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The properties of geographical phenomena vary with changes in the scale of measurement. The information observed at one scale often cannot be directly used as information at another scale. Scaling addresses these changes in properties in relation to the scale of measurement, and plays an important role in Earth sciences by providing information at the scale of interest, which may be required for a range of applications, and may be useful for inferring geographical patterns and processes. This paper presents a review of geospatial scaling methods for Earth science data. Based on spatial properties, we propose a methodological framework for scaling addressing upscaling, downscaling and side-scaling. This framework combines scale-independent and scale-dependent properties of geographical variables. It allows treatment of the varying spatial heterogeneity of geographical phenomena, combines spatial autocorrelation and heterogeneity, addresses scale-independent and scale-dependent factors, explores changes in information, incorporates geospatial Earth surface processes and uncertainties, and identifies the optimal scale(s) of models. This study shows that the classification of scaling methods according to various heterogeneities has great potential utility as an underpinning conceptual basis for advances in many Earth science research domains. © 2019 Elsevier B.V.

Although the development of Gobi Desert in central and eastern Asia has greatly affected the regional and even the global climate, its precise origin and evolution have yet to be determined. The three preconditions for the formation of Gobi Desert are: i) a dry climate, ii) basin landforms and iii) abundant sediment production. In this study, we present a synthesis of both new and published data on the formation and evolution of Gobi Desert in central and eastern Asia. We conclude that the combined effects of mountain building, the mid-latitude westerly circulation and changes in the Asian monsoon, accompanied by global cooling, were principally responsible for the formation of modern Gobi Desert landscapes in central and eastern Asia during the late Pliocene. The arid climate in central and parts of eastern Asia probably developed in the early Cenozoic, from ~50 Ma. Related events included the collision of the Indian and Asian plates, the closure and complete retreat of the Paratethys Ocean from central Asia, and the growth of the Himalayas and the Tibetan Plateau in the Eocene through late Miocene, which blocked the water vapor supply and intensified the aridification of the Asian interior. Superimposed on the topographic changes was the process of stepwise global cooling since the early Oligocene, and in particular since the late Miocene, which controlled the formation and evolution of the Gobi Desert landscape. Global cooling weakened the Asian monsoon circulation, strengthened the westerly circulation and enhanced physical weathering processes in mountain areas, which together promoted both the aridification of the Asian interior and sediment production. These processes finally resulted in the establishment of the modern Gobi Desert landscape in the late Pliocene. We estimate that the modern Gobi Desert landscape was formed at ~2.6 Ma and was the result of the stepwise evolution of Asian topography and climate during the Cenozoic, dominated by Asian tectonic deformation and uplift, and the evolution of Asian monsoon climate and the westerly circulation, forced by global temperature change.

Since Australia is the driest inhabited continent, it is a natural laboratory to study on a large scale dust, its composition, its sources, transport and geochemical composition. This is necessary as there has been a lack of appreciation of the diversity of the Australian regolith characterized by a great array of ages and compositions. This is particularly true of studies that examined the geochemistry of Australian dusts and links with potential deposition sites such as in Antarctica and comparison with South America. Hence, the first part of this paper provides an overview of the surficial geology of Australia with emphasis on regions from where dust can become deflated. A review follows on the investigations of significant dust transport and events in Australia. The second part of the paper provides a review of the sites of potential deflation of dust. It includes the study of different geomorphological sites of dust deflation, with a discussion on how dust particles can accumulate in regions linked to large playa lakes that are under the influence of groundwater below them. This is an important mode of dust deflation, a process of which had insufficiently been detailed before. The processes involving evaporative pumping are explained and several illustrations are provided to document those processes and location of dust deposits. Another region of importance to dust deflation consists of extensive alluvial plains and these are also documented, with an area in the upper reaches of the Darling River being now documented more fully. Finally, the inter-dunal corridors in large dune fields are also mentioned as a source of dust as previous studies already show. This second part ends with the description of the two main Potential Source Areas (PSA) of dust in Australia and these are the Kati Thanda-Lake Eyre region of central Australia, and the Darling Riverine Plain in the upper reaches of the Darling River. These two regions are important for their geochemical fingerprints for transcontinental studies, and supported by satellite imagery that identify dust plumes originating from these regions. The third part of the paper examines the geochemical composition of Australian PSAs by paying particular attention to Neodymium, Strontium and Lead isotopic ratios from both continents. We also suggest the possibility of combining Nd and Pb isotopes as a way of fingerprinting geochemically between different Australian regions, and for comparison with other continental PSAs. This part also reviews previous studies that aimed at geochemically fingerprinting the Australian regolith by referring also how these studies were applied to reconstruct past environmental conditions.

The Sediment-Hosted Geothermal Systems are hybrid geological systems, where geothermal and sedimentary domains interact, leading to mixtures of inorganic and biotic gases. They are named Sediment-Hosted Geothermal Systems (SHGS) or Sediment-Hosted Hydrothermal Systems (SHHS), a clear and univocal definition is not available. They are generally characterized by geothermal (thermometamorphic or mantle-derived) CO2 and thermogenic CH4, and occur in sedimentary basins crossed by magmatic intrusions or involved in volcanic plumbing systems. These systems can be of considerable interest for petroleum exploration and global climate change studies but systematic studies aimed to pinpoint an univocal definition, a detailed characterization and a worldwide location, are quite scarce. Here, we offer a first global review of the potential Sediment-Hosted Geothermal (or Hydrothermal) Systems focusing on: definition; development of an investigation methodology; geochemical and geological characterization of the new identified systems; worldwide mapping of potential SHG(H)S areas and discussion of the environmental and energy implications. We clarify the different meaning between hydrothermal and geothermal and we propose the univocal use of the term Sediment-Hosted Geothermal Systems (SHGS). We propose an investigation methodology and, following it, eight new SHG(H)Ss have been identified. These are located in Italy, Western U.S.A.-Wyoming, Japan and Taiwan. The identified SHGSs have CO2 mean concentration between 66 and 98 vol.% and CH4 mean concentration between 0.95 and 32 vol.%. The CO2 is inorganic and related to the decarbonation processes and magma/mantle degassing whereas the CH4 is thermogenic and associated to the last stages of catagenesis. The sites are mainly located in geodynamic active regimes as back-arc basins, rift zones and foredeep basins. They are not far from volcano complexes and hydrocarbon fields, the distance is within 75 km. They are characterized by anomalous heat flux (>50mW/m2), included between 75 and 190 mW/m2, and basin sediment thickness major than 1000 meters. Following these parameters, a first global map of potential SHGS areas has been created. The obtained results represent an important step toward a better knowledge of the SHGSs providing essential information for the climate change studies, petroleum exploration and development of new energy scenarios.

Interactions between dissolved trace elements and organic ligands in seawater play an important role in ocean biogeochemistry, ranging from regulating primary production in surface waters to element cycling on basin-wide scale, with strong feedbacks to climate variability. In this study, we review different aspects in the field of marine trace elements and their organic ligands: recent instrumental innovation, factors that affect the fate of trace element complexes at the molecular level, spatial distribution of organic matter – trace element complexes in the ocean, modeling approaches as well as prospect in the scenarios of climate variability. We also assess the critical issues of parameterization in the numerical simulation that incorporate the trace elements – organic ligands interactions. Given the predicted climate changes, we examine the potential of exchange between inorganic and organic complexes for trace elements in different oceanic provinces.

Ooid shoals, sedimentary structures consisting of carbonate grains, are often used as proxies to explore changes in seawater chemistry over Earth history. Despite their importance as contributors to the global carbonate budget and as paleo-environmental indicators for water depth, pH, temperature and water energy, the mechanism of formation of these concentric, sub-spherical concretions of tangentially or radially arranged aragonite or calcite crystals is still the subject of intense debate. Unlike oncoids, whose microbial origins are well acknowledged, ooids are traditionally viewed as abiotic grains, mainly produced in suspension by agitated, warm waters that are supersaturated with respect to CaCO3. Yet, there is considerable evidence, including geochemical bio-signatures and detection of viable microbes capable of mineralization and biofilm production and degradation, to suggest otherwise. The emergence of new and sophisticated technologies reveals that the level of microbial diversity of these sedimentary grains exceeds that of some microbialite systems. These findings have refined our understanding of ooid genesis and ooid accretion processes and argue toward microbial mediation both as a direct result of metabolic activities inducing changes in the environment conducive to precipitation and by a passive mechanism, in which mucilaginous extracellular polymeric substances (EPS) act as a template for mineral nucleation. Furthermore, new developments in the field indicate that carbonate mineralization in marine ooids occurs through sequential precipitations that involve an amorphous calcium carbonate phase (ACC), which some argue are of biotic origins. Herein, we discuss the most relevant theories of ooid formation, including some of the early pioneering studies that laid the groundwork for new theories attempting to decode the origins of these controversial grains.

