Long-term Geological Processes Research Articles

An elastoplastic constitutive model for frozen soil considering fracture of cryostructure and propagation of cracks

The natural frozen soil is formed in long-term geological processes under complex climatic conditions, and the special cryogenic structures are engendered in it. Investigation on the mechanical model of frozen soil with cryostructure can provide reliable measures to control and dispose the deformation of engineering foundations in cold regions. In this research, the crack initiation criterion and propagation path of frozen soil containing ice lens were studied based on available laboratory results. For the frozen soil containing ice lenses, the failure was formed by the propagation and penetration of the wing cracks at tip of ice lens. According to the fracture mechanics and strain energy theory, the structural damage variable of frozen soil was established, the effects of ice lens geometric parameters on the damage variable were analyzed. The elastoplastic tensor of frozen soil with cryostructure was modified using the damage variable which considering fracture of cryostructure and propagation of cracks, and an elastoplastic model was established. The PDE module in COMSOL was adopted to redevelop the proposed model, the rationality of the model was verified and the mechanical properties of natural frozen soil was investigated.

Methodology and Results of Staged UAS Photogrammetric Rockslide Monitoring in the Alpine Terrain in High Tatras, Slovakia, after the Hydrological Event in 2022

There are numerous talus cones that have formed by long-term geological processes and sudden hydrological events in the Small Cold Valley (High Tatras National Park in Slovakia). Frequent hiking trails lead here; therefore, their safeness needs to be monitored due to recent rock avalanches and landslides. A complex methodology for monitoring changes in talus cones was developed to determine the extent, pace, nature, and origin of the morphological changes in the land in this complex high-mountain terrain. Non-contact UAS photogrammetry with SfM-MVS processing was applied as a quick, reliable, and environment-friendly data acquisition method. For proper georeferencing, a network of GCPs and stabilized surveying points were established by terrestrial geodetic surveying. Together with an evaluation of the methodology, the results comparing the actual state of a talus cone in 2018 and 2022 (after the significant hydrological event) are presented. Comparing and analyzing spatial models represented by point clouds, with an accuracy of centimeter level, was obtained. The detected morphological changes reached values in meters. A differential model expresses the distribution of the morphological changes. In conclusion, geodetic and geological knowledge is synthesized to evaluate the phenomena occurring in this territory.

Time-dependent frictional properties of granular materials used in analogue modelling: implications for mimicking fault healing during reactivation and inversion

Abstract. Analogue models are often used to model long-term geological processes such as mountain building or basin inversion. Most of these models use granular materials such as sand or glass beads to simulate the brittle behaviour of the crust. In granular material, deformation is localised in shear bands, which act as an analogue to natural fault zones and detachments. Shear bands, also known as faults, are permanent anomalies in the granular package and are often reactivated during a test run. This is due to their lower strength compared to the undeformed material. When the fault movement stops, time-dependent healing immediately begins to increase the strength of the fault. Faults that have been inactive for a long time therefore have a higher strength than younger faults. This time-dependent healing, also called time consolidation, can therefore affect the structure of an analogue model as the strength of the fault changes over time. Time consolidation is a well-known mechanism in granular mechanics, but it is poorly described for analogue materials and on the timescales of typical analogue models. In this study, we estimate the healing rate of different analogue materials and evaluate the impact on the reactivation potential of analogue faults. We find that healing rates are generally less than 3 % per 10-fold increase in holding time, which is comparable to natural fault zones. We qualitatively compare the frictional properties of the materials with grain characteristics and find a weak correlation of healing rates with sphericity and friction with an average quality score. Accordingly, in models where there are predefined faults or reactivation is forced by blocks, the stability range of the fault angles that can be reactivated can decrease by up to 7∘ over the duration of 12 h. The stress required to reactivate an existing fault can double in the same time, which can favour the development of new faults. In a basin inversion scenario, normal faults cannot be inverted because of the strong misorientation, so time consolidation plays little additional role for such models.

