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PSPermian-Jurassic
Tectonic and 
Depositional
Control on Oil Fields in the Central Moesian Platform,
Romania*
By
Aurelia Liliana Stan1 and Adriana Raileanu2
Search and Discovery Article #10046 (2003)
*Adapted for online presentation from poster session presented at the AAPG Convention, Salt Lake City, Utah, May, 2003.
1Geophysicist, Romanian Oil Corporation Petrom-S.A.,Geological Exploration Research and Design Center, Bucharest, Romania ([email protected])
2Sedimentologist, Romanian Oil Corporation Petrom-S.A.,Geological Exploration Research and Design Center, Bucharest, Romania ([email protected])
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The study area is located in the Romanian part of the Central Moesian Platform. The focus of this paper is the recognition of the main Permian-Jurassic fault systems in order to define the major events: tectonics, eustacy, and sedimentation.
The basement faults are responsible for igneous intrusions and extrusions. Permian-Triassic magmatism is associated with a W-E rift area, generating horst-graben structures. Three Jurassic intracratonic basins were recognized: a basin characterized by syndepositional faults and thermal subsidence; a strike-slip basin; and a fossil rift basin, with en echelon external faults.
In the first basin, deposition took place as a result of subsidence and eustacy interaction. In the second basin, a strike-slip fault system developed, with two main faults. The direction of sedimentary influx is identical to the direction of the block movement. The source area for this basin is located on the uplifted horst, which was cannibalized. In the fossil rift basin, the direction of the Jurassic sediment influx is opposed to the block movement. Active bi-directional erosion was generated externally along the normal fault escarpment of the fossil rift shoulder. Internally, an active depocenter shifted to the source area.
Middle Jurassic offshore distal sandbars, littoral bars, and delta-front and fan delta represent the prospects for hydrocarbon fields. The main Upper Jurassic prospect is represented by carbonate shelf margin, with diagenetic control on the pore system.
The hydrocarbon fields are distributed asymmetrically, and they are mostly encountered in the strike-slip basin.
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The study area is located in the Central Moesian Platform between Oltet-Teleorman rivers, the Danube River, and the Peri-Carpathian Fault (Figure 1). The Moesian Platform presents four major sedimentary cycles of sedimentation. Permian and Triassic deposits belong to the second cycle, while the Jurassic deposits to the third one. Locally, erosional hiatus or non-deposition characterizes the sedimentary record. In the NW part of the area, Middle Jurassic siliciclastic facies presents an argillaceous depocenter, which is the seal for the Aalenian and Bajocian sandstone reservoirs. Fractured dolomite deposits (Figure 2) represent Tithonian reservoirs.
The focus of this article is the recognition of the main
Permian-Jurassic fault systems in order to define the connection between
the major events in basin evolution: tectonics, eustacy, and
sedimentation. The Jurassic hydrocarbon fields lie in the northern part
of the study area. The well data were integrated into the seismic lines
highlighting the seismic markers, formation succession, and fault
systems, as well (Figure 3). The analysis of seismic data was achieved
using seismic stratigraphic techniques, the A few representative N-S and W-E trending seismic profiles were selected in order to recognize the main fault systems (Figures 4, 5, 6, 7, 8, 9, 10, and 11). The Permian-Triassic basement faults present N-S and E-W trends. The latter faults are responsible for igneous intrusions and extrusions associated with pyroclastic rocks along Craiova-Optasi Uplift, due to Hercynian and Cimmerian Orogenesis. In the north of the Moesian Platform, the Permian-Triassic magmatism is associated with an extensional rift area, along W-E trending fault system, generating horst-graben structures. The components of the structures are: Mamu-Mitrofani-Spineni northern horst; Fauresti-Iancu Jianu and Optasi-Ciesti-Buzoiesti median horst; Strejesti-Oporelu-Mogosesti and Braniste southern horst, structurally attached to Slatina-Ciuresti highest horst (Figures 12, 13, and 14). Three types of the Jurassic intracratonic basins were recognized (Figure 15). The first (1) is the southern-central basin characterized by normal syndepositional faults and thermal subsidence (Corabia, Studina, Plopii-Slavitesti, Diosti, Boianu, and Malu Mare structures). The second (2) basin is strike-slip type and is located between SS1 and SS2 strike-slip faults (Ciuresti, Priseaca, Oporelu, Strejesti, Fauresti, Mamu, and Draganu structures). The third (3) type is a fossil rift basin, with external en echelon, normal faults (Tatulesti, Braniste, and Tomsanca structures). 1. Jurassic deposition in the southern-central basin took place as a result of subsidence and eustacy interaction. The source areas were the former Triassic uplift (Leu, Corabia, and Harlesti structures), and the main transport trend was SE-NW, and locally NE-SW. 2. In the second basin, the strike-slip fault system presents 2 km displacement. It consists of: - Two main faults, a sinistral one (SS1) and a dextral one (SS2). - Normal splay faults (Fx1, Fx2, Fx3, Fy). - Antithetic and synthetic en echelon faults (Mamu, Fauresti, and Ciuresti areas) - A normal transfer fault and a horsetail splay fault (Varteju and Golumbu areas). The direction of sedimentary influx was the same as the direction of the uplifted block movement. The source area for this basin was located laterally on Iancu Jianu, Fauresti and Mamu uplifted horst, the latter one being cannibalized to the north (escarpment fault with conglomerates facies in Mitrofani-Dumitresti area), and to the south towards the deeper Draganu basin. 3. In the third, fossil rift basin - Spineni, the direction of the Jurassic sedimentary influx was opposed to the block movement, externally generating active bi-directional erosion along the normal fault escarpment of the fossil rift shoulder, and internally an active depocenter shifted to the source area.
