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991.
Seasonal and spatial variability of particulate matter of a muddy intertidal flood front 总被引:1,自引:0,他引:1
The concentration and composition of suspended particulate matter (SPM) were measured weekly for a period of one year in the flood front waters traversing a muddy tidal flat. SPM concentrations were lowest in the winter when portions of the tidal flat were covered with ice, and biological activity was minimal. In contrast, the summer months had the highest SPM concentrations which reflected increased bottom resuspension. The two main sources of SPM were suspended matter carried in from offshore on the flooding tide and resuspended in situ bottom sediments. The offshore source was characterized by low SPM concentrations, coarse textures, and a high content of protein and chlorophyll ‘a’. Samples taken during resuspension events (storms/showers) had high SPM concentrations, finer textures, and were enriched in dead detrital organic material (phaeophytin). At any one time the SPM was primarily an admixture of these two sources. The highest SPM measurements were taken during storm events, with rainfall seeming to play a dominant physical role in aiding resuspension. SPM concentrations, textures, and compositions collected during the storms closely approximated SPM measurements made over newly dug ‘clam flats’. 相似文献
992.
Charles M. Onasch 《Tectonophysics》1984,110(1-2)
Compression and extension axes are deduced from quartz deformation lamellae in a quartzite and a graywacke folded into an asymetrical syncline. Deformation lamellae fabrics in the two sandstones are distinctly different. In the graywacke, regardless of bedding orientation or position on the fold, compression axes are normal or nearly normal to the axial planar rough cleavage. Extension axes generally lie in the cleavage plane, parallel to dip. In most quartzite samples, compression axes are parallel or subparallel to bedding, at high angles to the fold axis and extension axes are normal to bedding. Two samples from the very base of the formation indicate compression parallel to the fold axis with extension parallel to bedding, at high angles to the fold axis. One of these two shows both patterns. The lamellae fabric geometry in these two samples suggests the presence of a neutral surface in the quartzite. The lamellae-derived compression and extension axes are in good agreement with the buckling behavior of a viscous layer (quartzite) embedded in a less viscous medium (graywacke and shale below and shale and carbonate above). 相似文献
993.
The sources of lithospheric stress and their distinctive features are briefly reviewed. It is suggested that there are two main categories of lithospheric stress: renewable stress which persists despite continuing stress relaxation and non-renewable stress which can be dissipated by relief of the initial strain. The two most important types of renewable stress arise from plate boundary forces and from isostatically compensated loads. Non-renewable stress systems include bending stresses, membrane stresses and thermal stresses. An important phenomenon generating large stresses at shallow depth is stress amplification caused by lower lithospheric creep. This applies to renewable stresses but not to the non-renewable type. It is suggested that only renewable stresses contribute significantly to tectonic activity. However, bending and thermal stresses are locally important in subducting lithosphere. 相似文献
994.
The Earth is the only terrestrial planet to have seas, by which it is covered to the extent of seventy percent. The oceans determine the climate of the Earth and it is through them that life and civilization have evolved, but they also have major influence on physical processes in the solid Earth. Tidal friction leads to the Earth's spin slowing down with a consequent recession of the Moon from the Earth, while the presence of the oceans controls the tectonic evolution of the Earth through the formation of oceanic crust, the erosion of land and the accumulation of sediment, the formation of mountains and the establishment of isostatic balance. 相似文献
995.
M.W. Fischer 《Journal of Structural Geology》1984,6(6):721-726
Balanced and restored cross-sections through the central and eastern Pyrenees, constructed using both surface and borehole data, demonstrate the presence of c.18km of shortening above a flat lying N-directed Alpine décollement surface. Hangingwall diagrams show how the North Pyrenean satellite massifs are culminations within this thrust system. Pre-thrusting structures such as subhorizontal stretching lineations in the North Pyrenean Fault zone became rotated above these culminations as the North Pyrenean Fault was cut by Alpine thrusts. Stratigraphic evidence demonstrates that N-directed thrust movements occurred between mid Eocene and Oligocene time, and this is similar to the age of major S-directed thrust movements on the south side of the Axial Zone. The N-directed thrust system probably originated as a series of backthrusts to the dominant S-directed structures. 相似文献
996.
