Holocene glacial history and sea-level changes on James Ross Island,Antarctic Peninsula     

Christian Hjort   lafur Inglfsson  Per Mller  Juan Manuel Lirio 《第四纪科学杂志》1997,12(4):259-273

A reconstruction of deglaciation and associated sea-level changes on northern James Ross Island, Antarctic Peninsula, based on lithostratigraphical and geomorphological studies, shows that the initial deglaciation of presently ice-free areas occurred slightly before 7400 ¹⁴C yr BP. Sea-level in connection with the deglaciation was around 30 m a.s.l. A glacier readvance in Brandy Bay, of at least 7 km, with the initial 3 km over land, reached a position off the present coast at ca. 4600 yr BP. The culmination of the advance was of short duration, and by 4300 yr BP the coastal lowlands again were ice-free. A distinct marine level at 16–18 m a.s.l. was contemporaneous with or slightly post-dates the Brandy Bay advance, thus indicating the relative sea-level around 4600–4500 yr BP. Our results from James Ross Island confirm that over large areas in this part of Antarctica the last deglaciation occurred late. © 1997 John Wiley & Sons, Ltd.  相似文献   

The dynamics of mountain erosion: Cirque growth slows as landscapes age     

Iestyn D. Barr  Jeremy C. Ely  Matteo Spagnolo  Ian S. Evans  Matt D. Tomkins 《地球表面变化过程与地形》2019,44(13):2628-2637

Glacial cirques are widely used palaeoenvironmental indicators, and are key to understanding the role of glaciers in shaping mountain topography. However, notable uncertainty persists regarding the rate and timing of cirque erosion. In order to address this uncertainty, we analyse the dimensions of 2208 cirques in Britain and Ireland and model ice accumulation to investigate the degree of coupling between glacier occupation times and cirque growth. Results indicate that during the last ~120 ka, cirques were glacier-free for an average of 52.0 ± 21.2 ka (43 ± 18%); occupied by small (largely cirque-confined) glaciers for 16.2 ± 9.9 ka (14 ± 8%); and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka (43 ± 16%). Over the entire Quaternary (i.e. 2.6 Ma), we estimate that cirques were glacier-free for 1.1 ± 0.5 Ma; occupied by small glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. Comparing occupation times to cirque depths, and calculating required erosion rates, reveals that continuous cirque growth during glacier occupation is unlikely. Instead, we propose that cirques attained much of their size during the first occupation of a non-glacially sculpted landscape (perhaps during the timeframe of a single glacial cycle). During subsequent glacier occupations, cirque growth may have slowed considerably, with the highest rates of subglacial erosion focused during periods of marginal (small glacier) glaciation. We propose comparatively slow rates of growth following initial cirque development because a ‘least resistance’ shape is formed, and as cirques deepen, sediment becomes trapped subglacially, partly protecting the bedrock from subsequent erosion. In support of the idea of rapid cirque growth, we present evidence from northern British Columbia, where cirques of comparable size to those in Britain and Ireland developed in less than 140 ka. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.  相似文献   

里下河古潟湖相软土基本工程特性与形成机理的关系     

姜鹏  贺富强  方磊  张德军 《工程地质学报》2006,14(6):769-775

淮盐高速公路穿越的里下河地区,广泛分布有高含水量、高压缩性古潟湖相软土,工程性质很差,该层软土的工程性质与里下河古潟湖的形成机理密切相关。本文在对潟湖形成一般模式总结的基础上,结合苏北地区第四纪以来沉积环境及区域地质地貌变化情况,得出里下河古潟湖相软土的形成机理,并对淮沿高速公路盐线典型地段土样工程性质进行分析,根据土的工程性质的垂直变化,判断古潟湖相软土的分布情况,进而寻找古潟湖相软土工程性质与其形成机理之间的关系。  相似文献   

Geomorphic assessment of active tectonics in the Acambay graben,Mexican Volcanic Belt     

