236 resultados para calcium profile
Resumo:
Results of petrographic, chemical and X-ray studies of zeolites in sediments in the Transpacific lithological profile from the coast of Japan to the coast of Mexico are reported. For ocean phillipsites constancy of Si/Al ratio (2.44-2.87) and unstable cation composition in quantitative predominance of potassium over sodium are characteristic. Two groups of ocean phillipsites are distinguished: of deep-water basins and of submarine rises. The first spread over broad areas of the pelagic zone, and are formed by diagenetic transformation of fine dispersed pyroclastic material in minimum sedimentation rates, the latter occur locally - in areas of basaltic volcanism manifestations.
Resumo:
Lithofacial types of sediments formed in certain geographic and physical-chemical conditions of the Pacific Ocean are distinguished and characterized. It is shown that the regular change of bottom sediment types forming a genetic series from the coast to the pelagic zone clearly demonstrates a leading role of biogenic-terrigenous sedimentation in their formation. In the pelagic zone of the ocean erosion of islands and seamounts, basalt volcanism of anticlinal uplifts, as well as exhalative contribution play some role in addition to the main source of terrigenous and pyroclastic material from continents. These sources do not change, but only complicate terrigenous sedimentation in the studied area of the ocean.
Resumo:
In the study, we establish centennial records of anthropogenic lead pollution at different locations in the North Atlantic (Iceland, USA, and Europe) by means of lead deposited in shells of the long-lived bivalve Arctica islandica. Due to local oceanographic and geological conditions we conclude that the lead concentrations in the Icelandic shell reflect natural influxes of lead into Icelandic waters. In comparison, the lead profile of the US shell is clearly driven by anthropogenic lead emissions transported from the continent to the ocean by westerly surface winds. Lead concentrations in the European North Sea shell, in contrast, are dominantly driven by local lead sources resulting in a much less conspicuous 1970s gasoline lead peak. In conclusion, the lead profiles of the three shells are driven by different influxes of lead, and yet, all support the applicability of Pb/Ca analyses of A. islandica shells to reconstruct location specific anthropogenic lead pollution.
Resumo:
A key feature of Greece is the large amount of historical and archaeological records. The sedimentary record of the Etoliko Lagoon, Aetolia, Western Greece, offers an ideal opportunity to study human-environment interaction and to disentangle natural and anthropogenic imprints in the sedimentary record. By applying an interdisciplinary approach of combining geoscientific methods (XRF, LOI, grain size analysis) with archaeological and historical records, the 8.8 m long sedimentary sequence ETO1C reveals the palaeoenvironmental history of the lagoon and its catchment since 11,670 cal BP. With a thorough chronology based on 14C age-depth-modelling including varve counting, different evolutionary stages were put in a chronological context. These stages include a lake period (11,670-8310 cal BP) followed by a period of sporadic saltwater intrusion (8310-1350 cal BP) as a result of continuing transgression. Phases of limnic predominance associated with freshwater inflow of episodically activated distributaries (around 5230 cal BP) still occurred. By 1350 cal BP, ongoing sea level rise had connected the lagoons of Etoliko and Messolonghi and freshwater influence had ceased. With the onset of settlement activity in the Late Helladic (1700-1100 cal BC) humans took advantage of the prevailing environmental landscape. A sudden increase in coarse sedimentation correlates with the history of human occupation with its peak of prosperity from the Late Helladic until the end of the Hellenistic Period (30 cal BC).