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U.S. Department of the InteriorU.S. Geological Survey

Bulletin 2204B

Pannonian Basin Province, Central Europe (Province4808)Petroleum Geology, Total Petroleum Systems,and Petroleum Resource Assessment


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Pannonian Basin Province, Central Europe

(Province 4808) Petroleum Geology,Total Petroleum Systems, and PetroleumResource Assessment

By Gordon L. Dolton

Bulletin 2204B

U.S. Department of the InteriorU.S. Geological Survey


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U.S. Department of the InteriorP. Lynn Scarlett, Acting Secretary

U.S. Geological SurveyP. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

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Although this report is in the public domain, permission must be secured from the individual copyright owners to

reproduce any copyrighted materials contained within this report.

Suggested citation:

Dolton, G.L., 2006, Pannonian Basin Province, Central Europe (Province 4808)Petroleum geology, total petroleum

systems, and petroleum resource assessment: U.S. Geological Survey Bulletin 2204B, 47 p.


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iii

Foreword

This report was prepared as part of the U.S. Geological Survey World Petroleum Assessment2000 (U.S. Geological Survey World Energy Assessment Team, 2000). The primary objective ofWorld Petroleum Assessment 2000 is to assess the quantities of conventional oil, natural gas,and natural gas liquids outside the United States that have the potential to be added to reservesin the next 30 years. Parts of these assessed volumes reside in undiscovered fields whose sizesexceed the stated minimum-field-size cutoff value for the assessment unit; the cutoff valuevaries, but it must be at least 1 million barrels of oil equivalent. Another part of these assessedvolumes occurs as reserve growth of fields already discovered. However, the contribution fromreserve growth of discovered fields to resources is not covered for the areas treated in thisreport.

In order to organize, evaluate, and delineate areas to assess, the Assessment MethodologyTeam of World Petroleum Assessment 2000 developed a hierarchical scheme of geographic andgeologic units. This scheme consists of regions, geologic provinces, total petroleum systems,and assessment units. For World Petroleum Assessment 2000, regions serve as organizationalunits and geologic provinces are used as prioritization tools. Total petroleum systems (TPS)and assessment units (AU) were delineated for each province considered for assessment. Theboundaries of the TPS and AU need not be entirely contained within a geologic province. TheTPS includes all genetically related petroleum that occurs in shows and accumulations (bothdiscovered and undiscovered) generated by a pod or closely related pods of mature sourcerock. TPSs exist within a limited mappable geologic space along with the geologic elements(source, reservoir, trap, seal, and overburden rocks) necessary for hydrocarbon accumulation.These geologic elements control the fundamental processes of generation, expulsion, migra-

tion, entrapment, and preservation of petroleum within the TPS. The AU is the basic elementassessed in this study. It is a mappable part of a total petroleum system in which discovered andundiscovered oil and gas fields constitute a single relatively homogeneous population such thatthe methodology of resource assessment is applicable.

The world was divided into 8 regions and 937 geologic provinces. These provinces have beenranked according to the discovered known (cumulative production plus remaining reserves) oiland gas volumes (Klett and others, 1997). Then, 76 priority provinces (exclusive of the UnitedStates and chosen for their high ranking) and 26 boutique provinces (exclusive of the UnitedStates) were selected for appraisal of oil and gas resources. Boutique provinces were chosen fortheir anticipated petroleum richness or special regional economic or strategic importance.


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iv

Contents

Foreword ........................................................................................................................................................iii

Abstract ...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Acknowledgments .........................................................................................................................................1

General Geologic Setting..............................................................................................................................6

Tectonic History ....................................................................................................................................6

Structure.................................................................................................................................................9

Stratigraphy .........................................................................................................................................12

Basement Rocks ........................................................................................................................12

Cenozoic Basin-Fill Sediments ................................................................................................13

Paleogene and Early Neogene .......................................................................................13

Middle to Late Neogene ..................................................................................................14

Synrift Sediments .....................................................................................................14

Postrift Sediments ...................................................................................................15

Petroleum Geology ......................................................................................................................................16

Reservoir Rocks ..................................................................................................................................16

Source Rocks and Maturity ..............................................................................................................16

Traps and Seals ...................................................................................................................................19

Exploration Status ...............................................................................................................................19

Total Petroleum Systems ...................................................................................................................23

Neogene Total Petroleum Systems .........................................................................................23

Mixed Mesozoic-Neogene Total Petroleum System ...........................................................23

Paleogene Total Petroleum Systems ......................................................................................24

Other Total Petroleum Systems ...............................................................................................24

Assessment Units ...............................................................................................................................29

Greater Hungarian Plain Basins AU (40480101) ....................................................................29

Zala-Drva-Sava Basins AU (40480201) .................................................................................34

Danube Basin AU (40480301) ...................................................................................................35

Transcarpathian Basin AU (40480401) ....................................................................................36

Hungarian Paleogene Basin AU (40480601) ..........................................................................37

Central Carpathian Paleogene Basin AU (40480501) ...........................................................38

Frontal Inner Carpathian AU ....................................................................................................38

Estimated Undiscovered Resources ...............................................................................................39

References ....................................................................................................................................................41

Figures

1. Index map .........................................................................................................................................2

2. Map of the Neogene Pannonian Basin .......................................................................................3

3. Diagrammatic cross sections of the Pannonian Basin.................. ................. ................ ..........4

4. Major structural elements of the Pannonian Basin ............... ................ ................. ................. .7


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v

5. Tectonic map of the Pannonian Basin ......................................................................................8

6. Generalized stratigraphic columns ................ ................. ................. ................ ................. .......10

7. Distribution of Paleogene rocks ................ ................. ................ ................. ................. ............11

8. Oil and gas fields of the Pannonian Basin ..............................................................................17 9. Discovered oil by depth interval ................ ................. ................ ................. ................. ............20

10. Discovered gas by depth interval ................ ................ ................. ................. ................ ..........20

11. Size distribution of discovered oil fields ................ ................ ................. ................. ...............22

12. Size distribution of discovered gas fields ................. ................ ................. ................. ............22

13. Map of total petroleum systems and assessment units ............... ................ ................. .......25

14. Burial history plot of Greater Hungarian Plain Neogene Total PetroleumSystem (404801) ...........................................................................................................................26

15. Burial history plot of Danube Neogene Total Petroleum System (404803) ............... .........27

16. Events chart for the Greater Hungarian Plain Neogene Total PetroleumSystem (404801) ...........................................................................................................................28

17. Events chart for the Danube Neogene Total Petroleum System (404803) ................ .........28 18. Events chart for the Transcarpathian Neogene Total Petroleum

System (404804) ...........................................................................................................................29

19. Burial history plot for the Sava depression (Zala-Drva-SavaMesozoic/Neogene Total Petroleum System (404802)) ................ ................ ................. .......30

20. Events chart for the Zala-Drva-Sava Mesozoic/Neogene TotalPetroleum System (404802) .......................................................................................................31

21. Burial history plot of the Hungarian Paleogene TotalPetroleum System (404806) .......................................................................................................32

22. Events chart for the Hungarian Paleogene TotalPetroleum System (404806) .......................................................................................................33

23. Events chart for the Central Carpathian Paleogene Total

Petroleum System (404805) .......................................................................................................33

Tables

1. Total petroleum systems and associated assessment units. ................. ................. ............24

2. Assessment results ............... ................ ................. ................. ................ ................. ................. .40


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Abstract

This report deals with the Pannonian Basin Province

of Central Europe and summarizes the petroleum geology,which was the basis for assessment, and presents results ofthat assessment. The Pannonian Basin Province consists of alarge compound extensional basin of Neogene age overlyingPaleogene basins and interior elements of the greater Alpinefoldbelt (fig. 1). Within it, six total petroleum systems (TPS)are defined and six assessment units established for estimationof undiscovered oil and gas resources. Other speculative TPSswere identified but not included for quantitative assessmentwithin this study.

Introduction

This report deals with the Pannonian Basin Province ofCentral Europe and summarizes the petroleum geology, whichwas the basis for assessment, and presents results of thatassessment. The report relies largely on a synthesis of pub-lished geologic information.

The Pannonian Basin Province consists of a large com-pound extensional basin of Neogene age overlying Paleogenebasins and interior elements of the greater Alpine foldbelt(fig. 1). The Neogene basin system is approximately 600 kmfrom east to west and 500 km from north to south, excluding

the associated Transylvanian and Vienna Basins. Geographi-cally, it lies within the Alpine mountain belts of east-centralEurope and is bounded by the Carpathian Mountains to thenorth and east, the Southern Carpathian or Dinaric Alps tothe south, and the Southern and Eastern Alps to the west. Itis located mostly within the confines of Hungary, Croatia,Romania, and Serbia-Montenegro (formerly Yugoslavia) andalso occupies parts of Austria, Slovakia, Ukraine, Bosnia andHerzegovina, Slovenia, and Poland.

The Neogene Pannonian Basin historically has been theprimary petroleum exploration target in the province and iscomposed of a complex system of extensional subbasins lyingwithin the arc of the Carpathian Mountains(figs. 1, 2, and 3).