María Teresa Ramírez-Herrera 《地球表面变化过程与地形》1998,23(4):317-332

Spatial variations of Quaternary deformation and tectonic activity of faults along the Acambay graben are assessed using geomorphic and morphometric approaches. The Acambay graben is an east–west trending structure of apparent Quaternary age, located in the central part of the Mexican Volcanic Belt, which gives rise to pronounced scarps over a distance of about 80 km. Continuing tectonic activity in the Acambay graben is confirmed by recent well documented seismic episodes. The intensity of active tectonics has been interpreted through a detailed geomorphic study of the fault-generated mountain fronts and fluvial systems. The combined geomorphic and morphometric data provide evidence for relative variations in tectonic activity among the Acambay graben faults. Geomorphic indices suggest a relatively high degree of tectonic activity along the Venta de Bravo and the Acambay–Tixmadeje faults, followed, in order of decreasing activity, by the Pastores, Temascalcingo and Tepuxtepec faults. Spatial variations within faults have also been identified, suggesting a higher level of tectonic activity at the tips of the faults. This pattern of variation in the relative degree of tectonic activity is consistent with field evidence and seismic data for the Acambay graben. Geomorphic evaluation of the Acambay graben faults suggests that the Acambay–Tixmadeje and Venta de Bravo faults, and specifically the tips of these faults and a central segment near the town of Venta de Bravo, should be considered as areas of potentially high earthquake risk. © 1998 John Wiley & Sons, Ltd.  相似文献   

则木河断裂带的演化历史及变形机制     

杜平山 《四川地震》2000,(1):65-79

主要讨论了第四纪以来则木河断裂带的演化过程和变形机制,同时也对该断裂带上基岩裸露区断层新活动的标志进行了研究。  相似文献   

第四系土层大直径超长桩的承载特性   总被引：2，自引：0，他引：2  

胡立明 《华东地质学院学报》2000,23(1):35-38

在没有良好的持力层 (基岩或砂、卵石层 )和成熟经验可借鉴的情况下 ,对第四系土层大直径超长桩 (钻孔灌注桩 )的承载特性进行了分析。并以分析结果为依据 ,预估单桩承载力 ,结果与静力试桩结论相吻合。  相似文献   

皖西北及邻区第四系分布与新构造运动特征   总被引：1，自引：0，他引：1  

李光  翟洪涛  李代娣  郑颍平  孟凡月  赵朋 《华北地震科学》2011,29(2):35-39

本文根据皖北及邻区区域调查报告[1]中第四系钻孔资料,通过插值法得到皖北及邻区第四系等厚线.结合该地区地震及断裂分布,分析皖北及邻区新构造运动特征,认为涡阳为研究区内破坏性地震最可能发生的地区.  相似文献   

巴彦浩特断裂北段晚第四纪活动特征及其区域地震构造意义     

陈桂华  李忠武  黄雄南 《震灾防御技术》2022,17(1):28-37

巴彦浩特断裂位于阿拉善地块与鄂尔多斯地块相互作用的边界构造带上,其晚第四纪活动特征和古地震数据对全面理解贺兰山周边区域地震构造和地震危险性具有重要意义,为此在研究相对薄弱的巴彦浩特断裂北段开展了断错地貌和古地震槽探研究。观测显示巴彦浩特断裂阿拉善左旗以北段以右旋走滑活动为主兼具逆倾滑,断层西盘相对抬升,在浅表形成半正花状构造组合。年代（56.28±4.04）~（82.2±5.78）ka的冲洪积地貌面上冲沟断错137 m,并在东侧形成断塞塘地貌,估计断层右旋走滑速率为1.67~2.43 mm/a。探槽揭示了3次具有显著地表逆倾滑破裂的强震事件,时间分别为（56.28±4.04）~（55.33±3.04）、（32.79±2.22）~（13.76±1.1）、（13.76±1.1）~（7.86±0.43）ka,逆倾滑量分别为0.44、0.35、0.29 m。与前人在巴彦浩特断裂南段的古地震研究进行对比,可知这3次古地震可能仅为部分事件记录。结合已有研究成果建立了贺兰山周边区域地震构造模型,贺兰山西侧右旋走滑的巴彦浩特断裂强震发震能力不容忽视,贺兰山两侧盆地不同性质断裂系共同构成了阿拉善地块与鄂尔多斯地块的活动边界构造带。  相似文献   

