Clay mineral variations in Holocene terrestrial sediments from the Indus Basin

We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.     

Kaolinite and smectite dissolution rate in high molar KOH solutions at 35° and 80°C

Experiments measuring kaolinite and smectite dissolution rates were carried out using batch reactors at 35° and 80°C. No potential catalysts or inhibitors were present in solution. Each reactor was charged with 1 g of clay of the ≤2 μm fraction and 80, 160 or 240 ml of 0.1–4 M KOH solution. An untreated but sized kaolinite from St. Austell and two treated industrial smectites were used in the experiments. One smectite is a nearly pure montmorillonite, while the second has a significant component of beidellitic charge (35%). The change in solution composition and mineralogy was monitored as a function of time. Initially, the 3 clays dissolved congruently. No new formed phases were observed by XRD and SEM during the pure dissolution stage. The kaolinite dissolution is characterized by a linear release of silica and Al as a function of the log of time. This relationship can be explained by a reaction affinity effect which is controlled by the octahedral layer dissolution. Far from equilibrium, dissolution rates are proportional to a^0.56±0.12_OH⁻ at 35°C and to a^0.81±0.12_OH⁻ at 80°C. The activation energy of kaolinite dissolution increases from 33±8 kJ/mol in 0.1 M KOH solutions to 51±8 kJ/mol in 3 M KOH solutions. In contrast to kaolinite, the smectites dissolve at much lower rates and independently of the aqueous silica or Al concentrations. The proportionality of the smectite dissolution rate constant at 35 and 80°C was a^0.15±0.06_OH⁻. The activation energy of dissolution appears to be independent of pH for smectite and is found to be 52±4 kJ/mol. The differences in behavior between the two kinds of minerals can be explained by structural differences. The hydrolysis of the tetrahedral and the octahedral layer appears as parallel reactions for kaolinite dissolution and as serial reactions for smectite dissolution. The rate limiting step is the dissolution of the octahedral layer in the case of kaolinite, and the tetrahedral layer in the case of smectite.     

Inorganic,isotopic, and organic composition of high-chloride water from wells in a coastal southern California aquifer

Chloride concentrations were as high as 230 mg/L in water from the surface discharge of long-screened production wells in Pleasant Valley, Calif., about 100 km NW of Los Angeles. Wells with the higher Cl⁻ concentrations were near faults that bound the valley. Depending on well construction, high-Cl⁻water from different sources may enter a well at different depths. For example, Cl⁻ concentration in the upper part of some wells completed in overlying aquifers influenced by irrigation return were as high as 220 mg/L, and Cl⁻ concentrations in water sampled within wells at depths greater than 450 m were as high as 500 mg/L. These high-Cl⁻ waters mix within the well during pumping and produce the water sampled at the surface discharge. Changes in the major ion, minor ion, trace element, and δ³⁴S and δ¹³C isotopic composition of water in wells with depth were consistent with changes resulting from SO₄ reduction, precipitation of calcite, and cation exchange. The chemical and isotopic composition of high-Cl⁻ water from deep wells trends towards the composition of oil-field production water from the study area. Chloride concentrations in oil-field production water present at depths 150 m beneath freshwater aquifers were 2200 mg/L, and Cl⁻ concentrations in underlying marine rock were as high as 4400 mg/L. High-Cl⁻ concentrations in water from deeper parts of wells were associated with dissolved organic C composed primarily of hydrophobic neutral compounds believed to be similar to those associated with petroleum in underlying deposits. These compounds would not be apparent using traditional sampling techniques and would not be detected using analytical methods intended to measure contamination.     

Sedimentation history of the northern North Sea Margin during the last 150 ka

The Norwegian Channel Ice Stream (NCIS) is one the defining features of the Fennoscandian icesheet. Still little is known of the detailed dynamics of this ice stream in relation to regional changes in ice cover, paleoceanographic and climatic changes. Sedimentological data from core MD99-2283 in combination with seismic data allow a detailed chronological reconstruction of the outbuilding of the margin and the ice extent in southern Scandinavia through the last 150 ka. An integrated stratigraphy of the margin is presented and compared to the glacial history. Changes in the regional ice cover are reflected in the accumulation rates, the clay mineralogy, the coarse chalk fraction and the number of IRD >2 mm in core MD99-2283, while the sedimentation on the North Sea Fan as derived from seismic data provides direct evidence for the glacial activity at the shelf edge. Tentative evidence was found for two Early Weichselian glacial advances in southern Scandinavia and possibly Scotland at around 110 and 80 ka BP. From 42 cal ka BP the ice cover expanded in southern Fennoscandia and led to increased deposition on the margin and the occurrence of local melt water outbursts. Significantly increased accumulation rates, coarse chalk, local meltwater output and smectite occur during the ice expansion in the North Sea from around 34 cal ka BP. The main outbuilding phase of the NSF during the last glacial cycle occurred after 30 cal ka BP. From around 24 cal ka BP the NCIS became highly active and advanced at least three times prior to the final retreat from the shelf edge around 19.0 cal ka BP.     

