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PSLithostratigraphy of the Upper Jurassic – Cretaceous Deposits and Hydrocarbon Perspective in the Romanian Shelf of the Black Sea*
By
Ovidiu Nicolae Dragastan1
Search and Discovery Article #10144 (2008)
Posted February 26, 2008
*Adapted from poster presentation at AAPG and AAPG European Region Energy Conference, Athens, Greece, November 18-21, 2007.
1Bucharest University, Bucharest, Romania ([email protected])
On the Romanian shelf of the Black Sea, Petromar Company has drilled and has obtained cores of Middle and Upper Jurassic - Cretaceous, as well as Paleogene and Neogene, deposits. Mesozoic and Cenozoic deposits belong to two main geological units: the North Dobrogea Orogenic Belt and the Moesian Platform. In the offshore of the North Dobrogea Orogenic Belt three cycles of sedimentation have been identified:
1. A lower transgressive cycle corresponding to the compressive phase of synrift 1 (Bajocian- Callovian?), the last stage possibly corresponding to a ”general” unconformity or to a break-up 1 between Middle and Upper Jurassic , with black calcitic and siltic turbidites (Heraclea Formation).
2. A middle transgressive compressive cycle composed by mudstones, claystones, and siltstones ( Pontus Formation), Upper Jurassic - Neocomian in age, corresponding to synrift 2, followed by break-up 2 up to the Jurassic-Cretaceous boundary and intra Neocomian hiatuses.
3. An upper post-rift cycle, Albian to Senonian in age, but which continued during the Paleogene and Neogene. Many short and long time hiatuses are recorded that include the Cretaceous deposits.
Three source rocks can be identified for hydrocarbon generation:
· Black argillaceous, siltic to sandstones of the Heraclea Formation (Middle Jurassic in age), about 1000 m in thickness.
· Black argillites of the Pontus Formation (Neocomian)
· Oligocene- Miocene bituminous shales, clays and marls generally known as the Maikop beds.
The reservoirs are Albian-Cenomanian bioturbated sandstones with intercalations of calcarenites, marly limestones, and limestones. They produce oil and gas in Lebada field, which also produces from the Senonian chalk.
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Geologic Framework and Location of Oil and Gas Fields
North Dobrogea Subunit (A) (Orogenic Belt)
Central Dobrogea Subunit (B--Vadu-Corbu)
South Dobrogea Subunit (C--Mangalia-Delfin)
Selective Bibliography Avram, I., A. Draganesu, L. Szasz, and Th. Neagu, 1988, The stratigraphy of the outcropping Cretaceous deposits in Southern Dobrogea (SE Romania): Mémoires Institute Geology and Geophysics of Romania, v. 33, p. 5-45. Bancila, I., Th. Neagu, R. Mutiu, and O. Dragastan, 1997, Jurassic-Cretaceoous stratigraphy and tectonic framework of the Romanian Black Sea offshore: Rev. roumaine, Géologie, tome 41, p. 65-76. Dragastan, O., 1985, Upper Jurassic and Lower Cretaceous formations and facies in the eastern area of the Moesian Platform (South Dobrogea included): Analele University Bucuresti, Géologie, v. 34, p. 77-85. Dragaston, O., E. Gradinaru, and C. Dinu, 1987/1988, Studiul litostratigrafic al carotelor din forajele executate pe selful romanese al Marii Negre: Raport intern MMPG. Dragastan, O., R. Mutiu, C. Sisman, and St. Popescu, 1993, Moesian Cretaceous carbonate Platform (the Eastern Romanian sector) and data about the adjacent Black Sea offshore (abs.): AAPG Annual Convention, New Orleans. Dragastan, O., Th. Neagu, Aurelia Barbulescu, and I. Pana, 1998, Jurasicul si Cretacicul din Dobrogea Centrala si de Sud., Edit. Supergraph., Bucuresti, 249 p., 54 pl.. Draganescu, A., 1976, Constructional to spongalgal, algal and coralgal facies in the Upper Jurassic carbonate formation of Central Dobrogea (the Casimcea Formation): International Colloq. Carbonate Rocks and Evaporites, Guidebook, Series 15, Institute Geology and Geophysics of Romania, p. 13-43. Einsele, G., 2000, Sedimentary Basins, Evolution, Facies and Sediment Budget: Springer Verlag, 792 p. Georgescu, D.M., 1994, Upper Jurassic-Cretaceous planktonic biofacies succession and the evolution of the Western Black Sea Basin: AAPG Memoir 62, p. 169-182. Gradinaru, E., C. Dinu, and O. Dragastan, 1989, Stratigrafia platformei continental dobrogene a Marii Negre: Raport, University Bucuresti, v. 1, 120 p. Ionescu, G., 1999, Modele faciale ale formatiunilor Paleogene pe selful nord-vestic al Marii Negre: University Bucuresti Thesis, 131 p. Ionescu, Nelu, 1993, Exploration history and hydrocarbon prospects in Romania. Mutihac, V., I.M. Stratulat, and M.R. Fechet, 2004, Geologia Romaniei: Edit. Didactica si Pedag. R.A., Bucuresti, 249 p. Meagu, Th., and O. Dragastan, 1984, Stratigrafia depozitelor Neojurasice si Eocretacice din Dobrogea de Sud.: Studii cerc. geol. geofiz. geogr. Seria Géologie, v. 29, p. 80-87. Salvador, A., 1994, International stratigraphic guide (2nd ed.): IUGS Intern. Comm. on Stratigraphy, GSA, 214 p. Sandulescu, M., 1984, Geotectonica Romaniei: Editura Technica, 334 p.
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