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Multiproxy approach to the reconstruction of soil denudation events and the disappearance of Luvisols in the loess landscape of south-western Poland
Loess landscapes are highly susceptible to soil redeposition processes and thus may provide detailed insights into the record of denudation processes. Using optically stimulated luminescence dating and the soil micromorphology of 12 soil profiles, we reconstructed a complete record of denudation processes in south-western Poland. The first episode of soil redeposition took place around 9.1 ka. The denudation events that followed were attributed to the Neolithic (6.4 ± 0.3 ka), early Bronze Age (3.8 ± 0.2 ka), early and late Middle Ages (1.5 ± 0.1 ka and 0.7 ± 0.03 ka, respectively) and early Modern (0.4 ± 0.02 ka). As a consequence of the denudation processes, the soil cover in the studied area had been strongly reshaped. The predominant Luvisols had experienced progressive erosion processes that led first to a significant shallowing of the eluvial and argic horizons (truncated Luvisol) and, after some time, to their complete removal. Further thinning of the loess mantles had exposed geological substrates with very weak pedogenic alternations, thus pushing their transformation towards Regosol types. Similarly, Regosols occurred in toeslopes where freshly eroded material had been deposited, and where diagnostic horizons had not yet developed. Modern soil erosion rates in the studied loess area have considerably increased, and it is estimated that the Luvisol status may be completely transformed within approximately 80–300 years, if not sooner, due to progressive climate change.
Late Pleistocene paleosol formation in a dynamic aggradational microenvironment - A case study from the Malá nad Hronom loess succession (Slovakia)
The geomorphological characteristics of the loess succession at Malá nad Hronom (Slovakia) mean that it provides a valuable opportunity for the investigation of differences in soil formation in various topographic positions. Along with the semiquantitative characterization of the paleosols (on the basis of physical properties, texture, the characteristics of peds, clay films, horizon boundaries), high-resolution field magnetic susceptibility measurements and sampling were carried out along four different sections of the profile. Samples for luminescence dating were also taken, in order to establish the chronostratigraphical position of the paleosols studied. The comparison of various proxies revealed the differences in soil formation in a dynamic aggradational microenvironment for the same paleosol horizons located in various positions along the slope. Contrary to expectation, paleosols developed in local top or slope topographical positions did not display significant differences in e.g. in their degree of development, nor the characteristics of their magnetic susceptibility curves. In the case of paleosols in positions lower down the slope, signs of quasi-permanent sediment input could be recognized as being present as early as during the formation of the soil itself. This sediment input would seem to be surpassed in the case of pedogenesis strengthened by the climate of the last interglacial (marine isotope stage - MIS 5). Pedogenesis seems to be sustained by renewed intense dust accumulation in the Late Pleistocene, in MIS 3, though compared to MIS 5, the climate of MIS 3 did not favor intense pedogenesis. Despite the general belief that loess series formed in plateau positions can preserve terrestrial records without significant erosion, in the case of the Malá nad Hronom loess this is not so. Compared to the sequence affected by erosional events in the local top position, the sequence affected by quasi-continuous sediment input in the lower slope position seems to have preserved the soil horizons intact. © 2020 The Author(s)
Geostatistical mapping of the depth to the bottom of magnetic sources and heat flow estimations in Mexico
The depth to the bottom of magnetic sources (DBMS) is widely used as a proxy for crustal thermal structures. In this study, the DBMS is calculated using the spectral analysis of aeromagnetic data for the whole territory of Mexico. By assuming the DBMS to be related to the Curie point depth, the heat flow distribution is estimated. The DBMS and heat flow maps were constructed using geostatistical simulations to quantitatively determine standard deviation as uncertainty. The results show a good agreement with the complex geologic and tectonic setting in Mexico. Small DBMS values (high heat flow) as expected appear in areas where recent volcanism occurs and at seafloor spreading zones. In contrast, large values are present in tectonically stable zones.
