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91.
DANIEL D. ARREOLA 《Geographical review》2010,100(3):291-294
Editors' note: This essay by Dan Arreola begins the second set of retrospective pieces commissioned to celebrate the centennial volume. Members of the Editorial Board responded to our request to prepare brief commentaries on landmark Geographical Review articles that were influential in their professional careers. Although many other articles touched the minds of emerging scholars, this small sampling covers a fairly wide swath of the fabric of American geography. It also reminds us that each future article has the potential to have a similar enduring value and help open new intellectual vistas. In addition to Arrreola's piece, the short essays include the musings of Barry Keim, Susan Walcott, Larry Ford, and Risa Palm. 相似文献
92.
任军平 王杰 孙宏伟 冯琳 左立波 古阿雷 贺福清 CHIPILAUKA Mukofu ALPHET PHASKANI Dokowe EZEKIAH Chikambwe CHIWSHIMBA Canisius DANIEL Malunga 《中国地质》2019,46(3):575-586
赞比亚东北部班韦乌卢地块受到其东北部的古元古代乌本迪构造带、西北部的中元古代基巴拉构造带、东南部的中元古代伊鲁米德构造带及西南部泛非期卢弗里安构造带的影响。班韦乌卢地块主要由基底和沉积盖层两部分组成。其中,基底主要由片岩带、安山质-流纹质变质火山岩、花岗岩类岩基及其他侵入体组成。沉积盖层从老至新依次为姆波罗科索群、卡萨马群、加丹加超群及新生代的河流相和湖泊相沉积。本文对卡萨马地区的卡萨马群地质特征、碎屑锆石U-Pb-Hf同位素及地球化学特征进行了系统研究,获得卡萨马群中紫红色粉砂岩的32颗碎屑锆石U-Pb年龄多集中在(1849±23)~(1993±21)Ma,卡萨马群的形成时代可能晚于(1434±14)Ma,属于中元古代,其中22颗锆石(176Hf/177Hf)i为0.281049~0.281618,εHf(t)为-12.8~-1.6,二阶段模式年龄变化范围为2406~3487 Ma。对卡萨马群的砂岩进行了稀土元素分析和微量元素分析,结果显示卡萨马群砂岩δEu负异常明显,投点主要落在沉积岩区;微量元素显示砂岩形成于被动大陆边缘环境。 相似文献
93.
RANSOME K. T. CORNEY† JEFFREY PEAKALL DANIEL R. PARSONS LIONEL ELLIOTT† KATHRYN J. AMOS JAMES L. BEST GARETH M. KEEVIL DEREK B. INGHAM† 《Sedimentology》2006,53(2):249-257
The planform patterns of meandering submarine channels and subaerial fluvial bends show many similarities that have given rise to strong analogies concerning the fluid dynamics of these channel types. Existing models of helical motion in open‐channel bends depict flow that is characterized by surface flow towards the outer bank, and basal flow towards the inner bank. This paper investigates and compares, through an analytical model and physical experiment, flows within fluvial meanders, and submarine channel bends that contain density‐driven gravity currents. The results indicate that the sense of helical motion can be reversed in submarine bends that contain density currents when compared with fluvial bends, and that the orientation of the helical flow is dependent on the vertical distribution of downstream velocity. Specifically, the sense of helical motion is reversed in bends when the maximum downstream velocity is near the bed, resulting in near‐bed flow towards the outer bank. These findings suggest that the dynamics of sediment transport and deposition in curved channels with such velocity profiles will be fundamentally different to those currently assumed from sinuous open‐channels. 相似文献
94.
DANIEL J. UTTING BRENT C. WARD EDWARD C. LITTLE 《Boreas: An International Journal of Quaternary Research》2009,38(3):471-481
Glaciofluvial corridor hummocks (GCHs) within the Walker Lake map area, Canada, were examined in order to determine the character and genesis of these geomorphic features and their associated deposits. Located south of the Chantrey Moraine and north of the Keewatin Ice Divide, these corridors occur within a belt extending approximately 120 km east–west and approximately 60 km north–south. They are spaced 5–10 km apart and are hundreds of metres to several kilometres in width. They have undulating longitudinal profiles, abrupt material boundaries with the surrounding till and occur in valleys and over interfluves. Hummocks were investigated using longitudinal and perpendicular ground-penetrating radar (GPR) surveys in conjunction with pit excavations. From these analyses, the hummocks comprise a single lithofacies consisting of coarsely stratified, matrix-supported gravely sand to a depth of approximately 10 m. This sediment is similar to that of a 'sliding bed facies' observed in esker sediments and hyperconcentrated flow deposits, both of which are attributed to high meltwater discharges. Therefore, we hypothesize that the Walker Lake GCHs formed from sedimentation in cavities at the base of the ice sheet by a rapid influx of meltwater. 相似文献
95.