The Urban Geography of Subsidiary Headquarters in North America: Explorations by sector and Foreign Linkage     

《Urban geography》2013,34(5):595-622

The complexity of the firm is a hallmark of the current economy. Corporate subsidiaries and their headquarters are a key expression of the development of businesses today. The analysis presented here extends on previous subsidiary research by analyzing the evolving headquarters location of foreign and domestic subsidiaries in the United States and Canada from 1996 to 2004. This study finds that certain U.S. and Canadian sectors are home to disproportionate numbers of subsidiaries. It also shows that different sectors in each country have seen major changes in their subsidiary communities, that foreign and domestic subsidiaries in the United States and Canada exhibit distinctive geographies, and that parent corporations from various countries follow distinctive strategies in locating their U.S. and Canadian subsidiary headquarters. The study argues that this line of research is one component in the strengthening of theory related to the location of elite corporate activities.  相似文献   

A sedimentary facies model for stepped,fluvial tufa systems in the Iberian Range (Spain): the Quaternary Piedra and Mesa valleys   总被引：1，自引：0，他引：1  

MARTA VÁZQUEZ‐URBEZ  CONCHA ARENAS  GONZALO PARDO 《Sedimentology》2012,59(2):502-526

Stratigraphic and sedimentological analyses of the Quaternary tufa and associated deposits in the Piedra and Mesa river valleys allowed a number of stages of their sedimentary evolution to be characterized, and a depositional sedimentary model for this north‐central sector of the Iberian Range (Spain) to be established. The proposed sedimentary facies model may explain tufa arrangements in other medium to high gradient, stepped, fluvial tufa systems with narrow transverse profiles occurring in temperate, semi‐arid areas, in both recent and past scenarios. There are several tufa deposits within the Piedra and Mesa river valleys that, over a maximum thickness of about 90 m, record one or more stages of tufa deposition produced following the fluvial incision of the bedrock or previous tufa deposits. Each depositional stage begins with coarse detrital sedimentation. Six fundamental, vertical sequences of tufa facies with small amounts of detrital material reveal the sedimentary processes that occurred in different fluvial environments: channel areas with: (i) free‐flowing water; (ii) barrages and/or cascades; and (iii) dammed water and palustrine floodplains. The proposed sedimentary model involves narrow, stepped, fluvial valleys in which tufa cascades were common. Alternating intervals of bryophyte and stromatolite facies commonly formed at some cascades. Many of these represented barrage‐cascade structures that consisted of phytoclast rudstones, thick phytoherms of mosses and associated stromatolites, and curtain‐shaped phytoherms of stems. Upstream of these structures, dammed areas with bioclastic sands and silts developed and palustrine vegetation grew. The channel stretches between barrages and/or cascades were loci for extensive stromatolite growth in fast flowing water. The palustrine floodplain was home to pools and drainage channels. The model also explains the growth of some barrages in the River Piedra that surpassed the height of the divide, with the diffluence of the main channel into a secondary course forming other tufa deposits in the area. The distribution and abundance of certain types of tufa facies in fluvial basins may be an indicator of differences in their gradients. The facies studied in this work suggest that the gradient of the ancient River Piedra was steeper than that of the ancient River Mesa. Assuming similar scenarios for climate and hydrology, the depositional settings mentioned above and their dimensions would have been determined mainly by the gradient and width of the associated river valleys. This sedimentary model may also be useful for inferring variations in other river basin slopes, as well as accounting for the presence of tufas in areas that normally have no permanent water input.  相似文献