Presence Of Slickensides Research Articles

Characterization and classification of soils of Bemetara under rice and soybean based cropping systems

A study was conducted on the soils under rice and soybean based cropping systems in Bemetara block of Bemetara District, Chhattisgarh in order to characterize and classify them. The investigation revealed that the rice growing soils were very deep, dark grayish in color (10 YR 3/2) and clayey in texture throughout the depth, with presence of slickensides in the sub-surface layers. During the summers, the soils exhibited wide spread cracks on the surface, extending to the surface of the slickensides. Periodic opening and closing of cracks, clay content more than 30% rich in smectites and the presence of slickensides thicker than 25 cm in these soils qualify them to Vertisols. In absence of slickensides and wedge shaped soil structure in the sub-surface and clay content less than 35% below the surface, the soybean growing soils could not qualify for Vertisols and placed in the other soil order, Inceptisols.

MORPHOLOGY AND GENESIS OF GILGAI

Gilgai morphology, genesis, distribution and role in the landscape are described on the base of literature data and personal investigations. Gilgai is a specific type of microrelief, formed by slow uplift and intrusion of a subsoil material due to soil heaving resulted from alternating drying and wetting. In terms of genetic classification of landforms gilgai could be classified as hydrogenic microrelief, along with cryogenic, karst and suffosion microrelief. Gilgais may be identified and distinguished from other types of microrelief by the presence of slickensides – slip planes demonstrating the direction of the vertical and lateral shearing. Gilgai are mostly presented in tropical and subtropical regions, but were also found in Russia and the former USSR.

Geologic Factors Affecting Coal Mine Roof Stability in the Eastern United States

Roof falls in underground coal mines are a continuing source of trouble for mine operators. Fatalities and injuries are a prominent concern, but lost time due to cleanup and disruption of mining operations presents an economic problem as well. Many geologic and geomechanical factors contribute to mine roof instability. These may be seen in rock core during exploration, or in the roof as mining progresses. Once these features are recognized, remedial action can then be taken. Geologic parameters attributed to roof falls in underground coal mines include both lithologic and structural discontinuities. The roof may be weakened where different lithologic materials are in contact with one another, such as paleochannels, scours, rider seams, clay veins, or crevasse splay deposits. Fractures, i.e., joints and faults, also contribute to roof falls. The trend, dip angle, and density of fractures, and the presence of slickensides are important in determining roof stability. Stress fields underground, both tectonic and mining-induced, not only can determine whether failure will occur, but also the mode of such failure. Detrimental features of a more localized nature include kettlebottoms, coal balls, and moisture fluctuations. The use of paleoenvironmental studies is important in determining hazardous roof conditions. Particular hazards are moremore » likely to be present in one paleoenvironment than another. When that environment is determined in advance of mining, precautions can be taken during the mine-planning phase.« less

Upper Pennsylvanian Paleosol in Stranger Shale and Underlying Iatan Limestone, Southwestern Iowa

ABSTRACT Cores of the Iatan Limestone and overlying Stranger Shale in southwestern Iowa display characteristics of paleosol development other than the weathered-clay or caliche horizons or underclay type of paleosol profiles from the Upper Pennsylvanian in the Midcontinent described by other authors. Paleosol features in the Iatan-Stranger sequence include clay-filled fractures and solution channels (cryptokarst) in the top of the Iatan Limestone which display some degree of secondary clay orientation along the edges (neostrians). The clay-filled fractures widen upward and grade into the gray to red mottled, non-calcareous, blocky mudstone of the Stranger Shale, which is characterized by an absence of fauna and presence of slickensides, clay coatings on grains (argillans), quartz silt-filled f actures (skeletans), and possible former rooted zones. The mudstone matrix locally displays the sepic plasmic fabrics that are characteristic of soil development. Pedogenesis in this unit resulted from subaerial exposure during retreat of the sea following the transgressive-regressive marine cycle that deposited the Iatan Limestone. Solution-channelling of the top of the Iatan and leaching of clays within its fractures indicates initial exposure to a humid climate with strong meteoric flux. The Stranger paleosol, however, displays features of Entisol, Inceptisol, or Vertisol development in terrestrial deposits under a somewhat drier climate following the partial solution of the upper Iatan. These features include a thick (1 to 2.4 m) paleosol profile with weak morphologic expression which contains crystalline illitic clays and oxidized iron minerals. Lack of fluvial-alluvial features in the thick, monotonous quartz-silty mudstone sequence of th lower Stranger Shale suggests that fine aeolian detrital influx (desert loess) may have contributed much of the material to this unit. The lack of caliche or weathered clays in the Stranger mudstone indicates the importance of using multiple lines of evidence for recognizing paleosols.

