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211.
The initiation and linkage of surface fractures above a buried strike-slip fault: An experimental approach 总被引:1,自引:0,他引:1
Surface fractures in the overburdened sedimentary rocks, formed above a deep-seated basement fault, often provide important
information about the kinematics of the underlying master fault. It has already been established that these surface fractures
dynamically evolve and link one another with progressive displacement on the master fault below. In the present study, two
different series of riedel-type experiments were carried out with clay analogue models under different boundary conditions
viz., (i) heterogeneous simple shear of the cover rocks above a buried strike slip fault (wrench system) and (ii) heterogeneous
simple shear with a component of shear-normal compression of the overburden package above a basement fault (transpressional
system), to observe the initiation and linkage of surface fractures with varying T′ (where T′ = thickness of the overburden normalized with respect to the width of the master fault). In the wrench system, Riedel (R)
shears were linked by principal displacement (Y) shears at early stages (shear strain of 0.8 to 1) in thin (2 < T′ < 18) models and finally (at a minimum shear strain of 1.4) gave rise to a through-going fault parallel to the basement fault
without development of any other fracture. Conjugate Riedel (R′) shears develop only within the thicker (T′ > 18) clay models at a minimum shear strain of 0.7. With increasing deformation (at a minimum shear strain of 1.2) two R′
shears were joined by an R shear and finally opened up to make a sigmoidal vein with an asymmetry antithetic to the major
fault-movement sense. Under transpression, the results were similar to that of heterogeneous simple shear for layers 2 < T′ < 15. In layers of intermediate thickness (15 < T′ < 25) early formed high angle R shears were cross cut by low angle R shears (at a minimum shear strain of 0.5 and shortening
of 0.028) and “Riedel-within-Riedel” shears were formed within thick (T′ > 25) models (at minimum shear strain of 0.7 and shortening of 0.1), with marked angularity of secondary fault zone with
the master fault at depth. 相似文献
212.
Diverse palynomorphs and phytoliths recovered from coprolites of ovi-caprids (sheep, goat) collected from Yang-Hai Tomb at Xinjiang Province, China, have been used to elucidate the dietary pattern of ancient livestock and to reconstruct the paleovegetation and paleoclimate of this part of northwest China ca. 2500 14C yr BP. Palynological and phytolith data suggest that a rich dry temperate vegetation prevailed in the area during the said period. Climatic conditions and grassland vegetation type of the area are explored using phytolith indices. 相似文献
213.
Debasis Ghosh 《Transactions in GIS》2008,12(3):365-375
Spatial decision making is characterized by problems associated with multiple and conflicting alternatives relating to geographical features and their attributes. As such, the search for the best possible alternative from a large set of such alternatives can be a daunting task. The aim of integrating GIS with Multi‐Criteria Decision Making (MCDM) is to develop a well‐defined process that can scan through such extensive fields of choice to arrive at the best possible solution. Goal Programming is one tool (developed in conjunction with MCDM) that can handle a problem with multiple, conflicting and incommensurable alternatives, and this article explains how the loose coupling technique can integrate MCDM with GIS to assist decision making among competing alternatives. As an example, this methodology has been applied for community development purposes in the Hooghly District of West Bengal, India. 相似文献
214.
Amitabha Ghosh 《Earth, Moon, and Planets》1988,42(1):69-75
Transfer of angular momentum from the Sun to the planetary system has been found to be inevitable in all evolutionary models for the origin of the solar system. In cold theories it has been proposed to be achieved through friction whereas electromagnetic forces are considered to be the agent for this transfer in hot theories. In the present paper it has been shown that the required order of magnitude of angular momentum can be transferred by another mechanism based on the principle of inertial induction. In the previous theories most of the transfer had been assumed to have taken place during the pre-Main-Sequence period whereas in this proposed theory most of the transfer takes place during the Main-Sequence period of the Sun. The paper does not intend to go into the details of planet formation and the evolutionary process but confines itself only to the problem of angular momentum transfer. 相似文献
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219.
Banded iron formations of the Iron Ore Group (Archean greenstone belts) of Jharkhand-Orissa region, India host a good number
of large iron ore deposits (Fe wt %> 62). Iron ore mineralization of Gandhamardan hill is one of them where iron ores occur
in two stratigraphic horizons. One is strictly confined within banded iron formation (stratabound mineralization) with irregular
geometry, and show fracture filling and replacement vein-type mineralization along the fringes of hard massive ores of the
core. This type of mineralization is exposed along the western slope of the hill. Hard massive and laminated ores dominate
this mineralization. The other type occurs as low dipping sheet like body above banded iron formation and covered by laterites
forming the top of the hill. Flaky ores dominate this mineralization with formation of hard goethitic crust near the top.
Both the mineralizations contain mineralized banded iron formation corestones surrounded by hard massive or flaky iron ores.
Hard massive ores are entirely represented by martite-microplaty hematite mineralogy. Hard laminated ores contain microplaty
hematite and few martite grains representing early magnetites of the banded iron formation. Flaky ores are high porosity ores
produced by leaching of silica, martite and microplaty hematite. Hard goethitic ores are developed due to replacement of martite
and microplaty hematite or precipitation of goethite in the pore spaces. 相似文献
220.
Anupam Ghosh 《Journal of the Geological Society of India》2012,80(1):65-74
A low diversity, epifaunal to infaunal Foraminiferal assemblage widely distributed in sand flats, mud flats and marshes along
the coastal tracts of the Gulf of Cambay. It is dominated by the species of Ammonia, Rotalidium, Murrayinella, Haynesina, Quinqueloculina, Nonionella, Florilus, Elphidium, Trochammina and Miliammina. A triserial planktonic foraminifer Gallitellia vivans, an indicator of stressed and upwelling areas, is also characteristically present in the sediments of the estuaries. The
paper discusses the systematics and distribution of the Foraminiferal species in the macrotidal estuaries of the Gulf of Cambay. 相似文献