Our knowledge of the history of our planet comes from deciphering the sedimentary record of biologic, ecologic, geochemical, climatic, physical and other systems using a vast array of tools and innovative techniques. To synthesize these trends and events into a coherent global history requires six inter-connected international efforts: (1) documentation and access to major research reference sections, including standardization of convenient and precise terminology for divisions of geologic time (e.g., Global Boundary Stratotype Section and Point (GSSPs) and within-stage levels), (2) inter-calibration of these marine and terrestrial records both within and among different regions to compile a global integrated scale, (3) improving and applying age models to understand cause-effect relationships and rates of processes, (4) public databases and syntheses, (5) international efforts and centers, and (6) Earth-systems geo-education that emphases relationships among fields in addition to training in particular specializations. In the past two decades, the careful analysis of the sedimentary records in China's marine and terrestrial basins have enabled major leaps in our understanding of Earth's history, such as major excursions of the carbon cycle during the Cambrian, “lethal” temperature excursions in Early Triassic, Cretaceous evolution of birds, and catastrophic impacts of large igneous eruptions. China has provided more reference sections for the international definition of GSSPs than any other country. It is vital to put those records from the China basins into a larger global context.

Submarine landslides pose a hazard to coastal communities as they can generate powerful tsunamis, and threaten critical offshore infrastructure such as seafloor cable networks that underpin global communications. Such events can be orders of magnitude larger than their onshore equivalents. Despite the hazard they pose, many aspects of submarine landslides remain poorly understood, such as why they fail on low angle (

The global cryosphere, Earth's frozen water, is in precipitous decline. The ongoing and predicted impacts of cryosphere loss are diverse, ranging from disappearance of entire biomes to crises of water availability. Covering approximately one-fifth of the planet, mass loss from the terrestrial cryosphere is driven primarily by a warming atmosphere but reductions in albedo (the proportion of reflected light) also contribute by increasing absorption of solar radiation. In addition to dust and other abiotic impurities, biological communities substantially reduce albedo worldwide. In this review, we provide a global synthesis of biological albedo reduction (BAR) in terrestrial snow and ice ecosystems. We first focus on known drivers—algal blooms and cryoconite (granular sediment on the ice that includes both mineral and biological material)—as they account for much of the biological albedo variability in snow and ice habitats. We then consider an array of potential drivers of BAR whose impacts may be overlooked, such as arthropod deposition, resident organisms (e.g., dark-bodied glacier ice worms), and larger vertebrates, including humans, that transiently visit the cryosphere. We consider both primary (e.g., BAR due to the presence of pigmented algal cells) and indirect (e.g., nutrient addition from arthropod deposition) effects, as well as interactions among biological groups (e.g., birds feeding on ice worms). Collectively, we highlight that in many cases, overlooked drivers and interactions among factors have considerable potential to alter BAR, perhaps rivaling the direct effects of algal blooms and cryoconite. We conclude by highlighting knowledge gaps for the field with an emphasis on the underrepresentation of genomic tools, understudied areas (particularly high-elevation glaciers at tropical latitudes), and a dearth of temporal sampling in current efforts. We detail a global framework for long-term BAR monitoring that, if implemented, would yield a tremendous amount of insight for BAR and would be particularly valuable in light of the rapid ecological and physical changes occurring in the contemporary cryosphere.

Freeze-thaw weathering is an important surface process and the complex underlying processes can be understood as an interplay between rock properties and its dynamic environment. Multiple researchers coming from different scientific disciplines have contributed to the present-day knowledge on the matter and misconceptions still prevail. In a changing climate, the multidisciplinary insights into freeze-thaw action are crucial for a better understanding of rock weathering in natural and anthropogenic environments. In this review, a series of laboratory and in-situ field tests are presented to illustrate the present-day methods to assess freeze-thaw weathering. Over the last century, these methods led to insights and the development of theories on damage mechanisms. Presently, it is accepted that crystallization pressure is responsible for the majority of stresses in the material's pores. Damage is induced when these stresses overcome the local tensile strength. Since most of the methods used to derive and validate stress build-up theories are indirect observations of parameters related to the phase transition, it is hard to reach a consensus on the exact explanation for stress development. Direct observations, which require actual real-time observation of the pore space during a freeze-thaw cycle, are therefore favoured to reach agreement. Eventually, the goal is to achieve a better insight on which processes potentially occur, how these vary with different environmental, temporal and spatial conditions and under which circumstances damage is inflicted.

Soils form the skin of the Earth’s surface, regulating water and biogeochemical cycles and generating production of food, timber, and textiles around the world. Changes in soil and its ability to perform a range of processes have important implications for Earth system function, especially in the critical zone (CZ)—the area that extends from the top of the canopy to the bottom of groundwater and that harbors most of Earth’s biosphere. A key aspect of the way soil functions results from its structure, defined as the size, shape, and arrangement of soil particles and pores. The network of pores provides storage space for at least a quarter of Earth’s biodiversity, while the abundance, size and connectivity of the pore space regulates fluxes of heat, water, nutrients and gases that define the physical and chemical environment. Here we review the nature of soil structure, focusing on its co-evolution with the plants and microbes that live within the soil, and the degree to which these processes have been incorporated into flow and transport models. Though it is well known that soil structure can change with wetting and drying events, often oscillating seasonally, the dynamic nature of soil structure that we discuss is a systematic shift that results in changes in its hydro-bio-geochemical function over decades to centuries, timescales over which major changes in carbon and nutrient cycles have been observed in the Anthropocene. We argue that the variable nature of soil structure, and its dynamics, need to be better understood and captured by land surface and ecosystem models, which currently describe soil structure as static. We further argue that modelers and empiricists both are well-poised to quantify and incorporate these dynamics into their studies. From these efforts, four fundamental questions emerge: 1) How do rates of soil aggregate formation and collapse, and their overall arrangements, interact in the Anthropocene to regulate CZ functioning from soil particle to continental scales? 2) How do alterations in rooting-depth distributions in the Anthropocene influence pore structure to control hydrological partitioning, biogeochemical transformations and fluxes, exchanges of energy and carbon with the atmosphere and climate, regolith weathering, and thus regulation of CZ functioning? 3) How does changing microbial functioning in a high CO2, warmer world with shifting precipitation patterns influence soil organic carbon dynamics and void-aggregate profile dynamics? 4) How deeply does human influence in the Anthropocene propagate into the subsurface, how does this depth relate to profile structure, and how does this alter the rate at which the CZ develops? The United Nations has recently recognized that 33% of the Earth's soils are already degraded and over 90% could become degraded by 2050. This recognition highlights the importance of addressing these proposed questions, which will promote a predictive understanding of soil structure.

In the last half-century, geoscience research has advanced due to multidisciplinary technologies, among which Information and Communication Technology (ICT) has played a vital role. However, scientifically organizing these ICTs toward improving geoscience measurements, data processing, and information services has encountered tremendous challenges. This paper reviews a profound revolution in geoscience that has resulted from the Geospatial Sensor Web (GSW), serving as a new cyber-physical spatio-temporal information infrastructure for geoscience on the World Wide Web (WWW). In contrast to previous experiment-based and sensor-based paradigms, the GSW-based paradigm is able to accomplish the following: (1) achieve integrated and sharable management of diverse sensing resources, (2) obtain real-time or near real-time and spatiotemporal continuous data, (3) conduct interoperable and online geoscience data processing and analysis, and (4) provide focusing services with web-based geoscience information and knowledge. As a benefit of the GSW, increasingly more geoscience disciplines are enjoying the value of real-time data, multi-source monitoring, online processing, and intelligence services. This paper reviews the evolution of geoscience research paradigm to demonstrate the scientific background of GSW. Then, we elaborates on four key methods provided by GSW, namely, integrated management, collaborative observation, scalable processing and fusion, and focusing service web capacity. Furthermore, current GSW prototypes and applications for environmental, hydrological, and natural disaster analysis are also reviewed. Moreover, four challenges to the future GSW in geoscience research are identified and analyzed, including integration with the Model Web initiative for sophisticated geo-processing, integration with humans for pervasive sensing, integration with Internet of Things (IoT) to achieve high-quality performance and data mining, and integration with Artificial Intelligence (AI) to provide smart geoservices. We have concluded that GSW has become an indispensable cyber-physical infrastructure, and will play a greater role in geoscience research and application.

