Piotr Krzywiec¹, Szczepan Porebski², Piotr Dziadzio³, Kazimierz Madej⁴, Janusz Siupik⁴, Tadeusz Peryt¹

(1) Polish Geological Institute, Warsaw, Poland
(2) Polish Academy of Sciences, Krakow, Poland
(3) Polish Oil & Gas Company, Gorlice, Poland
(4) Polish Oil & Gas Company, Jaslo, Poland

ABSTRACT: Compression Versus Extension in the Eastern Polish Carpathian Foredeep Basin (Miocene) and Its Bearing on Hydrocarbon System

Carpathian Foredeep basin (CFb) developed in Miocene times in front of the Carpathian orogenic wedge, at the junction area between the East European (Precambrian) and Palaeozoic Platforms, and is superimposed on the Trans-European Suture Zone. Its development was controlled to a large degree by structure of the foreland plate, especially by reactivated NW-SE trending basement faults related to Mesozoic history of the Mid-Polish Trough. Numerous gas fields of biogenic origin have been discovered within CFb infill.

Various genetically linked extensional and compressional features are present within the CFb. Systems of normal faults of total offset in range of 2.5km dominate in the most eastern part of the basin. They are associated with compressional deformations (hangingwall-vergent backthrusts), and towards NW are replaced by basement pop-up structures. This was interpreted as a result of Miocene complex reactivation of inherited Mesozoic fault zones related to flexural extension (normal faults) and transmission of compressional stresses oriented obliquely to inherited basement structures (dextral strike-slip movements and formation of pop-up structures). Such a linked extensional - compressional tectonic activity resulted in development of numerous hydrocarbon traps controlled by basement structures.

Basin-fill is dominated by heterolithic facies intercalated with sandstones. They form a series of 4th-order, offlaping deltaic bodies that were predominantly orogene-sourced. Initally, thrust front resulted in a steep shelf-to-slope clinoform that promoted sand deposition within lowstand deltaic mouth bars around offlap break and as thick, clean turbidites on the basin floor. Later, basin margin have evolved into a ramp-type slope that grew mainly through forced regressive deposition of detached deltas with the delta front and prodelta abounding in thin, muddy turbidite sands. Main stratigraphic traps include basin floor turbidites and mouth bar sands located below transgressive outer shelf muds.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado