Lithological Controls Research Articles

Lithologic controls on landscape dynamics and aquatic species evolution in post-orogenic mountains

Determining factors that modify Earth's topography is essential for understanding continental mass and nutrient fluxes, and the evolution and diversity of species. Contrary to the paradigm of slow, steady topographic decay after orogenesis ceases, nearly all ancient mountain belts exhibit evidence of unsteady landscape evolution at large spatial scales. External forcing from uplift from dynamic mantle processes or climate change is commonly invoked to explain the unexpected dynamics of dead orogens, yet direct evidence supporting such inferences is generally lacking. Here I use quantitative analysis of fluvial topography in the southern Appalachian Mountains to show that the exhumation of rocks of variable erosional resistance exerts a fundamental, autogenic control on the evolution of post-orogenic landscapes that continually reshapes river networks. I characterize the spatial pattern of erodibility associated with individual rock-types, and use inverse modeling of river profiles to document a ∼150 m base level fall event at 9 ± 3 Ma in the Upper Tennessee drainage basin. This analysis, combined with existing geological and biological data, demonstrates that base level fall was triggered by capture of the Upper Tennessee River basin by the Lower Tennessee River basin in the Late Miocene. I demonstrate that rock-type triggered changes in river network topology gave rise to the modern Tennessee River system and enhanced erosion rates, changed sediment flux and dispersal patterns, and altered bio-evolutionary pathways in the southeastern U.S.A., a biodiversity hotspot. These findings suggest that variability observed in the stratigraphic, geomorphic, and biologic archives of tectonically quiescent regions does not require external drivers, such as geodynamic or climate forcing, as is typically the interpretation. Rather, my findings lead to a new model of inherently unsteady evolution of ancient mountain landscapes due to the geologic legacy of plate tectonics.

Lithologic controls on hydrologic and geochemical processes in constructed Everglades tree islands

Tree islands have been hypothesized to induce calcite precipitation by concentrating ions in the groundwater through evapotranspiration processes. This research investigates how lithology regulates the hydrologic and geochemical conditions within two types of constructed Everglades tree islands: peat-based and limestone-core surrounded by peat. Three years of hydrochemical and hydrologic data (2013–2015) obtained from the constructed tree islands suggest that under current climatic and managed hydrologic conditions, calcite dissolution is prevalent within the top meter of soil in both types of tree islands. Mass-balance calculations along groundwater flow paths in one peat-based tree island that contained clay at depth, indicated that calcite precipitation is likely 1 m below the soil surface. The lithological characteristics of that peat-based island supported a persistently depressed groundwater table, while tree islands with elevated ratios of peat-to-sand content did not. Limestone-core tree islands also supported a depressed water table, particularly during the dry season. This study determined that the lithology of a set of man-made Everglades tree islands played a primary role in regulating the seasonal fluctuation of the water table and hydrogeochemical processes. Understanding the mechanisms of tree-island formation and maintenance is important for preserving the overall ecosystem function of the freshwater-Everglades.

Geochemical vectors for stratiform Zn-Pb-Ag sulfide and associated dolomite-hosted Cu mineralization at Zinkgruvan, Bergslagen, Sweden