Peatlands cover approximately 2.84% of global land area while storing one third to one half of the world's soil carbon. While peat erosion is a natural process it has been enhanced by human mismanagement in many places worldwide. Enhanced peat erosion is a serious ecological and environmental problem that can have severe on-site and off-site impacts. A 2007 monograph by Evans and Warburton synthesized our understanding of peatland erosion at the time and here we provide an update covering: i) peat erosion processes across different scales; ii) techniques used to measure peat erosion; iii) factors affecting peat erosion; and iv) meta-analyses of reported peat erosion rates. We found that over the last decade there has been significant progress in studying the causes and effects of peat erosion and some progress in modelling peat erosion. However, there has been little progress in developing our understanding of the erosion processes. Despite the application of new peat surveying techniques there has been a lack of their use to specifically understand spatial and temporal peat erosion dynamics or processes in a range of peatland environments. Improved process understanding and more data on rates of erosion at different scales are urgently needed in order to improve model development and enable better predictions of future peat erosion under climate change and land management practices. We identify where further research is required on basic peat erosion processes, application of new and integrated measurement of different variables and the impact of drivers or mitigation techniques that may affect peat erosion.

Bedrock mega-grooves are assemblages of straight and parallel troughs eroded in bedrock, typically over 1000 m in length; most sites occur within the limits of the Last Glacial Maximum, both on- and off-shore. In this paper, we review the current understanding of these important yet enigmatic landforms and propose a framework for their future research. Mega-grooves are important to our understanding of ice sheet dynamics, ice–bedrock interactions and bedrock landscape evolution in glaciated areas. The overall straightness of mega-grooves across the landscape, their parallel alignment to palaeo-ice flow direction, and occurrence below the general land-surface level, has led to their unanimous interpretation as landforms of subglacial erosion. Scenarios proposed for mega-groove formation focus on either glacier ice or subglacial meltwater as the principal agent of erosion, yet none offers a comprehensive explanation. At locations where mega-grooves occur along lines of structural geology, their location, formation and morphology were largely controlled by the bedrock characteristics. Where no underlying structural control is apparent, mega-grooves were likely initiated through glacial abrasion, and subsequently modified through a range of erosional processes, potentially involving multiple morphogenetic agencies and feedbacks operating between bedrock topography and basal ice flow. In the absence of absolute dates, morphostratigraphic analyses suggest mega-groove survival through multiple glacial cycles. No specific ice-flow characteristics have been identified as a condition for bedrock grooving, but it has been suggested that some bedrock mega-grooves are related to ice streaming, which deserves further study. An initial analysis of bedrock grooves with seemingly similar morphology at a range of scales hints at a bedrock – groove landform size continuum, which could be a useful framework for exploring process - landform relationships. Future research could usefully focus on quantitative analysis of mega-groove morphology, augmented with detailed field analysis of landform relationships to bedrock structure and lithology, and thereby potentially provide further insight into the age and glaciological significance of these landforms.

Because of anthropogenic global warming, the world ocean is currently losing oxygen. This trend called ocean deoxygenation is particularly pronounced in low-latitude upwelling-related oxygen minimum zones (OMZs). In these areas, the temperature-related oxygen drawdown is additionally modulated by biogeochemical feedback mechanisms between sedimentary iron (Fe) and phosphorus release, water column nitrogen cycling and primary productivity. Similar feedbacks were likely active during past periods of global warming and ocean deoxygenation. However, their integrated role in amplifying or mitigating climate change-driven ocean anoxia has not been evaluated in a systematic fashion. Moreover, many studies on past (de)oxygenation events emphasize anoxic-sulfidic (i.e., euxinic) basins such as the Black Sea rather than upwelling-related OMZs as modern analogue systems. In this review, I summarize the current state of knowledge on biogeochemical processes in the water column and sediments of OMZs. Nitrate-reducing (i.e., nitrogenous) to weakly sulfidic conditions in the water column and Fe-reducing (i.e., ferruginous) to sulfidic conditions in the surface sediment are identified as key-features of anoxic OMZs in the modern ocean. A toolbox of paleo-redox proxies is proposed that can be used to identify OMZ-type biogeochemical cycling in the geological record. By using a generalized model of sedimentary Fe release and trapping, I demonstrate that the extent of Fe mobilization and transport in modern OMZs is comparable to that inferred for the euxinic Black Sea and ferruginous water columns in Earth history. Based on this result, I suggest that many sedimentary Fe enrichments in the geological record are broadly consistent with OMZ-type redox conditions in the water column and surface sediment, especially if enhanced chemical weathering and reactive Fe supply to the ocean during past periods of global warming are taken into account. Future studies on paleo-(de)oxygenation events with a combined focus on Fe, sulfur and nitrogen cycling may reveal that OMZ-type redox conditions were an important feature of the ocean through Earth's history.

By their impressive paper title “Ichnological analysis of contourites: Past, present and future”, Rodriguez-Tovar and Hernandez-Molina (2018) have implied that the paper is about a comprehensive review of the topic in space (i.e., global) and time (i.e., past, present, and future). But in reality, the paper has covered only three case studies in Europe. In the real world, bioturbation and burrows are not unique to contourites; they are equally abundant in turbidites, hyperpycnites, tempestites, and even in deformed seismites. Therefore, the immediate challenge is in distinguishing contourite facies from other facies (e.g. hyperpycnites with intense bioturbation). Disappointingly, the review has neglected to address this fundamental issue. Without resolving the basic issue of distinguishing contourites, any ichnological analysis of “contourites” is purely academic and has no relevance in advancing contourite research.

Carbonate mineral weathering coupled with aquatic photosynthesis on the continents, herein termed coupled carbonate weathering (CCW), represents a current atmospheric CO2 sink of about 0.5 Pg C/a. Because silicate mineral weathering has been considered the primary geological CO2 sink, CCW's role in the present carbon cycle has been neglected. However, CCW may be helping to offset anthropogenic atmospheric CO2 increases as carbonate minerals weather more rapidly than silicates. Here we provide an overview of atmospheric CO2 uptake by CCW and its impact on global carbon cycling. This overview shows that CCW is linked to climate and land-use change through changes in the water cycle and water-born carbon fluxes. Projections of future changes in carbon cycling should therefore include CCW as linked to the global water cycle and land-use change.

Biomineralization – the formation of minerals by organisms – is a key aspect in the understanding of the fossil record. Knowing how biominerals form and their properties is important in the correct use of fossils in geochemistry, the understanding of evolution, and in the interpretation of how geological events have influenced the fossil record throughout the Phanerozoic. The focus of this contribution, rather than a conventional review on the status of this research field, is on the importance of highlighting the traditional link between paleontology and biomineralization.

Soil and regolith creep have been analyzed for at least the last 140 years, using many methodological configurations and temporal and spatial scales. The general concept of creeping soil and its mechanism, first proposed by W.M. Davis and G.K. Gilbert at the end of the 19th century, evolved since the 1940s towards theoretical models and precise short- and long-term field measurements. This fruitful epoch continued with results enhanced at the turn of the 20th century by the application of new research methods (e.g. radiometry) and a redefinition of the term soil creep to encompass the sum of stochastic shallow subsurface and near-surface processes causing net downslope movement of soil or regolith. Simultaneously, another possibility of creep detection was noticed in dendrochronology, and since the 1970s, in the formally defined discipline of dendrogeomorphology, indirect evaluations of creep activity were performed based on tree-ring analyses of bent trees. This method found many followers, but was also heavily criticized as imprecise and lacking in evidence of which kind of tree trunk curvature (e.g. “pistol-butt”- like deformation, S-shape curvature) could be ascribed to creep movement. From the beginning, soil creep was associated with the activity of living organisms on hillslopes. However, this aspect of creep studies has never been fully developed, in spite of the solid foundations and directions of potential studies pointed out by Charles Darwin at the end of the 19th century. In this paper we focus on the historical context of soil creep studies, and highlight forest ecosystems as probably the most active environment of biogenic creep, mainly due to tree uprooting and other biomechanical effects of living and dead trees (root channel infilling, tree root mounding etc.) that are a factors in biotransport. In the final sections the position of biogenic creep in the structure of biogeomorphic systems is discussed in relation to such important conceptual frameworks as the biogeomorphic ecosystem, biogeomorphic feedback window and ecosystem engineering. We also describe several hypotheses that should be carefully tested in the future, and propose several research methods that have the ability to further our knowledge about soil creep: radiometry, laser scanning and soil micromorphology.

