--> Abstract: Petroleum Geochemistry of the Zala Basin, Hungary, by J. L. Clayton and I. Koncz; #90987 (1993).
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CLAYTON, JERRY L., U.S. Geological Survey, Denver, CO; and I. KONCZ, Hungarian Hydrocarbon Institute, Nagykanisza, Previous HitHungaryNext Hit

ABSTRACT: Petroleum Geochemistry of the Previous HitZalaNext Hit Previous HitBasinNext Hit, Previous HitHungaryNext Hit

The Previous HitZalaNext Hit Previous HitBasinNext Hit is a small, deep sub-Previous HitbasinNext Hit located within the Pannonian Previous HitBasinNext Hit system. Production in the Previous HitZalaNext Hit Previous HitBasinNext Hit began in 1943 with the discovery of the Nagylengyel field which has the largest initial reserves of any field found to date in Previous HitHungaryNext Hit. The Previous HitZalaNext Hit Previous HitBasinNext Hit contains as much as about 7,000 m of sedimentary rocks of Mesozoic and Tertiary age. The main producing intervals are Triassic and Upper Cretaceous carbonate rocks, with secondary production occurring in rocks of Miocene age sandstones. Organic geochemical analyses indicate that two main genetic Previous HitoilNext Hit types are present in the Previous HitZalaNext Hit Previous HitBasinNext Hit--"Nagylengyel" and "Szen" types. Oils of the Nagylengyel type have low gravity (API 13-30 degrees), high concentrations of V, Ni, and S, isotopically light hydrocarbons, low pristane/phytane (P /Ph) ratio (<1.0), and no oleanane. Oils of the Szen type have higher gravity (31-39 degrees ) and Pr/Ph ratios (>1.0), low metal and sulfur content, high amounts of oleanane, and isotopically heavy hydrocarbons. Geochemical features of the Szen group are variable and may indicate more than one sub-type of Previous HitoilNext Hit within this larger group.

Explorationists previously hypothesized that Miocene shales were the major source rocks for Previous HitZalaNext Hit Previous HitBasinNext Hit oils. Geochemical composition of the Nagylengyel-type oils, however, strongly suggest a carbonate source rock, which led us to hypothesize a Mesozoic carbonate source rock. Geochemical analyses confirmed that organic-rich (as much as 10% organic carbon) marls of the Triassic Kossen Marl are the source of the Nagylengyel Previous HitoilNext Hit-type. Secondary amounts of Previous HitoilNext Hit have been expelled by Miocene clastic source rocks, which are the likely source of the Szen Previous HitoilNext Hit-type. The Triassic source rocks expelled Previous HitoilNext Hit at fairly low thermal maturities during Miocene time. These Triassic source rocks are equivalent to the Triassic source rocks of northern Italy that formed the giant Molassa field in the Po Basi . An understanding of the distribution and thermal maturity of the Triassic source rocks is important for further exploration in the Pannonian Previous HitBasinNext Hit system and other parts of eastern Europe.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.