The Zinkgruvan deposit is the largest stratiform Zn-Pb-Ag mineralization in Sweden. The most recent genetic model attributes ore formation to the discharge of oxidized, near-neutral pH, metalliferous brines into a reduced basin, forming laterally extensive, stratiform sulfide mineralization on the seafloor. It has a known strike extent of 5 km and is underlain by a regionally extensive zone of K-altered metavolcanic rock and dolomitic marble, the latter hosting Cu-(Co-Ni) replacement mineralization near the inferred hydrothermal vent to the stratiform sulfides. The deposit is stratigraphically overlain by migmatized, pyrrhotite- and graphite-rich pelite that is in turn overlain by a banded almandine-biotite-quartz-ferrosilite-bearing unit at the base of a regionally extensive metasedimentary succession. These laterally continuous units are interpreted as metamorphosed organic-rich sulfidic mudstone and silicate-dominated Fe formation, respectively.The favorable stratigraphic interval contains anomalously high Zn, Pb, Ag, Cu, K2O/(K2O + Na2O), Mn, Co, Tl, Ba and B relative to adjacent metatuffite. However, only Zn, Pb, Ag, K2O/(K2O + Na2O) and Mn are significantly enriched relative to adjacent strata beyond the known lateral extent of the ore. Elevated copper, Co and Tl only occur in the vent-proximal part of the deposit, whereas anomalous enrichments of Ba and B are sporadic and occur mainly in the stratigraphic footwall. Many elements such as Si, Fe, Mg, Ca and Cs are of limited use in vectoring due to low enrichment factors relative to inferred background compositions and/or strong lithological controls on their distribution.Although ore metal (Zn, Pb and Ag) enrichments are the best quantitative and qualitative guides to ore, K, Mn and Co enrichments also provide corroborative support. The most useful elements for vectoring have been synthesized into exploration indices. The Modified Sedex Metal Index (MSMI; Zn + 3Pb + 100Ag) is a vector towards stratiform Zn-Pb-Ag mineralization, whereas MSMI2 [Zn + 3Pb + 10(Cu + Co)] also allows targeting of proximal Cu mineralization.The banded iron formation and the pyrrhotite- and graphite-rich pelite of the stratigraphic hanging wall are consistently enriched in base metals (e.g. 500–1000 ppm Zn), total S and Mn throughout the entire Zinkgruvan area. However, these units are not known to grade laterally along strata into economic base metal sulfide mineralization, and they are not obviously products of the same hydrothermal system which formed the stratiform Zn-Pb-Ag deposit.In a vent-distal setting, the somewhat spurious metal anomalies of the hanging wall units can be difficult to distinguish from those of the favorable interval. The favorable stratigraphic interval can, however, be recognized by also taking into account that positive Zn anomalies are mainly coincident with positive anomalies in both K and Mn only in the favorable interval. Furthermore, samples from the favorable interval generally have Co/Ni > 1 and display a positive Co/Ni vs. Zn trend, whereas samples of the pyrrhotite- and graphite-rich pelite have Co/Ni < 1 and define a negative Co/Ni vs. Zn trend. Thus, the index (Co/Ni)*Zn allows easy detection of weak Zn anomalies associated with the stratiform Zn-Pb-Ag mineralization.

Lithological controls on light penetration into rock surfaces – Implications for OSL and IRSL surface exposure dating

Luminescence surface exposure dating is a newly developed geochronological technique that allows the age of geological or archaeological rock surfaces to be accurately constrained. This dating method requires measuring and calibrating the depth-dependent luminescence signal below an exposed surface and relies on the assumption that neither the shape of the daylight spectrum nor the light attenuation change significantly with depth into the rock. However, lithologies with mm-scale heterogeneity in their mineral distribution or those lacking high sensitivity quartz present a challenge, partly because light attenuation with depth is not necessarily constant in such samples. Addressing these challenges is important for further development of the luminescence surface exposure dating technique.Here we investigate the shape of luminescence-depth profiles in lithologies revealing complex fabrics such as coarse-grained granitic gneisses or gneisses with distinct planar metamorphic layering. We also present luminescence-depth profiles from quartzite, a lithology that appears – at first glance – highly homogenous. We find that the spatial distribution of opaque mineral phases in the metamorphic samples and precipitation of iron hydroxides in the quartzite strongly influence the 3-dimensional transparency and, consequently, the light attenuation with depth, and are the main cause for the observed scatter in the OSL- and IRSL-depth profiles in our samples. The data suggest that for rocks of heterogeneous lithology (i) close petrographic analysis of luminescence-depth profiles are required to ensure that the cores used for calibration have similar mineralogical composition (and thus light attenuation with depth) to those used to calculate a luminescence rock surface exposure age, and that (ii) RGB depth profiles appear to provide a useful semi-quantitative tool for such analysis.

