An Organic Maturation Study of the Hód-I Borehole (Pannonian Basin)
Published:January 01, 1988
Cs. Sajgó, Z. A. Horváth, J. Lefler, 1988. "An Organic Maturation Study of the Hód-I Borehole (Pannonian Basin)", The Pannonian Basin: A Study in Basin Evolution, Leigh H. Royden, Ferenc Horváth
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Several maturation parameters were determined for a 5800-m-thick Neogene sequence in the Pannonian basin of southeastern Hungary. The oil window was found to start at 3450 m corresponding to a vitrinite reflectance of about 0.7% Ro. This is typical of a mixture of Type II-Type III kerogen such as occurs in the U.S. Gulf Coast. The carbon preference index (CPI) of n-alkanes in the rock extracts also approaches 1.0 at this depth. Hydrocarbon generation appeared to continue to the bottom hole depth of 5800 m with an oil generation minimum or gap occurring in the 5000-5400 m interval that might be due to a change in the nature of the organic matter. Two isomerizations of biological marker compounds, the shift of steranes from 20(R) to 20(S) and of hopanes from 22(R) to 22(S) were found to reach equilibrium at 4000 and 3000 m, respectively, just prior to the threshold of intense oil generation. Also, the C29-monoaromatic steranes were converted almost 100% to C28-triaromatic steranes prior to this depth.
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The Pannonian Basin: A Study in Basin Evolution
The Pannonian basin system is an integrap part of the Alpine mountain belts of east-central Europe. It is completely encircled by the Carpathian Mountains to the north and east, the Dinaric Alps to the south, and the Southern and Eastern Alps to the west. In 1912, Kober defined the Pannonian basin as one of the type “Zwischengebirge,” a relatively un-deformed region characterized by block faulting and situated between externally vergent thrust belts. More recent studies using subsurface data have shown that the Pannonian area was extensively deformed by Mesozoic thrusting and subsequently disrupted by a complex system of Cenozoic normal and wrench faults. Thus, the Pannonian “massif” has undergone several types of deformation, which are partly hidden by a thick sequence of sedimentary rocks of Neogene-Quaternary age. The Pannonian basin is actually a system of small, deep basins separated by relatively shallow basement blocks. The Neogene-Quaternary sedimentary rocks exceed 7 km in thickness in some areas, and the basin system (including the Transylvanian basin) is about 400 km from north to south and 800 km from east to west. It is currently interpreted by most workers as a Mediterranean back arc extensional basin of the middle Miocene age. The Carpathians, Eastern Alps, and Dinarides, which surround the Pannonian basin, are the result of Mesozoic and Cenozoic continental collision between Europe and several continental fragments to the south, including Africa. Thrusting was direted outward from the present Pannonian basin toward the European platform and the Adriatic region. In all the orogenic belts, the interior parts of the thrust belts were deformed in Mesozoic time, while the outer parts were deformed in Tertiary time. The volume presents 26 papers and eight regional maps resulting from a joint five-day symposium held in Veszprem, Hungary, in 1982 entitled “Evolution of Extensional Basins within Regions of Compression with Emphasis on the Intra-Carpathian Region.” The symposium was sponsored jointly by the Hungarian Oil and Gas Trust, the Hungarian Geological Survey, and the U.S. National Science Foundation.