Cristian Panaiotu

A high resolution optical dating study of the Mostiştea loess-palaeosol sequence (SE Romania) using sand-sized quartz

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.

Remagnetization of Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania): tectonic implications

Abstract We present a pioneering paleomagnetic study on Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania). Thermal and alternating field demagnetizations were applied to define the characteristic remanent magnetization component in all six localities (81 samples). All samples have a normal polarity characteristic remanent magnetization. Negative regional and local fold tests suggest that this remanent magnetization is in fact a remagnetization produced by late diagenetic processes. The studied limestones were probably remagnetized during the collision of the Getic Unit and Danubian Unit which took place during the long normal polarity Chron C34 (82-118 Ma). The area mean direction (D = 75.5°, I = 50.0°, α95 = 10.2°, k = 44) implies about 75° clockwise rotation post remagnetization. Our paleomagnetic results further indicate the absence of significant relative rotation between the Getic Unit and the Danubian Unit during the Cenozoic.

The Lower Danube Loess, New Age Constraints from Luminescence Dating, Magnetic Proxies and Isochronous Tephra Markers

Loess and loess-derivative deposits currently form some of the most ubiquitous sedimentary landforms in Europe, including important parts of Romania. Loess-palaeosol sequences (LPS) are continental archives of Quaternary paleoclimates since these deposits are a direct product of geomorphic processes driven by past climate variability. Understanding these processes needs data input provided by absolute chronologies. Loess is generally considered an ideal material for the application of luminescence dating. In this chapter, we present a review of the latest methodological advances in constraining the chronology of several key Romanian LPS alongside the dating of several loess-alluvial deposits that harbour tephra layers. Luminescence chronologies as well as time-depth models based on magnetic susceptibility variations assign the topmost loess layer to the last glacial cycle that comprises, according to the north European stratigraphic terminology, the Weichselian glaciation (Marine Isotope Stage (MIS) 4 and MIS 2 phases). The uppermost palaeosol is assigned to MIS5 especially to the Eemian interglacial (MIS5e), an equivalent to the north European stratigraphy, and to the Riss–Wurm interglacial in the Alpine stratigraphy. As proved by the high-resolution chronologies, the sedimentation rates of loess varied during the last glacial both within a specific loess section, as well as between different loess sections, the major controlling factor being the topographic context. The luminescence chronologies discussed here improved and expanded the long-held stratigraphy of Romanian loess constructed decades ago by using relative methods, suggesting that a re-evaluation of the regional chronostratigraphic inferences in a high-resolution absolute dating approach has to be conducted.

SAR-OSL dating of Late Pleistocene loess in Southern Romania using fine and coarse-quartz

Loess deposits cover significant areas in Europe, extending from NW-France and Belgium through to central Europe, the Ukraine and Western Russia. The loess palaeosol sequences of the Carpathian Basin-Lower Danube region (Romania, Serbia and Bulgaria) are thought to represent the most continuous and high resolution archives of regional climate and environmental change during the Late and Middle Pleistocene in SE Europe and a link between similar deposits in central Europe and Eurasia. However, in comparison to other loess sequences elsewhere in Western, Central and Eastern Europe, the deposits in Romania have been much less extensively studied. Luminescence dating is, at present, the only method that allows establishing an absolute chronology for loess deposits by virtue of its ability to directly date the moment of sediment deposition. Moreover, the aeolian nature of loess ensures that the luminescence signal is completely reset prior to deposition, a prime requisite for luminescence dating. Thus, loess sediments are ideal materials for developing, testing and applying luminescence techniques. This approach is essential for securely linking loess records from Romania in a chronologically reliable regional framework and to extend this information to other sites from central and eastern European loess belt, in order to understand past paleoenvironmental dynamics at both regional and continental scales.

Palaeomagnetism of the Upper Miocene- Lower Pliocene lavas from the East Carpathians: contribution to the paleosecular variation of geomagnetic field

Investigations of the paleosecular variation of the geomagnetic field on geological timescales depend on globally distributed data sets from lava flows. We report new paleomagnetic results from lava flows of the East Carpathian Mountains (23.6°E, 46.4°N) erupted between 4 and 6 Ma. The average virtual geomagnetic pole position (76 sites) includes the North Geographic Pole and the dispersion of virtual geomagnetic poles is in general agreement with the data of the Time Averaged geomagnetic Field Initiative. Based on this study and previous results from the East Carpathians obtained from 0.04–4 Ma old lava flows, we show that high value of dispersion are characteristic only for 1.5–2.8 Ma old lava flows. High values of dispersion during the Matuyama chron are also reported around 50°N, in the global paleosecular variation data set. More data are needed at a global level to determine if these high dispersions reflect the behaviour of the geomagnetic field or an artefact of inadequate number of sites. This study of the East Carpathians volcanic rocks brings new data from southeastern Europe and which can contribute to the databases for time averaged field and paleosecular variation from lavas in the last 6 Ma.

Paleoclimatic signal of the Dobrogea loess-paleosol sections (Romania)

The investigated area is located in Dobrogea (SE Romania). One site is near the village of Mircea Vodă; the section is ~26 m thick; it comprises six well-developed palaeosols and intercalated loess layers. The second studied site is near Costinesti village, on the Black Sea coast; the section is 12.7 m thick; it comprises five well-developed palaeosols and intercalated loess layers. Samples were collected at 5-10 cm interval. For each sample granulometry was measured with a Horiba laser instrument (LA950) and magnetic susceptibility was measured on a MS2B Bartington susceptibility meter. Throughout the entire sections, the airborne dust (silt and fine sand above 16 µm) is present in large amount (generally over 50%). The pedogenic processes which involve hydrolysis of silicate minerals leading to formation of new clay-sized minerals (< 5 µm) can also be seen throughout the entire section with values always above 10% in the loess layers and values above 20% in the paleosol layers, suggesting that even during loess deposition, weak pedogenesis was present. Fine silt, coarse silt and fine sand material are present in substantial amount in the loess layers (above 10%, above 30% and above 10% respectively). This shows that the wind transportation competency was quite high at the time of loess deposition. Most of the grain-size distributions in the loess layers are bi-modal or even three-modal distribution, reflecting multiple sources of the clastic material. The studied loess sections are of Chinese loess type with a significant enhancement of magnetic susceptibility in paleosol horizons and low values in loess units. The new results from the Costisti section confirm change in the climate during the last two interglaciar stages (paleosols S1 and S2) with respect to the previous ones (paleosols S3, S4 and S5). This transition toward a dryer interglacial is reflected both in the amplitude of the magnetic susceptibility and the type of the paleosols.

The Campanian Ignimbrite tephra layer - a regional stratigraphic marker for the MIS 3 loess deposits of Romania

Loess deposits are widespread in Romania and many open profiles are found along the river valleys crossing the southern plains of the country, and these records are important resources for understanding paleoclimate dynamics and the Paleolithic cultural dispersal at the continental scale. However, loess deposits show significant lateral compositional variations, which bring about regional stratigraphic uncertainties, especially when site-to-site correlations still rely mainly on stratigraphic relationships, and only a handful of profiles having been investigated with more precise dating methods