Subbasins are separated from one another by uplifted base-ment blocks but are tied together by a widespread blanketof younger Neogene and Quaternary sediment fill (Horvthand Royden, 1981; Royden and Horvth, 1988). Among theprincipal subbasins are those of the Great Hungarian Plain,including the Jszsg, Derecske, Nysg, Nagykunsg andBks Basins and Mak trough; the Zala Basin, Drva andSava depressions, and Graz (Styrian) Basin; the Danube (LittlePlain) Basin and the Transcarpathian (East Slovak) Basin.These basins rest on thrust sheets of the Inner Carpathianfoldbelt in northern and central areas and, to the south, onthose of the Dinarides and associated Vardar Zone (fig. 1). Notincluded within this assessment are the Vienna and Transylva-nian Basins, which are sometimes considered as parts of theoverall Pannonian system (Royden and Horvth, 1988). Withinthe geologic framework of the province, six total petroleumsystems are defined and six assessment units established forestimation of undiscovered oil and gas resources. Three otherTPSs were identified but not quantitatively assessed.

Acknowledgments

The author wishes to acknowledge the invaluable

research by a wide range of authors concerning the geologicframework of this area, upon which this paper relied. Themanuscript has benefited greatly from critical and construc-tive reviews by Gregory Ulmichek, Tim Klett, and KathyVarnes. The author thanks Rick Scott for a constructive editof the manuscript. The author is grateful to Susan Walden andMargarita Zyrianova for preparation of digital illustrations andwishes to acknowledge authorship for those figures, whichhave been derived or modified from published sources.

Pannonian Basin Province, Central Europe (Province

4808)Petroleum Geology, Total Petroleum Systems, andPetroleum Resource Assessment

By Gordon L. Dolton


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16E18E 20E 22E

24E 26

48N

50N

46N

44N

SERBIA and

MONTENEGRO

CROATIA

BOSNIA and

HERZEGOVINA

SLOVENIA

Zagreb

Graz

Vienna

DINARIDES

SavaRiver

Savadepression

Drva

dep

ression

Adriatic

Sea

MOESIAN PLATFORS.

CARPATHIAN

Belgrade

Budapest

Cluj

TransylvanianBasin

APUSENIMOUNTAINS

GREA

THU

NGAR

IAN

EASTERNALPS

SOUTHERNALPS

Peri-Adriaticline

ZalaB

asin

MECSEK MOUNTAINS

VILLNY MTNS

TRANS

DANUBIAN

CEN

TRAL

Vie

nnaBasin

GrazB

asin

D

erecskeB

asin

Bks

BasinNa

gykuns

g

Basin

DanubeRiver

DrvaRiver

NORTH

HUNG

ARIAN

RANG

E

TranscarpathianBasin

Jszs

gBasin

AUSTRIA

CZECH

REPUBLIC

HUNGARY

ROMANIA

BULG.

OUTER

CARPATHIA

NS

EU

RO

PE

ANPLATFORM

0

Maktrough

TiszaRiv

er

Dan

ubeB

asin

VAR

DARZONE

W.CARPATHIANS

POLAND

UKRAINE

SLOVAKIA

E. CARPATH

TRAN

SDAN

UBIA

EXP

CitiesCountry bou

Pieniny Klip

Outer Carpat

Inner Carpat

Upper Cenoz

Pannonian B

Figure 1. Index map showing main tectonic and geographic units of Alpine Foldbelt and Alpine-Carpathian-Dinaric Mountains, and th

units inside these mountains, shown in white, to which the collective name Pannonian Basin is generally applied, including the associa

Basins. Modified from Horvath, 1985b. The Pannonian Basin Province (4048) boundary is shown in blue.


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16E18E 20E 22E

24E 26

50N

48N

46N

44N

0

AdriaticSea

EXPLA

Thickness of Neogene

> 0 2

2 4

> 4

Outer Alpine-Carp

Outcrop of Neoge

Inner Alpine-CarpInner Alpine-Carp

Neogene Pann

V

TR

A

B

B

C

C

Figure . Map of the Neogene Pannonian Basin, showing depocenters of the subbasins. The associated Transylvanian (TR) and Vienn

Modified from Horvath (1985a). Cross sections are in figure 3.


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Figure . Diagramatic cross sections of the Pannonian Basin. Section A-Amodified from Horvth and others (1996); section B-B

modified from Sztan and Tari (1993; with permission from Elsevier); section C-Cmodified from Haas (1989). Locations of cross

sections are shown in figure 2. (Figure continued on next page.)

A

W

DanubeRiver

TRANSDANUBIA

PANNONIAN BASIN

2

1

0

1

2

3

4

5

6

km

EXPLANATION

Holocene and Pleistocene

Late Miocene (postrift)

Middle-early Miocene (synrift)

Mesozoic, Paleozoic, andPrecambrian basement complex

Early Miocene andPaleogene

Cenozoic volcanics

A

E

ASPUSENI

MOUNTAINS

TRANSYLVANIANBASIN

GARIAN PLAIN

Sea level

GREAT HUN-

4 Pannonian Basin Province, Central EuropePetroleum Geology, Total Petroleum Systems and Resource Assessment


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DANUBE BASIN

TRANSDANU

BIAN

CENTRALRA

NGE

LAK

EBALATON

MECSEK

MOUNTAINS

VILL

NY

MOUNT

AIN

S

NW S

TRANSDANUBIA

GREAT HUNGARIAN PLAIN

B B'

SN

C C'

0 100 KILOMETERS

PANNONIAN BASIN

PANNONIANBASIN

Horizontal Scale

2

1

0

1

2

3

4

5

6

2

1

0

1

2

3

4

5

6

km

km

Sea level

Sea level

Acknowledgments

Figure . Continued.


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General Geologic Setting

Tectonic History

The present tectonic setting of the Pannonian BasinProvince is characterized by a major system of Cenozoicbasins superimposed on inner elements of highly deformedand complexly faulted nappes of Mesozoic, Paleozoic, andPrecambrian rocks of the Alpine-Carpathian foldbelt (fig. 4).

Paleozoic events affecting the Pannonian Basin Provinceare poorly known; however, the Hercynian (Variscan) orogenyof middle and late Carboniferous time involved local crustalelements in the collision between Gondwana and Laurentia.This collision resulted in closure of the Tethys Sea, a suturealong the margin of the European plate immediately west ofthe present Pannonian Basin, metamorphism of older Paleo-zoic rocks in the area, and the creation of Pangea.

Collapse of the Hercynian orogen in Late Permian timewas followed by reopening of the Tethys Sea and riftingand foundering of marginal crustal fragments, including theApulian, south European, and Tisza blocks. Rift basins weresuperimposed on Hercynian structural trends and became sitesof predominantly continental and evaporitic deposition.

Triassic time was characterized by continued openingof the Tethys Sea and graben formation on adjoining crustalblocks (Yilmaz and others, 1996). Basin and platform paleo-geography persisted into the Jurassic. Pelagic sediments weredeposited in troughs and on open-marine shelves, and shal-low-water marine carbonates commonly occupied platformswhere they were generally succeeded by marine shelf sedi-ments. Plate motions between Africa and Europe were largelysinstral from Late Jurassic through Early Cretaceous time butincluded counterclockwise rotation of Apulia and developmentof a subduction zone with flysch sedimentation at its margin,accompanied by calc-alkaline volcanism.

During the late Mesozoic and Cenozoic, closure of theTethys Sea resumed, accompanied by collision of the Euro-pean plate with small crustal fragments ahead of an advancingAfrican plate. This collision produced the Paratethys and thefoldbelts of the Alpine orogen upon which the Tertiary Pan-nonian Basin system rests (fig. 4). Disparate crustal elementswere assembled into the Inner Carpathian foldbelt during Cre-

taceous and Paleogene time, and outer parts, comprising theOuter Carpathian foldbelt, were deformed during the Neogene.Separate Apulian, Tisza, and Pelso crustal blocks

impinged on the European plate by the Late Cretaceous, andSandulescu (1988) suggests that virtually the whole innerCarpathian realm attained its present structure and morphol-ogy by Late Cretaceous, with the result that, during Cenozoictime, these areas of Cretaceous deformation acted roughly asrigid blocks, and their differential movement was accommo-dated by large strikeslip faults. More recent work by Yilmazand others (1996) indicates that the Tisza block separated

from Europe in Late Jurassic time and became attached toApulia, before again colliding with Europe in Eocene time.In any case, interior elements of the foldbelt were modifiedby Cenozoic compression, shearing, and compression. Balla(1990) reconstructed the evolution of the present Pannoniancrustal fragment, comprised of the Pelso and Tisza blocks, as

beginning in the Eocene, with its final assembly in the middleMiocene. Compressional deformation of Paleogene flyschsediments on margins of the Pelso and Tisza blocks and withinthe Szolnok trough accompanied this assembly (see fig. 7).

During Eocene and early Oligocene time, convergencehad pushed the Apulian, Pelso, and Tisza blocks farther intothe European plate, accompanied by transpression and rota-tion, and caused development of epicontinental basins on thePannonian fragment, most prominently the Hungarian Paleo-gene Basin and flysch basins at margins of crustal blocks (seefig. 7). The epicontinental basins have been viewed as wrenchbasins by several authors (Royden and Bldi, 1988; Csontosand others, 1992; Nagymarosy, 1990), whereas other inves-

tigators have proposed a flexural basin model of a retroarcforedeep basin system south of the backthrust inner WestCarpathians (Tari and others, 1993). This system persisted intothe early Miocene. The Hungarian Paleogene Basin underwentstructural inversion in the middle Oligocene, accompaniedby development of an offset trough to the east, followed bygeneral uplift and erosion.

By late Oligocene or early Miocene, assembly of thepresent Pannonian crustal fragment took place, accompaniedby considerable rotationparticularly of the Tisza blockandbehaved as a loose knot within the collision zone between theApulian and European plates, and, with continuing compres-sion, began escaping to the east, accompanied by rotation andshearing, producing the Carpathian arc at its verge (Roydenand Bldi, 1988; Balla, 1987; Balla, 1990; Csontos and others,1992). Thrusting and strong folding in the Outer Carpath-ian arc began in the early Miocene, moving progressivelynorth and east, with associated compressional features of theDinarides Alpine system seen at the southern margin of thePannonian crustal fragment.