The process of drilling, in general, always produces sound. Though sound is used as a diagnostic tool in mechanical industry, its application in predicting rock property is not much explored. In this study, an attempt has been made to estimate rock properties such as uniaxial compressive strength, Schmidt rebound number and Young's modulus using sound level produced during rotary drilling. For this purpose, a computer numerical controlled vertical milling centre was used for drilling holes with drill bit diameters ranging from 6 to 20 mm with a shank length of 40 mm. Fourteen different rock types were tested. The study was carried out to develop the empirical relations using multiple regression analysis between sound level produced during drilling and rock properties considering the effects of drill bit diameter, drill bit speed and drill bit penetration rate. The F-test was used to check the validity of the developed models. The measured rock property values and the values calculated from the developed regression model are fairly close, indicating that the developed models could be efficiently used with acceptable accuracy in prediction of rock properties. 相似文献
997.
998.
V CHOWKSEY D M MAURYA PARUL JOSHI N KHONDE ARCHANA DAS L S CHAMYAL 《Journal of Earth System Science》2011,120(6):979-999
The Kachchh Mainland Fault (KMF) is a major E–W trending seismically active fault of the Kachchh palaeorift basin whose neotectonic
evolution is not known. The present study deals with the eastern part of the KMF zone where the fault is morphologically expressed
as steep north facing scarps and is divisible into five morphotectonic segments. The Quaternary sediments occurring in a narrow
zone between the E–W trending KMF scarps and the flat Banni plain to the north are documented. The sediments show considerable
heterogeneity vertically as well as laterally along the KMF zone. (The Quaternary sediments for a northward sloping and are
exposed along the north flowing streams which also show rapid decrease in the depth of incision in the same direction.) The
deposits, in general, comprise coarse as well as finer gravelly deposits, sands and aeolian and fluvial miliolites. The Quaternary
sediments of the KMF zone show three major aggradation phases. The oldest phase includes the colluvio-fluvial sediments occurring
below the miliolites. These deposits are strikingly coarse grained and show poor sorting and large angular clasts of Mesozoic
rocks. The sedimentary characteristics indicate deposition, dominantly by debris flows and sediment gravity flows, as small
coalescing alluvial fans in front of the scarps. These deposits suggest pre-miliolite neotectonic activity along the KMF.
The second aggradation phase comprises aeolian miliolites and fluvially reworked miliolites that have been previously dated
from middle to late Pleistocene. The youngest phase is the post-miliolite phase that includes all deposits younger than miliolite.
These are represented by comparatively finer sandy gravels, gravelly sands and sand. The sediment characteristics suggest
deposition in shallow braided stream channels under reduced level of neotectonic activity along the KMF during post-miliolite
time evidenced by vertical dips of miliolites and tilting of gravels near the scarps. The tectonically controlled incision
and dissection of the Quaternary deposits is the result of neotectonic activity that continues at present day. The overall
nature, sedimentary characteristics and geomorphic setting of the sediments suggest that the KMF remained neotectonically
active throughout the Quaternary period. 相似文献
999.