Classification of slag material by spectral induced polarization laboratory and field measurements
Historical slag dumps are of increasing interest due to economic, environmental or archaeological reasons. Geophysical investigations can help accessing the potential reuse of slag material to recover metallic raw material or for the estimation of the hazard potential of the buried slag material due to dissolution occurrence. In our study, we have investigated various slag material in the laboratory with the spectral induced polarization (SIP) method, obtained from different historical slag dumps, located in the Harz Mountains, Germany. We also present SIP results from field measurements at a historical slag dump where most of the slag samples reveal high amounts of iron, zinc, silica, and barium. Our results reveal a discrimination between three different slag grades (low, medium, high) by using the imaginary conductivity σ″ at a medium frequency (1–10 Hz) in both laboratory and field. Furthermore, additional information is obtained by a classification based on the spectral polarization behaviour and considering the field frequency range (0.1 Hz – 100 Hz). Five different types of spectra (ascending, descending, constant, maximum and minimum type) can be discriminated and recognized in the laboratory and in distinct areas of the slag dump. Even though a direct comparison between the laboratory and field results still needs to be proven, the buried slag material can be differentiated from the surrounding material by the polarization magnitude.
OSL-dating of the Pleistocene-Holocene climatic transition in loess from China, Europe and North America, and evidence for accretionary pedogenesis
Loess deposits intercalated by paleosols are detailed terrestrial archives of Quaternary climate variability providing information on the global dust cycle and landscape dynamics. Their paleoclimatic significance is often explored by quantifying their mineral magnetic properties due to their sensitivity to local/regional hydroclimate variability. Detailed chronological assessment of such regional proxy records around the climatic transitions allow a better understanding of how regional records react to major global climatic transitions such as the Pleistocene-Holocene climatic transition. Logs of high-resolution magnetic susceptibility and its frequency dependence were used as paleoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil as reflected in nine loess-paleosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, USA. The onset of increase in magnetic susceptibility above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. High-resolution luminescence dating was applied on multiple grain-sizes (4–11 μm, 63–90 μm, 90–125 μm) of quartz extracts from the same sample in order to investigate the timing of Pleistocene-Holocene climatic transition in the investigated sites. The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. The initiation of this increase, interpreted as recording the initiation of the Pleistocene-Holocene climatic transition at each site, was dated to 14–17.5 ka or even earlier. Our chronological results highlight the need of combining paleoclimatic proxies (magnetic susceptibility) with absolute dating when investigating the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid chronostratigraphic misinterpretations in loess-paleosol records caused by simple pattern correlation. The detailed luminescence chronologies evidence the continuity of eolian mineral dust accumulation regardless of glacial or interglacial global climatic regimes. Coupled with magnetic susceptibility records this indicates that dust sedimentation and pedogenesis act simultaneously and result in a non-negligible accretional component in the formation of Holocene soils in loess regions across the Northern Hemisphere. The luminescence ages allowed the modeling of accumulation rates for the Holocene soil which are similar for European, Chinese and U.S.A. loess sites investigated and vary from 2 cm ka−1 to 9 cm ka−1. While accretional pedogenesis has often been implicitly or explicitly assumed in paleoclimatic interpretation of loess-paleosol sequences, especially in the Chinese Loess Plateau, our luminescence data add direct evidence for ongoing sedimentation as interglacial soils formed.
Provenance and paleoenvironmental context of the Late Pleistocene thin aeolian silt mantles in southwestern Poland – A widespread parent material for soils
Thin loess deposits are widespread soil parent materials and important archives for paleoenvironmental reconstruction. The origin of loess in SW Poland is attributed to the Great Odra Valley (GOV), following the general concept that large rivers play a major role in regional silt supply. Yet, the precise provenance (glacier sources and/or local rocks) of silts, possibly deflated from dry GOV braided riverbeds, is not clear. Our study of thin and thick loess mantles in SW Poland for the first time indicates the provenance of thin loess based on mineralogical (MLA-SEM) and isotopic analyses (143Nd/144Nd, 87Sr/86Sr). Luminescence ages of five localities point to thin loess mantle formation during and shortly (23.0 to 17.7 ka yr) after the Last Glacial Maximum (LGM). Our isotopic data indicate that thin loess deposits in SW Poland are the mixtures of two main components – local Sudetic and Scandinavian, the latter delivered by the Fennoscandian ice sheet (FIS). Also, detailed analyses of heavy minerals show that a single mineral (e.g., hornblende) may come from both Sudetic and Scandinavian sources. This research highlights the role of the (Pleistocene) GOV in collecting and homogenizing materials, while supplying the region with fine particles to be deflated by paleowinds from open surfaces. Anomalies in mineralogy and isotopic composition are connected with influence of Sudetic mountain rivers and locally blowing silt material by katabatic winds. Regional grain size differentiation of thin loess mantles explains transport distance and altitude. © 2021 The Authors
