Stratigraphy of the Pliocene deposits of the Black Sea (Ukraine) according to evidence from ostracods (Arthropoda, Crustacea) Текст научной статьи по специальности «Биологические науки»

ISSN 2617-2909 (print) ISSN 2617-2119 (online)

Journ.Geol. Geograph.

Geology, 28(2), 250-261.

doi: 10.15421/111926

Dykan N.I. Journ. Geol. Geograph. Geoecology, 28(2), 250-261.

Stratigraphy of the Pliocene deposits of the Black Sea (Ukraine) according to evidence from ostracods (Arthropoda, Crustacea)

N.I. Dykan

Institute of Geological Sciences of the National Academy of Sciences of Ukraine, Kyiv, Ukraine, e-mail: natalidykan@gmail.com

Received: 18.02.2019 Abstract. This article presents a detailed analysis of the taxonomic composition of the

Received in revised form: 05.03.2019 Pliocene (Kimmerian, Kujalnikian) and Eopleistocene (Gurian) ostracods in the northern Accepted: 29°4.2019 part of the Black Sea. It presents the patterns of the stratigraphic position of the fossil

ostracods in the Miocene - Quaternary and their geographic distribution in Western and Eastern Europe (the Pannonian Basin, the Dacian Basin, the Euxinian basin of the Paratethys) and the Mediterranean region.We determined the characteristic species for the Kimmerian, Kujalnikian and Gurian in the northern part of the Black Sea. We established a change in the taxonomic composition of ostracods at the Pliocene (Kujalnikian)/Eopleistocene (Gurian) boundary, namely the disappearance of a large number of Pliocene species and the appearance of new species. Ten species disappeared in the Kujalnikian: Cyprideis pontica, Euxinocythere (M.) crebra, Amnicythere mironovi, Camptocypria lobata, Loxoconcha subcrassula, Loxoconcha verticalitercostata, Xestoleberis (X.) cellulocus, Xestoleberis (P.) communis, Candona (C.) expressa, Ilyocypris caspiensis; one species Amnicythere postbissinuata appeared in the Gurian. The brackish water species Cyprideis pontica is the Kujalnikian index species. The stratigraphic position of Cyprideis pontica in the Mediterranean Basin, Pannonian Basin, Dacian Basin, Euxinian Basin (Black Sea) in the Miocene-Quaternary is analyzed. The time of the disappearance of Cyprideis pontica in the Mediterranean, Pannonian and Dacian basins (Messinian, Pontian/Zanclean, Dacian, Kimmerian boundary) and in the Black Sea (Kujalnikian/Gurian boundary) is established. The diagnostic morphological features of the shell Cyprideis pontica (morphology of the surface pore canals) are established and described, which allows us to place this species in the Neogene deposits. Surface pore canals are different shape, sieve-typed, deepened in relation to the surface of the valve. Sieve-shaped lamella contains 110-270 internal pores. The internal pores have a staggered shape, the diameter of the osculum of the internal pore is 302-994 nm; diameter of the central pore is 977 nm-1.8 ^m). The evolution of Cyprideis pontica, which was separated from the parent species Cyprideis torosa in the Late Miocene, was reconstructed. In the occupation of a new ecological niche with a reduced oxygen content in deeper water biotopes, in the process of adapting to the conditions of hypoxia and necessity of increasing the volume of water filtration, there was a restructuring of the morphology of the surface pore canals of the shell Cyprideis torosa. This involved an increase in the size of the sieve-shaped lamella, the number of internal pores in the sieve-shaped lamella and the size of the osculum of the inner pore. A new morphotype Cyprideis pontica was thus formed within the existing Parathetys-Mediterranean basins. It had a mosaic, ecologically isolated range that coincided geographically or overlapped with the range of the species Cyprideis torosa (sympatric evolutionary speciation). The range of Cyprideis pontica and the dynamics of its populations in the Euxinian Basin during the Sarmatian-Kujalnikian have been reconstructed.

Keywords: stratigraphic boundary, Pliocene, Quaternary, Ostracoda

Стратиграфiя плюценових B^^aAiB Чорного моря (УкраУна) за остракодами (Arthropoda, Crustacea)

Н.1. Дикань

1нститут ¿eonozinnux наук НАН УкраХни, м. Кшв, Украта, e-mail: natalidykan@mail.ru

Анотащя. Дано детальний аналiз TaKC0H0Mi4H0r0 складу плюценових (юммершських, куяльницьких) i еоплейстоценових (гуршських) остракод у швшчнш частиш Чорного моря. Встановлено закономiрностi стратиграфiчного положення викоп-них остракод у мiоценi-квартерi та географiчного поширення в межах Захщно!' i Сходно! Свропи (Панонський, Дакшський, Свксинський басейни Паратетису) i Середземноморсько!' область Визначено характерш види для юммершського, куяльниць-