A global study of dolomite stoichiometry and cation ordering through the Phanerozoic

ABSTRACTVarious geochemical proxies are used to constrain the diagenetic origin and evolution of ancient dolomites. Dolomite stoichiometry (mole % MgCO3) and cation ordering, two mineralogical attributes that define dolomite, have also been shown to demonstrate utility in this regard. Observations from laboratory experiments and field studies suggest that these attributes broadly reflect the fluid chemistry and temperature of the dolomitizing environment. The degree to which these parameters reflect global conditions during dolomitization (e.g., seawater chemistry, eustasy, atmospheric pCO2) and long-term geological processes is poorly understood, however. Here, a large dataset consisting of mineralogical data from over 1,690 Phanerozoic dolomites from various geographic locations, stratigraphic ages, platform types, and depositional environments are queried to investigate the broader geological controls on dolomite stoichiometry and cation ordering in dolomites formed by early, near-surface dolomitization. A suite of statistical analyses performed on the global dataset indicate: 1) despite wide ranges at the eon, period, and epoch level, dolomite stoichiometry and cation ordering broadly increase with geologic age; 2) significant variations in dolomite stoichiometry and cation ordering throughout the Phanerozoic do not correlate with global parameters, such as seawater chemistry, eustasy, orogenic events, and ocean crust production; 3) dolomites associated with restricted depositional settings, such as restricted lagoons, and the intertidal and supratidal zones, are more stoichiometric than dolomites associated with open marine settings, such as the deep-subtidal and shallow-subtidal zones; and 4) dolomites from shallow ramps and epeiric carbonate platforms are generally more stoichiometric than dolomites from open shelves and isolated carbonate platforms. These observations permit a number of inferences to be drawn. First, the principal signal observed in the data is that local environmental conditions associated with platform type and depositional setting are the strongest control on dolomite mineralogy. The observation that more stoichiometric dolomites correlate with shallow and restricted depositional environments is consistent with laboratory experiments that show environmental factors, such as higher Mg:Ca, temperature, and salinity of the dolomitizing fluids yield more stoichiometric dolomite. Second, a weaker secondary signal is also observed such that dolomite stoichiometry and cation ordering both increase with geologic age, suggesting that progressive recrystallization driven by mineralogical stabilization during burial is also occurring. Collectively, these data suggest that spatial and temporal variations in stoichiometry and cation ordering reflect the interplay between local dolomitizing conditions near the surface and long-term mineralogical stabilization during burial.

Characterization of Evolution Stages, Groundwater and Soil Features of the Mud Forest Landscape at Qian-an (China)

The research on geological landscape has received more and more attention worldwide. The National Geological Park of Qian-an mud forest, located in Qian-an Country, Songyuan City (Jilin Province, China) is a rare natural geological landscape formed by erosion. Mud forest landscape has undergone long-term geological processes, and it is still in continuous evolution due to subsurface erosion. In the process of the mud forest landscape formation and evolution, distinct stages have been recognized. The subsurface erosion factors of the mud forest area were identified by groundwater and soil samples characterization, and the mechanism of the formation of the mud forest is studied. Results show that the occurrence of subsurface erosion is controlled by four factors: (1) The head difference of terrace increases due to geological structure, (2) The dry and cold paleoclimate increases the accumulation of soluble salts. Concentrated precipitation in the short term also promotes subsurface erosion. (3) The high content of sodium ions in groundwater promotes the dispersion of soil, and (4) Loess-like soil is characterized by high porosity, low plasticity, and dispersibility.

Mountain biodiversity and ecosystem functions: interplay between geology and contemporary environments

Although biodiversity and ecosystem functions are strongly shaped by contemporary environments, such as climate and local biotic and abiotic attributes, relatively little is known about how they depend on long-term geological processes. Here, along a 3000-m elevational gradient with tectonic faults on the Tibetan Plateau (that is, Galongla Mountain in Medog County, China), we study the joint effects of geological and contemporary environments on biological communities, such as the diversity and community composition of plants and soil bacteria, and ecosystem functions. We find that these biological communities and ecosystem functions generally show consistent elevational breakpoints at 2000–2800 m, which coincide with Indus-Yalu suture zone fault and are similar to the elevational breakpoints of soil bacteria on another mountain range 1000 km away. Mean annual temperature, soil pH and moisture are the primary contemporary determinants of biodiversity and ecosystem functions, which support previous findings. However, compared with the models excluding geological processes, inclusion of geological effects, such as parent rock and weathering, increases 67.9 and 35.9% of the explained variations in plant and bacterial communities, respectively. Such inclusion increases 27.6% of the explained variations in ecosystem functions. The geological processes thus provide additional links to ecosystem properties, which are prominent but show divergent effects on biodiversity and ecosystem functions: parent rock and weathering exert considerable direct effects on biodiversity, whereas indirectly influence ecosystem functions via interactions with biodiversity and contemporary environments. Thus, the integration of geological processes with environmental gradients could enhance our understanding of biodiversity and, ultimately, ecosystem functioning across different climatic zones.

