Abstract Sixty-three maps illustrate geodynamic evolution and development of palaeoenvironments and palaeolithofacies of the Circum-Arctic region during Phanerozoic times. After the break-up of Rodinia and Pannotia in the Early Palaeozoic, the major Arctic plates Baltica, Siberia and Laurentia drifted from their original position around the South Pole towards the Supercontinent Pangea, which existed in the equatorial position during Late Palaeozoic and Early Mesozoic times. During the Mesozoic and Cenozoic plates gathered around newly formed Arctic Ocean. Large continental masses were assembled from major plates and numerous small plates and terranes on the northern hemisphere and around the North Pole. All the continents were by now connected. Carbonates were abundant in Siberia and Laurentia during Palaeozoic times. Clastic sedimentation prevailed during Mesozoic and Cenozoic times. The distribution of lithofacies shows climatic change associated with continental assembly and disassembly as well as with the steady northward drift of the continents.

Abstract The Jurassic System (199.6-145.5 Ma; Gradstein et al. 2004 ), the second of three systems constituting the Mesozoic era, was established in Central Europe about 200 years ago. It takes its name from the Jura Mountains of eastern France and northernmost Switzerland. The term ‘Jura Kalkstein’ was introduced by Alexander von Humboldt as early as 1799 to describe a series of carbonate shelf deposits exposed in the Jura mountains. Alexander Brongniart (1829) first used the term ‘Jurassique', while Leopold von Buch (1839) established a three-fold subdivision for the Jurassic (Lias, Dogger, Malm). This three-fold subdivision (which also uses the terms black Jura, brown Jura, white Jura) remained until recent times as three series (Lower, Middle, Upper Jurassic), although the respective boundaries have been grossly redefined. The immense wealth of fossils, particularly ammonites, in the Jurassic strata of Britain, France, Germany and Switzerland was an inspiration for the development of modern concepts of biostratigraphy, chronostratigraphy, correlation and palaeogeography. In a series of works, Alcide d'Orbigny (1842-51, 1852) distinguished stages of which seven are used today (although none of them has retained its original strati graphic range). Albert Oppel (1856-1858) developed a sequence of such divisions for the entire Jurassic System, crucially using the units in the sense of time divisions. During the nineteenth and twentieth centuries many additional stage names were proposed - more than 120 were listed by Arkell (1956) . It is due to Arkell's influence that most of these have been abandoned and the table of current stages for the Jurassic (comprising 11 internationally accepted stages, grouped into three series) shows only two changes from that used by Arkell: separation of the Aalenian from the lower Bajocian was accepted by international agreement during the second Luxembourg Jurassic Colloquium in 1967, and the Tithonian was accepted as the Global Standard for the uppermost stage in preference to Portlandian and Volgian by vote of the Jurassic Subcommission ( Morton 1974 , 2005 ). As a result, the international hierarchical subdivision of the Jurassic System into series and stages has been stable for many years.

Abstract The South Caspian Basin was formed as a result of the interaction of the Eurasia, India, Arabia, and numerous microplates starting from the Trias-sic. During the Late Triassic–Early Jurassic, several microplates were sutured to the Eurasian margin, closing the Paleotethys Ocean. A Jurassic–Cretaceous north-dipping subduction was developed along this new continental margin south of the Pontides, Trans-Caucasus, and Iranian plates. This subduction zone trench-pulling effect caused rifting, creating the back-arc basin of the Greater Caucasus–proto-South Caspian Sea, which achieved a maximum width during the Late Cretaceous–early Paleogene. During the Eocene, the Lesser Caucasus, Sanandaj-Sirjan, and Makran plates were sutured to Trans-Caucasus–Talesh–South Caspian–Lut system. The subduc-tion zone jumped to the Scythian-Turan margin. The South Caspian underwent reorganization during the Oligocene–Neogene. Northward movement of the South Caspian microcontinent (SCM) resulted in rifting between SCM and Alborz plate. The southwestern part of the South Caspian Basin was reopened, whereas the northwestern part was gradually reduced in size. The source rocks of the Maikop Formation were deposited in the South Caspian Basin during the Oligocene–early Miocene. The collision of India and the Lut plate with Eurasia caused the deformation of Central Asia and created a system of northwest–southeast wrench faults. The remnants of the Jurassic–Cretaceous back-arc system oceanic and attenuated crust, as well as Tertiary oceanic and attenuated crust, were locked between adjacent continental plates and orogenic systems. Thick molasse-type sediments that accumulated during the Pliocene–Quaternary provided reservoir rocks and contributed to the burial and maturation of source rocks.

Abstract This volume of 30 chapters authored by 107 geologists and geophysicists from Austria, Czech Republic, Hungary, Poland, Romania, Slovakia, Ukraine, United Kingdom, and the USA provides a comprehensive and understandable account of geology and hydrocarbon resources of the entire Carpathian system from northeastern Austria to southern Romania, including the Neogene foredeep, the foreland platform both in front and beneath the thrust belt, the Carpathian thrust belt, and the late and post orogenic intermontane basins. Principal chapters on regional geology are supplemented by thematic contributions on geodynamic reconstructions, regional geophysical investigations, hydrocarbon systems, and case studies of major oil and gas fields. To date, close to 7 billion barrels of oil and more than 53 trillion cubic feet of natural gas have been produced from the entire Carpathian system. Additional new reserves may be found, especially at deeper structural levels below the Neogene foredeep and the thin-skinned Carpathian thrust belt. Seventeen chapters of Memoir 84 have been printed in full. The remaining chapters have been printed as abstracts only, with the full paper for all 30 chapters as .pdf files on the CD-ROM in the back of this publication. The publication is intended as a source of information to schools, governmental and private institutions, oil companies, and potential investors.

Abstract The Carpathians represent the eastern extension of the European Alps (Figure 1 ), but unlike the well-known classical Alps of Western Europe, the Carpathians of Central and Eastern Europe remain less known and are even somewhat mysterious to the outside world. The tumultuous political history as well as the language barriers prevented ideas and information from flowing freely through and outside the region. However, the area greatly contributed to the common knowledge in science and technology. Enormous amounts of geological work have been conducted, and thousands of papers have been published on the geology of the Carpathian region during the past 200 yr (see references in various articles of the volume). However, because of the language barriers and diverse concepts and interpretations, it is not easy for students of Carpathian geology and potential investors to cut through all the information and to get a clear picture about the geology and the hydrocarbon potential of the region. This situation has been well known to the editors of this volume, who both worked in the Carpathians and also spent a great deal of their careers in the American petroleum industry and had a chance to see the Carpathians from the view of outside world. In the early spring of 2000, they met in Krakow, where Jan Golonka, after retiring from Mobil, had just begun his new career as a professor at the Jagiellonian University and Frank Picha, after retiring from Chevron, had completed his AAPG Distinguished Lecture tour through the countries of Eastern Europe

Abstract Sixteen time interval maps were constructed that depict the latest Precambrian to Neogene plate-tectonic configuration, paleogeography, and lithofacies of the circum-Carpathian area. The plate-tectonic model used was based on PLATES and PALEOMAP software. The supercontinent Pannotia was assembled during the latest Precambrian as a result of the Pan-African and Cadomian orogenies. All Precambrian terranes in the circum-Carpathian realm belonged to the supercontinent Pannotia, which, during the latest Precambrian–earliest Cambrian, was divided into Gondwana, Laurentia, and Baltica. The split of Gondwana during the Paleozoic caused the origin of the Avalonian and then Gothic terranes. The subsequent collision of these terranes with Baltica was expressed in the Caledonian and Hercynian orogenies. The terrane collision was followed by the collision between Gondwana and the amalgamation of Baltica and Laurentia known as Laurussia. The basement of most of the plates, which was an important factor in the Mesozoic–Cenozoic evolution of the circum-Carpathian area, was formed during the late Paleozoic collisional events. The older Cadomian and Caledonian basement elements experienced Hercynian tectonothermal overprint. The Mesozoic rifting events resulted in the origin of oceanic-type basins like Meliata and Pieniny along the northern margin of the Tethys. The separation of Eurasia from Gondwana resulted in the formation of the Ligurian–Penninic–Pieniny