Diatomites constitute a widely represented lithology in the Messinian sections of the circum-mediterranean Neogene marginal basins. Although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the Mediterranean just before the Messinian salinity crisis, their coeval occurrence with a global intensification of the opaline production in the world oceans (late Miocene-early Pliocene biogenic bloom) suggests that an integrative analysis of the origins of these sediments is necessary. A comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic (tectonic and climate reconfigurations) and biotic (expansion of grass-dominated, opal-rich biomes) controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans, which in turn can explain the opaline burst that occurred during the late Miocene, at both the global and Mediterranean scale. The finely laminated pattern and the rich fossil content of diatomaceous deposits, that are usually considered to be byproducts of anoxic conditions, are briefly discussed. Some studies seem to indicate that, instead of anoxia, the aggregation and sedimentation of diatom tests may play a critical role in these processes. The lower Messinian diatomites of the Mediterranean region are generally interbedded with organic-rich sediments (sapropels) clearly attesting prolonged, precessionally-controlled periods of basin stratification and bottom water anoxia or hypoxia. A causal relationship between sapropel and diatomite deposition in the Mediterranean is proposed, considering the possible interplay between stratification-adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle.

The Philippines is an area of persistent volcanism, being located in one of the most tectonically active regions in the world. Taal Volcano in Southern Luzon is the second most frequently erupting volcano of the 24 active volcanoes in the Philippines. A comprehensive and critical review of published and unpublished references describing the 33 known historical eruptions of Taal may provide answers to knowledge gaps on past eruptive behavior, processes, and products that could be utilized for hazard and risk assessment of future eruptions. Data on the prehistoric eruptions and evolution of Taal Caldera and subsequent deposits are limited. Only four caldera-forming events were identified based on four mapped ignimbrite deposits. From oldest to youngest, these are the silicic Alitagtag (ALI) and Caloocan (CAL) Pumice Flow deposits, the dacitic Sambong Ignimbrite (SAM), and the basaltic-andesitic Taal Scoria Flow, renamed Scoria Pyroclastic Flow (SFL). Except for SFL with 14C dating yielding 5380 ± 70 to 6830 ± 80 ky, there are no age constraints or estimates of extent for the three older deposits. A comprehensive review of the historical eruptions of Taal Volcano is the central element of this paper and includes all eruptions from AD1572 (the first known historic event) to AD1977. Eruption styles and the interplay between processes and products for each eruption are reinterpreted based on the narrative descriptions from all available accounts. A change of classification of eruption styles and eruptive products is undertaken for some events. At least nine reported eruptions were deemed uncertain including the AD1605-AD1611 event (more likely seismic swarms), the AD1634, AD1635, and AD1645 (may simply be solfataric or hydrothermal activity) events, and the AD1790, AD1825, AD1842, AD1873 and AD1903 events that were listed in recent published and unpublished documents but do not provide any details to describe and confirm the eruptions except for listing a default VEI of 2. Pyroclastic density currents brought devastating impacts to the communities around Taal during the AD1749, AD1754, AD1911 and AD1965 eruptions and remain the biggest threat in the case of renewed volcanic activity. Significant implications for aviation are implied by the narrative of tephra fall dispersal towards Manila, the central gateway of international aviation operation in the Philippines, during the AD1754 eruptions. The dispersal of tephra in the event of an explosive eruption at Taal towards Metro Manila would have catastrophic effects to transport, utilities and business activity, potentially generating enormous economic losses. Hazards from earthquake events associated with future volcanic activity may also have localized impacts. Occurrences of liquefaction phenomena as a consequence of severe ground shaking are interpreted during the AD1749, AD1754, and AD1911 eruptions. More work needs to be done to develop a comprehensive understanding of the hazards and risks associated with an explosive eruption at Taal Volcano, especially related to the older Quaternary caldera-forming eruptions that produced large-volume pyroclastic deposits that are extensively distributed and exposed. We acknowledge that there may be additional prehistoric eruptions where the eruptive products have not been preserved, recognized or reported. Events that cannot be verified or do not have sufficient details to confirm the eruption, have been downgraded to “uncertain”. Eruptions that are confirmed with identified dispersal and emplacement of tephra fall and other eruptive deposits, as interpreted from narrated records, could provide crucial information that may be utilized in hazard assessment.

Fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity. We review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches. The targeted volcanoes belong to the Aeolian Arc located in the Tyrrhenian Sea (Italy), and they have exhibited different activity states during the monitoring activities reported here. La Fossa cone on Vulcano Island has been in an uninterrupted quiescent stage characterized by variable solfataric activity. In contrast, Stromboli Island has shown a persistent mild explosive activity, episodically interrupted by effusive eruptions (in 1985, 2002, 2007, and 2014). Panarea Island, which is the summit of a seamount rising from the seafloor of the southern Tyrrhenian Sea, showed only undersea fluid release. The only observable clues of active volcanism at Panarea Island have been impulsive changes in the undersea fluid release, with the last submarine gas burst event being observed in November 2002. The geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and/or the fumarole vents, thermal waters, and diffuse soil degassing, depending on the type of manifestations and the level of activity encountered. Through direct access to the magmatic samples (when possible) and the collection of as much observable data related to the fluid release as possible, the aim has been (i) to verify the thermodynamic equilibrium condition, (ii) to discern among the possible hydrothermal, magmatic, marine, and meteoric sources in the fluid mixtures, (iii) to develop models of the fluid circulation supported by data, (iv) to follow the evolution of these natural systems by long-term monitoring, and (v) to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards. The examples provided in this review article show the close relationships among data analysis, interpretation, and modeling. We particularly focus on describing the fieldwork procedures, since any theoretical approach must always be verified and supported by field data, rather than just by experiments controlled in laboratory. Indeed the natural systems involve many variables producing effects that cannot be neglected. The monitored volcanic systems have been regarded as natural laboratories, and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped. An appendix is also included that explains the scientific approach to the systematic activities, regarding geochemical monitoring of volcanic activity.

Coal, containing all the elements that are present in nature and more than 200 minerals, has a complex chemical structure, making it one of the most complex geological materials. Inorganic matter in coal includes minerals (in which element concentration may vary from trace to major), non-crystalline mineraloids, and elements with non-mineral associations such as those occurring in pore waters, organically bound, or in an organic association. Understanding the modes of occurrence of elements in coal is important because, theoretically, they provide useful information on peat deposition, diagenesis and epigenesis of coal, coal-hosted basin formation, and the regional geological background or evolution. Practically, the modes of occurrence of elements play a significant role in affecting coal mining, coal preparation, coal combustion, and coal utilization, and in exerting adverse effects on both the environment and human health. The modes of occurrence of critical elements in coal and coal ash are key factors for designing the method and technology required for extracting critical metals from coal or coal ash. In this paper, the following aspects are reviewed, including the modes of occurrence of 73 elements and rare gases that occur in coal (with the exceptions of organically associated C, H, O, and N), the definition of modes of occurrence and their practical and academic significance, analytical methods for determining modes of occurrence of elements in coal and their advantages and limitations, and reported modes of occurrence of elements in coal and their likely associations. Overall, the modes of occurrence of elements in coal are classified into inorganic, organic, and intimate organic associations. Although there are common modes of occurrence of many elements in coal, there are many exceptions and most, if not all, elements have multiple modes of occurrence. Each mode of occurrence of an element may also show different levels of confidence, namely, certain, probable, possible, doubtful, unlikely, and may occur in coal with different frequencies, namely abundant, common, uncommon, rare, and unlikely. For each element, the authors present concluding comments viewpoints on the modes of occurrence of almost each element in coal that is listed in the old literature. The different modes of occurrence for each element in different coals depend on the geological conditions of coal formation, and do not necessarily indicate inconsistency in the reported results. However, due to limitations of the analytical methods used, some data relating the modes of occurrence of elements in coal are not convincing, and in some cases are invalid or even misleading. Overall, while precisely determining the concentrations of many elements in coal is not difficult, determination of the modes of occurrence of some elements, particularly those with low concentrations and high volatility, is still a challenge. Although analytical methods certainly play critical roles in determining the modes of occurrence of elements in coal, in-depth understanding of the nature of the coal and host-rocks and the geological background of coal formation is very useful in investigating when and how these modes of occurrence of elements were formed.