СОПРОТИВЛЕНИЕ ПЕСЧАНЫХ И ГЛИНИСТЫХ ГРУНТОВ ПО БОКОВОЙ ПОВЕРХНОСТИ И ПОД ОСТРИЕМ БУРОВЫХ СВАЙ ГЛУБОКОГО ЗАЛОЖЕНИЯ

Introduction : Saint Petersburg is characterized by complex engineering and geological conditions due to the presence of a significant mass (with a thickness of 20…30 m or more) of highly deformable soils with deformation moduli of 5…10 MPa. Besides, due to long-term geological processes that took place in the territory of Saint Petersburg thousands of years ago, these soils are extremely unevenly distributed in depth and area of occurrence. However, according to modern requirements for city development, deeper underground structures and higher buildings are needed. In terms of geotechnical solutions, it is possible to meet these requirements by using deep piles. Purpose of the study: The authors of the paper made an approximate brief classification of the geological conditions of Saint Petersburg based on the genesis, depth of occurrence, and physical and mechanical properties, and developed a method for more accurate calculations of the bearing capacity of deep bored piles. Methods: In the course of the study, the authors performed statistical processing of 600 values of the bearing capacity of bored piles, calculated according to the requirements of standards and determined by the results of field tests. In addition, they performed a non-linear extrapolation of side friction and resistance values (for soils with a depth of up to 100 m). Results: The paper presents the assessment of the bearing capacity of bored piles depending on their depth in glacial moraine and pre-quaternary vendian deposits. Using the nonlinear extrapolation, the authors calculated the side friction and resistance under the toe of bored piles for further design of pile foundations with deep bored piles (at a depth of up to 100 m). Discussion: According to statistical studies, the actual bearing capacity of bored piles is significantly higher than the design one calculated according to the requirements of corresponding standards (by 1.6...2.6 times). This is due to the fact that soils with significantly differing strength and deformation characteristics are located along the side and under the toe of bored piles. The stronger the soil where the most part of the pile is located, the more the bearing capacity error is (towards underestimation). The paper presents studies confirming this statement.

Iron-rich carbonates stabilized by magnetic entropy at lower mantle conditions

Constraining the flux of carbon in and out of the interior of the Earth due to long-term geological processes is important, because of the influence that it has on climate change. On timescales of billions of years, host minerals such as carbonate phases could play a significant role in the global carbon cycle, transporting carbon into the lower mantle as a component of subducting slabs. We use density functional theory based calculations to study the high-pressure, high-temperature phase stability of Mg1-xFexCO3. Our results show that iron-rich phases, where carbon is in tetrahedral coordination, are only stable at lower mantle conditions due to their magnetic entropy, which is also responsible for the unusual shape of their phase boundary. Low-pressure carbonate phases are found to be highly anisotropic, but high-pressure carbonate phases are not, which has important implications for their seismic detectability. Our work confirms that future discussions of the global carbon cycle should include the deep Earth.

Episodic events in long-term geological processes: A new classification and its applications

Long-term geological processes are usually described with curves reflecting continuous changes in the characteristic parameters through the geological history, and such curves can be employed directly for recognition of episodic (relatively long-term) events linked to these changes. The episodic events can be classified into several categories according to their scale (ordinary and anomalous events), “shape” (positive, negative, and neutral events), and relation to long-term trend change (successive, interruptive, facilitative, stabilizing, transformative, increasing, and decreasing). Many types of these events can be defined depending on the combination of the above-mentioned patterns. Of course, spatial rank, duration, and origin can be also considered in description of these events. The proposed classification can be applied to events in some real long-term geological processes, which include global sea-level changes, biodiversity dynamics, lithospheric plate number changes, and palaeoclimate changes. Several case examples prove the usefulness of the classification. It is established that the Early Valanginian (Early Cretaceous) eustatic lowstand (the lowest position of the sea level in the entire Cretaceous) was negative, but ordinary and only interruptive event. In the other case, it becomes clear that the only end-Ordovician and the Permian/Triassic mass extinctions transformed the trends of the biodiversity dynamics (from increase to decrease and from decrease to increase respectively), and the only Cretaceous/Paleogene mass extinction was really anomalous event on the Phanerozoic biodiversity curve. The new palaeontological data are employed to reconstruct the diversity dynamics of brachiopods in Germany (without the Alps) and the Swiss Jura Mountains. The further interpretation of the both diversity curves implies that the Early Toarcian mass extinction affected the regional brachiopod faunas strongly, but this event was only decreasing (biotic radiation continued after it, although “restarted” from the lower point) similarly to the end-Triassic and Cretaceous/Paleogene mass extinctions. The number of lithospheric plates decreased in the Early Cretaceous; however, the previous trend to increase in this number re-established after the noted event. The Oi-1 glaciation in the very beginning of the Oligocene was anomalous event, but it only stabilized the earlier trend of temperature decline and did not transform it. Further development of the comprehensive classification of geological events is necessary. For instance, it has become clear that the Silurian environmental perturbations and the Cretaceous oceanic anoxic events should be classified as discrete events that differ essentially from episodic events, the latter of which are relevant to continuous changes in geological processes.

