Calcareous nannofossil dating of Ionian and Gavrovo flysch deposits in the External Hellenides Carbonate Platform (Greece): Overview and implications

Tectonophysics 595–596 (2013) 235–249

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Calcareous nannofossil dating of Ionian and Gavrovo flysch deposits in the External Hellenides Carbonate Platform (Greece): Overview and implications Maria V. Triantaphyllou ⁎ University of Athens, Faculty of Geology and Geoenvironment, Department of Historical Geology — Palaeontology, Panepistimiopolis 15784, Athens, Greece

a r t i c l e

i n f o

Article history: Received 4 June 2011 Received in revised form 12 March 2012 Accepted 15 May 2012 Available online 26 May 2012 Keywords: Flysch Nannofossils Ionian unit Gavrovo unit Hellenides Greece

a b s t r a c t The available biostratigraphic data based on calcareous nannofossil analysis determine the mean ages for the onset of flysch sedimentation (base of transitional beds) of the Ionian unit at ~ 34–35 Ma (external/internal Ionian), and at ~ 41 Ma (middle Ionian). The top of the Ionian flysch at ~ 25 Ma constrains the emplacement of Gavrovo nappe, providing an average duration of at least 11–16 Myr for the flysch sedimentation. Gavrovo flysch deposition started at a mean age of ~ 34 Ma and lasted till ~ 29 Ma (emplacement of Pindos nappe), suggesting an average duration of approximately 5 Myr. Phenomena of synsedimentary tectonism have been reported at the external Ionian unit, indicating that pre-flysch extension of the basin lasted at least 4 Myr. The ~ 6–7 Myr difference of the onset of flysch sedimentation between the external/internal and middle parts of Ionian unit implies evidence for an axial symmetry of the basin before the underthrusting of Mani unit under Pindos nappe. © 2012 Elsevier B.V. All rights reserved.

1. Introduction The Hellenic peninsula is geotectonically divided into the External Hellenides to the west and Internal Hellenides to the east (Brunn, 1956). The Internal Hellenides consist of metamorphic sequences whereas the External Hellenides consist of sedimentary sequences (Aubouin, 1959; Jacobshagen, 1986; Renz, 1955). The External Hellenides Carbonate Platform (Terrane H1) was a continuous shallow water carbonate platform throughout the Upper Triassic–Lias (Papanikolaou, 1997; Papanikolaou et al., 2004; Royden and Papanikolaou, 2011), comprising the well known non metamorphic units of Paxos (Pre-Apulian), Ionian, Gavrovo and Tripolis and their metamorphosed equivalent, Mani unit (Papanikolaou, 1986, 1997, 2009). The Ionian basin and the shallow-water carbonate platforms to east and west (the Gavrovo and Apulian platforms respectively) were formed during the Early Mesozoic opening of Tethys (Aubouin and Dercourt, 1962). They were originally part of the passive continental margin of the Apulian Plate that was separated from the Pelagonian microplate by an oceanic domain, the Pindos Ocean (Jones et al., 1992; Robertson et al., 1991), during Triassic and Jurassic times. From the Middle Jurassic onward, ophiolite obduction occurred during the closure of this ocean. The External Hellenides Platform is characterised by post-Eocene compressional deformation that still continues in its external parts along the periphery of the active Hellenic Arc. Sedimentary units were overthrusted between late Eocene and early Miocene

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time, a time interval of 17 Myr (Royden and Papanikolaou, 2011). A model of foreland propagating thrust faults is accepted for the External Hellenides (Brooks et al., 1988; Jacobshagen, 1986; Kamberis et al., 1996; Underhill, 1989), while out-of-sequence thrusting and simultaneous movement of thrusts is supported (Sotiropoulos et al., 2003). The foreland basin was formed as the result of the overthrust loading and the subsequent lithospheric flexure during the migration of the fold-and-thrust belt to the west in the Tertiary period (Clews, 1989; Dercourt and Thiebault, 1979; Fleury, 1980; IGRS–IFP, 1966; Underhill, 1989). Thrusting activity and eustatic sea-level changes control the palaeogeographic evolution of the foreland basin (Avramidis et al., 2002; Kamberis et al., 2005), which is distinguished into the Ionian and Gavrovo basins (Kamberis et al., 2005; Papanikolaou and Lekkas, 2008; Sotiropoulos et al., 2003). Thus, the External Hellenides Carbonate Platform is nowadays part of the active margin of the Eurasian Plate, whose westernmost sector is marked by an impressive, narrow accretionary prism built up by active compressional tectonics (Finetti, 1976; Kokinou et al., 2005; Rabinowitz and Rayan, 1970). The main difference between the Ionian and the Gavrovo unit is the palaeogeographic change that occurred in the Ionian during Late Lias when the taphrogenetic processes (Karakitsios, 1992, 1995) divided the water platform in two parts. One part (Gavrovo and Tripolis units) remained shallow throughout Late Triassic–Eocene characterised by a thick neritic carbonate succession of about 3000 m, and another part (Ionian unit), formed a deeper basin (Papanikolaou, 1997). The Ionian unit consists of three distinct sequences (Fleury, 1980; Karakitsios, 1992, 1995), a prerift which is represented by shallow water early Liassic lmestones, a synrift that corresponds to the general sinking of the Ionian domain in half-graben geometry, and a postrift sequence

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with pelagic carbonate sedimentation until the late Eocene. The preflysch sediments of the Ionian unit are represented by basinal facies. Great volumes of deep-water sediments, mainly submarine fan deposits (flysch), accumulated in this basin in the syn-orogenic period (B.P. Co. LTD., 1971; Clews, 1989; IGRS–IFP, 1966; Piper et al., 1978). Due to phenomena of syn-sedimentary tectonism, the thickness of transitional beds varies significantly; in several locations transitional beds are missing and flysch rests directly on the limestone (e.g. Kato Retsina; Papanikolaou and Lekkas, 2001, 2008). Orogenetic processes and flysch sedimentation initiated at early Tertiary (Late Eocene–Oligocene) on both units. The flysch sediments of the Ionian and Gavrovo units were considered in the past as one common succession resting between the Ionian and Gavrovo geotectonic units, the Western Hellenic Flysch (Richter, 1976a) ranging stratigraphically from Late Eocene to Early Miocene (Aubouin, 1959; Dercourt, 1964; Dürr et al., 1978; Fleury, 1980; Godfrieaux, 1968; Katsikatsos, 1969; Papanikolaou, 1986, 1997, 2009; Richter, 1976b; Thiébault, 1982). An internal cordillera (Pindos Cordillera) as a common source terrain is assumed to have supplied the Western Hellenic Flysch through different feeder channels, excluding an intensive reworking of Pindos Flysch sediments (Faupl et al., 1998). Recently Papanikolaou and Lekkas (2008) provided significant lithostratigraphic evidence, implying that the flysch is not continuous and common for both units, and verified the identification of Gavrovo thrust (Sotiropoulos et al., 2008) based on seismic profiles and biostratigraphic analysis. The age of the Ionian flysch deposits at the northern part of the foreland basin at Epirus region, has been determined as Late Eocene–Early Miocene on the basis of planktonic foraminifera (IGRS– IFP, 1966) and calcareous nannofossils (Bellas, 1997). On the contrary the age of the flysch in the Etoloakarnania region has remained a controversial point among researchers for several years. Bizon et al. (1963) when studying planktonic foraminiferal assemblages, have considered the basal flysch deposits that overlie conformably the Ionian and Gavrovo limestones as Oligocene in age, whereas B.P. Co. LTD. (1971) suggested for the same deposits an Early Miocene age, pointing to the existence of an unconformity between flysch and the underlying Eocene limestones. In a recent study, Triantaphyllou in Sotiropoulos et al. (2008) verified the onset of clastic sedimentation in the Gavrovo foreland basin in the Etoloakarnania region, occurring in the Late Eocene/latest Priabonian, confirming previous studies in the area, as also in Epirus region (Bellas, 1997; Bizon et al., 1963; Fleury, 1980; Karakitsios, 1995; Triantaphyllou in Sotiropoulos et al., 2003) and NW Peloponnesus (Kamberis et al., 2005). In SW Peloponnesus, the foreland basin overlies Palaeocene to Eocene Gavrovo neritic carbonates (Fleury, 1980; Thiébault, 1982). According to the above authors, the flysch sedimentation began in the earliest Oligocene, whereas Fytrolakis (1971) considers that it took place in Late Eocene. Earlier, it had already been suggested, on the basis of planktonic foraminiferal assemblages,

