Hydro-Damage Properties of Red-Bed Mudstone Failures Induced by Nonlinear Seepage and Diffusion Effect

Nonlinear catastrophes caused by geological fluids are a fundamental issue in rock mechanics and the geoengineering hazard field. For the consideration of hydrodynamic force on red-bed mudstone softening damage, X-ray visualization test on the fissure flow in mudstone block failure under hydrodynamic force was performed in this study based on block scale and the physical phenomena of fissure seepage and nonlinear diffusion were further explored. A new method for evaluating the hydro-damage degrees of rocks using an X-ray image analysis was proposed, and the quantitative relation of diffusion coefficients of hydro-damage and seepage was established. The research results revealed that the hydrodynamic force promoted the fluid-filled fissure behavior in mudstone specimen failure. Also, the seepage and diffusion phenomena of fluid in rocks during failures were indicated using X-ray imaging. A dual mechanical behavior was presented in the nonlinear seepage and abnormal diffusion of a red mudstone geological body under hydrodynamic conditions. The damaged degree of mudstone was aggravated by the effect of hydrodynamic force, and the initial seepage–diffusion coefficient with respect to lower hydro-damage was larger than the final seepage–diffusion coefficient with respect to higher hydro-damage of rocks with a decreasing nonlinear trend.

Eocene fault-controlled fluid flow and mineralization in the Paradox Basin, United States

Sedimentary rocks of the Paradox Basin of the Colorado Plateau (southwestern USA) record widespread manifestations of paleo–fluid flow and fluid-rock reactions including Cu, U-V, and Fe-Mn mineral deposits, Si and Ca metasomatism, hydrocarbon accumulations, and bleached sandstones. Many of these are spatially associated with faults. Here we show evidence for a widespread phase of fault-related fluid migration and mineralization at 41–48 Ma in the Paradox Basin. We measured K-Ar dates of multiple size fractions of clay-rich fault gouge, yielding statistically overlapping dates of authigenic (1Md) illite for the Salt Valley (47.0 ± 3.0 Ma), Kane Springs (47.7 ± 3.8 Ma), Cliffdweller (43.4 ± 4.6 Ma), Courthouse (41.9 ± 2.3 Ma), Lisbon Valley (45.3 ± 0.9 Ma), and GTO (48.1 ± 2.6 Ma) faults. The latter two have an illite Rb-Sr isochron age of 50.9 ± 3.5 Ma, and fault-adjacent bornite has a Re-Os isochron age of 47.5 ± 1.5 Ma. Authigenic illite from a paleo–oil reservoir near the Courthouse fault formed from the interaction of reduced fluids with oxidized red-bed sandstones at 41.1 ± 2.5 Ma. The Moab and Keystone faults have older authigenic illite ages of 59.1 ± 5.7 Ma and 65.2 ± 1.0 Ma, respectively. Our results show a close temporal relationship between fault gouge formation, red-bed bleaching, and Cu mineralization during an enigmatic time interval, raising questions about drivers of Eocene fluid flow.

The Aztec Siltstone: an Upper Devonian Alluvial Plain Red Bed Sequence, Southern Victoria Land, Antarctica