Hydrogeology of Al-Lith Sabkha,Saudi Arabia

In Saudi Arabia, coastal sabkhas cover extensive areas along the coasts of the Red Sea and Arabian Gulf in addition to the continental sabkhas scattered in many places inland. Al-Lith sabkha is one of the typical coastal sabkhas located along the Red Sea coast. Sabkhas, in general, pose a number of geotechnical problems and need to be carefully investigated before being urbanized.A generalized geologic section in Al-Lith sabkha indicates a salty crust at the surface followed by yellowish brown silt and silty sand, olive gray silt and sandy silt and bottomed by coralline reefal limestone. Within this succession, there are several isolated lenticular bodies of sandy silt, silty sand and shelly silty sand. The clay minerals constituting the fine-grained portion of the soil are, in decreasing order, kaolinite, illite and montmorillonite in addition to minor chlorite.The depth to groundwater in 17 observation wells ranged from 0.18 to 1.81 m with a maximum fluctuation of 0.60 m between summer and winter. The permeability of the top silt layer was found to be very low with an average of 5.4×10⁻⁴ m/day. A pumping test was performed in a deep well penetrating the coralline limestone. The measured permeability is 1.1×10² m/day and the estimated storage coefficient is 4×10⁻⁵.Soil water evaporation was measured using a lysimeter constructed with undisturbed soil samples having different depths to the water level. The rate of evaporation ranges from 2.8 to 27.8 ml/day decreasing with an increase in depth to the water level.Groundwater samples were analyzed for their major anions and cations. Salt concentrations show a general increase toward the sea except for the calcium and carbonates that show a landward increase. The groundwater could be classified as a Cl+SO₄ brine. The salinity of the groundwater was determined at different depths in the pumping well and was found to be low in the top 4 m. It sharply increases until it reaches a value approximately 10 times the salinity of the top layer indicating groundwater intermixing with freshwater and salt-water intrusion. The change in the salinity during pumping was erratic but within a range of 2%.     

Quantitative analysis of the clay minerals in the Shurijeh Reservoir Formation using combined X-ray analytical techniques

The Shurijeh Reservoir Formation of Neocomian age is represented by a sandstone sequence, occasionally interbedded with shale, in the Gonbadli gas field, Kopet-Dagh Basin, Northeastern Iran. In this study X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques were used together to characterize the Shuirjeh clay minerals in 76 core samples collected from two deep Gonbadli wells. The results of XRF analysis showed high percentages of silicon and moderate to low percentages of aluminum, sulfur, calcium, potassium, sodium, magnesium, and iron in both wells. The XRD analysis indicated that the above elements were concentrated in the form of quartz, anhydrite, dolomite, calcite, plagioclase, K-feldspar, hematite, and clay minerals. Further XRD examination of the clay fraction revealed that illite, chlorite, and kaolinite were the major types of clay minerals. Unlike, glauconite, smectite, and a mixed layer clays of both the illite–smectite and chlorite–smectite types were observed only in very few samples. The percentages of individual clay minerals were determined using external standard calibration curves and successfully validated by a system of simultaneous linear equations acquired from detailed elemental information based on the XRF analysis. The error reached ± 5% for the main mineral constituent and ± 15% for minor minerals. A local regression relationship was also derived, based on the XRF elemental information, which can be used to estimate the clay contents of other Shurijeh drilled wells with data of pulsed-neutron spectroscopy tools. According to the proposed quantitative approach, the amount of illite varied considerably, reaching 18.3%. In contrast, the amounts of kaolinite and chlorite were generally small, i.e., less than 8.4%. The amount of total clay minerals changed greatly from a minimum of 5% to a maximum of 32.5%. An increase in illite with increasing burial depth and temperature was an obvious indication of deep burial diagenesis in this formation.     