On the supposed existence of the Kisap thrust in the Langkawi Islands, Northwest Peninsular Malaysia

The Kisap thrust in Langkawi is the only large thrust fault described in Peninsular Malaysia. Its existence has been accepted by several authors and it has frequently been cited as evidence in support of plate collision hypothesis. A re-examination of the evidence shows that there are many aspects of the proposed thrust fault that cannot be substantiated and that the existence of large scale thrusting in the area has yet to be proven. All the structures attributed to the proposed thrust movement occur either within rocks of the same formation or between conformable sequences. The strikes of the proposed fault planes and the adjacent beds are markedly different and the dips of the known fracture planes are too steep to be associated with low angle over-thrusting. Present knowledge of the geology of these islands indicates that the geological boundaries shown in published geological maps need to be revised. Correspondingly, the location of the proposed fault plane, if it is present. will be at some distance from the fault trace drawn in the maps. The nature of the contact between the Lower and Upper Palaeozoic rocks interpreted as a thrust in the eastern part of the Langkawi islands cannot be satisfactorily resolved at present. The Kisap thrust in the Langkawi Islands has, since its postulation by Koopmans (1965), been frequently cited in papers on Malaysian geology. Its implications on the geology and tectonic history of Northwest Peninsular Malaysia are fairly considerable as it has also been generally regarded as one of the major faults in the peninsula. Being the only well documented example of large scale thrusting in the country, it has often been referred to as evidence in support of the paleo-plate collision hypothesis for the peninsula, currently advocated by some writers. The trace of the thrust plane and its geometry has been the subject of some discussion and various modified versions of this thrust have been proposed but the existence of the Kisap fault has yet to be questioned. A critical analysis of the field evidence put forward in favour of this thrust revealed that several aspects of the proposed thrust fault cannot be substantiated and that the existence of large thrusting in the area has yet to be proven. In his geological map of the Langkawi Islands, Jones (1966) introduced several large faults based mainly on the presence of slickensides and brecciated rocks and the contact relationship of rocks of widely differing ages. Most of these faults are shown to follow the geological boundaries on the eastern part of the island group. The faults separating the sedimentary formations were attributed to an east-west regional stress giving rise to thrust planes with a general strike of 300 0 and dipping eastwards and

Cretaceous and Cenozoic faulting in eastern North America

Cretaceous and Cenozoic faults in eastern North America provide evidence of modest intraplate tectonic activity in this region. Thrust and gravity faults are found; strike-slip movement is not demonstrable but could have occurred in some cases. Fault movements are dated by offset Cretaceous, Tertiary, and Quaternary sediments, Cretaceous kimberlite, and Pleistocene glacial stria. Cretaceous and Cenozoic displacements range from about 1 mm to several tens of metres. The faults are found in the central Mississippi River valley, the southeastern and northeastern United States, and eastern Canada. Correlations among historic seismicity, fault plane solutions, and the Cretaceous and Cenozoic faulting in the central Mississippi River valley and the southeastern United States suggest a close causal relationship. The quality of the correlation between historic seismicity and Cretaceous and Cenozoic faulting in the northeastern United States and eastern Canada varies considerably from area to area; hence the relation there between Cretaceous and Cenozoic faulting and contemporary seismotectonics is uncertain. Sharp offsets in loosely consolidated sediments, the presence of slickensides and fault gouge, and the involvement of Precambrian or Paleozoic bed rock provide the best evidence that faulting was associated with tectonic earthquakes. The displacement of near-surface deposits implies that surface faulting has occurred, although it has not been documented for modern earthquakes in eastern North America. At least some of the displacements occurred along pre-existing faults. The number and amounts of Cretaceous and Cenozoic movements on each fault have not been determined, but on one fault a displacement of 0.6 m during a short time span suggests that an earthquake of about magnitude 6 was associated with the displacement. The largest Cretaceous and Cenozoic displacements must represent more than one movement. The presence of thrust and gravity faults and the inconsistent trends of the faults imply that stresses that vary spatially and (or) temporally, rather than a single stress field acting steadily throughout the entire North American plate, are responsible for causing this intraplate tectonic activity.