that the onset of Gavrovo flysch sedimentation took place either in Late Eocene (Priabonian) or Early Oligocene (Bizon et al., 1963). The present study is an effort to synthesise and critically evaluate all available biostratigraphic data based on calcareous nannofossil analysis, in order to clarify the onset of clastic sedimentation in Ionian and Gavrovo units, refine the stratigraphic age of the Ionian and Gavrovo flysch deposits of the External Hellenides Carbonate Platform and explain the differences in age, duration of flysch sedimentation and thickness of the flysch formations in the two units. 2. Materials and methods This study is based on a review of published data on the calcareous nannofossil assemblages (Bellas, 1997; Stoykova in Makrodimitras et al., 2010; Triantaphyllou in Pavlopoulos et al., 2010; Triantaphyllou in Sotiropoulos et al., 2008; Stoykova et al., 2003) and compiled with new data produced in this work. The nannofossil data are presented using the standard biozonal scheme (Martini, 1971), as this has been incorporated in the magnetobiochronologic framework (Berggren et al., 1995) and revised concerning the numerical ages (Lourens et al., 2004; Luterbacher et al., 2004). Data have been evaluated and converted, where possible, to more recent calcareous nannofossil schemes available for the considered stratigraphic interval in the Mediterranean area (e.g. Bellas, 1997; Catanzariti et al., 1997; Fornaciari and Rio, 1996). Concerning the methodology of counting techniques used in the nannofossil studies discussed in this review (see Table 1), mostly semi-quantitative analysis were used, rather than the quantitative studies (e.g. Catanzariti et al., 1997; Fornaciari and Rio, 1996). All involved semi-quantitative analyses results are typically comparable (see Table 1), however the more extensive the analysis is, the more feasible is to face successfully typical difficulties such as scarcity, reworking and preservation state when dating flysch deposits using calcareous nannofossil assemblages. Therefore the analyses listed in column 1 (Table 1), referring to the highest number of fields of view per sample, enabled the finding of the most scarce biostratigraphic indices in the assemblages. 3. Flysch successions and calcareous nannofossil biostratigraphic evidence 3.1. Ionian flysch Bellas (1997) was the first author to contribute to the biostratigraphic assignment for a number of sections in Epirus/Arta, Prevesa and Parga regions using calcareous nannofossils (Fig. 1; Tables 2 and 3). Elatos section (ref. 1; Tables 1 and 2) in the internal Ionian unit, displaying the transitional beds between carbonate and flysch sedimentation, provided evidence for nannofossil biozone

Table 1 Methodology of counting techniques used in the nannofossil studies discussed in the present study. 1. Triantaphyllou in Sotiropoulos et al. (2008), Pavlopoulos et al. (2010) and present study

2. Stoykova in Stoykova et al. (2003) and Makrodimitras et al. (2010)

3. Bellas (1997)

Extensive semiquantitative analysis in up to 1500 fields of view per slide in longitudinal traverses randomly distributed (15 traverses; 100 fields of view per traverse). The traverses were representing low density material content in order to make accurate nannofossil determinations and trace even the rarest species. Countings of at least 500 specimens have been achieved using a Leica DMLSP optical polarising light microscope at 1250×. Semiquantitative abundances of the taxa encountered were recorded as follows: common: at least 1 specimen/10 fields of view; rare: 1 specimen/10–100 fields of view; present: 1 specimen/>100 fields of view.

Semi-quantitative evaluation in dense samples under the light microscope with 1250 × magnification. The authors have examined their samples extensively; however several important markers were absent or scarce. Then in most cases they used combined range of recorded taxa. The relative abundance was determined as: abundant: more than 10 specimens/field of view, common: 9–2 specimens/field of view, rare: b 2 specimens/field of view.

Modified semi-quantitative technique, by selecting an appropriate number and position of traverses at the magnification of ca. 934× (150–170 optical fields of view observed along the long axis of the cover slip and 80–90 fields of view along the short axis). The relative abundance was determined as follows: present: 1–2 specimens after all the traverses were made, rare: 3–5 specimens after all the traverses were made, few: more than 5 specimens and less than optical fields of view/5, common: 1 specimen/3– 5 fields of view, abundant: more than 1 specimen every at least 2 fields of view.

M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

237

Fig. 1. Geological map of western Greece and location of Ionian and Gavrovo flysch sites included in this study (details for the figured sections are presented in Tables 1 and 2).

NP21 (co-occurrence of Isthmolithus recurvus, Ericsonia formosa, Reticulofenestra umbilicus, absence of rosette-shaped discoasters and Ilselithina fusa). Bellas (1997) correlated this biostratigraphic interval with the Latest Eocene. In the same area the biozones NP21 (common E. formosa, few R. umbilicus, rare Clausicoccus spp.), NP22 (absence of E. formosa, rare to absent R. umbilicus, few Helicosphaera compacta), NP23 (Sphenolithus predistentus, Cyclicargolithus abisectus, H. compacta), NP24 (Sphenolithus distentus, S. ciperoensis), NP25 (S. ciperoensis, Reticulofenestra scissura (synonyms: Reticulofenestra bisecta, Dictyococcites bisectus)), NN1 (absence of R. scissura, presence of C. abisectus, Helicosphaera cf. carteri) have been determined in Korfovouni section (ref. 2; Tables 2 and 3). In the outer part of middle Ionian unit, the transitional beds have been studied (Bellas, 1997) in the sections Kato Despotiko (earliest Oligocene, NP21), (ref. 3, Tables 2 and 3) and Strouga Goumenou (latest Eocene, NP21), (ref. 4, Tables 2 and 3). The latter section extends up to NP23 (absence of R. umbilicus, R. hillae). The transitional beds in the middle Ionian unit have also been dated

as latest Eocene (NP21) in section Ekklisia (Bellas, 1997) based on E. formosa, very rare Ilselithina recurvus and few R. umbilicus (ref. 5, Tables 2 and 3). The youngest flysch deposits in the same section have been dated as Late Oligocene (lower NP25, few to common C. abisectus, common R. scissura, Sphenolithus cf. ciperoensis, S. cf. dissimilis, presence of poorly preserved and rare S. distentus, rare Sphenolithus delphix). In the external Ionian unit, the transitional beds form the base of Argyrotopos section (ref. 6, Tables 2 and 3), which includes the Eocene–Oligocene boundary on the basis of the Lowest Occurrence (LO) of I. fusa and extends up to nannofossil biozone NP24. The uppermost flysch deposits have been dated in the sections National Road (NP25), (ref. 8, Tables 2 and 3), Monos (NP25–NN1), (ref. 9, Tables 2 and 3) and Anacharavi (NN1), on Corfu Island (Bellas, 1997; see Tables 2 and 3). The study of calcareous nannofossil assemblages in clastic deposits exposed on scattered sequences on Diapondia Islands (Erikoussa, Othonoi, Mathraki; Makrodimitras et al., 2010), at the westernmost part of the external Ionian unit, revealed the presence of Late

238 Table 2 The reviewed sections for the Ionian and Gavrovo flysch deposits and their biostratigraphic correlations. (*) Numbered sections are presented in Fig. 1, (**) Correlations between different nannofossil biozonal schemes are mostly established within this review; question marks indicate our evaluations concerning doubtful biozonal assignments (details are presented in Table 3). Ref. number Area (*)

Section

Nannofossil biozones (**) Martini (1971) Fornaciari and Rio (1996), (1) Fornaciari et al. (1996) (2)

Reference Study Bellas (1997) (4)

MNP21a

E. formosa Partial-range zone

Bellas (1997)

I. fusa/E. formosa Concurrent-range zone–Triquetrorhabdulus spp. Partialrange zone I. fusa/E. formosa Concurrent-range zone–C. abisectus Partial‐range zone E. formosa Partial-range zone

Bellas (1997)

E. formosa Partial-range zone–R. scissura Interval zone E. formosa Partial-range zone–E. formosa–R. umbilicus/R. hillae Interval zone Rhabdospha‐era spp. Interval zone– R. scissura Interval zone S. delphix Abundance subzone

Bellas (1997)

Ionian flysch 1 Epirus/Arta

Elatos (internal Ionian)

NP21

–

2

Epirus/Arta

Korfovouni (internal Ionian)

NP21–NN1

Oligocene not considered — MNP19–MNP24, Miocene not MNP25a,b–MNN1a considered

3

Epirus/Prevesa

NP21–NP23

–

MNP21b–MNP23

4

Epirus/Prevesa

NP21

–

MNP21a

5

Epirus/Prevesa

Kato Despotiko (middle Ionian) Strouga Goumenou (middle Ionian) Ekklisia (middle Ionian)

NP21–NP25

6

Epirus/Parga

NP21–NP22

MNP21a–MNP24, for latest Oligocene see (2) MNP21a–MNP22

7

Epirus/Parga

NP22–NP24

–

MNP22–MNP24

8

Epirus/Parga

NP25

MNP25a

–

9

Epirus/Parga

Lower Argyrotopos (external Ionian) Upper Argyrotopos (external Ionian) National Road (external Ionian) Monos (external Ionian)

For Eocene–Oligocene see (3) — MNP25b –

NP25–NN1

MNP25b–MNN1

–

10/1 10/2

Epirus/Botzara, central part Klematia Paramythia/A–A′ of the Botzara syncline (middle Ionian)

NP21–?NN1

MNP21a–MNP24, for L. Oligocene Miocene see (2)

11/1 11/2

Epirus/Botzara, western Klematia Paramythia/B–B′ part of the Botzara syncline (middle Ionian)

NP17/20–? NN1

Epirus/Dragopsa syncline

Klematia Paramythia/C–C′ (middle Ionian)

NP16–?NN1

Northern Corfu

Anacharavi (external Ionian) NN1

Eocene, not considered, MNP19– MNP24, for L. Oligocene Miocene see (2) M. Eocene not considered — MNP19–MNP24, for L. Oligocene Miocene see (2) –

Eocene not considered, E. formosa Partial-range zone–S. conicus Interval subzone Eocene not considered, E. formosa Partial-range zone–S. conicus Interval subzone Triquetrorhabdulus spp. Partial-range zone–S. conicus Interval subzone

Stoykova et al. (2003)

12/1 12/2 12/3

Eocene, Oligocene not considered, MNP25a–? MNN1d Eocene, Oligocene not considered, MNP25a–? MNN1d Eocene, Oligocene not considered, MNP25a–? MNN1d MNN1b

Diapondia Islands

Erikoussa (external Ionian)

?NP25–?NN4

?MNP25a–?MNN4

–

Makrodimitras et al. (2010)

Diapondia Islands

Othonoi (external Ionian)

?NP25–NN3

?MNP25a–?MNN3b

–

Diapondia Islands

Mathraki (external Ionian)

?NP25–?NN8

?MNP25a–?MNN8

–

Epirus/south of Ioannina

Ellinikon (internal Ionian)

NP21

–

MNP21

? R. scissura Interval zone–S. conicus Interval subzone, for Miocene see (2) ? R. scissura Interval zone–S. conicus Interval subzone, for Miocene see (2) ? R. scissura Interval zone–S. conicus Interval subzone, for Miocene see (2) E. formosa Partial-range zone–I. fusa/ E. formosa Concurrent-range zone

Dodoni (middle Ionian)

NP21

–

MNP21

Bellas (1997) Bellas (1997)

Bellas (1997) Bellas (1997) Bellas (1997)

S. delphix Abundance subzone– Bellas (1997) S. conicus Interval subzone E. formosa Partial-range zone–S. conicus Stoykova et al. (2003) Interval subzone

Stoykova et al. (2003)

Bellas (1997)

Ionian flysch

Makrodimitras et al. (2010) Makrodimitras et al. (2010) Kissel et al. (1985) Kissel et al. (1985)

M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

Catanzariti et al. (1997) (3)

Botzara (middle Ionian)

NP24–NP25

13

Epirus/east of Botzara syncline Botzara syncline/Radhovizi Formation Etoloakarnania

Ag. Nikolaos

MNP19–MNP20

–

14

Etoloakarnania

Kato Retsina

NP23–NP24

–

MNP23–MNP24

C. abisectus Partial‐range zone– R. scissura Interval zone

15

Etoloakarnania

Agrilia

NP23–NP24

–

MNP23–MNP24

16

Etoloakarnania

Kalidona

NP24

–

MNP24

C. abisectus Partial‐range zone–R. scissura Interval zone R. scissura Interval zone

17

Etoloakarnania

Ano Koudouni

NP24–NP25

MNP24 — see (2)

R. scissura Interval zone

18

Etoloakarnania

Ag. Georgios

NP24–NP25

for Oligocene see (3) — MNP25a,b for Oligocene see (3) — MNP25a,b

MNP24 — see (2)

R. scissura Interval zone

Gavrovo flysch 19 Etoloakarnania

Riza

NP19–20

–

MNP19–MNP20

–

20

Etoloakarnania

Pitsineika

NP22

–

MNP22

21

Etoloakarnania

Makrivouni

NP24

–

MNP24

22

Etoloakarnania

Koutsoheri

NP23–NP24

–

MNP23–MNP24

23

Etoloakarnania

Trikorfo

NP23–NP24

–

MNP23–MNP24

24

Etoloakarnania

Ano Vassiliki

NP23–NP24

–

MNP23–MNP24

25

Etoloakarnania

Douneika

NP23–NP24

–

MNP23–MNP24

26

Etoloakarnania

Potamoula

NP23–NP24

–

MNP23–MNP24

27

Etoloakarnania

Kastraki

NP23–NP24

–

MNP23–MNP24

28

Messinia/Filiatra

Mali West

NP22

–

MNP22

29

Messinia/Filiatra

Ag. Varvara

NP23–NP24

–

MNP23–MNP24

30

Messinia/Filiatra

Plati

NP23–NP24

–

MNP23–MNP24

31

Messinia/Filiatra

Mali East

NP24

–

MNP24

Messinia/Filiatra

Stavros

NP24

–

MNP24

Messinia/Filiatra

Ag. Mavra

NP24

–

MNP24

Kissel et al. (1985) Triantaphyllou in Sotiropoulos et al. (2008) Triantaphyllou in Sotiropoulos et al. (2008) Triantaphyllou (present study) Triantaphyllou in Sotiropoulos et al. (2008) Triantaphyllou in Sotiropoulos et al. (2008) Triantaphyllou in Sotiropoulos et al. (2008) Triantaphyllou in Sotiropoulos et al. (2008)

Triantaphyllou al. (2008) E. formosa–R. umbilicus/R. hillae Interval Triantaphyllou zone al. (2008) R. scissura Interval zone Triantaphyllou al. (2008) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2008) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2008) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2008) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2008) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2008) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2008) E. formosa–R. umbilicus/R. hillae Interval Triantaphyllou zone al. (2010) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2010) C. abisectus Partial‐range zone–R. Triantaphyllou scissura Interval zone al. (2010) R. scissura Interval zone Triantaphyllou al. (2010) R. scissura Interval zone Triantaphyllou al. (2010) R. scissura Interval zone Triantaphyllou al. (2010)

in Sotiropoulos et in Sotiropoulos et in Sotiropoulos et in Sotiropoulos et in Sotiropoulos et in Sotiropoulos et in Sotiropoulos et in Sotiropoulos et in Sotiropoulos et in Pavlopoulos et in Pavlopoulos et

M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

MNP24 — see (2)

NP19/20

for Oligocene see (3) — MNP25a,b –

E. formosa Partial-range zone–I. fusa/ E. formosa Concurrent-range zone R. scissura Interval zone

in Pavlopoulos et in Pavlopoulos et in Pavlopoulos et in Pavlopoulos et

239

Ref. number (*)

Nannofossil assemblages-bioevents in the original reference study

Nannofossil biozone Martini (1971)/correlation to other biozonal schemes

NP16 12/1 12/2 12/3

D. bifax, Ch. modestus (restricted to NP16), N. cristata, Ch. solitus, Ch. expansus, Ch. grandis, D. barbadiensis, D. saipanensis, D. nodosus

NP16

NP17 Klematia Paramythia/section in the eastern part of the Botzara syncline 11/1 11/2

NP19–20 13 19 NP21 1 2 3 4 5 5 4 6 6

10/1 10/2

11/1 11/2

Ellinikon

Critical evaluation (Triantaphyllou, present study)

Abundant D. bisectus and C. pelagicus, common R. hillae, Ch. grandis, Ch. consuetus, E. formosa, D. barbadiensis, D. saipanensis Dominance of D. bisectus and D. scrippsae. D. barbadiensis, D. saipanensis, D. tanii nodifer, R. umbilicus, are reported as common. Few R. oamauruensis. The FO of E. subdisticha (=Clausicoccus subdistichus) marks the upper boundary of the zone. The lower boundary is approximated by the FOs of D. tanii nodifer, D. bisectus, D. scrippsae, H. compacta. D. barbadiensis, D. saipanensis, R. umbilicus, R. hillae, Ch. consuetus, R. dictyoda, T. gammation are reported as common.

