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Tertiary Tectonic and Sedimentological Evolution of the South Carpathians Foredeep: Tectonic Vs Eustatic Control

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Tertiary Tectonic and Sedimentological Evolution of the South Carpathians Foredeep: Tectonic Vs Eustatic Control Marine and Petroleum Geology 16 (1999) 719±740 Tertiary tectonic and sedimentological evolution of the South Carpathians foredeep: tectonic vs eustatic control T. RabaÆ gia a,*,1, L. Mat° enco b aProspect° iuni S.A., Hydrocarbon Division, 20 Coralilor str., Bucharest, 1, Romania bBucharest University, Faculty of Geology and Geophysics, 6 Traian Vuia str., sect. 1, 70139, Bucharest, Romania Received 25 October 1998; received in revised form 2 August 1999; accepted 6 August 1999 Abstract A detailed seismic sequence stratigraphy study based on a dense network of seismic pro®les is integrated with structural observations from interpreted geological sections to derive a tectonic and sedimentological model for the Miocene±Pliocene evolution of the South Carpathians foredeep (Getic Depression). Following Paleogene and older orogenic phases, the ®rst tectonic event which aected the studied area was characterised by Early Miocene large scale extension to transtension which is responsible for the opening of the Getic Depression as a dextral pull-apart basin. Further Middle Miocene contraction caused WNW±ESE oriented thrusts and associated piggy-back basins. The last tectonic episode recognised in the studied area relates to general transpressive deformations during the Late Miocene±Early Pliocene interval, a ®rst NW±SE oriented dextral episode is followed by second N±S sinistral deformations. The detailed sequence stratigraphy study allows for the de®nition of the dominant tectonic control of the sedimentary sequences in foreland basins. A eustatic control may be associated, but has a clear subordinated character. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: South Carpathians; Sequence stratigraphy; Tectonics; Eustasy 1. Introduction sional deformations, the entire system being buried by 1±2 km of ¯at-lying Pliocene sediments, slightly The South Carpathians foredeep, named the Getic deformed in the last, late Pliocene tectonic event Depression or the South Subcarpathians (SaÆ ndulescu, (Dicea, 1996; Mat° enco, Bertotti, Dinu & Cloetingh, 1984), represents a sedimentary basin developed at the 1997; RaÆ baÆ gia & FuÈ lop, 1994). contact between the South Carpathians nappe pile and Previous studies of the eustatic and tectonic control the Moesian Platform (SaÆ ndulescu, 1984) (Fig. 1). The on the development of the sedimentary bodies in active 50±100 km wide basin comprises more than 6 km of tectonic basins (Crumeyrolle, Rubino & Clauzon, Uppermost Cretaceous to Tertiary sediments deposited 1991; Leckie & Smith, 1992; Prosser, 1993; Robertson, in a polyphase tectonic regime. Following a general Eaton, Follows & McCallum, 1991) have demon- tectonic scheme, the evolution of the Getic Depression strated the importance of the sequence analysis in was characterised by Paleogene to Lower Early revealing the detailed architecture of the sedimentary Miocene extension/transtension followed by large scale basins. Several uncertainties arise in de®ning the in¯u- Middle to late Miocene contractional to transpres- ence of tectonic in respect to eustatic control in active tectonic areas, especially in foreland basin settings (Robertson et al., 1991; Vail et al., 1977). * Corresponding author. Tel.: +40-1-3110922; fax: +40-1- Previous studies of the South Carpathians generally 3111168. focused on the northern nappe pile (Berza & E-mail address: [email protected] (T. RabaÆ gia) 1 Present address: Schlumberger Logelco, Romanian Branch, Hotel DraÆ gaÆ nescu, 1988; Codarcea, 1940; Mat° enco et al., Diplomat 106, 13-17 Sevastopol str., sect. 1, Bucharest, Romania. 1997; Murgoci, 1905; Ratschbacher et al., 1993). 0264-8172/99/$20.00 # 1999 Elsevier Science Ltd. All rights reserved. PII: S0264-8172(99)00045-8 720 T. RabaÆgia, L. Mat ° enco / Marine and Petroleum Geology 16 (1999) 719±740 Fig. 1. Geological structural map of the external part of the South Carpathians. Compiled from geological maps 1:200.000, 1:50.000, published by the Geological Institute of Romania and results of this paper structural work. Thick lines, 1±14, indicate the position of pro®les in Figs. 5±8. SI to SV indicates the position of Figs. 9±13, respectively. Inset indicate the position of the structural map detailed in Fig. 4. T. RabaÆgia, L. Mat° enco / Marine and Petroleum Geology 16 (1999) 719±740 721 Fig. 2. General time correlation table and stratigraphyic column for the Tertiary deposits and sketch of the main tectonic events (modi®ed after Mattenco & Schmid, 1999). Correlation with Central and Eastern Parathethys for the Oligocene and Miocene and Pliocene ages after RoÈ gl (1996). Hatched areas represent the