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1.
The north coast of the United Arab Emirates (UAE) provides a typical example of coastal sabkha (supratidal flat) formation. Various stages of sabkha development can be recognized along this coast. This paper combines previous studies of sabkha environment with the results of field investigation of sabkha geomorphology, sedimentology, and stratigraphy on the north coast of UAE, to formulate a model of sabkha evolution.The model has six stages in the evolution of coastal sabkhas following the early Holocene sea-level rise. These are: Stage 1: sea-level rise results in the formation of an embayment. Stage 2: involves subsequent spit development and progradation across the bay as a result of sediment availability. Stage 3: coincident with spit evolution is the development of a khor (tidal inlet) with or without mangrove. Channel depth of Khors varies from 4 to 6 m. Stage 4: sediment accumulates in the khor reducing the khor depth, turning it into a lagoon. There are three sub-stages of the lagoon stage. (a) With lagoon depths of 1–2 m, (b) with lagoon depths 0.5 m or less, (c) when the lagoon floor is exposed at low tide. Stage 5: is sabkha formation; development occurs in two sub-stages. In the first the sabkha is immature and flooded during rain storms and spring tides (0.1 m above present sea-level). Later the sabkha is only flooded after rainstorms, when it reaches an elevation of about 1 m or more above present sea-level. Stage 6: in sabkha development is the coastal plain, which results when large sabkhas are linked together.  相似文献   

2.
A detailed geomorphologic and morphostratigraphic investigation of raised marine terraces at Cape Cuvier, Western Australia, reveals two morphologically distinct units. A lower, well-developed accretional reef terrace between 3 and 5.5 m above MLWS (mean low-water springs; hereafter denoted as “+”) represents an extended interval of stable sea level. An upper erosional terrace and incipient coralgal rim between + 8.5 to 10.5 m represents a brief sea-level stillstand at this higher elevation. These features suggest the lower and upper terraces developed during discrete sea-level events. In an attempt to better define the timing of emplacement of each marine unit, 20 coral samples collected along vertical and lateral reef growth axis from both terraces were analysed with U-series dating. Unfortunately, all coral samples exhibited elevated δ234Uinitial values, suggesting that pervasive uptake of 234U-enriched uranium and 230Th thorium had occurred. Despite the shortcomings of absolute dating, a succession of events can be resolved though morphostratigraphic relationships. Comparison of the facies relationships, coral growth, and morphostratigraphic features between the lower and upper terraces indicates that an early to mid MIS 5e stillstand at + 3 to 5 m was followed by a late rise to + 8.5 to 10.5 m. This agrees with an emerging global view of MIS 5e sea-level history derived from stable carbonate platforms, rejecting the hypothesis that these higher sea-level benchmarks are an artefact of localized tectonic processes.  相似文献   

3.
The Antarctic ice sheet is arguably the most critical in terms of future sea-level rise, primarily because it contains 70% of the world's fresh water. While there exists evidence of accelerated ice-sheet ablation during the past decade, the possibility that the ice sheets contributed little to 20th century sea-level rise could result in Antarctica becoming the largest contributor to sea-level rise during the 21st century. Here we review the findings of studies published following the 2007 Intergovernmental Panel for Climate Change (IPCC) study, focusing on the role of Antarctica in present-day (1992–2006) sea-level rise. We show that the choice of glacial isostatic adjustment (GIA) model significantly affects GRACE-estimated Antarctic mass loss, adding 0.25–0.45 mm/yr to the estimate of sea-level rise. The current estimate of Antarctica's contribution to sea-level rise has a wide range: from −0.12 to +0.52 mm/yr. The discrepancy between observed sea-level trend of 1.8 mm/yr and those estimated from various geophysical sources (2.10 ± 0.99 mm/yr) is 0.30 mm/yr. The role of Antarctica in sea-level rise might be better constrained by lengthening satellite observations, using long-term GPS data to discriminate subglacial vertical motion from ice mass balance, and detecting the sea-level signal due to elastic loading from the melting ice-sheets.  相似文献   

