Bedding Faults Research Articles

Constrained fitting of faulted bedding planes for three-dimensional geological modeling

Structural surfaces such as bedding planes and faults are the most important information for studying a geological body. In engineering investigation, this information mainly comes from a limited number of discrete data by field artificial investigation and borehole exploration. For effective utilization of the limited exploration data and more accurate reconstruction of complex geological body, a three-dimensional (3D) fitting function method that can satisfy positional and directional constraints is presented in this paper. A unified fitting function is established for fitting a group of faulted bedding planes with the consideration of local discontinuities due to faults. Finally, the effectiveness of this method is demonstrated through a 3D virtual geological modeling on the background of a hydroelectric project of western China in planning.

Major and minor structural features of a bedding shear zone along a coal seam and related gas outburst, Pingdingshan coalfield, northern China

Abstract A fractured coal band, traditionally called a soft-coal band, or structurally referred to as a bedding shear zone, within the Wu coal seam in the Pingdingshan coalfield, northern China, was structurally studied. Based on field examination and observations by reflectance microscopy and scanning electron microscopy (SEM), the bedding shear zone is not consistent with a simple bedding fault defined by pioneering geologists, but rather a complexly deformed band locally overprinted by ductile shearing fabrics. Dominant small-scale structures within the bedding shear zone are thrusts, folds, cleavage duplexes and related structures, but local, refolded folds, kink bands, and S–C band structures also indicate ductile shear deformation, typically developed in areas of steep dip such as within the limb of a subordinate fold. Bed-parallel shearing within the coal seam has been considered a serious influence on gas outburst in underground mining production in addition to thickening the seam and reducing the quality of coal. Locally, abnormal thickening of a shear zone and extensive compressive structures where ductile fabrics frequently occur are closely related with the site of an outburst. Thickening of a shear zone increases the capacity of methane storage, and compressive structures within a shear zone may act as a tectonic screen, blocking methane migration, which can result in a pocket of high methane pressure. A potential risk of outburst is indicated as a working face approaches an area of high methane pressure. Three abnormal phenomena encountered during a mining operation presage methane outburst for seams with a bedding shear zone.

Major and minor structural features of a bedding shear zone along a coal seam and related gas outburst, Pingdingshan coalfield, northern China

A fractured coal band, traditionally called a soft-coal band, or structurally referred to as a bedding shear zone, within the Wu coal seam in the Pingdingshan coalfield, northern China, was structurally studied. Based on field examination and observations by reflectance microscopy and scanning electron microscopy (SEM), the bedding shear zone is not consistent with a simple bedding fault defined by pioneering geologists, but rather a complexly deformed band locally overprinted by ductile shearing fabrics. Dominant small-scale structures within the bedding shear zone are thrusts, folds, cleavage duplexes and related structures, but local, refolded folds, kink bands, and S–C band structures also indicate ductile shear deformation, typically developed in areas of steep dip such as within the limb of a subordinate fold. Bed-parallel shearing within the coal seam has been considered a serious influence on gas outburst in underground mining production in addition to thickening the seam and reducing the quality of coal. Locally, abnormal thickening of a shear zone and extensive compressive structures where ductile fabrics frequently occur are closely related with the site of an outburst. Thickening of a shear zone increases the capacity of methane storage, and compressive structures within a shear zone may act as a tectonic screen, blocking methane migration, which can result in a pocket of high methane pressure. A potential risk of outburst is indicated as a working face approaches an area of high methane pressure. Three abnormal phenomena encountered during a mining operation presage methane outburst for seams with a bedding shear zone.

Contribution to the knowledge of the geology of Attica. The Peninsula of Lomvarda (Zostir)

In deposits of coherent, foliaceous marls, in Lomvarda's Peninsula (Attica), the biozones NN15 (Reticulofenestra Pseudoumbilica zone) till NN19 (Pseudoemiliania lacunosa zone) were determined, based on a rich calcareous nannoplankton fauna. These deposits are part of irregular alternations of reefal limestones, conglomerates, marls, and red sandstones. After the upper Pleistocene, an extensional faulting took place, created small grabbens and horsts. These events follow a compressional stage, which gave up mesoscopic folds. A numerous discontinuous (bedding planes, joins and faults) controls the shape of the coast. These discontinuities in combination with the different weathering degree of the various lithological units are responsible for the fallings rocks which take place along the steepness coast.