As the elevated Pannonian fragment overrode the Euro-pean plate, extension, crustal thinning, and fragmentationbegan with adjustments along normal and strike-slip faults anddevelopment of a complex system of successor extensionalbasins behind the Carpathian arc (fig. 5). As a consequence,

the basement and earlier Paleogene basins were overprinted byNeogene back-arc rift basins, which were essentially coevalwith the compressive deformation in the Outer Carpathians.According to Royden (1988), extension within the system wasdiachronous, beginning first in the most external subbasins inOttnagianKarpatian time (early Miocene; see fig. 6 for strati-graphic stages), shifting to more interior basins through time.Rifting was characterized by local high relief, deep grabens,and synrift sedimentation, followed by a general relaxationand differential thermal subsidence and widespread, rapidpostrift sedimentation.

Pannonian Basin Province, Central EuropePetroleum Geology, Total Petroleum Systems and Resource Assessment


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Tisza

River

100 KILOMETERS0

DravaR

iver

DanubeRiver

Belgrade

Budapest

Vienna

SavaRiver

MID-H

UNGARIAN

FAULT

ZONE

EXP

Outer A

Inner Aand Din

Outcrovolcani

Area of

and subNorma

Strike-displacby the

Adriatic

Sea

50N

16E18E 20E 22E

24E26

48N

46N

44N

Figure . Tectonic map of the Pannonian Basin and surrounding regions showing the main extensional faults of Neogene age. After Rum

Area of Pannonian Basin Tertiary rocks within the Alpine-Carpathian foldbelts shown as white.


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Volcanism accompanied extension and climaxed in themiddle Miocene as a result of subduction of European conti-nental crust beneath the fold-thrust belt. Rhyolite tuff volca-nic activity was intense during the synrift phase, and severalcycles of eruption produced thick tuffaceous layers, particu-larly throughout the northern Pannonian Basin system (Pka,

1988). Along with shearing in late Miocene, reverse faultingis found in several subbasins, particularly in the Sava Basin atthe southern margin of the Pannonian Basin (Baric and others,2000).

Major extension largely stopped by the end of Miocenetime. Mild extension, with strike-slip and normal faulting,continued into Pliocene time, as did uplift around the marginsof the Pannonian Basin system, and accompanied compressionin the Eastern Carpathians. The Pannonian Basin presentlyshows a complex system of faults and deformation related tolate strike-slip movements and wrench faulting involving veryyoung sediments. Many of these faults appear to be reactiva-tions of old features, including the Mid-Hungarian lineament

or fault zone, which separates the Tisza and Pelso basementterranes. Nevertheless, the Pliocene generally reflects awaning of tectonic activity. By the late Pliocene, most of thehorst blocks within the Pannonian Basin system were buried,excepting the uplifts of the Transdanubian Central Rangeand North Hungarian Range and the margins of the basinsystem. During the Quaternary, the Panonnian Basin showedgeneral uplift around its margins, continued subsidence incentral parts, and late strike-slip adjustments (Horvth andothers, 1996). Detail of the structural evolution of the basin issubject to varied interpretation, and for overviews the reader isparticularly referred to Hmor and Brczi (1986), Sandulescu(1988), Royden and Bldi (1988), Balla (1990), Kkai andPogcss (1991), Csontos and others (1992), Tari and others(1993), and Morley (1993).

Structure

The Pannonian Basin Province is characterized by amajor system of Neogene basins superimposed on inner ele-ments of highly deformed and complexly faulted nappes ofMesozoic, Paleozoic, and Precambrian rocks of the Alpine-Carpathian foldbelt (figs. 2 and 4).

In the northern part of the province, an additional system

of Paleogene to early Neogene basins (fig. 7) were producedduring Alpine deformation by transpression and shearing,accompanying rotation of the Pannonian crustal fragments(Royden and Bldi, 1988; Csontos and others, 1992; Nagyma-rosy, 1990) or within a flexural basin setting, as proposed byTari and others (1993), and locally underlie Neogene rocks.Most prominent of the epicontinental basins is the HungarianPaleogene Basin, which contains thick sequences of exten-sionally deformed and faulted, largely marine, epicontinentalsedimentary rocks, now mostly uplifted and eroded. In addi-tion, compressively deformed Paleogene flysch sediments rest

on margins of the Pannonian crustal fragments and within theSzolnok trough.

The most prominent feature of the province is the largeNeogene extensional Pannonian Basin within the loop or arcof the Outer Carpathian foldbelt. Resting on highly deformedolder rocks of the Inner Carpathians and the Paleogene basins,

the basin is actually a complex composed of many subbasinsseparated by basement horst blocks and uplifts. These sub-basins typically contain early to middle Miocene age synriftsediments and intercalated volcanics and are, in turn, blan-keted by a postrift late Neogene fill that covers the entiresystem and defines the present Pannonian Basin. Pervasivesyndepositional rifting, growth faulting, and strike-slip defor-mation characterized the synrift stage, whereas the postriftstage was marked by a structural setting in which thermalsubsidence and rapid sedimentation took place. The latterstage was accompanied by differential subsidence withoutmajor deformation, continuing from the late Miocene to theHolocene (Royden, 1988; Grow and others, 1994; Milicka and

others, 1996).The Neogene subbasins occur as pull-apart features

and as graben structures, the latter particularly commonsouth of the Mid-Hungarian fault zone (fig. 5) (Rumpler andHorvth, 1988; Royden, 1988). The deeper basins are com-monly bounded by sets of normal faults of large displacement,some listric in nature. Locally, low-angle extensional normalfaulting appears to play a particularly important role, as inthe Danube Basin, commonly interacting with old basementfeatures as noted by Tari (1996). Syndepositional structuralgrowth caused deformation and faulting of sediments and,as noted by Pogcss, Mattick, Tari, and Vrnai (1994),the opening of these basins resulted from strike slip motionalong a set of roughly NESW trending, left-lateral shearsaccompanied by a conjugate set of NW trending, right-lateralshears. A resultant complex fault pattern is observed withinthe system, dominated by the large Mid-Hungarian fault zone,which separates major basement terranes (fig. 4), as well asstructural inversions noted in some areas. Thermal subsidenceand rapid sedimentation of the following postrift stage wereaccompanied by differential sagging and caused relatively flatlying, undisturbed postrift sediments to rest unconformably onsynrift sequences in most subbasins and on basement rocks ofold highs.

Of the Neogene depressions, eight reach depths of greater

than 3,000 m, namely the Danube Basin, the Zala Basin andDrva and Sava troughs or depressions, the TranscarpathianBasin, and the Jszsg, Drescske, Bks-Mak-Nagykunsgsubbasins of the Great Hungarian Plain. The Bks Basin-Mak trough alone exceeds a depth of 7,000 m, largelyconsisting of postrift sediments. Most subbasins are less than70 km in long dimension, though the Danube Basin exceeds150 km, as do the Sava and Drva depressions. Very youngsediments are involved in a complex system of faults anddeformation related to late strike-slip movements andwrenching within the Pannonian Basin system.

General Geologic Setting


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? ?

Belezna Fm

Izsk Marl

Pannonian

Pontian

Dacian

Romanian

Sarmatian

Sarmatian

BadenianBadenian

Pannonian

Tamanian

KiscellianKiscellian

EgerianEgerian

Eggenburgian

Eggenburgian

Karpatian

Karpatian Ottnangian

Ottnangian

(Sensu lato)

Hungarian Usage4

PriabonianPriabonianBartonian Bartonian

Lutetian Lutetian

Ypresian Ypresian

CENO

ZOIC

PALEOZOIC

MESOZOIC

PLEISTOCENE

PLIOCENE

NEOGENE

MIOCENE

PALEOCENE

CRETACEOUS

JURASSIC

PALEOGENE

OLIGOCENE

EOCENE

early

early

Early

E

E

middle

M

late

late

Late

L

L

2

1

3

4

5

10

20

30

40

50

60

80

GEOLOGICTIME SCALE

Postrift

Synrift

Standard3

TRIASSIC

PERMIANPENNSYLVANIAN

MISSISSIPPIAN

DEVONIANSILURIAN

ORDOVICIAN

CAMBRIAN

PRECAMBRIAN

100

200

300

400

500

Veszprm MarlBuchenstein

Tata Ls

Dorog

Dachstein

MaPelso Block1 Tisza Block2

Hansg Fm

Rbakz Fm

Soml Fm

jfalu Ss

Drva Fm TrtelF

m

Zagyva Fm

Nagyafld Fm

Zala Marl

Polny Marl

Jk Ls

Debrecen FmUgod Ls

Tard Clay

Kiscell Clay

EgerFm

SzcsnyFm

Padrag Fm

Szc Ls

Buda Marl

Tfej Ss

Nagylengyel Marl

S zo l n

o k

Fl y

sc

h

Szolnok Fm

Algy Fm

Ttkomls Bks Cg

Nagykr

Presentb

ut

metam

orph

osed

Presentb

ut

metam

orph

osed

LktEplnyi Ls

Magyarsdomb

Plihls

SmegMagya

regregycg.

KssenHauptdolomit

FORMATIONS CENTRAL PARATETHYS STAGESTECTONIC

PHASE

1Neogene usage from Danube, Zala, and DravaBasins. Modified from Hmor and Brczi (1986).Paleogene principally Hungarian Paleogene Basin,after Tari and others (1993).