eography and Wuntrmfiof ^jBoecology

Journal of Qaology, Geography and

GeoecoCogo

Journal home page: geology-dnu-dp.ua

кого i гуршського регюярусш для швтчно! частини Чорного моря. Встановлено змну TaKC0H0MÍ4H0r0 складу остракод на границi плiоцену (куяльницького регiоярусу)-еоплейстоцену (гурiйського регюярусу), а саме зникнення у куяльницький час значно! частки плiоценових видш, появi у гуршський час нових видш. Видом-шдексом куяльнику у Чорному морi е солонува-товодних вид Cyprideis pontica. Проаналiзовано стратиграфiчне положення Cyprideis pontica у Середземноморскому, Панонсь-кому, Дакшському, Евксiнському (Чорноморському) басейнах у мюцеш-квартер^ Встановлено час зникнення Cyprideis pontica у Середземноморському, Панонському i Дакшському басейнах (границя мессiну, понту -занклта, дакта, кiмерiю), у Чорному морi (границя куяльника-гурия). Встановлено та описано дiагностичну морфологiчну ознаку черепашки Cyprideis pontica (морфолопю поверхневих порових каналiв), яка дозволяе чiтко iдентифiкувати цей вид у неогенових вiдкладах. Поверхневi поровi канали рiзноl форми, ситовидт, заглибленi по вiдношенню до поверхт стулки. Ситовидна пластинка мiстить 110-270 внутршшх пор. Bнутрiшнi пори мають стовбчасту форму, дiаметр вустя внутршньо! пори 302-994 nm; дiаметр центрально! пори 977 nm-1,8 цш). Реконструйовано еволющю Cyprideis pontica, яка ввдшшла вiд материнського виду Cyprideis torosa у тзньому мiоценi. При занята ново! еколопчно! н1ши iз зниженим вмiстом кисню у бiльш глибоководних бiотопах, в процесi адаптаци виду до умов гшоксй та пов'язаною з цим необхiднiстю у збшьшент об'емш фшьтраци води вiдбулась перебудова морфологи поверхневих порових каналiв черепашки Cyprideis torosa (збшьшення розмiру ситовидно! пластинки, кшькосп внутрiшнiх пор у пластинщ та розмiру вустя внутршньо! пори).В межах iснуючих басейтв Паратетис-Середземноморсько! областi сформувався новий морфотип Cyprideis pontica iз моза!чним. екологiчно iзольований ареалом, що географiчно сшвпадав чи перекривався з ареалом виду Cyprideis torosa (симпатричне еволюцшне формоутворення). Реконструйовано аре-али Cyprideis pontica та динамжу його популяцiй в Евксинському басейнi протягом сармату-куяльнику.

Ключовi слова: cтратиграфiчна границя, плiaцен, квартер, остракоди

Introduction. In the Geologic Time Scale (2012) the biostratigraphic divisions of the Pliocene deposits and the Quaternary base (2.588 Ma, between the Gelasian and Piacenzian (Riccardi, 2009) was substantiated by chronostratigraphy, event stratigraphy, magnetostratigraphy, radiometric dating (40Ar/39Ar dating, 14C and 230Th/234U dating, U/Pb dating, 87Sr/86Sr), climate change and Milankovich cycles (sedimentation cycles), and oxygen and carbon isotopes S18O, S13C curves. Palaeontological characteristic of the Gelasian and Piacenzian derive from different faunal groups (mammals, planktonic foraminifera, calcareous nannofossils, diatoms, radiolarians, dinoflagellates). However, formally, the Neogene-Quaternary boundary is uniquely substantiated on the appearance at the beginning of the Gelasian of dinoflagellate cysts of Spiniferites pachyderma and Invertocysta tabulata (middle part of D21, northwestern Europe) and the radiolarian Pterocanium prismatium (RN12b, northwestern Europe), as well as the disappearance at the end of the Piacenzian of the radiolarian Anthocyrtidium jenghisi (zone RN12a; northwestern Europe) and the planktonic foraminiferan Dentoglobigerina altispira (zone PL 5, Pacific Ocean). The Pliocene-Quaternary boundary (2,588 Ma) in the Paratethys region is compared with the boundary of the megacycle Gel without paleontological substantiation. It is located in the upper part of the Pannonian and within the Kimmerian (Fig. 29. Neogene-Quaternary Regional Subdivisions: Hilgen, Lourens, Van Dam, 2012).

In the Quaternary stratigraphic scheme for Ukraine, the Pliocene/Quaternary boundary is placed at the level between the Kujalnikian (Gelasian) and the Gurian (Calabrian) at 1.81 Ma (Stratigraphic Code of Ukraine, 2012). This is based on the appearance in the Gurian of the molluscs Dreissena distanta, D.

polymorpha, Didacna digressa, D. giriana, Modiolus phaseolinus, nannoplankton Pseudoemiliania, Gephyrocapsa oceanica, Emilia hyxleyi, as well as the disappearance of the Kujalnikian form Dreissena theodori. The planktonic Foraminifera Ammonia beccarii, Ammonia tepida, Fissurina porecta, Cananifera parcarae, nanoplankton Discoaster brouweri and D. pentaradiatus (Tabl. 17.) are represented in the stratigraphic scheme of Cenozoic deposits of the Ukrainian sector of the Black Sea: Stratigraphic Code of Ukraine, 2012). The National Stratigraphic Committee of Ukraine adopted the decision on the recognition of the ICS Pliocene/Quaternary boundary at the level of 2.588 Ma (Resolution of the NSCU dated April 18, 2018: Geological Journal, 2018). Accordingly, the Pliocene/ Quaternary boundary is now placed at a lower level in the Kujalnikian horizon, which needs additional palaeontological fauna-floristic substantiation.