Ocean as a continuation of the Central Atlantic Ocean and as part of the Pangean breakup tectonic system. During the Late Jurassic–Early Cretaceous, the Outer Carpathian rift developed. Copyright ©2006. The American Association of Petroleum Geologists. DOI:10.1306/985606M843066 The latest Cretaceous–earliest Paleocene was the time of the closure of the Pieniny Ocean. The Adria–Alcapa terranes continued their northward movement during the Eocene–early Miocene. Their oblique collision with the North European plate led to the development of the accretionary wedge of the Outer Carpathians and foreland basin. The northward movement of the Alpine segment of the Carpathian–Alpine orogen has been stopped because of the collision with the Bohemian Massif. At the same time, the extruded Carpatho-Pannonian units were pushed to the open space toward the bay of weak crust filled up by the Outer Carpathian flysch sediments. The separation of the Carpatho-Pannonian segment from the Alpine one and its propagation to the north were related to the development of the north–south dextral strike-slip faults. The formation of the Western Carpathian thrusts was completed by the Miocene. The thrust front was still progressing eastward in the Eastern Carpathians. The Carpathian loop, including the Pieniny Klippen structure, was formed. The Neogene evolution of the Carpathians resulted also in the formation of the genetically different sedimentary basins. The various basins were formed because of the lithospheric extension, flexure, and strike-slip-related processes.

Abstract The Western Carpathians in the territory of Moravia (the eastern part of the Czech Republic) and northeastern (Lower) Austria represent the westernmost segment of the entire Carpathian orogenic system linked to the Eastern Alps. Based on differences in their depositional and structural history, the Carpathians are divided into two primary domains: the Inner Carpathians deformed and thrusted in the Late Jurassic to Early Cretaceous, and the Outer Carpathians deformed and thrusted over the European foreland during the Paleogene and Neogene. These two domains are separated by the Pieniny Klippen Belt, which bears signatures of both these domains and stands out as a primary suture in the Western Carpathians. Only the Outer Carpathians, including the thin-skinned thrust belt partly overlain by the Vienna basin and the undeformed Neogene foredeep, are present in the territory of Moravia and, as such, are subjects of our deliberation. The foreland of the Carpathians in Moravia is represented by the Bohemian Massif, which is a part of the West European plate. It consists of the Hercynian orogenic belt and the late Precambrian (Cadomian) foreland terrane of the Brunovistulicum. The unmetamorphosed sedimentary cover of the cratonic basement of the Bohemian Massif in Moravia extends through two plate-tectonic cycles, the Paleozoic Hercynian and the Mesozoic to Cenozoic Tethyan-Alpine. The Bohemian Massif continues far below the Carpathian foredeep and the thin-skinned Outer Carpathian thrust belt. Various deep antiformal structures have been identified in the subthrust plate by seismic methods and drilling. Some of these structures apparently formed during the Hercynian orogeny, whereas others are related either to the Jurassic rifting or to the compressional Alpine tectonics extending from the Late Cretaceous to Miocene. During the Laramide uplifting of the European foreland, in the Late Cretaceous to early Paleogene, two large paleovalleys and submarine canyons were cut into the foreland plate and filled with deep-water Paleogene strata. The Carpathian orogenic system, as we know it today, evolved during the late Paleozoic, Mesozoic, and Cenozoic through the divergent and convergent processes of the plate-tectonic cycle. In the Outer Western Carpathians of Moravia, the divergent stage began in the Middle to Late Jurassic by rifting, opening of Tethyan basins, and development of the passive margins dominated by the carbonate platforms and basins. Further rifting and extension occurred in the Early Cretaceous. The convergent orogenic process in the Outer Carpathians began in the Late Cretaceous by the subduction of the Penninic-Pieninic oceanic basin and collision of the Inner Carpathians with the fragmented margins of the European plate. Since the Late Cretaceous, a major foreland basin dominated by the siliciclastic shelf and deep-water