Cu-Au mineralisation in the Curnamona Province, South Australia: A hybrid stratiform genetic model for Mesoproterozoic IOCG systems in Australia

The Proterozoic Curnamona Province lies between two of the most endowed Cu-bearing mineral belts on the Australian continent – the Gawler Craton, which hosts the giant Olympic Dam iron oxide copper gold (IOCG) system, and the Mount Isa Inlier, which hosts the giant Mount Isa Cu system and IOCG belt of the Eastern Succession. This study focuses on Cu-Au deposits within the Proterozoic rocks of the Benagerie Ridge Magnetic Complex in the central Curnamona Province. The Benagerie Ridge is buried beneath Neoproterozoic and Phanerozoic cover sequences. We use drillcore and geophysical data to determine the structural architecture and structural controls of Cu-Au mineralisation in the Benagerie Ridge. The Portia and North Portia deposits are the most significant Cu-Au mineral deposits in the Benagerie Ridge and lie adjacent to an extensive regional redox boundary that separates lower magnetic units from upper non-magnetic units. The redox boundary is extensive throughout the Curnamona Province and is linked with mineralisation in the region. Significant chalcopyrite, bornite and molybdenite occur along bedding-parallel layers and shear structures. These factors support a strong lithological control on Cu-Au mineralisation at all scales. Deformation in the Benagerie Ridge involved the development of a D1 layer-parallel foliation (S1), which is overprinted by D2 recumbent folds and D3 upright folds. The deformation history is associated with the c. 1610–1580 Ma Olarian Orogeny. Overprinting of D2 structures during D3 has resulted in a type 2 interference pattern, which we have successfully mapped using aeromagnetic data. Several later phases of post-Olarian faults overprint F2 and F3 fold interference patterns, and have resulted in the remobilisation of some of the Cu-Au mineralisation. We propose that the stratiform Cu-Au mineralisation occurred prior to the onset of the Olarian Orogeny. Mineralisation is preserved within the thickened hinge zone of a similar-type F2 fold proximal to the hinge of an overprinting F3 fold, which we propose has enhanced mineralisation within the North Portia deposit. Consequently the identification of the redox boundary within F2 folds elsewhere in the Curnamona Province – particularly when located proximal to F3 fold hinges, which place the mineralised zones into structurally favourable locations – provide good targets for future mineral exploration.

Lithologic control of frictional strength variations in subduction zone sediment inputs

Lithologic control of frictional strength variations in subduction zone sediment inputs

Geochronological and geochemical study of the Baixintan magmatic Ni-Cu sulphide deposit: New implications for the exploration potential in the western part of the East Tianshan nickel belt (NW China)

Several newly discovered magmatic Ni-Cu sulphide deposits are located in the East Tianshan nickel belt in the southern part of the Central Asian Orogenic Belt in NW China. The Baixintan magmatic sulphide deposit is one of these new discoveries. The host mafic-ultramafic intrusion of the Baixintan deposit is composed of plagioclase-bearing lherzolite, Pl-bearing olivine websterite, olivine norite and gabbro. Zircon crystals from olivine norite yielded a U-Pb age of 286.0 ± 1.6 Ma, similar to the ages of other magmatic Ni-Cu sulphide ore deposits in this belt. Disseminated sulphide mineralization is present in olivine-bearing rocks. The Fo and Ni contents of olivine crystals from the sulphide-barren samples vary from 81.7 to 85.6 mol% and from 956 to 2837 ppm, respectively, exhibiting a positive Fo-Ni correlation that is consistent with the fractional crystallization of olivine plus removal of small amounts of immiscible sulphide liquid. The Baixintan mafic-ultramafic rocks are characterized by light REE enrichment, pronounced negative Nb–Ta anomalies, low initial 87Sr/86Sr ratios from 0.7035 to 0.7039, positive εNd(CHUR, 286 Ma) values from 6.0 to 7.4 and zircon εHf(CHUR, 286 Ma) values from +11.6 to +15.8. These data indicate that the parental magmas were derived from a depleted mantle source with moderate degrees of contamination by the upper crust. The variations in PGE tenor in the Baixintan deposit, which are characterized by positive correlations between IPGE and PPGE, can be explained by variable R factors (R = 400–3000). Mass balance calculations indicate that the parental magma was severely depleted in PGE, which could be likely due to prior sulphide segregation at depth or sulphide retention in the mantle during partial melting. Both fractional crystallization and crustal contamination may have played a role in triggering second stage sulphide saturation in the Baixintan magma. The similarities in ages, lithological controls and bulk sulphide composition between the Baixintan deposit and other known magmatic Ni-Cu sulphide ore deposits in the East Tianshan nickel belt encourage further exploration in the Baixintan mafic-ultramafic intrusion, as well as expansion of the on-going regional Ni exploration program.

