COMPARATIVE ANALYSIS OF HUNGARIAN MAAR-TYPE OIL SHALES (ALGINITES) ON THE BASIS OF SULFUR CONTENT

Abstract

Basaltic volcanism has built tuff rings (maars) around the craters of Western Hungary and the Balaton Highlands within the Carpathian Basin during the Pliocene. Oil shales (alginites) have been found in four maar basaltic tuff craters so far. Some years ago the distribution of sulfur in alginites from two craters at Pula and Gerce villages was determined. This paper presents additional data on the sulfur content and forms of further alginite deposits from adjacent craters at Egyhazaskesző village in order to find an explanation for the reasons of the differences in the total sulfur content and forms among the samples from the twin maars with the help of modern research methods. Furthermore, the alginites from the four craters are compared on the basis of their sulfur content. Despite the same sedimentation conditions and petrological composition, the total sulfur content (average St a = 2.3 %) of the samples taken from the crater at Egyhazaskesző differs not only from that of the neighbouring crater at Varkesző (average St a = 0.7 %) but also from the data of the samples from the tuff rings at Pula (average St a = 0.4–0.5 %) and Gerce (average St a = = 0.5 %). The reason for the moderately high total sulfur content of the alginite-bearing samples from the crater at Egyhazaskesző is not precisely known. According to a former theory, the higher-salinity water from Lake Pannon might have infiltrated through the pores and fissures of the tuff ring to this crater lake, resulting in an increase in the total sulfur content. Results of recent investigations did not corroborate the presence of continuous Lake Pannon coverage in these areas. Most likely, large amount of sulfur compounds got into the crater lake at Egyhazaskesző as a part of a post-volcanic activity disrupting the majority of planktonic life. Therefore the oil shales of Egyhazaskesző contain the largest amounts of total sulfur among the Hungarian maar-type alginites. Furthermore, these alginite deposits are of the smallest thickness.