SE Romania Research Articles

Chitinozoan implications in the palaeogeography of the East Moesia, Romania

Palaeomagnetic data from Moesia are absent and previous palynological and macrofaunal studies could not show clearly the palaeogeographical position of Moesia between the larger palaeocontinents Gondwana, Baltica, or Avalonia. Cutting samples from three boreholes on East Moesia (SE Romania) have been investigated in this study using S.E.M technique. Chitinozoan assemblages prove the presence of Wenlock–Ludlow (possibly Homerian and Gorstian), Přídolí, and Lochkovian. Those of the last have a pronounced distribution in North Gondwanan localities; one of them, Cingulochitina plusquelleci, is illustrative only in North Gondwanan regions. These chitinozoans argue that East Moesia and probably West Moesia were in good communication with the Ibarmaghian Domain of the Northern Gondwana palaeocontinent.

The crustal structure beneath SE Romania from teleseismic receiver functions

SUMMARY Due to vigorous Neogene geodynamic processes, including oceanic subduction, slab break-off and mountain building in the Carpathian Arc, the architecture of the lithosphere in Romania is quite complicated. To improve the knowledge about the lithosphere‐asthenosphere system in this region the passive seismological CALIXTO99 experiment was conducted in 1999 in the SE part of Romania. Here we present crustal models derived from the analysis of teleseismic recordings with the receiver function (RF) method of the 120 temporarily installed stations and of the permanent GEOFON stations MLR and TIRR. The RF results extend the known crustal models which are based mainly on seismic refraction work and analysis of regional earthquakes. We apply a grid-search inversion at 30 stations and use two different error estimation methods to determine the Moho depth and the average crustal vp/vs ratio. The complex 3-D intracrustal structure, especially the deep sedimentary basins, distorts significantly the RF waveforms within the whole station network. This leads to ambiguous results at some stations. Our model of the Moho depth has a maximum crustal thickness in the SE Carpathian Mountains at station MLR with a depth of about 45 km and an average crustal vp/vs ratio of 1.79. The surrounding crust in SE Romania has a thickness of mainly 35‐40 km. The RFs at MLR are characterized by clear azimuthal effects that can be correlated with the variation of the sediment thickness in the foredeep of the Carpathian Mountains. A RF waveform inversion verifies these results and gains improved 1-D S-wave velocity models at several stations in SE Romania.

High-resolution teleseismic body-wave tomography beneath SE Romania - I. Implications for three-dimensional versus one-dimensional crustal correction strategies with a new crustal velocity model

SUMMARY The CALIXTO (Carpathian Arc Lithosphere X-Tomography) experiment offers a dense, high-quality data set to study the lithospheric/asthenospheric system underneath SE Romania, an earthquake-prone region in SE Europe. To increase the image resolution of structures in the uppermost mantle, the application of crustal traveltime corrections by a priori information before the teleseismic traveltime inversion has become a well-accepted procedure. For such a correction we present a regional 3-D crustal seismic velocity model that serves as the basis for a high-resolution teleseismic tomography (forthcoming paper by Martin et al.). Our 3-D crustal model is based on recent research in the region. We collect new results from two long-range seismic refraction lines, 3-D refraction tomography and teleseismic Ps conversions. Adding previously published models of the sediment distribution, Conrad and Moho depths, as well as crustal seismic P-wave velocities, we compile a 3-D crustal model for SE Romania. This 3-D model does not contain shallow small-scale heterogeneities (<10 km), but it reflects the large-scale structures such as variations in sediment thickness, average seismic velocities and 3-D Moho depth. It is well suited for the correction of teleseismic traveltime residuals, a prerequisite for a high-resolution teleseismic tomography study: for example, traveltime delays of up to 1.3 s are caused by the almost 20-km thick layer of sediments in the Focsani Basin. Such delays are comparable to or larger in size than the expected upper mantle traveltime residuals. We study the significance of 3-D crustal traveltime corrections relative to 1-D station corrections and show that the complex basin structures in SE Romania require a 3-D approach to reduce the smearing of crustal anomalies into the mantle. By modelling synthetic mantle structures with a slab, as it is expected for SE Romania, we also investigate how to adapt the inversion strategy, if crustal corrections are applied. Significant improvements are found by including the already corrected crustal layers in the inversion procedure, thereby enabling the inversion algorithm to project still remaining uncertainties in the less-resolved upper crustal layers. However, the fixing of the upper layers during the inversion due to the a priori knowledge of the crustal velocity anomalies clearly leads to smearing of uncorrected anomalies that are possibly located close to the crust–mantle boundary.

Halmyris, a settlement and fort near the mouth of the Danube: interim report

Ancient Halmyris lies in the NW corner of the Dobrudja region in SE Romania. It liesc.2.5 km east of the village of Murighiol on a rocky promontory which is slightly higher than the surrounding marshes. This is at the E end of the Dunavat peninsula (known in antiquity asExtrema Scythiae Minoris: Jord., Get.266) and it is bordered by the Danube delta on the north and east, Razelm lake on the south, and the Tulcea hills on the west (fig. 1). The site was occupied continuously from at least the mid-first millennium B.C. up to the 7th c. A.D. The local environment, flora and fauna were favourable to settlement until as a result of natural causes the Danube became almost inaccessible; from that point on, the settlement became vulnerable to human and other natural events and eventually it became deserted.The site is known today as Bataraia or Cetatea. In the early 20th c. the locals still called it the Genoese stronghold (Geneviz-Kaleh). In antiquity it lay on the bank of the southern arm of the Danube called Peuce (now known as Sfantu Gheorghe). Today the southern arm of the Danube runs 2 km north of the site and it is connected to Lake Murighiol by the Periboina canal. Until 1983 there were two lakes,c.100 andc.200 m from the site, modern relics of the ancient course of the river. To the east lie the Dunavat hills and to the south is Dealul Cetatea (“fort hill”) (fig. 2).

Comparative analysis of aerosols elemental distribution in some Romanian regions

The study's main aim is obtaining aerosols particulate elemental distribution and mapping it for some Romanian regions, in order to obtain preliminary information regarding the concentrations of aerosol particles and networking strategy versus local conditions. For this we used the mobile sampling strategy, but taking care on all local specific conditions and weather. In the summer of 1993, in July we took about 8 samples on a rather large territory of SE Romania which were analysed and mapped. The regions which showed an interesting behaviour or doubts such as Bucharest and Dobrogea were zoomed in near the same period of 1994, for comparing the new details with the global aspect previously obtained. An attempt was made to infer the minimum necessary number of stations in a future monitoring network. A mobile sampler was used, having tow polycarbonate filter posts of 8 and 0.4 μm. PIXE elemental analysis was performed on a 2.5 MV Van de Graaff accelerator, by using a proton beam. More than 15 elements were measured. Suggestive 2D and 3D representations were drawn, as well as histogram charts for the concentrations' distribution in the specific regions at the specified times. In spite of the poor samples from the qualitative point of view the experiment surprised us by the good coincidence (good agreement) with realities in terrain known by other means long time ago, and highlighted the power of PIXE methods in terms of money and time. Conclusions over the link between industry, traffic, vegetation, wether, surface waters, soil composition, power plant exhaust and so on, on the one hand, and surface concentration distribution, on the other, were drawn. But the method's weak points were also highlighted; these are weather dependencies (especially air masses movement and precipitation), local relief, microclimate and vegetation, and of course localisation of the sampling point versus the pollution sources and their regime. The paper contains a synthesis of the whole of the maps and graphs we made, intended in its turn to demonstrate the necessity of a national integrated network for monitoring aerosols.