The purpose of this article is to detail the microfaunistic characteristics (using ostracods) of the Pliocene (Kimmerian, Kujalnikian) and Eopleistocene (Gurian) marine sediments, and to substantiate the Pliocene/Quaternary boundary in the northern part of the Black Sea.

Neogene ostracods of the Paratethys and Mediterranean regions and the Quaternary ostracods of western and eastern Europe, the Black Sea, Caspian Sea and Mediterranean Sea have been well studied in their systematic, ecological, zoogeographical and palaeogeographical aspects. They are used for detailed relative-age determination and correlation of marine deposits, but fossil ostracods as a biostratigraphic tool have not been used in the international stratigraphic scales of the Neogene-Quaternary (Geologic Time Scale, 2004, 2012) and Ukrainian stratigraphic schemes of the Neogene-Quaternary (Stratigraphic

Code of Ukraine, 2012). This biostratigraphic analysis using ostracods was the first of its kind.

Fossil ostracods are a uniquely informative group of fossil microorganisms. In sediments, ostracods are often the only (and usually numerous) representatives of the fossil fauna. They had a predominantly autochthonous type of burial, often beautifully preserved or at least with a sufficient degree of conservation of the shell to allow species identification. Local and regional biostratigraphic divisions in the Neogene-Quaternary deposits of the Black Sea are distinguished using ostracods (Dykan, 2011; Dykan, 2012; Dykan 2016 a, b, c, d, f). Therefore, the application of fossil ostracods to stratigraphic correlation schemes, as a biostratigraphically important group of fossil microorganisms, is scientifically sound and expedient. Material and methods of research. The Neogene-Quaternary and recent ostracods of the Black Sea were collected over a period of forty years (1978-2017) from outcrops on the northern coast of the Black Sea (from the Danube to the Taman Peninsula), well cores (Odessa region, Kerch Peninsula, Taman Peninsula, the estuaries of the northwest coast of the Black Sea) and stations (the shelf and continental slope of the

morphology) (Dykan, 2006). Electronic-microscopy, taphonomic, statistical, population, geochemical and facial methods, and zoogeographical analyses have been used in the study of fossil ostracods. The determination of the geological ages of the marine deposits was based on biostratigraphic and ecological criteria derived from ostracods. The biostratigraphy is based on the presence of index species; groups of fossil ostracods, which have the upper and lower boundaries, well established first and last appearances of characteristic species; in the presence of periods of optimum of ostracod species (genera); on the ratio of zoogeographical species (Mediterranean, Caspian) and species of different ecological specialization (marine, brackish water, freshwater). Literary sources on the stratigraphic position and geographical distribution of fossil ostracods in the Holarctic belt were also taken into account.

Results and their analysis. In the northern part of the Black Sea, Pliocene deposits are represented by Kimmerian and Kujalnikian horizons. The Kimmerian deposits are distributed on the western shelf from the mouth of the Tiligul estuary, on the Crimean continental slope from isobaths 287 m to 1750 m, to the southern slope of the Kerch-Taman shelf to the

Fig. 1. Map of the research area in the northern part of the Black Sea

northern part of the Black Sea, SRV NASU) (Fig. 1).

The biostratigraphic conclusions were based on the systematic study of fossil ostracods (the identification of species, the principles and criteria for the determination oftaxonomic features, the estimation of the taxonomic weight of the morphological features, the determination of diagnostic features of the different taxonomic ranks, taxonomic diagnoses, unified method of the description of shell

isobaths 150-200 m. They are presented by a layer of sandy clayey silts on the north-western shelf; oolitic iron ores with clay layers in the Crimean continental slope; iron-bearing sandstone on the eastern part of the northwestern shelf and the Kerch shelf. The thickness of the Kimmerian deposits decreases from east to west and is 40-50 m (Semenenko, 1987; Shuraev, 2015). The lectostratotype of the Kimmerian is the section near the village Arshintsevo (Kamish-Burun)

(Stratigraficheskij slovar SSSR. Paleogen. Neogen. Chetvertichnaya sistema, 1982).

The Kimmerian ostracods comprise 19 genera and 38 species. They include some inherited Pontian ostracod genera (Cyprideis, Tyrrhenocy there, Euxinocythere (Mae otocy there), Amnicythere, Loxoconchissa (Loxocaspia), Xestoleberis (Pontoleberis), Advenocypris, Bacunella, Camptocypria, Caspiocypris, Pontoniella) as well as some species. The peculiarity of the Pontian relic species in the Kimmerian deposits is that it is poor in crustaceans, which is also manifested in small shells. Typical species of the beginning of the Kimmerian are Tyrrhenocythere amnicola donetziensis Dub., Loxoconchissa (Loxocaspia) eichwaldi (Liv.), Loxoconchissa (Loxocaspia) immodulata (Step.), Loxoconchissa (Loxoconchissa) bairdyi (G.W. Müll.), Loxoconcha lepida Step., Pseudocytherura pontica Dub., Camptocypria gracilis (Liv.), Caspiocypris merculiensis Vek., Candona (Candona) angulata G.W. Müll., Cypria candonaeformis (Schw.), Ilyocypris caspiensis (Neg.) (Table. 1). In the northwestern part of the Kimmerian Basin, ostracods formed stable associations of the species Bacunella dorsoarcuata, Camptocypria acronasuta, Camptocypria lobata, Cyprideis torosa, Tyrrhenocythere azerbaidjanica (Liv.), and Cryptocyprideis bogatschovi. The Kimmerian species Camptocypria lobata and Bacunella dorsoarcuata had large shells in comparison with the Pontian individuals. This is a clear marker for separating the Pontian and Kimmerian deposits in the northern part of the Black Sea (Dykan, 2016 a).

