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This paper aims to establish the role of the local topography of Sălcuța Plain (subdivision of the Oltenia Plain) in the subsidence process of loess-like deposits. The relevant features of the topography, especially the slope, were generated using SAGA GIS v.7.8.0 and QGIS v.3.22 software based on an altimetric terrain model. The results obtained highlight the fact that 303 microdepressions were formed following the chemical and mechanical subsidence of the loess deposits. The most important characteristic, which conditions the genesis of the subsidence process and implicitly the formation of microdepressions, is the slope; in this case, the subsidence process occurs in areas where the slope has values lower than 2 degrees. The research advanced by generating the Topographic Wetness Index (TWI) in order to identify areas with moisture excess, the moistening of loess-like deposits being one of the basic conditions in the genesis of the subsidence process. The highest values of the Topographic Wetness Index (TWI), over 10, were recorded in the areas with microdepressions. [ABSTRACT FROM AUTHOR]

The key reference loess sequence of Viatovo in NE Bulgaria, lying within the lower Danube basin, records climatic and environmental changes over the last 800 ka. This 20 m thick loess sequence consists of seven loess units (L1 to L7) intercalated by six paleosols (S1 to S6) below the modern soil (S0). The Matuyama-Brunhes palaeomagnetic boundary has been identified in the lowest loess unit (L7). This reference loess sequence remains so far undated by radiometric techniques. Its chronostratigraphy relies only on pedostratigraphic and magnetostratigraphic evidence. This contrasts with the adjacent reference loess sequences of SE Romania (Tuzla, Mostistea, Mircea Vodă) whose luminescence chronology is now securely established up to MIS 8. The aim of this study is to validate the chronostratigraphic framework of the Viatovo loess sequence using the luminescence dating method. For this purpose, the luminescence method is applied to the three upper loess units (L1, L2, L3) from two adjacent sites: the reference site of Viatovo and the nearby site of Kaolinovo, both located in the Ludogorie region (NE Bulgaria) and showing the same superposition of loess (L1 to L7) and interbedded paleosols. Luminescence dating (Infrared stimulated luminescence; IRSL) was carried out using the feldspar fine sand-size grain fraction (60–80 μm), applying the IRSL 50 and the pIRIR 290 dating techniques. For the equivalent dose (De) determination we used both the SAR post-infrared infrared (pIRIR 290) protocol on single aliquots and the multiple-aliquot additive dose (MAAD IRSL 50) protocol. The pIRIR 290 ages and the fading corrected MAAD-IRSL 50 ages are self-consistent. It demonstrates for the first time, that the three upper loess layers (L1, L2, L3) at Viatovo and Kaolinovo were deposited during the marine isotope stages (MIS) 2–4, 6 and 8, thus constraining the youngest well-developed paleosol (S1, a chernozem) to the Last Interglacial. These IRSL 50 and pIRIR 290 ages are in good agreement with the luminescence ages obtained for (1) the two upper loess layers (L1, L2) from the Harletz sequence in NW Bulgaria and (2) the three upper loess units (L1, L2, L3) from the adjacent SE Romanian loess sequences. The luminescence chronology of the loess sequences is presented along with the pedogenic and magnetic property data. The pedostratigraphic records of the NE Bulgarian and SE Romanian loess sequences show the same palaeoclimatic trends, with progressive aridification during interglacial periods (from S6 to S0). [ABSTRACT FROM AUTHOR]

