Orogenic Evolution of the External Dinarides in the NE Adriatic Region: a Model Constrained by Tectonostratigraphy of Upper Cretaceous to Paleogene Carbonates
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Earth-Science Reviews 96 (2009) 296–312 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Orogenic evolution of the External Dinarides in the NE Adriatic region: a model constrained by tectonostratigraphy of Upper Cretaceous to Paleogene carbonates Tvrtko Korbar ⁎ Croatian Geological Survey, Department of Geology, Sachsova 2, HR-10001 Zagreb, Croatia article info abstract Article history: Mesozoic to Cenozoic evolution of the central part of the Adriatic plate (External Dinarides and Adriatic Received 14 February 2008 foreland) is still a matter of debate. This is expressed by opposing paleogeographic models: single carbonate Accepted 17 July 2009 platform (Adriatic or Adriatic–Dinaridic) versus two carbonate platforms (Adriatic and Dinaridic) separated Available online 19 August 2009 by the inter-platform Budva–Cukali basin. Estimates of shortening during Adria NE subduction, that resulted in the development of the Dinaric Alps, differ substantially. The single-platform model involves minor Keywords: shortening achieved by folding and faulting along steep reverse faults. The two-platform model involves Adriatic Region fi Adriatic–Dinaridic carbonate platform(s) signi cant shortening achieved mainly by thrust stacking, which resulted in almost complete underthrusting Alpine orogenesis of the intervening basinal deposits. External Dinarides Analysis of Upper Cretaceous to Paleogene stratigraphical data from both outcrops and boreholes allows Mesozoic regional correlation and the interpretation of major lithostratigraphic units.Asaresult,afew Cenozoic tectonostratigraphic units are recognized. The tectonostratigraphy is used as a basis for a new model on the late Mesozoic to Cenozoic evolution of the region. Generally, Adriatic and Dinaridic segments acted as major regional crustal entities of Adria. The upper portions of the sedimentary cover were differentially affected by progressive, southwestward verging thin- skinned deformations during the Paleocene to Eocene (Miocene?). The Adriatic foreland stayed out of the deformations, and is characterized predominantly by wrench and salt tectonics. The regional tectonic map shows arcuate thrust fronts of the External Dinarides. They could be a consequence of both, differential propagation of early-orogenic thin-skinned deformations over crustal fragments separated by transversal faults, and/or differential (isostatic?) movements of the fragments. The collision zone of the Adriatic and Dinaridic segments is characterized by late-orogenic (Oligocene to Miocene) thick-skinned compressional uplift (exhumation), related gravity gliding, and still active escape tectonics (wrenching). These processes masked primary thin-skinned deformations. A significant amount of shortening within and between the thin-skinned sedimentary covers is proposed. Therefore, the question of the general paleogeography of the region and the original NW extent of the Budva–Cukali basin (NE Adriatic trough) remains open. © 2009 Elsevier B.V. All rights reserved. Contents 1. Introduction .............................................................. 297 2. Geological setting ........................................................... 299 3. Mesozoicpaleogeographyofthenorthern-centralMediterranean...................................... 300 4. Upper Cretaceous to Paleogene stratigraphy of the ADCP domain ..................................... 300 4.1. Stratigraphy of platform carbonates ................................................ 300 4.2. Stratigraphy of basinal carbonates ................................................ 301 5. Tectonostratigraphic units of the ADCP domain ............................................. 301 5.1. The Dinaridic NE unit (DNEu) or Inner Karst ........................................... 301 5.2. The Dinaridic SW unit (DSWu) or High Karst ........................................... 303 5.3. The NE Adriatic trough (NEAT) .................................................. 303 5.4. The Adriatic NE unit (ANEu) or Dalmatian Karst .......................................... 303 5.5. The Adriatic SW unit (ASWu) or Istrian Karst ........................................... 304 6. Geological profile............................................................ 304 ⁎ Tel.: +385 1 6160 709; fax: +385 6144 718. E-mail address: [email protected]. 0012-8252/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.earscirev.2009.07.004 T. Korbar / Earth-Science Reviews 96 (2009) 296–312 297 7. Cenozoic orogenic evolution ...................................................... 305 7.1. Tectonic overview ........................................................ 