By DANIEL ROSENFELD JIM PETERSON ARON GINGIS 《Tellus. Series B, Chemical and physical meteorology》2009,61(4):694-700
Rosenfeld (2000, hereafter R00), in applying new satellite methodology to analyse case studies in Southeastern Australia and elsewhere, provided evidence that urban and industrial air pollution can suppress precipitation from shallow clouds. He concluded that 'Air pollution must be an important factor in determining the precipitation amounts in the Snowy Mountains'. These satellite observations were the impetus for our proposed detailed follow-on research program to further validate and quantify these inferences, publicly offered in Rosenfeld et al. (2006, hereafter R06) and repeated here, thereby recognizing the remaining large uncertainties. In response, Ayers (2009, hereafter A09) attempts to deny the significance and validity of the observations of R00. His scientific arguments are refuted here. Furthermore, A09 wrote erroneously that 'a hypothesis that air pollution in the form of small particles has caused a secular decrease in precipitation over SE Australia was advanced by Rosenfeld (2000) , who concluded that the hypothesis was proven.' But R00 did not make such a claim, although this is a viable hypothesis that warrants testing (R06). In fact, R00 wrote: 'trend analyses of snow, winter temperature, and total winter rainfall for the period 1910–1991 showed statistically insignificant decreases… ( Duus, 1992 )'. 相似文献
96.
Nepheline- and analcime-bearing syenite occurs at the uppercontact of a quartz diabase sill with the Lockatong Argilliteat Brookville, New Jersey. The syenite is intimately mixed withgranophyre that formed by fractional crystallization of basalticmagma and accumulated near the top of the sill. Some of theresidual liquid now represented by granophyre reacted with silica-poor,sodium-rich argillite to form the syenite. Initial Sr87/Sr86 ratios (assuming an age of 190 m. y.) are0.71440.7147 for the unmetamorphosed and the hornfelsedargillite, 0.7067 for the granophyre, 0.7058 for the diabase,and intermediate values of 0.71280.7131 for the syenite. The isotopic evidence agrees with field, petrographic, experimental,and chemical data supporting assimilation. Alternative hypothesesof syenite formation by separate intrusion, differentiation,or partial melting of Lockatong Argillite are contradicted bythe data. Isotopic and normative data strongly suggest that syenite formedfrom argillite and granophyre in the proportions three or fourto one; during the assimilation process the country rock actedas solvent and the intrusive as solute. 相似文献
97.
任军平 王杰 左立波 古阿雷 孙宏伟 许康康 CHIPILAUKA Mukofu ALPHET PHASKANI Dokowe EZEKIAH Chikambwe CHISHIMBA Canisius DANIEL Malunga 《地质学报》2019,93(11):2832-2846
石英闪长岩锆石U-Pb和Lu-Hf同位素及地球化学特征研究对赞比亚东北部班韦乌卢地块的形成时代及构造演化具有重要的研究意义。采用LA-MC-ICP MS方法测得班韦乌卢地块中卡萨马西部地区出露的两个石英闪长岩体中锆石的~(207)Pb/~(206)Pb年龄加权平均值分别为1964±8 Ma(MSWD=0.87,N=32)和1913±10 Ma(MSWD=0.77,N=19),表明两期石英闪长岩均形成于古元古代且可能与古元古代乌本迪构造带的活动有关。全岩地球化学分析显示,石英闪长岩属准铝质、高钾钙碱性系列岩石。稀土配分曲线均呈右倾型,具有富含轻稀土元素(LREE)、贫重稀土元素(HREE)以及δEu (0.77~0.80)弱负异常特点。微量元素均显示大离子亲石元素(如Rb、Ba及K)和活泼的不相容元素(如Th及U)相对富集,高场强元素Nb、Ta、P、Sr和Ti相对亏损。Nd/Th=3.60~4.65,Nb/Ta=12.05~13.87,Th/Ta=11.14~11.81,Ti/Zr=36.84~41.71,Ti/Y=220.28~300.00和具有不均一的ε_(Hf)(t)值(分别为-3.8~1.3和-4.3~8.6)均显示石英闪长岩的原始岩浆具有壳幔混合的特点。Zr/Y=5.98~7.19,La/Nb=2.91~3.88,La/Yb=12.19~13.92及构造判别图解均显示石英闪长岩形成于安第斯型活动大陆边缘。 相似文献
98.
DANIEL D. ARREOLA 《Geographical review》2012,102(1):111-131
The creation of the present United States‐Mexico boundary in the mid‐nineteenth century interrupted and disregarded the traditional territorial space of the Chiricahua Apache, whose ancestral homeland transcended this new line. As a result of their land claims, the United States created a reservation for the Chiricahua Apache, but it was later withdrawn. Today members of this group officially reside among Mescalero Apache in New Mexico and Fort Sill Apache in Oklahoma. This essay assesses the historic and contemporary impact of geographical borderland changes for the Chiricahua Apache and discusses the legacy of a transformed homeland. 相似文献
99.
100.