NP17–20

Presence of D. barbadiensis, D. saipanensis, D. tanii. Common D. barbadiensis, D. saipanensis, D. tanii.

NP19/20 NP19/20

I. recurvus, E. formosa, R. umbilicus, absence of disc-shaped discoasters and I. fusa Common E. formosa, few R. umbilicus, rare Clausicoccus spp. (sensu Bellas, 1997) Few to rare E. formosa, few to common R. umbilicus, rare R. hillae, rare I. fusa and I. recurvus E. formosa, I. recurvus, R. hillae, R. umbilicus, absence of disc-shaped discoasterids and I. fusa. E. formosa, very rare I. recurvus, few R. umbilicus Few R. umbilicus, R. hillae, Rhabdosphaera spp. Presence of I. fusa, absence of E. formosa Common E. formosa, rare R. umbilicus, common Clausicoccus spp., presence of I. recurvus. Absence of I. fusa and disc-shaped discoasters Few to common E. formosa, I. recurvus, R. hillae, R. umbilicus, absence of disc-shaped discoasters and I. fusa. Few to common E. formosa, I. recurvus, R. hillae, R. umbilicus, I. fusa, first representatives of S. distentus, small forms of C. abisectus, sharp decline of the Clausicoccus group (corresponding to C. subdistichus acme-end, of Bukry, 1973) E. subdisticha, D. bisectus, C. pelagicus, C. floridanus, R. dictyoda, S. moriformis, R. umbilicus, D. deflandrei, D. nodifer, S. pseudoradians. Because of the uncertainty of reworking the LO of E. formosa could not be used as a reliable datum for the upper boundary of this biozone. Instead the FOs of C. abisectus, D. adamanteus, D. calculosus have been used. The lower boundary is defined by the FO of E. subdisticha (= Clausicoccus subdistichus)

NP21/Ericsonia formosa Partial-range zone (Bellas, 1997)

D. saipanensis and D. barbadiensis have their LO at the top of NP20, D. bisectus (=R. bisecta) has its FO within NP17, D. scrippsae has a stratigraphic range NP16–NP25; in addition R. umbilicus spans NP16–NP21 biostratigraphic interval (Perch-Nielsen, 1985). M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

12/1 12/2 12/3

240

Table 3 Presentation and critical evaluation of the available calcareous nannofossil biostratigraphic data for the Ionian and Gavrovo flysch deposits. (*) Numbered sections are presented in Fig. 1. Note that Reticulofenestra scissura, Reticulofenestra bisecta and Dictyococcites bisectus are considered as synonyms. Ericsonia subdisticha and Clausicoccus subdistichus are considered as synonyms.

NP21/Ilselithina fusa/Ericsonia formosa Concurrent-range zone NP21/Ilselithina fusa/Ericsonia formosa Concurrent-range zone (Bellas, 1997) NP21/Ericsonia formosa Partial-range zone (Bellas, 1997) NP21/Ericsonia formosa Partial-range zone (Bellas, 1997) NP21/Ilselithina fusa/Ericsonia formosa Concurrent-range zone (Bellas, 1997) NP21/Ericsonia formosa Partial-range zone (sensu Bellas, 1997) NP21/Ericsonia formosa Partial-range zone (Bellas, 1997) NP21/Ilselithina fusa/Ericsonia formosa Concurrent-range zone (Bellas, 1997)

The author uses the small C. abisectus forms as subordinate and auxiliary elements of this zone; the classical range of the species is NP23–NN1 (e.g. Bellas, 1997).

NP21

The use of the FO of C. abisectus, D. adamanteus, D. calculosus is not particularly valid for the definition of the upper boundary of NP21, since C. abisectus appears in NP23 (Bellas, 1997; Martini and Muller, 1986; Varol, 1998), and D. adamanteus, D. calculosus appear above the NP22/NP23 boundary (Perch-Nielsen, 1985).

NP21

E. subdisticha spans the NP20–NP21 biostratigraphic interval (Perch-Nielsen, 1985). No acme of this species is reported by the authors, which is typical for the basal Oligocene NP21 (C. subdistichus acme; Berggren et al., 1995).

NP21

Dodoni 19

Common R. umbilicus, absence of Eocene discoasterids

NP22 2

Absence of E. formosa, rare to absent R. umbilicus, few H. compacta

5

Very rare E. formosa, few R. umbilicus, R. hillae

3

Few to rare E. formosa, rare R. hillae and R. umbilicus. FO of C. abisectus, presence of I. fusa Presence of I. recurvus, R. hillae, R. umbilicus, I. fusa

6 19 20

NP21 NP21–22

NP22/Ericsonia formosa–Reticulofenestra umbilicus/R. hillae Interval zone (Bellas, 1997) NP22/Ericsonia formosa–R. umbilicus/R. hillae Interval zone (Bellas, 1997) NP22/Ericsonia formosa–Reticulofenestra umbilicus/R. hillae Interval zone (Bellas, 1997) NP22/Ericsonia formosa–Reticulofenestra umbilicus/R. hillae Interval zone (Bellas, 1997) NP21–22 NP22

28

Common R. umbilicus, absence of Eocene discoasterids Common to present R. hillae, R. umbilicus, C. floridanus, S. predistentus S. predistentus, R. umbilicus and R. hillae

NP23 2

S. predistentus, C. abisectus, H. compacta

NP23/C. abisectus Partial-range zone (Bellas, 1997)

3 5

Absence of R. umbilicus, R. hillae H. recta, S. distentus, S. predistentus

7

Common to abundant Cy. floridanus, C. pelagicus, few R. scissura (=D. bisectus), rare to few S. distentus and S. predistentus, scarce D. deflandrei Common C. floridanus, presence of S. distentus, S. predistentus, absence of R. umbilicus Common C. floridanus, presence of S. distentus, S. predistentus, absence of R. umbilicus Rare C. floridanus, C. abisectus, R. bisecta, S. predistentus and S. distentus Presence of C. abisectus, common R. bisecta, common to rare S. predistentus, rare S. distentus Rare C. abisectus, common R. bisecta, rare S. predistentus, S. distentus Rare C. abisectus, common R. bisecta, rare S. predistentus, S. distentus Common R. bisecta, rare S. predistentus, presence of S. distentus common R. bisecta, rare S. predistentus, S. distentus S. predistentus, S. distentus, R. bisecta, H. compacta S. predistentus, S. distentus S. predistentus, S. distentus, C. abisectus S. predistentus, S. distentus S. predistentus, S. distentus, C. abisectus, H. recta

NP23/Cyclicargolithus abisectus Partial range zone (Bellas, 1997) NP23/Cyclicargolithus abisectus Partial range zone (Bellas, 1997) Upper NP23/upper Rhabdosphaera spp. Interval zone (Bellas, 1997)

15 19 22 23 24 25 27 Ag. Mavra 29 30 Stavros 31 NP24 2 5

7

10/1, 10/2

S. distentus, S. ciperoensis. Few to common C. abisectus, common R. scissura (= D. bisectus), S. cf. ciperoensis, S. cf. dissimilis, presence of poorly preserved and rare S. distentus C. abisectus, few to common R. scissura (= D. bisectus), common S. distentus and S. predistentus, very rare S. cf. ciperoensis, few H. recta, rare to few H. compacta. FO of C. abisectus (indicating the lower boundary of the zone), D. adamanteus, D. calculosus. For the upper boundary the LO of D. bisectus and S. pseudoradians and/or the FO of S. conicus and H. scissura have been used.

