首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Geografisk Tidsskrift, Danish Journal of Geography 107(2):59–68, 2007

Meteorological stations have been in operation since 1993 at Sermilik (65°40'N, 38°10'W), Ammassalik Island, southeast Greenland. This note presents meteorological observations for the year 2005 from the two meteorological stations: Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). The year 2005 was dominated by a temporal break down of Station Nunatak and defect instrument recordings at both stations. Average yearly measurements at both meteorological stations: Station Nunatak (1994–2004) and Station Coast (1998–2005) are presented to illustrate the climatic variability within the Mittivakkat Glacier catchment, and further compared with simultaneous standard synoptic meteorological DMI station climate observations (1994–2004) at the town Tasiilaq (Ammassalik) in order to establish transfer functions (linear regressions) and describe the spatial variability of climate variables.  相似文献   

2.
This article investigates the spatial logic and different moments of place‐making during the expansion of Mato Grosso's agribusiness frontier, in the southern section of the Brazilian Amazon. The analysis is informed by three conceptual concerns: the tensions between representation and experience, between humanist and class‐based explanations, and between the intensity of place‐making and place‐framing. Empirical results from a qualitative case study (carried out between 2013–2015, when agribusiness was the undisputed locomotive of the Brazilian economy) demonstrate that socio‐spatial changes in the last four decades evolved due to the complementary pressures and controversies of displacement (particularly in the 1970s–1980s) and replacement (in the 1990s–2000s), which eventually resulted in the widespread sense of misplacement due to accumulated inequalities and entrenched forms of socioeconomic exclusion. The principal conclusion found that the places dominated by agribusiness in Mato Grosso evolved around a totalizing spatial strategy that undermined alternative forms of production and livelihoods that do not fit in the export‐oriented agricultural model.  相似文献   

3.
We analyzed the latest Early Cretaceous to Miocene sections (~110–7 Ma) in 11 New Jersey and Delaware onshore coreholes (Ocean Drilling Program Legs 150X and 174AX). Fifteen to seventeen Late Cretaceous and 39–40 Cenozoic sequence boundaries were identified on the basis of physical and temporal breaks. Within‐sequence changes follow predictable patterns with thin transgressive and thick regressive highstand systems tracts. The few lowstands encountered provide critical constraints on the range of sea‐level fall. We estimated paleowater depths by integrating lithofacies and biofacies analyses and determined ages using integrated biostratigraphy and strontium isotopic stratigraphy. These datasets were backstripped to provide a sea‐level estimate for the past ~100 Myr. Large river systems affected New Jersey during the Cretaceous and latest Oligocene–Miocene. Facies evolved through eight depositional phases controlled by changes in accommodation, long‐term sea level, and sediment supply: (1) the Barremian–earliest Cenomanian consisted of anastomosing riverine environments associated with warm climates, high sediment supply, and high accommodation; (2) the Cenomanian–early Turonian was dominated by marine sediments with minor deltaic influence associated with long‐term (107 year) sea‐level rise; (3) the late Turonian through Coniacian was dominated by alluvial and delta plain systems associated with long‐term sea‐level fall; (4) the Santonian–Campanian consisted of marine deposition under the influence of a wave‐dominated delta associated with a long‐term sea‐level rise and increased sediment supply; (5) Maastrichtian–Eocene deposition consisted primarily of starved siliciclastic, carbonate ramp shelf environments associated with very high long‐term sea level and low sediment supply; (6) the late Eocene–Oligocene was a starved siliciclastic shelf associated with moderately high sea‐level and low sediment supply; (7) late early–middle Miocene consisted of a prograding shelf under a strong wave‐dominated deltaic influence associated with major increase in sediment supply and accommodation due to local sediment loading; and (8) over the past 10 Myr, low accommodation and eroded coastal systems were associated with low long‐term sea level and low rates of sediment supply due to bypassing.  相似文献   

