Palaeo-environmental evolution of Central Asia during the Cenozoic: new insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)

The Valley of Lakes basin (Mongolia) contains a unique continental sedimentary archive, suitable for constraining the influence of tectonics and climate change on the aridification of Central Asia in the Cenozoic. We identify the sedimentary provenance, the (post)depositional environment and the palaeo-climate based on sedimentological, petrographical, mineralogical, and (isotope) geochemical signatures recorded in authigenic and detrital silicates as well as soil carbonates in a sedimentary succession spanning from ∼34 to 21 Ma. The depositional setting was characterized by an ephemeral braided river system draining prograding alluvial fans, with episodes of lake, playa or open-steppe sedimentation. Metamorphics from the northern adjacent Neoarchean to late Proterozoic hinterlands provided a continuous influx of silicate detritus to the basin, as indicated by K–Ar ages of detrital muscovite (∼798–728 Ma) and discrimination function analysis. The authigenic clay fraction is dominated by illite–smectite and “hairy” illite (K–Ar ages of ∼34–25 Ma), which formed during coupled petrogenesis and precipitation from hydrothermal fluids originating from major basalt flow events (∼32–29 and ∼29–25 Ma). Changes in hydroclimate are recorded in δ18O and δ13C profiles of soil carbonates and in silicate mineral weathering patterns, indicating that comparatively humid to semi-arid conditions prevailed in the late(st) Eocene, changing into arid conditions in the Oligocene and back to humid to semi-arid conditions in the early Miocene. Aridification steps are indicated at ∼34–33, ∼31, ∼28 and ∼23 Ma and coincide with some episodes of high-latitude ice-sheet expansion inferred from marine deep-sea sedimentary records. This suggests that long-term variations in the ocean–atmosphere circulation patterns due to pCO2 fall, reconfiguration of ocean gateways and ice-sheet expansion in Antarctica could have impacted the hydroclimate and weathering regime in the basin. We conclude that the aridification in Central Asia was triggered by reduced moisture influx by westerly winds driven by Cenozoic climate forcing and the exhumation of the Tian Shan and Altai Mountains and modulated by global climate events.

A Study of Innovative Alkali-Activated Binders for Soil Stabilisation in the Context of Engineering Sustainability and Circular Economy

In the context of sustainability in the civil engineering industry, chemical ground improvement is becoming increasingly used, as a generally more sustainable alternative to replacing and landfilling unsuitable for construction ground. However, traditional soil stabilisers such as Portland cement or lime are not environmentally impact-free; international research effort is thus focusing on the development of innovative cementing agents. This paper presents results from a feasibility study on the development of suitable alkali-activated slag cements for the stabilisation of two soils. A number of alkali-activators were considered, comprising potassium hydroxide, a range of alkali salts, as well as a material retrieved from waste (Paper Sludge Ash, PSA) which contains free lime. Indicative results of an extensive parametric study in terms of unconfined compressive strength (UCS) are shown, followed by results of ongoing oedometer tests to determine soil compressibility and some preliminary tests on selected soil/binder mixes to observe the durability to wetting-drying cycles. Overall, all alkali-activated cement mixes increased the UCS and stiffness of the soil. Carbonates and Na2SiO3 used on their own gave lower strength increases. The highest strengths were achieved from AAC with KOH and Ca(OH)2 from PSA, which showed similar strength gain. The latter material has shown consistently a lot of promise in terms of strength, stiffness and volumetric stability of the soil as well as treatment durability. Ongoing research focuses on further mix optimisation and a comprehensive mechanical and durability property testing supported by material analysis (mineralogical, chemical and microstructural) to gain a better understanding of the complex mechanisms involved.