305 7.2. Orogen geometry ........................................................ 305 7.3. Role of evaporite horizons .................................................... 306 7.4. Foredeep migration and flysch deposition ............................................ 307 7.5. Upper Eocene to Oligocene (Miocene?) “molasse” ......................................... 307 7.6. Shortening rate ......................................................... 308 7.7. Late Neogene geodynamics ................................................... 308 8. Conclusive remarks .......................................................... 308 Acknowledgements ............................................................. 310 References ................................................................. 310 1. Introduction In the middle of the 70's of the 20th century, teams from the Institute of Geology in Zagreb (today Croatian Geological Survey), As pointed out by Cassinis (2006, and references herein), along with colleagues from Slovenia, Bosnia and Herzegovina, and lithospheric-scale transition between “… the Adria plate and the Montenegro, produced a comprehensive geological mapping of the Dinaric domain…” remains up to now the most problematic geo- region which resulted in 40 sheets of the official Basic Geological Map tectonic issue in the NE Adriatic region (Fig. 1). One of the crucial facts of the former Yugoslavia, scale 1:100,000 (available on www.hgi-cgs. is the absence of geological evidence of any oceanic crust between hr). The region has also been comprehensively investigated by French these two domains. Thus, if two lithospheric units exist, they would be geologists (so-called Aubouin's team) during the same period. separated by a transform plate boundary. However, both would One of the earlier paleogeographic models of the region is based on belong to a unique unit — the Adriatic microplate or Adria (Channell a clear tripartite paleogeographic subdivision in its southeastern part et al., 1979), even if the plate may have been fragmented during the (D'Argenio et al., 1971). The model comprises two carbonate late Cenozoic (Oldow et al., 2002; Piromallo and Morelli, 2003; platforms — Adriatic and Dinaric, and the intervening Budva–Cukali Marton, 2006). Basin (BCB). The idea was followed by Chorowicz (1975a), who The External Dinarides are fold-and-thrust belt, part of the Alpine suggested NW prolongation and termination of the BCB (NW end of orogenic system, characterized by generally SW verging structures, the NEAT on Fig. 2). and can be considered as the detached, backthrust and highly The second early model considers the region as a more or less deformed upper crust of the Adria during subduction to the NE. The unique carbonate shelf of the External Dinarides (Grandić, 1974) belt, along with the related part of the Adriatic foreland (Fig. 1)is characterized by maximal subsidence in the central zone and geographically situated within the Dinaric Karst region. Differing intrashelf troughs that developed during the Late Cretaceous. opinions about the geologic evolution of the system in the NE Adriatic region highlight its complexity (Aubouin et al., 1970; D'Argenio et al., 1971; Chorowicz, 1975a,b; Herak, 1987; Buser, 1989; Cati et al., 1989a; Jelaska et al., 1994; Lawrence et al., 1995; Grandić et al., 1997; Pamić et al., 1998; Grandić et al., 1999, 2001; Picha, 2002; Tari, 2002; Marton et al., 2003; Vlahović et al., 2005). Fig. 2. Conservative paleogeographic map of the Adriatic region for the Late Cretaceous time (some present-day geographic lineaments are indicated, see Fig. 1; redrawn and simplified after Dercourt et al., 2000; Bosellini, 2002). The Adriatic–Dinaridic carbonate platform (s. lato) is split into the Dinaridic and Adriatic platforms (s. str.) by the supposed continuous NE Adriatic trough (NEAT, thick dashed lines). Hypothetical Fig. 1. Tectonic map of the Adriatic region showing the deformation fronts of the major transform faults (thin dotted lines). Basins on the continental and oceanic crust — light Alpine orogenic belts. grey. Carbonate platforms and shelfs — dark grey. BCB — Budva–Cukali Basin. 298 T. Korbar / Earth-Science Reviews 96 (2009) 296–312 Other interpretations can be generally referred to one of the above single-platform model involves minor shortening achieved predom- mentioned end-member models as follows: inantly by folding and faulting along steep reverse faults. The two- platform model involves significant shortening achieved predomi- – single carbonate platform: External Dinarides Carbonate Platform nantly by thrust stacking, which resulted from more or less complete (Grandić et al., 1999), Adriatic–Dinaridic Carbonate Platform — underthrusting of the inter-platform basinal unit. ADCP (Gušić and Jelaska, 1993; Pamić et al., 1998), Adriatic