flysch sedimentation has formed in the Outer Carpathian domain. The Carpathian foreland basin, especially during the Late Cretaceous to the early Eocene, displayed a complex topography marked by an existence of intrabasinal ridges (cordilleras) such as the Silesian cordillera. We interpret them as preexisting rift-related crustal blocks activated during the Late Cretaceous-early Paleocene uplifting as foreland-type compressional structures. During the Paleogene and early Miocene, the Upper Jurassic to lower Miocene sequences of the Outer Carpathian depositional system were gradually deformed and thrusted over the European foreland. The tectonic shortening occurred not only in the decoupled thin-skinned thrust belt but also at the deeper crustal level, where various blocks of the previously rifted margins were apparently at least partly accreted back to the foreland plate instead of being subducted. Since the early Miocene, the synorogenic, predominantly deep-water flysch sedimentation was replaced by the shallow-marine and continental molasse-type sedimentation of the Neogene foredeep, which remained mostly undeformed. Also during the Miocene, the Vienna basin formed in the Carpathian belt of southern Moravia and northeastern Austria as a result of subsidence, back-arc extension, and the orogen-parallel pull-apart strike-slip faulting. During its entire history, the evolution of Outer Western Carpathians in Moravia was significantly affected by the existence of two main structural elements, the Western Carpathian transfer zone and the Dyje-Thaya depression. The southwest-northeast-trending Western Carpathian transfer zone actually separated the Alps from the Carpathians. During the divergent stage, in the Early Cretaceous, the dextral motion in this zone accommodated a significant extension in the Outer Carpathian domain. Conversely, during the convergent stage in the Paleogene and Neo-gene, the sinistral transpressional motion in this zone facilitated the northeastern translation (escape) of the Carpathian belt and the opening of the pull-apart depocenter in the Vienna basin. The northwest-southeast-trending Dyje-Thaya depression, in southern Moravia and northeastern Austria, formed, or at least was activated, during the Jurassic rifting. Within the fault-bounded limits of this depression, thick, organic-rich marls were deposited in the Late Jurassic, shallow-marine clastic strata were laid down and preserved in the Late Cretaceous, two paleovalleys were excavated in the Late Cretaceous-early Paleogene, and finally, the Vienna basin formed in the Miocene. The complex structural and depositional history of the depression and its surroundings created one of the most prolific petroleum systems in the entire Carpathian region, from which more than 850 million bbl of oil has been produced to date. Historically, the Vienna basin has been the dominant producer in Austria and Moravia. More recently, however, the subthrust European platform with multiple hydrocarbon plays has become the main producing province in Moravia. Some of the identified deep subthrust structures represent significant exploration prospects, which yet have to be tested.

Abstract Several oil and gas fields have been discovered recently in the Neogene foredeep, in the European foreland plate, which underlies the foredeep and the thin-skinned Carpathian thrust belt. The fields are reservoired in the Neogene strata of the foredeep plate and in the crystalline basement rocks and the Jurassic, Paleogene, and Neogene strata of the European platform. The most significant accumulations of hydrocarbons in the subthrust plate have been found in the erosional relicts (buried hills) of the Jurassic rocks on the northern side of the Nesvacilka graben and paleovalley and in the fractured and weathered surface of the Precambrian granite massifs of the Chriby and Zdanice elevations. The thickness of the saturated parts of these reservoirs typically ranges from several tenths of a meter to as much as 200 m (660 ft). The geological reserves of the discovered fields are in a range of hundreds of thousands to a few million cubic meters (less than 1 million bbl to several million barrels) of crude oil and hundreds of millions to billions of cubic meters (several to tens of billions cubic feet) of gas. They represent a significant economical potential for petroleum companies operating in the territory of the Czech Republic.

