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11.
E. G. RHODES 《Sedimentology》1982,29(2):201-221
The southern coast of the Gulf of Carpentaria, Northern Australia, consists of a broad chenier plain which is comparable in size and morphology to those reported on the coasts of Surinam and south-western Louisiana. The Carpentaria chenier plain has, at some locations, prograded over 30 km since the Middle Holocene by deposition of low-tide muds over subtidal muds during periods of increased sediment input by the rivers. Chenier ridges are formed during periods of reduced sediment flux by wave induced sorting and redistribution processes. An alternation of increased and decreased sediment flux from fluvial sources has occurred several times during the upper Holocene. Such variation in sediment supply is believed to be related to temporal fluctuations in rainfall over the drainage basin which surrounds the southern and eastern Gulf. 相似文献
12.
Magmatic Processes During the Prolonged Pu'u 'O'o Eruption of Kilauea Volcano, Hawaii 总被引：4，自引：1，他引：3
GARCIA MICHAEL O.; PIETRUSZKA AARON J.; RHODES J. M.; SWANSON KIERSTIN 《Journal of Petrology》2000,41(7):967-990
The Pu’u ’O’o eruption is exceptional amonghistorical eruptions of Kilauea Volcano for its long duration( 相似文献
13.
CHRISTOPHER S. ROMANEK EUGENE C. PERRY ALLAN H. TREIMAN RICHARD A. SOCKI JOHN H. JONES EVERETT K. GIBSON 《Meteoritics & planetary science》1998,33(4):775-784
Abstract— Samples from a suite of Shergotty—Nakhla—Chassigny (SNC) meteorites were analyzed for their O isotopic ratios by a modified version of the laser fluorination technique. Measured isotopic ratios (17O/16O and 18O/16O) from bulk samples of the Shergottites, EETA79001, Shergotty and Zagami; the Nakhlite Lafayette; and Chassigny are similar to those reported in the literature, as are those from olivine and pyroxene mineral separates from Lafayette. Iddingsite, a preterrestrial alteration product of Lafayette, was measured for the first time as a separate phase. Oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum δ18O of 14.4% for a ～90% separate. Based on these measurements, end-member iddingsite has a δ18O of 15.6%, which places it among other 18O-enriched secondary phases (carbonate and silica) observed in SNC meteorites. The relatively large difference in δ18O between iddingsite and the olivine and pyroxene it replaces (～11%) is typical of low-temperature alteration products. A range of crustal fluid δ18O values can be interpreted from the δ18O for end-member iddingsite, assuming isotopic equilibrium was achieved during low-temperature hydrous alteration (<100 °C; Treiman et al., 1993). The calculated range of values, ?15 to 5%, depends on many factors including: (1) the modal mineralogy of iddingsite, (2) potential isotopic exchange among other O-bearing phases such as host silicate and carbonate, and (3) exchange with evolved or exotic O reservoirs on Mars. Despite the lack of constraints, the calculated range is consistent with isotopic exchange, and possibly equilibria, among components of the CO2-carbonate-iddingsite-H2O system at low temperature. The SNC meteorite samples in this study have Δ17O values that are indistinguishable from bulk Mars (0.30%), except for a single, small sample of iddingsite that has an anomalous Δ17O of ～1.4%. While analytical difficulties make isotopic measurements for this sample problematic, the Δ17O is similar in direction to Δ17O reported for waters extracted from bulk samples of Lafayette (Karlsson et al., 1992). If the Δ17O for iddingsite is confirmed, it can be concluded that evolved or exotic fluids on Mars have contributed volatiles to the O reservoir from which iddingsite formed 130 to 700 Ma ago. 相似文献
14.
IAN M. HOWAT EUGENE W. DOMACK 《Boreas: An International Journal of Quaternary Research》2003,32(1):56-75
This study analyses acoustic profiles of two mid-shelf troughs, the JOIDES Basin and Pennell Trough in the western Ross Sea, Antarctica. These troughs are subglacial erosion features formed by repeated advance of streaming ice onto the Ross Sea continental shelf. Sediment wedge formations, interpreted to have been deposited at the most seaward grounding zone during the Last Glacial Maximum (LGM), are observed within the mid-shelf region of these troughs. By correlating high-resolution acoustic profiles with core samples, we resolve the stratigraphy of these wedge formations to assess the relationships between bathymetry, subglacial sediment distribution and palaeo-ice-stream configuration. The grounding zone wedge geometries were controlled by the pre-existing topography. The JOIDES and Pennell Troughs were only partially infilled during the LGM. Axial diamict progradation from the landward margin of the troughs indicates enhanced flow (debris supply) along the axis of ice flow. Differences in grounding zone geometries indicate a decrease in basal debris deposition and/or supply during ice recession. The lack of a recessional ice-shelf facies indicates that either the ice shelf was absent during retreat, or that there was no melt-out of basal debris. 相似文献
15.
