HR: 1340h
AN: GP53B-1220    [Abstracts]
TI: Modern Sediments as Enviromagnetic Archives. A Case Study: Danube Delta and Northwestern Black Sea
AU: * Radan, S C
EM: radan_sc@yahoo.com
AF: Geological Institute of Romania, 1 Caransebes St., Bucharest, RO-012271, Romania
AU: Radan, S
EM: radan@geoecomar.ro
AF: GeoEcoMar, 23-25 Dimitrie Onciul St., Bucharest, RO-024050, Romania
AB: The Danube Delta and the Razim - Sinoie Lagoonal Complex are two special units of the Danube - Black Sea hydrosedimentary geosystem, acting as a buffer interface between the Danube River water and sediment supplies collected from a large catchment area, and the Black Sea semi-enclosed marine basin. A vast enviromagnetic archive of modern sediments from this aquatic system was sampled in the 1976-2007 time span. The magnetic signatures identified in the sediments are able to characterize and differentiate the depositional environments inside of an extended, diversified, and at the same time, unitary complex of fluvial, lacustrine, lagoonal, deltaic and marine ecosystems. Confined versus dynamic deltaic environments were compared and defined by specific magnetic fingerprints. The sediments of the lakes that are successively located along a main water flowing way modify their lithological, mineralogical and chemical characteristics, as a consequence of differential transport and sedimentation, and by passing from a dynamic aquatic environment towards a more or less stagnant environment. This situation is well reflected by the magnetic signatures and it is investigated at a regional scale, when two lacustrine areas - situated far, respectively close of the main fluvial influx points - are discussed, and at a local scale, when several interconnected `couples of lakes` are analyzed. Besides, as in certain cases the bottom sediments were sampled in the same zones, in successive phases, at time intervals of 5-10 years, the modified magnetic fingerprints clearly demonstrated the presence or the absence of the anthropogenic impact on the ecosystems. Special cases are concerned with the harmful influence exerted by (artificial) canals crossing lacustrine areas or cutting Danube Delta Branch meanders. Much higher intensities were detetermined for the magnetic fingerprints of the fluvial-deltaic environments of the Danube Branches as compared with those detected in the lake sediments. With regard to the Razim - Sinoie Lagoonal Complex, the magnetic susceptibility (MS) maps pointed out a good correlation with the morphostructural details of the emerged adjacent areas, showing connections between the (higher intensity) magnetic signatures and the structure of the surrounding sand ridges. Besides, an increasing trend of finer sediments occurrence southwards is accompanied by a simultaneous decreasing trend of the MS values. This remark is supported by the results obtained within three periods spanning 31 years. As regards the fluvial-marine interaction zone, the MS maps of the sediments sampled in the northwestern Black Sea showed good connections with the main sedimentary environments in this area. The magnetic signatures with a higer intensity reflect the area directly influenced by the Danube River sediment discharge, particularly the Danube Delta front area and the Danube prodelta area. The area showing the southward drift of the Danube originated sediment flux, as well as the sediment starved area - both located within the northwestern Black Sea shelf area - are reflected by higher, and respectively lower intensities of the magnetic fingerprints. To calibrate the modern sediments and to compare different magnetic signatures recovered from the various aquatic environments, an original Magnetic Susceptibility Scale was conceived by the authors. The MS classes characterizing the recent sediments are used to define the sediment quality, which is also evaluated by geochemical and ecological scales.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1834 Human impacts
DE: 1861 Sedimentation (4863)
DE: 1890 Wetlands (0497)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting