695 GeologischeRundschau81/3 [ 695-716/ Stuttgart1992 Gravity-flow dominated sedimentation on the Buda paleoslope (Hungary): Record of Late Eocene continental escape of the Bakony unit By L. FODOR, A. MAGYARI, M. KAZMI~R and A. FOGARASI, Budapest*) With 15 figures Zusammenfassung demonstriert den Deformationsstil innerhalb des ab- wandernden Blockes eng an der stidlichen Grenz- Die obereoz~ine Folge der Budaer Berge wird aus zone. Die tektonisch kontrollierte Sedimentation un- fluviatilen und Abtragungskonglomeraten, Sandstei- terstreicht, dass die Ausquetschungstektonik bis in hen, bioklastischen Flachwasserkalken, Mergelge- das sprite Eoz~in hinein aktiv war. steinen sowie pelagischen Globigerina-Mergelnauf- gebaut. Die Abfolge weist eine rapide, im gesamten Abstract Gebiet vonstatten gehende Absenkung von kontinen- taler Entwicklung bis zu bathyalen Tiefen nach. The Upper Eocene sequence of the Buda Hills con- Die Sedimentation tritt auf Pal~ioabhfingen an den sists of fluvial and shallow marine conglomerates, Flanken von synsediment~iren Antiklinalen auf Ge- sandstones, bioclastic shallow-water limestone, marl- steinen des Basements auf. Die Hebung der An- stone and pelagic Globigerina marl. The succession tiklinalen verursachte eine progressive Kippung der illustrates rapid, overall subsidence of the area, from Sedimente eine schichtparallele Dehnung, durch terrestrial environments to bathyal depths. Sedimenta- Boudinage und Verwerfungen und induzierte eine tion occurred on slopes situated on the flanks of Umlagerung dutch Massenstr6me. Die Antiklinalen synsedimentary basement antiforms. Vertical growth sind staffelf6rmig in der rechtsdrehenden Scherzone of antiforms caused progressive tilting of beds, layer- von Buda6rs und in der verschuppten Brandungs- parallel extension by boudinage and faulting, and in- s~iule yon Buda angeordnet, die die Verwerfung be- duced redeposition by mass flow. Antiforms are local- gleiten. Die Zone von Buda korrespondiert zu einem ised in the dextral Buda/3rs shear zone and in the Buda SE-vergenten komplexen Abhang. Es liegt eine imbricate stack, which accommodated the dextral dis- Unterlagerung von antithetischen Blindverwer- placement. The latter is underlain by blind reverse faults fungen vor, die vermutlich in geringer Tiefe in eine probably merging into a detachment tault at shallow Abscherungsverwerfung/dbergeht. Alle Strukturen depths. These structures were formed by WNW-ESE wurden durch WNW-ESE gerichtete Kompressionen oriented compression and NNE-SSW directed tension. und NNE-SSW orientierte Dehnungen geformt. The morphological expression of the imbricate stack is Die Einheit des Bakony war w~ihrend der Ab- the SE-facing Buda slope. trennung von den Alpen umgrenzt dutch eine n6rdli- The Bakony unit, while "escaping" from the Alps, che sinistrale und eine siidliche dextrale Scherzone. was bordered by a northern sinistral and a southern dex- Die synsediment~ire Tektonik in den Budaer Bergen tral shear zone. Synsedimentary tectonics in the Buda *) Authors' addresses: L. FODOR, A. MAGYARI,A. FOGARASI,Department of Geology,E/Stv/Ss University, Mfizeum krt. 4/A, H-1088 Budapest, Hungary,and M. KAZMt~R,Department of Palaeontology,E{3tv/Ss University, Ludovika tdr 2, H-1083 Budapest, Hungary Present address: L. FODOR,Department of Applied and EngineeringGeology, E6tv6s University,Mfizeum krt. 4/A, H- 1088 Budapest, Hungary. Manuscript received: 19.1.91; accepted: 13.7. 