The Kujalnikian deposits occur in wells on the shelf and in the deep-water zone of the continental slope; their areal distribution coincides with the Kimmerian deposits (Semenenko, 1987). They are presented by sand, silts, sandstones and clay with a total thickness of 40-50 m. The lectostratotype of the

Kujalnikian is the section near the village Kryzhanivka (Odesa region, Ukraine) (Stratigraficheskij slovar SSSR. Paleogen. Neogen. Chetvertichnaya sistema, 1982).

Kujalnikian ostracods comprise 19 genera and 42 species. A characteristic feature of the Kujalnikian ostracods is the transitional Kimmerian-Kujalnikian type fauna, where 62% are Kimmerian relics:

Pseudocytherura pontica, Cyprideis torosa (Jones), Cyprideis pontica Krstic, Tyrrhenocythere amnicola donetziensis Dub., Tyrrhenocythere azerbaidjanica (Liv.&Agal.), Euxinocythere (Maeotocythere) crebra (Schn.), Amnicythere palimpsesta (Liv.), Amnicythere multituberculata (Liv.), Amnicythere mironovi (Schn.), Loxoconchissa (Loxocaspia) eichwaldi (Liv.), Loxoconchissa (Loxocaspia) immodulata (Step.), Loxoconcha lepida (Step.), L. subcrassula Suz., Xestoleberis (Pontoleberis) laevis (Karm.), Camptocypria acronasuta (Liv.), Camptocypria gracilis (Liv.), Caspiocypris labiata (Zal.), Bacunella dorsoarcuata (Zal.), Pontoniella acuminata (Zal.), Cryptocyprideis bogatschovi (Liv.), Advenocypris centropunctata (Suz.), Candona (Candona) expressa, Candona (Candona) angulata (G.W. Müll.), Candona (Candona) elongata (Schw.), Cypria candonaeformis (Schw.), Cypria arma (Schn.). Caspian immigrants accounted for 28% of the total number of species: Caspiocypris lobata (Zal.), Caspiocypris merculiensis Vek., Cyprideis ruggierii Dec., Amnicythere spectabilis (Mark.), Loxoconcha bulgarica Car., Loxoconcha verticalitercostata Dyk., Candona (Candona) neglecta Sars, Candona (Eucandona) balatonica Dad., Cyprinotus salinus (Br.), Ilyocypris bradyi Sars, Il. gibba (Ramd.), Il. caspiensis (Neg.). Mediterranean immigrants account for 10% of the total number of species: Aurila notata (Reuss), Xestoleberis (Pontoleberis) communis G.W. Müll., Xestoleberis (Xestoleberis) cellulosus Vek., X. (Xestoleberis) chanakovi Liv.&Agal. (Fig. 2).

Kujalnician relicts

I Caspian immigrants

Kimmerian relics

Fig. 2. The ratio of zoogeographic groups of ostracods in Kujalnikian deposits

Table 1. Stratigraphic position of ostracodes in Neogene-Quaternary deposits of the northern part of the Black Sea

Species composition of ostracods Pliocene Neopleistocene Holocene

km gu ch de eu kg pk ne bg vz kl fn gz

Cyprideis torosa**

Cyprideis pontica**

Cyprideis ruggierii** - —

Cyprideis acervumis**

Cyprideis complcporiferus**

Cyprideis subtorosus**

Cryptocyprideis bogatschovi*

Cythcridea sakarauli***

Paracyprideis naphtatscholana* * * —

Tyrrhenocytherc amnicola donetziensis**

Tyrrhenocythere azerbaidjanica**

Tyrrhenocythere trabzonensis**

Tyrrhenocythere solîertissimorete** -

Tyrrhenocythere pontica** —

Tyrrhenocythere complexolacunisae**

Hemicytheria dubokensis**

Aurila dubowskyi*** - — —

Aurila notata*** — —

Urocythereis margaritifera***

Euxinocythere (E.) rclicta** ?

Euxinocythere (E.) magma**

Euxinocythere (E.) multipunctata***

Euxinocythere (E.) bosqueti**

Euxinocythere (M.) bacuana**

Euxinocythere (M.) lopatici**

Euxinocythere (M.) crebra**

Euxinocythere (M.) praebaquana**

Amnicythere quinquetuberculata**

Amnicythere resupina**

Amnicythere plana**

Amnicythere postbissinuata**

Amnicythere longa**

Amnicythere palimpsesta**

Amnicythere multituberculata** ?-

Amnicythere polymorpha**

Amnicythere spectabilis**

Amnicythere striatocostata**

Amnicythere cymbula**

Amnicythere mironovi** 7-

Amnicythere volgensis**

Amnicythere pirsagatica**

Amnicythere gracillotdes** —

Note; * - freshwater species; ** - brackishwater species; *** - marine species

Continuation of Table 1. Stratigraphic position of ostracods in Neogene-Quaternary deposits of the northern part of the Black Sea

Species composition of ostracods Pliocene Eopkis tocene Neopleistocene Holocene

km kj g4 ch de eu kg pk ne bg vz kl fn gz

Amnicythere histriana*** —

Calistocythere flavidofusca*** — —

Calistocythere diffusa*** — — — —

Calistocythere cristata***

Mediocytherideis apatoica**

Loxoconchissa (L.) petasus** —

Loxoconchissa (L.) eichwaldi** —

Loxoconchissa (L.) babazananica** —

Loxoconchissa (L.) immodulata**

Loxoconchissa (L.) praeimmodulata**

Loxoconchissa (L.) endocarpus** — —

Loxoconchissa (L.) bairdyi** —

Loxoconcha subcrassula** —

Loxoconcha ljuljevi***

Loxoconcha lepida** —

Loxoconcha bulgarica*** —

Loxoconcha gibboides*** — — —

Loxoconcha rhomboidea***

Loxoconcha verticalitercostata

Loxoconcha granulata***

Loxoconcha rennata***

Loxoconcha globosa*** —

Loxoconcha elliptica***

Loxoconcha aestuarii***

Loxoconcha pontica***

Palmoconcha agilis*** —

Paracytheridea paulii*** — — —

Paradoxostoma variabile*** —

Paradoxostoma guttatum*** — —

Paradoxostoma naviculum***

Paradoxostoma simile*** — — —

Pseudocytherura pontica*** —

Cushmanidea tschernjawskiii***

Cushmanidea bacescoi*** —

Carinocythereis carinata***

Carinocythereis rubra***

Costa edwardsii runcinata*** — —

Xestoleberis (P.) laevis**

Xestoleberis (P.) communis*** —

Xestoleberis (X.) decipiens***

Xestoleberis (X.) acutipensis*** —

Xestoleberis (X.) aurantia***

Xestoleberis {X.) cornelii*** —

Xestoleberis (X.) cellulosus*** -

Xestoleberis (X.) eiongata***

Xestoleberis (X.) chanakovi*** —

End of Table 1. Stratigraphic position of ostracods in Neogene-Quaternary deposits of the northern part of the Black Sea

Species composition of ostracods Pliocene Eopleis tocene Neopleistocene Holocene

km gu ch de eu kg pk ne bg V/ l. '•I gz

Semicytherura sulcata*** — — —

Semicytherura euxinica*** — — —

Cytherois cepa*** — —

Camptocypria acronasuta**

Camptocypria gracilis**

Camptocypria lobata**

Caspiocypris labiata**

Caspiocypris merculiensis** —

Bacunella dorsoarcuata**

Pontonieila acuminata**

Advenocypris centropunctata*

Limnocythere inopinata*

Metacypris cordata*

Darwinula stevensoni*

Candona (C.) expressa* —

Candona (C.) Candida* —

Candona (C.) angulata*

Candona (C.) iliensis* —

Candona (C.) neglecta*

Candona (C.) clongata*

Candona (C.) rawsoni*

Candona (C.) angulata*

Candona (E.) balatonica* - — —

Candona (E.) caucasica* —

Typhlocypris rostrata* —

Typhlocypris compressa* —

Cyclocypris ovum*

Cyclocypris laevis* —

Cypria candonaeformis

Cypria arma*

Cypria lacustris*

Cyprinotus salinus*

Ilyocypris bradyi*

llyocypris gibba*

Ilyocypris caspiensis* — ?

Eucythere ex.gr.declivis* —

Eucypris clavata* —

Zonocypris membranae* - —

Herpetocypris reptans* —

I leterocypris incongruens* —

Bairdia raripila *** —

Bythocythere schornikovi *** —

Cytheropteron rotendatum*** —

Cytheridea acuminata*** —

Heterocytherideis reticulata*** — —

i marine specis

i freshwater species ■ brackishwater species

I» n 69

i

31 Bil

12

Kujanician Gurian

Fig. 3. Percentage ratio of different ecologically specialized northern part of the Black Sea

Typical species of the Kujalnikian ostracods are Cyprideis ruggierii Dec., Aurila notata (Reuss), Amnicythere spectabilis (Mark.), Loxoconcha bulgarica Car.,Xestoleberis (Xestoleberis) chanakovi, Candona (Eucandona) balatonica Dad., Cypria arma (Schn.) (Dykan, 2006, 2016 a). Kujalnikian ostracod associations had a brackish water-freshwater-marine composition: brackish water species accounted for 57 %, freshwater - 31 %, marine - 12 % of the total number of species (Fig. 3).

Gurian deposits are embedded low down in the marine Quaternary deposits and they are mosaically distributed between isobaths 10-90 m in the northwestern and northeastern shelf of the Black Sea. They are represented by silts and clays with a total thickness of up to 20 m.