Geophysical,magmatic, and metallogenic manifestations of a mantle plume in the upper reaches of the Aldan and Amur Rivers

Gravity models of the crust and upper mantle to a depth of 100 km are analyzed to study structural relationships of tectonic and tectonophysical media of different rigidities with the distribution of shallow ore deposits above the Aldan-Zeya plume. The spatial correlation of ore clusters and districts with high crustal viscosity inhomoheneities at depths of 10, 20, and 35 km shows distinct stepwise behavior. On the other hand, media of decreased viscosity are observed in the lower crust (at depths of 25–30 km), subcrustal (40–50 km) layers, and asthenosphere (at a depth below 70 km). They are related to chambers of the complete or partial melting (heat sources) of magmatic and ore occurrences near the Earth’s surface. Lateral metallogenic zoning in the spatial distribution of the ore deposits is due to the spread and redistribution of magmas and ore-forming fluids, shielded by rigid plates in the lower crust. A naturally determined series of ore parageneses is observed from center to flanks of the plume: Au, Mo → Au, Ag, Pb, Zn → Au, Pb, Zn → Au, W → Au, Sb → W, Sn → Sn. The mutual position of the tectonomagmatic structures of different ranks within the plume head obeys hierarchical and fractal laws.     

A magnetic and gravity investigation of the Liberia Basin,West Africa

Gravity and magnetic analysis provide an opportunity to deduce and understand to a large extent the stratigraphy, structure and shape of the substructure. Euler deconvolution is a useful tool for providing estimates of the localities and depth of magnetic and gravity sources. Wavelet analysis is an interesting tool for filtering and improving geophysical data. The application of these two methods to gravity and magnetic data of the Liberia Basin enable the definition of the geometry and depth of the subsurface geologic structures. The study reveals the basin is sub-divided and the depth to basement of the basin structure ranges from about 5 km at its North West end to 10 km at its broadest section eastward. Magnetic data analysis indicates shallow intrusives ranging from a depth of 0.09 km to 0.42 km with an average depth of 0.25 km along the margin. Other intrusives can be found at average depths of 0.6 km and 1.7 km respectively within the confines of the basin. An analysis of the gravity data indicated deep faults intersecting the transform zone.     

Genetic implications of a retransported loess profile near Córdoba,Argentina

This paper deals with a loess profile located southeast of Córdoba (64° 05′ 30 W to 31°30′ S) that was dated in Beijing University using the OSL method according to Simple Aliquot Regeneration Protocol. This study provides some inferences regarding climatic and environmental features, such as transport agents and probable sources of the materials.The profile, located inside Llanura Pampeana, is approximately 6.80 m in depth and comprises ages between 22.4 ± 3.2 and 9.9 ± 0.3 ka. Throughout the profile, and for all grain sizes, major minerals are quartz and feldspar, with micas, and opaques as subordinates. Illite and chlorite appear as traces, though the last one was not confirmed in the finest fraction analysis. Calcite is abundant in the uppermost sample and decreases downwards. In the base of the profile, and in the clay fraction, XRD showed illite, swellable clay minerals (smectite + mixed layers) and kaolinite traces. It was concluded that the profile would have been derived from the accumulation of sediments, along several events very similar in transport conditions, even though there are some indications that about 21 ka BP, water availability was slightly smaller than for the rest of the profile. This change was also established in some other places, allowing some regional correlations. According to the analyzed data, about 19 ka BP, water availability again increased.     

High-Al and high-Cr podiform chromitites from the western Yarlung-Zangbo suture zone,Tibet: Implications from mineralogy and geochemistry of chromian spinel,and platinum-group elements

