Annual to decadal morphodynamics of the foredune system at Greenwich Dunes,Prince Edward Island,Canada     

Jeff Ollerhead  Robin Davidson‐Arnott  Ian J. Walker  Sojan Mathew 《地球表面变化过程与地形》2013,38(3):284-298

The purpose of this study was to quantify relationships between season, sediment availability, sediment transport pathways, and beach/foredune morphology at Greenwich Dunes, PEI. This was done for periods ranging from a few days to multiple decades using erosion pins, bedframe measurements, annual surveys, and digital photogrammetry using historical aerial photographs. The relative significance of seasonal/annual processes versus response of the foredune system to broader geomorphic controls (e.g. relative sea level rise, storms, etc.) was also assessed. The data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at Greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area, resulting in ongoing differences in foredune morphology. They also demonstrate that models that incorporate wind climate alone, or even models that include other factors like beach moisture, would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology, especially the presence or absence of a dune ramp. Finally, the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope, over the crest, and onto the lee slope. Although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback, the overall decadal evolution of the foredune system at Greenwich is consistent with, and supports, the Davidson‐Arnott (2005) conceptual model of dune transgression under rising sea level. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Colluvial sedimentation in a hyperarid setting (Atacama Desert,northern Chile): Geomorphic controls and stratigraphic facies variability     

Dario Ventra  Guillermo Chong Dìaz  Poppe l. De boer 《Sedimentology》2013,60(5):1257-1290

Research on colluvial depositional systems has recently emphasized periglacial and high‐altitude settings, and the relations between Quaternary slope stratigraphy and climate change. This article examines the role of variable slope morphology, surface hydrology and microclimate in controlling colluvial sedimentation along a coastal tract of the hyperarid Atacama Desert in northern Chile. Direct accessibility of active surfaces is accompanied by uninterrupted stratigraphic exposures along the base of slopes, allowing direct comparisons between surface processes and the resulting sedimentary record. Four slope sectors are identified, based on differences in morphology and processes over active surfaces. Colluvial sedimentation is controlled by complex interactions of slope gradients and profiles, exposure to dominant winds, and potential runoff pathways, which vary considerably between different sectors. Major differences are evident between these hyperarid deposits and slope sedimentation in periglacial and temperate settings, including the complete absence of pedogenic activity and clay minerals; the volume of aeolian deposits and their role in controlling processes which redistribute sediment downslope, extending colluvial aprons; and the occurrence of runoff processes only where favoured by particular topographic configurations. Depositional surfaces range from steep talus cones, to debris‐flow‐dominated and aeolian‐dominated colluvial aprons, to an aeolian ramp subject to reworking by mass flows and flash floods. Consequently, facies associations and architectures at outcrop are highly variable and highlight the importance of spatial variations in slope morphology and processes in producing distinct, coeval colluvial stratigraphies within a single environmental context. Discrepancies between active processes and the corresponding stratigraphic signatures are also evident in some sectors; for example, preservation of alluvial and aeolian facies in stratigraphic sections does not always reflect the dominant processes over active slopes. Together with the spatial variability in processes and deposits along these slopes, this suggests that caution is required when extracting palaeoenvironmental information from analyses of colluvial successions.  相似文献   

Heavitree Quartzite,a Neoproterozoic (ca 800–760 Ma), high‐energy,tidally influenced,ramp association,Amadeus Basin,central Australia     

J. F. Lindsay 《Australian Journal of Earth Sciences》2013,60(1):127-139

The Neoproterozoic Heavitree Quartzite is widespread in the Amadeus Basin and has correlatives in all of the major central Australian intracratonic basins. The origin of the formation is enigmatic, not only because of its widespread sheet‐like distribution and uniformity of composition, but also because intense silicification makes facies studies difficult. Recently discovered exposures at the eastern end of the basin are relatively free of diagenetic quartz allowing a detailed study of sedimentary structures and an understanding of the depositional architecture of the formation. The formation, which consists largely of pale‐tan or white quartzose sandstone interbedded with rare laminated mudstone and conglomerate intervals, was deposited in at least four depositional sequences. The sheet‐like nature of the sandstone results from an abundant supply of sediments deposited in a high‐energy, open, shelf‐like environment on a regionally subsiding, low‐gradient ramp. Environmental settings switched both laterally and temporally between sand waves deposited by reversing tidal flow and higher velocity unidirectional currents involving dunes and plane beds. In the early stages of deposition, mud‐dominated, tidal‐flat environments alternated with higher energy, sand‐dominated, tidally influenced settings. However, in the later stages of deposition a major eustatic sea‐level fall moved base‐level basinwards, earlier sediments were reworked by streams to form a ravinement surface, gravel was carried well into the basin and fines largely disappeared from the environment. Gravel deposition was followed by a return to high‐energy, tidally influenced deposits involving large sand waves or dunes. Towards the top of the formation sand waves deposited by reversing tidal currents gradually decline and are eventually replaced by dunes deposited by unidirectional current flow. The transition to the shallow‐marine, anoxic rocks of the Bitter Springs Formation is gradational in response to increased accommodation in a ramp setting which lacked a clearly defined shelf break. The Heavitree Quartzite was probably deposited as a direct response to the events surrounding the assembly and breakup of Rodinia, in particular peneplanation during regional uplift in response to a rising mantle plume followed by broad regional subsidence as the plume decayed prior to the breakup of the supercontinent. The large supply of quartz sand resulted from peneplanation associated with the rising plume and the lack of soil‐stabilising vascular plants, an environmental setting with no modern analogue. The ultimate disposition of fines is not known but, given the environment of deposition, it is likely that they were removed during peneplanation and bypassed the sag basin completely.  相似文献   

