珠江三角洲乡村城市化的形成机制与调控措施   总被引：8，自引：0，他引：8  

阎小培  刘筱 《热带地理》1998,18(1):7-11

根据数据分析和实地调查，总结了珠江三角洲乡村城市化的特征。即乡村劳动力非农化速度快，非农化具空间分散性，乡村城市化滞后于工业化，以自来而上为主体的城市化；着重分析了乡村城市化的形成机制，认为地理环境是乡村城市化发生的最基本的前提，由农业生产的推动力和乡镇企业产生的吸引力构成的动力结构是乡村城市化发生的关键，而对外开放则是乡村城市化发生的最重要的外部因素；讨论了乡村城市化过程中存在的问题和矛盾，认为  相似文献   

某污水截流顶管工程中的施工控制     

杨转运 《岩土钻凿工程》2008,(1):115-118

结合某污水截流工程的工程实践,探讨了长距离顶管施工中存在的一些主要技术措施,提出了一些顶管施工过程中的施工控制方法,并探讨了其效果和存在的不足之处。  相似文献   

江西省柑桔冻害及其变化和防御对策   总被引：3，自引：1，他引：3  

罗冰  胡菊芳 《气象与减灾研究》2005,28(1):25-27

江西是中国柑桔主要产区之一，冻害是江西发展柑桔的主要障碍。1991年底，江西发生了近50a来最为严重的冻害，冻死柑桔约3．3万hm^2。从近50a冻害资料来看，江西冻害的变化尚无明县规律可循。冻害往往是突发的、随机的，这给冻害的防御带来了很大困难。因此要树立有备无患的思想，在布局上选择有利小气候环境，在管理上采取多种措施，增强柑桔抗冻能力，以达到减灾防灾的目的。  相似文献   

商洛市水资源功能规划及保护措施     

李雪敏  杨海娟 《地下水》2011,(1):133-135

水资源的有效保护是实现水资源可持续利用和社会经济可持续发展的重要环节。在商洛市水资源调查的基础上,合理划分水功能区,计算出重点河段各水功能分区相应的纳污能力,并以此为依据提出水资源保护措施,为商洛市水资源保护、监督和管理提供依据。  相似文献   

云南贡山县地质灾害调查及防治建议     

徐瑞智  何为  杨海鹏  李明杰 《云南地质》2013,(4):488-490,487

贡山县滑坡、泥石流、潜在不稳定斜坡等多种地质灾害并存,与大气降水强度、河水淹没和侵蚀作用、地形地貌、岩土类型、地质结构、人类不合理工程活动等相关.提出“以防为主、防治结合、全面规划、综合治理”的防治对策.  相似文献   

Age and significance of the Platypus Tuff Bed,a regional reference horizon in the Upper Permian Moranbah Coal Measures,north Bowen Basin   总被引：1，自引：1，他引：0  

P. Michaelsen  R. A. Henderson  P. J. Crosdale  C. M. Fanning 《Australian Journal of Earth Sciences》2013,60(2):183-192

The Platypus Tuff Bed in the Permian Moranbah Coal Measures provides a basin‐wide marker horizon traceable for over 300 km along strike. The bed is a tephra event unit, the product of a large‐scale volcanic eruptive episode involving a pyroclastic volume > 10 km³. The relatively even thickness (～1–1.5 m) of the tuff across the entire northern Bowen Basin (～10 000 km²) implies a distant source. The tuff is ash‐rich and its original geochemistry has been compromised by diagenetic alteration. Crystal content (10–15%) is dominated by quartz, suggesting a rhyolitic association. SHRIMP U–Pb analysis of zircons indicates an age of 258.9 ± 2.7 Ma for the Platypus Tuff Bed, confirming the Late Permian age that has generally been assigned to the Blackwater Group. The age framework now apparent for the coal‐bearing Blackwater Group suggests an average depositional rate ranging from ～133 m/10⁶ years for its eastern depocentre in the northern Bowen Basin to ～70 m/10⁶ years in more marginal settings to the west.  相似文献   

Greta Coal Measures in the Muswellbrook Anticline area,New South Wales     

R. Boyd  D. Leckie 《Australian Journal of Earth Sciences》2013,60(2):259-279

The Greta Coal Measures are the lower of two main coal‐bearing intervals in the Permian northern Sydney Basin. High quality outcrop and continuous core data are available from the Muswellbrook Anticline area in the Hunter Valley, enabling a sequence‐stratigraphic interpretation of the Greta Coal Measures to be presented for the first time. Age and core relationships indicate an unconformity at the base and the top of the Greta Coal Measures. A correlation between dated tuffs in the upper Greta Coal Measures in the Muswellbrook area and the Maitland Group in the Cessnock area establishes a clear diachronous upper boundary for the Greta Coal Measures resulting from a northwest‐ward marine transgression. The Greta Coal Measures are interpreted to occupy a single sequence in which the lower fluvial and lacustrine Skeletar Formation makes up a transgressive systems tract, the Ayrdale Sandstone Member is an estuarine unit around the maximum flooding surface, and the upper fluvial to deltaic Rowan Formation occupies a highstand systems tract. The overlying Jasdec Park Sandstone Member of the Maitland Group infills incised valleys above a sequence boundary and then occurs as a transgressive shoreline system before passing into the glacial marine Branxton Formation. The Greta Coal Measures represent high accommodation where subsidence and sediment supply were approximately balanced over more than 100 m of accumulation, and the development of 14 recognisable coal seams occurred in a single sequence.  相似文献   