4.
A 61-cm core was obtained from 4 m below the water table in Cenote Aktun Ha, on the Yucatan Peninsula, Mexico. The cenote is 8.6 km from the Caribbean coast and its formation and evolution have been largely affected by sea-level change. The base of the core dates to 6,940–6,740 cal year BP and overlying sediments were deposited rapidly over the subsequent ~200 years. The pollen record shows that the cenote evolved from a marsh dominated by red mangrove (Rhizophora mangle) and fern (Polypodiaceae) to an open-water system. These vegetation changes were controlled by water level and salinity and are thus useful indicators of past sea level. At the base, the δ13Corg isotopic ratios reveal the influence of terrestrial vegetation (−29‰ VPDB), but shift to more negative values up-core (−33‰), indicating an influence from particulate matter in the flooded cenote pool. Although microfossil populations were nearly absent through most of the core, the microfossil assemblage in the upper 6 cm of the core is dominated by the juvenile foraminifer Ammonia tepida and the thecamoebian genus Centropyxis. These populations indicate open-water conditions in the cenote and a major environmental shift around 6,600 cal year BP, which is related to sea-level rise in the Caribbean basin. These data fit well with previously established sea-level curves for the Caribbean Sea. Our reconstruction of the environmental history of Cenote Aktun Ha helps elucidate the floral and hydrological history of the region, and highlights the utility of cenote sediments for studying the Holocene sea-level history of the Caribbean Sea.  相似文献   

5.
The paper focuses on the shoreline changes following the construction of a power station cooling harbor in Hadera, Israel, and uses a statistical analysis method capable of mitigating the effect of short-term changes on the measurement of long-term changes. The changes in shoreline position detected 25 years after the harbor's construction were compared with forecasts of the Central Lab for Hydraulics of France (LCHF) in 1976, which correctly predicted the effects of the construction on the nearby coast and with studies conducted a few years after the construction. A comparison between later studies and the study described herein shows a spatial effect of the harbor on shoreline position of 750 m north of the northern breakwater. No effect was found south of the harbor. The harbor's temporal effects extend over a few years from the beginning of the construction until the coast reaches a new sedimentary equilibrium. The statistical analysis method employed was found useful for the detection of long-term changes in shoreline position such as those caused by the construction of coastal structures; it will not be suitable for the detection of long-term changes resulting from a rise in sea-level.  相似文献   

6.
Shoreline positions established from beach profile surveys combined with wave data are jointly analyzed, as a function of their contribution to coastal processes, to investigate the interaction between waves, shoreline orientation and coastal structures along the Nile delta promontories, Rosetta, Burullus and Damietta. Repeated beach profile surveys along the promontory sectors (64 km long in total) have been analyzed to determine rates of shoreline changes prior to construction (1971–1990) and after construction of protective structures (1990–2000). The behavior of coastline pre- and post-construction indicates that coastal erosion fronting protective structures has declined in the case of the seawalls at the tips of the Rosetta and Damietta promontories, or has been partially replaced by sand accumulation in the case of detached breakwaters at Baltim (east of Burullus promontory) and at Ras El Bar (west of the Damietta promontory). As a consequence, downdrift erosion has been initiated in local areas adjacent to these structures in the direction of longshore sediment transport. The 5-km-long seawall protecting the Rosetta promontory has stopped the dramatic erosion of this highly eroded area (formerly shoreward retreated 88 m/year), with adverse local erosion at its west and east ends, being 3 and 13 m/year, respectively. Similarly, the 6-km-long seawall built on the eastern tip of the Damietta Promontory, still under construction, has nearly stopped the severe erosion, which was formerly 10 m/year. The detached breakwaters at both Baltim and at Ras El Bar have accumulated sand at accretion rates of 37 and 14 m/year, respectively. This sand accumulation is associated with downdrift erosion of 25 and 13 m/year at Baltim and Ras El Bar, respectively. Results reaffirm that the original erosion/accretion patterns along the Nile delta promontories have been reshaped due to the massive protective structures built during the last decade. This reshaping along the examined promontories is generally controlled by the temporal variability in the intensity and reversibility of wave directions and associated longshore currents, coastline orientation and by the existing coastal protection structures.  相似文献   