Evolution of the Large-scale Active Manisa Fault,Southwest Turkey: Implications on Fault Development and Regional Tectonics     

《Geodinamica Acta》2013,26(6):427-453

This paper aims to illustrate and discuss mechanism(s) responsible for the growth and evolution of large-scale corrugated normal faults in southwest Turkey. We report spectacular exposures of normal fault surfaces as parts of the Manisa Fault - a ?50-km-long northeast-ward arched active fault that defines the northwestern edge of the Manisa graben, which is subsidiary to the Gediz Graben. The fault is a single through-going corrugated fault system with distinct along-strike bends. It follows NW direction for 15 km in the south, then bends into an approximately E-W direction in the northwest. The fault trace occurs at the base of topographic scarps and separates the Quaternary limestone scree and alluvium from the highly strained, massive bed-rock carbonates. The fault is exposed on continuous pristine slip surfaces, up to 60 m high. The observed surfaces are polished and ornamented by well-preserved various brittle structural features, such as slip-parallel striations, gutters and tool tracks, and numerous closely spaced extension fractures with straight or crescentic traces. The rocks both in the footwall and hanging-wall of the fault possess a well-developed fault rock stratigraphy made up, from structurally lowest to the top, of massive undeformed recrystallized limestone, a zone of cemented breccia sheets, corrugated polished slip planes, and first brecciated, then unbrecciated scree.

The observed slip surfaces of the Manisa Fault contain two sets of striations that suggest an early phase of sinistral strike-slip and a subsequent normal-slip movements. The first phase is attributed to: (i) approximately E-W-directed compression that commenced during either (?) Early-Middle Pliocene time or (ii) the current extensional tectonics and consequent modern graben formation in southwest Turkey that initiated during the Plio-Quaternary. During this period, the Manisa Fault was reactivated and it became a major segment. Stress inversion of fault slip data suggests that southwest Turkey has been experiencing multidirectional crustal extension, with components of approximately N-S, E-W, NE-SW and NW-SE extension. Following the reactivation, the inherited fault segments were connected to each other through interaction, linkage and amalgamation of previously discontinuous and overlapping smaller stepping adjacent faults. Linkage was via the formation of new connecting (breaching) fault(s) or by curved propagation of fault-tips. The result is a single through-going corrugated fault trace with distinct along-strike bends. The final geometry of the Manisa Fault is thus the combined result of reactivation and continuing interaction between previously discontinuous segmented fault traces.  相似文献   

Carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp (Miocene, Great Bahama Bank)     

C. Betzler  M. Pfeiffer  S. Saxena 《International Journal of Earth Sciences》2000,89(1):140-153

Received: 10 May 1999 / Accepted: 16 October 1999  相似文献   

海洋碳酸盐沉积相模式   总被引：2，自引：0，他引：2  

曾允孚  王成善 《矿物岩石》1991,11(3):107-117

本文在评述国内外有关碳酸盐相模式研究基础上提出,海洋碳酸盐沉积相模式研究已摆脱了60—70年代的静态的束缚而进入了一种动态研究阶段并强调碳酸盐缓坡(ramp)的重要性。同时,文中还对台地和缓坡的定义重新进行了厘定,并提出碳酸盐相模式的端元类型概念及其分类。此外,建隆的形成、海平面变化和大地构造背景对其有着不可忽视的控制作用,而碳酸盐相模式又控制了储集层的分布型式。  相似文献   

多特征约束下的复杂交叉路口主辅路识别     

张鸿刚  李成名  于美娜  武鹏达  郭曼 《测绘通报》2020,(10):21

主干道、辅路的准确识别对于实现复杂交叉路口的自动综合至关重要。传统方法多依赖于路段的笔直程度和弯曲程度描述路口的主干道和辅路，然而复杂交叉路口结构错综复杂、形态变化多样，仅依赖这两种特征进行主辅路识别的准确度有限，且部分形态相似的主辅路无法识别。为此，本文提出了一种多特征约束下的复杂交叉路口主辅路识别方法。首先提取复杂交叉路口的特征点，根据特征点对弧段进行打断，依据路段的笔直程度识别出平行弧段；然后依据道路延展性、角度、距离等特征识别平行簇获取复杂交叉路口中的主干道；最后通过紧凑度和距离关系识别匝道获取复杂交叉路口中的辅路。以南京OSM城市路网为例的试验表明，本文方法能够准确识别出复杂交叉路口的主干道和辅助路段，识别精度分别达到93.60%和89.43%。  相似文献   