2Neogene usage from Bks Basin of Great HungarianPlain. Modified from Kkai and Pogcss (1991).

3After Haq and Van Eysinga (1998).

4Neogene usage after Pogcss, Mattick, and others(1994); Paleogene and early Miocene, usage at rightside after Tari and others (1993).

Podhale

Flysch

HierlatzKardoskt

Tzeg FmTisztaberek-Vszta Fms

General

"Miocene"

"Miocene"

Figure . Generalized stratigraphic columns of Pannonian Basin Province showing selected formations. Volcanic rocks

not represented.



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SLOVEN IAN BAS IN MID-HU

NGAR

IANLINE

16E18E 20E 22E

24E26

50N

48N

46N

44N

Belgrade

Budapest

Vienna

SavaRiver

AdriaticSea

MOESIAN PLATFORM

DanubeRiver

Drav

aRiv

er

EUROP

EAN P

LATFOR

M

Tis

zaRiv

er

OUTER CARPATHIAN FLYSCH BELT

SZOL

NOKTR

OUGH

HUNGARIA

NPALE

OGEN

EBA

SIN

TRANSYLVANIAN

BASIN

CENTRAL

CARPATHIAN

BASIN

Zagreb

EASTEUROPEAN

(RU

EX

Flysch

"Epicon

Bound

Inner Aand D

Inner Aand D

0

Figure . Distribution of Paleogene rocks showing principal basins. Modified from Nagymarosy (1990), Hamor (1989), and Tari and othe

used with permission from Elsevier).


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Stratigraphy

The stratigraphy of the Pannonian Basin Province is char-acterized by a Tertiary basin-fill sequence resting on a highlydeformed substrate of Proterozoic, Paleozoic, and Mesozoicrocks of the Inner Carpathian foldbelt (figs. 4 and 6). The pre-

Tertiary basement rocks represent two geographically sepa-rated and distinct terranes, the Pelso and Tisza blocks (fig. 4).Within these blocks, virtually every nappe has its individualcharacter and stratigraphic nomenclature (Csontos andothers, 1992; Brezsnyanszky and Haas, 1989). Paleogene andlowermost Neogene rocks reflect the histories of their respec-tive crustal units, whereas succeeding Neogene rocks show alargely shared depositional history. Stratigraphic nomenclatureis complex due to the large area involved, varied depositionaland lithologic facies, political and language divisions, andlocal usage. Cenozoic rocks are assigned to regional stagesof the Central Paratethys (Haq and Van Eysinga, 1998). Thechronostratigraphy used here is essentially that of Hungarian

usage, and representative formation names are not intended tobe inclusive.

Basement Rocks

The pre-Tertiary basement of the Pannonian Basinsystem consists of a complex of igneous, metamorphic, andsedimentary rocks of Precambrian, Paleozoic, and Mesozoicage that have been strongly folded, faulted, and assembled innappes of the Inner Carpathian foldbelt (Csontos and others,1992; Brezsnyanszky and Haas, 1989). These rocks occurwithin two terranes, the Pelso (or North Pannonian) and Tiszablocks (fig. 4), and include a variety of continental rocks aswell as obducted Jurassic and Cretaceous oceanic crust. ThePelso block of the northern and western parts of the Pannoniansystem is characterized by a Mesozoic sedimentary sequenceof Calc-Alpine facies, including the Triassic Hauptdolomit,Dachstein Limestone, and Kssen Marl; Upper Permian sedi-mentary rocks; and a Paleozoic metamorphic-igneous complex(fig. 6). At the northern margin of the Pannonian Basin, Ter-tiary rocks in the Vienna Basin lap onto the CretaceousPaleo-gene flysch of the Outer Carpathian foldbelt. A zone of marinelower Paleozoic and predominantly carbonate-facies Mesozoicbasement rocks is present in the area of the Mid-Hungarian

lineament and fault zone (figs. 5 and 6). South of this line, theTisza terrane is characterized by rocks composed of Precam-brian and Paleozoic metamorphic and igneous rocks; upperPaleozoic and Mesozoic sedimentary rocks, including a Perm-ianTriassic sequence similar to that found in Germany; andCretaceous and Jurassic sedimentary rocks. Subassemblagesare recognized within these terranes, and the basement exhib-its much heterogeneity due to tectonic juxtaposition.

Metamorphic and igneous rocks include the OrdovicianSilurian quartz phyllite series in the Transdanubian CentralRange uplift of the Pelso block and Precambrian and Paleo-zoic metamorphics and intrusives in the central and southern

part of the Tisza block. However, no pre-Hercynian crust isknown to occur within the old Apulian block south of the Peri-Adriatic line (fig. 4) (Yilmaz and others, 1996). Precambriancrystalline rocks and Paleozoic metamorphic rocks pierced byacidic intrusions of various ages are exposed in the ApuseniMountains and Southern Carpathians as well as in interior

basins of the Pannonian system. In the Mecsek Mountains(refer to fig. 1), Paleozoic metamorphics are associated witha Permian quartz phorphyry and are overlain by a Triassicsedimentary sequence. Upper Paleozoic quartz porphyry andcrystalline metamorphic complexes date from the Hercynianin several areas, and metamorphosed Devonian and middle toupper Carboniferous sedimentary rocks are present. The base-ment composition exhibits much heterogeneity, for example,in the Bks Basin, granite, mica schist, quartzite, and quartzporphyry are present and provide oil and gas reservoirs inburied fractured and weathered basement highs.

Sedimentary rocks of the basement generally occur asfault-fragmented sequences. Older Paleozoic sedimentary

rocks are strongly metamorphosed; however, some lightlymetamorphosed to unmetamorphosed middle to upper Car-boniferous sedimentary rocks are present and include neriticand marine shelf sequences as well as continental sequencesdeposited around uplifts related to Hercynian tectonism(Yilmaz and others, 1996). Upper Permian sedimentary rocksinclude continental sequences deposited in rift basins andneritic marine rocks deposited on shelf areas. In the Transda-nubian area of the Pelso block, the Permian is represented bya red detrital, fluviatile-lacustrine sequence, whereas to thenortheast, continental sediments are replaced by a lagoonalanhydrite-dolomite sequence, overlain by shallow-watermarine limestones. In eastern parts of the Pelso block, mostPaleozoic and Mesozoic sedimentary rocks have been meta-morphosed.

On the Tisza block, Lower Triassic sedimentary rocksinclude varigated terrigenous shale, red sandstone, and anhy-drite, grading upward into cherty carbonates. In the MecsekMountains, Triassic beds directly overlie Permian quartz por-phyry. By Middle Triassic time, marine platforms accumulatedshelf carbonates, reefal limestones, and evaporites. Upper Tri-assic rocks are locally represented by red siltstone, sandstone,and gray limestone of the Carpathian Keuper and equivalents.

In the Pelso block, the Lower Triassic is composed ofsandstone overlain by evaporites and shale, succeeded by

marine carbonates. Rift-basin and platform sedimentationcontinued into Late Triassic time, producing shallow-watercarbonates and reefal limestones on platformsespecially theHauptdolomit and Dachstein Limestoneand organic-richshales and marlstones in adjacent anoxic troughs, includingthe Kssen and Veszprm Marls. In the Transdanubian CentralRange, the basal Upper Triassic is a succession of dark-graymarls of restricted basin facies and limestones, with reef-lime-stone bodies to the southwest, succeeded by great thicknessesof dolomite and limestone of backreef facies comprising theHaupdolomit and Dachstein. These rocks contain source rocksand reservoirs for oil and gas.



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Jurassic rocks on the Pelso block unconformably overliethe Triassic and comprise mostly marine shelf and neritic sedi-ments deposited upon an increasingly fragmented basement.Basins accumulated deep-water sediments, including benthiclimestones and radiolarites, before again shallowing in latestJurassic time. A Lower Cretaceous pelagic argillite facies is

seen in the Transdanubian Central Range grading into marland flysch. Elsewhere, the Lower Cretaceous is represented bynearshore facies and limestone breccias, succeeded by marlsinterbedded with thin sandstone layers. Commonly, theserocks were slightly metamorphosed during the Alpine orogenyand are now of limited distribution.

During the Early Jurassic, a mix of shales, marls andlimestones were deposited on the Tisza block, and significantcoal-bearing sequences are found in Middle and Upper Juras-sic sequences, as in the Mecsek Mountains. Upper Jurassicand Lower Cretaceous rocks are characterized by limestones,as in the Villany Mountains and Bks Basin, where shal-low-water marine limestones of Early Cretaceous age rest on

Upper Jurassic strata. Over parts of the Tisza block, the LowerCretaceous is commonly represented by an open-marine pelitefacies; however, no Lower Cretaceous rocks occur in the Mec-sek Mountains and in some other areas. As noted by Kkaiand Pogcss (1991), the middle part of the Cretaceous Periodis characterized by erosion, nondeposition, and karst and baux-ite formation on both the Pelso and Tisza blocks.

The Upper Cretaceous appears as varied lithotypes onboth Pelso and Tisza blocks and includes sandstones, breccias,and argillites. On the Pelso block, shallow-marine units suchas the Jk Marl, Ugod Limestone, and Polny Marl uncon-formably overlie Halimba Breccia and older Jurassic andTriassic rocks. On the Tisza block, sandstones of the Debrecenor equivalent argillites and marls rest unconformably on olderrocks. At the same time, deep-marine silty marls and bathyalclays and turbidite sandstones of the Carpathian and MaguraFlysches of the Carpathian foredeep were deposited anterior tothe ancestral Carpathian arc. An inner proximal flysch, includ-ing the Podhale Flysch, lapped onto the Pannonian fragmentand into the Szolnok trough and, at the south margin of theTisza block, flysch was deposited (fig. 7).