4.
Late early–early middle Miocene (Burdigalian–Langhian) time on the island of Corsica (western Mediterranean) was characterized by a combination of (i) postcollisional structural inversion of the main boundary thrust system between the Alpine orogenic wedge and the foreland, (ii) eustatic sealevel rise and (iii) subsidence related to the development of the Ligurian‐Provençal basin. These processes created the accommodation for a distinctive continental to shallow‐marine sedimentary succession along narrow and elongated basins. Much of these deposits have been eroded and presently only a few scattered outcrop areas remain, most notably at Saint‐Florent and Francardo. The Burdigalian–Langhian sedimentary succession at Saint‐Florent is composed of three distinguishing detrital components: (i) siliciclastic detritus derived from erosion of the nearby Alpine orogenic wedge, (ii) carbonate intrabasinal detritus (bioclasts of shallow‐marine and pelagic organisms), and (iii) siliciclastic detritus derived from Hercynian‐age foreland terraines. The basal deposits (Fium Albino Formation) are fluvial and composed of Alpine‐derived detritus, with subordinate foreland‐derived volcanic detritus. All three detrital components are present in the middle portion of the succession (Torra and Monte Sant'Angelo Formations), which is characterized by thin transitional deposits evolving vertically into fully marine deposits, although the carbonate intrabasinal component is predominant. The Monte Sant'Angelo Formation is characteristically dominated by the deposits of large gravel and sandwaves, possibly the result of current amplification in narrow seaways that developed between the foreland and the tectonically collapsing Alpine orogenic wedge. The laterally equivalent Saint‐Florent conglomerate is composed of clasts derived from the late Permian Cinto volcanic district within the foreland. The uppermost unit (Farinole Formation) is dominated by bioclasts of pelagic organisms. The Saint‐Florent succession was deposited during the last phase of the counterclockwise rotation of the Corsica–Sardinia–Calabria continental block and the resulting development of the Provençal oceanic basin. The succession sits at the paleogeographic boundary between the Alpine orogenic wedge (to the east), its foreland (to the west), and the Ligurian‐Provençal basin (to the northwest). Abrupt compositional changes in the succession resulted from the complex, varying interplay of post‐collisional extensional tectonism, eustacy and competing drainage systems.  相似文献   

5.
《Basin Research》2018,30(5):835-862
We used detrital zircon U/Pb geochronology and apatite (U–Th–Sm)/He thermochronology to better constrain depositional ages and sedimentation rates for the Pliocene Productive Series in Azerbaijan. U/Pb analysis of 1,379 detrital zircon grains and (U–Th–Sm)/He analysis of 57 apatite grains—from Kirmaky Valley and Yasamal Valley onshore sections, Absheron Peninsula—yielded two distinct sub‐populations: “young” Neogene grains and “old” Mesozoic, Palaeozoic and Proterozoic/Archean grains. The large numbers of Neogene age grains (around 10% of all grain ages) provided a new absolute age constraint on the maximum depositional age of the Lower Productive Series of 4.0 Myr. These “young” Neogene zircon grains most likely originated from volcanic ash falls sourced from the Lesser Caucasus or Talesh Mountains. In this paper we propose a timescale scenario using the maximum depositional age of the Productive Series from detrital zircon grain U/Pb constraints. Potential consequences and limitations of using apatite (U–Th–Sm)/He dating method in estimating maximum depositional ages are also discussed. These new age constraints for the Lower Productive Series gave much faster sedimentation rates than previously estimated: 1.3 km/Myr in the South Caspian Basin margin outcrops and up to 3.9 km/Myr in the basin centre. The sedimentation rates are one of the highest in comparison to other sedimentary basins and coeval to global increase in sedimentation rates 2–4 Myr. The older group of detrital zircon grains constitutes the majority of grains in all sample sets (~80%). These older ages are inferred to reflect the provenance of the Productive Series sediment. This sediment is interpreted to have been derived from the Proterozoic and Archean crystalline basement rocks and Phanerozoic cover of the East European Craton, Proterozoic/Palaeozoic rocks of the Ural Mountains and Mesozoic sedimentary rocks of the Greater Caucasus. This sediment was likely supplied from northerly sourced drainage that emptied into the South Caspian Basin.  相似文献   