EUGENE C. RANKEY 《Sedimentology》2011,58(7):1831-1859
Islands rimming Pacific atolls typically form narrow, low‐lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea‐level rise. As these, low islands form the only habitable land for many island nations, understanding the character of shorelines, and the rates and controls that operate to bring about changes, is an issue of central importance. The purpose of this study is to unravel the characteristics of coastal change on atoll islands of the Gilbert Island chain of the equatorial Pacific nation of Kiribati, especially as they relate to autogenic shoreline processes and El Niño/Southern Oscillation variability. Integration of field observations, differential global positioning system data, historical aerial photographs and ultra‐high resolution remote sensing images demonstrates the nature, spatial patterns and rates of change from 17 islands on Maiana and Aranuka atolls. The results illustrate that, between 2005 and 2009, ca 50% of the shorelines on these islands displayed a discernable shift in position; some shorelines were accretionary (at net rates up to ca 8 m year?1) and others were erosional (up to ca 18 m year?1). Long‐term net rates of change on Maiana between 1969 and 2009 were lower than short‐term net rates measured between 2005 and 2009. Both short‐term and long‐term observations illustrate some of the greatest change occur near terminations of the largest, north–south oriented islands, associated with longshore movement of coarse sand and gravel. Direct hits by tropical depressions and marked seasonality, factors interpreted as being essential in island growth and shoreline dynamics elsewhere, do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics. Similarly, observations over four years suggested that shoreline variability probably is not influenced directly by marked sea‐level change, although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long‐term increase in the rate of sea‐level rise. Within this framework of global change, local anthropogenic effects, autogenic shoreline processes and El Niño/Southern Oscillation‐influenced wind and wave variability control many aspects of these dynamic shorelines. These results provide quantitative insights into the character and variability of rates of shoreline change, information essential for evaluating and mitigating the vulnerability of island nations such as Kiribati. 相似文献
16.
Sedimentology of glacial and glacial marine deposits on the George V-Adelie continental shelf, East Antarctica 总被引：1，自引：0，他引：1
Mineralogic and textural data suggest that glacial ice derived from the region of the present day Cook Ice Shelf extended to the edge of the d'Urville Sea continental shelf. As part of this glacial maximum, basal tills and glacial marine sediments were deposited over an irregular subglacial surface. Extensive redeposition of eroded material took place in the middle and outer portions of the continental shelf. Retreat of glacial ice was relatively rapid and was associated with widespread deposition of a thin residual glacial marine unit and turbidity current deposits in the far western and eastern parts of the region. Today, sedimentation on the continental shelf of the d'Urville Sea is controlled by biogenic and physical oceanographic processes. Deposition of ice-rafted detritus from icebergs undoubtedly occurs but is relatively insignificant. Glacial advances along this periphery of East Antarctica appear to the regulated by adjacent outlet glaciers rather than direct advance of the grounded ice sheet. 相似文献
17.
ABSTRACT. Although residential concentrations of immigrant ethnic groups in cities were common a century ago, it is not clear to what extent members of more recently arrived groups live near each other. We attempt to determine how common such clustered settlement is today, using 2000 census data to measure concentrations of Asians, Hispanics, and their larger ethnic subgroups in fifteen large metropolitan areas. The percentage of an ethnic group that is residentially concentrated correlated significantly with the group's proportion in an area. With metropolitan areas weighted equally, 38 percent of Hispanics and 13 percent of Asians were concentrated. However, when we analyzed eight specific nationality groups, the residentially concentrated proportion ranged from 14 to 59 percent. Level of cultural assimilation appears to explain group differences in level of concentration. Although ethnic concentrations were more pronounced in the largest metropolitan areas, important concentrations were also found in many of the smaller areas in our study. 相似文献
18.
ABSTRACT. The war in Iraq has spanned the full spectrum of military operations: intense combat, stability‐and‐support operations, and peacetime activities. Regardless of their nature and relative intensity, military operations are shaped by the characteristics of the military operating environment. Consequently, the scale, tempo, and complexity of any type of military endeavor are linked to the physical and cultural landscapes of the region in which it is conducted. Military geographers use geographical information, tools, and techniques to examine those links. Iraq's operating environment is studied to identify the relevant components of its physical and human geography. This military geographical examination of Iraq tells us a great deal about how the physical and cultural environment have influenced the war, as well as how the complexity of its human landscape continues to affect the postwar rebuilding of the country. 相似文献
19.
This paper seeks to contribute to Rwanda's ongoing restructuring of protected area management. The early part of the paper draws on experiences elsewhere in Africa, as well as key contexts in Rwanda, to assert that conservation of national parks may best be served by flexible and inclusive partnerships that seek to integrate conservation activities across different agents and scales. This assertion is then explored more critically through empirical research that investigates the views of potential conservation partners. The findings suggest that attempts to develop partnerships that are built around national parks will face difficulties. Whilst there is a general willingness to be further involved in park management, this is complicated by cleavages in beliefs about how wider participation might be implemented. In particular, it is only international conservation NGOs that currently seem to be comfortable with the national park approach to conservation management: only they see themselves as having the expertise to be decision-making partners and only they would want their role in a partnership to be formalized. 相似文献
20.
EUGENE A. SHINN 《Sedimentology》1969,12(1-2):109-144