The LCO (Last Common Occurrence) of S. predistentus that is used for the upper boundary of Bellas Partial-range zone (1997) is difficult to recognise when sphenoliths are very rare in the assemblages. Absence of the index species S. distentus.

NP23 NP23 NP23 NP23 NP23 NP23 NP23 NP23 NP23 NP23 NP23 NP23 NP23

M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

14

NP22

NP24 Upper NP24/Reticulofenestra scissura Interval zone

Upper NP24/Reticulofenestra scissura Interval zone

NP24–25

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(continued on next page)

242

Table 3 (continued) Ref. number (*)

Nannofossil assemblages-bioevents in the original reference study

Nannofossil biozone Martini (1971)/correlation to other biozonal schemes

Critical evaluation (Triantaphyllou, present study)

Klematia Paramythia/section in the eastern part of the Botzara syncline

FO of C. abisectus (indicating the lower boundary of the zone), D. adamanteus, D. calculosus, H. recta. For the upper boundary the FO of S. conicus and H. scissura have been used.

NP24–25

This biozone is not well established. Concerning the basal boundary, C. abisectus is present since NP23 (e.g. Martini and Muller, 1986). No index species such as S. distentus and S. ciperoensis have been detected. Concerning the upper boundary, S. conicus may appear since the Late Oligocene (NP25, Bellas, 1997; Perch-Nielsen, 1985).

11/1, 11/2

H. recta, H. compacta, D. calculosus, C. abisectus, C. floridanus, D. bisectus, D. adamanteus, D. deflandrei.

NP24–25

Botzara Akarnania Erikoussa

14 15 17 18 21 22 23 24 25 26 27 Ag. Mavra 29 30 Stavros 31 NP25 2 5

5 8

S. ciperoensis, R. bisecta Few to common C. abisectus, common R. scissura (=D. abisectus), S. cf. ciperoensis, S. cf. dissimilis, presence of poorly preserved and rare S. distentus, rare S. delphix. FCO of S. delphix. Few to common C. abisectus, R. scissura (=D. abisectus) and D. deflandrei, rarely present I. fusa, scarcely present H. obliqua, H. recta. Few to rare S. conicus, sporadically few S. delphix and presence of S. ciperoensis. Presence of T. carinatus, T. cf. milowii, absence of S. predistentus.

NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24 NP24

NP25/R. scissura Interval zone Lower NP25/R. scissura Interval zone

NP25/S. delphix Abundance subzone (upper R. scissura Interval zone) NP25/S. delphix Abundance subzone (upper R. scissura Interval zone)

The NP24 biozone is not safely determined as the assemblage lacks of the index species S. distentus and S. ciperoensis. The contact between clastic (flysch) sediments and the underlying carbonates has not been recorded. M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

16

Coccolithus pelagicus, C. eopelagicus, Cy. floridanus, Cy. abisectus, S. moriformis, D. bisectus, D. scrippsae, H. compacta, H. intermedia, H. euphratis, Pontosphaera multipora, Reticulofenestra retiformis, Helicosphaera kamptneri, D. deflandrei, Discoaster cf. calculosus, Transversopontis sp. indet. Common R. bisecta, rare S. predistentus, presence of S. distentus, S. ciperoensis and H. recta. Common R. bisecta, rare S. predistentus, presence of C. abisectus, S. distentus, S. ciperoensis and H. recta. Rare S. predistentus, C. abisectus, presence of S. distentus, S. ciperoensis and H. recta. Rare S. predistentus, C. abisectus, S. ciperoensis, presence of S. distentus and H. recta. Common to present C. abisectus, S. predistentus, rare to present S. distentus, S. ciperoensis, H. recta Rare C. abisectus, common to rare S. predistentus, S. ciperoensis, presence of S. distentus. Present to rare C. abisectus, S. predistentus, S. ciperoensis, S. distentus, H. recta Rare S. distentus, H. recta, presence of S. ciperoensis. Rare S. predistentus, presence of S. distentus, S. ciperoensis Common C. abisectus, S. predistentus, rare to present S. distentus, S. ciperoensis common to present C. abisectus, S. predistentus, S. distentus, S. ciperoensis Rare C. abisectus, rare to present S. predistentus, S. distentus, S. ciperoensis. S. distentus, S. ciperoensis S. distentus, S. ciperoensis S. distentus, S. ciperoensis S. distentus, S. ciperoensis C. abisectus, S. ciperoensis

NP24, NP24–NP25 NP24–NP25 NP24–NN1

9

Erikoussa

Othonoi Mathraki 17 18

Anacharavi 2 9 9

NN1–NN4 10/1, 10/2 11/1, 11/2

Klematia Paramythia/section in the eastern part of the Botzara syncline 12/1, 12/2, 12/3

Erikoussa

Erikoussa

Triquetrorhabdulus spp., S. delphix, S. conicus, sporadic H. recta, R. scissura above its LCO, common D. deflandrei, absence of D. druggii, I. fusa only at the bottom S. conicus C. abisectus (no acme), H. cf. carteri, above the LCO of R. scissura (=R. bisecta) LO of I. fusa just above LCO of R. scissura, marked acme of C. abisectus Including an acme of Triquetrorhabdulus spp. and D. deflandrei, the LO of S. delphix and S. capricornatus. The acme end of H. euphratis is present towards the top of the interval.

NP25/S. delphix Abundance subzone (upper R. scissura Interval zone)

NP25–NN3

NP25–NN1 NP25–NN1 NP25 NP25

NN1/Triquetrorhabdulus spp. Partial-range subzone

NN1/S. conicus Interval subzone NN1/Triquetrorhabdulus spp. Partial-range subzone NN1/Triquetrorhabdulus spp. Partial-range subzone NN1/S. conicus Interval subzone

C. pelagicus, S. moriformis, C. floridanus, H. recta, S. conicus, H. scissura, S. belemnos S. conicus, S. belemnos, H. scissura, D. calculosus, C. abisectus, C. pelagicus, C. miopelagicus

NN1–2

S. conicus, H. scissura, H. intermedia, C. pelagicus, C. miopelagicus, C. pelagicus, C. abisectus, D. deflandrei, S. moriformis

NN1–3

S. conicus, C. floridanus, C. abisectus. Also common D. deflandrei, H. intermedia, D. calculosus, D. adamanteus, D. bisectus, C. miopelagicus, C. pelagicus. Cy. abisectus, Cy. floridanus, S. moriformis, S. compactus, S. conicus, Bicolumnus ovatus, C. pelagicus, C. miopelagicus, Helicosphaera granulata, H. kamptneri, Discoaster sp., D. deflandrei, D. calculosus, S. dissimilis, R. daviesi, P. multipora, S. calyculus, Pyrocyclus orangensis, D. adamanteus, H. intermedia, R. minuta, small-sized Reticulofenestra, Helicosphaera californiana, B. bigelowii, Micrantholithus spp., H. paleocarteri, S. belemnos (NN3 only), C. eopelagicus, S. heteromorphus, S. belemnos, H. elongata, H. carteri, H. euphratis, H. ampliaperta, C. leptoporus Small-sized Reticulofenestra, S. disbelemnos, C. pelagicus, Cy. abisectus, Cy. floridanus, H. kamptneri, H. carteri hyalina, R. minuta, D. adamanteus, C. miopelagicus, C. eopelagicus, R. daviesi, S. dissimilis, D. deflandrei, C. leptoporus, P. multipora

NN1–3

NN1–3

The Miocene (younger than Aquitanian) deposits of the Botzara syncline have been considered by several authors (IGRS–IFP, 1966; Papanikolaou, 1986; Richter, 1978), as molassic deposits. To be considered that all the sites sampled in Radhovizi Formation in the Botzara syncline by Kissel et al. (1985) have provided a biostratigraphic assignment to nannofossil NP25 or NP24–25 biozones. These authors provided Oligocene age for this formation, which was formerly considered as Aquitanian (Kissel et al., 1985, p.193). The biostratigraphic correlation of biozones NN2–NN3 is rather ambiguous, since no index species such as S. belemnos, S. dissimilis and D. druggii are present.

M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

NN1 Anacharavi

Few to common C. abisectus, S. conicus, S. delphix, H. recta absence of S. predistentus, presence of I. fusa, Triquetrorhabdulus spp., Z. bijucatus. Top defined by LCO of R. scissura (=R. bisecta). The first acme of S. delphix is recorded towards the top. C. pelagicus, C. miopelagicus, Cy. abisectus, Cy. floridanus, H. compacta, H. euphratis, S. compactus, S. moriformis, S. conicus, S. calyculus, Pontosphaera multipora, D. calculosus, D. bisectus, D. scrippsae, C. eopelagicus, R. daviesi, Pyrocyclus orangensis, H. kamptneri, R. minuta, S. compactus, D. druggii (NN2–3), H. paleocarteri. C. pelagicus, C. eopelagicus, Cy. floridanus, Cy. abisectus, D. scrippsae, D. bisectus, S. moriformis, D. adamanteus. C. pelagicus, Cy. floridanus, Cy. abisectus, D. scrippsae, S. moriformis, D. deflandrei. Rare C. abisectus, common S. ciperoensis, absence of S. predistentus and S. distentus Presence S. ciperoensis, C. abisectus, H. recta, absence of S. predistentus and S. distentus

NN1–4

NN1–5

Biozone NN5 is not justified by the assemblage, absence of D. exilis, S. heteromorphus, H. walbersdorfensis.

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244

Table 3 (continued) Nannofossil assemblages-bioevents in the original reference study

Nannofossil biozone Martini (1971)/correlation to other biozonal schemes

Critical evaluation (Triantaphyllou, present study)

Othonoi

C. pelagicus, C. eopelagicus, Cy. floridanus, Cy. abisectus, D. scrippsae, Helicosphaera elongata, H. perch-nielseniae, H. scissura, S. moriformis, D. adamanteus

NN1–3

These biozones are not well justified by the assemblage. Index species are absent and H. elongata ranges between NN1–NN6 (Aubry, 1984–1990).

S. conicus, S. belemnos, H. scissura, C. floridanus, C. pelagicus, S. moriformis

NN3

The Miocene (younger than Aquitanian) deposits of the Botzara syncline have been considered by several authors (IGRS–IFP, 1966; Papanikolaou, 1986; Richter, 1978), as molassic deposits. To be considered that all the sites sampled in Radhovizi Formation in the Botzara syncline by Kissel et al. (1985) have provided a biostratigraphic assignment to nannofossil NP25 or NP24–25 biozones. These authors provided Oligocene age for this formation, which was formerly considered as Aquitanian (Kissel et al., 1985, p.193).

D. kugleri, D. deflandrei, D. variabilis common D. kugleri, D. variabilis, D. exilis, C. pelagicus, C. miopelagicus, abundant R. pseudoumbilicus, C. abisectus

NN7 NN7

The Miocene (younger than Aquitanian) deposits of the Botzara syncline have been considered by several authors (IGRS–IFP, 1966; Papanikolaou, 1986; Richter, 1978), as molassic deposits. To be considered that all the sites sampled in Radhovizi Formation in the Botzara syncline by Kissel et al. (1985) have provided a biostratigraphic assignment to nannofossil NP25 or NP24–25 biozones. These authors provided Oligocene age for this formation which was formerly considered as Aquitanian (Kissel et al., 1985, p.193).

Common D. pansus, D. variabilis

? NN8–12

D. exilis, D. bollii, D. deflandrei, D. druggii, D. cf. kugleri, C. macintyrei, C. tropicus, C. pelagicus, Cy. floridanus, Cy. abisectus, Pontosphaera spp., D. scrippsae, S. moriformis, H. kamptneri

NN8–9

The reference study considers this biostratigraphic correlation questionable. In any case the Miocene (younger than Aquitanian) deposits of the Botzara syncline have been considered by several authors (IGRS–IFP, 1966; Papanikolaou, 1986; Richter, 1978), as molassic deposits. To be considered that all the sites sampled in Radhovizi Formation in the Botzara syncline by Kissel et al. (1985) have provided a biostratigraphic assignment to nannofossil NP25 or NP24–25 biozones. These authors provided Oligocene age for this formation, which was formerly considered as Aquitanian (Kissel et al., 1985, p.193). Lack of index species, e.g. D. calcaris, D. hamatus. In the assemblage D. druggii (NN2–3) should be considered as reworked. According to Aubry (1984–1990), D. bollii ranges between NN9–NN10 and D. exilis between NN5–NN7; their discontinuous occurrence may overlap in NN8 (Perch-Nielsen, 1985).

NN3 10/1, 10/2

NN7 10/1, 10/2 11/1, 11/2

NN8 10/1, 10/2

Mathraki

M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

Ref. number (*)

M.V. Triantaphyllou / Tectonophysics 595–596 (2013) 235–249

245

Fig. 2. Stratigraphic range for Ionian and Gavrovo flysch synthetic stratigraphic successions in the External Hellenides Carbonate Platform.

Oligocene–Middle Miocene ?NP24/NP25–NN4/?NN8 biozones (Tables 2 and 3). These results are very interesting; however we treat them with caution, as they prove to bear some biostratigraphic uncertainties (see Table 3). Moreover the analysed sets of samples do not have a clear stratigraphic order, not proving to come from an uppermost Ionian unit sequence with a justified stratigraphic contact between the clastic deposits and the underlying carbonates. Stoykova et al. (2003) suggested that the deposits of Pindos foreland in the middle Ionian unit/Klematia–Paramythia Basin (Fig. 1; Tables 2 and 3) range from the Middle Eocene to Middle Miocene. Nannofossil biozone NP16 was determined in the Dragopsa syncline at the eastern margin of the basin (section C–C′, in Stoykova et al., 2003), (ref. 12/13, Tables 2 and 3) on the basis of the co-occurrence of rare Discoaster bifax and Chiasmolithus modestus, both being restricted to NP16 (e.g. Perch-Nielsen, 1985), and common Nannotetrina cristata, Chiasmolithus solitus, Chiasmolithus expansus, Chiasmolithus grandis,

Discoaster barbadiensis, Discoaster saipanensis, Discoaster binodosus. In addition, Stoykova et al. (2003) determined the biozones NP17– 20 without further precision, at three locations in the Klematia– Paramythia Basin. At the eastern part of the Botzara syncline they report abundant D. bisectus and Coccolithus pelagicus, common Reticulofenestra hillae, C. grandis, Chiasmolithus consuetus, E. formosa, D. barbadiensis, D. saipanensis. The western part of the Botzara syncline (section B–B′), (ref. 11/1-2, Tables 2 and 3) is characterised by the dominance of D. bisectus and D. scrippsae. D. barbadiensis, D. saipanensis, D. tanii nodifer, R. umbilicus are reported as common in addition to few Reticulofenestra oamauruensis. According to the authors the LO of E. subdisticha (synonym Clausicoccus subdistichus) marks the upper boundary of the reported NP17–20 biozonal interval. Finally in the Dragopsa syncline (section C–C′), (ref. 12/1-3, Tables 2 and 3) at the eastern margin of the basin, they document the lower boundary of NP17 by the LOs of D. tanii nodifer, D. bisectus, D. scrippsae and

