The Campanian Ignimbrite/Y5 tephra layer - A regional stratigraphic marker for Isotope Stage 3 deposits in the Lower Danube region, Romania

摘要

A number of volcanic ash layers embedded in Pleistocene loess and fluvial deposits of the lower Jiu and Olt valleys in south-western Romania have been analyzed for glass chemical compositions and general chronological relations. The WDS-EPMA chemical analyses document remarkably similar major and minor element compositions at the four investigated sites, and total alkali—silica diagrams ascribe these volcanic ashes a phonolite to trachyte affinity. A comparison with the Quaternary Carpathian volcanism chemical data refutes this volcanic field as the primary source, even though earlier works have tentatively taken some of these volcanic ashes as evidence of volcanic activity in this particular field. Instead, the chemical data suggest an origin in the Campi Flegrei volcanic province in Italy, and a comparison with chemical data from proximal and distal outcrops of the Campanian Ignimbrite/Y5 tephra confirm that the ash layers presented here are distal occurrences of this widespread tephra layer. The Campanian Ignimbrite/Y5 tephra is the product of one of the largest late Quaternary explosive events in the Mediterranean, and is consistently dated elsewhere to about 39—40 ka. It is one of the most important chronologic/stratigraphic markers of western Eurasia that provide an independent basis for establishing age-depth relationships for the embedding deposits. Optical luminescence age estimates obtained at two of the investigated sites further confirm that these volcanic ash occurrences represent a regionally synchronous depositional event, around 40 ka. These results highlight the important role that the Campanian Ignimbrite/Y5 tephra could play as marker horizon at sub-continental scale, providing that more potential tephra locations such as these from the Pleistocene sedimentary deposits in the Lower Danube region are chemically and chronologically constrained.