Abstract: The Eastern European loess steppe represents one of the most substantial landform types on the continent, yet the impact on this region of the last glacial maximum (LGM), the coldest climatic episode during the last full glacial cycle, is relatively poorly understood. This is in part due to the comparatively small number of sites which have been reliably dated, and in part due to the need to better elucidate depositional models for loess environments at both local and regional scales. Here we present a high-frequency age–depth profile for the last 40 ky from a loess deposit at Urluia in southeastern Romania, using fine-grained quartz optically stimulated luminescence (OSL) dating and environmental magnetism analyses. Loess accumulation at the site for this period is well constrained by a clearly identifiable tephra deposit corresponding to the ca. 39 ka Campanian Ignimbrite. We show that the tephra is directly overlain by a relatively thin layer of loess corresponding to marine isotope stage (MIS) 3, which is partially overprinted by a weakly developed paleosol. The sequence is dominated by a 6–8 m package of primary loess of LGM age. The eight OSL samples from this package group together around a mean age of 21.6 ± 1.5 ka, and suggest rapid and substantial deposition during this phase. The uppermost part of the section indicates significantly reduced loess accumulation, during the deglacial period into the Holocene, less than 2 m in total thickness. The rapid accumulation of loess during the LGM at Urluia is consistent with increased sedimentation at other loess profiles in the Lower Danube basin, although the variable thickness of these deposits across the catchment highlights the need to more explicitly investigate depositional models for loess. The Urluia record complements emerging data which suggests that the Lower Danube loess steppe was cold, dry and windy during the LGM, yet experienced milder climates than comparable latitudes further west and north, and did not undergo periglacial activity. [Copyright &y& Elsevier]

Abstract: The paper reports on continuing luminescence investigations of Romanian loess using samples collected from the loess-palaeosol sequence near Mircea Vodă (SE Romania). Previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11μm and 63–90μm) yielded discrepant chronologies for the last interglacial–glacial cycle. In this study, a double-SAR protocol is used to determine the age of polymineral fine (4–11μm) grains through their infrared stimulated luminescence (IRSL) and post-IR optically stimulated luminescence (post-IR OSL) emissions in the UV. Laboratory tests confirm the suitability of the protocol for both signals. Fading measurements indicate a significant feldspathic contribution to the post-IR OSL signal. In general, the fading-corrected IRSL and post-IR OSL age results are mutually consistent, and they agree with previously reported OSL ages for fine-grained (4–11μm) quartz. This agreement enhances the reliability of the ages obtained using luminescence signals from fine-grains, and allows more confident correlation of the weakly-developed palaeosol in the uppermost loess unit (L1) with marine isotope stage 3 (MIS3). The fading-corrected ages underestimate the depositional age of older material (units L2–L4), probably owing to limitations of the correction model. [Copyright &y& Elsevier]

Abstract: A detailed rock-magnetic investigation of loess/palaeosol samples from the section at Mircea Vodă (Dobrogea Plateau, Romania) is presented. Investigation of climatic control on magnetic granulometry used several grain-size and concentration-dependent proxies (magnetic susceptibility and its frequency dependence, anhysteretic remanent magnetization, isothermal remanent magnetization, hysteresis properties and FORC distributions) and an unmixing model for isothermal remanent magnetization curves. The paleosol layers in the Mircea Vodă sequence experienced significant pedogenic alteration, resulting in high amounts of ultrafine grained SP, grains at SP/SD threshold, stable SD grains and PSD magnetite/maghemite grains. The loess layers in the Mircea Vodă sequence are dominated by MD and/or PSD oxidized magnetite probably of aeolian origin. The unmixing model for IRM curves shows the presence of three components with different coercivities. The soft (∼21 mT) and medium (∼42 mT) coercivity components are produced by pedogenesis during interglacial and interstadial periods. The hard coercivity component (∼60 mT) is of aeolian origin, being dominant in loess layers. [Copyright &y& Elsevier]

In this study we test the potential of the elevated temperature infrared stimulated luminescence (IRSL) signals for dating Romanian loess. The recently developed post-IR IRSL protocol is applied to Romanian loess using polymineral fine grains extracted from the loess-palaeosol sequence at Mircea Vodă (SE Romania). This approach is aimed at obtaining an additional age control to examine the age discrepancy obtained from previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11 μm and 63–90 μm). Two preheat post-IR IR stimulation temperature combinations were used, 250–225 °C and 325–300 °C, respectively. The signals obtained are documented in terms of dose response curve, laboratory tests and fading. Although both post-IR IRSL signals exhibit small fading rates, dose response characteristics indicate that these rates may be laboratory artefacts. The post-IR IRSL signal stimulated at 300 °C is observed to suffer from dose dependent initial sensitivity changes as both natural and regenerated signals are observed to lie above the saturation level of the dose response curve. Uncorrected age results obtained using both post-IR IRSL signals are in general agreement with previously reported silt-sized quartz OSL ages for samples collected from the uppermost loess unit L1. For older material, the post-IR IRSL signal stimulated at 225 °C is considered to provide reliable age results, in agreement with independent age control available for this sequence. [ABSTRACT FROM AUTHOR]