Reconstruction of the Yangtze Ramp during Floian to Darriwilian (Ordovician) in South China: Its Morphology, Controlling Factors and Significances     

LUAN Xiaocong  André DESROCHERS  WU Rongchang  LIU Jianbo  WANG Guangxu  LIANG Yan  ZHANG Yuchen  WEI Xin  LI Lixi  ZHAN Renbin 《《地质学报》英文版》2023,97(6):1756-1777

A robust stratigraphic framework and a coherent depositional ramp model for the Zitai, Dawan, Meitan and Ningkuo formations of Floian–Darriwilian age (Early–Middle Ordovician) in the Yangtze (Daoba, Xiangshuidong, Daling, Gudongkou and Honghuayuan sections) and Jiangnan regions (Nanba section) was created based on lithofacies and major element analysis. Three siliciclastic (LF1–3) and six carbonate (LF4–9) lithofacies are recognized representing sediments that were deposited in mixed siliciclastic and carbonate ramp environment. The intensity of mixed sedimentation and terrigenous input were evaluated using the elemental proxies Intensity of Mixed sedimentation (IM) and Aluminum Accumulation Rate (AlAR), as well as their mean values during certain time intervals. Mixed sediments are most well-developed along the marginal Yangtze region, strongly impacted by recurrent influx of westerly derived terrigenous materials in response to global eustatic changes and regional tectonic movements, shaping the gently southeast-dipping morphology. Regular terrigenous influx resulted in periods of enhanced primary productivity on the Yangtze Ramp as evidenced by matching biodiversity peaks in planktonic organisms, i.e., chitinozoans and acritarchs. Brachiopods and other shelly fauna were also able to proliferate as new niches developed along the gently dipping ramp floor with substrate changes. The biodiversification patterns suggest that terrigenous influx controlled in part by regional tectonics played a more important role than previously thought in the development of Great Ordovician Biodiversification Event in South China.  相似文献   

Depositional model for a prograding oolitic wedge,Upper Jurassic,Iberian basin     

《Marine and Petroleum Geology》2015

Facies architecture and bedding patterns of the Kimmeridgian Pozuel Formation (Iberian Basin) evidence that this 50–70-m thick oolitic-grainstone unit conforms to the Infralittoral Prograding Wedge (ILPW) model instead of the classic models used for interpreting oolitic grainstones sandbodies on carbonate ramps or platforms (i.e., bank-margin shoal complexes, beaches and beach ridges).Ten lithofacies have been distinguished in the Pozuel Formation: 5–10° dipping clinobedded oolitic grainstone foresets passing to tabular oolitic packstones-grainstones, which interfinger the muddy basinal bottomsets. Landwards, the clinobeds pass into subhorizontal topsets composed of trough cross-bedded to structureless oolitic grainstones; oolitic-skeletal grainstones with stromatoporoids and coral-stromatoporoid-microbial mounds. Siliciclastic lithofacies and oncolitic/peloidal packstones occur at the innermost position. These lithofacies stack in strike elongated, 5–20-m thick, 0,5–2 km dip-oriented wide, aggradational-progradational packages with complex sigmoid-oblique geometries.Lithofacies, depositional geometries and stacking pattern permit to summarize the main characteristic of such Upper Jurassic oolitic infralittoral prograding wedge potentially to be applied in other oolitic sandbodies both in outcrops and subsurface: 1) sediment production within the wave action zone, 2) grainstone-dominated textures, 3) prograding basinward onto basinal muds, 4) laterally (strike) extensive, paralleling the shoreline, 5) variable thickness, commonly of few tens of meters, 6) broadly sigmoidal to oblique internal architecture, with topsets, foresets and bottomsets, 7) dip of foresets close to the angle of repose, 8) topsets deposited in shallow-water, extending through the shoreface, from the shoreline down to the wave base, 9) mounds, either microbial or skeletal, may occur in the topsets.The coated-grains factory was along the high-energy, wave-dominated outer platform (topset beds), from where the mud was winnowed and the grains transported both landward to the platform interior, and seaward to the platform edge, from were the grains cascaded down the slopes as grain flows and mass flows, forming clinobeds. This genetic model can be applied to other grain-dominated lithosomes, some of them forming hydrocarbon reservoirs, e.g., the Jurassic Hanifa Formation and some Arab-D (e.g., Qatif Field) in Arabia, the Smackover Formation in northern Louisiana and south Arkansas, the Aptian Shuaiba Formation (e.g., Bu Hasa Field) and the Cenomanian Mishrif Formation (e.g., Umm Adalkh Field) of the Arabian Gulf.  相似文献   

两淮地区奥陶系沉积相及相模式   总被引：2，自引：0，他引：2  

陆彦邦  李勇  王栋  杨清和  喻根 《安徽地质》1994,(3)

安徽两淮地区，奥陶系发育良好，以浅水碳酸盐岩为主，根据岩石类型、结构、构造、生物和剖面结构特征，可划分潮坪、局限潮下、浅滩、开阔潮下４个相带及２２个主要碳酸盐微相类型。碳酸盐相模式为均斜缓坡类型。  相似文献