6.
The Xiaohe Cemetery archaeological site (Cal. 4–3.5 ka BP) is one of the most important Bronze Age sites in Xinjiang, China. Although the surrounding environment is an extremely arid desert now, abundant archaeological remains indicate that human occupation was common during certain periods in the Holocene. Field investigations and laboratory analyses of a sediment profile near the Xiaohe Cemetery indicate that while the regional environment was arid desert throughout the Holocene there were three episodes of lake formation near the site in the periods 4.8–3.5 ka BP, 2.6–2.1 ka BP and 1.2–0.9 ka BP. Geomorphic and hydrological investigations reveal that a lake or lakes formed in a low-lying area when water was derived initially from the Kongque River and then shunted into the Xiaohe River basin. Low amounts of active chemical elements in lacustrine sediment between 4.8–3.5 ka BP indicate abundant and continuous water volume in the lake; the content of active chemical elements increased between 2.6–2.1 ka BP but was still at a relatively low level, suggesting a declining amount of water and diminished inflow. Between 1.2–0.9 ka BP there was a very high content of active elements, suggesting decreased water volume and indicating that the lake was stagnate. In contrast, the general climate condition shows that there had a warm-humid stage at 8–6 ka BP, a cool-humid stage at 6–2.9 ka BP and a warm-dry stage at 2.9–0.9 ka BP in this region. The hydrological evolutions around Xiaohe Cemetery did not have one-to-one correspondence with climate changes. Regional comparison indicates that broad-scale climatic conditions played an important role through its influences on the water volume of the Tarim River and Kongque River. But, the formation of the lakes and their level were controlled by geomorphic conditions that influenced how much water volume could be shunted to Xiaohe River from Kongque River. Human occupation of the Xiaohe Cemetery and nearby regions during the Bronze Age and Han-Jin period (202 BC–420 AD) corresponded to the two earlier lake periods, while no human activities existed in the third lake period because of the decreased water volume.  相似文献   

7.
Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (~2.14 km) during the last two centuries. High retreat rates (51 m a?1 1986–2001, 43 m a?1 2001–2011) have produced a large (1.22 km2) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate.  相似文献   

8.
Mantle-induced dynamic topography (i.e., subsidence and uplift) has been increasingly recognized as an important process in foreland basin development. However, characterizing and distinguishing the effects (i.e., location, extent and magnitude) of dynamic topography in ancient foreland basins remains challenging because the spatio-temporal footprint of dynamic topography and flexural topography (i.e., generated by topographic loading) can overlap. This study employs 3D flexural backstripping of Upper Cretaceous strata in the central part of the North American Cordilleran foreland basin (CFB) to better quantify the effects of dynamic topography. The extensive stratigraphic database and good age control of the CFB permit the regional application of 3D flexural backstripping in this basin for the first time. Dynamic topography started to influence the development of the CFB during the late Turonian to middle Campanian (90.2–80.2 Ma) and became the dominant subsidence mechanism during the middle to late Campanian (80.2–74.6 Ma). The area influenced by >100 m dynamic subsidence is approximately 400 by 500 km, within which significant (>200 m) dynamic subsidence occurs in an irregular-shaped (i.e., lunate) subregion. The maximum magnitude of dynamic subsidence is 300 ± 100 m based on the 80.2–74.6 Ma tectonic subsidence maps. With the maximum magnitude of dynamic uplift being constrained to be 200–300 m, the gross amount of dynamic topography in the Late Cretaceous CFB is 500–600 m. Although the location of dynamic subsidence revealed by tectonic subsidence maps is generally consistent with isopach map trends, tectonic subsidence maps developed through 3D flexural backstripping provide more accurate constraints of the areal extent, magnitude and rate of dynamic topography (as well as flexural topography) in the CFB through the Late Cretaceous. This improved understanding of dynamic topography in the CFB is critical for refining current geodynamic models of foreland basins and understanding the surface expression of mantle processes.  相似文献   