This tentative synopsis mainly focusses on the aspects of dating the loess - palaeosol sequences in the Romanian Plain and Dobrogea. The approach - placed in a historical framework - is defined by two characteristics. The first part is a short review of important achievements concerning the estimation or evaluation of the loess age, starting ca 120 years ago and ending in 1961. The second part continues with the loess dating history in a comprehensive table systematizing significant contributions of the last half-century. Actually, this article has been generated by another paper (under review), dedicated to a conceptual sedimentary model of the loess in the Lower Danube Basin (Jipa, submitted). The table emphasizes the interest for the loess dating during the last 50 years, and follows the chronological order of contributions. Implicitly, it is remarked the way passed through time in order to know the loess age, i.e. from the classic stratigraphy/pedostratigraphy to magnetostratigraphy, astronomically tuned ciclostratigraphy, magnetoclimatology, and up to the multi-proxy approach and optical/luminescence dating. In most of the sections, ages up to 781 ka are determined (the loess - palaeosol horizons are assigned to the Brunhes Chron of the ATNTS20004/ATNTS2012), but the synopsis includes a section from Dobrogea (analysed by the Infrared Stimulated Luminescence/IRSL dating method; Bălescu et al., 2003), wherefore the "estimated geological age" of 800 ka and the Marine Isotope Stage 20 are mentioned. Moreover, a recent result (Rădan, 2000, updated in 2012 - references therein) for a loess - palaeosol borehole profile (ca 30m thick) from the Romanian Plain points out, according to the palaeomagnetic investigation of the basal part and to the magnetic susceptibility vertical variation along the sampled borehole (40m depth), the possible identification of the Matuyama/Brunhes boundary (0.781 Ma), located at the base of the MIS 19. This subject has generated a dispute in the scientific literature on both the Chinese and the European loess. A tentative discussion on the "observed MBB" (within the loess horizon L8) and the "corrected/true MBB" (placed within the palaeosol S7) is done, by comparing our results from the Romanian Plain with data from the Chinese Loess Plateau [ABSTRACT FROM AUTHOR]

Abstract: The loess-palaeosol sequence near Mircea Vodă (Dobrogea, SE Romania) is thought to comprise at least five glacial/interglacial cycles. It is considered as one of the most significant records of Late Quaternary environmental and climatic change in the region. Age information for the sequence was previously obtained through time–depth modeling of magnetic susceptibility data and optically stimulated luminescence dating (OSL) of fine silt-sized (4–11 μm) quartz. This study documents the granulometric properties of the sequence, and compares the OSL characteristics and age of fine sand-sized (63–90 μm) quartz to those of silt-sized quartz. OSL signals from both sand and silt-sized quartz are dominated by a thermally-stable fast decaying component. A suite of laboratory test confirms that the single-aliquot regenerative dose (SAR) protocol is suitable for these samples. Each grain-size fraction yields a set of optical ages that is consistent with the stratigraphic position of the samples. The ages obtained using sand-sized grains, however, are up to 70% higher than those obtained using silt-sized quartz. The discrepancy in age results is not understood as, according to procedural tests, the OSL signal from both fractions should be suitable for dating the deposits. As such, it cannot be established whether the uppermost weakly-developed palaeosol was formed during MIS3 or MIS5 and if the rate of loess accumulation varied during the Last Glacial, only by using standard SAR-OSL techniques. Both sets of ages do confirm, however, that the first well-developed palaeosol (S1) is of Last Interglacial age. [Copyright &y& Elsevier]