The Mechanism of Structural Control of Ore Formation and Geochemical Characteristics in the Massive Sulfide Deposits of the Wushan Copper Ore Field, Jiangxi

Abstract The ore‐controlling mechanism of the bedding fault system in the massive sulfide deposits of the Wushan copper orefield may be generalized as the control of ore deposition by optimum surface in an ore‐ forming structural trap. The mechanism has three major features: (1) timing of mineralization; (2) positioning of host formation; and (3) dependence of ore‐controlling structure on properties of rocks. The “optimum surface” is a divisional structural plane which marks obvious difference in physical, chemical and mechanical properties and is favorable for mineralization. It is also a unity of structures, lithofacies and orebodies.The structural and geochemical characteristics of the ore deposits indicate the migration trend of the major characteristic elements in the ore‐ controlling fault belt: elements with a small radius (Si, Fe, Mg and Al) moved towards and concentrated at the center of the belt while large‐radius ones (Ca, K and Na) were remote from the center.

Influence of geological structure on slope stability in the Maentwrog Formation, Harlech Dome, North Wales

Many road cutting slopes within the Maentwrog Formation bordering the Harlech Dome are potentially unstable. The rocks are low-grade metapelites and metasiltstones with frequent metadolerite sheet intrusions and they are folded by N to NNE trending folds, tectonic ripples and crenulations. Bedding, two cleavages and at least two persistent sets of steep dipping joints and faults form a close interconnective discontinuity system, which is favourable for secondary groundwater flow and weathering migration and is the major factor controlling rock slope stability. The rock mass is categorized into six major structural domains and there are abrupt lateral changes from one domain to another. The regional structure dictates to a considerable extent where each domain may occur. Rapid weathering and slope degradation occurs in fault zones and in the vicinity of major faults. The basic friction angle for the rocks is around 30° while the effective friction angle for most rock surfaces is 38°, which is the initial critical scree slope angle. Slope failures controlled by the structural system are plane slides on bedding, first cleavage and ENE striking fault surfaces, and toppling as a result of steep inward dipping second cleavage and other joint sets.

Origin and provenance of some exotic blocks in lower Mesozoic red-bed basin deposits, southern Arizona

In southern Arizona, a profound change in tectonic regime from quiescence to major instability took place near the beginning of Mesozoic time. One manifestation of this instability was the free gliding of large blocks of Paleozoic sedimentary rocks into fault troughs containing volcanic material and continental sediments. In the northwestern Canelo Hills, a succession of exotic blocks composed of Permian sedimentary rocks is intercalated with the Canelo Hills Volcanics of Triassic(?)-Jurassic age. The blocks are as large as 400 m thick and 2 km in strike length. Bedding faults, slickensides, and open-space breccias formed near the base of each Permian block during epidermal gliding, whereas the underlying sediments of the Canelo Hills Volcanics deformed by penecontemporaneous flow. Slickenside and fold-axis orientations place northeast-southwest constraints on the direction of block emplacements. The sense of movement is interpreted to have been northeast to southwest because paleocurrent directions for red beds within the Canelo Hills Volcanics are dominantly southwest and the stratigraphy of the glide blocks is most similar to Permian rocks to the northeast. Palinspastic reconstruction of the blocks to a provenance northeast of the Canelo Hills fits present models of distribution of Permian formations in southern Arizona. Slide block emplacement was synchronous with Triassic(?)-Jurassic vertical movements along northwest-striking fault zones in southern Arizona. One of these fault zones, the Sawmill Canyon, marks the approximate northeast boundary of the Canelo Hills and in early Mesozoic time furnished a scarp from which the slide blocks were derived.

Probable faulting on a minor, reverse, bedding fault adjacent to the Alfredton Fault, North Wairarapa, during the 1 August 1942 earthquake

Abstract A near-white line, 1.4 km long, is present on air photographs taken about 18 months after the 1 August 1942 earthquake. The line marks the trace of an active, minor, reverse, bedding fault, named McKay Fault, which lies c. 180 m east of the important active, dextral Alfredton Fault near Alfredton. Such near-white lines are absent on air photographs from all other late Quaternary traces in the Eketahuna District and is the chief evidence for attributing the latest faulting on the fault to the 1 August 1942 earthquake. Present day freshness of the fault scarp suggests that the trace is the youngest in the Eketahuna District, north Wairarapa, New Zealand.