7.
Sandy clinothems are of interest as hydrocarbon reservoirs but there is no proven, economic, clinothem reservoir in the Norwegian Barents Sea. We used high-resolution, 2D and 3D seismic, including proprietary data, to identify a previously untested, Barremian, clinoform wedge in the Fingerdjupet Subbasin (FSB). Data from recent well 7322/7-1 plus seismic have been used to characterize this wedge and older Lower Cretaceous clinoforms in the FSB. In the latest Hauterivian – early Barremian, during post-rift tectonic quiescence, shelf-edge clinoforms (foreset height > 150 m) prograded into an under-filled basin. Increased sediment input was related to regional uplift of the hinterland (northern Barents Shelf). Early Barremian erosion in the north-western FSB and mass wasting towards the SE were followed by deposition of delta-scale (<80 m high), high-angle (c. 8°) clinoform sets seaward of older shelf-edge clinoforms. This may be the local expression of a regional, early Barremian, regressive event. By the close of the Barremian, clinoforms had prograded, within a narrow, elongate basin, across the FSB and towards the uplifted Loppa High. A seismic wedge of high-angle (10–12°), low-relief, delta-scale (25–80 m) clinoform sets occurs between shelf-edge clinoforms to the NW and the uplifted area to the SE. Well 7322/7-1, positioned on a direct hydrocarbon indicator, <1 km NNW of the high-angle, low-relief, delta-scale clinoforms, found upward coarsening siltstone-cycles linked to relative sea-level fluctuations on a marine shelf. Sand may have accumulated, offshore from the well, in high-angle, low-relief foresets of the delta-scale clinothems (which are typical geometries elsewhere interpreted as ‘delta-scale, sand-prone subaqueous clinoforms’). Deposition was controlled by the paleosurface, storms and longshore currents on an otherwise mud-dominated shelf. The study highlights challenges associated with exploration for sandstone reservoirs in seismic wedges on an outer shelf.  相似文献   

8.
A resource selection function is one that yields values proportional to the probability of use of a resource unit. This quantity is influenced by the heterogeneity of landscape structures, which occurs over multiple spatial scales. To provide input into wildlife management strategies, we investigated the scale dependency and functional responses of Japanese macaques using multiple scale analysis. The multiple buffers with radii of 100, 500, 1000, 1500, 2000, and 2500 m were defined as the spatial scale. Crop damage was predicted at the within-home range scale, using the Random Forests algorithm with environmental variables linked to resource selection of Japanese macaques. Sixteen environmental variables were defined, covering aspects of landscape configuration, human disturbance, topography, and adopted countermeasures. Crop damage was most accurately predicted within a buffer zone of 1000 m, although radii exceeding 1000 m were also highly accurate. Although the importance of variables differed among spatial extents, the functional responses for each environmental variable were independent of spatial extent. These results suggest that the limiting factors of crop damage depend on spatial extent, while functional responses in resource selection remain constant across spatial extents. We also compared a multi-scale gradient map with a typical binary map to demonstrate the uncertainty in damage predictions at different spatial scales. Our results may aid wildlife management planning, for which differences in resource selection across different spatial scales are critically important.  相似文献   

9.
Tsunamis can cause catastrophic loss of life, destruction of property, engineered structures and coastal infrastructure, and they can lead to major economic losses. Even though tsunamis are relatively rare in the Mediterranean Sea, their potential danger to cities along the Mediterranean coast cannot be neglected. In order to create awareness among the potentially affected people it is important to know the risk and vulnerability of the population and infrastructure related to a possible tsunami impact. In this work a hazard, vulnerability and risk analysis for buildings in two districts of Alexandria was carried out. Relevant input parameters were derived mainly from remote sensing and field data and were analyzed with a geographical information system (GIS). Based on historical records of past tsunamis, two inundation scenarios of 5 m and 9 m were defined and modeled applying a bath-type model. The resulting tsunami building risk zone maps showed that 12% of the buildings in El Gomrok district are at high or very high risk for the 5 m scenario, while the risk for El Montazah area is low. For the 9 m scenario, on the other hand, the majority of the buildings in both districts, 56% of El Gomrok, and 60% of El Montazah, are in the high or very high risk zone. An analysis of the building use indicated that the majority of these buildings are residential and commercial types, highlighting that the potential consequences of a tsunami could be severe. Due to the scarcity of historical data no frequency could be associated with the two selected scenarios. While both are credible we consider the 5 m scenario as possible but unlikely and the 9 m scenario as unlikely.  相似文献   

10.
Incised coastal channels are a specific form of incised channel that are found in locations where stream channels flowing to cliffed coasts have the excess energy required to cut down through the cliff to reach the outlet water body. The southern coast of the Isle of Wight, southern England, comprises soft cliffs that vary in height between 15 and 100 m and which are retreating at rates ≤ 1.5 m a− 1, due to a combination of wave erosion and landslides. In several locations, river channels have cut through the cliffs to create deeply (≤ 45 m) incised gullies, known locally as ‘Chines’. The Chines are unusual in that their formation is associated with dynamic shoreline encroachment during a period of rising sea-level, whereas existing models of incised channel evolution emphasise the significance of base level lowering. This paper develops a conceptual model of Chine evolution by applying space for time substitution methods using empirical data gathered from Chine channel surveys and remotely sensed data. The model identifies a sequence of evolutionary stages, which are classified based on a suite of morphometric indices and associated processes. The extent to which individual Chines are in a state of growth or decay is estimated by determining the relative rates of shoreline retreat and knickpoint recession, the former via analysis of historical aerial images and the latter through the use of a stream power erosion model.  相似文献   