S-wave experiments for the exploration of a deep geothermal carbonate reservoir in the German Molasse Basin
There are many successful geothermal projects that exploit the Upper Jurassic aquifer at 2–3 km depth in the German Molasse Basin. However, up to now, only P-wave seismic exploration has been carried out. In an experiment in the Greater Munich area, we recorded S-waves that were generated by the conventional P-wave seismic survey, using 3C receivers. From this, we built a 3D volume of P- to S-converted (PS) waves using the asymptotic conversion point approach. By combining the P-volume and the resulting PS-seismic volume, we were able to derive the spatial distribution of the vp/vs ratio of both the Molasse overburden and the Upper Jurassic reservoir. We found that the vp/vs ratios for the Molasse units range from 2.0 to 2.3 with a median of 2.15, which is much higher than previously assumed. This raises the depth of hypocenters of induced earthquakes in surrounding geothermal wells. The vp/vs ratios found in the Upper Jurassic vary laterally between 1.5 and 2.2. Since no boreholes are available for verification, we test our results against an independently derived facies classification of the conventional 3D seismic volume and found it correlates well. Furthermore, we see that low vp/vs ratios correlate with high vp and vs velocities. We interpret the latter as dolomitized rocks, which are connected with enhanced permeability in the reservoir. We conclude that 3C registration of conventional P-wave surveys is worthwhile.
Loess landscapes of Europe – Mapping, geomorphology, and zonal differentiation
Paleoenvironmental reconstructions on a (supra-)regional scale have gained attention in Quaternary sciences during the last decades. In terrestrial realms, loess deposits and especially intercalations of loess and buried soils, so called loess-paleosol sequences (LPS) are important archives to unravel the terrestrial response to e.g. climatic fluctuations and reconstruct paleoenvironments during the Pleistocene. The analysis of LPS requires the knowledge of several key factors, such as the distribution of the aeolian sediments, their location relative to (potential) source areas, the climate conditions that led to their emplacement and the topography of the sink area. These factors strongly influence the sedimentological and paleoenvironmental characteristics of LPS and show broad variations throughout Europe, leading to a distinct distribution pattern throughout the continent. We present a new map of the distribution of aeolian sediments (mainly loess) and major potential source areas for Europe. The map was compiled combining geodata of different mapping approaches. Most of the used geodata stems from accurate national maps of 27 different countries. Problematic aspects such as different nomenclatures across administrative borders were carefully investigated and revised. The result is a seamless map, which comprises pedological, geological, and geomorphological data and can be used for paleoenvironmental and archeological studies and other applications. We use the resulting map and data from key geomorphological cross-sections to discuss the various influences of geomorphology and paleoenvironment on the deposition and preservation of Late Pleistocene loess throughout Europe. We divided the loess areas into 6 main loess domains and 17 subdomains to understand and explain the factors controlling their distribution and characteristics. For the subdivision we used the following criteria: (1) influence of silt production areas, (2) affiliation to subcatchments, as rivers are very important regional silt transport agents, (3) occurrence of past periglacial activity with characteristic overprinting of the deposits. Additionally, the sediment distribution is combined with elevation data, to investigate the loess distribution statistically as well as visually. Throughout Europe, the variations, and differences of the loess domains are the results of a complex interplay of changing paleoenvironmental conditions and related geomorphologic processes, controlling dust sources, transport, accumulation, preservation, pedogenesis, alongside erosional and reworking events. Climatic, paleoclimatic, and pedoclimatic gradients are on the continental scale an additional important factor, since there are e.g. latitudinal differences of permafrost and periglacial processes, an increase in continentality from west to east and in aridity from northwest to southeast and south, strongly affecting regional sedimentary and geomorphic dynamics. We propose three main depositional regimes for loess formation in Europe: (1.) periglacial and tundra loess formation with periglacial processes and permafrost in the high latitude and mountainous regions; (2.) steppe and desert margin loess formation in the (semi-)arid regions; and (3.) loess and soil formation in temperate and subtropical regions. Loess deposits of (1.) and (2.) show coarser, sandier particle distributions towards the glacial and desert regions. In the humid areas (3.) forest vegetation limited dust production and accumulation, therefore, there is an increase in finer grain sizes due to an increase in weathering.
