LATE QUATERNARY MORAINES ALONG THE SEKHOKONG RANGE, EASTERN LESOTHO: CONTRASTING THE GEOMORPHIC HISTORY OF NORTH- AND SOUTH-FACING SLOPES

Considerable Quaternary environmental reconstruction for the high Drakensberg is based on geomorphological and sedimentological work undertaken along the northern aspects of the Sekhokong mountain range of eastern Lesotho. Given that no previous investigations have focused on the southern aspects, this paper documents the observed geomorphology and provides a more complete palaeo-environmental picture for this range. Data on the morphology, sedimentology and micromorphology for two linear debris ridges are presented. It is demonstrated that the two ridges are most likely moraines originating from a small niche glacier. The combined use of macro- and micro-scale sedimentology is proven to be an essential tool in ascribing a glacial process origin for the landforms, given the complex depositional history they have undergone. AMS ages obtained from the deposits (14 700 cal. yrs bp and 19 350 cal. yrs bp ) places these in the time-scale of the Last Glacial Maximum. The study demonstrates rather contrasting aspect-controlled palaegeomorphological environments along the Sekhokong range, which is also reflected in the dissimilar contemporary biophysical micro-environments. It is suggested that the south-facing slopes were dominated by glacial processes during the Last Glacial Maximum (LGM), as is evident from the moraines, while the proposition for previously described north-facing glacial cirques is rejected based on the absence of erosional/depositional evidence and greater insolation received on these warmerequator-facing slopes. Rather, we propose that the observed north-facing hollows are a product of a multitude of geomorphic processes spanning several tens to hundreds of thousands of years.     

秦岭北麓断裂带晚第四纪活动的地貌表现

本区地貌特征反映秦岭北麓断裂带的活动特点是：①第四纪以来主要发生垂直运动，其活动性质与程度有差异性、阶段性。第一、二级阶地的形态和年代资料表征秦岭北麓断裂带晚更新世和全新世垂直位错幅度和平均速率。②河流阶地在上升盘出口处高度大，而向上游逐渐减小，反映第四纪以来，秦岭断块山地继续发生由北向南的掀斜运动。③被断层切割的冲洪积扇体的结构和堆积层的产状特征，反映出山麓带多发育铲形断层。     

浅谈新疆罗布泊地区第四纪下限

罗布泊地区东部AK1孔地层根据岩石地层单元和古地磁、孢粉、氧化铁、易溶盐、^14C等测定结果，划分为全新统（Q4）、上更新统（Q3）、中更新统（Q2）、下更新统（Q1）和上新统（N2）。在孔深416.90m处，岩石、构造、古地磁、气候、地球化学等标志均非常明显，结合现在新疆第四纪划分方案，我们认为宜将此界线作为罗布泊地区第四系下界。其位于凯纳事件稍下，年龄约305万年。     

TREE INVASION IN MEADOWS OF LASSEN VOLCANIC NATIONAL PARK,CALIFORNIA*

The causes of tree invasion into meadows in Lassen Volcanic National Park were investigated by dating invasive trees and associating age structure patterns with regional variations in fire history, grazing, and climate change. Massive invasion was associated primarily with cessation of livestock grazing and burning between 1905 and 1933, but climatic change may also have contributed. Maintenance of meadows may require continued use of unnatural processes due to uncertainties about pre-European fire regimes and other resource considerations.     

GEOMORPHIC AND STRATIGRAPHIC COMPLEXITY: HOLOCENE ALLUVIAL HISTORY OF UPPER WOLLOMBI BROOK, AUSTRALIA

Holocene and post‐European settlement alluvial histories of three nested drainage basins were reconstructed from detailed litho‐ and chronostratigraphy of cut and fill terraces and flood‐plains in the upper Wollombi Brook catchment. Fernances Creek (13.8 km²) valley fill consisted of intercalated thin mud sheets deposited in ephemeral swamps and thick sand sheets deposited by discontinuous channels. Dairy Arm (39.8 km²) valley fill was more complex, with inset alluvial fills in the upper basin and overlapping vertically stacked fills in the lower basin. However, correlative lithostrati‐graphic units were not found on all tributaries. Furthermore, basal radiocarbon dates on the last inset fill of four tributaries did not overlap, allowing for plus or minus twice the standard deviation of the reported ages. Wollombi Brook (341 km²) valley fill was also complex, with longitudinally discontinuous units, most of which were not found in the two tributaries. Upstream late Holocene channel incision was coeval with downstream chain of ponds because sediment generated by incision was stored in the intervening valley. Historical channel incision occurred between 1838 and 1867 on Fernances Creek at a locally steeper section of valley floor during the period of peak population and frequent floods immediately after a road crossing was constructed, but coincided with a catastrophic flood on Dairy Arm (June 1949) and on Wollombi Brook (1927). Lack of correlative litho‐ and chronostrati‐graphic units plus out‐of‐phase post‐European incision indicate that stratigraphic complexity is a function of geomorphic complexity due to the operation of geomorphic thresholds and complex response.     