Tectonic and lithologic control over landslide activity within the Larji–Kullu Tectonic Window in the Higher Himalayas of India

The purpose of this study is to analyze and characterize recent landslide events in the Larji–Kullu Tectonic Window (LKTW), and to establish a relationship between the tectonic and lithologic characters of the terrain and the landslides activity. Using multispectral satellite image analysis with selected field investigation, a landslide occurrence database has been generated for the period between 1984 and 2015. To decipher the accelerated occurrences of landslides in the region, an integrated study is undertaken in the Kullu (also known as Kulu) valley of Beas River basin within the LKTW complex, to analyze the litho-structural and terrain slope interactions using morpho-tectonic parameters such as Topographic/Bedding Plane Interaction Angle (TOBIA) index, terrain surface roughness index and lithological competency analysis. A prominent clustering of landslides is observed in the north of Sainj River, contained within the tectonic window. Major sites of landslides are found to be located in the intensely fractured Manikaran Quartzite occurring within the core of the LKTW. The landslides are mostly associated with southern and southwestern-facing slopes and activations are pronounced in the ‘Orthoclinal’ slope class with gradient of 37°–48°. Thematic maps, e.g., geological, structural, geomorphological, slope and slope-aspect maps are generated and considered together to understand the morpho-tectonic scenario of the tectonic window. Observations from the above-stated thematic maps along with the occurrences of moderate magnitude earthquake epicenters helped to infer neotectonic movements along the Sainj River fault. Tectonic upliftment of the northern bank of the Sainj River along with increased precipitation through decades has resulted in recurrent landslides within the LKTW.

Lithological controls on hillslope sediment supply: insights from landslide activity and grain size distributions

AbstractThe volumes, rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems. Moreover, hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations. However, there are very few detailed field studies characterizing hillslope sediment supply as a function of lithology and delivery process. Here, we present new empirical data from tectonically‐active areas in southern Italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes. Landslides are the major source of hillslope sediment supply in this area, and our inventory of ~2800 landslides reveals that landslide sediment flux is dominated by small, shallow landslides. We find that lithology and rock strength modulate the abundance of steep slopes and landslides, and the distribution of landslide sizes. Outcrop‐scale rock strength also controls the grain sizes supplied by bedrock weathering, and influences the degree of coarsening of landslide supply with respect to weathering supply. Finally, we show that hillslope sediment supply largely determines the grain sizes of fluvial export, from catchments and that catchments with greater long‐term landslide rates deliver coarser material. Therefore, our results demonstrate a dual control of lithology on hillslope sediment supply, by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Geochemistry of sediments of the Peninsular rivers of the Ganga basin and its implication to weathering, sedimentary processes and provenance