Coastal beach aquifers are biogeochemically active systems that mediate chemical and material fluxes across the land-sea interface. This paper provides a review of major physical stressors and geologic features that influence flow and solute fate and transport in coastal beach aquifers. We outline current understanding of the interactions between these factors and their associated impacts on water and geochemical fluxes within and across these aquifers. The physical processes that control flow, transport, and the formation and distribution of reactive zones in beach aquifers (e.g., tides, waves, density gradients, precipitation, episodic ocean events, and evaporation) operate across overlapping temporal and spatial scales, and present challenges for measuring and modeling physical flow and biogeochemical processes in coastal groundwater systems. Geologic heterogeneity introduces further complexity by modifying flowpaths, mixing patterns, and rates of biotransformation. Interactions between these physical stressors and geological controls are likely to evolve with changes in sea level, climate variability, human settlement, coastal erosion, and other natural and anthropogenic stresses, providing avenues for scientific exploration into the future role of beach aquifers as chemical mediators between the land and ocean.

Oxygen is one of the most crucial elements on earth and equally affects life and inorganic redox processes. After its transition to water with moderate solubility and slow diffusion rates, most aquatic organisms depend on permanent renewal of dissolved oxygen (DO). Recharge of this pivotal aqueous gas may become hampered by anthropogenic and climatic influences with so far unknown consequences for surface freshwater systems and entire ecosystems. Because rivers integrate biogeochemical information of catchments, their oxygen dynamics may also reflect ecosystem and landscape health. Here we summarize the most important sources and sinks of DO and its role in river systems. These considerations also extend to associated water compartments and fluxes including lakes, reservoirs, soils, groundwater and the hyporheic zone. In addition, for continental-scale considerations, we analysed the GLObal RIver CHemistry (GLORICH) database with 170,369 DO measurements. These analyses revealed that DO in rivers relates to water temperature, pH and nutrient availability. On larger scales, it is also influenced by catchment area, slope, ratios of forests to managed land and population density. Our review also highlights important links between physical and biological influences on DO transfer as well as its sources and sinks in streams and rivers. We conclude that DO monitoring should be combined with novel interdisciplinary tracing techniques such as stable isotope ratios, radon gas and biological analyses. Such combined analyses have the potential to improve our understanding of transfer and transformations of oxygen in rivers as essential integrators of landscapes.

Bekker et al. (2020) and Philippot et al. (2018) discussed implications of the geological and geochemical records of the Turee Creek Basin in Western Australia with regards to the understanding of the Great Oxidation Episode (GOE). Whereas Bekker et al. (2020) inferred that, due to its deposition in a foreland basin with high sedimentation rates, the succession bears a high-resolution record leading to, and of, the early stage of the GOE, Philippot et al. (2018) maintained that it provides a detailed and continuous (i.e., stratigraphically unbroken) record spanning 2.45 Ga to 2.22 Ga. The disagreement is largely rooted in different readings of the geochronological data presented in Caquineau et al. (2018) and Philippot et al. (2018), but also in different views on the tectonostratigraphic evolution of the Turee Creek Basin, chemostratigraphic records of the succession, and correlation with other early Paleoproterozoic sequences. The disagreement has far-reaching implications for the GOE and its relationship to early Paleoproterozoic climate changes. Philippot et al. (2021) provided a detailed critique of our approach, allowing us to clarify our original interpretations. Based on the analysis provided below, we stand by our original reading, and provide a more nuanced view of the early Paleoproterozoic global correlations and events. By combining global records, we infer that the ~2.45–2.22 Ga time interval experienced so-far underappreciated large-scale swings in atmospheric oxygen level across the 10−5 PAL threshold that were associated with, and likely led to, early Paleoproterozoic glaciations by impacting atmospheric levels of methane, a powerful greenhouse gas in an anoxic atmosphere.

Understanding the origin and evolution of life on Earth and potentially other planets in our solar system is of fundamental interest for humanity. For the longest time in Earth's history, life evolved in microbial communities. It is, however, still incompletely understood how, when and where such habitable environments formed and how microbial communities adopted to the drastic changes of the atmosphere-hydrosphere-lithosphere systems through deep time. Stromatolites, i.e., lithified microbial mats that occur in sedimentary successions from at least 3.4 billion years ago until today, hold the geochemical key to our understanding of the evolution of microbial life on Earth and may also provide a blueprint for planetary studies. This review targets the potential and pitfalls of emerging and established isotope applications to stromatolites based on improved and newly developed analytical and technical capabilities in the last decades. We provide a comprehensive overview of present data and the interpretation of applications of radiogenic (U Pb, Rb Sr, Sm Nd) and stable (O, C-N-S, Fe, Mo, Cr, U, Cd) isotope systems in stromatolites. Although the behaviour and fractionation processes of different isotope systems in stromatolites and microbial mats are incompletely understood, the different isotope proxies are used to better understand and reconstruct microbial habitats in stromatolite-forming environments through deep time. Primarily, radiogenic isotopes are used to directly date stromatolites and determine the source of elements in ancient stromatolite environments, while stable isotopes are used to understand redox conditions, metal availability, and (biogenic) metal cycling processes in microbial habitats. We provide deep insights into each isotope application in stromatolites and show their unique potential and future perspectives to bridge the gap between geochemistry and microbiology and to better understand the evolution of microbial life on Earth and beyond.

Despite a continuous increase in fossil charcoal records from Late Palaeozoic deposits, which are used as direct evidence for palaeo-wildfires, detailed studies on the charcoal particles are still rare. To investigate the relationship between wildfire activities and the evolution of the terrestrial ecosystem at the end of the Permian, we report on the charcoal recovered from the classic non-marine Permian–Triassic Dalongkou section in Jimsar, Xinjiang Uygur Autonomous Region, Northwest China. Allochthonous and parautochthonous charcoals, identified by both macroscopic and microscopic morphological techniques, were collected from several stratigraphic horizons. These charcoals were classified into 11 categories (which do not represent the taxonomic group) according to their anatomical characteristics and gross morphology. The reflectance values of the charcoals indicate that surface fires were dominant throughout the sequence, with fire regime changing in a distinct interval. The distribution and abundance of all categories and the reflectance of the charcoals suggest that the intensity of wildfires increased in the upper part of the Guodikeng Formation. This trend coincides with the Hg/TOC peaks and a conspicuous excursion in the organic carbon isotope (δ13Corg) values, which may indicate volcanic activities and the disturbance of the carbon cycle that occurred during the Permian–Triassic transition. It is reasonable to infer that the end-Permian mass extinction (EPME) is located at the intensive wildfire interval. The reduction in spore pollen and the decrease in charcoal reflectance hint at a vegetational impoverishment that occurred after this interval. We proposed that increased wildfires, promoted by dry climate conditions and volcanism, aggravated the collapse of the forest ecosystem during the latest Permian.

Southeast Asia is located in an important regional geodynamic intersection zone surrounded by inward subduction systems on three sides, consisting the largest and most complicated convergent subduction system in the earth. The deep circulation and ultimate destination of the subducted material have always been an elusive scientific mystery, lacking both systematic scientific observation and accepted theoretical models. In this review we present geophysical, geochemical and geodynamical models in last decades regarding the seismic tomographic deep structure, material exchanges and evolution history of the Curved Subduction System (CSS) in SE Asia, and identify remained challenges in constructing the deep mantle structure and quantifying the feedback between the subducting slab and the interior recycling materials relevant to the dynamic processes within the theme of mass and energy transfer. We propose that increased understanding of seismic tomography within the CSS, combined with geochemical analysis and computational geodynamic modeling, will aid clearer portrayal of the dynamic mechanisms controlling the evolution of such ring-shape subduction systems on Earth.