11.
Little is known about the effects of grazing on vegetation composition on the Arabian Peninsula. The aim of this study therefore was to analyse the vegetation response to environmental conditions of open woodlands along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of Oman. The species composition, vegetation structure, grazing damage and several environmental variables were investigated for 62 samples using a nested plot design. Classification analysis and a Canonical Variate Analysis (CVA) were used to define vegetation types and to identify underlying environmental gradients. The relationship between environmental variables and diversity was analysed using correlation coefficients and a main-effects ANOVA. The plant species richness followed a unimodal distribution along the altitudinal gradient with the highest number of species at the intermediate altitudinal belt. The cluster analysis led to five vegetation groups: The Sideroxylon mascatense–Dodonaea viscosa group on grazed and the Olea europaea–Fingerhuthia africana group on ungrazed plateau sites at 2000 m a.s.l., the Ziziphus spina-christi–Nerium oleander group at wadi sites and the Moringa peregrina–Pteropyrum scoparium group at 1200 m a.s.l, and the Acacia gerrardii–Leucas inflata group at 1700 m a.s.l. The CVA indicated a clear distinction of the groups obtained by the agglomerative cluster analysis. The landform, altitude and grazing intensity were found to be the most important variables distinguishing between clusters. Overgrazing of the studied rangeland is an increasing environmental problem, whereas the plant composition at ungrazed sites pointed to a relatively fast and high regeneration potential of the local vegetation.  相似文献   

12.
Two nested clinoform set types of different scales and steepness are mapped and analysed from high-resolution seismic data. Restoration of post-depositional faulting reveals a persistent pattern of small-scale, high-angle clinoforms contained within platform-scale, low-angle clinothems, showing a combined overall progradational depositional system. The large clinoforms lack a well-defined platform edge, and show a gradual increase in dip from topset to foreset. A consistent recurring stratal pattern is evident from the architecture, and is considered a result of interplay between relative sea-level change and autocyclic switching of sediment delivery focal points that brought sediment to the platform edge. This un-interrupted succession records how intra-shelf platforms prograde. Quantitative clinoform analysis may assist in determining the most influential depositional factors. Post-depositional uplift and erosion requires restoration with re-burial to maximum burial depth. Backstripping, decompaction and isostatic correction was performed assuming a range of lithologic compositions, as no wells test the lithology. Nearby wells penetrate strata basinward of the clinoforms, proving mudstone content above 50%, which in turn guide restoration values. Typical restored platform heights are 250–300 m, with correspondingly sized platform-scale clinoform heights. Typical large-scale clinoform foreset dip values are 1.3°–2.4°. Small-scale clinothems are typically 100 m thick, with restored foreset dip angles at 4.4° - > 10°. The results suggest that intrashelf platform growth occurs in pulses interrupted by draping of strata over its clinoform profile. The resultant architecture comprises small-scale clinoforms nested within platform-scale clinothems.  相似文献   

13.
Devils Lake, a terminal lake in eastern North Dakota, has risen nearly 9.0 m since 1993, resulting in over $1 Billion in direct federal payments for disaster mitigation. More than 500 homes and 700 total structures have either been relocated or destroyed by the rising lake. The City of Minnewaukan, once nearly 13.0 km from the lake shoreline, is now facing the possibility of partial or complete relocation.We use the Hazus-MH MR4 Flood Model to examine potential flood damages in Minnewaukan associated with potential future lake levels ranging from 442.57 to 445.01 m at fixed water surface elevation (WSE) increments. We use three data sets to conduct a level 2 analysis in which user-supplied data allows for a site-specific analysis of flood damages. These include: 1) structure elevation surveyed by the U.S. Army Corps of Engineers, b) the 2010 Real Property Assessment Book for the City of Minnewaukan, and c) more than 200 individual property cards. Flood depth grids were provided by the Federal Emergency Management Agency in the form of bare-earth digital elevation models derived from LiDAR point clouds. Results include a series of graduated circle flood maps showing the location and assessed value of inundated buildings, and flood damage profiles showing the cumulative number of buildings inundated and their assessed value over a range of WSE increments.We show that the functionality of Hazus-MH can be extended to examine lakeshore flood hazards, and that it provides an important geovisualization tool in evaluating relocation as a flood mitigation alternative.  相似文献   