On the basis of their mineral chemistry, podiform chromitites are divided into high-Al (Cr# = 20–60) (Cr# = 100 1 Cr/(Cr + Al)) and high-Cr (Cr# = 60–80) varieties. Typically, only one type occurs in a given peridotite massif, although some ophiolites contain several massifs that can have different chromitite compositions. We report here the occurrence of both high-Cr and high-Al chromitite in a single massif in China, the Dongbo mafic-ultramafic body in the western Yarlung-Zangbo suture zone of Tibet. This massif consists mainly of mantle peridotites, with lesser pyroxenite and gabbro. The mantle peridotites are mainly composed of harzburgites and minor lherzolites; a few dike-like bodies of dunite are also present. Seven small, lenticular bodies of chromitite ores have been found in the harzburgites, with ore textures ranging from massive through disseminated to sparsely disseminated; no nodular ore has been observed. Individual chromitite pods are 1–3 m long, 0.2–2 m wide and strike NW, parallel to the main trend of the peridotites. Chromitite pods 3, 4, and 5 consist of high-Al chromitite (Cr# = 12–47), whereas pods 1 and 2 are high-Cr varieties (Cr# = 73 to 77). In addition to chromian spinel, all of the pods contain minor olivine, amphibole and serpentine. Mineral structures show that the peridotites experienced plastic deformation and partial melting. The mineralogy and geochemistry of the Dongbo peridotites suggest that they formed originally at a mid-ocean ridge (MOR), and were later modified by suprasubduction zone (SSZ) melts/fluids. We interpret the high-Al chromitites as the products of early mid-ocean ridge basalt (MORB) or arc tholeiite magmas, whereas the high-Cr varieties are thought to have been generated by later SSZ melts.     

Authigenic potassic silicates in the Rathdowney Trend,southwest Ireland: New perspectives for ore genesis from petrography of gangue phases in Irish-type carbonate-hosted Zn-Pb deposits

Petrographic studies of Zn-Pb ore zones hosted by Lower Carboniferous dolomitized Waulsortian reef limestones in the Rathdowney Trend reveal a paragenetic association between sphalerite and potassium silicates: (Ba, K)-feldspar, adularia, and albite as well as rare quartz, illite and phengite. The dominant mineral assemblage is composed of 1) sphalerite ± (K,Ba) feldspar ± pengite/illite near the putative feeder conduit for the Lisheen Main Zone, and 2) a sphalerite ± pengite/illite assemblage distal to the major normal faults (NW of Main Zone, Island Zone and Rapla occurrence). In addition, clay minerals have been identified in fault gouges located at the interface between the Waulsortian reef and argillaceous limestone of the Ballysteen Formation. This mineral assemblage has provided additional constraints on the physico-chemical conditions of ore formation (eH, pH, sulfur and metal species). Another implication of the mineral assemblage, is a revision of fluid rock interaction processes, in which mineral solution-precipitation reactions are contributing to the development of hydrothermal breccias, with dolomitic black matrix breccias interpreted as a by-product of massive sulfide precipitation. Additionally, textural studies of the breccias through fractal dimension analysis of fragment geometry extracted from large scale scanning electron microscope element maps (1 cm² areas or more), indicates the prevalence of chemical brecciation-corrosion processes in the generation of the black matrix breccias. Integration of these new observations allows for comparison of ore forming processes across the Irish Midlands from the perspective of gangue mineralogy and may provide further links with classic Mississippi-type deposits from the mid-continent region of the United States of America.     

Lithospheric structure of the North China Craton: Integrated gravity,geoid and topography data

The lithospheric structure of ancient cratons provides important constraints on models relating to tectonic evolution and mantle dynamics. Here we present the 3D lithospheric structure of the North China Craton (NCC) from a joint inversion of gravity, geoid and topography data. The NCC records a prolonged history of Archean and Paleoproterozoic accretion of crustal blocks through subduction and collision building the cratonic architecture, which was subsequently differentially destroyed during Mesozoic through extensive magmatism. The thermal structure obtained in our study is considered to define the lithosphere-asthenosphere boundary (LAB) of the NCC, and reflects the density variations within the mantle lithosphere. Employing the Moho depths from deep seismic sounding profiles for the inversion, and based on repeated computations using different parameters, we estimate the Moho depth, LAB depth and average crustal density of the craton. The Moho depth varies from 28 to 50 km and the LAB depth varies from 105 to 205 km. The LAB and Moho show concordant thinning from West to East of the NCC. The average crustal density is 2870 kg m^− 3 in the western part of the NCC, higher than that in the eastern part (2750 kg m^− 3). The results of joint inversion in our study yielded LAB depth and lithospheric thinning features similar to those estimated from thermal and seismic studies, although our results show different depth and variations in the thickness. The lithosphere gently thins from 145 to 105 km in the eastern NCC, where as the thinning is much less pronounced in the western NCC with average depth of about 175 km. The joint inversion results in this study provide another perspective on the lithospheric structure from the density properties and corresponding geophysical responses in an ancient craton.     