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H. compacta. D. barbadiensis (actually the First Appearance Datum (FAD) of the species is in mid NP16), D. saipanensis, R. umbilicus, R. hillae, R. dictyoda, C. consuetus, Toweius gammation are reported as common in the whole NP17–20 interval. Within the Oligocene interval, biozone NP21 has been reported (Stoykova et al., 2003) based on the occurrence of E. subdisticha and biozones NP24–25 were determined by Helicosphaera recta, Discoaster calculosus and C. abisectus. Early Miocene (NN1, NN2–3) is based on the presence of Sphenolithus conicus, S. belemnos, and Middle Miocene has been considered at least within NN7 (below the Highest Occurrence (HO) of Discoaster kugleri). However, the Miocene (younger than Aquitanian) deposits of the Botzara syncline have been proved by several authors lying unconformably on the Oligocene flysch (IGRS– IFP, 1966; Papanikolaou, 1986; Richter, 1978), therefore considered as molassic deposits. Moreover it must be noted that all sites sampled in Radhovizi Formation/Botzara syncline by Kissel et al. (1985), have provided a biostratigraphic assignment to nannofossil NP25 or NP24– 25 biozones. In addition the planktonic foraminiferal fauna from Botsara (van Hinsbergen et al., 2005a) provided conclusive evidence for an early Oligocene age for the Ionian flysch and an Aquitanian to late Burdigalian age for the entire Klematia–Paramythia Basin fill, in contrast with the conclusion reached by Avramidis et al. (2002) and Stoykova et al. (2003). Apparently the existing data do not favour any Middle Miocene age for the top of the flysch sequence in the middle Ionian unit, on the contrary the uppermost flysch deposits (flysch supérieur/os formation) have been reported as Aquitanian in age (IGRS–IFP, 1966). Thus, due to the mentioned uncertainties and the lack of our own evidence, we are evaluating for the purpose of the current review study only the available nannofossil data for the base of the flysch sequence concerning the Klematia–Paramythia Basin (Tables 2 and 3). A latest Eocene–Late Oligocene age has been provided for the basal flysch deposits in Etoloakarnania region (internal Ionian), based on calcareous nannofossil biostratigraphy (Triantaphyllou in Sotiropoulos et al., 2003). A series of sections (Fig. 1; Table 2) were studied in the entire Etoloakarnania region, displaying the detailed stratigraphic range of Ionian flysch in the area. Triantaphyllou in Sotiropoulos et al. (2008) refined the biostratigraphic assignment of both the transitional beds and the base of the flysch sequence to calcareous nannofossil biozones NP19–20. The change from carbonate to clastic deposits is transitional, the flysch sequence overlie conformably the carbonate sequences of the Ionian unit (e.g. Ag. Nikolaos section; ref. 13, Tables 2 and 3). It consists of alternations of limestones, marly limestones and marls, bearing the nannofossil species D. barbadiensis, D. saipanensis and D. tanii. In Kato Retsina section (ref. 14, Tables 2 and 3) flysch deposits rest directly on the pelagic limestones due to phenomena of syn-sedimentary tectonism (Papanikolaou and Lekkas, 2001, 2008). Triantaphyllou in Sotiropoulos et al. (2008) and Triantaphyllou (present study), provide a biostratigraphic assignment of these deposits with biozone NP23 (common Cyclicargolithus floridanus, presence of S. distentus, S. predistentus, absence of R. umbilicus). The presence of C. floridanus, S. distentus and S. predistentus together with the absence of R. umbilicus allows the recognition of NP23 biozone in the Ionian flysch deposits of the lower part of Kato Retsina and Agrilia sections (ref. 14, 15, Tables 2 and 3). The occurrence of S. ciperoensis and C. abisectus in the uppermost part of both sections implies the presence of biozone NP24. Kalidona section (ref. 16, Tables 2 and 3) and the lower parts of Ano Koudouni and Aghios Georgios sections (ref. 17, 18, Tables 2 and 3) display deposits assigned to biozone NP24. The youngest flysch sediments in the internal Ionian basin at Etoloakarnania region have been found at the footwall of Gavrovo thrust (e.g. Ano Koudouni and Aghios Georgios sections). They belong to nannofossil biozone NP25 (common presence of S. ciperoensis in the overlying sandy–pelitic sequence, along with the absence of S. predistentus and S. distentus).

3.2. Gavrovo flysch The calcareous nannofossil analysis at the base of the transitional beds between Gavrovo flysch and the underlying carbonate sequence observed at the south-eastern end of Klokova Mountain (Riza section; ref. 19, Tables 2 and 3), indicates the common presence of Discoaster deflandrei, D. tanii and D. barbadiensis, enabling the biostratigraphic correlation with the uppermost Eocene NP19–20 nannofossil biozones. The presence of the Lower Oligocene nannofossil biozones NP21–22 is recognised in the overlying marly alternations, on the presence of R. umbilicus and absence of Eocene discoasterids. Additionally the calcareous nannofossil species C. floridanus, C. abisectus, R. bisecta, S. predistentus, S. distentus, recognised in the upper flysch deposits of the same section, are characteristic for the NP23 biozone. Biozone NP22 has also been determined in the deposits of Pitsineika section (ref. 20, Tables 2 and 3) by the co-occurrence of the nannofossil species R. hillae, R. umbilicus, C. floridanus, S. predistentus. The presence of S. distentus, S. predistentus, S. ciperoensis, C. abisectus, C. floridanus, R. bisecta correlates the deposits of Makrivouni section (ref. 21, Tables 2 and 3) with the biozone NP24. Biozones NP23 and NP24 were recognised in Koutsoheri, Trikorfo, Ano Vassiliki, Douneika, Potamoula and Kastraki sections (ref. 22–27, Tables 2 and 3). The lower Gavrovo flysch sequence in SW Peloponnesus/Messinia area (Fig. 1; Tables 2 and 3), has been indicated by Triantaphyllou in Pavlopoulos et al. (2010) as of earliest Oligocene age (Mali West section, ref. 28, Tables 2 and 3; biozone NP22 detected by the co-occurrence of S. predistentus, R. umbilica and R. hillae combined with the absence of S. distentus and S. ciperoensis). The rest of the studied flysch sequences (Ag. Mavra, Ag. Varvara, Plati, Stavros sections; ref. 29, 30, Tables 2 and 3), is of Oligocene age; (biozone NP23: co-occurrence of S. predistentus, S. distentus, R. bisecta, H. compacta; biozone NP24: co‐ occurrence of S. distentus and S. ciperoensis). Similar to Etoloakarnania region (Sotiropoulos et al., 2003), the end of the flysch sedimentation in the Gavrovo foreland basin at southwestern Peloponnesus took place in Late Oligocene (Mali East section, ref. 31, Tables 2 and 3; NP24 biozone), accordingly to the age provided for the younger sediments at the footwall of the Pindos thrust (Pavlopoulos et al., 2010). 4. Discussion 4.1. Dating of Ionian and Gavrovo flysch deposits Concerning the Ionian flysch deposits, the data from the internal Ionian (Etoloakarnania region; Triantaphyllou in Sotiropoulos et al., 2008) suggest that the onset of clastic sedimentation (base of transitional beds) can be placed between 36.2 and 34.4 Ma (mean 35; NP19–20) in the latest Eocene. The basal Ionian flysch beds are dated in between 32.3 and 29.9 Ma (mean 31), in places where flysch rests directly on the limestone due to phenomena of syn-sedimentary tectonism. The younger latest Oligocene age of the flysch deposits in the internal Ionian has been determined in front of Gavrovo thrust, between 27.2 and 23.2 Ma (mean 25; NP25). In accordance to the ages provided from the Etoloakarnania region, the Ionian flysch sedimentation in the NW Peloponnesus (internal Ionian) took place between latest Eocene and Late Oligocene (Kamberis et al., 2005). Similar ages have been provided from the Epirus/Arta (internal Ionian), Prevesa (outer part of middle Ionian), Parga regions (external Ionian), (Bellas, 1997); the basal clastic sediments in the area have been dated between 34.4 and 33.0 Ma (mean 34), in the latest Eocene– Early Oligocene (NP21). A Middle Eocene age has been provided for the basal flysch deposits in Epirus/Botzara region, middle Ionian (NP16/42.6–39.7 Ma (mean 41); Stoykova et al., 2003). The youngest flysch deposits have been spotted in Parga area and Corfu Island, external Ionian (Bellas, 1997), reaching a Late Oligoceneearliest Miocene age of 27.2–22.8 Ma (mean 25 Ma; NP25–NN1) that specifies the time of the Gavrovo nappe emplacement on the Ionian unit. Overall the mean ages

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can be estimated for the base [~ 34–35 Ma (external/internal Ionian), ~ 41 Ma (middle Ionian)] and the top (~ 25 Ma) of the Ionian flysch respectively, providing an average duration of at least 11 and 16 Myr for the flysch sedimentation in the external/internal and middle Ionian unit respectively (Fig. 2). Gavrovo flysch deposition in Etoloakarnania region started between 36.2 and 34.4 Ma (mean 35) in the latest Eocene (NP19–20), whereas in SW Peloponnesus/Messinia the basal flysch deposits have been estimated in between 32.9 and 32.4 Ma (mean 33, NP22). It lasted till 30.0–27.2 Ma (mean 29) both in Etoloakarnania (NP24; Triantaphyllou in Sotiropoulos et al., 2008) and Peloponnesus/Messinia areas (NP24; Triantaphyllou in Pavlopoulos et al., 2010). The relative emplacement of Pindos nappe on the Gavrovo unit is estimated within NP24 biozone (mean 29 Ma) as supported by the nannofossil analysis results of the youngest Gavrovo flysch deposits in front of Pindos thrust (Triantaphyllou in Sotiropoulos et al., 2008). The mean ages can be estimated for the base [~35 Ma (Etoloakarnania), ~33 Ma (SW Peloponnesus)] and the top (~29 Ma) of the Gavrovo flysch respectively, provide an average duration (34–29 Ma) of approximately 5 Myr for the flysch sedimentation (Fig. 2), which is considerably shorter in respect to what has been documented for the Ionian unit at the External Hellenides Platform. 4.2. Implications on the age and duration of flysch sedimentation in Ionian and Gavrovo geotectonic units Flysch sedimentation in the two units displays distinct differences in the onset, end, duration and thickness. The mean duration of approximately 5 Myr for the Gavrovo, and 11–16 Myr estimated for the Ionian flysch sedimentation respectively, suggests the time interval of underthrusting of both units during the subduction of the entire External Hellenides Carbonate Platform, with the shallow Gavrovo Platform being underthrusted for a considerably shorter time interval. Thickness of flysch deposits in the Ionian unit varies significantly between its different parts. The internal Ionian is featured by thick flysch successions; more than 3 km (e.g. IGRS–IFP, 1966), whereas the external Ionian displays flysch deposits of approx. 2 km thick (e.g. Richter, 1976a). In contrast the middle Ionian shows significantly thinner flysch deposits (0.6–1.7 km; e.g. Avramidis et al., 2000; Richter, 1974). During Earliest Oligocene (mean 33.5 Ma; NP21–22) Ionian and Gavrovo foreland basins showed features of early evolution stages when the rate of subsidence is higher than the rate of sediment supply, representing under filled basins with restricted accumulation of sediments, mainly composed of clays and silts (Papanikolaou and Lekkas, 2008; Sotiropoulos et al., 2008). The presence of thick flysch deposits accumulated in both basins during Early Oligocene (mean 31 Ma; NP23), indicates an increasing rate of sediment supply in a distal depositional environment of the Ionian basin and a more proximal one in Gavrovo, although evidence of gradual deepening and deep water facies have been observed in its internal part (Sotiropoulos et al., 2008). At the interval between the upper part of Early Oligocene and the lower part of Late Oligocene (mean 29 Ma, NP24) the deposition of coarse grained sediments in both basins indicates a shift to shallower depositional environment (Sotiropoulos et al., 2008). Although a remarkable eustatic sea level fall occurs at the base of Late Oligocene (Haq et al., 1987), the above change of the environmental conditions seems to be mostly related to the intense thrust activity in the Gavrovo zone and the westward progradation of the orogenic wedge. As a result, the Gavrovo flysch sequence has undergone a significant tectonic thickening (maximum flysch thickness 4 km; Sotiropoulos et al., 2003) and presents a complicated tectonic structure (Papanikolaou and Lekkas, 2008; Sotiropoulos et al., 2003). The nature of the contact between the flysch and the pre-flysch carbonate sediments obviously affected the type of transition between carbonate and clastic sedimentation (e.g. Papanikolaou and

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Lekkas, 2008). Gradual transition begins simultaneously in both units, consisting of marly and limestone alternations which conformably overly the Ionian and Gavrovo carbonate sequences. However, a differentiation of the depositional environment is inferred in Ionian and Gavrovo basins during the transition to clastic sedimentation. The relatively thick (~35 m) Ionian transitional beds (e.g. Ag. Nikolaos section, ref. 13, Tables 2 and 3), bear an age of 36.2–34.4 Ma (mean 35; NP19– 20) and correspond to outer fan deposits (Sotiropoulos et al., 2008). On the contrary the transition in the Gavrovo basin (e.g. Riza section, ref. 19, Tables 2 and 3) occurs through ~1.5–2 m transitional beds deposited within 1.5 Myr time interval [36.2–34.4 Ma (mean 35; NP19–20) till 34.4–32.5 Ma (mean 33.5; NP21–22)], and represents relatively shallow water depositional conditions (middle fan environment; Sotiropoulos et al., 2008). It is apparent that the transition to clastic sedimentation took place abruptly, or even unconformably (e.g. Papanikolaou and Lekkas, 2008), in the shallow marine – not exceeding 50–100 m depth – carbonate platform of Gavrovo unit, prior to flysch sedimentation. In contrast, in the 1 km deep trench of the Ionian unit the sedimentation between the limestone and the flysch continued without interruption leading to the formation of relatively thick transitional beds at 35 Ma (external/internal Ionian) or 41 Ma (middle Ionian). The up to 7 Myr time difference between the beginning of transition from carbonate to terrigeneous clastic sedimentation at the middle Ionian and Gavrovo units respectively, can be related to the bathymetric difference of the palaeorelief between the two basins. Phenomena of synsedimentary tectonism are reported in the Ionian foreland basin, caused by pre-flysch extensional faulting (Papanikolaou and Lekkas, 2001, 2008). In such places (e.g. Kato Retsina section, ref. 14, Tables 2 and 3) the age of the first flysch deposits laying directly on the carbonate strata has been estimated as 32.4–30 Ma (mean 31; NP23), indicating that pre-flysch extension of the basin related to the entering of the External Carbonate Platform to the subduction zone after 34 Ma (e.g. Royden and Papanikolaou, 2011; Van Hinsbergen et al., 2005b), lasted at least 4 Myr, depending on subduction and sedimentation rates. The evaluation of the age of the basal flysch deposits at the external/internal (34–35 Ma) and middle parts (41 Ma) of the Ionian unit provides evidence for axial symmetry of the basin. This is a remarkable feature concerning a foreland basin that should normally tend to be asymmetrical, with its deepest parts nearest the emplaced thrust sheets. Most probably, synsedimentary tectonism resulted to the function of different subbasins within the Ionian foreland basin, at least after ~40 Ma. A significant differentiation has taken place around Late Eocene within the basin, when a major breakup caused the underthrusting of Mani unit that was apparently acting till then as a subbasin at the external parts of Ionian foreland basin. Mani unit (also known as Plattenkalk unit), with a stratigraphic column similar to that of the Ionian (Thiébault, 1979) and Paxos (Jacobshagen, 1986), is exposed in tectonic windows below the nappes of Arna, Tripolis and Pindos, suggesting a palaeogeographic position between Paxos and Ionian (Papanikolaou, 1986). It has been interpreted as the underthrusted equivalent of the Ionian unit (Bizon and Thiébault, 1974; Jacobshagen, 1986; Kowalczyk and Zügel, 1997) with flysch deposits at the top dated as Early Oligocene (Bizon et al., 1976). Overthrusting of Ionian and Mani units began in late Oligocene time (~25 Ma) and went on through late Miocene time in its most external part where it was emplaced over the Paxos unit (Royden and Papanikolaou, 2011). The overthrusted deepest middle Ionian parts (Botzara) continued to act as a piggy-back basin, filling up with molassic deposits till the Middle Miocene (e.g. Stoykova et al., 2003). 5. Conclusions The onset of clastic sedimentation (base of transitional beds) of the Ionian unit can be placed at ~34–35 Ma (internal/external Ionian) and at ~41 Ma (middle Ionian, Botzara). The top of the Ionian flysch at ~25 Ma constrains the emplacement of Gavrovo nappe. Gavrovo flysch

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deposition started at ~35 Ma (Etoloakarnania) or at ~ 33 Ma (SW Peloponnesus/Messinia) and lasted till ~29 Ma (emplacement of Pindos nappe). The mean duration of approximately 5 Myr for the Gavrovo flysch sedimentation, and 11–16 Myr estimated for flysch sedimentation in the Ionian unit suggests the time interval of underthrusting of both units during the subduction of the entire External Hellenides Carbonate Platform, with the shallow Gavrovo Platform being underthrusted for a considerably shorter time interval. The transition to clastic sedimentation took place abruptly in the shallow marine carbonate platform of Gavrovo unit; in contrast, in the deep trench of the Ionian unit the sedimentation between the limestone and the flysch continued without interruption leading to the formation of tens of metres thick transitional beds. Phenomena of synsedimentary tectonism are also reported, indicating that pre-flysch extension of the Ionian basin lasted at least 4 Myr. 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