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1.
Middle Miocene to Pleistocene sedimentary record of rift evolution in the southern Albert Rift (Uganda) 总被引：2，自引：1，他引：1
S. Roller J. Hornung M. Hinderer I. Ssemmanda 《International Journal of Earth Sciences》2010,99(7):1643-1661
This study presents an almost complete Middle Miocene to Pleistocene sequence of synrift sediments in the western branch of
the East African Rift. The studied succession is exposed in several patches on an eastward tilted block between the northern
tip of the Rwenzori Block and the eastern shoulder of the Albert Rift. In this position, it reaches a maximum thickness of
600 m of which 350 m have been logged systematically by analysing lithofacies and sediment architecture. Stratigraphic subdivision
of the succession relies on published biostratigraphic data of endemic mollusc associations and their correlation across East
Africa. The synrift sediments encountered are siliciclastics ranging from clay to coarse gravel with gypsum and ferrugineous
interlayers or impregnations. Lithofacies and architectural analysis indicate alluvial plain, delta plain, nearshore, delta
front, or lacustrine depositional environments. Based on the vertical stacking pattern, prograding and retrograding trends
of the depositional environments, and climatic indicators (e.g. conservation of feldspar, gypsum, and/or iron hydroxide precipitation),
four evolutionary phases can be distinguished: (i) a first phase between ca. 14.5 and 10.0 Ma is characterised by bedload-dominated
fluvial environment with massive sandy to gravelly bedforms, feldspar-rich sands, rare iron impregnations and relatively low
accommodation space. This phase is interpreted as pre- and early synrift sedimentation under a semiarid climate. (ii) From
ca. 10.0 to 4.5 Ma predominantly fine-grained siliciclastics were deposited in a distal fluvial plain to lacustrine setting
characterised by limited accommodation space. Fluctuation of thin beds, dominance of clay and frequent iron impregnations
point to a more humid climate with seasonality and weak tectonic activity. (iii) During the third phase between 4.5 and 2.0 Ma
delta plain and nearshore deposits with frequent ferrugineous impregnations and rich mollusc associations occurred, indicating
a humid period with lake-level highstands and accelerated subsidence. (iv) During the final sedimentary interval between 2.0
and 1.5 Ma gravel units reoccurred with less iron- but more carbonate and gypsum impregnations, and arkosic sandstones. This
phase recorded a general aridisation trend most probably caused by the upcoming rain barrier of the Rwenzori Mountains together
with accelerated rift-flank uplift and strong subsidence of the rift floor. The results of this study are of particular importance
for delineating key controls on sedimentation in the Albert Rift. 相似文献
2.
Tests were conducted to determine the performance and safety characteristics of specially designed, nonmagnetic Li/BrCl in SOCl2 (Li/BCX) and Li/Cl2 in SO2Cl2 (Li/CSC) battery cells. Discharge tests showed that D-size battery cells yield energy densities of 1.07 Wh/cc3 at currents of 0.17 A. The combination of high energy density and nonmagnetic properties allows smaller, lighter battery packs to be placed in close proximity to guidance systems without magnetic interference to the navigational systems. The safety testing results indicate that these systems possess explosion resistance and other characteristics necessary for a variety of applications 相似文献
3.
Total mercury concentrations were determined in surficial sediments, eleven species of benthic organisms and six species of fish from Haifa Bay, Israel. The results show that essentially all of the shallow water zone of the Bay receives anthropogenic mercury. A mercury-cell chlor-alkali plant was identified as the source of pollution. Surficial sediments in the vicinity of the plant, containing up to 0·99 μg Hg/g dry weight, were up to 157 times enriched in mercury relative to an unpolluted area. Mercury levels in the benthic organisms reflected the levels in the sediments. Maximal concentrations reaching 38·7 and 18·2 μg Hg/g dry weight were found in the carnivorous gastropod molluscs Arcularia circumcinta and Arcularia gibbosula, respectively. In all fish species, specimens caught in Haifa Bay had higher mercury concentrations in the muscle tissue than specimens caught south of the Bay. A maximal value of 1·66 μg Hg/g wet weight was recorded in Diplodus sargus. 相似文献
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5.
A combined study of radar facies,lithofacies and three‐dimensional architecture of an alpine alluvial fan (Illgraben fan,Switzerland) 
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下载免费PDF全文 Alluvial fans serve as useful archives that record the history of depositional and erosional processes in mountainous regions and thus can reveal the environmental controls that influenced their development. Economically, they play an important role as groundwater reservoirs as well as host rocks for hydrocarbons in deeply buried systems. The interpretation of these archives and the evaluation of their reservoir architecture, however, are problematic because marked heterogeneity in the distribution of sedimentary facies makes correlation difficult. This problem is compounded because the accumulated sedimentary deposits of modern unconsolidated fan systems tend to be poorly exposed and few such systems have been the focus of investigation using high‐resolution subsurface analytical techniques. To overcome this limitation of standard outcrop–analogue studies, a geophysical survey of an alpine alluvial fan was performed using ground‐penetrating radar to devise a scaled three‐dimensional subsurface model. Radar facies were classified and calibrated to lithofacies within a fan system that provided outcropping walls and these were used to derive a three‐dimensional model of the sedimentary architecture and identify evolutionary fan stages. The Illgraben fan in the Swiss Alps was selected as a case study and a network of ca 60 km sections of ground‐penetrating radar was surveyed. Seven radar facies types could be distinguished, which were grouped into debris‐flow deposits and stream‐flow deposits. Assemblages of these radar facies types show three depositional units, which are separated by continuous, fan‐wide reflectors; they were interpreted as palaeo‐surfaces corresponding to episodes of sediment starvation that affected the entire fan. An overall upward decline in the proportion of debris‐flow deposits from ca 50% to 15% and a corresponding increase in stream‐flow deposits were identified. The uppermost depositional unit is bounded at its base by a significant incision surface up to 700 m wide, which was subsequently filled up mostly by stream‐flow deposits. The pronounced palaeo‐surfaces and depositional trends suggest that allocyclic controls governed the evolution of the Illgraben fan, making this fan a valuable archive from which to reconstruct past sediment fluxes and environmental change in the Alps. The results of the integrated outcrop–geophysical approach encourage similar future studies on fans to retrieve their depositional history as well as their potential reservoir properties. 相似文献
6.