Gurian ostracods total 11 genera and have a poor species composition (17 species). They are presented by Miocene-Pliocene relics, which accounted for 94 % of the total: Loxoconchissa (Loxoconchissa) bairdi (G.W. Müll.), Loxoconchissa (Loxocaspia) babazananica (Liv.), Bacunella dorsoarcuata (Zal.), Pontoniella acuminata (Zal.), Tyrrhenocythere amnicola donetziensis Dub., Tyrrhenocythere azerbaidjanica (Liv.), Camptocypria acronasuta (Liv.), Camptocypria gracilis (Liv.), Amnicythere palimpsesta (Liv.), Cyprideis torosa (Jones), Cypria candonaeformis (Schw.), Ilyocypris gibba (Ramd.), Il.

species in the Kujalnikian and Gurian deposits of the

bradyi Sars, Advenocypris centropunctata (Suz.), Cryptocyprideis bogatschovi (Liv.), Darwinula stevensoni (Brady & Rob.). The index species of the beginning of the Gurian is Amnicythere postbissinuata (Neg.) (Dykan, 2016 a) (Table 1). Gurian ostracod associations had a brackish water-freshwater composition: brackish water species dominated (accounting for 69 % of the total number of species ), with freshwater ostracods comprising 31 %; Fig. 3).

The Pliocene/Quaternary boundary, as defined by ostracods between the Kujalnikian and Gurian horizons in the northern part of the Black Sea, is based on the change in taxonomic composition of ostracods, with the disappearance of Pliocene species and the appearance of new Quaternary ones. Ten species disappeared in the Kujalnikian: Cyprideis pontica Krstic, Euxinocythere (Maetocythere) crebra (Schn.), Amnicythere mironovi (Schn.), Camptocypria lobata (Zal.), Loxoconcha subcrassula Suz., Loxoconcha verticalitercostata Dyk., Xestoleberis (Xestoleberis) cellulosus Vek., Xestoleberis (Pontoleberis) communis G.W. Müll., Candona (Candona) expressa Karm., Ilyocypris caspiensis (Neg.): and one species, Amnicythere postbissinuata, appeared in the Gurian (Figs. 4, 5).

Also, the biostratigraphic marker of the Kujalnikian in the Black Sea is Cyprideis pontica Krstic, 1968 (Dykan, 2016 b). The brackish-water

Fig. 4. Index species of the Gurian Amnicythere postbissinuata (Neg.), collection No. 2567-5-132/9, right valve, female, adult, Gurian horizon, Taman Peninsula, Akhtanizivsky station

Fig. 5. Characteristic species of the Pliocene that disappeared at the Kujalnikian/Gurian boundary: 1 - Camptocypria lobata (Zal.), collection No. 2567-64/21, left valve, adult, Kimmerian horizon, northeastern part of the Black Sea; 2 - Cyprideispontica Krstic, collection No. 2567-6/2, left valve, female, adult, Kimmerian horizon, northwestern part of the Black Sea; 3 - Loxoconcha subcrassula Suz., collection No. 2567-21/16, left valve, female, adult, Kujalnikian horizon, northwestern part of the Black Sea; 4 - Loxoconcha verticalitercostata Dyk., collection No. 2567-6/17, left valve, female, adult, Kimmerian horizon, northwestern part of the Black Sea; 5 - Xestoleberis (Xestoleberis) cellulosus Vek., collection No. 2567-86/20, right valve, female, adult, Kujalnikian horizon, northwestern part of the Black Sea; 6 - Xestoleberis (Pontoleberis) communis Müll., collection No. 256781/19, left valve, adult, Kujalnikian horizon, northwestern part of the Black Sea; 7 - Candona (Candona) expressa Karm., collection No. 2567-5-1/26, right valve, adult, Kimmerian horizon, Taman Peninsula, Zaliznyy Rih section; 8 - Ilyocypris caspiensis (Neg.), collection No. 2567-5-129/26, right valve, adult, Kujalnikian horizon, Taman Peninsula, Akhtanizivsky station

species Cyprideis pontica has a narrow stratigraphic range (in the upper half of the Middle Miocene-Pliocene) and a widespread geographic distribution within Western and Eastern Europe (Pannonian Basin,

Dacian Basin, Euxinian Basin of Paratethys), and the Mediterranean region. The stratigraphic position of the species Cyprideis pontica in the Mediterranean region (eastern Mediterranean Basin, Crete and

Table 1. Stratigraphic position of Cyprideis pontica Krstic in Parathetys-Mediterranean region

Period Epoch MEDITERRANEAN BASIN (ATNTS2004) PANNONIAN BASIN (SCU, 2012) DACIAN BASIN (SCU, 2012) EVKSIN1AN BASIN (SCU 2012)

QUATER NARY 1 < № I- It PLEISTOCENE IJNM CALABRIAN LOWER PLEISTOCENE GURIAN

2.5KH GELAS1AN

3.600 PIACENZIAN RUMUNIAN KUJALNICIAN

M RIIMUNIAN

td U O ZANCLEAN DACIAN

DACIAN

5J32 KIMMERIAN

U

z tad PONTIAN

y o 7.246 PONTIAN

u

■ MAEOTIAN MAEOTIAN

MIOCENE TORTON1AN pannonian

11.608

SARMATIAN SARMATIAN SARMATIAN

KONKIAN

13.82 BADENJAN KARAGAMAN

CIIOKRAKIAIS

15.97 I.ANGHIAN [ARkltAMAN

The stratigraphic position of Cyprideis pontics

Pliocene/Quaternary boundery

northern Greece) covers the upper Serravallian- of water filtration, there was a reorganization of

Messinian interval (Mostafawi, 1989, 1996); in the the morphology of the surface pore channels in the

