Integrated stratigraphy of an upper miocene lignite-bearing succession based on wireline log, seismic and organic petrographic data in the Tiszapalkonya-1 core section, NE Hungary

Abstract

An intriguing problem of the Upper Miocene stratigraphy in the Pannonian Basin is the correlation of marginal lignite-bearing units to the thick siliciclastic succession in the basin centre; however, it is inevitable in the stratigraphic investigation of the Jászság Basin, necessitated by a regional scale hydrogeological study. An essential precondition of this investigation is integrating data from lignite and hydrocarbon research of very different scales. The Tiszapalkonya-1 long core traversing the lignite-bearing succession across 1300 m enabled this data integration, as (i) it was measured by wireline logs, (ii) its lignite samples were subjected to laboratory and coal petrological analyses and (iii) the logs can be correlated with seismic sections.

Three lignite-bearing units were identified in the section. According to lithological and organic petrological data, the lower represents mostly floodplain conditions with intermediate complex and marsh. The middle indicates a change from aquatic to unbalanced wet forest swamp, floodplain. In the upper unit more stable, balanced accumulation could develop. The density log proved to be a reliable proxy on the occurrence and ash content of peat-forming environments, and the lignite-bearing units occur as autonomous seismic facies based on their higher seismic amplitude. These enable the basin-scale tracking of the identified lignite-bearing units. A log-based multi-proxy time-series analysis revealed regular cycles in the succession but raised some necessity of re-consideration of the existing magnetostratigraphy of the section. The density log gained eminent cyclostratigraphic potential due to the sensitivity of the “coal window” to climate changes.