Hydrothermal vents are among the most fascinating environments that exist within the modern oceans, being home to highly productive communities of specially-adapted fauna, supported by chemical energy emanating from the Earth's subsurface. As hydrothermal vents have been a feature our planet since the Hadean, their history is intricately weaved into that of life on Earth. Despite an overall scant fossil record due to the improbabilities of preservation of vent deposits and organisms, recent fossil findings from ancient vent environments, accompanied by molecular data as well as fossils from ecologically-similar environments, have yielded invaluable new insights into the history of life at hydrothermal vents. Fossils from hydrothermal vents are among the earliest contenders for direct evidence of life on Earth, while a range of additional fossil finds indicate that vent habitats were readily exploited by microbes during the Precambrian. The first metazoans possibly appeared within vents during the Cambrian, and by the Ordovician-Silurian, hydrothermal vents in the deep ocean were colonised by mollusc, brachiopod and tubeworm taxa whose large abundances and sizes suggest these early animals were well-adapted to this setting. A transition in vent community composition occurred during the Mesozoic, as modern vent faunas began to occupy these environments and replace Paleozoic taxa. Molecular evidence indicates that many additional taxa radiated within vents during the Cenozoic, demonstrating that throughout Earth history, organisms were repeatedly able to overcome the challenges of adapting to the harsh conditions at vents to exploit their productivity. Targeting ancient vent deposits that have undergone low degrees of diagenetic or metamorphic change during mining-related exposure has great potential to provide further insights into the vent fossil record and fill existing gaps in knowledge.

The Earth's mantle has provided a ready redox gradient of sulfur compounds (SO2, H2S) since the stabilization of the crust and formation of the ocean over 4 billion years ago, and life has evolved a multitude of metabolic pathways to take advantage of this gradient. These transitions are recorded in the sulfur and carbon isotope signals preserved in the rock record, in the genomic records of extant microorganisms, and in the changing mantle and crust structure, composition and cycling. Here, we have assembled approximately 20,000 sulfur (δ34S, Δ33S, Δ36S) and carbon (δ13C) isotope data points from scientific publications spanning over five decades of geochemical analyses on rocks deposited from 4.0 to 1.5 Ga. We place these data in the context of molecular clock and tectonic and surface redox indicators to identify overarching trends and integrate them into a holistic narrative on the transition of the Earth's surface towards more oxidizing conditions. The greatest extreme in δ34S values of sulfide minerals (− 45.5 to 54.9‰) and sulfate minerals (− 13.6 to 46.6‰) as well as δ13C values in carbonate minerals (− 16.8 to 29.6‰) occurred in the period following the Great Oxidation Event (GOE), while the greatest extremes in organic carbon δ13C values (− 60.9 to 2.4‰) and sulfide and sulfate mineral Δ33S and Δ36S values (− 4.0 to 14.3‰ and − 12.3 to 3.2‰, respectively) occurred prior to the GOE. From our observations, we divide transitions in Earth's history into four periods: Period 1 (4.00 to 2.80 Ga) during which geochemical cycles were initialized, Period 2 (2.80 to 2.45 Ga) during which S and C isotope systems exhibit changes as conditions build up to the GOE, Period 3 (2.45 to 2.00 Ga) encompassing the GOE, and Period 4 (after 2.00 Ga) after which S and C isotopic systems remained relatively constant marking a time of Earth system geochemical quiescence. Using these periods, we link changes in S and C isotopes to molecular clock work to aid in interpreting emerging metabolic functions throughout Earth's history while underscoring the need for better proxies for robust evolutionary analyses. Specifically, results indicate: 1) an early development of sulfide oxidation and dissimilatory sulfite reduction followed by disproportionation and then sulfate reduction to sulfite resulting in a fully biologically mediated sulfur cycle by ~ 3.25 Ga; 2) support for the acetyl coenzyme-A pathway as the most likely earliest form of biologically mediated carbon fixation following methanogenesis; 3) an increasingly redox-stratified ocean in the Neoarchean with largely oxic surface water and euxinic bottom water during the first half of the Paleoproterozoic; and 4) that secular changes in Earth system crustal cycling dynamics and continent formation likely played a key role in driving the timing of the GOE. Finally, based on geochemical data, we suggest that the Paleoproterozoic be divided into a new Era of the Eoproterozoic (from 2.45 to 2.00 Ga) and the Paleoproterozoic (from 2.00 to 1.60 Ga).

Types of rock, such as komatiite, which formed entirely or dominantly during restricted time periods in solar system history, are important indicators of how planetary bodies evolved in deep time. In this paper we characterize three different types of temporally-restricted anorthosites, and discuss their significance to the broad-scale evolution of planetary processes. Primordial anorthosites, which constitute the bulk of the lunar crust, were sampled during Apollo and Luna missions, and have subsequently been identified in our meteorite collections. They are characterized by very calcic plagioclase (An93–98), and all have magmatic crystallization ages > 4.3 Ga, suggesting that the earliest planetary crust-forming processes on the Moon, and possibly elsewhere, involved substantial, if not total melting. The “magma ocean” hypothesis, which has endured for nearly 50 years, argues that the lunar anorthositic rocks represent global flotation cumulates of plagioclase, which crystallized after extensive precipitation and sinking of olivine and pyroxene. Another possibility, revitalized by critical filtering of age data, involves “serial magmatism”, whereby the lunar crust was constructed by younger, smaller, episodic magmatic events. On Earth, two distinct types of temporally-restricted anorthosites offer opportunities to understand the evolution of terrestrial geodynamics, tectonics and magmatic processes. Archean megacrystic anorthosites formed only between 3.73 and 2.49 Ga as small bodies (

In our modern economy, tantalum has become a ‘technology-critical element’ which is increasingly used in new technologies. This has led to a need to evaluate potential environmental impacts, which, in turn, requires knowledge of its concentration in the environment along with better understanding of the chemical processes underlying its environmental behaviour. This review is an attempt to summarize our current knowledge about tantalum in the environment. The attention paid to tantalum in the environmental field lags far behind what it attracts in some geosciences: while a wealth of tantalum concentration values in meteorites and rocks is available – allowing for good estimates of its content in the continental crust and of the Nb/Ta ratio (a precious geochemical tool) – data on tantalum concentrations in the different environmental compartments is scarce, particularly in natural waters where reliable estimates of ‘dissolved’ tantalum concentrations in seawater and freshwaters cannot even be produced. What is more, tantalum appears to be mostly present in ‘particulate’ form in natural waters, not ‘dissolved’. Values exist for concentrations in soils, bed sediments and atmospheric aerosols; these are close to tantalum UCC values, thus pointing to a detrital origin. No signs of pollution effects linked to human use of the element are visible. At first sight, tantalum appears to be a very conservative element in biogeochemical terms but real understanding of its cycling and reactivity would require extensive and meaningful data collection. This is hindered by analytical difficulties, mainly: (i) ‘dissolved’ concentrations are well below current analytical capabilities in natural waters and require pre-concentration procedures that, for the moment, do not give consistent results; (ii) solid samples require complex mineralisation procedures that exclude tantalum from routine multielement studies. Lastly, there is scant reliable data on stability constants (i.e., absence or highly uncertain values) for relevant tantalum complexes. No sorption studies exist on tantalum binding by natural organic matter or inorganic particles.

Classical geomorphological models consider that escarpment retreat of cuesta landforms is fastest in arid and semiarid regions, which would be expected to lead to increased talus production. However, this is in disagreement with the piedmont zone of the Colorado Plateau cliffs (arid/semiarid region of southwestern USA), where talus is as inconspicuous as the deposits of the cuesta escarpment footslopes of the Parana Basin (wet tropical region of southeastern Brazil). Thus, this paper discusses the evolutionary processes of cuesta escarpments, pediments, and piedmont deposits in both wet tropical regions and arid zones, considering the key areas of the Serra Geral Ridge in the Parana Basin and the eastern central Colorado Plateau as examples. This manuscript constitutes a comprehensive and critical review of the principal literature on the landform development of such regions. Research has revealed that despite the production of sediment (fine–coarse) from the escarpments in the arid southwestern USA, geochemical weathering and freeze–thaw cycles quickly destroy talus deposits. Furthermore, chemical weathering dissolves minerals and forms caverns within the rock walls of mesas and in amphitheaters and canyons, influencing escarpment retreat directly, despite mechanical processes being the most important factors controlling landform development. On the other hand, in regions characterized by the wet tropical climate of Brazil, geochemical processes are more intense and they destroy the talus very quickly, enhancing deep weathering. However, mechanical morphogenesis is also frequent in such regions, forming, in deforested areas, features very similar to those found in the badlands of dry zones. Chemical and physical/mechanical processes have very different intensities in dry/arid and wet/tropical areas, but these processes are very relevant to landform development in both environments. The rates of escarpment retreat are higher in the dry areas of the Colorado Plateau than estimated for the Brazilian tropical zones, which is in accordance with classical models. These variations are probably related not only to climate but also to lithological differences; the tops of the mesas on the Colorado Plateau are supported by thin strongly cemented conglomeratic fluvial sandstones, whereas the caprocks of the Brazilian cuesta landforms comprise thick basalt flows capped by ferruginous cuirasses. In some cases, lithological characteristics are more important than climate regarding escarpment retreat.