Dissolution kinetics of soil clays in sulfuric acid solutions: Ionic strength and temperature effects

Significant amounts of sulfuric acid (H₂SO₄) rich saline water can be produced by the oxidation of sulfide minerals contained in inland acid sulfate soils (IASS). In the absence of carbonate minerals, the dissolution of phyllosilicate minerals is one of very few processes that can provide long-term acid neutralisation. It is therefore important to understand the acid dissolution behavior of naturally occurring clay minerals from IASS under saline–acidic solutions. The objective of this study was to investigate the dissolution of a natural clay-rich sample under saline–acidic conditions (pH 1–4; ionic strengths = 0.01 and 0.25 M; 25 °C) and over a range of temperatures (25–45 °C; pH 1 and pH 4). The clay-rich sample referred to as Bottle Bend clay (BB clay) used was from an IASS (Bottle Bend lagoon) in south-western New South Wales (Australia) and contained smectite (40%), illite (27%), kaolinite (26%) and quartz (6%). Acid dissolution of the BB clay was initially rapid, as indicated by the fast release of cations (Si, Al, K, Fe, Mg). Relatively higher Al (pH 4) and K (pH 2–4) release was obtained from BB clay dissolution in higher ionic strength solutions compared to the lower ionic strength solutions. The steady state dissolution rate (as determined from Si, Al and Fe release rates; R_Si, R_Al, R_Fe) increased with decreasing solution pH and increasing temperature. For example, the highest log R_Si value was obtained at pH 1 and 45 °C (−9.07 mol g⁻¹ s⁻¹), while the lowest log R_Si value was obtained at pH 4 and 25 °C (−11.20 mol g⁻¹ s⁻¹). A comparison of these results with pure mineral dissolution rates from the literature suggests that the BB clay dissolved at a much faster rate compared to the pure mineral samples. Apparent activation energies calculated for the clay sample varied over the range 76.6 kJ mol⁻¹ (pH 1) to 37.7 kJ mol⁻¹ (pH 4) which compare very well with the activation energy values for acidic dissolution of monomineralic samples e.g. montmorillonite from previous studies. The acid neutralisation capacity (ANC) of the clay sample was calculated from the release of all structural cations except Si (i.e. Al, Fe, K, Mg). According to these calculations an ANC of 1.11 kg H₂SO₄/tonne clay/day was provided by clay dissolution at pH 1 (I = 0.25 M, 25 °C) compared to an ANC of 0.21 kg H₂SO₄/tonne clay/day at pH 4 (I = 0.25 M, 25 °C). The highest ANC of 6.91 kg H₂SO₄/tonne clay/day was provided by clay dissolution at pH 1 and at 45 °C (I = 0.25 M), which is more than three times higher than the ANC provided under the similar solution conditions at 25 °C. In wetlands with little solid phase buffering available apart from clay minerals, it is imperative to consider the potential ANC provided by the dissolution of abundantly occurring phyllosilicate minerals in devising rehabilitation schemes.     

Crustal structure of the Gujarat region,India: New constraints from the analysis of teleseismic receiver functions

In this study, receiver function analysis is carried out at 32 broadband stations spread all over the Gujarat region, located in the western part of India to image the sedimentary structure and investigate the crustal composition for the entire region. The powerful Genetic Algorithm technique is applied to the receiver functions to derive S-velocity structure beneath each site. A detail image in terms of basement depths and Moho thickness for the entire Gujarat region is obtained for the first time. Gujarat comprises of three distinct regions: Kachchh, Saurashtra and Mainland. In Kachchh region, depth of the basement varies from around 1.5 km in the eastern part to 6 km in the western part and around 2–3 km in the northern part to 4–5 km in the southern part. In the Saurashtra region, there is not much variation in the depth of the basement and is between 3 km and 4 km. In Gujarat mainland part, the basement depth is 5–8 km in the Cambay basin and western edge of Narmada basin. In other parts of the mainland, it is 3–4 km. The depth of Moho beneath each site is obtained using stacking algorithm approach. The Moho is at shallower depth (26–30 km) in the western part of Kachchh region. In the eastern part and epicentral zone of the 2001 Bhuj earthquake, large variation in the Moho depths is noticed (36–46 km). In the Saurashtra region, the crust is more thick in the northern part. It varies from 36–38 km in the southern part to 42–44 km in the northern part. In the mainland region, the crust is more thick (40–44 km) in the northern and southern part and is shallow in Cambay and Narmada basins (32–36 km). The large variations of Poisson’s ratio across Gujarat region may be interpreted as heterogeneity in crustal composition. High values of σ (∼0.30) at many sites in Kachchh and few sites in Saurashtra and Mainland regions may be related to the existence of high-velocity lower crust with a mafic/ultramafic composition and, locally, to the presence of partial melt. The existing tectono-sedimentary models proposed by various researchers were also examined.     

