The Medobory Hills (Ukraine): Middle Miocene Reef Systems in the Paratethys, Their Biological Diversity and Lithofacies
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BIULETYN PAŃSTWOWEGO INSTYTUTU GEOLOGICZNEGO 449: 147–174, 2012 R. THE MEDOBORY HILLS (UKRAINE): MIDDLE MIOCENE REEF SYSTEMS IN THE PARATETHYS, THEIR BIOLOGICAL DIVERSITY AND LITHOFACIES MIODOBORY – ŚRODKOWOMIOCEŃSKI SYSTEM RAFOWY, JEGO ZRÓŻNICOWANIE BIOLOGICZNE I LITOFACJE MARCIN GÓRKA1, BARBARA STUDENCKA2, MAREK JASIONOWSKI3, URSZULA HARA3, ANNA WYSOCKA1, ANDRIY POBEREZHSKYY4 Abstract. The unique Middle Miocene reef belt formed within the Paratethyan realm constitutes at present the Medobory Hills in western Ukraine and northernmost Moldova. Not only is the size of this structure (almost 300 km long) quite unusual, but also the develop- ment of peculiar facies and their spatial distribution. Two distinct reef generations appear in Medobory (Late Badenian and Early Sarma- tian), both separated by a sharp erosional boundary. Two Upper Badenian calcareous lithofacies dominate – organodetrital and biohermal (with coralline-algae as main framework builders accompanied by a rich invertebrate assemblage). The Lower Sarmatian strata, although megascopically very similar to Upper Badenian ones, differ drastically when studied closely. The main reef components here are serpulids and microbialites, usually with ubiquitous, but taxonomically highly impoverished fauna. Differences in lithofacies and biotic communities between both reef systems unveil open-marine environment during formation of Upper Badenian reefs and a drastic change of conditions at the Badenian/Sarmatian boundary (including emersion and intense weathering). The Early Sarmatian basin was established soon after and highly restricted conditions prevailed in it (e.g. with mesohaline waters and intense evaporation occurring simultaneously); its deposits are the last record of Middle Miocene sedimentation within the Medobory area. Key words: coralline algae-vermetid reefs, serpulid-microbialite reefs, lithofacies, biodiversity, Badenian/Sarmatian boundary, Ukraine, Moldova. Abstrakt. Wzgórza Miodoborów, rozciągające się na przestrzeni niemal 300 km na obszarze zachodniej Ukrainy i północnej Mołdawii, założone są na pasie raf miocenu środkowego, uformowanych w obrębie północno-wschodnich peryferii Paratetydy. Znaczne zróżnicowanie litofacjalne, jak i zmienność zespołów biotycznych wśród utworów rafowych jest rezultatem obecności dwóch generacji raf (późnobadeńskiej i wczesnosarmackiej) oddzielonych wyraźną powierzchnią erozyjną. Wśród wapiennych osadów górnego badenu dominują litofacje organodetrytyczne i biohermalne. Ich głównym składnikiem skałotwórczym są krasnorosty, którym towarzyszą bo- gate taksonomicznie zespoły bezkręgowców, obejmujące m.in. korale, mięczaki, szkarłupnie. Rafy sarmatu dolnego budowane są przez mikrobiality, w obrębie których występują serpule (i podrzednie mszywioły). Silnie zubożona taksonomicznie fauna zamieszkująca rafy sarmackie zdominowana jest przez mięczaki. Różnice bio- i litofacjalne w obrębie wymienionych generacji raf są efektem drastycznej zmi- any warunków sedymentacji, połączonej z emersją i intensywnym wietrzeniem, do której doszło na przełomie badenu i sarmatu w efekcie przebudowy basenu przedkarpackiego. W jej wyniku pełnomorski zbiornik późnobadeński został zastąpiony przez silnie izolowany basen wczesnego sarmatu, zaś powstałe w tym ostatnim osady wieńczą sukcesję utworów miocenu w tej części zapadliska przedkarpackiego. Słowa kluczowe: rafy krasnorostowo-wermetidowe, rafy serpulowo-mikrobialitowe, litofacje, bioróżnorodność, granica baden/sarmat, Ukraina, Mołdawia. 1 Institute of Geology, Faculty of Geology, University of Warsaw, ul. Żwirki i Wigury 93, 02-089 Warsaw, Poland; e-mail: [email protected] 2 Polish Academy of Sciences Museum of the Earth in Warsaw, Al. Na Skarpie 20/26, 00-488 Warsaw, Poland; e-mail: [email protected] 3 Polish Geological Institute – National Research Institute, ul. Rakowiecka 4, 00-975 Warsaw, Poland; e-mail: [email protected] 4 Institute of Geology and Geochemistry of Combustible Minerals NASU, Naukova 3a, 79060 Lviv, Ukraine; e-mail: [email protected] 148 Marcin Górka et al. The Medobory Hills (Ukraine): Middle Miocene reef systems in the Paratethys, their biological diversity and lithofacies 149 INTRODUCTION Mediterranean Paratethyan regional stages Epoch stages The Medobory reefs are unique in the Paratethys Sea. deep Basin constituting since the Kiscellian the northern me [Ma] Pannonian Carpathian Foredeep Euxinian-Caspian Ti Basin System Basin Basin System Two generations of the Middle Miocene reefs originating in part of the Central Paratethys became a marginal basin of Pontian different environments are distributed widely in the north- the Eastern Paratethys (Fig. 2), showing stronger