Abstract Geochemistry of the Himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate. Among the Himalayan rivers, the Ganga and its Himalayan catchment have been studied extensively. However, the Peninsular rivers constituting a significant part of the Ganga basin have not received much attention, heretofore. In the present geochemical study of the Peninsular river's sediments, we have found that the initial chemical weathering of rocks in the catchment produces texturally, mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine-grained suspended sediments. The overbank sediments possess an intermediate texture and geochemistry, but more towards the suspended sediments. The sediment geochemistry data indicates that the Peninsular river's sediments show an increase in the weathering intensity from the west (Banas river) to the east (Son river) along the climate gradient, i.e., from the arid-semiarid to the sub-tropical condition. The higher chemical index of alteration (CIA) values of the Peninsular river's sediments than the Yamuna and Ganga river sediments reflect the control of weatherable lithology in the tectonically stable, low relief and subtropical climate condition. The Yamuna and Ganga river sediments with lower CIA values show more physical weathering in the tectonically active Himalaya. The suspended and overbank sediments of the Yamuna and Ganga rivers show an increase in their CIA values after the confluence of the Peninsular rivers, indicating the contribution of more weathered materials by the Peninsular rivers. It has been found that there is a geochemical split between the channel and suspended sediments of the Peninsular rivers for sharing different sources, i.e., the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments. The weathering geochemistry, trace element systematics, and REE patterns suggest that the dominant sources of the channel sediments of the Peninsular rivers are the felsic crystallines and sedimentary lithologies of the Aravalli range, Bundelkhand and Chhotanagpur granite and gneisses, and Vindhyan sandstones. Whereas, the mafic lithologies such as the Deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments. Within the range of intermediate composition, the overbank sediment chemistry reflects more contribution of the mafic sources except for the Ken which shows a higher contribution of the felsic sources. The geochemical split between the channel and suspended sediments of the Peninsular river's sediments for the different provenances indicates differential weathering of the Deccan basalts, Bundelkhand crystalline, and Vindhyan sedimentary rocks; and also the hydrodynamic control of the Peninsular rivers during erosion, transport, and deposition. However, the Himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the Himalayan catchment.

Controls on Mississippi Valley-Type Zn-Pb mineralization in Behabad district, Central Iran: Constraints from spatial and numerical analyses

The Behabad district, located in the central Iranian microcontinent, contains numerous epigenetic stratabound carbonate-hosted Zn-Pb ore bodies. The mineralizations formed as fault, fracture and karst fillings in the Permian-Triassic formations, especially in Middle Triassic dolostones, and comprise mainly non-sulfides zinc ores. These are all interpreted as Mississippi Valley-type (MVT) base metal deposits. From an economic geological point of view, it is imperative to recognize the processes that have plausibly controlled the emplacement of MVT Zn-Pb mineralization in the Behabad district. To address the foregoing issue, analyses of the spatial distribution of mineral deposits comprising fry and fractal techniques and analysis of the spatial association of mineral deposits with geological features using distance distribution analysis were applied to assess the regional-scale processes that could have operated in the distribution of MVT Zn-Pb deposits in the district. The obtained results based on these analytical techniques show the main trends of the occurrences are NW–SE and NE-SW, which are parallel or subparallel to the major northwest and northeast trending faults, supporting the idea that these particular faults could have acted as the main conduits for transport of mineral-bearing fluids. The results of these analyses also suggest that Permian-Triassic brittle carbonate sedimentary rocks have served as the lithological controls on MVT mineralization in the Behabad district as they are spatially and temporally associated with mineralization.