Down to the Crust: Chemical and Mineralogical Analysis of Ceramic Surface Encrustations on Bronze Age Ceramics from Békés 103, Eastern Hungary

Békés 103, a primarily Middle Bronze Age (c. 1600–1280 calBC) cemetery and settlement on the Great Hungarian Plain, has been investigated by the BAKOTA project since 2011. Ceramics from the site are covered in dense white concretions, and it has been noted during compositional analyses that these vessels exhibit elevated concentrations of several potentially mobile elements in comparison to vessels from regional tell sites. Here, we use a multimethod (optical mineralogy, FT-IR, XRD, XPS, PXRF, SEM-EDS, and LA-ICP-MS) mineralogical and chemical approach to characterize the composition of surface encrustations on ceramics samples from Békés 103. We also chemically map interior paste composition using LA-ICP-MS to identify potential leaching of mobile elements into or out of vessel bodies. We demonstrate that the surface encrustations are primarily composed of calcite but also contain a variety of other mineral and organic constituents indicative of deposition of soil carbonates, phosphates, nitrates, and other inorganic and organic components. We further document the leaching of several mobile elements into ceramic pastes as well as formation of secondary calcite along void, pore, and temper boundaries. The presence of cremated bone and possibly bone ash in close vicinity to many of the studied vessels may also have contributed to the observed patterns of diagenesis. It is likely that similar post-burial processes might affect ceramics from other sites located in low-lying, seasonally inundated contexts.

Palaeo-environmental evolution of Central Asia during the Cenozoic: New insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)

The Valley of Lakes basin (Mongolia) contains a unique continental sedimentary archive, suitable for constraining the influence of tectonics and climate change on the aridification of Central Asia in the Cenozoic. We identify the sedimentary provenance, the (post)depositional environment and the palaeo-climate based on sedimentological, petrographical, mineralogical and (isotope) geochemical signatures recorded in authigenic and detrital silicates as well as soil carbonates in a sedimentary succession spanning ~34 to 21 Ma. The depositional setting was characterized by an ephemeral braided river system draining prograding alluvial fans, with episodes of lake, playa or open steppe sedimentation. Metamorphics from the northern adjacent Neoarchean to late Proterozoic hinterlands provided a continuous influx of silicate detritus to the basin, as indicated by K-Ar ages of detrital muscovite (~798-728 Ma) and discrimination function analysis. The authigenic clay fraction is dominated by illite-smectite and “hairy” illite (K-Ar ages: ~34-25 Ma), which formed during coupled petrogenesis and precipitation from hydrothermal fluids originating from major basalt flow events (~32-29 Ma and ~29-25 Ma). Changes in hydroclimate are recorded in δ18O and δ13C profiles of soil carbonates and in silicate mineral weathering patterns, indicating comparatively humid to semi-arid conditions prevailed in the late(st) Eocene, changing into arid conditions in the Oligocene and back to humid to semi-arid conditions in the early Miocene. Aridification steps are indicated at ~34-33 Ma, ~31 Ma, ~28 Ma and ~23 Ma and coincide with some episodes of high-latitude ice sheet expansion inferred from marine deep-sea sedimentary records. This suggests long-term variations of the ocean/atmosphere circulation patterns due to pCO2 fall, re-configurations of ocean gateways and ice-sheet expansion in Antarctica could have impacted the hydroclimate and weathering regime in the basin. We conclude that the aridification in Central Asia was triggered by reduced moisture influx by westerly winds driven by Cenozoic climate forcing and the exhumation of the Tian Shan and Altai mountains and modulate by global climate events.

Pedogenic carbonates accumulation in a calcareous Mediterranean soil following introduction of irrigation

<p>In calcareous Mediterranean soils, pedogenic and lithogenic carbonates can be important constituents of the soil matrix. However, their relative proportion and their relation to soil functioning has been scarcely studied. The interest in determining the proportion of pedogenic carbonates relies on the fact that they can be related to the physical, chemical and biological properties of the soil and, therefore, affect plant growth and soil productivity. Carbonates dynamics can be affected by some farming management practices and land-use changes, such as the adoption of irrigation, due to changes in the soil water regime, the composition of the soil solution, the concentration of CO<sub>2</sub> in the soil atmosphere, and the changes related to fertilization.</p><p>To gain knowledge on the importance of the effect of the introduction of irrigation on carbonates dynamics in the tilled layer of agricultural soils, we studied the evolution of the proportion of pedogenic carbonates in a Mediterranean calcareous soil after seven years of irrigation. We used the isotopic signature of C in soil carbonates for these estimations. The study was conducted in two plots under contrasting agricultural management on the same soil unit: dryland wheat cropping, and irrigated corn for 7 consecutive years, in Enériz (Navarre, Spain).</p><p>Our results showed that the transformation of dryland wheat to irrigated corn, produced a preferential accumulation of pedogenic carbonates (31-56%) in the tilled layer (0-30 cm) of the irrigated soil only over 7 years after the land-use change. Therefore, the processes related to this land use change can alter the soil carbonates dynamics in a very short period of time, and they may have consequences in terms of plant nutrient dynamics and the soil structure. Future research on the origin of the soil carbonates (pedogenic or geogenic) in agricultural soils will help to understand the actual significance of carbonates dynamics in terms of the global C balance in these soils.</p>