14.
An evolutionary model for sabkha development on the north coast of the UAE   总被引：1，自引：0，他引：1  
The north coast of the United Arab Emirates (UAE) provides a typical example of coastal sabkha (supratidal flat) formation. Various stages of sabkha development can be recognized along this coast. This paper combines previous studies of sabkha environment with the results of field investigation of sabkha geomorphology, sedimentology, and stratigraphy on the north coast of UAE, to formulate a model of sabkha evolution.The model has six stages in the evolution of coastal sabkhas following the early Holocene sea-level rise. These are: Stage 1: sea-level rise results in the formation of an embayment. Stage 2: involves subsequent spit development and progradation across the bay as a result of sediment availability. Stage 3: coincident with spit evolution is the development of a khor (tidal inlet) with or without mangrove. Channel depth of Khors varies from 4 to 6 m. Stage 4: sediment accumulates in the khor reducing the khor depth, turning it into a lagoon. There are three sub-stages of the lagoon stage. (a) With lagoon depths of 1–2 m, (b) with lagoon depths 0.5 m or less, (c) when the lagoon floor is exposed at low tide. Stage 5: is sabkha formation; development occurs in two sub-stages. In the first the sabkha is immature and flooded during rain storms and spring tides (0.1 m above present sea-level). Later the sabkha is only flooded after rainstorms, when it reaches an elevation of about 1 m or more above present sea-level. Stage 6: in sabkha development is the coastal plain, which results when large sabkhas are linked together.  相似文献   

15.
We investigated the impact of African elephants (Loxodonta africana) on the structure and composition of Acacia tortilis woodland in northern Gonarezhou National Park, southeast Zimbabwe. A. tortilis woodland was stratified into high, medium and low elephant utilisation categories based on evidence of elephant habitat use as determined through dung-count surveys in relation to distance of woodland patches from perennial and natural surface water sources. The following variables were recorded in each study plot: tree height, species name, number of species, plant damage, basal circumference and number of stems per plant. A total of 824 woody plants and 26 woody species were recorded from the sampled A. tortilis woodland patches. Mean tree densities, basal areas, tree heights and species diversity were lower in areas with medium and high elephant utilisation as compared to low elephant utilisation areas. Plants damaged by elephants increased with increasing elephant utilisation. The study findings suggest that A. tortilis woodland is gradually being transformed into an open woodland. We recommended that protected area management in arid and semi-arid areas should consider (i) formulating clear thresholds of potential concern to allow for the conservation of sensitive woodlands such as A. tortilis woodlands and (ii) establishing long-term vegetation monitoring programmes.  相似文献   

16.
Zhang  Qiming  Wang  Enyuan  Feng  Xiaojun  Wang  Chao  Qiu  Liming  Wang  Hao 《Natural Resources Research》2021,30(2):1817-1834

With the increasing depth of underground engineering, the risk of coal–rock dynamic disasters such as rockburst is becoming more and more serious and complex, which seriously threatens the safety of coal resource, mine production and the surface ecological environment. However, the existing risk indices and methods used for evaluating rockburst risk cannot be fully applied to deep goal seam group (DCG) mining. For the safe exploitation of coal resources, in this paper, based on statistical analyses of 300 cases of rockburst, six new indices are proposed for evaluating rockburst risk in the DCG, namely dip angle, moisture content, stability of coal seam, advancing speed of working face, disturbance factors and support patterns. In addition, the influence of multiple factors coupling and superposition on rockburst risk was considered. Thus, the Comprehensive Index Method of rockburst risk of Deep Coal seam Group (DCG–CIM) based on analytic hierarchy process was established. Finally, rockburst risk in the evaluation area was quantitatively assessed into four grades, including “No rockburst risk”, “Weak rockburst risk”, “Medium rockburst risk” and “Strong rockburst risk”. Taking the 2233 working face of Hengda Coalmine as an example, the evaluation results show that the ranges of 0–184 m, 224–284 m, 324–384 m, 424–484 m, 524–584 m and 594–624 m from terminal line of haulage roadway on 2233 working face were the medium rockburst risk zones, which are in accordance with the on-site impact damage results and are more accurate than the traditional method. The DCG–CIM can consider more inducing factors and obtain more accurate and reliable evaluation results and is more suitable for deep coal seam group mining.