9.
Tectonic inversion models predict that stratigraphic thickening and local facies patterns adjacent to reactivated fault systems should record at least two phases of basin development: (1) initial extension‐related subsidence and (2) subsequent shortening‐induced uplift. In the central Peloncillo Mountains of southwestern New Mexico, thickness trends, distribution, and provenance of two major stratigraphic intervals on opposite sides of a northwest‐striking reverse fault preserve a record of Early Cretaceous normal displacement and latest Cretaceous–Paleogene reverse displacement along the fault. The Aptian–Albian Bisbee Group thickens by a factor of three from the footwall to the hanging‐wall block, and the Late Cretaceous?–Eocene Bobcat Hill Formation is preserved only in the footwall block. An initial episode of normal faulting resulted in thickening of upper Aptian–middle Albian, mixed siliciclastic and carbonate deposits and an up section change from coarse‐grained deltas to shallow‐marine depositional conditions. A second episode of normal faulting caused abrupt thickening of upper Albian, quartzose coastal‐plain deposits across the fault. These faulting episodes record two events of extension that affected the northern rift shoulder of the Bisbee basin. The third faulting episode was oblique‐slip, reverse reactivation of the fault and other related, former normal faults. Alluvial and pyroclastic deposits of the Bobcat Hill Formation record inversion of the Bisbee basin and development of an intermontane basin directly adjacent to the former rift basin. Inversion was coeval with latest Cretaceous–Paleogene shortening and magmatism. This offset history offers significant insight into extensional basin tectonics in the Early Cretaceous and permits rejection of models of long‐term Mesozoic shortening and orogen migration during the Cretaceous. This paper also illustrates how episodes of fault reactivation modify, in very short distances (<10 km), regional patterns of subsidence, the distribution of sediment‐source areas, and sedimentary depositional systems.  相似文献   

10.
The Imja Glacier Lake (Imja Tsho) (1.03 km2 in 2007) is repeatedly cited as one of the most dangerous glacial lakes in the Himalaya with a glacial lake outburst flood (GLOF) claimed to be imminent. Knowledge of lake development and its dynamics, however, is limited and forecasts of a possible outburst are not scientifically based. Nevertheless, prospects for such a catastrophe are repeatedly exaggerated, attracting alarmist mass media coverage. The paper provides an assessment of the lake expansion rates from 1956 to 2007. Stage 1 (1956–1975), slowest: coalescence of several small supra-glacial ponds; Stage 2 (1975–1978), a short period of most rapid expansion; Stage 3 (1978–1997), slow: gradual expansion of single lake; and Stage 4 (1997–2007), renewed acceleration: mainly eastward expansion into the glacier surface. The lake's water level has fallen from 5041 m to 5004 m (1964–2006). The results show that there is no immediate danger of catastrophic outburst although the dynamics of up-glacier and down-valley lake expansion, fluctuation of lake water level, and dead-ice morphology changes should be continuously and comprehensively monitored. Alarmist prognostications based solely upon rapid areal expansion are counterproductive.  相似文献   

11.
Chronic wind is an important ecological factor, but its direct roles in shaping plant communities remain poorly understood. We hypothesized that chronic wind can modulate community productivity, inter-specific competition, and species abundance in inland dunes. We conducted an experiment with three shrubs (Artemisia ordosica, Caragana intermedia, and Hedysarum laeve) common to semi-arid sandlands, set up seven kinds of plant communities (i.e. Artemisia monoculture, Caragana monoculture, Hedysarum monoculture, ArtemisiaCaragana mixture, ArtemisiaHedysarum mixture, CaraganaHedysarum mixture, and ArtemisiaCaraganaHedysarum mixture), and communities subjected to two levels of wind exposure: shielded (by means of fencing) or exposed (no fencing). We measured total biomass per plot, competitive effects, and relative species abundance. Wind exposure did not significantly affect the total biomass of monocultures but increased their root weight ratio. However, wind exposure enhanced the total biomass of three-species mixtures but not two-species mixtures, and had no effects on root weight ratio of all mixtures. Wind exposed condition increased the competitive ability and relative abundance of Artemisia, decreased the competitive ability of Hedysarum but had no effects on its abundance, and did not affect the competitive ability of Caragana but decreased its abundance. These results suggest that chronic wind, as an environmental filter, can directly modulate plant communities through altering competitive outcomes and thus affect community functioning.  相似文献   