This paper presents one of the richest and most complete vertebrate faunas of the late Middle Miocene (~12 Ma) of Central Europe. Up to now, sixty-two vertebrate taxa, comprising all major groups (fishes, amphibians, reptiles, birds, mammals), have been recorded. Based on sedimentological and palaeobiological evidences, this Fossillagerstätte is assumed to originate from a floodplain paleosol formed on top of a braided river sequence. The fauna points to a highly structured, somewhat vegetated landscape with a wide array of habitats (e.g., fluvial channels, sporadically moist floodplains, short-lived ponds, savannah-like open areas and screes). It was preserved due to a rapid drowning and the switch to a freshwater lake environment. Palaeoclimatological data, derived from pedogenic features as well as from biota, indicate an overall semi-arid, subtropical climate with distinct seasonality (mean annual precipitation 486 ± 252 mm, mean annual temperature ~15°C). This underlines the late Middle/early Late Miocene dry-spell in Central Europe. From taphonomical point of view, the irregularly distributed but roughly associated larger vertebrate remains refer to an in situ accumulation of the bone bed. Splintered bones, gnawing marks as well as rhizoconcretions and root corrosion structures record some pre- and post-burial modification of the taphocoenose. However, the findings of pellet remains argue for a very fast burial and thus to a low degree of time-averaging. For this reason, the fossil fauna reflects the original vertebrate community rather well and is a cornerstone for the understanding of late Middle Miocene terrestrial ecosystems in this region. Certainly, Gratkorn will be one of the key faunas for a high-resolution continental biostratigraphy and the comprehension of Europe’s faunal interchanges near the Middle/Late Miocene transition. 相似文献
1000.
N. V. Chukanov A. A. Mukhanova R. K. Rastsvetaeva D. I. Belakovsky S. M?ckel O. V. Karimova S. N. Britvin S. V. Krivovichev 《Geology of Ore Deposits》2011,53(7):583-590
Oxyphlogopite is a new mica-group mineral with the idealized formula K(Mg,Ti,Fe)3[(Si,Al)4O10](O,F)2. The holotype material came from a basalt quarry at Mount Rothenberg near Mendig at the Eifel volcanic complex in Rhineland-Palatinate,
Germany. The mineral occurs as crystals up to 4 × 4 × 0.2 mm in size encrusting cavity walls in alkali basalt. The associated
minerals are nepheline, plagioclase, sanidine, augite, diopside, and magnetite. Its color is dark brown, its streak is brown,
and its luster is vitreous. D
meas = 3.06(1) g/cm3 (flotation in heavy liquids), and D
calc = 3.086 g/cm3. The IR spectrun does not contain bands of OH groups. Oxyphlogopite is biaxial (negative); α = 1.625(3), β = 1.668(1), and
γ = 1.669(1); and 2V
meas = 16(2)° and 2V
calc = 17°. The dispersion is strong; r < ν. The pleochroism is medium; X > Y > Z (brown to dark brown). The chemical composition is as follows (electron microprobe, mean of 5 point analyses, wt %; the ranges
are given in parentheses; the H2O was determined using the Alimarin method; the Fe2+/Fe3+ was determined with X-ray emission spectroscopy): Na2O 0.99 (0.89–1.12), K2O 7.52 (7.44–7.58), MgO 14.65 (14.48–14.80), CaO 0.27 ((0.17–0.51), FeO 4.73, Fe2O3 7.25 (the range of the total iron in the form of FeO is 11.09–11.38), Al2O3 14.32 (14.06–14.64), Cr2O3 0.60 (0.45–0.69), SiO2 34.41 (34.03–34.66), TiO2 12.93 (12.69–13.13), F 3.06 (2.59–3.44), H2O 0.14; O=F2 −1.29; 99/58 in total. The empirical formula is (K0.72Na0.14Ca0.02)(Mg1.64Ti0.73Fe0.302+ Fe0.273+Cr0.04)Σ2.98(Si2.59Al1.27Fe0.143+ O10) O1.20F0.73(OH)0.07. The crystal structure was refined on a single crystal. Oxyphlogopite is monoclinic with space group C2/m; the unit-cell parameters are as follows: a = 5.3165(1), b = 9.2000(2), c = 10.0602(2) ?, β = 100.354(2)°. The presence of Ti results in the strong distortion of octahedron M(2). The strongest lines of the X-ray powder diffraction pattern [d, ? (I, %) [hkl]] are as follows: 9.91(32) [001], 4.53(11) 110], 3.300(100) [003], 3.090(12) [112], 1.895(21) [005], 1.659(12) [−135], 1.527(16)
[−206, 060]. The type specimens of oxyphlogopite are deposited at the Fersman Mineralogical Museum in Moscow, Russia; the
registration numbers are 3884/2 (holotype) and 3884/1 (cotype). 相似文献