Palaeomagnetic determination of transgressive and regressive movements during the quaternary in the Black Sea

Summary The piston core with a length of 60·8 m from the Samotino-east structure of the Bulgarian Black Sea shelf (about 28·2 E, 42·8 N) is studied palaeomagnetically. 129 levels from the interval 2·5–60·2 m, generally represented by clays and aleurolitic muds, were sampled. The age of the sediments of this core was determined by correlation with another core, situated very close to the one concerned (3 km), whose fauna is known very well. Its age is Eopleistocene (Gurinian deposits), Upper Pleistocene (Neweuxinian deposits) and Holocene.Standard palaeomagnetic methods are used to determine the components of NRM and the main carriers of primary magnetization (AF and thermal demagnetization of NRM, thermodemagnetization of J_rs and J_s).It is assumed that the basic carrier of NRM is coarse-grained ferrimagnetic monoclinic pyrrhotite (T_B of 300 °C) or partly oxidized pyrite (T_B of 400 °C).It is shown that the pyrite concentration varies along the depth of the section. This palaeomagnetically established variation corresponds very well to the data on the transgressive and regressive phases in the Black Sea basin. For the Gurinian deposits these phases are connected with the Danube and Güns glacials, the D-G interglacial and G1-G2 interstadial. No such correlation has so far been mentioned in the literature to our knowledge.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990.     

Particle image velocimetry evaluation of flow-altering countermeasures for local scour around a submerged circular cylinder

The effect of scour countermeasures on the mechanism of local scour around a cylinder requires clarification in order to develop design methodology for use in practice. Previous investigations on countermeasure performance, though useful, have not provided adequate measurements to support this understanding. In the present investigation, particle image velocimetry(PIV) measurements were acquired at several streamwise-vertical planes in the flow field surrounding a submerged circular cylinder wit...     

Rock magnetic properties of recent soils from northeastern Bulgaria

In this paper, basic rock magnetic studies of Holocene loess-soil samples from northeastern Bulgaria are reported. The sites are related to the Danube river and located at different distances southwards, thus representing various pedogenic conditions. The study is primarily aimed at determining the main magnetic carrier(s) and their physical characteristics (grain-size distribution, magnetic enhancement, etc.). Oxyhydroxides, maghemite and titanomagnetites of various oxidation degrees are assumed to be the main ferromagnetic minerals present. Our results suggest that the uppermost part of recent soil profiles is rich in stable, near-single-domain (SD) particles, while the illuvial horizons are characterized by a gradual decrease in grain sizes, from highly viscous to a true superparamagnetic (SP) domain state. The properties of samples from carbonate-rich horizons of recent soils are basically controlled by detrital minerals, while those from sites with more intensive pedogenesis and especially grey forest soils are influenced by strongly magnetic minerals formed ' in situ '.