We report on SAR-OSL dating of closely-spaced samples from the loess-palaeosol sequence near Mostiştea lake (Danube Plain, SE Romania). We used sand-sized quartz and a SAR protocol that involved a preheat of 10s at 220°C and a test dose cutheat to 180°C. It is shown that these thermal pretreatments isolate a quartz OSL signal that is dominated by the fast component. The behaviour of this signal in the SAR protocol is then documented. The ratio of the measured to given dose tends to lie slightly but systematically above unity (∼5% on average) and the recycling ratio below unity (∼6% on average); for all samples, the recuperated signal is negligible. Within analytical uncertainty, the nineteen optical ages are internally consistent and agree with the predictions from a palaeomagnetic age-depth model. Although it may be possible to optimize the SAR measurement procedure, the optical ages already confirm the chronostratigraphic position of the uppermost welldeveloped palaeosol in that it formed during MIS 5. The established chronology allows correlating the sequence near Mostiştea lake with that near Mircea VodĂ that we investigated earlier. [ABSTRACT FROM AUTHOR]

Abstract: Located in the South Carpathians in Romania, the Haţeg Basin contains a thick sequence of Maastrichtian continental deposits yielding a rich dinosaur and mammalian fauna. Stable isotope analyses of both calcretes and dinosaur, crocodilian and turtle remains from two localities (Tuştea and Sibişel) were integrated in order to reconstruct environmental conditions during Maastrichtian time and to gain further insights into the metabolism and behaviour of the vertebrates. The large difference observed between the δ 18O and δ 13C of the eggshells and the surrounding mudstones, as well as the preservation of the 9‰ difference between the oxygen isotope composition of the Telmatosaurus eggshell and tooth enamel, indicate that diagenesis has not significantly altered the primary isotopic signal. The presence of smectite in the fraction less than 2μm and the preservation of dinosaur eggshell structure also indicate that diagenesis was not significant in the studied outcrops. Stable isotope compositions of both calcretes and phosphatic remains suggest warmer conditions during the deposition of the Tuştea sequence (mean annual temperature of around 14°C) than during the deposition of the Sibişel sequence (mean annual temperature of 10°C). The intra-tooth δ 18O patterns for Zalmoxes and Allodaposuchus show different magnitudes of isotopic variation, with lower values for Tuştea and higher for Sibişel. The calculated δ 18Obody water enrichment for Kallokibotion bajazidi is similar to that found in living turtle taxa. By contrast, in the case of Allodaposuchus, the isotopic enrichment is higher than for recent taxa. This suggests that, for Allodaposuchus, the body water was less buffered by a watery environment, which probably indicates more time spent outside water (i.e. more terrestrial habit). The δ 18O values for the teeth of Telmatosaurus and Zalmoxes are similar to those of Allodaposuchus, suggesting that, at the investigated sites, the body temperature of both dinosaurs was similar to that of the crocodile. The isotopic composition of calcretes, teeth and eggshells indicates a C3 vegetation and diet with δ 13C values between −27 and −29‰ (PDB) and the absence of large-scale habitat partitioning between the dinosaurs. [Copyright &y& Elsevier]

Abstract: In the Haţeg basin, South Carpathians, a thick continental sequence accumulated during the Maastrichtian. The alluvial sequences are characterized by the formation of paleosol horizons developed on the alluvial plain. In order to investigate the environmental signal stable isotope and mineralogical investigations have been carried out on smectites from paleosol. The RX as well as the FTIR spectra of the fraction <2 µm indicate that the main clay mineral is smectite. Based on XRF analysis, the smectite is a montmorillonite with the formula {Na0.67 Ca0.1}[Al1.19 Mg0.62 Fe3+ 0.19] (Si3.78 Al0.22 O10) (OH)2. FTIR data show that interlayer water from smectite is liberated after ~24 h heating at 200 °C. Stable isotopic composition of precipitations have been monitored in the Hateg basin and in a neighbored area situated in the Apuseni mountains. The results show the same meteoric water line (LMWL) with the equation δD=7.9⁎δ18O+8.14 for both sites. Stable isotope data on clay fraction less than 2 µm show that the structural water from smectites formed under different environmental conditions during the Maastrichtian have re-equilibrated isotopically with the present meteoric water. [Copyright &y& Elsevier]