ages used in this study. Note especially the dierences at the Miocene/Pliocene boundary between the ages used in the present study and the standard Tethys scale. Thick light grey and dark grey arrows represent an attempt to de®ne a foreland-breaking sequence for the extensional deformation and for the contractional deformation respectively. SSQ represent the seismic sequences de®ned in the present study. General deformation patterns represent results of this paper and correlation with Ratschbacher et al. (1993), Mat° enco (1997), Schmid et al. (1998) and Mat° enco and Schmid (1999). However, few studies have taken into account the is still to be pursued (e.g., Mat° enco, 1997; RaÆ baÆ gia & detailed analysis of the foredeep sedimentary architec- FuÈ lop, 1994) (Fig. 1). ture as a whole (Dicea, 1996; Motas° , 1983), while the The Getic Depression is analysed in this paper detailed kinematic and tectonic evolution of the basin through a dense network of roughly 3500 km of seis- 722 T. RabaÆgia, L. Mat° enco / Marine and Petroleum Geology 16 (1999) 719±740 as a result of the Late Cretaceous ``Laramian'' defor- mations, namely the Dacidic molasse (SaÆ ndulescu, 1984). A thick coarse-grained clastic succession was deposited on the inner basement formed by the Getic, Severin and the Danubian nappes, and on the Mesozoic carbonates and Paleozoic series of the Moesian platform (Dicea, 1996). An Uppermost Cretaceous (Campanian±Maastrictian) succession can be observed at surface in the east, as well as at depth, westward, close to the northern basin border. Thick (1000±1500 m) coarse-grained clastic deposits are transgressively covering the northern border in the eastern region (Szasz, 1975). The Paleogene is charac- terised by a thick succession (roughly 5000 m in the Fig. 3. 1D basement subsidence evolution based on backstripping northern parts), transgressively covering the techniques (Steckler & Watts, 1978; Watts, Karner & Steckler, 1982). Cretaceous deposits in the NE areas (Jipa, 1980, 1982, 1=Ticleni, 2=Bibesti, 3=Bulbuceni, 4=Bustuchini, 5=Alunu 1984), onlapping southward the top-Cretaceous uncon- representative wells in various oil®elds (for location see Fig. 4). Note that the curves represent the basement subsidence, i.e. no isostatic formity of the Moesian platform (Dicea, 1996) and compensation was performed to derive tectonic subsidence curves, recording up to 2500 m basement subsidence in the due to the ¯exural behaviour of the foreland (Moesian) platform in western parts of the Getic Depression (Fig. 3). the front and below the foredeep (Mat° enco, 1997). Note the signi®- The Miocene sedimentary cycle (Fig. 2) is mainly cant Eocene subsidence in the Ticleni structure, the Early composed by clastic deposits, the basal coarse sedi- Burdigalian subsidence related to the onset of the extension and the large Sarmatian subsidence in the frontal part of the Pericarpathian ments being gradually replaced upward by ®ner sedi- thrust (Bibesti, Bulbuceni). ments. A regional unconformity, the ``Paleogene morphology'' (Paraschiv, 1975), marks the beginning of this cycle. The Lower Miocene is characterised by mic lines, distributed both along the E±W strike of the major subsidence (Fig. 3), accommodating up to 2000 basin and on the N±S cross sections. The average dis- thick conglomerates (Dicea, 1996), followed by tance between the lines is about 5 km, their calibration roughly 500 m of ®ner marine deposits (Fig. 2). Upper being made with 65 correlation wells. The high data Burdigalian sediments are deposited above a regional density has allowed the de®nition of a detailed local unconformity, observed both on seismic lines and on seismic/sequence stratigraphy, correlation of the outcrops, marking the transition to an evaporitic or sequences being possible directly between the lines. lacustrine episode. Further Badenian deposits are Further conclusions enabled a detailed Miocene tec- characterised by tus, marine marls and salt deposits. tonic and sedimentary model, focused mainly on the The top of the Miocene sedimentary cycle is de®ned sedimentary response of the tectonic deformations by the Lower to Middle Sarmatian (Upper Miocene in within the South Carpathians foredeep. These ®ndings Paratethys time scale) siliciclastic deposits, which de- are important for the quantitative assessment of the ®ne the most important syntectonic sediments. role of the structural and eustatic control, providing The third sedimentary cycle (Upper Sarmatian± further constraints on the mode of tectonic and sedi- Pliocene ) (Fig. 2) is mainly characterised by up to mentary evolution. The latter has major implications 2000 m clastic deposits covering the deformed part of for the processes controlling the formation and archi- the foredeep. The various basins separated by the tecture of sedimentary basins along the external Miocene tectonic activity were ®lled during the
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