12.
Fine‐grained Palaeogene–early Neogene strata of the South Caspian basin, specifically the Oligocene–Lower Miocene Maikop Series, are responsible for the bulk of hydrocarbon generation in the region. Despite the magnitude of oil and gas currently attributed to the source interval offshore, geochemical evaluation of 376 outcrop samples from the northern edge of the Kura basin (onshore eastern Azerbaijan) indicates that depositional conditions in these proximal strata along the basin margins were dominantly oxic to mildly suboxic/anoxic throughout three major depositional stages: the Palaeocene–Eocene, Oligocene–early Middle Miocene and late Middle–Late Miocene. Palaeocene–Eocene samples have low average total organic carbon (TOC) values (0.3%), with higher total inorganic carbon (TIC) values (average=2.6%), extremely low sulphur content (0.2%) and relatively high detrital input as indicated by Fe/Al and Ti/Al ratios. C–S–Fe associations, along with relatively lower concentrations of redox‐sensitive trace elements (e.g. V, Ni, Mo, U) indicate dominantly oxic environments of deposition during much of the Palaeocene–Eocene. A pronounced geochemical shift occurred near the Eocene–Oligocene boundary, and continued through the Early Miocene. Specifically, this interval is characterized by a distinct increase in TOC (ranging from 0.1 to 6.3% with an average of 1.5%), C–S–Fe associations that reveal an abrupt relative increase of carbon and sulphur with respect to iron‐dominated Palaeocene–Eocene samples, and higher concentrations of redox‐sensitive trace metals. These changes suggest that a shift away from unrestricted marine conditions and towards more variable salinity conditions occurred coincident with the initial collision of the Arabian plate and partial closure of the Paratethys ocean. Despite periodic basin restriction, the majority of Upper Eocene–Lower Miocene strata in the northern Kura basin record oxic to slightly dysoxic conditions.  相似文献   

13.
To determine the effects of and the interactions between salinity and temperature, and alkalinity and temperature, we conducted three germination tests of Medicago ruthenica (L.) Sojak cv. ‘Zhilixing’ seeds in growth chambers. In experiment 1, the seeds were placed at a range of temperatures (5, 10, 15, 20, 25, 30, 35, or 40 °C), and in experiments 2 and 3, we varied the salinity (0, 50, 100, 150, 200, or 250 mM NaCl) and alkalinity (1, 5, 10, 15, 20, or 25 mM Na2CO3), respectively, within three ranges of alternating temperatures (10–20, 15–25, and 20–30 °C). The seeds of M. ruthenica (L.) Sojak cv. ‘Zhilixing’ showed high percentage germination at all temperatures, except for 5 °C. Seeds germinated well at low NaCl and Na2CO3 concentrations under all three alternating temperature regimes. Approximately half the seeds germinated at high salinity and alkalinity at 15–25 °C, whereas the ungerminated seeds germinated when the high-saline and alkaline stresses were removed. These results suggest that M. ruthenica (L.) Sojak cv. ‘Zhilixing’ has potential utility as a forage legume in saline and alkaline environments.  相似文献   

14.
It can be advantageous to revisit coring locations in lakes years after an initial paleolimnological study is completed, to assess environmental changes in the intervening time interval. We revisited sediment core sites in Lake Pepin (Minnesota, Wisconsin) more than a decade after an original set of 10 cores was collected, dated radiometrically, and studied in 1996. Prominent magnetic susceptibility features were used to align the new core set with the older set, such that traditional radiometric dating was not necessary to obtain a chronology for the new cores. The procedure used to align the two core sets accounted for compaction of former surface sediments by burial with new sediment. The amount of new sediment, mercury, and phosphorus accumulated at each core site was determined and extrapolated to the depositional area of the lake to estimate recent (1996–2008) whole-basin loads. Recent sediment accumulation in Lake Pepin compared well (within 3%) with monitored inflow data from a gauging station on the upper Mississippi River just before it enters the lake. Bulk sediment accumulation rate remained very high (772,000 t/year) for the recent period (1996–2008), down slightly from the peak in 1990–1996 (876,000 t/year), and almost an order of magnitude above pre-settlement rates. Total phosphorus deposition remained constant since a peak in the 1960s, but was also well above pre-settlement rates. Mercury continued its precipitous decline since peaking in the 1960s.  相似文献   