influ- 6 Messinian 6.04 (1.92) Meotian eastern and eastern borders of the Carpathian Foredeep Ba- ence of its water masses (cf. Studencka, 1999; Studencka, 7 7.25 sin in western Ukraine, Moldova and north-east Romania Jasionowski, 2011). At the same time a significant faunal 7.40 (Fig. 1). These reefs provide an excellent opportunity to reorganization also occurred, as inferred from drastically 8 TE E Pannonian LA Khersonian show how reef-building organisms and reef-dwellers re- reduced diversity of faunal assemblages and absence of 9 Tortonian flected the temporary closure of seaways between the Para- marine stenohaline taxa. The separation of the Paratethys is (4.36) s.l. tethys and the Mediterranean around the Badenian/Sarma- indicated also by the vast development of endemic species 10 10.00 tian boundary. (Paramonova, 1994; Popov et al., 2005; Harzhauser, Piller, 11 Bessarabian Coralline algae-vermetid reefs originated in normal ma- 2007; Roshka, 2008; Nevesskaja et al., 2009; Studencka, 11.42 Sarmatian 11.61 rine environments and give evidence for the last marine inva- Jasionowski, 2011). 12 12.30 Serravallian Sarmatian s.s. sion into western Ukraine during the Late Badenian (Kováč The process, which led to the separation of the Paratethys Volhynian 13 LE (2.21) et al., 2007; Studencka, Jasionowski, 2011). Originally full from the Mediterranean and formation of the peripheral Gali- 13.32 13.32 Kosovian Konkian of caverns, provided shelter for numerous reef-dwellers cian Bay, resulted in the development of extremely stressed 13.82 ~13.64 Karaganian 14 Wielician M I D D M I O C E N ~14.20 represented mainly by typical epibenthic forms, byssally at- environments related to mesohaline salinity, elevated alka- Langhian Chokrakian tached, and those cementing to the substrate. linity and eutrophic conditions. At that moment, the develop- 15 (2.15) Badenian Moravian The connection between the Mediterranean and the Cen- ment of serpulid-microbialite reefs started, characterised by Tarkhanian 16 15.97 Y 16.30 tral Paratethys was interrupted in the latest Badenian. Prob- distinct ecological, biological and sedimentological aspects Burdigalian ably only a narrow strait existed at that time, linking the (Jasionowski et al., 2003; Jasionowski, 2006). 17 (4.46) Karpatian Kozakhurian EARL Paratethys with the Mediterranean, located in the present- The main objective of this paper is to present the litho- day Bosphorus region (Popov et al., 2004). The Badenian/ facies of the Upper Badenian coralline algae-vermetid reefs Fig. 2. Correlation chart of the Miocene regional stages of the Central and Eastern Paratethys and Mediterranean provinces Sarmatian boundary witnessed fundamental reorganization and Lower Sarmatian serpulid-microbialite reefs as well as (after Studencka, Jasionowski, 2011) of the Paratethys palaeogeography. The Carpathian Fore- their biological diversity. PREVIOUS STUDY OF MEDOBORY R LUBLIN EAS T Pidkamin Medobory reefs The pioneering study of the excellently exposed Medo- OZTOCZE A (Badenian and Sarmatian) UPLAND bory reefs was carried out at the end of the 19th century. TIAN Dashava Fm. present-day extent toutras (Sarmatian) Volhyn Beds A (clays, sands, of Miocene deposits Hai Roztotski The western part (west of the Zbruch River) was studied in (sands, clays, key exposures bentonites) reefal and oolitic limestones, Ditkivtsi detail by Hilber (1882) and Teisseyre (1884, 1895, 1900) as Lower sandstones, conglomerates) HI Zbarazh VOLHYNIAN E U R O PEAN SARM LL Maksymivka B part of the geological mapping of Galicia (from 1873 to 1914 Rzeszów CARP S Haluschyntsi being an autonomous province of the Austrian part of the Buhliv Beds (sands) TERNOPIL Polupanivka E AT Lviv MEDOBOR HIAN B Novosilka Dual Monarchy). The eastern part was studied by Laskarew Vyshhorodok Beds (sands) (1903, 1914) as part of the geological mapping of the Rus- Kosiv Fm. Ternopil Beds CAR FOREDEEP KhmelnytskyiKhmelnytskyi Vikno PLAT F O R M (clays, (organodetrital, Ternopil sian Empire. siltstones) algal PA Upper YH and Pidhirtsi Beds TH It was the impetus for rigorous geological examination KOSOVIAN reefal (sands, BASIN Ivano- ILLS Lysohirka limestones) IA and interpretation of depositional history of Medobory reefs AN sandstones) SK NO -Frankivsk Sere Zakupne (Siemiradzki, 1909). Synthetic sedimentological and strati- I t VERTHRUS t Demkivtsi Kamianets- graphical studies encompassing data from Medobory reefs Ratyn Beds (limestones) Zbruch e -Podilskyi Tyras Fm. Bila Sakhkamin in Ukraine were undertaken by Korolyuk (1952), Maslov, SmotrychSmotrych (gypsum) Nihyn Verbka Utrobin (1958), Kudrin (1966) and Vialov (1970). Data con- Middl T WIELICIAN MD Humentsi cerning stratigraphy of Medobory reefs in Moldova were Kryvchytsi Beds PL ChernivtsiChernivtsi D E N UA (limestones, sands and presented by Roshka, Khubka (1981), whilst