1992 696 L. FODOR, A. MAGYARI, M. Kg,ZMI~R, A. FOGARASI Hills demonstrates the style of deformation inside the qbyH~IaMeHTa. HO/IH~ITHe aHTHKJIHHaaefl BbI3BaJIO escaping block, close to the southern border zone. nporpeccrmHoe HaKJIOHeHHe C0IOeB, paCT~t>KeHHe, Tectonically controlled sedimentation suggests that es- OWMe,-IaeMoe 6y)IHHa>KeM H pa3:IOMaMI4, H nepe- cape tectonics was active as early as Late Eocene time. OT0m:,Ir ~3emecTBa c HOTOKaMH MaccbI. AHTg- Ir HpOCTHpaloTC~ B HpaBocTOpOHHefI ByaaepmcKoh 3OHe CaBHrOB ByalaficI~ofI ~Iemyfe4a- R6sum6 TOfI 06JmCTH, B KOTOpO~I HaKOnHJIC~t MeOlaH:,K. ByjIa/acKa~ 30Ha COOTBeTCTByeT CJIO>KHOMy La s6quence sddimentaire d'fige 6oc~ne sup6rieur cKJIOHy, o6pameHHOMy Ha loPO-BOCTOK. OHa rIO~I- des collines de Buda est constitude de conglomdrats CTmiaeTc~ CKpMTbIMH B36pocaMH, BepOgTHO HpH- fluviatiles et matins, de gr&, de calcaires na~HHbIMI4 K 3OHe cpbIBa Ha ue6oJIbnlOfI rJIy6HHe. bioclastiques et de mames n6ritiques ou pdlagiques h Bce aTH cTpyKTyp~,I o6paaoBaamcl, npH C*aTHH U Globigerina. Cette succession correspond h une npocwHpanm~ WNW-OSO u paCT~:~eHHH B aa- subsidence rapide, r6gionale, passant d'un environ- npaBJIemm NNO-SSW. nement terrestre fi un environnement bathial. La BaKOHBCKI~Ie cTpyKTypHble aJIeMeHTbI, BbI)KH- s6dimentation s'est effectu6e sur les pentes situ6es MaeMble H3 AOIBII, @blJIH orpaHHqeHbI JIeBBIM sur les fiancs des anticlinaux synsddimentaires. Le C~BHFOM Ha ceBepe vt IlpaBHM Ha lore. CHHCellI/I- souRvement de ces anticlinaux a provoqu6 le MeHTaKHOHHa~I TaKTOHHKa B ByJIaflcK~x ropax basculement progressif des couches, une extension JIeMOHCTpHpyeT CT~IaI~ ~IeqbopMalmH BWTpU paralRle h la stratification avec boudinage et fractu- BbDKFIMaeMoFO 6aIOKa, pacIloJIO)KeHHOFO B~JIH3H res, ainsi que le remaniement de sddiments par divers ~O>KHOfI rpaHgKbI. OcatlKOHaKOII.neHHe, KOHTpOOIH- 6coulements gravitaires. Les anticlinaux se situent pyeMoe TeKTOHHKOfI, CBHJIeTeJIbCTByeTO TOM, qTO dans la zone d6crochante de Buda6rs dont le ddplace- BbI:,KI/IMaHHe gMealo MeCTO yme B IIO3~IHeM aoKeHe. ment dextre a 6t6 accompagn6 par un syst~me d'dcailles: la zone de Buda. Cette zone correspond une pente complexe sddimentaire h vergence SE. Elle Introduction est caract6ris6e par des failles inverses aveugles qui se raccordent probablement h faible profondeur h une Continental escape is a common process in orogenic surface de ddcollement. Toutes ces structures ont dt6 belts (TAPPONNIER, 1977; BURKE & SENGOR, 1986). engendrdes par une compression WNW-ESE et une Brittle deformation is often concentrated at the bound- extension NNE-SSW. ary of the escaping wedge, but faults formed in the same Durant l'dchappement continental, l'unit6 de kinematic system cross-cut the internal part, too. Bakony 6tait bord6e au nord par une zone cisaillante Tectonically controlled sedimentation, if connected to s6nestre et au sud par une zone cisaillante