15.
The well‐constrained seismic stratigraphy of the offshore Canterbury basin provides the opportunity to investigate long‐term changes in sediment supply related to the formation of a transpressive plate boundary (Alpine Fault). Reconstructions of the relative motion of the Australian and Pacific plates reveal divergence in the central Southern Alps prior to ~20.1 Ma (chron 6o), followed by increasing average rates of convergence, with a marked increase after ~6 Ma (late Miocene). A strike–slip component existed prior to 33.5 Ma (chron 13o) and perhaps as early as Eocene (45 Ma). However, rapid strike–slip motion (>30 mm yr?1) began at ~20.1 Ma (chron 6o). Since ~20.1 Ma there has been no significant change in the strike–slip component of relative plate motion. Sedimentation rates are calculated from individual sequence volumes that are then summed to represent sequence groups covering the same time periods as the tectonic reconstructions. Rates are relatively high (>22 mm yr?1), from 15 to ~11.5 Ma (sequence group 1). Rates decrease to a minimum (<15 mm yr?1) during the ~11.5–6 Ma interval (sequence group 2), followed by increased rates during the periods of ~6–2.6 Ma (21 mm yr?1; group 3) and 2.6–0 Ma (~25 mm yr?1; group 4). Good agreement between sedimentation and tectonic convergence rates in sequence groups 2–4 indicates that tectonism has been the dominant control on sediment supply to the Canterbury basin since ~11.5 Ma. In particular, high sedimentation rates of 21 and ~25 mm yr?1 in groups 3 and 4, respectively, may reflect increased plate convergence and uplift at the Southern Alps at ~6 Ma. The early‐middle Miocene (~15–11.5 Ma) high sedimentation rate (22 mm yr?1) correlates with low convergence rates (~2 mm yr?1) and is mainly a response to global climatic and eustatic forcing.  相似文献   

16.
Jing  Cheng  Tao  Hui  Jiang  Tong  Wang  Yanjun  Zhai  Jianqing  Cao  Lige  Su  Buda 《地理学报(英文版)》2020,30(1):68-84
The countries throughout the Belt and Road region account for more than 60% of the world's population and half of the global economy. Future changes in this area will have significant influences on the global economic growth, industrial structure and resource allocation. In this study, the proportion of the urban population to the total population and the gross domestic product were used to represent the levels of urbanization and economic development, respectively. The population, urbanization and economic levels of the Belt and Road countries for 2020–2050 were projected under the framework of the IPCC's shared socioeconomic pathways(SSPs), and the following conclusions are drawn.(1) The population, urbanization and economic levels in the Belt and Road region will likely increase under all five pathways. The population will increase by 2%–8%/10 a during 2020–2050 and reach 5.0–6.0 billion in 2050. Meanwhile, the urbanization rate will increase by 1.4%–7.5%/10 a and reach 49%–75%. The GDP will increase by 17%–34%/10 a and reach 134–243 trillion USD.(2) Large differences will appear under different scenarios. The SSP1 and SSP5 pathways demonstrate relatively high urbanization and economic levels, but the population size is comparatively smaller; SSP3 shows the opposite trend. Meanwhile, the economy develops slowly under SSP4, but it has a relatively high urbanization level, while SSP2 exhibits an intermediate trend.(3) In 2050, the population will increase relative to 2016 in most countries, and population size in the fastest growing country in Central Asia and the Middle East countries will be more than double. Urbanization will develop rapidly in South Asia, West Asia and Central Asia, and will increase by more than 150% in the fastest growing countries. The economy will grow fastest in South Asia, Southeast Asia and West Asia, and increase by more than 10 times in some counties with rapid economic development.  相似文献   

17.
Qualitative knowledge representation of spatial locations and relations is popular in many text-based media, for example, postings on social networks, news reports, and encyclopedia, as representing qualitative spatial locations is indispensable to infer spatial knowledge from them. However, an integrative model capable of handling direction-based locations of various spatial objects is missing. This study presents an integrative representation and inference framework about direction-based qualitative locations for points, lines, and polygons. In the framework, direction partitions of different types of reference objects are first unified to create a partition consisting of cells, segments, and corners. They serve as a frame of reference to locate spatial objects (e.g., points, lines, and polygons). Qualitative relations are then defined to relate spatial objects to the elements in a cell partition, and to form the model of qualitative locations. Last, based on the integrative representation, location-based reasoning mechanism is presented to derive topological relations between objects from their locations, such as point–point, line–line, point–line, point–polygon, line–polygon, and polygon–polygon relations. The presented model can locate any type of spatial objects in a frame of reference composed of points, lines, and polygons, and derive topological relations between any pairs of objects from the locations in a unified method.  相似文献   