Abstract Through conventional geoscientific research, a fundamental knowledge of the Vienna basin was acquired with the limited data available at the time. Since then, vast exploration programs of the Austrian, Czech, and Slovakian oil industries have contributed significantly to a more detailed understanding of the geological evolution of the basin. The pull-apart or piggyback nature of the basin at present is well understood and commonly accepted. Basically, it resulted from an easterly directed extrusion of the Central Alpine block alternating with compressional events during the final stages of the Alpine convergent phase. The basin evolved in several stages that finally resulted in an intricate arrangement of prominent highs and partly deeper subsided depocenters. The basin was filled by Miocene to Pleistocene sediments that can be subdivided into sequences separated by unconformities; the most pronounced are between the early and the middle Miocene. The basin-floor section below the Neogene fill consists of the Alpine-Carpathian imbricated system. From north to south, these individual thrust piles are the Waschberg-Zdanice zone, the Flysch zone, the Calcareous Alps (including its Paleozoic base, the Grauwacken zone), the Central Alps, and the Tatrides. All these units lie on top of the Miocene Molasse, a Mesozoic series, and the crystalline basement. This section is well known from wells drilled in the molasse zone sensu stricto but were also drilled in the Vienna basin. Ultradeep wells targeting the autochthonous basement reached total depths of between 6.3 and 8.5 km (3.9 and 5.3 mi). Oil and gas are trapped in all units of the basin, from the Neogene fill down to the autochthonous sedimentary cover. Generally, the traps are structural, but recently, stratigraphic traps have also been drilled successfully. The main source rocks are autochthonous Jurassic marls, which seem to form a substantially thickening package in an easterly direction, according to the sporadic well information available. Although the ultradeep well program was believed to be uneconomic at that time, indications point to an unconventional tight-gas play type in the autochthonous Jurassic marls. The contribution of all Vienna basin member countries made it possible to present a comprehensive surface and subsurface compilation. A cross section through the deepest known part of the basin without border limitations was an additional result of this cooperative effort.

Abstract Geophysical, sequence-stratigraphic, and petrophysical evaluation of the main oil and gas reservoirs of the Matzen field in the central Vienna basin resulted in a revised field architecture, and provided new insights into middle Miocene (Badenian, Sarmatian) depositional settings. The latest analysis suggests that the reevaluation of this mature field not only allows a better explanation of production history, but has also led to further successful redevelopment activities. The structural setting of the Vienna basin is the result of subsidence, extension, and a final phase of subsidence. Compressional, transgressional, and extensional events had a strong influence on the basin configuration and sediment distribution. The Matzen field illustrates these pull-apart and piggyback mechanisms clearly. It is an elongated anticline (Matzen anticline), bounded by a pull-apart graben in the north (Matzen fault system), a fault complex in the west (Bockfliess fault system), and another fault zone in the south (Markgraneusiedl fault zone). Three depositional cycles (Matzen cycles) have been subdivided into some 30 sequences. The first Matzen cycle culminates with the transgressive Matzen sand, the main producing horizon in the field. Produced during the Matzen main cycle (second Matzen cycle), marine prograding delta systems of Badenian age contain the main oil reservoirs. The 9th Tortonian horizon is a textbook example of a shelf-slope basin sucession. Within six sublayers, the shelf edge advances some 2 km (1.2 mi) from north to south. Transgressive meandering channel systems of Sarmatian age hold the main gas reservoirs that are partly used as gas storage. The 5th Sarmatian horizon was deposited in a shallow-marine deltaic setting. During a sea level drop, the depocenter shifted southward with simultaneous incision of a widespread channel system into the underlying 6th Sarmatian horizon. The base of the system represents an important sequence boundary. Final isolation of the Vienna basin created brackish conditions. The third Matzen cycle developed as a thick series of lacustrine prograding delta sequences of the Pannonian (upper Miocene).

Abstract The purpose of this chapter is to provide the general overview of the stratigraphy and tectonics of the Polish, Ukrainian, and adjacent parts of the Slovakian Outer Carpathians. The Polish and Ukrainian Outer Carpathians form the north and northeastern part of the Carpathians that expand from the Olza River on the Polish–Czech border to the Ukrainian–Romanian border. Traditionally, the Northern Carpathians are subdivided into an older range, known as the Inner Carpathians, and the younger ones, known as the Outer Carpathians. These ranges are separated by a narrow, strongly tectonized belt, the Pieniny Klippen Belt. The Outer Carpathians are made up of a stack of nappes and thrust sheets showing a different lithostratigraphy and tectonic structures. Generally, each Outer Carpathian nappe represented separate or partly separate sedimentary subbasin. In these subbasins, enormous continuous sequence of flysch-type sediments was deposited; their thickness locally exceeds 6 km (3.7 mi). The sedimentation spanned between the Late Jurassic and early Miocene. During the folding and overthrusting, sedimentary sequences were uprooted, and generally, only sediments from the central parts of basins are preserved. The Outer Carpathian nappes are overthrust on each other and on the North European platform and its Miocene–Paleocene cover. In the western part, overthrust plane is relatively flat and becomes more and more steep eastward. Boreholes and seismic data indicate a minimal distance of the overthrust of 60–80 km (37–50 mi). Copyright ©2006. The American Association of Petroleum Geologists. DOI:10.1306/985610M843070 The evolution of the Northern Outer Carpathian Flysch basins shows several tectonostratigraphic stages. The first period (Early Jurassic–Kimmeridgian) began from the incipient stage of rifting and formation of local basins. The next stage (Tithonian–Early Cretaceous) is characterized by rapid subsidence of local basins where calcareous flysch sedimentation started. The third period (Late Cretaceous–early Miocene) is characterized by compression movements, appearance of intensive turbiditic sedimentation, and increased rate of subsidence in the basins.

Abstract This chapter presents a stratigraphic review of reservoirs and their parameters, trap types, and important fields in all of the tectonic units (nappes) in the Polish Outer Carpathians, where hydrocarbon deposits have been discovered and exploited for more than 150 yr. The first part of this chapter is an introduction to the information about the occurrence of reservoir rocks in the Carpathians; however, the variability of these parameters is commonly surprising. Well-known examples are present where reservoir parameters vary greatly even in the same field, but this is a separate problem, and this is only mentioned here. Despite the very large number of wells drilled in the Polish Carpathians, the quantity of detailed petrophysical data is not so large. Good-quality data have been obtained only during the last 30 yr. The most recent and best quality data originate from wells drilled by Polish Petroleum Industry in areas of known fields during research of deeper prospects and from recognized wells. Copyright © 2006. The American Association of Petroleum Geologists. DOI:10.1306/985611M843071 The best reservoir data are from the Skole and Silesian nappes, and these are presented in this chapter in great detail. Within the region of the Outer Polish Carpathians, reservoir rocks are found to have good potential as in shallow as well as deep structures in deposits of Lower Cretaceous to lower Oligocene in age. The majority of hydrocarbon accumulations in the thrusted and folded Carpathians are within structural style traps. Exploration for them throughout the past 150 yr has enabled geologists to recognize their many different types, such as those related to thrust anticlines and folds, but which before were only interpreted as related to folds. Most of the oldest exploited oil accumulations in the Carpathians are of the contractional anticline type, commonly associated with thrusting. Most of these fields can only be illustrated by line-drawn sections based on drilling information because no seismic data are available. Some of the more spectacular traps in the Outer Carpathians are connected to disharmonic thrusted folds, tilted thrust faults, overturned frontal parts of thrust sheets, imbricate fan types, sandstone pinch-out, and traps sealed by asphalt. In this chapter, selected and more important oil and gas fields that can be examples of characteristic hydrocarbon accumulations are also described. The most southern nappe is the Dukla unit, which lies beneath the Magura nappe, where six hydrocarbon accumulations have been discovered in the Oligocene Cergowa sandstone to date. A good example of the hydrocarbon accumulations and tectonic styles of the fields in the Dukla unit is the Slopnice– Limanowa oil and gas field. Here, the hydrocarbons have accumulated in recumbent thrust folds. The Silesian nappe is represented by two important fields: the Bobrka oil field, which is located in the Bobrka anticline, and the Potok oil and gas field in the Potok anticline. Both of these fields have hydrocarbon accumulations in the Ciezkowice and Istebna reservoirs, which are trapped by thrust-related anticlines. The minor tectonic elements, such as thrust-related anticlines and synclines that separate the two fields, however, do not yield hydrocarbons. The Bobrka oil field lies in the world’s oldest area of petroleum exploration and production. This field is taken as the symbol of the Polish and international oil industry and is presented here from a historical point of view. The Potok oil and gas field is located approximately 10 km (6 mi) to the north of the Bobrka oil field. It is one of the six most productive oil fields in the region and produces from an anticlinal structure more than 40 km (25 mi) long. The Skole nappe is a similarly important unit for hydrocarbon exploration. Four oil fields have produced 1.7 million t of oil and more than 180 million m 3 (3.8 bcf) of gas from accumulations in the Menilite sandstone. One example of such an accumulation is seen in the Lodyna oil field. Here, the hydrocarbons are accumulated in a series of almost vertical beds of menilites within pinching out of Kliwa Sandstone.

ABSTRACT The Polish and Ukrainian Carpathian Foredeep, about 600 km (376 mi) long and as much as 100 km (62 mi) wide, is part of the large sedimentary basin that stretches for more than 1300 km (816 mi) from the Danube in Vienna (Austria) to the Iron Gate on the Danube (Romania). To the west, the Carpathian Foredeep is linked with the Alpine Molasse Basin, and to the east, it passes into the Balkan foreland basin. Like other foreland basins, the Carpathian Foredeep is asymmetric and filled with predominantly clastic sediments of the Miocene age as much as 3 and 6 km (1.8 and 3.6 mi) thick at the Carpathian front in Poland and Ukraine, respectively. The molasse deposits of the Carpathian Foredeep are underlain by the basement of the European Platform, covered mainly by Permian-Mesozoic terrestrial and shelf sediments and locally by the Paleogene deposits. According to seismic, magneto-telluric, and well data, the platform basement with Miocene molasse cover dips southward underneath the Outer Carpathian nappes to a distance of at least 50 km (31 mi). The early to middle Miocene Carpathian Foredeep developed as a peripheral foreland basin related to the moving Carpathian front. The Paleozoic-Mesozoic and Tertiary strata of the Carpathian Foredeep are oil and gas productive.

Abstract The intention of this chapter is to present a short description of the reservoir rocks, recognized types of the hydrocarbons traps, and a few chosen oil and gas fields in the basement and in the Miocene cover of the Carpathian Foredeep. Most of the oil produced from the Carpathian Foredeep basin has come from Oxfordian carbonates and Cenomanian sandstones, two of the most oil-productive reservoir rocks. The Devonian, Carboniferous, and Cretaceous carbonates are the secondary basement reservoirs. However, from the commercial point of view, the overlying Miocene clastic deposits cover has the prominent status. It consists of excellent source and reservoir rocks that have produced large amounts of gas. The primary reservoirs are sandstones of different depositional elements of submarine fans, sandstones of deltaic environments (large mouth bar, distributary channels, and others), the shallow-marine clastic deposits of estuaries, and sandy barriers. Sporadically, the gas accumulations are located in the secondary porous anhydrites. The most common basement oil and gas trap is the combination structural-stratigraphic type with varying systems of sealing. Traps are related mainly to the sub-Miocene and less to the sub-Cretaceous unconformity. The pinching-out stratigraphic traps are known from the Cenomanian sandstones. The stratigraphic traps in the carbonate buildups (reefs) have still-undiscovered potential. Copyright ©2006. The American Association of Petroleum Geologists. DOI:10.1306/985613M843073 The traps for gas accumulations in the Miocene (Badenian and Sarmatian) deposits of the Carpathian Foredeep are related, first of all, to the paleomorphology of the pre-Miocene basement formed by the erosion supported by the faulting processes. This type of trap is classified as the compactional trap. The second, very productive structural traps were recognized beneath the Carpathian sole thrust, at the front of the Carpathians. The fault-related trapping mechanism is also known from several gas fields. The pinching-out trap types caused by the horizontal and the vertical facies changes are sparse and occur most commonly in the topmost part of the Miocene succession because of the more favorable facies and less compactional deformation of the strata. During last 50 yr of exploration, more than 120 gas and oil fields were discovered in the Carpathian Foredeep. The bulk of the produced hydrocarbons (97%, mainly gas) were contained in the Miocene deposits, with a further 3% in the Miocene basement. The Miocene contains only gas fields, whereas both oil and gas were found in the basement rocks. The Miocene gas fields are typically multihorizontal and saturated by gas with a very high methane content, normally from 95 to 99%. About 90 billion m 3 (3.2 tcf) of this kind of gas has already been produced. The Przemysl gas fields group is the largest in Poland with gas initially in place (GIIP) of nearly 71 billion m 3 (2.5 tcf), and the cumulative field production, as of December 31, 2002, amounted to 55 billion m 3 (1.9 tcf). The Grobla and Plawowice are the biggest oil fields accumulated in the Oxfordian carbonates and Cenomanian sandstones of the Carpathian Foredeep basement. A few important gas fields, like Tarnow and Lubaczow, were also founded in the Oxfordian carbonates. According to the results of the latest deep wells, the basement of the Carpathian Foredeep is still highly prospective for hydrocarbons, especially the Devonian and Carboniferous carbonates in the central part of the foredeep and the Oxfordian buildups in the more western part. The deep wells like Hermanowa proved to be a very high source potential of the lower Paleozoic rocks, which allows for the prediction of new significant oil and gas discoveries in the nearest future. The improvement of methods, particularly the direct hydrocarbon indicators method, opened a new stage of exploration for gas accumulations in the Miocene deposits. In only the last 8 yr, nearly 20 new gas fields were discovered on the basis of such interpretation results.

ABSTRACT Multiple petroleum systems occurring in different tectonic elements of the Polish and Ukrainian parts of the Flysch Carpathians, their foredeep, and the Paleozoic–Mesozoic basement have been identified and characterized using various geochemical methods. The Carpathian flysch sequence, containing the main oil fields in the area, contains two main potential source rock intervals: the Early Cretaceous and Oligocene. The Oligocene Menilite shales, which are widespread in the Polish and Ukrainian parts of the Carpathian flysch belt, contain high-quality source rocks, with mainly type II kerogen and high petroleum potential. A suitable tectonic position in several units of the flysch belt, especially in its frontal nappes of the Ukrainian part, provided the maturation level of this series, corresponding to different parts of the oil window. Modeling of hydrocarbon generation and expulsion in Menilite rocks shows that these processes are related mainly to Miocene overthrusting. Geochemical studies of oils from different fields occurring in the flysch sequence show that they belong to the same family. The presence of oleanane probably indicates that they have been generated from Menilite rocks. Lower Cretaceous organic-rich rocks, which contain mainly type II and III kerogen with good petroleum potential and a maturation level corresponding to the oil window, should be considered as another important potential source rock sequence in both the Polish and Ukrainian Carpathian flysch belt. The autochthonous Miocene nonfolded molasse sequence contains most of the gas fields in the Polish and Ukrainian Carpathian Foredeep. Geochemical studies of Badenian and Sarmatian strata show that they contain sufficient amounts of immature terrestrial organic matter, which generated methane-rich microbial gases. Molecular and isotopic compositions of natural gases from Miocene reservoirs confirm that they were produced during microbial carbon dioxide reduction. Molecular and stable isotope compositions of gases from Paleozoic -Mesozoic reservoirs of the Polish part of the basement show that they were generated by both microbial and thermogenic processes. Gas from the Lachowice field in Devonian rocks is a typical nonassociated thermogenic gas, generated from type III kerogen with a high degree of maturation. This gas probably migrated from Carboniferous source rocks. The oils accumulated in Upper Cretaceous and Upper Jurassic reservoirs in the Polish part and, southeast of the Ukrainian part of the basement, contain oleanane and other specific biomarkers and belong to the same geochemical family. They were probably generated from the Oligocene flysch rocks and Middle Jurassic beds.