Cenozoic Basin-Fill Sediments

Within the area of the Pannonian Basin, Cenozoic sedi-ments, following a major hiatus, overlie deformed pre-Tertiarybasement. From late Eocene through early Miocene time, awrench-basin complex (Royden and Bldi, 1988; Nagymarosy,1990; Nagymarosy and Bldi-Beke, 1993) or, alternatively, aretroarc foredeep basin complex developed (Tari and others,1993). It included the Hungarian Paleogene Basin, whereepicontinental, largely marine sediments accumulated, whileflysch sediments accumulated in marginal areas and troughs(fig. 7). Sedimentation was controlled largely by tectonic andeustatic processes (Sztan and Tari, 1993; Kkai andPogcss, 1991).

As the Pannonian crustal fragment subsequently over-rode the European plate, the elevated Pannonian lithosphereunderwent active back-arc extension and attenuation, produc-ing a compound system of Neogene rift basins characterizedby initial synrift sedimentation overlain by a generally thickblanket of relatively undeformed postrift sediments (Horvth

and Royden, 1981; Royden and Horvth, 1988). Neogenesedimentation was dominated by both tectonic and eustaticprocesses, and depositional sequences commonly were boundby unconformities (Kkai and Pogcss, 1991; Sztan andTari, 1993; Csat, 1993). Synrift sediments, although domi-nantly terrigenous, included marls, algal limestones, evapo-rites, nonmarine clastics, and coals. Tuffs and pyroclasticsare also common, and extensive blankets of rhyolite tuff weredeposited in the middle Miocene, mainly in the northern halfof the Pannonian Basin (Pka, 1988). Synrift sedimentationended with a regional unconformity over much of the Pan-nonian Basin system, often of pronounced angularity, exceptin deep interior subbasins where continuous sedimentation

appears to have occurred. Postrift sedimentation was rapid anddominated by relaxation, thermal subsidence, and differentialdownwarping. The rift basins were covered by a widespreadblanket of relatively undeformed sediments that expandedto encompass the present Pannonian Basin and overlap mosthigh blocks by the late Pliocene (Grow and others, 1994).The postrift stage records the final isolation of the PannonianBasin from the Tethys Sea with evolution of a large lacustrinebody and its reduction by fluvial-dominated delta progradation(Royden and Horvth, 1988; Kzmr, 1990; Mller and others,1999). The postrift sequence is marked by a suite of largelynonmarine, lacustrine, deltaic, and fluvial clastic facies.

As noted by Royden (1988), the older sedimentary rockswithin each basin were deposited mainly during active faultingand generally lie within well defined fault-bounded troughsthat form the deepest part of each basin and are overlain, oftenunconformably, by younger, flat lying, posttectonic depositsand, as characterized by Pogcss, Mattick, Tari, and Vrnai(1994), the style of sedimentation within individual basinsis influenced by proximity of the basin to active thrusts of thebounding Outer Carpathians and Dinarides. Basins locatedclose contain a thick, synextensional faulted sedimentaryrock section overlain by a thin post tectonic section. Basinslocated in a more internal position in the Pannonian Basin arecharacterized by the dominance of a post extension unfaulted

flat-lying sedimentary sequence.

Paleogene and Early Neogene

During the Paleogene and early Neogene, a predomi-nantly structurally controlled depositional pattern persisted(fig. 7). Initially, the Pannonian crustal blocks (Pelso andTisza) were high-standing, and sedimentation was restrictedto the adjoining Carpathian foredeep where flysch sedimentsconsisting of deep-marine silty and marly clay and turbiditicsandstones were deposited, as represented by highly deformedCarpathian and Magura Flysches of the Outer Carpathian

General Geologic Setting 1


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foldbelt. Deposition continued there, and, during the Eoceneand Oligocene, a flysch belt also developed interior to the arc,producing the Podhale, Szolnok, and Transcarpathian Fly-sches, which lapped onto the margins of the Pannonian crustalblocks and into the Szolnok trough and became involved insubsequent Neogene compressive deformation. As a conse-

quence, moderately folded and thrust Podhale Flysch rests onhighly deformed Mesozoic rocks along the present northernmargin of the Pannonian block, as do equivalent Szolnok andTranscarpathian Flysches elsewhere (fig. 7).

Within the interior of the Pelso block, rocks of Eoceneand Oligocene age were deposited in an epicontinental basinsetting (fig. 7) (Royden and Bldi, 1988; Nagymarosy, 1990;Nagymarosy and Bldi-Beke, 1993; Tari and others, 1993).The large Hungarian Paleogene Basin accumulated bothmarine and nonmarine sediments. Within it, middle Eocenerocks are represented by the Szc Limestone and lagoonalsequences containing paralic coal seamsthese sequences arefollowed by mostly marine rocks in the upper Eocene, includ-

ing bathyal marls and neritic sandstones. Structural inversionof the Hungarian Paleogene Basin in late Eocene time pro-duced a trough immediately east of the uplifted earlier basin,and an upper Eocenelower Oligocene sequencerepresentedmainly by marls, laminated clays, and silty clays of the BudaMarl, Tard Clay, and Kiscell Clayis followed by bathyalsilty, marly clay and silty sandstone of the Szcsny Forma-tions in axial areas and the Eger Sandstone and equivalentsin marginal areas. During the following Egerian time (lateOligocene to early Miocene), bathyal siltstones and shales ofthe upper Szcsny Formation were deposited in deep partsof the basin, and sublitoral marine, clayey and sandy silt,and brackish littoral sand, silt, gravel, and conglomerate andminor coals were deposited in marginal areas. This continuedinto late Eggenburgian (early Miocene) time and terminatedwith a regional unconformity, except in deep basinal areaswhere sedimentation appears to be virtually continuous. In theSlovenian Paleogene Basin, upper Eocene limestones weresucceeded by euxinic silty clay of the Oligocene Sotzka bedsand local paralic coal seams; Nagymarosy (1990) further sug-gests that the Slovenian Basin represents a part of the Hungar-ian Paleogene Basin that was left behind during rifting along aBalaton and Mid-Hungarian transform.

Middle to Late Neogene

The back-arc extensional basin system, which wasestablished in the Miocene on deformed older rocks in theCentral Paratethys region, was characterized by a thick,marine, brackish, lacustrine, continental, and fluvial clastic fill(figs. 2 and 3). The surrounding Carpathian Mountains weremildly uplifted during most of the period, although marineconnections were intermittently maintained with adjoiningMediterranean and Caspian seaways. Initial sedimentationconsisted of an earlymiddle Miocene synrift-stage depositionthat reflected a dominant role of extension, strike-slip defor-mation, and rifting during sedimentation. During this stage,

the principal basins of the Pannonian system took shape andaccumulated locally thick sequences, separated by horsts andupwarps of basement blocks. This was followed in middle tolate Miocene time by a postrift stage dominated by thermalsubsidence, differential downwarping, and rapid accumulationof a widespread, often thick, blanket of relatively undeformed

sediments, which buried most high blocks by late Neogene(Royden and Horvth, 1988; Grow and others, 1994).

Synrift Sediments

Synrift sediments were deposited in a framework ofmultiple, active, pull-apart basins, grabens and half-grabens,and shear basins (fig. 5). Deposition was initially limited tomarginal subbasins of the Pannonian system, and becamemore widespread through time, resulting in proportionallylarge thicknesses of synrift rocks in marginal areas, such asin the Transcarpathian Basin. In much of the interior Panno-nian Basin area, such rocks are thin or absent. Nearshore and

shallow-marine conditions surrounded scattered islands anduplifted blocks; island areas were gradually covered by suc-cessive transgressive sequences controlled largely by tectonicand eustatic processes (Brczi and others, 1988; Kkai andPogcss, 1991; Csat, 1993). Conglomerates were commonlydeposited on margins of subbasins, whereas interior partswere characterized by finer sediments, including sandstonesand silty marls and, in clear-water reef environments, litho-thamnion-bearing limestones. In general, marginal subba-sins contain coarser grained facies than those of the interior.Thicknesses of synrift rocks range from a few meters to morethan 3,000 m. Sequences are characterized by lateral discon-tinuities, faulting and rotation, truncation and rapid thicknesschanges, and by bounding unconformities. The synrift phase isgenerally terminated by a regional unconformity in Sarmatiantime (middle Miocene), except in deep basinal areas wheredeposition appears to have been continuous.

Synrift sedimentation was initiated with a rapid trans-gression in Eggenburgian time (early Miocene) with a mas-sive influx of terrigenous sediments derived from faulted anduplifted blocks into marginal subbasins of the Pannoniansystem. In subbasins of the southwest, coarse-grained fluvialsediments and variegated shales are overlain by transitionaland shallow-marine conglomerates, sandstones, marls, andlimestones. In northern Hungary, transgression produced

nearshore facies of conglomerate, limestone, and sandstone;shallow-marine deposits of glauconitic sandstones; clays andsiltstones in basinal areas; and lignites in lagoonal areas.

