Downloaded from http://sp.lyellcollection.org/ by guest on December 8, 2017 Tectonic Evolution of the Eastern Black Sea and Caucasus: an introduction MARC SOSSON1*, RANDELL STEPHENSON2 & SHOTA ADAMIA3 1Universite´ Coˆte d’Azur, CNRS, Observatoire de la Coˆte d’Azur, IRD, UMR Ge´oazur, 250 rue Albert Einstein, 06560 Valbonne, France 2University of Aberdeen, School of Geosciences, Meston Building, King’s College, Aberdeen AB24 3UE, UK 3Ivane Javakhishvili Tbilisi State University, M. Nodia Institute of Geophysics, Alexsidze Street 1, 0171, Tbilisi, Georgia *Correspondence: [email protected] Abstract: This Special Publication presents the results of 15 different studies in the Black Sea– Caucasus segment of the Alpine–Tethys orogenic realm. The main focus of these studies is the style and timing of key tectonic events occurring primarily during the area’s post-Pangaean evo- lution. The methodologies encompass: geophysics, including active and passive crustal-scale seis- mology and common depth point reflection seismic profiling (both onshore and marine), palaeomagnetism and magnetostratigraphy; field geology, including biostratigraphic recorrelation; radiochronology; igneous rock geochemistry, including analyses of the obducted ophiolites; and low-temperature thermochronology. The geological record of the area is essentially one of sedi- mentary basins formed in an extensional back-arc setting and their subsequent compressional deformation during the closure of at least two branches of the Neotethys Ocean system. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. Among the many goals of the DARIUS programme, continental lithosphere of the Eurasian plate. The based at the University of Paris VI (Universite´ northern part of this pre-Black Sea pre-Caucasus Pierre et Marie Curie) and chaired by Eric Barrier Orogen lithosphere is represented by the so-called (CNRS, Universite´ Pierre et Marie Curie), was the Scythian Plate (or Scythian Platform, although this interpretation of the tectonic history of the sedimen- terminology is neither well defined nor consistent tary basins of the eastern Black Sea–Caucasus and in its usage; Fig. 1), which forms the crystalline surrounding areas. The programme also aimed to basement north of the Crimea–Caucasus compres- interpret the geodynamic processes governing the sional belt (e.g. Saintot et al. 2006a). When and formation and deformation of these basins and the how the continental lithosphere of the Scythian development of the related mountain belts. The rai- Plate actually formed, and when it was accreted to son d’eˆtre of DARIUS was to investigate the the European craton to its north, have been poorly 6000 km long continuous orogenic belt running studied, but it is probable that it is at least as old from Crimea–Anatolia in the west to the Tien-Shan as earliest Palaeozoic and, more likely, Precambrian in the east, through the Caucasus, northern Iran and (e.g. Gee & Stephenson 2006). Numerous large- Zagros. This scientific activity was loosely separated scale studies of the European lithosphere using geo- into regionally defined subgroups and this Special physical, thermal and/or geoid data to determine Publication reports some of the results of studies the lithospheric properties – such as the integrated carried out by the DARIUS Caucasus Working strength – infer strong, cold lithosphere below Group in and on the margins of the eastern Black most of the present day Black Sea (e.g. Tesauro Sea, including Crimea and Turkey, and in the Cauca- et al. 2009) and presumably also the areas immedi- sus domain between the Black and Caspian seas ately to its east. An exception is the SE corner, adja- (Fig. 1). cent to the Cenozoic magmatic province found in the Turkish eastern Pontides, which is an issue Regional tectonic setting and issues in the addressed in this volume. eastern Black Sea–Caucasus realm The papers in this Special Publication deal with the evolution of the geology of the eastern The sedimentary basins of interest in the study Black Sea–Caucasus realm primarily during its area are largely formed on top of and within the post-Pangaean tectonic setting. Accordingly, only From:Sosson, M., Stephenson,R.A.&Adamia, S. A. (eds) 2017. Tectonic Evolution of the Eastern Black Sea and Caucasus. Geological Society, London, Special Publications, 428,1–9. First published online June 9, 2017, https://doi.org/10.1144/SP428.16 # 2017 The Author(s). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on December 8, 2017 2 M. SOSSON ET AL. Fig. 1. Tectonic map of the Black Sea–Caucasus domain and surrounding areas, modified from Sosson et al. (2015), showing the field locations of studies reported in this Special Publication: 1, Adamia et al. (2015); 2, Ha¨ssig et al. (2015);3,Danelian et al. (2015), Sahakyan et al. (2016) and Cavazza et al. (2015);4,Avagyan et al. (2016);5,Meijers et al. (2015);6,van der Boon et al. (2015);7,Alania et al. (2015);8,Starostenko et al. (2016); Sydorenko et al. (2016);9,Gobarenko et al. (2015); 10, Nikishin et al. (2015b); 11, Sheremet et al. (2016b); and 12, Hippolyte et al. (2015). minor attention is given to its pre-Early Mesozoic Ocean (and its predecessors), in favour of the later history, which can be broadly correlated with the Mesozoic and Cenozoic. During this time, the tec- closure of what is known as the Palaeotethys tonic setting of the area can be characterized as Downloaded from http://sp.lyellcollection.org/ by guest on December 8, 2017 INTRODUCTION 3 one of general plate convergence as the Neotethys (starting with the oldest) separately within each of Ocean (or the branches of a Neotethys Ocean these two sections. system) was subducted and eventually closed. The The first section deals with the geology recorded geological record documents the formation of sedi- from processes that largely occurred prior to and in mentary basins in an extensional back-arc setting the Cretaceous, which are linked to the closure of through to the eventual compressional deforma- what is referred to here as the northern branch of tion (inversion) of these basins linked to the closure the Neotethys Ocean. This section includes the of the Neotethys Ocean and the processes and de- results of new field mapping in Turkey, Georgia, formation associated with this closure. The inver- Armenia, Azerbaijan and Iran, as well as palaeo- sion of the basins occurred in two main phases: magnetic, biostratigraphic, magnetostratigraphic the first was in the Cretaceous and, in this work, and geochemical analyses. It opens with an over- linked broadly to the closure of what is referred to view of the tectonic history of this domain based as the northern branch of the Neotethys Ocean; on the geology of Georgia, including the Neoproter- and the second was in the Cenozoic, linked broadly ozoic–Palaeozoic crystalline and sedimentary base- to the closure of what is referred to as the southern ment of this area, which can be considered as part of branch of the Neotethys Ocean, which corresponds the contiguous Eurasian plate from the point of view to the eventual suturing of the Arabian plate with of subsequent Alpine–Tethys convergence and col- Eurasia. lision. This is followed by papers dealing with the The main problems to resolve in the eastern Cretaceous emplacement of ophiolitic units during Black Sea and Caucasus regions of the Alpine– the closure of a northern branch of the Neotethys Tethys belt are: (1) the evolution in space and Ocean, suturing or juxtaposing the Taurides–Ana- time of the geodynamic processes (subduction, tolides–South Armenian Microplate (TASAM) to obduction and collisions) responsible for the closure Eurasia. A series of papers then addresses the struc- of the northern and southern branches of the Neote- tural styles and timing of Cenozoic compressional thys Ocean and how these processes are related deformation related to the closure of a southern to the opening and inversion of back-arc basins branch of the Neotethys Ocean (as it is called in in space and time in the realm of interest; (2) the this Special Publication), suturing the Arabian timing and evolution of the extensional and syn- plate to Eurasia–TASAM. compressional sedimentary basins; (3) the continu- The second section consists of papers dealing ity of structures and their evolution in time between with the eastern Black Sea, documenting the mainly the eastern Black Sea, the Greater Caucasus, the Cretaceous extensional tectonic regime in which the Lesser Caucasus and those of the Taurides–Anato- eastern Black Sea formed, as well as the subsequent lides, Pontides belt and NW Iran; and (4) the evolu- Cenozoic compressional tectonic regime in which tion of Paratethys along this belt since the Eocene. the margins and intra-basinal structures of the east- ern Black Sea were (and are continuing to be) struc- turally inverted. This section starts with the results Contents of this Special Publication of new field observations and structural mapping in Crimea, including a revised stratigraphic correla- This Special Publication includes 15 multidisciplin- tion, and the Pontides of northern Turkey. This is ary studies covering topics in structural geology/ followed by the characterization of the subsurface tectonics, passive and active source seismology geology of the eastern Black Sea from seismic and seismic profiling, geochemistry, palaeontology, reflection profiling. It closes with crustal and petrography, sedimentology and stratigraphy, re- upper mantle scale models of the Crimea–eastern porting results obtained during the DARIUS pro- Black Sea margin from controlled source and pas- gramme and related projects in the eastern Black sive seismology, both of which illustrate complex Sea and Caucasus realm. All are aimed at addressing regional crustal geometries consisting of ancestral the general issues highlighted in the preceding sec- structures and those developed during the Creta- tion.