Granitic rocks play special role in the dynamics and evolution of the Earth and its thermal regime. First, their compositional variability, reflected in the distribution of concentrations of radiogenic elements, provides constraints on global differentiation processes and large scale planetary evolution, where emplacement of granites is considered a particularly important process for the formation of continental crust. Second, heat production by radioactive decay is among the main heat sources in the Earth. Therefore knowledge of heat production in granitic rocks is pivotal for thermal modelling of the continental lithosphere, given that most radiogenic elements are concentrated in granitic rocks of the upper continental crust whereas heat production in rocks of the lower crust and lithospheric mantle is negligible. We present and analyze a new global database GRANITE2017 (with about 500 entries) on the abundances of heat producing elements (Th, U, K) and heat production in granitic rocks based on all available published data. Statistical analysis of the data shows a huge scatter in all parameters, but the following conclusions can be made. (i) Bulk heat production in granitic rocks of all ages is ca. 2.0 μW/m3. It is very low in Archean-Early Proterozoic granitic rocks (1.67 ± 1.49 and 1.25 ± 0.83 μW/m3, respectively) and there is a remarkable peak in heat production in Middle Proterozoic granites (presently 4.36 ± 2.17 μW/m3) followed by a gradual decrease towards Cenozoic granites (3.09 ± 1.62 μW/m3). Low heat production in the ancient continental crust may be important for preservation of cratonic lithosphere. (ii) There is no systematic correlation between the tectonically controlled granite-type and bulk heat production, although A-type (anorogenic) granites are the most radioactive, and many of them were emplaced in Middle Proterozoic. (iii) There is no systematic correlation between heat flow and concentrations of radiogenic elements. (iv) The present-day global average Th/U value is 4.75 ± 4.27 with a maximum in Archean-Early Proterozoic granites (5.75 ± 5.96) and a minimum in Middle-Late Proterozoic granites (3.78 ± 2.69). The Th/U ratio at the time of granite emplacement has a minimum in Archean (2.78). (v) The present-day K/U ratio is close to a global estimate for the continental crust only for the entire dataset (1.46 ± 1.63) × 104, but differs from the global ratio for each geological time, and all anomalously high values are observed only in Archean-Early Proterozoic granites. (vi) We do not observe a systematic difference in radiogenic heat production between Archean and post-Archean granites, but rather recognize a sharp change in radiogenic concentrations and ratios from the Early Proterozoic to Middle Proterozoic granites. The Proterozoic anomaly may be caused by major plate reorganizations possibly related to the supercontinent cycle when changes in the granite forming processes may be expected, or it may even indicate a change in global thermal regime, mantle dynamics and plate tectonics styles. (vii) Our results provide strong evidence that secular change in the Urey ratio was not monotonous, and that plate motions may have been the fastest in Middle Proterozoic and have been decreasing since then. (viii) We estimate the total present-day heat production in the granitic crust as 5.8–6.8 TW and in the continental crust as 7.8–8.8 TW.

Spectacular rock-cut landscapes consisting of closely spaced residual rock blocks separated by narrow intersecting corridors are variously termed as ‘rock cities’ and ‘ruiniform relief’. The former term has apparently never been formally defined except in the local Czech literature, whereas the latter was applied in various contexts, making the terminology confusing. This paper provides a global overview of forms, processes and controls behind such rock city/ruiniform landscapes and develops geomorphological terminology for such rock-cut landscapes, including the proposal that ‘rock city’ becomes a legitimate scientific term. Rock cities and ruiniform relief are two different types of rock erosional morphology, typified by the presence of a ‘street pattern’ in the former and highly weathered surfaces of rock residuals in the latter, although there is some overlap between the two. Examples of rock cities or ruiniform relief may be found in different lithologies and in a wide range of climates, from hyper-arid to humid. Classic localities include northern Czechia and adjacent parts of Poland and Germany, Australia, central Sahara, and the Gran Sabana in Venezuela. Lithologies particularly suitable to the development of this type of erosional morphology include mainly sandstones, followed by limestones, dolomites, conglomerates, tuffs, but igneous rocks such as granites or rhyolites are also known to support this type of relief. The combination of sufficient rock strength to support steep rock faces and the presence of discontinuities which, preferentially eroded, turn to ‘streets’ and ‘squares’ in the rock cities, appears as the basic prerequisite. A wide range of processes are involved in their formation, including surface and subsurface weathering, mass movements, salt tectonics, karst processes in both carbonate and silicate rocks, piping, fluvial erosion and aeolian abrasion. Despite being spectacular landscapes, very few models of long-term evolution of rock city and ruiniform relief have been presented in the literature and it is unlikely that any one scenario would apply to all situations. Rather, rock cities are examples of geomorphological convergence.

Aeolian processes, the entrainment, transport and deposition of sediments by wind, impacts climate, biogeochemical cycles, food security, environmental quality and human health. Considering the multitude of interactions between aeolian processes and all the major components of the Earth system, there is a growing interest in the scientific community to quantify the wind-related sediment movement process and redistribution rates at different spatial and temporal scales. However, this quantification is rather challenging, due to the complexities of physical mechanisms involved in aeolian processes and the inherent fundamental differences from the rather well-studied processes controlling fluvial erosion. Traditional techniques, such as erosion plots and surveying methods for monitoring wind erosion, are capable of quantifying sediment movement on small scales but they have a number of limitations in terms of the representativeness of the data obtained, spatial and temporal resolution and the patterns over extended areas, and the costs involved. The demand for alternative methods of soil loss and sediment redistribution assessment, in order to complement and enhance the existing methods, has directed attention to use tracing approaches for monitoring rates and spatial patterns of sediment redistribution at various scales. A comprehensive synthesis of available information from different scientific disciplines on aeolian tracer techniques, their applications and limitations are important in understanding the role of aeolian processes and their interactions with the Earths systems in changing climate and management scenarios. The objective of this paper is to provide a scientific review of the current tracer approaches in aeolian studies, including fallout radionuclides, rare earth elements, sediment finger printing and soil magnetism, as well as giving an introduction of the potential tracers that are in development.

The application of advanced remote sensing technologies, including terrestrial laser scanning (TLS), to the Earth sciences has increased rapidly in the last two decades, improving the spatial and temporal resolution of data. Terrestrial laser scanning units have evolved into a common tool in studies of spectral and structural geology, seismology, natural hazards, geomorphology, and glaciology. Special consideration of the advantages and limitations of TLS in each of these fields is discussed in depth in the context of important work published in each field. The workflow used in a TLS survey is crucial to the success of the survey, and field-specific Earth science workflows are therefore also discussed. Products based on TLS data, such as triangulated irregular networks (TIN) and digital surface models (DSM), are commonplace tools throughout the Earth sciences and the use of these tools to measure slip distributions, fault geometries, aeolian transport, river bed morphologies and flows, and other research problems is expanded on where appropriate. The review concludes with a discussion of recent trends in TLS instrument development and their potential impact on the use of TLS in the Earth sciences in the future.

During the past few decades, time-variable volcano gravimetry has shown great potential for imaging subsurface processes at active volcanoes (including some processes that might otherwise remain “hidden”), especially when combined with other methods (e.g., ground deformation, seismicity, and gas emissions). By supplying information on changes in the distribution of bulk mass over time, gravimetry can provide information regarding processes such as magma accumulation in void space, gas segregation at shallow depths, and mechanisms driving volcanic uplift and subsidence. Despite its potential, time-variable volcano gravimetry is an underexploited method, not widely adopted by volcano researchers or observatories. The cost of instrumentation and the difficulty in using it under harsh environmental conditions is a significant impediment to the exploitation of gravimetry at many volcanoes. In addition, retrieving useful information from gravity changes in noisy volcanic environments is a major challenge. While these difficulties are not trivial, neither are they insurmountable; indeed, creative efforts in a variety of volcanic settings highlight the value of time-variable gravimetry for understanding hazards as well as revealing fundamental insights into how volcanoes work. Building on previous work, we provide a comprehensive review of time-variable volcano gravimetry, including discussions of instrumentation, modeling and analysis techniques, and case studies that emphasize what can be learned from campaign, continuous, and hybrid gravity observations. We are hopeful that this exploration of time-variable volcano gravimetry will excite more scientists about the potential of the method, spurring further application, development, and innovation.