In Ottnangian time (early Miocene), a widespreadvolcaniclastic sequence was deposited in the west and south,largely rhyolite tuff and ignimbrites, accompanied by andes-ite intrusions. In the southernmost Pannonian Basin system,shallow-marine breccias and conglomerates, marls, and sandswere deposited on volcanics (including andesites, dacites, andpyroclastics), especially bordering the Dinarides. Locally,coarse-grained clastic sediments with intermittent ligniteseams are found. In northern Hungary, pebbly variegated



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terrigenous rocks are overlain by a sandstone and shalesequence containing limnic and paralic lignite seams. Thepaleogeographic pattern of both the late Eggenburgian andOttnangian is dominated by a rough northeast-trendingstructural grain modified by northwest structures and containsmany areas of nondeposition, particularly in interior parts of

the Pannonian Basin system.During succeeding Karpatian time (early Miocene),

marine conditions transgressed further into the depressionsof the Pannonian Basin system. These rocks overlie a well-defined unconformity at the Ottnangian-Karpatian boundaryin most areas, particularly at basin margins. The oldest bedsare commonly of brackish water origin, overlain by nearshore-marine facies and by an open-marine facies in a narrow north-east-striking axial depression of the system. In littoral envi-ronments, sandstone and conglomerate were deposited, as inthe Transdanubia area where the basal Karpatian is a coarse-grained sequence with intercalations of shale and siltstone andvariegated, brackish, lignitic, and lagoonal sediments. In much

of the Great Hungarian Plain, coarse clastics rest directly upona folded basement of Mesozoic and Paleozoic rocks. In neriticzones, clay and siltstone are found. Lagoonal rocks dominatedby the close of Karpatian time. In late Karpatian time, volca-niclastics were widely deposited, and andesites, dacites, andrhyolites erupted.

Badenian (middle Miocene) rocks represent a widespreadtransgression in which open-marine and nearshore rockssurrounded many small, emergent basement blocks. Basaldeposits are conglomerates along the margins of the basinsystem but are usually sandstones in the central Pannonianarea. Sedimentation was affected by differential subsidence,resulting in considerable local variation in facies. Marls andclays were deposited in open-marine areas, including hemipe-lagic sequences, while limestones of littoral and shallow-waterorigin were deposited in shelf-margin reef complexes andshallow, offshore banks. Brackish-water lagoonal sediments,including lignites, also accumulated along basin margins.Tuffs and andesite and rhyolite intrusives are locally inter-calated in the sequence, particularly in upper parts, and areespecially prominent in the northeastern Pannonian Basin.

This block-faulted tectonic framework and depositionalsetting persisted into late Badenian and early Sarmatian(middle Miocene) time, accompanied by uplift of the Carpath-ian Mountains. An increase in subsidence produced a late

Badenian marine transgression, causing these beds to restunconformably on lower Badenian beds in marginal subbasinsof the system. Sedimentation was widespread and typicallymarked by an argillaceous marl sequence containing upwardlyincreasing reef intercalations. Shales and marls occupiedbasinal settings, and limestone facies of littoral and shal-low-water origin were deposited along local shelf margins inreef complexes and in offshore banks. Andesite, rhyodacite,and rhyolite tuffs are locally intercalated in the late Badeniansequence, and andesites and rhyolites are locally intruded. Thelate Sarmatian is marked by regression, a predominance oflittoral facies, and the appearance of lagoonal and halite- and

gypsum-bearing deposits, which are particularly well devel-oped in the Transcarpathian Basin (refer to fig. 1). Brackishwater limestones that grade into silty and shaly rocks andmarls also appear during this time.

Postrift Sediments

The postrift depositional cycle records the isolation ofthe Pannonian Basin from the Tethys Sea and the evolution ofa large lake that was subsequently filled by sediment broughtin largely from the north and west, as summarized by Roy-den and Horvth (1988) and Mller and others (1999). Thesequence represents a major sediment influx, and most ofthe fill of the Pannonian Basin system belongs to this postriftstage, especially in the interior subbasins. Differential sub-sidence was pronounced, and thicknesses that reach 67 kmoccur in some of the deepest troughs, as in the Bks Basin.Sediments are largely undeformed and unfaulted except forcompaction features over basement highs and deformation

associated with late strike-slip faults. They generally rest withregional unconformity on synrift rocks or on pre-Tertiary base-ment, as in much of the central Pannonian system, but locallyappear to rest conformably on synrift sediments in severalbasinal areas. By the late Neogene, sediments had buried mosthigh blocks and expanded to encompass the present PannonianBasin.

Postrift sedimentation began in late Sarmatian (latestmiddle Miocene) and early Pannonian time (late Miocene)and continued into the Quaternary. The Pannonian sequenceexhibits considerable variation in thickness due to differen-tial subsidence. In individual subbasins in central parts of thesystem, it is represented by a thick sequence overlain by arelatively thin Pleistocene blanket. According to Mattick andothers (1985), the infilling, as reflected in the Bks Basin,resulted from a single cycle of sedimentation starting withwater depths locally greater than 1,000 m, followed by gradualshallowing. During this time, deposition changed from marineconditions to lake, fluvial, and marsh conditions. As notedby Brczi (1988), this was the final marine withdrawal in thecentral Paratethys region, during which marine faunal assem-blages gave way to brackish and freshwater faunas. The lithicsequence is made up primarily of a varied mix of fine- andcoarse-grained clastic rocks and subordinate, locallyimportant, coals.

The base of the Pannonian sequence is commonlymarked by transgressive sandstones and conglomerates,particularly around margins of the system and uplifted blocks.This is succeeded by generally marly sediments depositedin deep brackish-water basins, followed by a mixed clasticsequence of sand, silt, clay, and marl, including occasionalturbidites in basin axial areas. The upper Pannonian sequenceshows a more variable composition, especially in uppermostparts where paludal, fluvial, and lacustrine interbeds becomeincreasingly common. Succeeding Quaternary sediments arecharacterized by highly variable paludal, fluvial, anddelta-plain deposits.

General Geologic Setting 1


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Petroleum Geology

Reservoir Rocks

Reservoir rocks of the Pannonian Basin province are var-ied in age and lithology. According to Dank (1987), Neogenereservoir units account for 61 percent of discovered petroleumresources in Hungary; Mesozoic and Paleozoic units accountfor 33 percent; and Paleogene rocks account for 7 percent.More recent data from Kkai (1994) indicate that 62 percentof oil production is from Tertiary sedimentary rocks, and 24percent of oil production is from Mesozoic carbonates; 70percent of natural gas production is from Tertiary reservoirs.Production is often from multiple zones, particularly in largeanticlinal closures.

Fractured and weathered crystalline Paleozoic andPrecambrian basement rocks are the oldest reservoirs in the

province and include a variety of igneous and metamorphictypes. They often produce along with overlying Cenozoicsedimentary rocks and, in some instances, as combined reser-voirs, particularly on the Great Hungarian Plain. The Algyfield (fig. 8), which is the largest oil and gas field in Hungary,produces from fractured Paleozoic metamorphics, a basal Pan-nonian conglomerate, and overlying Miocene sandstones. Inthe Battonya field, production is from weathered and fracturedPaleozoic granites and quartz porphyries and Miocene con-glomerates and marls. In the Sarkadkeresztr field, produc-tion is from fractured and fissured mica schist and Mioceneconglomerate. In the large Pusztafldvr field, production isfrom mica schist as well as Pannonian sandstones (refer to

fig. 8 for field locations). Fractured Devonian carbonate schistreservoirs are productive in the northwest Drva trough.

Crystalline basement reservoirs constitute about 5 percentof reservoirs in the Pannonian Basin system, and, in them,porosities range from 1 to about 20 percent and commonlyaverage less than 11 percent. Fractured Devonian carbonateschist reservoirs in the Drva Basin exhibit average porosi-ties around 2 percent, with fractured Lower Triassic quartzitesand meta-arenites ranging from 05 percent (Baric and others,1991).

Mesozoic sedimentary rocks are important reservoirsin the Zala and Drva subbasins. At Nagylengyel field, theyinclude Cretaceous rudistid limestone (Ugod Limestone) and

Upper Triassic Haupdolomit and, elsewhere, include marls andlightly metamorphosed limestones. In the Serbian part of theDrva Basin, Lower Jurassic and Middle Triassic dolomitesand coarse clastic reservoirs are productive, with reportedporosities of 12 percent, 8 percent, and 3 percent, respectively(Baric and others, 1991). Triassic limestones are also produc-tive in the Hungarian Paleogene Basin. Reported averageporosities of Mesozoic reservoirs in the Pannonian Basinsystem range from 2 to 25 percent and average about14 percent. Fracture enhancement of these reservoirs iseverywhere important.

Eocene and Oligocene sandstones, tuffaceous sand-stones, limestones, and marlsparticularly the Eocene SzcLimestone and the Oligocene sandstones associated with theKiscell Clayconstitute primary reservoirs in the HungarianPaleogene Basin (Kkai, 1994). Conglomerates, sandstonesand siltstones, along with marls, shales, and limestones are

reservoirs in the Szolnok Flysch and in the Podhale Flysch andequivalents of the Central Carpathian area, where they includecoarse-grained arenaceous reservoirs, which average 8 to 10percent porosity (Nemcok and others, 1996). Others are oflow matrix porosity, and fracture enhancement is important forreservoir development.

Neogene rocks are the principal reservoirs of the Pan-nonian Basin Province and account for more than 80 percentof all reservoirs reported. Of these, sandstones make up about95 percent, and, of these, about 90 percent are Miocene inage; the balance are Pliocene. Badenian, Sarmatian, and lowerPannonian reservoir units are the most productive and includeshallow-water sandstones and conglomerates of fluvial,

marine, and lacustrine origin, as well as turbidites, marls, algallimestones, and freshwater limestones. The Pliocene producesrelatively small amounts of oil and gas, including scatteredgas accumulations of biogenic origin. Quaternary rocks alsoproduce small quantities of gas in a few areas. Algal limestonereservoirs are largely limited to the synrift sediments, particu-larly in Badenian sequences. A few Neogene volcanoclasticreservoirs are reported. According to Kkai and Pogcss(1991), the eastern and southwestern Hungarian subbasinscontain the following Neogene reservoir types: basinal andprodelta turbidites (40 percent), delta-slope turbidites (30percent), mouth bars (15 percent), channel fills (8 percent),barrier bars (3 percent), and point bars (2 percent).