Jurassic
Neglecting Jurassic post-tectonic events, the restored geometry of
In Callovian, due to regional extensional conditions, the Moesian
Platform tilted and rotated, and an important discontinuity occurred as
a maximum flooding surface. This surface was used as a marker in
restoring of the Due to the strike-slip deformation in the NW, high subsidence prevailed. The uplift influenced the sedimentation in the NE and SE, where subaerial erosion resulted in intraformational hiatus or re-sedimentation (Figures 19, 20, and 21). In late Bajocian, late Callovian, and late Tithonian, the strike-slip system was more active, while the influence of the syndepositional normal faults decreased.
To illustrate the distribution of the linkage and contemporaneous
The Middle Jurassic
In Late Jurassic, the
The defining of the major events in the basin evolution of Central Moesian Platform (Figure 22) led to the following conclusions : - Based on older and new considerations, Permian-Jurassic successions may be interpreted in terms of intracratonic extensional basins followed by subaerial erosion and strike-slip deformation in the northern part of the study area; in the southern-central areas, conditions for thermal subsidence of the basin prevailed. - The hydrocarbon fields are distributed asymmetrically. The fields producing from the Triassic and the Dogger are located in Malu Mare, Iancu Jianu, Negreni; South Ciuresti, Fauresti, Spineni, Simnic, Ghercesti, Circea, Malu Mare, and Ciuresti fields are producing from the Dogger, only, while North Ciuresti and Barla fields are also producing from the Tithonian. - It is worth noting that most of the Jurassic commercial hydrocarbon accumulations are encountered in the strike-slip basin, and they are controlled by antithetic and synthetic, en echelon faults and other typical secondary features.
Sandulescu, M. 1984, Geotectonics of Romania (in Romanian): Bucharest, Editura Technika Publishing House, 336 p. Tari, Gabor, Oprea Dicea, Joe Faulkerson, Georgi Georgiev, Svetlozar Popov, Mihai Stefanescu, and Gary Weir, 1997, Cimmerian and Alpine stratigraphy and structural evolution of the Moesian Platform (Romania, Bulgaria), in Regional and petroleum geology of the Black Sea and surrounding region: AAPG Memoir 68, p. 63-90. |
Figure 1. Tectonic sketch map of the Moesian Platform (after Sandulescu,
1984; Tari et al., 1997).
Figure 2. Jurassic chrono-litho-bio-stratigraphic diagram, Moesian
Platform.
Figure 3. Location of seismic and 
Figure 4. Uninterpreted time migrated seismic profile across
Draganu-Fauresti area.
Figure 5. Interpreted seismic profile across Draganu-Fauresti area,
showing
Figure 6. Uninterpreted time migrated seismic profile across
Draganu-Manu-Dumitresti area.
Figure 7. Interpreted seismic profile across northern eroded faulted
horst (Mamu Field); different structural types are present: normal fault
block of northern Triassic horst (FN1), strike-slip zone showing
positive flower structure type (transpression).
Figure 8. Uninterpreted time migrated seismic profile across
Tatulesti-Negreni-North Ciuresti area.
Figure 9.
Interpreted seismic profile across the highest southern
Triassic
Figure 10. Uninterpreted time migrated seismic profile across
Oporeolu-Ciuresti-Crampoaia area.
Figure 11. Intrepeted seismic profile across Oporeolu-Ciuresti-Crampoaia
Figure 12. Sketch map showing areal distribution of Permian-Triassic
igneous and pyroclastic rocks.
Figure 13. Tectonogram with Permian-Triassic rift configuration.
Figure 14. Areal distribution of erosion/non-deposition during the
Triassic and of depocenters during late Dogger.
Figure 15. Sketch map of Jurassic elements, Central Moesian Platform.
Figure 16. 
Figure 17. 
Figure 18. Chronostratigraphy and 
Figure 19. Jurassic tectonic and eustatic events on the Moesian
Platform.
Figure 20. Late Bajocian 
Figure 21. Late Tithonian 
Figure 22. Systems tracts related to the oil fields.