  相似文献   

17.
The most pervasive threats to biological diversity are directly or indirectly linked to the road networks. For this reason, over the last few decades, interest in the study of the ecological characteristics of the edges associated with roads has increased. This work aims to investigate the effect of roads as a human-induced disturbance on the plant diversity in two managed Mediterranean forest sites, focusing on the responses of plants species richness, evenness, composition and taxonomic diversity.A stratified random sampling was performed in two protected areas located in Tuscany, Central Italy. The species richness, composition and abundance were measured in 53·20 × 20 m plots. Ordinary Least Square and quantile regressions were used to study the effect of the roads on species richness, evenness and taxonomic distinctness, and redundancy analysis was used to examine the species composition. Generalized linear models in conjunction with an Information Criterion-based approach to model selection were used to test the role of road distance in the structure of forest plant biodiversity.Our findings indicated a clear relationship between road distance and different plant biodiversity facets, which showed its maximum effect in the first 0–20 m forest-to-road segment and a mitigation after the 200 m threshold. Furthermore, the presence and abundance of many key forest species, such as Fagus sylvatica and Abies alba, were influenced more by the road distance than by other environmental gradients. The few remnants of core forest habitats in the Mediterranean basin highlight the need to recognize that road construction and maintenance have several ecological implications and accordingly require long-term monitoring programs.  相似文献   

18.
The giant cactus Isolatocereus dumortieri is a dominant species of the semiarid scrub of central Mexico. Its reproductive period is during the dry season, and it produces essential resources (pollen, nectar and fruits) for a great variety of animal species. We related the production of reproductive structures with water variables in the soil–plant system. The main goal of the present study was to evaluate the consequences of a change in rainfall pattern on the phenology of I. dumortieri. We watered some plants in the dry season to simulate heavy rain events, and to test the hypothesis that water availability during the reproductive season has a negative effect on fruiting and a positive effect on vegetative growth. The seasonality of rain events caused variations in soil water potential and plant osmotic potential, and we found that both variables influenced fruit production. The regression models relating the number of fruits with soil water potential, rainfall and osmotic potential were significant for all three study periods. The highest production of reproductive structures occurred in the driest year (2009), during which there was an ENSO event. Watering did not have a significant effect on osmotic potential or growth in the cacti. However, the watering × time interaction had a negative effect on the number of immature fruits. That is, at the end of the experiment, the plants that received the most water showed a decrease in the number of fruits. Plant growth during the rainy period was significantly greater than during the dry period. The results support the hypothesis that a change in rainfall pattern during the dry season has an effect on fruit production. Vegetative growth, however, occurred only during the wet season.  相似文献   

19.
A Late Miocene delta complex is located in the Danish Central Graben. The delta complex provides the opportunity to study the spatial development of a wave-fluvial dominated delta complex in three dimensions. Based on 3D seismic data (seismic sections and amplitude maps) and well data the complex has been investigated. The delta was developed during an initial rise and then a significant fall (approximately 90 m) in relative sea-level. The prograding clinoformal package of the delta complex has clinoform dips of 2–3° and a thickness of maximum 115 m. The sediments are deposited in five elongated depositional units with the long axis parallel to the delta slope, and progradation occurred in a south-westerly direction. The grain size of the units vary from muddy to coarse-grained sand. Incised canyons running parallel to the depositional direction tend to be straight or have low sinuosity and incise approximately 90 m into the top of the delta. The delta complex has been subdivided into two systems tracts based on a study of clinoform migration patterns: (1) Rising trajectory in Unit 1–4 of the complex, the sea-level was rising as documents a highstand systems tract (HST). (2) Descending trajectory in Unit 5 documenting a forced regression wedge systems tract (FRWST) as the sea-level was falling, creating incised canyons.  相似文献   

20.
The effect of topography on moss vegetation is examined to clarify the processes that affect the colonization of polar deserts on continental Antarctica. Data on the presence of the mosses Bryum pseudotriquetrum and Pottia heimii, and relative altitude were recorded. The altitude measurements were used to infer the underlying topographical attributes of the substrate in the study plots. Specifically, the local distribution of moss plants was clarified using the topographical attributes to construct generalized linear mixed models (GLMMs). The models suggested that steep slopes and convex microhabitats within areas of concave general relief (at the plot scale 4 × 4 m) promoted the establishment of moss. This correspondence to general relief was more apparent for B. pseudotriquetrum than for P. heimii. Among the study plots, general relief was found to be an important determinant of the precise spatial distribution of B. pseudotriquetrum. The standard surface estimated using the robust methods presented in this study is shown to be more accurate for describing moss distribution than the prevailing least-squares method.  相似文献   

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