During part of 1991, while a graduate student at the University of Texas at Austin Institute For Geophysics (UTIG), I interned at Exxon Production Research Company (EPR) in Houston. I spent most of my time in a team of explorationists at Exxon International, working on a regiojnal frontier project assessing the hydrocarbon potential of the Carpathian Fold and Thrust Belt in Czechoslovakia and Poland.
      

The "Pravcicka" Arch

An eastward extension of the Alps, the Carpathian Orogen runs northeast between the Czech Republic and Slovakia (the "Beskydy Mountains", turns due east along the border between Poland and Slovakia (the "Tatra Mountains"), then curves in a giant arc through western Ukraine into Romania (the "Carpathian Mountains").

Trilobite from the "Barrandien" Basin

To the north (outboard) of the fold and thrust belt lies the West European Plate; itself a mess of crystalline basement, an old northeast-dipping Variscan subduction zone, a small Lower Paleozoic basin southwest of Prague (the Barrandien Basin), and a thin Cretaceous cover of shallow marine and fluvial sandstones in the northern part of the Czech Republic (the "Czech answer" to Arches National Park). To the south of the fold and thrust belt, atop the Apulian Plate, lies the Pannonian Basin.
       The fold and thrust belt consists of several nappes of varying ages, each with its own distinct lithologic character. These nappes are the remains of the Tethys Ocean that once existed between the Asian and Europeans Plates.

Carpathian Fold and Thrust Belt (From Picha, 1996) (Click to see a larger picture)

The Tethys opened gradually during a Jurassic period of rifting. In the early stages of the Tethyan opening an important formation of organic-rich calcareous mud (the Mikulov Marl) was deposited on the floor of the Tethys. It is believed my most geoscientists that it is this formations that serves as the source of hydrocarbons for all the fields in the Vienna Basin and production elsewhere along the fold and thrust belt.
       Grand-Canyon-size canyons were cut into the edge of the European Plate (e.g. the Nesvacilka Graben) and probably served as conduits that funneled submarine fans onto the abyssal plain of the Tethys.
       In the Early Tertiary, when the Tethys began to contract, deep-water turbidites (Sub-Silesian and Silesian nappes) were thrust over the margin, followed by older and older units (e.g. Triassic limestones of the Pieniny Klippen Belt), until the final stages of the shortening when the crystalline Inner Carpathian nappe was plastered onto the inside of the fold and thrust belt.
      

Satellite image of the Vienna Basin located between the eastern end of the Alps (left side) and the Neusiedler See. Notice the Danube River and the cities of Vienna and Bratislava (bright spots). Image taken from ESA 1993, Courtesy The Univ. of Vienna (Click to see a larger picture)

Meanwhile, in the Miocene, a curious thing happened along the outer edge of the fold and thrust belt, in the area where Vienna and Bratislava lie today. A pull-apart basin opened on top of the still-advancing nappes: the Vienna Basin. Because of the extremely arcuate nature of the fold and thrust belt, this area was briefly subjected to transtension and the Vienna Basin was formed.
       As it subsided, the Vienna Basin was filled by Miocene and Pliocene turbidites, deltas, shoreline and fluvian deposits. These rocks are generally similar in age and depositional setting to those deposits that filled the narrow foredeep basing outboard of the advancing nappes.
      

Moravian wineyard

In terms of geomorphology, the Carpathian fold and thrust belt is an area of stunning natural beauty. Each one of the nappes composing the fold and thrust belt, has somewhat different lithology, and therefore forms its own distinct landscape. Each one of the nappes composing the fold and thrust belt, has somewhat different lithology, and therefore forms its own distinct landscape. The Vienna Basin, lying on top of the Sub-Silesian and Magura nappes, is a flat, low-lying plain covered with corn fields and orchards.

Eastern Carpathians in Ruthenia

To the northwest the outcropping Sub-Silesian nappe gives rise to low limestone hills (The "Palava" Highlands) dotted with vineyards producing a nice variety of delicious semi-dry red wines. To the northeast, the Silesian and Magura nappes form rounded hills, characteristic for landscape underlain by turbidite and other interbedded clastic rocks. In stark contrast to the wooded wills of the Magura and Silesian nappes are the jagged white limestone cliffs formed by the Pieniny Klippen Belt nappe.

The "Pieniny" National Park

Deep narrow valleys, swift wild rivers, ancient castles and chateâux provide a backdrop fit for a romantic painting (say by Eugène Delacroix).
      

The "Spis" Castle

In even more contrast, to the east lie the Tatra Mountains, jagged nine-thousand-foot peaks rising majestically to the sky. The Tatras provide hiking and skiing comparable only to the Alps and the Colorado Rockies. Although nearly not as high as many of the mountain ranges in Colorado, the Tatras convey a much more rugged and austere "mountainous" feel (due mostly to the fact that this ares is much farther north than Colorado).

View from the "Ostrva" Peak of the tarn "Popradske Pleso" and the valley "Mengusovska Dolina"

       The results of my summer internship project remain proprietary and cannot be published without Exxon's consent.
       However, AAPG Bulletin published in 1996 a very comprehensive paper by Frank Picha, a senior geoscientist with Chevron Overseas Petroleum Inc. (The paper is based on his 1991 talk at the AAPG International Conference in London where it won the AAPG International Best Paper Award.) My results were very similar to this work.

Frank J. Picha, 1996, Exploring for Hydrocarbons Under Thrust Belts: A Challenging New Frontier in the Carpathians and Elsewhere, AAPG Bulletin, v.80, No.10 (October 1996), p.1547-1564.