Nils Lenhardt Harald Böhnel Klaus Wemmer Ignacio S. Torres-Alvarado Jens Hornung Matthias Hinderer 《Bulletin of Volcanology》2010,72(7):817-832
The volcaniclastic Tepoztlán Formation (TF) represents an important rock record to unravel the early evolution of the Transmexican
Volcanic Belt (TMVB). Here, a depositional model together with a chronostratigraphy of this Formation is presented, based
on detailed field observations together with new geochronological, paleomagnetic, and petrological data. The TF consists predominantly
of deposits from pyroclastic density currents and extensive epiclastic products such as tuffaceous sandstones, conglomerates
and breccias, originating from fluvial and mass flow processes, respectively. Within these sediments fall deposits and lavas
are sparsely intercalated. The clastic material is almost exclusively of volcanic origin, ranging in composition from andesite
to rhyolite. Thick gravity-driven deposits and large-scale alluvial fan environments document the buildup of steep volcanic
edifices. K-Ar and Ar-Ar dates, in addition to eight magnetostratigraphic sections and lithological correlations served to
construct a chronostratigraphy for the entire Tepoztlán Formation. Correlation of the 577 m composite magnetostratigraphic
section with the Cande and Kent (1995) Geomagnetic Polarity Time Scale (GPTS) suggests that this section represents the time
intervall 22.8–18.8 Ma (6Bn.1n-5Er; Aquitanian-Burdigalian, Lower Miocene). This correlation implies a deposition of the TF
predating the extensive effusive activity in the TMVB at 12 Ma and is therefore interpreted to represent its initial phase
with predominantly explosive activity. Additionally, three subdivisions of the TF were established, according to the dominant
mode of deposition: (1) the fluvial dominated Malinalco Member (22.8–22.2 Ma), (2) the volcanic dominated San Andrés Member
(22.2–21.3 Ma) and (3) the mass flow dominated Tepozteco Member (21.3–18.8 Ma). 相似文献
7.
Historical reconstructions and predictions of streamwater acidification are presented for moorland and afforested catchments in the Welsh Uplands at Plynlimon. MAGIC (Model of Acidification of Groundwater In Catchments) is validated by application to an afforested catchment. MAGIC is used to illustrate that atmospheric deposition is primarily responsible for stream acidification but that conifer afforestation can enhance stream acidity. The historical trends determined by the model illustrate that long-term acidification has been present since the turn of the century and will continue unless either deposition levels are reduced significantly or liming is undertaken on a major scale. 相似文献
8.
Karroo (Triassic-Jurassic) sediments and lavas occupy a N.N.E.-trending trough known as the Tuli Syncline 230 km in length by 45 km wide along the southern margin of Rhodesia. The structure is fault bounded, especially on the north, and comprises a sequence of gently inward dipping lava flows cut by numerous E-W and N.N.E. striking dolerite dykes. The igneous rocks have been subdivided on the basis of mineralogy and chemistry into a stratigraphic sequence of limburgites near the base, olivine basalts and upper augite-plagio-clase-phyric basalts. In addition, rare shoshonite and absarokite types occur. Twentyfour new silicate analyses are comparable to those from rocks in the neighbouring Nuanetsi Province of Rhodesia, and show strong affinities to the northern province Karroo basalts of southern Africa as defined by Cox,McDonald andHornung (1967). 相似文献
9.
Barak Herut Hava Hornung Michael D. Krom Nurit Kress Yuval Cohen 《Marine pollution bulletin》1993,26(12):675-682
Concentrations of mercury, lead, copper, zinc, cadmium, iron and aluminium were recorded in coastal and river mouths surficial sediments, collected along the Mediterranean coast of Israel, during 1988–1991. The levels of trace metal concentrations when normalized against Fe concentration (trace metal/iron ratios) indicated no contamination at most of the stations along the coast. Enrichment of Hg, Cu, Zn and Cd attributed to land-based point sources of pollution, was found in the estuaries of the Kishon and Yarkon rivers. The normalized Pb, Cu and Zn data showed a trend of increasing values from the south toward the north. This S-N trend could be a result of three processes which may be occurring simultaneously: progressive mixing between sediment with a low trace metal/iron ratio in the south, which probably represents a single source derived from the Nile region with (a) non-point source input of pollutants by atmospheric transport, or (b) with point sources of pollutants introduced by rivers and streams, or (c) a natural change in the mineralogy of the sediments along the coast with a relative increase in the trace metals or a decrease in iron as one progresses further north. The relative importance of these three possible processes remains to be established. 相似文献
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