The geodynamic and limnological evolution of Balkan Lake Ohrid, possibly the oldest extant lake in Europe
Studies of the upper 447 m of the DEEP site sediment succession from central Lake Ohrid, Balkan Peninsula, North Macedonia and Albania provided important insights into the regional climate history and evolutionary dynamics since permanent lacustrine conditions established at 1.36 million years ago (Ma). This paper focuses on the entire 584-m-long DEEP sediment succession and a comparison to a 197-m-long sediment succession from the Pestani site ~5 km to the east in the lake, where drilling ended close to the bedrock, to unravel the earliest history of Lake Ohrid and its basin development. 26Al/10Be dating of clasts from the base of the DEEP sediment succession implies that the sedimentation in the modern basin started at c. 2 Ma. Geophysical, sedimentological and micropalaeontological data allow for chronological information to be transposed from the DEEP to the Pestani succession. Fluvial conditions, slack water conditions, peat formation and/or complete desiccation prevailed at the DEEP and Pestani sites until 1.36 and 1.21 Ma, respectively, before a larger lake extended over both sites. Activation of karst aquifers to the east probably by tectonic activity and a potential existence of neighbouring Lake Prespa supported filling of Lake Ohrid. The lake deepened gradually, with a relatively constant vertical displacement rate of ~0.2 mm a−1 between the central and the eastern lateral basin and with greater water depth presumably during interglacial periods. Although the dynamic environment characterized by local processes and the fragmentary chronology of the basal sediment successions from both sites hamper palaeoclimatic significance prior to the existence of a larger lake, the new data provide an unprecedented and detailed picture of the geodynamic evolution of the basin and lake that is Europe’s presumed oldest extant freshwater lake.
Porosity estimation of a geothermal carbonate reservoir in the German Molasse Basin based on seismic amplitude inversion
The Molasse Basin is one of the most promising areas for deep geothermal exploitation in Germany and the target horizon is the aquifer in the Upper Jurassic carbonates. Carbonate deposits can be very heterogeneous even over a small area due to diagenetic processes and varying depositional environments. The preferential targets for geothermal exploitation in carbonate deposits are fault zones, reef facies and karstified areas, since they are expected to act as hydraulically permeable zones due to high porosity and high permeability. Therefore, identifying these structures and characterizing, e.g., their internal porosity distribution are of high importance. This can be accomplished using 3D reflection seismic data. Besides structural information, 3D seismic surveys provide important reservoir properties, such as acoustic impedance, from which a porosity model can be derived. In our study area in Munich we carried out a seismic amplitude inversion to get an acoustic impedance model of the Upper Jurassic carbonate reservoir using a 3D seismic data set, a corresponding structural geological model, and logging data from six wells at the ‘Schäftlarnstraße’ geothermal site. The impedance model and porosity logs were than used to calculate a porosity model. The model shows a wide porosity range from 0 to 20% for the entire reservoir zone and the lithology along the wells reveals that dolomitic limestone has the highest porosities and calcareous dolomite has the lowest porosities. The study area is cut by a large W–E striking fault, the Munich Fault, and the footwall north of it shows higher porosities and more intense karstification than the hanging wall to the south. Considering the entire study area, an increase in porosity from east to west is observed. Furthermore, we identified a complex porosity distribution in reef buildups and pinnacle reefs. The reef cores have mostly low porosities of, e.g., < 3% and the highest porosities of up to 7 to 14% are observed at the reef caps and on the reef slopes. The reef slopes show a characteristic interfingering of the reef facies with the surrounding bedded facies, which indicates a syn-sedimentary reef development with slightly varying build up growth rates. We also assessed the reservoir quality with regard to porosity distribution and determined areas with moderate to good quality for geothermal exploitation by defining porosity evaluation levels. The porosity evaluation maps show that the carbonate rocks of Berriasian to Malm ζ1 are preferential targets for exploitation, especially in the footwall of the Munich Fault and to the west of the hanging wall, because these areas are characterized by high porosities due to intense karstification of bedded and massive facies, although the latter is mainly restricted to reef caps and reef slopes.