18.
The Xunhua, Guide and Tongren intermontane basin system in the NE Tibetan Plateau, situated near the Xining basin to the N and the Linxia basin to the E, is bounded by thrust fault‐controlled ranges. These include to the N, the Riyue Shan, Laji Shan and Jishi Shan ranges, and to the S the northern West Qinling Shan (NWQ). An integrated study of the structural geology, sedimentology and provenance of the Cenozoic Xunhua and Guide basins provides a detailed record of the growth of the NE Tibetan Plateau since the early Eocene. The Xining Group (ca. 52–21 Ma) is interpreted as consisting of unified foreland basin deposits which were controlled by the bounding thrust belt of the NWQ. The Xunhua, Guide and Xining subbasins were interconnected prior to later uplift and damming by the Laji Shan and Jishi Shan ranges. Their sediment source, the NWQ, is constrained by strong unidirectional paleocurrent trends towards the N, a northward fining lithology, distinct and recognizable clast types and detrital zircon ages. Collectively, formation of this mountain–basin system indicates that the Tibetan Plateau expanded into the NWQ at a time roughly coinciding with Eocene to earliest Miocene continental collision between India and Eurasia. The Guide Group (ca. 21–1.8 Ma) is inferred to have been deposited in the separate Xunhua, Guide and Tongren broken foreland basins. Each basin was filled by locally sourced alluvial fans, braided streams and deltaic‐lacustrine systems. Structural, paleogeographic, paleocurrent and provenance data indicate that thrust faulting in the NWQ stepped northward to the Laji Shan from ca. 21 to 16 Ma. This northward shift was accompanied by E–W shortening related to nearly N–S‐striking thrust faulting in Jishi Shan after 11–13 Ma. A lower Pleistocene conglomerate (1.8–1.7 Ma) was deposited by a through‐flowing river system in the overfilled and connected Guide and Xunhua basins following the termination of thrust activity. All of the basin–mountain zones developed along the Tibetan Plateau's NE margin since Indian–Tibetan continental collision may have been driven by collision‐induced basal drag of old slab remnants in the manner of N‐dipping and flat‐slab subduction, and their subsequent sinking into the deep mantle.  相似文献   

19.
The application of dendrochronological techniques to shrubs found in arctic and alpine plant communities is opening previously untapped regions to the exploration of plant‐climate ecological relationships and climate reconstruction. In this pilot study, we present growth (1963–2004), reproduction (1963–2004), and stable carbon isotope ratio (1975–2004) chronologies for Cassiope mertensiana from a subalpine site in Mount Rainier National Park, Washington, USA. Based on simple linear correlation analysis, positive correlations characterize plant growth and previous year mean maximum temperature in April and June, suggesting the influence of temperature on snowpack and, in turn, on growing season length, plant and soil insulation, and nutrient and moisture availability. Plant growth and reproduction are significantly correlated with current year July mean maximum temperature and total precipitation, indicating the importance of a warm and extended growing season for optimal plant development. Using step‐wise multiple linear regression analysis, we developed a preliminary calibration model for July mean maximum temperature (R = 0.63), extending over the 1974–2004 time period. This archive has the potential to elucidate multi‐scale, spatially‐explicit, ecological and climatic information for alpine ecosystems situated along a north‐south transect from the southern Yukon to the Pacific Northwest of the United States.  相似文献   

20.
Backstripping analysis of the Bass River and Ancora boreholes from the New Jersey coastal plain (Ocean Drilling Project Leg 174AX) provides new Late Cretaceous sea‐level estimates and corroborates previously published Cenozoic sea‐level estimates. Compaction histories of all coastal plain boreholes were updated using porosity–depth relationships estimated from New Jersey coastal plain electric logs. The new porosity estimates are considerably lower than those previously calculated at the offshore Cost B‐2 well. Amplitudes and durations of sea‐level variations are comparable in sequences that are represented at multiple boreholes, suggesting that the resultant curves are an approximation of regional sea level. Both the amplitudes and durations of third‐order (0.5–5 Myr) cycles tend to decrease from the Late Cretaceous to the late Miocene. Third‐order sea‐level amplitudes in excess of 60 m are not observed. Long‐term (108–107 years) sea level was approximately constant at 30–80 m in the Late Cretaceous, rose to a maximum early Eocene value of approximately 100–140 m, and then fell through the Eocene and Oligocene.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号