Role of bedrock serpentinization on the development of nickel laterite deposit in Sorowako, Sulawesi, Indonesia

The objective of this research is to analyze the role of bedrock serpentinization on the development of Ni-Laterite deposits in Sorowako, Sulawesi Island, Indonesia. Samples were obtained from coring data in three areas, namely the West Block, East Block, and Petea, which are subject to mineralogical and geochemical analyses. Petrography of the bedrocks was conducted to analyze the mineral composition, texture, and serpentinization degree, and later correlated with the distribution of geochemical elements from X-ray fluorescence method in each laterite zone. The bedrock in the West Block is dunite which consists of predominantly olivine with low degree serpentinization. The bedrock in the East Blocks and Petea consists of peridotite in the form of lherzolite and harzburgite which have been moderate to highly serpentinized. The distribution of elements in each block shows that MgO, SiO2, and Ca elements significantly decrease towards the upper laterite profile while Fe, Al, and Cr are enriched in the limonite zone and Ni, Mn, and Co are significantly enriched in the saprolite zone. Ni, Fe, SiO2, Cr, MgO, and Mn in the West Block are relatively higher than the East Block and Petea. This study shows that Ni content is relatively higher in West Block compare to East Block and Petea in averages of 1.7%, 1.53%, and 1.3%, respectively. Olivine-rich bedrock and a low degree of serpentinization resulted in high-Ni concentration in the laterite profile, particularly in the saprolite layer. This means that bedrock characteristics and degree of serpentinization were responsible for the development of nickel.

Physicochemical Property Indexes of Sediment Lixiviums in Sea–Land Interaction Zone of Subei Basin and Their Significance to Transgression

In current studies, the physicochemical properties of water, such as total dissolved solids, salinity, and electrical conductivity, are used mainly to investigate changes in the properties of surface water and groundwater. In our experimental study, we aimed to introduce the physicochemical properties of water bodies into the field of paleoenvironmental changes. We employed the physicochemical property indexes of sediment lixiviums in two research sections of the sea–land interaction zone in the eastern margin of the Subei Basin (China). Preliminary tests determined that the optimal solvent for preparing the sediment lixiviums is ultrapure water; the use of this water can prevent errors caused by soluble solids in the solvent. Using a container with a lid to prepare the sediment lixiviums could reduce errors caused by evaporation. Furthermore, we determined the appropriate process and duration for testing the physicochemical properties of sediment lixiviums. The optimal time for testing the physicochemical properties was 120 h (mixture fully stirred daily) or 168 h (no stirring). The weight of the sediment, volume of the solvent, and test time should be consistent in the same research section. Comparing the physicochemical property indexes of sediment lixiviums with geochemical elements and diatom indicators, we found that these indexes show obvious indications of transgression, and have an obvious advantage in indicating transgression.

Effects of climate change on a subtropical montane peatland over the last two centuries: Evidence from diatom records

Climate variability can induce rapid changes in peatland ecosystems, affecting both carbon cycling and vegetation succession. Diatoms are an important group of ubiquitous and diverse algae in peatlands. Until now, the responses of diatom communities to climate variability have rarely been explored in peatlands, especially in subtropical regions. In this study, monitoring and paleolimnological datasets were combined to decipher environmental changes of a subtropical montane peatland (central China) over the last two centuries. Seasonal monitoring data revealed that diatom communities were closely correlated with precipitation, depth to the water table, conductivity, nitrate and temperature. Sedimentary records revealed that temporal changes in diatom assemblages and geochemical elements displayed similar trends in two peat cores after the 1950s. The first gradient in diatom composition represented a shift from Pinnularia species to taxa preferring less-acidic habitats, which was closely linked to climate warming and the enrichment of inorganic elements (e.g. sodium and calcium) since the early 20th century. Meanwhile, changes in diatom communities were further related to precipitation variability, atmospheric deposition and local hydrogeomophic setting. Taken together, the succession of diatom communities was closely linked to climate-regulated availability of nutrients and moisture in this subtropical peatland over the last two centuries. In order to achieve sustainable management of these scarce peatlands, further biological monitoring and paleoecological studies are needed to improve our knowledge of peatland ecosystem evolution in response to future climate change.

Evaluation of soil erosion and sediment sources in two contrasting sub-basins, using fingerprinting and 137Cs techniques in Uruguay. Preliminary results.

