Formulation of the problem. The article is devoted to detail geological and mineralogical description of quaternary volcanic ash in Kharkiv region.
The purpose of the article is to ground its origin.
Presentation of the main material. Quaternary volcanic ash was discovered in Kharkiv region in the middle of last century. There are a few Late Neo-Pleistocene deposits of volcanic ash in Kharkiv region now. They are located in Kharkiv and near such villages as Russki Tishki, Novoselivka, Levkivka, Donetzke and Krasnokutsk. Such deposits of volcanic ash were found in the neighboring regions of the Eastern Ukraine - Lugansk, Donetsk, Dnieperpetrovsk and some other regions.
Volcanic ash forms the elongated lenticular deposits in the loess loam strata. The contact of ash beds is clear with underlying loess and gradual with overlying loess. The ash lies 3-5 m below the surface of loess. These ashes are light-grey with feeble yellow or brown shades. Its thickness is up to 0.4 m.
The particles of the ash are volcanic colourless isotropic glass with refraction index 1,517. Its forms are various. Plate isometric and elongated ash particles with even straight or cambered sides are the most widespread. Predominance of 0.005-0.1 mm particles in this ash rocks is confirmed by the results of mechanical analyses. This tephra is badly sorted. Their sort factor is 4.2-5.9. The ash deposits were formed by wind transportation of ash particles to wind shadow zones.
The results of X-ray investigation are typical for glass. IR-spectra investigation revealed molecular water and hydroxyl groups in the volcanic ash. Chemical composition of the volcanic ash of Kharkiv region is characterized by the average percentage of SiO2 – 58.88, Al2O3 – 18.79, Na2O – 5.03, K2O – 6.30, Na2O+K2O – 11.33. Relation of Na2O to K2O is 0.80 and Na2O+K2O to Al2O3 is 0.60. It corresponds to trachyte and phonolite and is confirmed by the refraction index of glass particles.
The volcanic glass particles are angular and non-rounded. This fact signifies the eolian origin of ash deposits.
Moreover, numerous manifestations of volcanic ash scattered in loess loams are found in Kharkiv region. These loams contain only a few per cents of poorly rounded volcanic ash particles. The loess loams with scattered volcanic ash and volcanic ash deposits belong to the same stratigraphic datum - to the Bugskij horizon, which correspond to Wurmian stage.
Conclusions. All tephra deposits of Kharkiv region are in the ash plume of the super-eruption, which occurred in Southern Italy about 39280 years ago (Campanian Ignimbrite eruption). Kharkiv objects fill territory in this plume between the ash depositions of Romania and Russian Voronezh region. They are similar to all other tephra localities of this plume. The volcanic ash was taken by air from the Phlegraean Fields though the distance between Kharkiv and this volcano is over 2000 km.
Scientific novelty and practical significance. We can affirm that Kharkiv ash deposits are the result of distant ashfall of Phlegraean Fields super-eruption. The volcanic ash is a horizon marker in the Neo-Pleistocene strata and a datum mark for archaeological study of the Paleolithic cultures.
Volcanic ash is a remarkable component of Kharkiv region geological monuments. Russki Tishki locality of volcanic ash is the best object in Kharkiv region. It is situated in 22 km north from Kharkiv. These geological sights have been used as objects of scientific tourism and native land study. Their protection is of highly necessity.
Quaternary volcanic ash of Kharkiv region