南极普里兹湾晚第四纪以来硅藻组合及气候变化的研究

对南极普里兹湾ＮＰ９３－２和ＮＰ９５－１两柱样沉积硅藻进行了定量分析。两柱样分别可划分出３个和７个硅藻组合带。前者的优势种是Ｎｉｔｚｓｃｈｉａｃｕｒｔａ和Ｔｈａｌａｓｉｏｓｉｒａａｎｔａｒｃｔｉｃａ，次优势种是Ｎ．ｋｅｒｇｕｅｌｅｎｓｉｓ和Ｎ．ｒｉｔｓｃｈｅｒｉ；后者常见的优势种有Ｎ．ｋｅｒｇｕｅｌｅｎｓｉｓ，Ｎ．ｃｕｒｔａ，Ｄｅｎｔｉｃｕｌｏｐｓｉｓｓｐｐ．和Ｔ．ｌｅｎｔｉｇｉｎｏｓａ，常见的次优势种有Ｅｕｃａｍｐｉａｂａｂｌａｕｓｔｉｕｍ，Ｔ．ａｎｔａｒｃｔｉｃａ和Ｔ．ｇｒａｃｉｌｉｓ。利用Ｎ．ｃｕｒｔａ／Ｎ．ｋｅｒｇｕｅｌｅｎｓｉｓ比值并结合１４Ｃ测年数据，可将１５０００年以来南极气候的变化划分出８个古气候带，其中完好地记录了Ｈｅｉｎｒｉｃｈ１事件、波令－阿德罗暖期、新仙女木冰期、全新世低温期等重大的气候变化事件，而南极的全新世低温期是首次报道。     

LATE QUATERNARY AEOLIAN GEOMORPHOLOGY OF THE DALE LAKE SAND SHEET,SOUTHERN MOJAVE DESERT,CALIFORNIA

Geomorphological and sedimentological analysis of aeolian deposits, combined with scanning electron microscopy (SEM) of quartz-grain surface characteristics, suggest six dune-building episodes during late Quaternary time in the southern Mojave Desert, California. The aeolian units accumulated largely in response to the lowering of water levels in lake basins and a consequent increase in fine sediment availability, and to stronger and more persistent winds, associated with rapidly changing environmental conditions. Peak dune deposition is believed to have taken place during the middle Holocene Altithermal between around 7.5 and 5 ka, a period characterized by greater aridity than the present. SEM analysis of the quartz surface textures indicates that mechanical and especially chemical weathering processes play a significant role in the post-depositional modification of aeolian sediments. Such evidence permits paleoenvironmental reconstruction during and since deposition, and a basis for the relative dating of aeolian sequences. Discriminant analysis using grain-size parameters, combined with principal components analysis of the SEM data from quartz-grain surfaces, is an effective analytical tool for distinguishing between spatially and temporally distributed aeolian deposits. [Key words: aeolian geomorphology, granulometry, quartz grain surface microfeatures, scanning electron microscopy, multivariate statistical analysis.]     

贵州晴隆碧痕营晚第四系及古环境研究

碧痕营洼地中的湖相层是在末次冰期盛冰期之前的温暖期中发育的.时代为距今3万年到2万年前后,当时洼地附近的山地上生长着以落叶阔叶林为主的针阔混交林,小有波动.这一时段,年均气温较今低1-6℃.距今3万年到2.6万年前后,生长含高比例水青冈的针阔混交林,气温较今约低2-6℃;距今2.3万年前后,附近山地生长常绿阔叶、落叶混交林,气温较今约低1-3℃;在距今2.6万年到2.3万年和距今2.3万年以后一段时期,本地区发育针阔混交林;步入盛冰期的过程中,气候转向干冷,蕨类植物蔓生;湖相层之后是混杂泥砾堆积,气温降低幅度更大.     

RATES OF SOIL FORMATION ON BLACK MESA,NORTHEAST ARIZONA: A CHRONOSEQUENCE IN LATE QUATERNARY ALLUVIUM

A chronosequence of 17 soils in late Quaternary alluvium on Black Mesa, northeast Arizona, permits quantification of rates of pedogenesis in a semi-arid region. Based on 24 tree-ring, radiocarbon, and archaeological dates, soil ages range from about 100 to 20,000 to 30,000+ years. Data indicate that ochric, cambic, argillic, natric, and calcic horizons form within about 100, 500, 1000, 3000, and 15,000 years, respectively, whereas mollic epipedons form within 1000 years. Bk horizons with Stage I, I+, II+, and III carbonate morphologies form within about 1000, 4000, 10,000, and 15,000 years, respectively. Thickness of Bt and Bk horizons, and Harden profile development and clay accumulation index values increase in a linear manner with increasing soil age. High resolution dating suggests rates of pedogenesis on Black Mesa are rapid relative to those documented elsewhere in the southwest United States and in the Rocky Mountains. Rates of soil formation recorded on Black Mesa, however, necessarily incorporate the combined effects of slight variations in elevation, climate, vegetation, topography, and parent materials throughout the region, as well as the influence of additions of atmospheric dust at the soil surface. [Key words: soil, pedogenesis, soil geomorphology, Quaternary, Arizona.]     