<p>The study site consists of two sub-basins (“Arbolito”, 20.94 km2; and “Horno”, 10.44 km2) divided by the Rolon stream, which in turn flows into the Baygorria hydroelectric dam reservoir (-32.77152 S; -56.84093 W). The "Arbolito" sub-basin consists of natural pasture with extensive cattle from the 19th century to the present day.  Soils are predominantly eutric brunosols and clayey haplic vertisols with slopes > 6% (MGAP, Uruguay). The “Horno” sub-basin consists of intensive agriculture since the mid-1980s, with a history of rice, wheat, oat, soybean and pastureland rotations. At the beginning of the 2000s, direct sowing began in this region of the country. Soils in Horno are predominantly clayey, deep Haplic Vertisols and Typical Eurethric Brunosols, clayey silt, vertically and moderately deep, with slopes ≤ 6 % (MGAP, Uruguay). Both soil types and their formation are associated with basaltic lithologies. A total of 50 surface samples from natural pastures, cropland and channel banks were used as sources to describe the mixture of sediments (fine-bed material) using geochemical elements and the FingerPro mixing model. For the 137Cs technique, a total of 120 surface samples were taken, multi-transect sampling was conducted in both sub-basins, and reference sites were established. Profile Distribution Model (PDM) and Diffusion Model (DM) were used as conversion model for the Arbolito sub-basin, while Mass Balance Model II (MBM II) was used for Horno sub-basin. MODERN model was used in both areas. Sediment fingerprinting results showed that the proportion of sediment sources is divided as follows: cropland (up to 70%), pastures (up to 25%) and channel banks (the remaining 5%). The reference value of 137Cs found was 369.0 bq.m-2 (SD 7.4 bq.m-2) on 01/01/2020 calibration date. The results of the net soil redistribution rates using different conversion models of 137Cs were consistent with each other, and showed erosion in both sub-basins, Arbolito: PDM (-0.72 Mg ha-1 yr-1), DM (-0.29 Mg ha-1 yr-1), MODERN (-0.69 Mg ha-1 yr-1); Horno: MBM II (-0.5 Mg ha-1 yr-1), MODERN (-0.56 Mg ha-1 yr-1). Although the net erosion rate in both sub-basins is similar, the redistribution of soil within each sub-basin is different. While the Arbolito shows on average preserved areas at the top of the slopes (MODERN 1.7 Mg ha-1 yr-1), with high erosion in the middle (MODERN -5.7 Mg ha-1 yr-1) and low erosion in lower areas (MODERN -0.47 Mg ha-1 yr-1); Horno sub-basin shows in average eroded areas at the top of the slopes (MODERN -4.3 Mg ha-1 yr-1) with low sedimentation in the middle (MODERN 0.4 Mg ha-1 yr-1) and high sedimentation in the lower areas (MODERN 2.21 Mg ha-1 yr-1). This would explain a greater redistribution of the soil from the high to the low areas in the Horno sub-basin compared to Arbolito, probably due to the mechanical movement of the soil by agriculture practice. These results may explain a greater export of soils in Horno compared to Arbolito, which agrees with cropland as the most important source of sediments (up to 70%) by fingerprinting techniques.</p>

The Efficiency of Elemental Geochemistry and Weathering Indices as Tracers in Aeolian Sediment Provenance Fingerprinting

Eight geochemical elements (Al, Ca, Fe, K, Na, Mg, Si, Ti) and 17 associated weathering indices were measured in 34 aeolian source samples and 10 sand dune target sediment samples in three absolute particulate size fractions. For each fraction, three final composite fingerprints (i.e., geochemical elements only, weathering indices only and a combination of the two) for discerning and ascribing the aeolian sediment sources were selected. The Modified MixSIR Bayesian un-mixing model was used to apportion aeolian source contributions using the final composite fingerprints. Regardless of the composite fingerprint used, all results across the different size fractions suggested that the south-eastern alluvial fan is the dominant (average contribution 50.6%, SD 19.0%) source of the sand dune samples, with the western alluvial fan being the second most important (average contribution 38.4%, SD 20.4%) source. Comparisons of the posterior distributions for the predicted source proportions generated using the nine composite fingerprints (three kinds of composite fingerprints*three particle size fractions) showed that the composite fingerprints combining the geochemical elements and weathering indices generated the most powerful source material discrimination. Our results demonstrate the use of weathering indices alongside more conventional elemental geochemistry tracers for investigations into sand dune sediment provenance.

