Abstract The Romanian territory had a very complex geological evolution. This evolution generated a diversified geology with extended platforms limiting, to the east and south, a folded chain where spectacular overthrusts are present. More than this, posttectonic covers (basins) common to different tectonic units are also present. Some sequences of these posttectonic covers are extended from the frontal part of the folded chain over the platforms. Most of the tectonic units, as well as the post-tectonic covers, host hydrocarbon fields. On some of the tectonic units, the oil generation is proved only by the seep presence. The aim of this chapter is to briefly present the geology of the Romanian onshore, except its western part, namely, the Apuseni Mountains and the Pannonian basin. Each platform (East European, Scythian, and Moesian), each the folded chains (North Dobrudjea Orogen and groups of nappes from the East and South Carpathians [Transylvanides, Median Dacides, Outer Dacides, Marginal Dacides, Moldavides]), as well as the posttectonic basins (Transylvanian Basin, Getic Depression, Focsani Depression), have been described. For all the above-mentioned units, the standard lithostratigraphy and their internal structure are discussed. More details are given for those units that proved to be important hydrocarbon producers, namely, the Moesian Platform, Getic Depression, Subcarpathian nappe, Tarcau nappe, Diapiric fold zone, and Transylvanian Basin. The petroleum systems (including source rocks, reservoirs, and traps) of most of the units are also analyzed. From almost 1000 oil and gas fields already discovered, a reduced number of fields are quoted, just in order to give an idea on the diversity of traps. Copyright ©2006. The American Association of Petroleum Geologists. DOI:10.1306/985619M843077 The history of the geologic evolution of the Romanian onshore related to hydrocarbon genesis and accumulation conclude the chapter. Finally, it is to remark that, in spite of its character of synthesis, the chapter could be a useful tool for those scientists who are interested in an overview of Romanian geology and the related hydrocarbon fields.

Abstract The East Carpathians Bend area has a very complex structure characterized by the presence of nappes, their post-tectonic cover and salt diapirs. The salt forming the studied diapirs is Early Miocene (Burdigalian) in age. After its accumulation the salt was more or less continuously involved in alternating extensional and compressional stages that deformed it from its original tabular position to the present-day diapir. Five stages of salt deformation have been established: initial, pre-nappe emplacement, nappe emplacement, post-nappe emplacement and Wallachian. During all of these stages the salt was configured into different shapes: it formed a truncated cone during the initial stage, a mushroom head during the prenappe emplacement stage, and an increasingly more tapered shape with nappe emplacement and during the post-nappe emplacement stages. Finally, it was squeezed out and refashioned by strike-slip faulting during the Wallachian compressional stage of Pleistocene age.

Abstract The vast thickness (>10 km) of relatively undeformed Cambrian to Recent sedimentary cover of the Moesian Platform in Romania and Bulgaria offers an exceptional record of Cimmerian and Alpine tectonics in the surrounding Carpathian and Balkan thrust-fold belts. Above the Hercynian unconformity, Permian to Middle Triassic continental to shallow marine sediments deposited in a facies succession are quite typical for the European passive margin. Widespread Anisian-Carnian vol- canism indicates an aborted rifting period also marked by locally very thick (>2000 m) evaporites. Based on systematic analysis of reflection seismic data and isopach maps, we interpret two large-scale subsurface features (Optasi- Peris uplift and North Bulgarian arch) as Middle Triassic rift flanks associat-ed with two aborted, E-trending branches of the Paleotethys Basin. The striking appearance of the crystalline basement and the deeper levels of the Paleozoic succession (Cambrian-Silurian systems) in the subcrop of the over-lying Jurassic can be understood in terms of rapid uplift and severe denuda-tion of the rift shoulders. The extensional period was replaced during the Norian-Rhaetian times by a compressional regime in the whole Moesian Platform. Although these Late Triassic Cimmerian folds were undoubtedly formed due to compression, detailed structural analysis permitted a more specific interpretation of the deformation in terms of fault-bend folding in a north-vergent, thin-skinned thrust-fold belt. Structural modeling of the anticlines suggests relatively minor shortening (9-18%). Whereas these structures are very characteristic for North Bulgaria, their structural significance is gradually diminishing to the north, in the Romanian part of the platform. In a wider paleotectonic sce-nario, the north-vergent anticlines beneath the Moesian Platform are inter-preted as the frontal, foreland thrust-fold belt of the Mediterranean Cimmerides propagating into the foreland. Above the Cimmerian unconformity, the sedimentary facies and thickness relations of Lower to Middle Jurassic carbonates clearly show the develop-ment of a south-facing passive margin. East-west-trending Jurassic troughs bounded by normal faults can be documented in the southern, Bulgarian side of the Moesian Platform. From the Early Cretaceous on, sedimentation was clearly influenced by successive compressional periods in the Balkans approaching the southern edge of the Moesian Platform. These consecutive Cretaceous through Eocene Alpine compressive periods, such as the Austrian, Mediterranean, Laramian, Illyrian, and Pyrenean, created the north-vergent thrust-fold belt of the Balkans separated from the platform sequence by a series of relatively narrow foredeeps. Whereas the final docking of the Balkans on the Moesian Platform margin occurred at the end of the Eocene, this did not happen on the northern edge until the late Miocene, when the Carpathians stopped moving onto the platform.