<p>The Aztec Siltstone (late Devonian) crops out for 150 km along the Transantarctic Mountains, between the Mawson and Mulock Glaciers of southern Victoria Land, Antarctica. It is the uppermost formation of the Taylor Group, the lower of the two subdivisions of the Beacon Supergroup of southern Victoria Land. The formation consists largely of fine to medium-grained sandstone, and greyish red (10R 4/2), grey (N5), and greenish grey (5G 6/1) siltstone and claystone. Other lithologies include carbonaceous siltstone and claystone, limestone and intraformational conglomerate. Conchostracans, fish fossils, plant fragments, and gypsum lenses are present also. Cross-stratification, horizontal stratification, channelling, and "fining-upwards" cycles indicate deposition from shallow, high sinuosity (tortuous), meandering streams that migrated laterally across a broad alluvial plain. The sandstone beds are laterally accreted channel deposits, whereas the siltstone and claystone beds represent overbank deposition by vertical accretion in the interchannel areas of the floodbasin. Other floodbasin deposits include lacustrinal sediments from pluvial ponds and ox-bow lakes, and palustrinal sediments from the backswamps. Overbank deposition of bed load material formed levees, and stream avulsion and crevassing during flood stage produced crevasse-splay deposits. The sandstone beds are quartzarenites, with detrital grains consisting largely of plutonic quartz; other grains include chert, feldspar, metamorphic quartz and a trace of heavy minerals. Sandstone textures average fine-grained and well sorted, although sandstone with textural inversion is common. Compositional and textural characteristics indicate that the sandstone is a product of the reworking of older quartzarenite in the source area. Subaerial exposure was a feature of the fine-grained floodbasin sediments; the evidence includes the abundance of mudcracks, and a variety of soil features. The latter include extensive kankar ('calichea') horizons, pseudo- or wavey bedding structures, a compositional and textural similarity to modern soils, vein networks (considered to be a product of deep cracking in the unconsolidated. substratum), burrowing, and root horizons with in some cases associated plant fragments. The kankar ('calichea') suggests that there was a period of prolonged subaerial exposure and soil development which followed the deposition of fine-grained, fine member lithologies of the "fining upwards" cycles. This period was probably in the range 5,000 to 50,000 years. The Aztec Siltstone is a typical "variegated" red-bed sequence, containing interbedded red and drab fine-grained lithologies. The fine-grained drab lithologies consist of quartz grains set in a matrix of green illitic and chloritic clay. The colour in the interbedded red and grey siltstone and claystone results from a haematite pigment, which in the red samples is present in a concentration sufficient to completely mask the green colour of the clay matrix. The reddening is believed to have been a penecontemporaneous process that took place in the floodbasin sediments during their prolonged subaerial exposure under a hot and seasonally wet and dry (savanna) climate. The haematitic pigment was derived from the in situ and progressive dehydration of detrital amorphous and poorly crystalline brown hydrated ferric oxide in those sediments which maintained an oxidizing environment and were above the ground-water table during the dehydration process. Sediments which remained in a water-logged state, below the water table, and in association with organic matter, were invariably reduced and lost their iron oxide in solution. Later post-depositional reduction of some red lithologies produced reduction spheres and channels, reduced burrows and vein networks, and the reduced layers immediately underlying the scoured surface at the base of the channel sandstones. Some chemical redistribution of iron contributed to the variegated and mottled horizons of the formation. The mineral composition of adjacent red and drab lithologies is essentially the same except for the haematite constituent. The red average 5.86 ([delta] = 1.09) percent total Fe (as Fe2O3), of, which 3.01 ([delta] = 0.63) percent is as haematite pigment, 1.57 percent Fe2O3 is in a combined form (probably as ferric silicates), and 1 14 ([delta] = 0.57) percent is as FeO. The green average 3.65 ([delta] = 1.81) percent total Fe (as Fe2O3) of which approximately 0.27 percent is as haematite pigment, approximately 1.4 percent Fe2O3 is in a combined form, and 1.77 ([delta] = 1.37) percent is as FeO. In the majority of the green lithologies the free ferric oxide (as haematite or hydrated ferric oxide) was removed in solution during reduction, and at the same time minor amounts of clay matrix were also leached out.</p>

The Aztec Siltstone: an Upper Devonian Alluvial Plain Red Bed Sequence, Southern Victoria Land, Antarctica

<p>The Aztec Siltstone (late Devonian) crops out for 150 km along the Transantarctic Mountains, between the Mawson and Mulock Glaciers of southern Victoria Land, Antarctica. It is the uppermost formation of the Taylor Group, the lower of the two subdivisions of the Beacon Supergroup of southern Victoria Land. The formation consists largely of fine to medium-grained sandstone, and greyish red (10R 4/2), grey (N5), and greenish grey (5G 6/1) siltstone and claystone. Other lithologies include carbonaceous siltstone and claystone, limestone and intraformational conglomerate. Conchostracans, fish fossils, plant fragments, and gypsum lenses are present also. Cross-stratification, horizontal stratification, channelling, and "fining-upwards" cycles indicate deposition from shallow, high sinuosity (tortuous), meandering streams that migrated laterally across a broad alluvial plain. The sandstone beds are laterally accreted channel deposits, whereas the siltstone and claystone beds represent overbank deposition by vertical accretion in the interchannel areas of the floodbasin. Other floodbasin deposits include lacustrinal sediments from pluvial ponds and ox-bow lakes, and palustrinal sediments from the backswamps. Overbank deposition of bed load material formed levees, and stream avulsion and crevassing during flood stage produced crevasse-splay deposits. The sandstone beds are quartzarenites, with detrital grains consisting largely of plutonic quartz; other grains include chert, feldspar, metamorphic quartz and a trace of heavy minerals. Sandstone textures average fine-grained and well sorted, although sandstone with textural inversion is common. Compositional and textural characteristics indicate that the sandstone is a product of the reworking of older quartzarenite in the source area. Subaerial exposure was a feature of the fine-grained floodbasin sediments; the evidence includes the abundance of mudcracks, and a variety of soil features. The latter include extensive kankar ('calichea') horizons, pseudo- or wavey bedding structures, a compositional and textural similarity to modern soils, vein networks (considered to be a product of deep cracking in the unconsolidated. substratum), burrowing, and root horizons with in some cases associated plant fragments. The kankar ('calichea') suggests that there was a period of prolonged subaerial exposure and soil development which followed the deposition of fine-grained, fine member lithologies of the "fining upwards" cycles. This period was probably in the range 5,000 to 50,000 years. The Aztec Siltstone is a typical "variegated" red-bed sequence, containing interbedded red and drab fine-grained lithologies. The fine-grained drab lithologies consist of quartz grains set in a matrix of green illitic and chloritic clay. The colour in the interbedded red and grey siltstone and claystone results from a haematite pigment, which in the red samples is present in a concentration sufficient to completely mask the green colour of the clay matrix. The reddening is believed to have been a penecontemporaneous process that took place in the floodbasin sediments during their prolonged subaerial exposure under a hot and seasonally wet and dry (savanna) climate. The haematitic pigment was derived from the in situ and progressive dehydration of detrital amorphous and poorly crystalline brown hydrated ferric oxide in those sediments which maintained an oxidizing environment and were above the ground-water table during the dehydration process. Sediments which remained in a water-logged state, below the water table, and in association with organic matter, were invariably reduced and lost their iron oxide in solution. Later post-depositional reduction of some red lithologies produced reduction spheres and channels, reduced burrows and vein networks, and the reduced layers immediately underlying the scoured surface at the base of the channel sandstones. Some chemical redistribution of iron contributed to the variegated and mottled horizons of the formation. The mineral composition of adjacent red and drab lithologies is essentially the same except for the haematite constituent. The red average 5.86 ([delta] = 1.09) percent total Fe (as Fe2O3), of, which 3.01 ([delta] = 0.63) percent is as haematite pigment, 1.57 percent Fe2O3 is in a combined form (probably as ferric silicates), and 1 14 ([delta] = 0.57) percent is as FeO. The green average 3.65 ([delta] = 1.81) percent total Fe (as Fe2O3) of which approximately 0.27 percent is as haematite pigment, approximately 1.4 percent Fe2O3 is in a combined form, and 1.77 ([delta] = 1.37) percent is as FeO. In the majority of the green lithologies the free ferric oxide (as haematite or hydrated ferric oxide) was removed in solution during reduction, and at the same time minor amounts of clay matrix were also leached out.</p>

Characteristics of polymetallic enrichment on oceanic red bed in Matano Formation, Baturubei, Central Sulawesi, Indonesia

The Matano Formation on Sulawesi Island has Cretaceous oceanic red bed (CORB) facies, but there is no further research on the geochemical characteristics of the sedimentary rocks. This study aims to classify the CORB of the Matano Formation and reveal the polymetallic element enrichment in CORB by using the X-ray fluorescence (XRF) analysis method. Matano Formation in the research area consists of two different facies: radiolarites facies and red clay facies. Radiolarites facies grouped as Si-ORB, dominated by siliceous pelagic bioclastic and deposited under oxic environment. The red clay facies grouped as Al-ORB, the components dominated by hemipelagic material with a small amount of silica shelled pelagically and deposited under reduction environment. Red clay facies have higher enrichment elements Mn, V, Ni, Zn and La than radiolarites facies. Oceanic red bed facies of Matano Formation deposited in basin plain environment below carbonate compensation depth in a passive margin tectonic setting.

Stability Reinforcement of Slopes Using Vegetation Considering the Existence of Soft Rock

This study investigates the effectiveness of vegetation reinforcement on the stability of a slope with red-bed soft rock in a slope along the Xining-Chengdu railway, China. Four kinds of vegetation were considered to reinforce the soil and the slope. The rooted soil parameters were determined based on the laboratory tests. A numerical model was developed based on the actual geometry and soil layer distributions. The soils were modeled as elastic perfectly plastic materials and the vegetation reinforcement was represented as addition cohesion of a series of subsoil layers within a given depth. The effectiveness of vegetation on slope reinforcement under both dry and rainfall conditions was investigated regarding this case. The potential failure surface and corresponding factor of safety of the red-bed soft rock slope for those different conditions were analyzed and compared. It has been found that the addition of vegetation increased the safety of slope stability whether the slope is under a dry condition or a rainfall condition, while the increasing proportion of factor of safety due to vegetation reinforcement for this case is very limited. The results and findings in this study are still significant for the practitioner to evaluate the reasonability of vegetation reinforcement.

Laboratory Study On Mechanical Response And Failure Mechanism of Red-Bed Soft Rock Under Water-Rock Interaction

Red-bed soft rock is a geomaterial that displays special deformation and failure characteristics. The stability of red-bed slopes can be negatively impacted by water and stepped excavation disturbance; however, there is limited research regarding the mechanical behavior and failure characteristics of red-bed soft rock under the action of water-rock hydro-mechanical coupling. In this study, to explore the mechanical response and failure mechanisms of red-bed soft rock under coupled water-rock hydro-mechanical action, a visual experimental platform based on digital radiography and a multi-level loading device was constructed. Angiography was used to visualize the rock fracture process by replacing fissure water with a contrast medium. Multi-level loading was applied to cubic red-bed mudstone samples, and acoustic emission signals, stress, flow rate, and digital radiography images were collected during the failure process. An original image processing method based on Hough transform and a convolutional neural network was used to segment and extract cracks from the imagery, and fissure water flow characteristics, rock mechanical response, and crack evolution were analyzed in detail (Liu et al., 2015; Lv et al., 2013, 2014). Results showed that when the Felicity ratio FR was lower than 1.2, water could induce secondary "water-damaged cracks" in the red-bed samples. Study findings were used to highlight the importance of improved early-warning methods for rainfall-induced landslides at an engineering scale. The original experimental platform proposed and evaluated in this study provides a new and powerful tool to investigate the mechanical behavior of different rock types under the action of water-rock hydro-mechanical coupling at a laboratory scale. These findings will facilitate improved disaster prevention strategies for red-bed geological bodies.