Pannonian Basin (Austria, Slovenia, northern and species Cyprideis torosa. This involved an increase

eastern Serbia) the Upper Pannonian-Upper Pontian in the size of the sieve-shaped lamellae, the number

(Gross et al, 2008); in the Dacian Basin (northern of internal pores in these lamellae and the size of

Bulgaria, Romania) the Pontian (KrstiC et al, 1989; the osculum of the inner pore, and a change in the

Olteanu, 1989); and in the Euxinian Basin (Black shape of the inner pore on the stack with a rim along

Sea) (northern shelf, the Indo-Kuban depression) the perimeter. As a result of these evolutionary

the Sarmatian-Kujalnikian (Dykan, 2016 a, b). The processes, a new morphotype Cyprideis pontica was

species Cyprideis pontica disappears at the boundary formed within the Paratethys-Mediterranean basins.

of the Late Miocene (Messinian, Pontian) and the It occupied a mosaic, ecologically isolated area that

Pliocene (Zanclean, Dacian, Kimmerian) (5.33 Ma) coincided geographically or overlapped with the area

in the Mediterranean, Pannonian Basin and Dacian occupied by the species Cyprideis torosa (sympatric

Basin (The Geologic Time Scale, 2012) (Table 1). evolutionary process) (Fig. 6).

i^^m the areal species Cyprideis pontica the areal species Cyprideis torosa

Fig 6. Map of the range of Cyprideis pontica Krstic and Cyprideis torosa (Jones) in the Paratethys-Mediterranean region (Middle Miocene-Pliocene)

Cyprideis pontica continued to exist during the Sarmatian-Kujalnikian in the Euxinian Basin. High density monotypic populations of the species were formed in the deep-water habitats of the eastern part of the Black Sea (Indo-Kuban depression) during the Sarmatian-Maeotian. The area with Cyprideis pontica declined in the Pliocene to the northwestern part of the sea, where this species was still widespread in the shallow coastal biotope, though with a population of low density. Cyprideis pontica was rare in the Kujalnikian, its few populations represented only, or mainly by, larvae. The species had disappeared in the Black Sea by the Kujalnikian/Gurian boundary.

Cyprideis pontica is a phylogenetic branch of the species Сyprideis torosa - separating from the parent species C. torosa in the Late Miocene. As a result of the occupation of a new ecological niche in deeper water biotopes of the shelf and continental slope with a reduced oxygen content, part of the population of Cyprideis torosa went through a narrow specialization process. In the process of adaptation to hypoxia and the necessity to increase the volume

The morphology of the shell of Cyprideis pontica Krstic has a diagnostic feature (the morphology of the surface pore canals), which allows this species to be recognised in the Neogene deposits (Dykan, 2016 a, b). The surface pore canals have a different shape (rounded, oval, flower-shaped, irregularly elongated, irregularly oval), different sizes (8-42 ^m), sieve-typed, deepened in relation to the surface of the valve. The sieve-shaped lamella contains from 110 to 270 internal pores. The internal pores have a staggered shape and a round osculum (302-994 nm in diameter) with a rim along the perimeter. The central pore is located in the centre of the sieve-shaped lamella, deepened in relation to the surface of the valve, with a round osculum (977 nm-1.8 ^m in diameter) (Fig. 7). Conclusions. A monographic study of the Neogene-Quaternary ostracods of the Black Sea, their stratigraphic position and geographical distribution in the Mediterranean-Black Sea-Caspian region allow one to conclude that a change in the taxonomic composition and ecological specialization of ostracods occurred at the Kujalnikian/Gurian boundary in the northern part

3

4

5

6

Fig. 7. Morphology of the fossil shell species Cyprideis pontica Krstic, 1968: 1 - right valve, female, adult, lateral external view (x 130), Upper Sarmatian horizon, north-western shelf of the Black Sea, drill hole 67; 2 - left valve, male, adult, lateral external view (x 95), Lower Maeotian horizon, north-western shelf of the Black Sea, drill hole 55; 3 -fragment of the outer surface of the shell (x 250); 4 - surface porous canals (x 1000);); 5 - sieve-shaped lamella of the surface porous canal (x 5000); 6 - internal pores of the surface porous canal (x 13000) (Dykan, 2016)

of the Black Sea. 24% of Pliocene species, including the index species Cyprideis pontica, disappeared in the Kujalnikian. Ostracod associations had a brackish water-freshwater-marine composition. In the Gurian, the new species Amnicythere postbissinuata appeared and brackish water-freshwater associations formed, with the domination of brackish water species.

Rreferences

Dykan N. I., 2006. Systematyka chetvertynnykh ostrakod Ukrainy [Systematics of Quaternary Ostracods of Ukraine]. IHN NANU, Kyiv(in Ukrainian). Dykan N. I., 2011. Biostratigrafiya srednemiocenovyh-nizhnepliocenovyh otlozhenij Tamanskogo poluostrova po ostrakodam [Biostratigraphy of the Middle-Miocene-Lower-Pliocene deposits of the Taman Peninsula by ostracods]. Geologicheskij zhurnal, № 3, 29-39 (in Russian). Dykan N. I. 2012. Rozchlenuvannia pliotsen-chetvertynnykh vidkladiv Chornoho moria

(pivnichnyi shelf) za ostrakodamy [Determining of the age of the Pliocene-Quaternary deposits of the Black Sea (Northern shelf) byostracodes]. Tektonika i stratyhrafija, № 39, 111-131(in Ukrainian).