Data from Petroconsultants (1996) indicate that aver-age porosities for Neogene synrift sandstone reservoirs rangefrom 5 percent to more than 30 percent, and cluster around 16percent. Average porosities for postrift reservoirs are some-what higher, ranging from 8 percent to 40 percent, and averagearound 22 percent.

Source Rocks and Maturity

The oldest known source rocks in the region are Trias-sic organic-rich shales and marlstones, namely the Rhaetian

Kssen Marl and Carnian Veszprm Marl of the basementcomplex (Kkai and Pogcss, 1991). They are locally presenton the Pelso block and provide potential source rocks wherenot thermally overmatured prior to Cenozoic burial. Accord-ing to Pogcss and others (1996), total organic carbon (TOC)of the Veszprm ranges from 3 to 5 percent, whereas that ofthe Kssen ranges from 3 to 20 percent; both source rockscontain type-I and type-II kerogen. Kssen Marl has yieldedmost of the oil in the Zala Basin according to Clayton andKoncz (1994b). There, at least five fields contain oils of Trias-sic origin, including the giant Nagylengyel field. In this area,



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26O

Adriatic

Sea

16E18E 20E 22E

24E

50N

48N

46N

44N

0

BARABSSZEGNAGYLENGYEL

MATZEN

GBELY

LIPANY

PUSZTAAPTISZILVAGY

BUJAVICA

GOJLO

BAK

SATCHINEZMOKRIN

VARJAS

TURNU

BATTONYAALGY

PUSZTAFLDVR

SARKADKERESZTR

SUPLACU DE BARCAU

HAJDSZOBOSZL

BUDAFAPEKLENICASELNICA

Thickness of Neogen

> 0 2

2 4

> 4

Outer Alpine-C

Outcrop of Neo

Inner Alpine-CInner Alpine-C

Neogene

Oil field centerOil field center

Gas field centeGas field cente

Oil and gas fielOil and gas fiel

EXPL

Figure 8. Map showing oil and gas fields of the Pannonian Basin Province (4048) and associated Vienna and Transylvanian Basins.

mentioned in text are named.


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generation and expulsion began in the Miocene, according toClayton and Koncz (1994b).

Equivalent rocks may be present in several other parts ofthe Pelso block; however, their distribution is poorly known.Milicka and others (1996) call on an early stage of generationprior to the Tertiary for Mesozoic rocks in the northern Dan-

ube Basin, although Mattick and others (1996) suggest that, inthe Hungarian part of this basin, upper Paleozoic or Meso-zoic rocks probably were not subjected to significant thermalmaturation until Miocene time. As with the Cenozoic, the topof the oil-generation zone is generally in the 2,200- to 2,500-m depth interval; the bottom of the wet-gas generating zoneis around 4,000 m, and that for dry gas is placed at 5,000 m(Kkai, 1994).

Upper Jurassic marl of the overridden European plateprovided most of the oil in the Vienna Basin. According toLadwein (1988) and Seifert (1996), this source has a high con-tent of type-II and type-III kerogen, locally exceeds 1,500 min thickness, and matured during Miocene loading. The result

was oil migration upward through fault systems of the flyschbelt into nappes of the inner foldbelt and the overlying Ter-tiary. Where sufficiently buried elsewhere along the margin ofthe Inner Carpathian foldbelt, equivalent rocks, if present, mayprovide sources for oil and gas to nappes of the Inner Carpath-ian foldbelt.

Jurassic rocks elsewhere also have source-rock potential.In the central part of the Pannonian Basin, fine-grained pelagicsediments of Early and Middle Jurassic age have been identi-fied as source rocks of fair to good potential (Milota, 1991;Kkai, 1994; Kkai and Pogcss, 1991; Pogcss and others,1996). The most prospective of the Jurassic sources is reportedas having an average total organic content (TOC) of 8 percent(Pogcss and others, 1996). Kkai and Pogcss (1991) andPogcss and others (1996) indicate that Lower Jurassic coalyformations provide possible sources within the Tisza blockand are viewed primarily as potential sources for gas.

Within the Hungarian part of the Pannonian Basin, Kkai(1994) indicates that 7 percent of the Upper Cretaceous vol-ume of sedimentary rocks could be source rocks. Pogcss andothers (1996) specifically identify the Jko and Polny Marlsof the Pelso block as potential source rocks of Cretaceousage, though of relatively low TOC and containing gas-pronekerogen.

Upper Cretaceous and Paleogene shales, marls, and

marly clays of the Carpathian Flysch and equivalents in theOuter Carpathian Flysch belt are potential source rocks at thenorthern margin of the Pannonian province. Oil and source-rock correlations and biomarkers indicate the Oligocene flyschseries to be an important source rock in the Outer Carpathianfoldbelt (Ziegler and Roure, 1996), and Francu and others(1996) suggest that they may have generated or co-sourcedsome of the Vienna Basin oils. Where sufficiently underthrustelsewhere beneath the Inner Carpathian nappes, these rocksmay provide hydrocarbons, although other than in the ViennaBasin and in the Central Carpathian Paleogene Basin, effectiveseals for the overlying nappes appear largely lacking.

Important Paleogene source rocks of the HungarianPaleogene Basin include the upper Eocenelower Oligoceneeuxinic Tard Clay and lower Oligocene Kiscell Clay (Kkaiand Pogcss, 1991). These rocks have good source potentialfor oil and gas, as probably do equivalent beds in the Slo-venian Paleogene Basin. In northern Hungary, the Tard and

Kiscell Clays have an average TOC content of 0.51.0 percent,with local concentrations of 0.81.8 percent to as much as4.5 percent (Kkai, 1994; Milota and others, 1995). Theirkerogen is mostly type I and type II, but type-III kerogen ispresent in the upper part of the sequence and in the oil-gener-ating zone at depth. According to Milota and others (1995),much of the Oligocene sequence in the southern part of theHungarian Paleogene Basin lies in the zone of hydrocarbongeneration, with the maturation level of the principal sourceintervals equivalent to the wet-gas zone in the south and to themain oil-generation zone in the north. Maturation is hypoth-esized to have occurred during maximum heat flow in the lateMiocene or Pliocene (62 Ma), and, according to Ziegler and

Roure (1996), the Oligocene Series in the Pannonian Basinaccounts for significant hydrocarbon reserves. In the CentralCarpathian Paleogene Basin, Nemcok and others (1996) reporttwo organic-rich intervals of Eocene age, the first containingbetween 0.1 to 1.5 percent total organic content (TOC) and thelatter containing between 1.1 and 10.3 percent. They containmostly type-III kerogen, along with some type-II kerogen.Maturity within the area varies considerably due to localvariation in structural and burial histories, but locally, theserocks are documented to be in the oil and wet-gas generativewindows. In the more distant Szolnok trough (fig. 7), Kkaiand Pogscs (1991) indicate that the CretaceousPaleogeneSzolnok Flysch and Debrecen Formation may have sourcepotential.

Neogene rocks of Miocene age are considered to be theprincipal source for oil and gas in most of the province. Theyare generally middle to upper Miocene shale, clay-marl, andmarl. Szalay and Koncz (1991) indicate that potential source-rock thickness in the Hungarian part of the Pannonian Neo-gene Basin system ranges from less than 1 m to 4 km, but therocks are generally of low quality. These rocks contain mostlytype-II and type-III kerogen. However, middle Miocene shaleand marl locally contain the richest source rocks (TOC as highas 5.0 weight percent), and upper Miocene rocks, in particularlower Pannonian lutites, locally contain good source beds,

as the Ttkomls Formation of the Bks Basin (as muchas 2 weight percent TOC, of mostly type-III kerogen). TheTtkomls is the probable source of the oil in fractured Paleo-zoic metamorphic basement rocks and the basal Pannonianconglomerates in the Bks Basin (Clayton, Koncz, and oth-ers, 1994; Clayton, Spencer, and Koncz, 1994). Source-rockevaluation and correlation of extracts with oils indicate threeseparate genetic oil types for the Neogene of the Bks Basin,originating from different beds within the sequence (Clayton,Koncz, and others, 1994).

In the Zala Basin, according to Clayton and Koncz(1994b), one of the oil types is probably from Miocene source



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rocks, although its variable composition suggests more thanone unit. In the nearby Drva and Sava depressions, Baric andothers (1998, 2000) indicate that, based on geochemical stud-ies, the oils originate from Miocene source rocks. In the Hun-garian part of the gas-prone Danube Basin, Mattick and others(1996) document the Neogene as a poor, largely gas-prone,

source rock; Milicka and others (1996) indicate Neogenesources for the Slovakian part of the basin, particularly lowerPannonian, Sarmatian, middle Badenian, and lower Miocenerocks, which contain largely type-III kerogen.