Geochemical variability in the soils of Bangladesh as affected by sources of irrigation water and inundation land types

Paddy soils in Bangladesh experience extensive irrigation with groundwater and surface water, both having variable geochemical constituents. The soils also have topological variations across the landscape. To understand the geochemical variability in the soils as affected by the different sources of irrigation water and the topographical variability, cultivation zones of paddy soils irrigated with both groundwater (n = 904) and surface water (n = 281) across Bangladesh were sampled and analyzed for a suit of seventeen geochemical elements. This study also assessed the extent and distribution of arsenic and the other geochemical elements in the paddy soils (n = 1209) as well as in a set of neighboring non-paddy soils (n = 235) within the different inundation land types (highland, medium highland-1, medium highland-2, medium lowland, lowland and very lowland) of Bangladesh. The mean concentrations of aluminum (26,000 mg/kg), cobalt (13 mg/kg), copper (32 mg/kg), iron (28,250 mg/kg), lead (18 mg/kg), magnesium (8050 mg/kg), molybdenum (1.02 mg/kg), nickel (41 mg/kg), potassium (4870 mg/kg), sodium (750 mg/kg) and zinc (70 mg/kg) in the surface water-irrigated paddy soils were found to be significantly (0.001 ≥ p ≤ 0.05) higher compared to the concentrations in the soils irrigated with groundwater (23,400; 12; 28; 25,650; 17; 7000; 0.96; 36; 4350; 600; and 62 mg/kg, respectively). Therefore, surface water used for paddy irrigation could increase the inputs of a number of toxic elements in the paddy soils having potential risk of crop contamination. Arsenic in the paddy and non-paddy soils varied significantly (F = 24.74, p < 0.001 and F = 3.42, p < 0.01, respectively) within the inundation land types, the very lowland (9.95 and 6.72 mg/kg, respectively) and lowland (8.33 and 5.20 mg/kg, respectively) having the highest mean arsenic concentrations and the medium highland-1 (5.27 and 5.17 mg/kg, respectively) having the lowest. The concentrations of the other geochemical elements analyzed were also observed to be higher, in general, in the soils of very lowland and lowland. Since the low-level lands are predominantly used for paddy cultivation, higher concentrations of various toxic elements, particularly arsenic, in such soils pose an increased risk of rice toxicity in Bangladesh. The results of this study present an inimitable geochemical database for the surface soils across Bangladesh which can be used in any future studies on the geomorphologically variable agricultural and non-agricultural Bangladeshi soils, providing a basis for environmental pollution assessment and sustainable mitigation approaches.

Complex network dynamics of the topological structure in a geochemical field from the Nanling area in South China

The topological classification of geochemical elements is widely used as a reference for regional prospecting prediction. In this study, we analyze the topological correlation structures of 39 representative geochemical elements from the Nanling area of South China by implementing the complex networks theory. The topological correlation structures of geochemical elements have a high clustering coefficient (0.8120–0.8880), but the magnitude of the shortest path (1.2950–2.3600) is small. In combination with the analysis of complex networks characteristics, we report that the topological correlation structures of the geochemical elements in this area have small-world characteristics, which reveals the self-organized criticality. As shown in the topological network, two random elements have some level of associations, which present a specific community feature. Our preliminary result shows that with changing the control parameter (k) of “coarse-graining”, the topological correlation structures undergo two critical phase transitions. As the control parameter (k) reaches 0.44, the entire element system evolves into two parts. When the control parameter (k) reaches 0.63, the system forms three “communities”. It is worth noting that the three “communities” are basically consistent with the Goldschmidt’s geochemical classification of the elements, which are lithophile, siderophile, and chalcophile groups, respectively. In these “communities”, we also found that a small level of component units is nested.

Elemental Geochemical Characterization of Sedimentary Conditions and Organic Matter Enrichment for Lower Cambrian Shale Formations in Northern Guizhou, South China

The black shale deposited in the Niutitang Formation and its adjacent strata is considered to be a favorable source rock in northern Guizhou of south China and has become a target horizon for shale gas exploration in recent years. Based on SQ-1 and CY-1 core samples, the organic matter properties and geochemical elements were obtained through experimental analysis. Provenance, paleoredox, paleoclimate, paleoproductivity and deposition conditions were analyzed, and the sedimentary effects on organic matter enrichment were discussed. The results show that total organic carbon (TOC) is between 0.22–10.10 wt.% in SQ-1, with an average of 2.60 wt.%, and TOC is between 0.23–7.7 wt.% in CY-1, with an average of 1.45 wt.%. The geochemical data of the samples indicate that the black shale of the Niutitang Formation and adjacent strata are deposited in the tectonic background of the passive continental margin. The provenance shows moderate weathering, with hot and humid paleoenvironmental characteristics and fast deposition rate. Using multiple ancient redox indicators, it is concluded that the formation has undergone changes in the oxidizing environment and anaerobic environment during deposition. According to the (La/Yb)N value (the average value of SQ-1 is 1.23 and the average value of CY-1 is 1.26), it shows a faster deposition rate of the two wells and shortens the residence time of organic matter in the microbial degradation zone. The Babio indicates that the bottom has a high paleoproductivity when deposited. Considering the influencing factors, the paleoproductivity mainly controls the organic matter enrichment, followed by ancient redox conditions and the deposition rate. The research results provide a reference for deepening sedimentary understanding and shale gas exploration in the study area.