The Three Gorges Area and the Linking of the Upper and Middle Reaches of the Yangtze River

The history of the Yangtze River is constituted by numerous river piracies that enabled the river to extend its drainage system. Two river captures are well recognized: the piracy of the Jinsha River (Jinshajiang) formerly tributary of the Red River at Shigu in Yunnan Province and the Three Gorges area that linked the upper and the middle Yangtze river reaches in Hubei province. The first one is well documented, while the second, because of difficulties to retrieve datable materials and the complexity of the area geomorphology, is still quite unknown. Numerous conflicting hypotheses have been formulated to explain the pattern of river piracy, no agreement exists on the location of the drainage divide and of the point of capture; chronologies extending from the Eocene to the late Quaternary are given. Geomorphic indices can be used to examine the geomorphological and tectonic processes responsible for the development of the drainage basins. In this paper, we analyzed drainage pattern, basin shape, basin asymmetry, stream junction angle to infer the drainage of the paleorivers that were pirated, and to propose a model of the pattern of river capture based on the importance of structure, tectonic and lithological controls in the area. We showed that the Three Gorges area has been very important to the history of the Yangtze river as the piracy of the upper and middle reaches enabled the river to reach its current extend.

Badass gullies: Fluvio-mass-movement gully complexes in New Zealand's East Coast region, and potential for remediation

This paper reviews gully erosion in the East Coast region of New Zealand's North Island and conceptualises fluvio-mass-movement gully complexes as badass gully systems. Tectonic setting and lithological control, with steep slopes and a climate influenced by tropical cyclones, predispose hill country in the East Coast region to gully erosion. The clearance of indigenous forest since the late 1800s has dramatically increased catchment erosion and paved the way for development of large-scale fluvio-mass-movement gully complexes. These features are a composite of fluvial and mass movement processes. They are conceptualised as ‘badass’ by not conforming to any existing gully model and by generating disproportionate results in East Coast catchment sediment cascades. Their remediation is discussed, but their nature means that prevention is better than a cure.

Auriferous shear zones in the central Allaqi-Heiani belt: Orogenic gold in post-accretionary structures, SE Egypt

The East-West Gondwana collision (0.75–0.5 Ga), by oblique convergence, was likely accompanied by high hydrothermal fluid flux and dispersed orogenic gold in the Arabian-Nubian Shield. Gold-bearing quartz veins along steep-dipping shear zones bordering or cutting through the ophiolitic and island arc rocks in the central Allaqi-Heiani belt in Wadi Defeit area deserved the interest of ancient miners. Field and remote sensing data revealed the structural and lithological controls of gold-bearing quartz veins, providing means of exploration for new targets in the larger Wadi Allaqi environ. The auriferous shear zones are attributed to D3 (a non-coaxial continuation of early NE-SW compression regime), and D4 (slip reactivation by E-W compression and transcurrent deformation). Microscopic investigations of quartz veins reveal the association of gold blebs and specks with fissure-filling galena-spahlerite-tetrahedrite assemblage and deformed Fe-As-sulfides (pyrite and arsenopyrite). As a gold-only province with abundant, variably deformed and carbonated metabasic rocks, metamorphic devolatilization is suggested to explain the discrete gold occurrences by fluid focusing in complex shear intersections. The available fluid inclusion data affirm the low salinity aqueous-carbonic composition of the ore fluids and mesothermal conditions of ore deposition, consistent with metamorphic devolatilization. Structures related to late ductile deformation in the post-accretionary stages of the evolution of the shield are, therefore, considered high priority zones for future exploration programs.

Estimating Belowground Carbon Stocks in Isolated Wetlands of the Northern Everglades Watershed, Central Florida, Using Ground Penetrating Radar and Aerial Imagery

AbstractPeat soils store a large fraction of the global soil carbon (C) pool and comprise 95% of wetland C stocks. While isolated freshwater wetlands in temperate and tropical biomes account for more than 20% of the global peatland C stock, most studies of wetland soil C have occurred in expansive peatlands in northern boreal and subarctic biomes. Furthermore, the contribution of small depressional wetlands in comparison to larger wetland systems in these environments is very uncertain. Given the fact that these wetlands are numerous and variable in terms of their internal geometry, innovative methods are needed for properly estimating belowground C stocks and their overall C contribution to the landscape. In this study, we use a combination of ground penetrating radar (GPR), aerial imagery, and direct measurements (coring) in conjunction with C core analysis to develop a relation between C stock and surface area, and estimate the contribution of subtropical depressional wetlands to the total C stock of pine flatwoods at the Disney Wilderness Preserve (DWP), Florida. Additionally, GPR surveys were able to image collapse structures underneath the peat basin of depressional wetlands, depicting lithological controls on the formation of depressional wetlands at the DWP. Results indicate the importance of depressional wetlands as critical contributors to the landscape C budget at the DWP and the potential of GPR‐based approaches for (1) rapidly and noninvasively estimating the contribution of depressional wetlands to regional C stocks and (2) evaluating the formational processes of depressional wetlands.