Stromatolites in caves of the Dead Sea Fault Escarpment: implications to latest Pleistocene lake levels and tectonic subsidence

A varied assemblage of algal stromatolites was encountered in caves along the northern section of the Dead Sea Fault Escarpment. The caves are situated at the lower part of the escarpment at altitudes ?310 to ?188 m relative to mean sea level (m.s.l.), i.e. ca 110–230 m above the present Dead Sea level. The cave stromatolites are mainly composed of aragonite yielding U–Th ages of ～75–17 ka. The altitude, mineralogy and ages, as well as comparison with previously documented stromatolite outcrops in the area, ascribe the cave stromatolites to the aragonite-precipitating hypersaline Lake Lisan—the Late Pleistocene predecessor of the Dead Sea.The stromatolites are used as a lake level gauge, based on the algae being reliant upon the light of the upper water layer. Preservation of the original structure and aragonite mineralogy of the stromatolites, suggests a closed system regarding the radioactive elements, enabling reliable U–Th dating. A curve of Lake Lisan levels is constructed based on the stromatolite ages and cave elevations. The following points are noted: (1) Lake levels of ?247 m relative to m.s.l., are recorded at ～75–72.5 ka; (2) relatively high lake levels above ?220 m relative to m.s.l., are achieved at ～41.5 ka, and are still recorded at ～17 ka; (3) the peak level is ?188 m relative to m.s.l., at ～35.5–29.5 ka. These results indicate lake stands up to 80 m higher than previously accepted, for large parts of the Lake Lisan time span. This difference is explained by tectonic subsidence of up to 2.2 m/ka within the Dead Sea depression since the latest Pleistocene. This subsidence rate is in the same order of magnitude with previously calculated subsidence rates for the Dead Sea depression [Begin, Z.B., Zilberman, E., 1997. Main Stages and Rate of the Relief Development in Israel. Geological Survey of Israel report, Jerusalem]. Unlike previous Lake Lisan level estimations, the new curve is measured at the relatively stable shoulders of the Dead Sea depression.     

Location of the pilot borehole for investigations of reservoir triggered seismicity at Koyna,India

Artificial water reservoir triggered earthquakes are now known to have occurred at over 120 sites globally. The part played by the reservoirs in triggering is not exactly known due to lack of near field observations of triggered earthquakes. Koyna, located near the west coast of India, where triggered earthquakes have been occurring since 1962 provides an excellent site for near field observations of the target M ≥ 2 earthquakes. A 6 borehole seismic network has been deployed recently in the Koyna region at depths of 981–1522 m to improve the hypocenter locations. During May–December 2015, a total of 1039 earthquakes of M_L ≥ 0.5 were located using the borehole seismic network. The region is also monitored through a dense network of 23 surface broad-band stations. Our analysis indicates a significant improvement in the estimation of absolute locations of earthquakes with errors of the order of ± 300 m, combining both the networks. Based on seismicity, and logistics, a block of 2 × 2 km² area has been chosen for drilling the first pilot borehole of ~ 3 km depth, where M ≥ 2 earthquakes have been occurring frequently since 2005.     

On the origin of saline fluids in the KTB (Continental Deep Drilling Project of Germany)