Some 300–600 Tg of volatiles are globally vented each year by arc volcanism. Such arc gas emissions have contributed to past and present-day evolution of the Earth atmosphere and climate by recycling mineral-bound volatiles subducted along active slabs. Carbon dioxide (CO 2 ) and total sulphur (S T ) are, after water, the major components of volcanic arc gases. Understanding their relative abundances (e.g., the CO 2 /S T ratio) in arc volcanic gases is important to constrain origin and recycling efficiency of these volatiles along the subduction factory, and to better constrain the global arc volcanic CO 2 flux. Here, we review currently available information on global variations of volcanic arc CO 2 /S T gas ratios. We analyse a dataset of > 2000 published volcanic arc gas measurements that comprise (i) low-temperature hydrothermal gas emissions, in which S T is dominated by hydrothermal hydrogen sulphide (H 2 S), and (ii) high temperature “magmatic” gases rich in sulphur dioxide (SO 2 ). We show that the global CO 2 /S T population of hydrothermal gases is mainly controlled by S loss to hydrothermal fluids/rocks. We then select a subset of high-temperature (≥ 450 °C) arc gases which, being less affected by S hydrothermal loss, can be used to infer the “deep” source of volatiles. Using a subset of time-averaged high-T gas compositions for 56 arc volcanoes, we identify sizeable along-arc and inter-arc variations in the “magmatic” arc gas CO 2 /S T ratio, which we ascribe to distinct volatile origins in the magma generation/storage zone. In the attempt to resolve the slab vs. crustal contributions to arc gas budgets, we explore the global association between volcanic gas CO 2 /S T ratios and non-volatile (trace elements) tracers in arc magmas. For the first time in a global study, we find evidence for higher carbon output (CO 2 /S T ) in arcs where carbonate sediment subducts on the seafloor. Indeed, most arc volcanoes exhibit gas vs. trace element relationships that are explained by addition of slab-sediment melts ± fluids to the mantle wedge. We also identify a subset of CO 2 -rich arc volcanoes with unusually high CO 2 /S T ratios (Etna, Stromboli, Vulcano Island, Popocatepetl, Soufriere of St Vincent, Bromo and Merapi), which we interpret as the product of magma-limestone interactions in the upper crust. Evidence for this process comes from carbonate xenoliths and/or carbonate basement that characterise these volcanic systems. Although the mean global CO 2 /S T ratio of arc gas (~ 2.5) reflects a predominant source from subducted sediment, limestone-assimilation-derived C may account for a substantial (~ 19–32%) fraction of the present-day global arc budget, and may have contributed to elevated atmospheric CO 2 levels and warmer climate in Earth's past. Our global CO 2 /S T vs. trace element association paves the way to identifying the gas signature of volcanoes (or arc segments) for which gas information is currently missing, and so improve our current global volcanic arc CO 2 flux inventory.

Mud volcanism, or sedimentary volcanism, represents one of the most intriguing phenomena of the Earth's crust, with important implications in energy resource exploration, seismicity, geo-hazard and atmospheric budget of greenhouse gases. Since the first review papers were issued at the beginning of 2000s, a large amount of new geological, geophysical and geochemical data has been acquired, which clarified ambiguous concepts and significantly improved our knowledge of mud volcanism. Here, we offer an updated review of the knowledge and implications of mud volcanoes, with emphasis on: the terminology used to describe different processes and structures; the physical, chemical and morphological characteristics of the several fluid emission structures; the chemical properties of the released fluids, in particular the molecular and isotopic composition of the gas; the mud volcano formation dynamics; and the several implications for petroleum exploration, geo-hazards and global atmospheric methane budget. This review integrates new fluids data collected in Azerbaijan and is complemented with field observations from various mud volcano provinces worldwide. Although the total number of mud volcanoes on Earth is still uncertain, > 600 main onshore structures, with a large variety in shapes and sizes, are documented in recent global data-sets, and several thousand are assumed to exist in the oceans. It is clear that: (a) mud volcanoes are broadly distributed throughout the globe in active margins, compressional zones of accretionary complexes, thrust and overthrust belts, passive margins, deep sedimentary basins related to active plate boundaries, as well as delta regions; (b) they are specifically located in hydrocarbon bearing basins, along anticline axes, strike slips and normal faults, and fault-related folds in Petroleum Systems; (c) they represent a specific category of natural gas/oil seepage manifestation, often related to deep and pressurised reservoirs; (d) the main engine driving mud volcanism is given by a combination of gravitative instability of shales and fluid overpressure build-up, followed by hydrofracturing; (e) hydrocarbons are generally of thermogenic origin, while microbial gas is released in only a few cases. Mud volcanism on other planets (e.g. Mars and Titan), and microbial activity associated with gas seepage represent emerging issues and opportunities for future research. Mazzini, Adriano, and Giuseppe Etiope. "Mud volcanism: an updated review." Earth-science reviews 168 (2017): 81-112. https://doi.org/10.1016/j.earscirev.2017.03.001 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license.

Remote sensing observations and rover missions have documented the presence of playas, salts, and wind erosion landforms of lacustrine sediments on Mars. All of these observations suggest Mars was aqueous in its early history. However, abundant questions remain: How wet was the environment, what were the properties of the liquids and the possibility of ancient habitability, and what kinds of geological processes shaped the present landforms? To explore these unknowns, analogue studies can play a key role. In this contribution, we introduce the Qaidam Basin, Tibetan Plateau, northwestern China as a new and unique analogue site for studying the past aqueous and present arid environments of Mars. The Qaidam Basin, the highest and one of the largest and driest deserts on Earth, is located in a dry, cold, and high UV environment, similar to the surface of Mars. We demonstrate a variety of landforms and also their counterparts on Mars, which include aeolian dunes and yardangs, polygons, gullies, valleys, and fluvial fans. In the Qaidam Basin, various environmental regimes for the formation of linear and asymmetric barchans have been described. Saline lakes and playas representing different stages of lake evolution in arid environment are also present in the Qaidam Basin and provide promising cases for studying the habitability in Mars-like environments. Results for microorganism isolation suggest that halophiles are the most important fraction in the hypersaline sediments and this may shed light on studying present Martian habitability. Moreover, the remote but ready accessibility of the Qaidam Basin make it a potential site for engineering testing in regards to future martin exploration missions. We propose that the variety of exogenic and endogenic geomorphic types, lacustrine sediments, evaporite mineral assemblages and Mars-like extreme environments collectively point to the Qaidam Basin as an optimal

Life requires a wide variety of bioessential trace elements to act as structural components and reactive centers in metalloenzymes. These requirements differ between organisms and have evolved over geological time, likely guided in some part by environmental conditions. Until recently, most of what was understood regarding trace element concentrations in the Precambrian oceans was inferred by extrapolation, geochemical modeling, and/or genomic studies. However, in the past decade, the increasing availability of trace element and isotopic data for sedimentary rocks of all ages has yielded new, and potentially more direct, insights into secular changes in seawater composition – and ultimately the evolution of the marine biosphere. Compiled records of many bioessential trace elements (including Ni, Mo, P, Zn, Co, Cr, Se, and I) provide new insight into how trace element abundance in Earth's ancient oceans may have been linked to biological evolution. Several of these trace elements display redox-sensitive behavior, while others are redox-sensitive but not bioessential (e.g., Cr, U). Their temporal trends in sedimentary archives provide useful constraints on changes in atmosphere-ocean redox conditions that are linked to biological evolution, for example, the activity of oxygen-producing, photosynthetic cyanobacteria. In this review, we summarize available Precambrian trace element proxy data, and discuss how temporal trends in the seawater concentrations of specific trace elements may be linked to the evolution of both simple and complex life. We also examine several biologically relevant and/or redox-sensitive trace elements that have yet to be fully examined in the sedimentary rock record (e.g., Cu, Cd, W) and suggest several directions for future studies.