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Petrologic investigations of martian rocks have been accomplished by mineralogical, geochemical, and textural analyses from Mars rovers (with geologic context provided by orbiters), and by laboratory analyses of martian meteorites. Igneous rocks are primarily lavas and volcaniclastic rocks of basaltic composition, and ultramafic cumulates; alkaline rocks are common in ancient terranes and tholeiitic rocks occur in younger terranes, suggesting global magmatic evolution. Relatively uncommon feldspathic rocks represent the ultimate fractionation products, and granitic rocks are unknown. Sedimentary rocks are of both clastic (mudstone, sandstone, conglomerate, all containing significant igneous detritus) and chemical (evaporitic sulfate and less common carbonate) origin. High-silica sediments formed by hydrothermal activity. Sediments on Mars formed from different protoliths and were weathered under different environmental conditions from terrestrial sediments. Metamorphic rocks have only been inferred from orbital remote-sensing measurements. Metabasalt and serpentinite have mineral assemblages consistent with those predicted from low-pressure phase equilibria and likely formed in geothermal systems. Shock effects are common in martian meteorites, and impact breccias are probably widespread in the planet's crustal rocks. The martian rock cycle during early periods was similar in many respects to that of Earth. However, without plate tectonics Mars did not experience the thermal metamorphism and flux melting associated with subduction, nor deposition in subsided basins and rapid erosion resulting from tectonic uplift. The rock cycle during more recent time has been truncated by desiccation of the planet's surface and a lower geothermal gradient in its interior. The petrology of Mars is intriguingly different from Earth, but the tried-and-true methods of petrography and geochemistry are clearly translatable to another world.

This study investigates the petrographic, mineralogical, geochronological, and geochemical signatures of river sands across southern Africa. We single out the several factors that control sand generation, including weathering and recycling, and monitor the compositional changes caused by chemical and physical processes during fluvial transport from cratonic sources to passive-margin sinks. Passive-margin sands have two first-cycle sources. Quartz and feldspars with amphibole, epidote, garnet, staurolite, and kyanite are derived from crystalline basements exposed at the core of ancient orogens and cratonic blocks (dissected continental block provenance). Volcanic rock fragments, plagioclase, and clinopyroxene are derived from flood basalts erupted during the initial phases of rifting (volcanic rift provenance). First-cycle detritus mixes invariably with quartzose detritus recycled from ancient sedimentary successions (undissected continental block provenance) or recent siliciclastic deposits (e.g., Kalahari dune sands; recycled clastic provenance). U-Pb ages of detrital zircons mirror the orogenic events that affected southern Africa since the Archean. Damara (0.5-0.6 Ga) and Namaqua (1 Ga) age peaks are prominent throughout Namibia, from the Orange mouth to the Namib and Skeleton Coast Ergs, and also characterize Kalahari dunes and sands of the Congo, Okavango, and Zambezi Rivers. Instead, sharp old peaks at 2.1 Ga and 2.6 Ga characterize Limpopo and Olifants sands, matching the age of the Bushveld intrusion and the final assembly of the Zimbabwe and Kaapvaal Cratons, respectively; discordant ages indicate Pb loss during the Pan-African event. Chemical indices confirm that weathering is minor throughout the tropical belt from South Africa and Zimbabwe to Namibia and coastal Angola but major for quartzose sands of the Congo, Okavango, and upper Zambezi Rivers, largely produced in humid subequatorial regions. Recycling of quartzose sediments is extensive in all of these catchments. From Congo to Mozambique, along the >5000-km Atlantic and Indian Ocean rifted margins, polycyclic detritus reaches commonly 50% and locally up to 100%, in line with the estimated incidence of recycling worldwide. Quantitative information provided by provenance studies of modern sands helps us to better understand the relationships between sediment composition and plate-tectonic setting and to upgrade the overly simplified and often misleading current provenance models. This is a necessary step if we want to decipher the stratigraphic record of ancient passive margins and reconstruct their paleotectonic and paleoclimatic history with greater accuracy.