Stereo and Mosaic Aerial Photo Study of Central Ouachita Mountain System in Oklahoma and Arkansas: ABSTRACT

A careful study of stereo aerial photographs of a central part of the Ouachita Mountains in Oklahoma and Arkansas, followed by a related study of photo-index sheets of a much larger area in the Ouachitas, yields the following tentative conclusions: 1. The earliest structural dislocations of field dimensions are a series of approximately parallel bedding faults in the Stanley Shale, increasing in numbers downward in the section. A slight schistosity, also nearly parallel with bedding, may likewise increase downward. Some large overthrusts may have formed at this time. The prime source of this deformation was probably an underthrusting basement moving northward. 2. The next recognizable tectonic movements were uplifts of three main anticlinoria, although these could have followed episode 3. At this time the Ouachitas began to shed much coarse and finer clastic sediments toward the west and probably in other directions. 3. The next major episode seems to be steep faulting probably involving the basement and overlying sediments, producing semi-fault-block structures with tight broken anticlines; this was followed by a collapse of the sediments into deep synclines. Most of the high synclinal and more complicated ranges have straight or gently curved bordering faults in the adjacent lowlands. 4. The Mid-Continent regional uplift which included the Ouachitas must have produced a flood of coarse clastics adjacent to the mountains. These tectonic conglomerates have been removed by subsequent deep erosion, but their distal equivalents--the Garber, Duncan-San Angelo, and Whitehorse sands--are present in the Lower and Middle Permian of western Oklahoma and the western part of north-central Texas. 5. The nearly vertical Big Cedar fault extends nearly 200 mi from near Big Cedar, Oklahoma, to Jacksonville, Arkansas, northeast of Little Rock. It probably was formed during a period of relaxation or tension in Jurassic or Cretaceous time, and roughly parallels other faults in the coastal plain in southwest Arkansas. The Big Cedar fault touches 9 or 10 separate local structures along its length. End_of_Article - Last_Page 422------------

Tectonics of Folded Appalachians of Pennsylvania as Deduced from Anthracite Region: ABSTRACT

The Anthracite region is the site of several decollements, many large fold systems, and numerous thrust, reverse, and bedding faults. A few of these structural features extend southwestward into Maryland and West Virginia. Detailed surface and mining data in the Anthracite region and less-detailed data in the areas on the southwest suggest that the Folded Appalachians of Pennsylvania are characterized by decollements that formed at widespread well-defined changes in rock competency. Originating at and rising from each decollement are numerous folds and faults. Competent rocks between two decollements commonly are flexed into large simple fold systems and are displaced by a relatively few large faults. In contrast, incompetent rocks between decollements are flexed characteristically into extremely complex fold systems cut by numerous small faults. The decollements functioned as stress adjustment zones separating differentially deforming blankets of relatively competent rocks from relatively incompetent rocks. Many of the larger anticlines appear to have formed in overlying rocks where a decollement ramped upward through a part of the sedimentary rocks section. The Folded Appalachians of Pennsylvania probably are separated at depth from the Precambrian basement by a master decollement. Northwestward gravity sliding induced by vertical uplift of the core of the Appalachians and supplemented by lateral compression as the core moved upward seems the most logical explanation for the tectonics of the Folded Appalachians of Pennsylvania. End_of_Article - Last_Page 2111------------

Gray quartz breccia ore body of the Highland Mine, Butte, Montana

The auriferous-quartz ore body of the Highland Mine is an open textured siliceous sponge-breccia. It occurs as a replacement of Cambrian dolomite along a subordinate bedding fault that follows the hanging wall of a major fault. The sponge structure is secondary, having arisen from the almost complete abstraction of sulphides, principally pyrite. Volumetric accommodation to the leaching was marked by the collapse of many primary ore structures and by prodigious slumping. Secondary silica now weakly cements the fragments. The leaching improved the grade of the ore by residual concentration.