Dickite‐ and kaolinite‐bearing sandstones and conglomerates in Illawarra Coal Measures of the Sydney Basin,New South Wales     

F. C. Loughnan  F. I. Roberts 《Australian Journal of Earth Sciences》2013,60(3):325-332

The recent discovery of dickite, intimately associated with ordered and disordered kaolinite, in quartzose sandstones and conglomerates of the Illawarra Coal Measures is of interest since in terms of the phase rule the co‐existence of two or more of these polytypes is evidence of either an unstable or metastable assemblage. A study has, therefore, been undertaken of the host rocks and accompanying strata in an attempt to gain insight into the mechanism of formation of the dickite and the reason for its development in preference to either of the other generally more abundant polytypes. From the results it would appear that although much still remains unresolved, the dickite is authigenic and precipitated from migrating groundwaters. Due probably to unusually low concentrations of silica in the groundwaters the rate of precipitation was inordinately slow and this apparently facilitated growth of relatively coarse crystals and development of the most stable phase.  相似文献   

U–Pb zircon age of the Walloon Coal Measures in the Surat Basin,southeast Queensland: implications for paleogeography and basin subsidence     

C. C. Wainman  P. J. Mccabe  J. L. Crowley  R. S. Nicoll 《Australian Journal of Earth Sciences》2013,60(7):807-816

The Jurassic Walloon Coal Measures of the Surat Basin were previously estimated to be of Middle Jurassic age, ranging from Aalenian to Callovian, based on an uncalibrated eastern Australian biostratigraphic framework. New U–Pb dates of 162.55 ± 0.05 Ma and 158.86 ± 0.04 Ma obtained from zircons in ash-fall volcanic tuffs now place the Walloon Coal Measures of the Surat Basin in the Upper Jurassic Oxfordian. The new dates have several implications for the interpretation of the Jurassic strata in the Surat Basin. First-order subsidence rates of 61 m/Myr for the Walloon Coal Measures are more akin to those of foreland basins than the previously assumed intracratonic setting. The dates also imply deposition of the Walloon coals in substantially higher latitudes than previously assumed and that they accumulated as peats in mires that experienced more than three months’ continual darkness each winter. Zircon dating of tuffs and associated geochemistry should assist with the correlation of the laterally impersistent coals, fluvial sandstone and mudstone of the Walloon Coal Measures, which are currently difficult to correlate over distances of more than a few kilometres. Dating of the palynostratigraphic zones APJ4.2 to APJ5 (Aequitriradites norrisii Association Zone to Murospora florida Association Zone) will also need to be recalibrated.  相似文献   

Understanding the geometry and distribution of fluvial channel sandstones and coal in the Walloon Coal Measures,Surat Basin,Australia     

《Marine and Petroleum Geology》2017

Understanding the controls on coal seam distribution and geometry is fundamental for planning coal seam gas production. In the Jurassic Surat Basin of South East Queensland, Australia, the spatial continuity of coal seams in the Walloon Coal Measures is highly variable and often difficult to map and predict, even with closely spaced (<1000 m) drillings. This paper investigates the frequency and location of thick sandstone in relation to thick coal seams or plies across three broad stratigraphic divisions, Upper Juandah (UJ), Combined Lower Juandah-Taroom (CLJT) and Condamine Coal Measures (CCM), within the Walloon Coal Measures. Basic depositional facies, e.g. channel, floodplain, marginal mire, and coal mire, were interpreted from geophysical logs. An in-house code was used to count the number of coal plies thicker than 2 m, and channel sandstones thicker than 5 m for the UJ and CLJT and 3 m for the CCM at each borehole. Isopleth maps of the numbers of both coal plies and channel sandstones were generated across the basin for the three subdivisions. Results show that there is an upward stratigraphic trend from thick to thin, and then to thick stacked coal plies. This corresponds to a similar vertical thickness change in channel sandstones. The incidence of thick coal and thick sandstone is associated with rising base level within an early transgressive systems tract which was followed by a high stand prior to a regional erosive event above the UJ. Thick and stacked coal plies have a marked tendency to occur in belts adjacent to the thick channel thoroughfares in the basin.  相似文献