As one of the most common disasters in deep mine roadway, floor heave has caused serious obstacles to mine transportation and normal production activities. The third section winch roadway in the third mining area of Qitaihe Longhu coal mine has a serious floor heave due to the large buried depths of the roadway and the semicoal rock roadway, and the maximum floor heave is 750 mm. For the problem of floor stability, this paper establishes a mechanical model to analyze the stability of roadway floor heave by analogy with the basement heave of deep foundation pit. It provides a model reference for analyzing the problem of roadway floor heave. Aiming at the problem of roadway floor heave in Longhu coal mine, the roadway model is established by using FLAC3D, and the roadway model after support is established according to the on-site support measures. Through the analysis of the distribution of roadway plastic area, stress nephogram, and displacement field simulation results, the results show that the maximum displacement of roadway roof and floor after support is reduced by 15% and 23%, but the maximum floor heave is still 770 mm, which is close to the measured floor heave of roadway. In order to solve the problem of roadway floor heave and integrate economic factors, this paper puts forward three support optimization schemes, simulates the support effect of each scheme, and finally determines that scheme 3 is the best support optimization scheme. Compared with that under the original support, the aamount of floor heave is reduced by 81%, and the final amount of floor heave is 150 mm, which can meet the requirements of roadway floor deformation. The results provide a scheme and guidance for roadway support optimization.

This article investigates how, where, and to what extent the mineralogical and chemical composition of sand-sized sediments is modified by extreme weathering in modern equatorial settings, with the ultimate goal of learning to read climate from the sedimentary record. To single out the weathering effect, we studied the compositional trends of fluvial sands along the western branch of the East African Rift between 5°S and 5°N. The relative durability of different detrital components, as well as potential hydraulic-sorting and grain-size effects, were assessed by comparing samples with similar provenances in different climatic and environmental conditions or of different size classes within the same sample. Sands of equatorial central Africa at the headwaters of the Congo and Nile basins display the full spectrum of petrologic suites characterizing rift-shoulder and volcanic rift provenances. Unlike in arid Arabia, quartzose sands are not restricted to areas where detritus is recycled from prerift sedimentary covers. In a hot humid climate, weathering can effectively obliterate the fingerprint of parent rock lithology and produce a nearly pure quartz residue even where midcrustal basement rocks are being actively uplifted and widely unroofed. In such settings garnet is destroyed faster than hornblende, and zircon faster than quartz. Weathering control on detrital modes is minor only in the rain shadow of the highest mountains or volcanoes, where amphibole-dominated quartzofelicdspathic metamorphiclastic sands (Rwenzori Province) or clinopyroxene-dominated feldspatholithic volcaniclastic sands (Virunga Province) are generated. Our detailed study of the Kagera basin emphasizes the importance of weathering in soils at the source rather than of progressive maturation in temporary storage sites during stepwise transport and shows that the transformation of diverse parent rocks into a quartzose \"white sand\" may be completed in one sedimentary cycle in hydromorphic soils of subequatorial lowlands. Micas and heavy minerals, which are less effectively diluted by recycling than main framework components, offer the best key to identify the original source-rock imprint. The different behavior of chemical indexes such as the CIA (a truer indicator of weathering) and the WIP (markedly affected by quartz dilution) helps us to distinguish strongly weathered first-cycle versus polycyclic quartz sands.

Pyroclastic material in the form of altered volcanic ash or tephra has been reported and described from one or more stratigraphic units from the Proterozoic to the Tertiary. This altered tephra, variously called bentonite or K-bentonite or tonstein depending on the degree of alteration and chemical composition, is often linked to large explosive volcanic eruptions that have occurred repeatedly in the past. K-bentonite and bentonite layers are the key components of a larger group of altered tephras that are useful for stratigraphic correlation and for interpreting the geodynamic evolution of our planet. Bentonites generally form by diagenetic or hydrothermal alteration under the influence of fluids with high-Mg content and that leach alkali elements. Smectite composition is partly controlled by parent rock chemistry. Studies have shown that K-bentonites often display variations in layer charge and mixed-layer clay ratios and that these correlate with physical properties and diagenetic history. The following is a review of known K-bentonite and related occurrences of altered tephra throughout the timescale from Precambrian to Cenozoic.

Mining accidents are sometimes preceded by high levels of crackling noise, which follow universal rules for the collapse of minerals. The archetypal test cases are sandstone and coal. Their collapse mechanism is almost identical to earthquakes: the crackling noise in large, porous samples follows a power law (Gutenberg-Richter) distribution P∼E-ε with energy exponents ε for near critical stresses of ε= 1.55 for dry and wet sandstone, and ε=1.32 for coal. The exponents of early stages are slightly increased, 1.7 (sandstone) and 1.5 (coal), and appear to represent the collapse of isolated, uncorrelated cavities. A significant increase of the acoustic emission, AE, activity was observed close to the final failure event, which acts as \"warning signal\" for the impending major collapse. Waiting times between events also follow power law distributions with exponents 2+ξ between 2 and 2.4. Aftershocks occur with probabilities described by Omori coefficients p between 0.84 (sandstone) and 1 (coal). The \"Bath's law\" predicts that the ratio between the magnitude of the main event and the largest aftershock is 1.2.Our experimental findings confirm this conjecture. Our results imply that acoustic warning methods are often possible within the context of mining safety measures, although it is not only the increase of crackling noise that can be used as early warning signal but also the change of the energy distribution of the crackling events.