dextre. La the internal or border fault zones, may offer excellent tectonique synsddimentaire dans les collines de Buda temporal constraints to the motion history of the faults montre le style de la ddformation h l'intdrieur du bloc (e.g. HEMPTON & DUNNE, 1984; TAPPONNIER et al., s6par6, pros de sa limite m6ridionale. La sddi- 1982; SENGOR et al., 1985). mentation, rdgie par la tectonique, indique que The Bakony Unit, the earliest recognized of the es- l'6chappement continental avait ddjh commenc6 h caping wedges of the Alpine-Pannonian region l'Eoc~ne supdrieur. (KOv~,cS, 1983) was forced out between the Eastern and Southern Alps during Tertiary time. Detailed struc- tural analysis and kinematic modelling describes the KpaTKOe coRep~Kaune Neogene escape history and related fault pattern (RATSCHBACHER et al., 1989; CSONTOS et al., 1991). BepxHeaolaeHoBas To:itaa By~IaflcKHx top npeJI- The idea of Paleogene motion is based mainly on dis- cTaBaleHa a6pa3HOHHbIMg KOHrJIoMepaTaMH, placed Permian-Oligocene facies boundaries and kin- HecqaHHKaMH, 6HOO~YlOMOqHBIMH FI3BeCTI-I,qKaMH~ ematic analysis (Fig. 1; KAZMt~R, 1984; KAZMI~R & MepreJIgMH H neJIaFHqeCKHMH FJIO6eFepI/IHOBblMH KOVr 1985; and BALLA, 1988a, FODOR et al., MepYeJI~lMH. ~Ta HOC01eTIOBaTe0IBHOCTb ocaJIKOB 1990a). In fact, kinematic models demonstrate that the OTo6pamaeT 6blCTpOe Bceo6tlIee npocelIaHHe Bakony Unit is only a part of the escaping North pafioHa OT BepxHero ypOBH~ KOHTFIHeHTa JIO 6a- Pannonian block (Fig. lb; BALLA, 1988a, b). It is gen- THaJIbHblX rJIy6ldH. HaKoIIaeHHe oCa~KOB npogcxo- erally accepted that during the Oligocene, dextral dis- ~HoIO Ha JIpeBHHX CKOIOHaX, paclIO0~O>KeHHblX Ha placement was already going on along the southern qbJIaHFaX CHHCe/IHMeHTaLIHOHHblX aHTHKalHHaJIeI4 border fault zone (Periadriatic and Mid-Hungarian Gravity-flow dominated sedimentation on the Buda paleoslope (Hungary) 697 O lOOkm I I / ",~ PAL"""\") O lOOkm t Fig. 1. Continental escape of the Bakony unit (a) Triassic palaeogeography: the facies boundary (dashed line) between Main Dolomite (oblique haching) and Dachstein Limestone (vertical haching) is displaced to the east (after KAZMI~R&; KOVA,CS, 1985). (b) Kinematic analysis: the Bakony unit is part of the escaping North-Pannonian Block (NPB) which is bordered by sinistral and dextral strike-slip zones (vertical and oblique haching, respectively; after BALLA, 1988b), Tectonic units are shown in actual positions. PAL: Periadriatic Lineament; PK: Pieniny Klippen Belt; M-H Z: Mid-Hungarian Zone. Solid triangles indicate the external boundary of the Carpathian fold belt. zone, BALLA, 1988a; RATSCHBACHER et al., 1989). eroded, partly covered by younger sediments and were The possibility of Eocene movement is generally ne- deformed by subsequent tectonics. glected, or can only be suggested without relevant tec- In the present study we discuss the sedimentology tonic and/or sedimentological data. and tectonics of the eastern part of the Transdanubian After an extended period of erosion and bauxite Central Range (referred to as Bakony, after the largest deposition during the Early Paleogene, marine sedimen- topographic unit), the Buda Hills. Here