Dykan N. I,. 2016 a. Neohen-chetvertychnye ostrakody severnoi chasty Chornoho moria [Neogene-Quaternary ostracods of the northern part of the Black Sea]. Chetverta khvylia, Kyiv (in Russian).

Dykan N. I., 2016 b.Popov Kamen section. Ostracods:Paleontological Journal, 50 (10), 7781.

Dykan N. I., 2016 c. Taman ostracods.Paleontological Journal, 50 (10), 142-150.]

Dykan N. I., 2016 d.Taman section. Ostracods: Paleontological Journal, 50 (10), 104-107.

Dykan N. I., 2016 f. Zelensky-Panagia section. Ostracods: Paleontological Journal, 50 (10), 24-25.

Dykan N. I., 2016 g. Vid Сyprideis pontica Krstic, 1968 (Ostracoda, Crustacea) - indikator granicy pliocen-chetvertichnyh otlozhenij (severnaya chast Chernogo morya [View of Сyprideis pontica Krstic, 1968 (Ostracoda, Crustacea) - indicator of

the boundary of Pliocene-Quaternary deposits (northern part of the Black Sea). Geologiya i poleznye iskopaemye Mirovogo okeana, Kyiv, № 1 (43), 19-43 (in Russian).

Lourens L., Hilgen F., Shackleton N. J., Laskar J., Wilson D., 2004. The Neogene Period: The Geologic Time Scale, 409-440. doi.org/10.1017/ CBO9780511536045.022.

Geologic Time Scale, 2004. Editors: Gradstein F. M., Ogg J. G., Smith A. G. Cambridge University Press. doi.org/10.1017/CB09780511536045.

Geologic Time Scale, 2012. Editors: Gradstein F. M. Ogg J. G. M. Schmitz, Ogg G. Gebrüder Borntraeger, Stuttgart, German. doi.org/10.1016/C2011-1-08249-8.

Gross M., Minati K., Danielopol D., Piller W., 2008. Environmental change and diversification of Cyprideis in the Late Miocene of the Styreal Basin (Lake Pannon, Austria). Senckenbergiana lethaea, 88 (1), 161-181.

Hilgen J., Lourens L.J., Van Dam J.A., 2012. The Neogene Period: The Geologic Time Scale, 923-964. doi. org/10.1016/C2011-1-08249-8.

Krstic N., Stancheva M., 1989.Ostracods of Eastern Serbia and Northern Bulgaria with notices on a Northern Turkey assemblage and some Mediterranean assemblage: Chronostratigraphe und Neostratotypen. Neogene der Westlichen (Zentrale) Paratethys. Pontien, VIII, 753-819.

Mostafawi N., 1996. Neogene Ostracodefaunen im Gebiet südlich von Thessaloniki (Nordgriechenland). Senckenbergiana lethaea, № 76 (1/2), 159-173.

Mostafawi N., 1989. Neogene ostracods of Chersonisos and Vrysses (Crete, Greece). Neues Jahrbuch für Geologie und Paläontologie. Abhandlungen, 178 (2), 183-201.

Olteanu R., 1989. La faune d'ostracodes ponties du Bassin Dacique: Chronostratigraphie und Neostyratotypen. Neogene der Westlichen (Zentrale) Paratetis. Pontien, VIII, 722-751.

Natsionalnyi stratyhrafichnyi komitet Ukrainy, 2018. Pro diyalnist Nacionalnogo stratygrafichnogo komitetu Ukrayiny [About the activities of the National Stratigraphic Committee of Ukraine]. Geologichnyj zhurnal, 2 (363), 95-100 (in Ukrainian).

Riccardi A. C., 2009. Ratification of the definition of the base of Quaternary System/Period (andtop of the Neogene System/Period), and redefinition of the base of the Pleistocene Series/Epoch (and top of the Pliocene Series/Epoch).IUGS. Retrieved from http://www.stratigraphy.org/upload/IUGS%20 Ratification_Q%20&%20Pleistocene.pdf.

Semenenko V. N., 1987. Stratigraficheskaya korrelyaciya verhnego miocena i pliocena Vostochnogo Paratetisa i Tetisa [Stratigraphic correlation of the Upper Miocene and the Pliocene of the Eastern Parathetis and Tetis]. Naukova dumka, Kyiv.

Shnyukov E. F., Shuraev I. N., 2015. Kimmerijskie peschaniki Krymskogo kontinentalnogo sklona [Cimmerian sandstones of the Crimean continental slope]: Stratotipovi ta oporni rozrizi fanerozojskih vidkladiv Ukraïni: suchasnij stan paleontologichnoï vivchenosti ta perspektivi podalshih doslidzhen. IHN NANU, Kyiv, 8, 215-221(in Russion).

Stratigraficheskij slovar SSSR. Paleogen. Neogen. Chetvertichnaya sistema, 1982. Leningrad.

Stratygrafichnyj kodeks Ukrayiny, 2012. [Stratigraphic Code of Ukraine]. Vidp. red. P.F.Gozhyk, 2-e vyd., Kyiv (in Ukrainian).