Evaluating influence of active tectonics on spatial distribution pattern of floods along eastern Tamil Nadu, India

Flooding is a naturally recurrent phenomenon that causes severe damage to lives and property. Predictions on flood-prone zones are made based on intensity–duration of rainfall, carrying capacity of drainage, and natural or man-made obstructions. Particularly, the lower part of the drainage system and its adjacent geomorphic landforms like floodplains and deltaic plains are considered for analysis, but stagnation in parts of basins that are far away from major riverine systems is less unveiled. Similarly, uncharacteristic flooding in the upper and middle parts of drainage, especially in zones of an anomalous drainage pattern, is also least understood. Even though topographic differences are attributed for such anomalous spatial occurrence of floods, its genetic cause has to be identified for effective management practice. Added to structural and lithological variations, tectonic movements too impart micro-scale terrain undulations. Because active tectonic movements are slow-occurring, long-term geological processes, its resultant topographical variations and drainage anomalies are least correlated with floods. The recent floods of Tamil Nadu also exhibit a unique distribution pattern emphasizing the role of tectonics over it. Hence a detailed geoinformatics-based analysis was carried out to envisage the relationship between spatial distribution of flood and active tectonic elements such as regional arches and deeps, block faults, and graben and drainage anomalies such as deflected drainage, compressed meander, and eyed drainages. The analysis reveals that micro-scale topographic highs and lows imparted by active tectonic movements and its further induced drainage anomalies have substantially controlled the distribution pattern of flood.

Differential Temporal and Spatial Preservation of Archaeological Sites in a Great Lakes Coastal Zone

AbstractAnalysis of regional site taphonomy that incorporates depositional and postdepositional histories has become increasingly important in understanding the nature of preserved site populations and the strategies necessary for their discovery. We applied a systematic archival and field strategy directed at understanding such taphonomic processes in the coastal sand dunes of the northern and eastern Lake Michigan basin, and coupled these with a tactically directed program of OSL, 14C, and AMS dating. We demonstrate that long-term geological processes including lake level variation, episodic dune activation and stabilization, and the long-term effects of postglacial isostatic adjustments have markedly affected the potential for preservation of sites in coastal dune contexts over time and across subregions of the basin. Preservation potential for different time periods in coastal dunes is largely not synchronous with that of southern Michigan floodplains, posing substantial inferential problems. The archaeology of coastal dunes specifically, and coastal zones generally, must be used with extreme caution when cast against archaeological data from landforms with different formation processes and histories. While particularly true for the Great Lakes region, these results have implications for regional research broadly.

The Boom Clay geochemistry: Natural evidence

ABSTRACTIn Belgium, the Boom Clay is studied as the reference formation for geological disposal of high-level radioactive waste and spent fuel. As the Boom Clay is considered as the main barrier for radionuclide migration/retention, a thorough characterisation of the clay and its pore water was done. This facilitates better understanding of the long-term geological processes and the distribution of the trace elements and radionuclides.From a mineralogical/geochemical point of view, the Boom Clay is considered as a rather homogeneous sediment, vertically as well as laterally. It is composed of detrital minerals, organic matter and fossils. Minerals are mainly clay minerals, quartz and feldspars. Minor amounts of pyrite and carbonates are also present. Small variations in mineralogical/geochemical composition are related to granulometrical variations. The radiochemical study indicates that the Boom Clay is in a state of secular radioactive equilibrium, meaning that the Boom Clay has not been disturbed for a very long time.Pore water sampling is done in situ from various piezometers, or by the squeezing or leaching of clay cores in the laboratory. These three pore water sampling techniques have been compared and evaluated. Boom Clay pore water is a NaHCO3 solution of 15 mM, containing 115 mg·1−1 of dissolved natural organic carbon. Some slight variations in pore water composition have been observed and can be explained by principles of chemical equilibrium.