The average geothermal gradient in the Pannonian systemis about 3.6C/100 m, and in places exceeds 5.8C/100 m.Because of the high geothermal gradients, organic-rich rocksprovide sources for oil and gas at relatively shallow depths.Although heat flow and depth of the oil window are variableregionally (as noted by Horvth and others, 1988; Dvnyiand Horvth, 1988; and evident in isotherm maps published byKkai, 1994), investigators generally suggest onset of thermalgeneration in much of the system at about 2,000 m for imma-

ture oils and at about 2,500 m for mature oils (Dvnyi andHorvth, 1988; Clayton, Koncz, King, and Tatr, 1994; Clay-ton, Spencer, and Koncz, 1994). Rocks below about 5,000 mare typically in the gas-generative realm. (Areas of inferredmature Neogene source rocks are shown in fig. 13.)

Oil generation in Neogene sediments started about85 Ma and has progressed so that sediments below a depthof 45 km have passed through the oil-generation window(Horvth and others, 1988; Szalay, 1988; Clayton, Koncz, andothers, 1994; Horvth and others 1996). The upper 2 to 3 kmof the Neogene sedimentary rocks are immature throughoutthe basin system, and, as a result, upper Pannonian organic-rich beds are insufficiently buried to have generated thermalhydrocarbons. However, in several areas, young sedimentscontain dry hydrocarbon gases consisting of isotopically light,biogenic or diagenetic methane derived from humic sources,including lignite and brown coal layers (Clayton and others,1990; Koncz and Etler, 1991; Clayton and Koncz, 1994a).

Oil and gas reservoirs are often situated in thermallyimmature rocks above basement highs or are laterally removedfrom areas of generation, indicative of pervasive vertical andlateral migration. Oil fields are commonly located on theperimeters of gas-generative areas, suggesting that gas mayhave displaced oil from areas more proximal to generation.Local chemical and isotopic analyses of gases and charac-

teristics of oils, indicate that significant vertical and lateralmigration has occurred, particularly for gas (Clayton andKoncz, 1994a; Clayton, Koncz, and others, 1994). Concur-rently, the lower Miocene sequence commonly appears to beoverpressured (Szalay, 1988; Spencer and others, 1994; Baricand others, 1991).

Throughout the Pannonian Basin system, gas reservoirscommonly contain substantial quantities of CO

2as a result of

high geothermal gradients and carbonate decomposition indeeply buried basement rocks (Clayton and Koncz, 1994a).Values of CO

2content range from 0.5 to 99.5 percent (Kertai,

1968) and average 28 percent (Kkai, 1994). In the Danube

Basin, in particular, the CO2

content is so high as to makemost of the gas unusable.

Traps and Seals

Producing traps in the Pannonian Basin Province (4048)range in depth from 80 m to about 5,000 m, with most oiloccurring between 800 and 3,000 m and most gas occurringsomewhat deeper (figs. 9 and 10). A wide variety of struc-tural, stratigraphic, and combination trap types are present.Within the Cenozoic basin fill, productive structural traps arecommon, particularly compactional anticlines over basementhighs, fault-closed features, roll-overs associated with growthfaults, and closures in flower structures along strike-slipfaults (Kkai, 1994). Inversion structures are noted in someareas as a result of shear and compression, such as at Budafaanticline in the Zala Basin. In most structurally controlledaccumulations, stratigraphy plays a secondary role; however,

many stratigraphic traps occur in the Tertiary rocks, includingpinch-outs in fluvial, shallow-water, and turbidite sandstonesand conglomerates, and in patch reefs and at truncationspar-ticularly at the unconformity between synrift and postriftrocks. Seals in the Tertiary fill are provided by associatedfine-grained sediments, particularly middle to upper Mioceneshale, clay-marl, and marl.

Traps involving the basement complex include paleotopo-graphic highs, folds and faults in the nappes, and truncationsat the Tertiary unconformity. They involve strongly foldedand faulted Mesozoic sedimentary rocks as well as crystal-line rocks. Seals are provided by associated fine-grained rocksand by overlying Tertiary sediments, such as mudstones andmarls of Sarmation and early Pannonian age, which are oftenoverpressured.

Exploration Status

The Pannonian region has a long history of petroleumexploration. Virtually all initial exploration was focused on theNeogene of the Pannonian Basin, and the principal producingsubbasins are those of the Great Hungarian Plain (primarilythe Jaszsag, Derecske, Nagykunsg, and Bks Basins andMak trough) and subbasins of southwestern Hungary and

adjoining Croatia and Slovenia (comprising the Zala Basinand the Drva and Sava troughs or depressions) (see fig. 1).Petroleum discovered through 1995 totals approximately2.1 billion barrels of oil and 11.2 trillion cubic feet of gas,mostly in Hungary, followed by Croatia, Romania, and Serbiaand Montenegro (Petroconsultants, 1996). In Hungary alone,Kkai (1994) reports 668 million barrels of recoverable oil(MMBO) and 8.5 trillion cubic feet (TCF) of recoverable gasas having been discovered, and, as of January 1, 1995, annualHungarian petroleum production was 11.6 MMBO and 187BCF of natural gas, with reserves estimated at 132.7 MMBOand 3.0 TCFG (Hungarian Geological Survey, 1996).

Petroleum Geology 1


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0 100 200 400 600 800300 500 700 900

0


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About 500 fields have been discovered (fig. 8). The sizedistribution of fields estimated to be greater than 1 MMBOor 6 BCFG, based on Petroconsultants data (1996), is shownin figures 11 and 12. Production is primarily from middleMiocene reservoirs, largely Badenian and Sarmatian synriftrocks, and upper Miocene Pannonian postrift sediments. More

than one quarter of the oil discovered in the province is foundin three fields: Nagylengyel and Algy (Hungary) and Suplacude Barcau (Romania). Approximately one-third of the gas is intwo fields: Algy and Hajdszoboszl (both in Hungary).

Although oil was produced from hand-dug wells as earlyas 1856 in Croatia (Filjak and others, 1969), the first commer-cially significant field in the country was discovered in 1917 inthe Sava trough at Bujavica gas field; this was followed by theGojlo oil and gas field in 1930.

The initial discovery of commercial oil in Hungary wasmade at Budafa field in the Zala Basin in 1937 in lower Pan-nonian sandstones in an anticline identified by surface map-ping and further delineated by gravity and seismic surveys.

In this area, the giant Nagylengyel field, one of the largestfields of the basin, was found in 1951, and has since producedmore than 128 million barrels from a Miocene (Karpatian)sandstone, Upper Cretaceous rudistid limestones, and Triassicdolomites (Kokai, 1994; Clayton and Koncz, 1994b). In theDrva depression, oil was first discovered in 1942, in Slove-nia. Today, the largest gas and gas-condensate accumulationsin the southwestern Pannonian Basin system occur in the Savaand Drva troughs, principally in Miocene reservoirs and infracture-enhanced Mesozoic basement reservoirs (Filjak andothers 1969; Baric and others, 1991).

Systematic exploration for oil and natural gas in thenorthern part of the greater Pannonian region began in 1909,spurred by use of the Eotvos torsion balance, and, in 1913,resulted in discovery of oil at the Egbell field (Gbely) in thenearby Vienna Basin (within the Austro-Hungarian Empire,now Slovakia). Although not included in this assessment,the Vienna Basin represents the northernmost element of theoverall Pannonian Basin system and provides useful perspec-tive. Following discovery of oil at Gbely, oil was found in anumber of small fields within the present Czech, Slovak, andAustrian sectors of the Vienna Basin and, in 1949, the Mat-zen oil field complex, the largest oil field in central Europe,was discovered. This field contained an estimated recovery of564 MMBO from multiple Miocene sandstone reservoirs and

fractured Triassic carbonates of the underlying nappe system(Rieder, 1996). In the Vienna Basin, Sarmatian and Badeniansandstones are the principal reservoirs, and most traps arerelated to faulted anticlinal structures.

In 1915, exploration began in the Great Hungarian Plainand Transdanubian areas in Hungary, and initially yieldeddiscouraging drilling results. The first seismic survey wasdone there in 1937, and this was followed after World WarII by intensive reflection and refraction seismic geophysicalefforts. These efforts resulted in discovery of a major gas field(approximately 434 BCFG) at Pusztafldvr in the Bks

Basin in 1958 (Kovcs and Teleki, 1994), which producedmostly from lower Pannonian sandstones and conglomerateson a large anticlinal feature over a basement high. Numerousother fields associated with basement highs on the peripher-ies of the subbasins have since been discovered. Among theseis the Algy field, the largest oil and gas field in Hungary

(more than 200 MMBO and 3,000 BCFG), discovered in1965, which produces from fractured Precambrian crystallinebasement and upper Pannonian sandstones on a structural highbetween the Bks Basin and Mak trough. Throughout Hun-gary, anticlinal features (particularly compactional anticlinesover basement uplifts), paleogeographic highs, horst blocks,growth faults, and rollover structures play significant rolesin trapping. Most large fields are associated with structuralhighs or with combination structural-stratigraphic traps aroundmargins of the deeper subbasins. Most of these structural-stratigraphic traps are situated in the area of the Great Hun-garian Plain, where today they account for major reserves ofboth oil and gas. According to Kkai (1994), more than 5,200

exploratory wells were drilled between 1935 and 1990 in theHungarian part of the Pannonian Basin system. Drilling therereached a peak in 1943, followed by a brief decline, which wassucceeded in 1947 by another long period of intense drillingactivity that lasted into the late 1980s.

In the Romanian part of the Pannonian Basin system,as elsewhere, anticlinal features, paleotopographic highs,growth faults, and rollover structures play a significant rolein trapping. Exploration activity began in 1942, and, accord-ing to Ionescu (1994), the first field was discovered in 1963 atTurnu, although Petroconsultants (1996) indicates discoveryof Suplacu de Barcau in 1956. More than 70 oil and gas fieldshave since been identified, mainly in Miocene and Pliocenesandstone res

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