RELATIONSHIPS BETWEEN THE MORPHOMETRY OF ALPINE AND SUBALPINE BASINS AND REMOTELY SENSED ESTIMATES OF LAKE TURBIDITY,GLACIER NATIONAL PARK,MONTANA

Relationships between characteristics of alpine and subalpine drainage basin form and estimates of lake turbidity were examined. The study was designed to provide insight into sediment removal and delivery systems in an environment where direct process studies are difficult because of logistical constraints. Remote sensing techniques were developed to assess lake turbidity levels through the acquisition of spectral responses by the Landsat Thematic Mapper. Topographic maps were interpreted to derive measurements of morphometric characteristics of 25 study basins within Glacier National Park, Montana. The morphometric variables were chosen to describe basin characteristics related to sediment removal and transport processes. Correlation analysis, principal components analysis (PCA), hierarchical clustering, and analysis of variance (ANOVA) were used to assess characteristics of basin form and the relationship to levels of lake turbidity. A significant correlation between the first principal component, which accounted for the general morphometric character of basins, and estimated lake turbidity was discovered. The areal extent of glacial ice and total stream length within the basins were the most significant variables related to estimated levels of lake turbidity.     

晚更新世晚期冰期鼎盛时期华南沿海地区的古环境*

本文讨论末次冰期鼎盛时期华南沿海地区的古环境特征。对有关单位近年调查成果的分析,估计当时该地区的冬季温度比今低11-15℃,2月海洋表层水温此今低4.6-2.2℃,珠江三角洲地区河流深切达-40-62m以下,古海岸线推移到今水深150m左右深处。达主要是冰期世界气候寒冷,海面大幅度下降,东亚冬季风强盛、南海北部东北季风漂流增强的结果。     

西南极乔治王岛长城站区晚第四纪燕窝湖岩芯元素地球化学特征

本文阐述了乔治王岛长城站区燕窝湖沉积物中微量元素及某些常量元素的含量、分布、富集系数和相关系数的变化规律 ,探讨了该湖岩芯物质来源及气候环境的阶段性变迁 ,认为一方面燕窝湖周围碎屑沉积岩 (包括火山沉积岩 )是进入沉积体系的主要物源 ;另一方面 ,地幔物质也是其物源之一 ;同时 ,并不排除南极大陆冰进期搬运来的陆源物质进入沉积体系。     

GEOMORPHOLOGICAL CHARACTERISTICS AND SIGNIFICANCE OF LATE QUATERNARY PARAGLACIAL ROCK-SLOPE FAILURES ON SKIDDAW GROUP TERRAIN, LAKE DISTRICT, NORTHWEST ENGLAND

ABSTRACT. Eight relict rock-slope failures (RSFs) on Skiddaw Group terrain in the Lake District, northwest England, are described. Five of the failures are rockslides, one is a product of slope deformation, and two are compound features with evidence for sliding and deformation in different sectors. As none appears to have been overrun and modified by glacier ice it is concluded that they all post-date the Last Glacial Maximum (LGM ; c. 21 ± 3 cal. ka bp ). Slope stress readjustments resulting from glacial and deglacial influences are considered to have weakened the slopes, and application of the term paraglacial is appropriate. Permafrost aggradation and degradation, seismic activity and fluvial erosion are among processes that may have contributed to failure at certain sites. The failures are significant as potential debris sources during future ice advances, contributing to valley widening and cirque enlargement and, possibly, for acting as sites of cirque initiation. Previously, Skiddaw Group rocks have been regarded as homogeneous and of limited resistance to the weathering and erosion associated with Quaternary glacial, periglacial and fluvial processes. These characteristics and processes have been used to explain the steep smooth slopes and rounded hills that dominate Skiddaw Group terrain. Rock-slope failure has also helped shape this terrain and should be incorporated in future interpretations of landscape development.     

观光旅游地客流时间分布特性的比较研究——以九寨沟、黄山及福建永安桃源洞鳞隐石林国家风景名胜区为例

旅游地与主要游客市场的空间结构（距离关系）在相当大程度上影响着游客年内分布、日变化等时间结构。旅游地旅游资源及旅游环境季节性特征也是游客年内分布的决定因子。