabbage-shaped and clustering cup-shaped. The thalli arc of certain tenacity and intensity. In the areas dominated by phylloid algae, other marine orgam＇sms arc relatively scarce. Obviously, phylloid algae arc stronger competitors for living space than other co-occurring organisms.  相似文献   

Principal components analysis of three-way tables     

Michael Edward Hohn 《Mathematical Geology》1979,11(6):611-626

A three-mode principal components method allows visualization of the structural or taxonomic relationships within three-way data tables. The fundamental model includes three sets of eigenvectors and a core matrix relating the principal components of each mode. Formal relationships between the method and the usual principal components formulation allow calculation of loadings and scores for each mode; taken with the core matrix, these provide a number of points of view in graphical analysis of three-mode data. The model compares favorably with alternative formulations in terms of simplicity of computation, generality, and symmetry of operation among the modes. An organic geochemical example illustrates the method.  相似文献   

The detection of Rhizosolenia (Bacillariophyceae) in sediment of Ontario lakes and implications for paleoecology     

Y. -K. Yung  K. H. Nicholls  A. G. Cheng 《Journal of Paleolimnology》1988,1(1):61-69

The detection of the freshwater genus Rhizosolenia (Bacillariophyceae) remains in sediments is affected by the oxidants used in the digestion procedures. The Rhizosolenia counts decrease from 30% H₂O₂>50% HNO₃>50% chromic acid>100% HNO₃>100% H₂SO₄. Rhizosolenia is mostly found in Ontario lakes with summer average pH ranging from 5.6 to 8.3, Gran alkalinity from 0.2 to 120 mg L^–1 as CaCO₃ and water colour from 4 to 105 Hazen units. Large Rhizosolenia populations are generally found in clear lakes, neutral pH and low alkalinity.  相似文献   

The finding of a paleo-spruce timber in Hunshandak sandy land and its paleoecological significance     

Haiting Cui  Hongyan Liu  Xishen Yao 《中国科学D辑(英文版)》1997,40(6):599-604

A paleo-spruce (Picea jezoensis) timber dated to (10 040+100) a B.P. was found in the Hunshandak sandy land, Inner Mongolia, which is also one of the oldest timber found in China. Pollen and mammal fossil further evidence that theropencedrymion dominated by birch and spruce existed in this area in the late period of the earlier Holocene. This finding has great significance for the analysis of paleoclimate, paleovegetation and landscape development in this area. Project supported by the National Natural Science Foundation of China.  相似文献