The Ediacara Member of the Rawnsley Quartzite of South Australia hosts some of the most ecologically and taxonomically diverse fossil assemblages of the eponymous Ediacara Biota—Earth's earliest fossil record of communities comprised of macroscopic, complex, multicellular organisms. At the National Heritage Site, Nilpena, fifteen years of systematic excavation and reassembly of bedding planes has resulted in reconstruction of over 400 square meters of Ediacaran seafloor, permitting detailed and sequential sedimentary, paleoecological and taphonomic assessment of Ediacara fossilized communities and the shallow marine settings in which these ecosystems lived. Sedimentological investigation reveals that the Ediacara Member consists of successions of sandstone event beds and a paucity of other lithologies. Moreover, these Ediacara sandstones are characterized by a suite of sedimentary features and style of stratigraphic packaging uncharacteristic of Phanerozoic sandstone successions considered to have been deposited in analogous shallow marine, storm-dominated environments, including: (1) extremely thin (sub-mm- to mm-scale) bed thickness; (2) lateral discontinuity; (3) textural uniformity, including lack of disparity in grain size, between adjacent beds; (4) lack of amalgamation; (5) lack of erosional bed junctions; (6) doubly rippled bedforms defined by rippled bed tops and bases which crisply cast the tops of underlying rippled beds; (7) ubiquity of textured organic surfaces (TOS); (8) positive correlation between body fossil size and abundance and bed thickness; and (9) texturally immature assemblages of sandstone rip-up clasts along bed tops. We interpret these features to reflect the presence of widespread matgrounds, which facilitated seafloor colonization by and ecological development of Ediacara macroorganisms in high-energy environments. Further, we argue that pervasive matgrounds directly mediated the formation and preservation of non-uniformitarian sedimentary features and stratigraphic packaging in the Ediacara Member and were responsible for the anactualistically complete nature of the Ediacara stratigraphic record.

Deformation bands are the most common strain localization feature found in deformed porous sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected sandstones in hydrocarbon reservoirs and aquifers. They occur as various types of tabular deformation zones where grain reorganization occurs by grain sliding, rotation and/or fracture during overall dilation, shearing, and/or compaction. Deformation bands with a component of shear are most common and typically accommodate shear offsets of millimetres to centimetres. They can occur as single structures or cluster zones, and are the main deformation element of fault damage zones in porous rocks. Factors such as porosity, mineralogy, grain size and shape, lithification, state of stress and burial depth control the type of deformation band formed. Of the different types, phyllosilicate bands and most notably cataclastic deformation bands show the largest reduction in permeability, and thus have the greatest potential to influence fluid flow. Disaggregation bands, where non-cataclastic, granular flow is the dominant mechanism, show little influence on fluid flow unless assisted by chemical compaction or cementation.

The lithostratigraphic characteristics of the iconic Blue Lias Formation of southern Britain are influenced by sedimentation rates and stratigraphic gaps. Evidence for regular sedimentary cycles is reassessed using logs of magnetic susceptibility from four sites as an inverse proxy for carbonate content. Standard spectral analysis, including allowing for false discovery rates, demonstrates several scales of regular cyclicity in depth. Bayesian probability spectra provide independent confirmation of at least one scale of regular cyclicity at all sites. The frequency ratios between the different scales of cyclicity are consistent with astronomical forcing of climate at the periods of the short eccentricity, obliquity and precession cycles. Using local tuned time scales, 62 ammonite biohorizons have minimum durations of 0.7 to 276 ka, with 94% of them <41 ka. The duration of the Hettangian Stage is ≥2.9 Ma according to data from the West Somerset and Devon/Dorset coasts individually, increasing to ≥3.7 Ma when combined with data from Glamorgan and Warwickshire. A composite time scale, constructed using the tuned time scales plus correlated biohorizon limits treated as time lines, allows for the integration of local stratigraphic gaps. This approach yields an improved duration for the Hettangian Stage of ≥4.1 Ma, a figure that is about twice that suggested in recent time scales.