Using Triple Oxygen Isotopes of Pedogenic Carbonate to Identify Ancient Evaporation: First Steps from Modern Soils

<p>The stable isotope composition of soil carbonates is commonly used to reconstruct continental paleoclimates, but its utility is limited by an incomplete understanding of how soil carbonates form. In particular, it is often unclear if the parent soil water has been enriched in <sup>18</sup>O due to evaporation, muddying our ability to infer meteoric water δ<sup>18</sup>O from paleosol carbonates. Here we demonstrate the potential use of triple oxygen isotopes (termed ∆’<sup>17</sup>O) to account for evaporation and identify formation process through a study of modern soil carbonate isotope values.  Evaporation results in a decreased slope in the relationship between δ<sup>17</sup>O and δ<sup>18</sup>O and deviations from the global meteoric water line, such that ∆<sup>’17</sup>O values in soil water and resulting carbonate decrease with increased evaporation. We report ∆<sup>’17</sup>O values of CO<sub>2</sub> derived from soil carbonates and measured as O<sub>2</sub> on a mass spectrometer, with 1-4 replicates per soil carbonate. We find a step-like relationship between ∆’<sup>17</sup>O in globally distributed Holocene soil carbonate samples and aridity, where aridity is defined using the aridity index (AI, mean annual precipitation/potential evapotranspiration). Low ∆<sup>’17</sup>O values occur in hyper-arid climates (AI < 0.05), with mean ∆<sup>’17</sup>O = -0.164 ‰, SD = 0.004 ‰. A transition, or step, occurs in arid climates (AI from 0.05 to 0.2), with ∆<sup>’17</sup>O values that range from -0.129 ‰ to -0.165 ‰, and mean ∆<sup>’17</sup>O of -0.148 ‰, SD = 0.010‰. High ∆<sup>’17</sup>O values occur in semi-arid through humid climates (AI >0.5) with mean ∆<sup>’17</sup>O of -0.135 ‰, SD = 0.008 ‰.  The lowest observed ∆<sup>’17</sup>O values are consistent with extensive evaporation – for context, the ∆<sup>’17</sup>O values are similar to those measured in lacustrine carbonates from closed lake basins. The highest ∆<sup>’17</sup>O values are consistent with little soil water evaporation. We interpret the step-like pattern in ∆’<sup>17</sup>O values as an indication of the threshold in the importance of evaporation vs. transpiration in soil dewatering. This data highlights the potential to use ∆<sup>’17</sup>O to identify the extent of evaporation in paleosol carbonates. Eventually, we hope that this novel technique will lead to quantitative accounting of evaporation in soil water and improved reconstructions of meteoric water δ<sup>18</sup>O from soil carbonates. The ability to constrain the evaporative conditions of soil carbonate formation will also aid interpretations of δ<sup>13</sup>C (including pCO<sub>2</sub> reconstructions) and clumped isotope-based temperatures. These efforts will ultimately aid in our ability to integrate paleoclimate data from soil carbonates with data from other terrestrial records.  </p>

The role of the westerlies and orography in Asian hydroclimate since the late Oligocene

Interactions between midlatitude westerlies and the Pamir–Tian Shan mountains significantly impact hydroclimate patterns in Central Asia today, and they played an important role in driving Asian aridification during the Cenozoic. We show that distinct west-east hydroclimate differences were established over Central Asia during the late Oligocene (ca. 25 Ma), as recorded by stable oxygen isotopic values of soil carbonates. Our climate simulations show that these differences are present when relief of the Pamir–Tian Shan is higher than 75% of modern elevation (∼3000 m). Integrated with geological evidence, we suggest that a significant portion of the Pamir–Tian Shan orogen had reached elevations of ∼3 km and acted as a moisture barrier for the westerlies since ca. 25 Ma.