Highly saline fluids were encountered during the German Continental Deep Drilling Project (KTB) from depths ranging between 2 and 3 km to about 9 km. The most reliable data were obtained from samples extracted during a long-term pumping test in the 4000-m deep KTB pilot hole. Some 460 m³ Ca–Na–Cl brines with about 68 g l⁻¹ total dissolved solids (TDS) and some 270 m³ associated gases, mainly N₂ and CH₄ were pumped to the surface from the main fracture system situated near the bottom of the pilot hole. Geochemical and isotopic data support the hydraulic tests which suggest the presence of an open and large fluid reservoir at depth. The pumped fluids from this main fracture system were released from a deep reservoir situated at more than 5500 m depth which is hydraulically connected with the 9101 m deep KTB main hole, drilled some 250 m to the northeast of the pilot hole.While Ca and Sr contents of the extracted brines may be the result of water–rock interaction, Cl is most likely of external origin. The Cl is hypothesized to derive from geotectonic processes rather than to descending infiltration of paleo-seawater (evaporitic brines). The sampled fluids have probably migrated from a deeper reservoir to their present position since the Cretaceous–Tertiary period due to tectonic activity. However, several isotopic studies have identified an admixture of descending paleowaters down to more than 4000 m depth. The high ³⁶Cl/Cl ratio of the fluids sampled during the long-term pumping test point to a host rock highly enriched in U–Th, unlike the sampled KTB country rocks. The fluid reservoir is believed to be in contact with the Falkenberg granite massif situated about 2 km to the E of the KTB holes, capable of supplying sufficient neutron flux for considerable subsurface production of ³⁶Cl. The Na–Cl–(K-, SO₄) precursor fluids of the Ca–Na–Cl brines were produced in the course of extensive tectonic processes since the Late Caledonian within the Bohemian Massif.     

Effect of suspended sediment concentration on local scour around cylinder for clay–sand mixed sediment beds

Suspended sediments present in the flow are known to affect the flow resistance, velocity distribution and turbulent characteristics. Experiments were conducted in the laboratory flume to see the effect of suspended sediment concentration (SSC) on local scour around a cylindrical pier for a wide range of clay–sand mixed sediment beds for SSC up to 2700 mg/L. It has been observed that the effect of SSC on equilibrium scour hole parameters such as maximum equilibrium scour depth, and longitudinal and transverse extent of scour hole can be significant. Present data showed that the presence of SSC in the range 993–1332 mg/L can increase maximum equilibrium scour depth as much as 1.54 times compared to the clear water case. However, tests made for SSC in the range 2456–2700 mg/L showed that the maximum equilibrium scour depth reduced compared to that for SSC in the range 993–1332 mg/L, but these maximum equilibrium scour depths were still larger than that obtained for clear water. The effect of SSC on time variation of scour and equilibrium scour hole geometry was further investigated.     

Holocene vegetation and climatic variations in Central India: A study based on multiproxy evidences

Palynology, texture, mineralogy, geochemistry, and magnetic susceptibility analysis of a 2 m deep sediment core from Padauna Swamp, southeastern Madhya Pradesh infers that between 8600 and 7500 cal yr BP a warm and relatively less-humid climate prevailed with open tree-savannahs dominated by grasses followed by sedges, Artemisia and members of Chenopodiaceae/Amaranthaceae with scanty trees viz., Schrebera, Aegle marmelos and Sterculia urens. This is well supported by lower organic to carbonate carbon ratio, coarser texture having relatively low CIA and magnetic susceptibility values and presence of some primary minerals. Between 7500 and 6250 cal yr BP the tree-savannahs were succeeded by open mixed deciduous forests with the invasion of a few more trees viz., Madhuca indica, Holoptelea, Emblica officinalis, Mitragyna parvifolia and members of Anacardiaceae in response to onset of a warm and humid climate. A considerable rise in organic carbon generated from the degradation of plentiful biomass along with increase in clay content with signs of kaolinite and increase in immobile over mobile elements with slightly higher CIA and magnetic susceptibility values also suggest climatic amelioration. The presence of ruderal plants such as Artemisia, Cannabis sativa and Cheno/Am further infers initiation of human activities in the region. Between 6250 and 2800 cal yr BP, the mixed deciduous forests became more diverse and dense, subduing grasses and other herbaceous elements. Sporadic incursion of Shorea robusta (Sal) in forest floristic was recorded around 5000 cal yr BP. The overall change in the vegetation mosaic reflects that a warm and more-humid climate prevailed in the region, probably on account of invigoration of southwest monsoon. This observation is further corroborated by other proxy data showing a spurt in organic/inorganic carbon ratio, increase in clay content with matured mineralogy, significantly higher CIA and magnetic susceptibility values. Since 2800 cal yr BP onwards, the modern Sal dominated deciduous forests were established indicating continuation of warm and more-humid climate including timely arrival of SW monsoon coinciding with the shedding of Sal seeds as they are viable for a very short period.     

Continuous growth of hydrogenetic ferromanganese crusts since 17 Myr ago on Takuyo-Daigo Seamount,NW Pacific,at water depths of 800–5500 m

Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07–0.11 g/cm²/Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts.