Organic buildups recognized upon well and seismic data within the Upper Jurassic formations of the Carpathian foreland, Poland; perspectives for hydrocarbon exploration

Abstract

The system of huge organic buildups (sponge-microbial bioherms and coral reefs) has recently been mapped in the Carpathian foreland, S Poland, using high-quality petroleum seismic and well data interpreted using original, newly developed techniques. The sponge-microbial bioherms were formed during the Oxfordian time and the flat and mound-shaped coral reefs replaced them during the Late Oxfordian through Tithonian time. Both the bioherms and reefs reflect the system of synsedimentary active extensional-transtensional blocks of the basement that controlled sea bottom highs which were likely colonized by the buildups constructors. It is possible to identify two systems of such faults: NW-SE oriented one and, less visible, W-E oriented one. The Late Jurassic organic buildups form excellent reservoirs for hydrocarbon accumulations. Effective seal for the traps is provided by the Upper Cretaceous (Senonian) marls. Late Cretaceous inversion resulted in reverse reactivation of main basement fault zones. During the Miocene, Carpathian thrusting-related flexural extension basement fault zones have been again reactivated in transtensional regime, which enhanced hydrocarbon prospectivity of selected areas due to juxtaposition of source and reservoir rocks. Miocene foredeep evaporates provide additional, very effective seal.