Neotectonic control on drainage systems: GIS-based geomorphometric and morphotectonic assessment for Crete, Greece

Geomorphic indices can be used to examine the geomorphological and tectonic processes responsible for the development of the drainage basins. Such indices can be dependent on tectonics, erosional processes and other factors that control the morphology of the landforms. The inter-relationships between geomorphic indices can determine the influence of regional tectonic activity in the shape development of drainage basins. A Multi-Criteria Decision Analysis (MCDA) procedure has been used to perform an integrated cluster analysis that highlights information associated with the dominant regional tectonic activity. Factor Analysis (FA) and Analytical Hierarchy Process (AHP) were considered within that procedure, producing a representation of the distributed regional tectonic activity of the drainage basins studied. The study area is western Crete, located in the outer fore-arc of the Hellenic subduction zone, one of the world's most tectonically active regions. The results indicate that in the landscape evolution of the study area (especially the western basins) tectonic controls dominate over lithological controls.

Lithological control on fracture cementation in the Keuper Marl (Triassic), north Somerset, UK

AbstractThe spatial arrangement of gypsum veins as preserved natural hydraulic fractures have been characterized in the Triassic Keuper Marl Formation (UK), a caprock for hydrocarbon reservoirs and CO2sequestration. The marls cropping out are subdivided into five discrete fracture units based on the presence and abundance of gypsum veins. The nodular gypsum in evaporite horizons provides excess gypsum for nodule-rooted horizontal gypsum veins. Our petrographic observations demonstrate that the development of gypsum veins in beds lacking macroscopic evaporites is closely associated with disseminated gypsum cement in the marls. We interpret that the gypsum veins in marl are sourced from disseminated gypsum cements in the host rocks, based on stratigraphic correlations, and much lower Sr concentrations than gypsum nodules. Gypsum was transported to adjacent veins mainly through diffusion in the low-permeability marls. The localization of gypsum veins and varied Sr concentrations of veins and nodules indicate that the diagenetic fluids are a mix of connate water with meteoric water rather than brines transported from evaporite beds along faults to non-evaporite beds. This results in the absence of gypsum fillings in fractures in rocks without primary gypsum cements. The study implies that the cementation of natural fractures in low-permeability rocks can highly depend on the presence of cement minerals in the host rock.

Multiband PSInSAR and long-period monitoring of land subsidence in a strategic detrital aquifer (Vega de Granada, SE Spain): An approach to support management decisions

This work integrates detailed geological and hydrogeological information with PSI data to obtain a better understanding of subsidence processes detected in the detrital aquifer of the Vega de Granada (SE Spain) during the past 13years. Ground motion was monitored by exploiting SAR images from the ENVISAT (2003–2009), Cosmo-SkyMed (2011–2014) and Sentinel-1A (2015–2016) satellites. PSInSAR results show an inelastic deformation in the aquifer and small land surface displacements (up to −55mm). The most widespread land subsidence is detected during the ENVISAT period (2003–2009), which coincided with a long, dry period in the region. The highest displacement rates recorded during this period (up to 10mm/yr) were detected in the central part of the aquifer, where many villages are located. For this period, there is a good correlation between groundwater level depletion and the augmentation of the average subsidence velocity and slight hydraulic head changes (<2m) have a rapid ground motion response. The Cosmo-SkyMed period (2011–2014) coincided with a rainy period, and the land subsidence is only concentrated in some points. Rates of average subsidence up to 11.5mm/yr are obtained for this period and are anthropogenic in origin, being related to earthmoving works. During the Sentinel-1A monitoring period (2015–2016) most of the region showed no deformation, except for some points of unknown origin in the NE sector. A general conclusion is that there is a clear lithological control in the spatial distribution of ground subsidence; all the subsiding areas detected are located where a higher clay content was identified. Although the SE sector of the aquifer had more intense groundwater exploitation, no land subsidence processes were detected, as coarse-grained sediments predominate in the substratum. This research will contribute to the drawing-up of a management plan for the sustainable use of this strategic aquifer, taking into account critical levels of groundwater depletion to avoid land subsidence in the areas identified as vulnerable. The European Space Agency satellite Sentinel-1A could be an effective decision-making tool in the near future.

Cryo-conditioned rocky coast systems: A case study from Wilczekodden, Svalbard

This paper presents the results of an investigation into the processes controlling development of a cryo-conditioned rock coast system in Hornsund, Svalbard. A suite of nested geomorphological and geophysical methods have been applied to characterise the functioning of rock cliffs and shore platforms influenced by lithological control and geomorphic processes driven by polar coast environments. Electrical resistivity tomography (ERT) surveys have been used to investigate permafrost control on rock coast dynamics and reveal the strong interaction with marine processes in High Arctic coastal settings. Schmidt hammer rock tests, demonstrated strong spatial control on the degree of rock weathering (rock strength) along High Arctic rock coasts. Elevation controlled geomorphic zones are identified and linked to distinct processes and mechanisms, transitioning from peak hardness values at the ice foot through the wave and storm dominated scour zones to the lowest values on the cliff tops, where the effects of periglacial weathering dominate. Observations of rock surface change using a traversing micro-erosion meter (TMEM) indicate that significant changes in erosion rates occur at the junction between the shore platform and the cliff toe, where rock erosion is facilitated by frequent wetting and drying and operation of nivation and sea ice processes (formation and melting of snow patches and icefoot complexes). The results are synthesised to propose a new conceptual model of High Arctic rock coast systems, with the aim of contributing towards a unifying concept of cold region landscape evolution and providing direction for future research regarding the state of polar rock coasts.

Conodont characteristic of the Lochkovian-Pragian boundary interval in the Mindigulovo section (western slope of the Southern Urals)

Conodonts from the Sherlubay (upper Lochkovian) and Kulamat (lower Pragian) Horizons of the Mindigulovo section (western slope of the Southern Urals) were studied in detail. The conodont sequence can be globally correlated. The sequence contains important cosmopolitan taxa. The taxon index of the global zone gilberti was discovered at the top of the Sherlubay Horizon. Overlying Kulamat Horizon in the lower Pragian is characterised by the proliferation of typical species of the irregularis Zone in addition to the taxon index. Almost all characteristic Lochkovian species completely disappear. The observed successive morphological changes in Masaraella pandora: Mas. pandora morphotype alpha → Mas. pandora morphotype beta → Mas. pandora cf. morphotype zeta and Eognathodus: Eognathodus cf. irregularis → Gondwania cf. profunda are close to the development of Masaraella pandora → Eognathodus phyletic lineage, proposed by Murphy (2005). In the revealed evolutionary lineage of Mas. pandora–Eognathodus, the starting of eognathodontid from Mas. pandora is a biostratigraphical criterion for the establishment of the Lohkovian/Pragian boundary, along with lithological and macrofaunal control. Together with the deep-sea eognatodontid fauna, another index taxa as Caudicriodus steinachensis morphotype eta and Pelekysgnathus cf. serratus brunsvicensis of the alternative scale (Slavik 2004; Slavik et al. 2007) were recorded. The parallel presence of shallow-water icriodontid and deep-water eognathodontid biofacies at the lower part of Kulamat Horizon of the Pragian sediments in the Southern Urals is relevant for interregional correlations.