Disponible en ligne sur www.sciencedirect.com
Revue de micropaléontologie 51 (2008) 287–308
Original article
Late Miocene ostracod assemblages from eastern Mediterranean coral reef complexes (central Crete, Greece) Les ostracodes marins dans les complexes coralliens du Mioc`ene sup´erieur de la M´editerran´ee orientale (Cr`ete, Gr`ece) Costanza Faranda a , Paola Cipollari a , Domenico Cosentino a , Elsa Gliozzi a,b,∗ , Giorgio Pipponzi a a
Dipartimento di Scienze Geologiche, Universit`a degli Studi Roma Tre, Largo S. Leonardo Murialdo, 1, 00146 Roma, Italy b IGAG, CNR, P.le A. Moro, 5, 00185 Roma, Italy
Abstract Ostracods from ten Late Miocene coral reef complexes built by Siderastrea, Tarbellastrea and Porites, cropping out in the Messara Plain (southern Iraklion basin, central Crete), have been investigated and five assemblages have been recognised, which point to different marine environments: (1) assemblage from the basal sandy silts, dominated by very shallow inner-infralittoral species, such as Cyamocytheridea meniscus, Cyamocytheridea obstipa, Cyamocytheridea dertonensis, Cytheretta semiornata and Nonurocythereis seminulum; (2) assemblage from the coral reef complexes within which Grinioneis haidingeri, Aurila cicatricosa, Cimbaurila diecii, Tenedocythere cruciata, Pokornyella italica and Callistocythere quadrangula are dominant and point to a stable inner-infralittoral environment characterised by warm, quiet and well-oxygenated waters; (3) assemblage from the silts intercalated among the coral reef complexes, mainly characterised by Neomonoceratina laskarevi, Cytheridea acuminata, Phlyctenophora farkasi and Aurila albicans together with Callistocythere spp., Xestoleberis communis and Xestoleberis dispar, which points to a very shallow marine environment rich in aquatic vegetation; (4) assemblage from the upper silts, which records the absolute dominance of Xestoleberis species, reflecting a very shallow and highly-vegetated environment and (5) assemblage from the uppermost silty clays, dominated by Hemicytherura defiorei, Xestoleberis spp. and Palmoconcha dertobrevis, accompanied by Acanthocythereis hystrix, Cytherella scutulum, Bairdoppilata conformis, Semicytherura spp., Krithe sp., Cytheropteron alatum, Bythocypris sp. and Pseudocythere caudata, which suggest deeper marine environments probably located in the outer infralittoral/inner-circalittoral zones. The studied section has been dated by means of calcareous nannoplankton to be not younger than Zone MNN9 (Early Tortonian), which is the biostratigraphical datum recorded in the fine-grained deposits that overlie the coral reef complexes. An age not older than Tortonian can be inferred by the stratigraphical distribution of the recognized ostracods. Thus, the coral reef complexes have been tentatively referred to the Early Tortonian. © 2007 Elsevier Masson SAS. All rights reserved. R´esum´e Dans ce travail, les ostracodes trouv´es dans dix complexes coralliens du Mioc`ene sup´erieur construits par Siderastrea, Tarbellastrea et Porites, localis´es dans la plaine de Messara (zone m´eridionale du bassin de l’Iraklion, Cr`ete centrale) sont e´ tudi´es et illustr´es. Cinq diff´erentes associations caract´eristiques des divers environnements marins ont e´ t´e reconnues par : (1) association des couches silteuses basales, caract´eris´ee par des esp`eces typiques des eaux marines du domaine infralittoral sup´erieur, parmi lesquelles Cyamocytheridea meniscus, Cyamocytheridea obstipa, Cyamocytheridea dertonensis, Cytheretta semiornata et Nonurocythereis seminulum sont tr`es repr´esent´ees ; (2) association des couches r´ecifales avec Grinioneis haidingeri, Aurila cicatricosa, Cimbaurila diecii, Tenedocythere cruciata, Pokornyella italica et Callistocythere quadrangula dominants qui indiquent un environnement marin infralittoral sup´erieur stable, caract´eris´e par des eaux chaudes et bien oxyg´en´ees ; (3) association des couches silteuses interpos´ees entre les complexes coralliens, parmi lesquelles Neomonoceratina laskarevi, Cytheridea acuminata, Phlyctenophora farkasi, Aurila albicans Callistocythere spp., Xestoleberis communis et X. dispar sont dominants. Ces esp`eces indiquent des eaux peu profondes avec v´eg´etation aquatique ; (4) association des couches silteuses sup´erieures, domin´ee par la pr´esence du genre Xestoleberis, caract´eristique des environnements marins moins profonds et tr`es riches en flore aquatique et (5) association des couches argilosilteuses terminales, domin´ee par Hemicytherura defiorei, ∗
Corresponding author. E-mail address:
[email protected] (E. Gliozzi).
0035-1598/$ – see front matter © 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.revmic.2007.06.002
288
C. Faranda et al. / Revue de micropaléontologie 51 (2008) 287–308
Xestoleberis spp. et Palmoconcha dertobrevis, accompagn´es par Acanthocythereis hystrix, Cytherella scutulum, Bairdoppilata conformis, Semicytherura spp., Krithe sp., Cytheropteron alatum, Bythocypris sp. et Pseudocythere caudata. Ces esp`eces sont indicatives d’un milieu marin plus profond, probablement situ´e en zone infralittorale inf´erieure ou circalittorale sup´erieure. L’ˆage des coupes e´ tudi´ees a e´ t´e d´etermin´e par le nannoplancton calcaire des e´ chantillons pr´elev´es au dessus des complexes coralliens, qui a indiqu´e un aˆ ge pas plus r´ecent que la Zone MNN9 (Tortonien inf´erieur). Un aˆ ge pas plus r´ecent que le Tortonien a e´ t´e aussi donn´e par les ostracodes. Par cons´equent les complexes coralliens du Gergeri–Raptis ont e´ t´e dat´es du Tortonien inf´erieur. © 2007 Elsevier Masson SAS. All rights reserved. Keywords: Marine ostracods; Coral reef environment; Community and cluster analyses; Calcareous nannoplankton; Crete; Early Tortonian Mots cl´es : Ostracodes marins ; Complexes coralliens ; Analyse de communaut´e et cluster analyse ; Nannoplancton calcaire ; Cr`ete ; Tortonien inf´erieur
1. Introduction Miocene coral reef complexes, mainly built by Porites and sometimes by Tarbellastrea and Siderastrea colonies, are rather widespread in the Mediterranean domain, particularly in the Tortonian–Messinian interval (Esteban, 1979; Rouchy et al., 1986; Moissette and Saint Martin, 1992; Franseen et al., 1996), both in the western and eastern sector: Sorbas and Agua Amarga basins (Spain) (Braga and Mart´ın, 1996; Mart´ın et al., 1996; Conesa and Babinot, 1999), Rosignano (Tuscany, Italy) (Bossio et al., 1996), Salento Peninsula (southern Italy) (Bosellini et al., 2001, 2002), Tyrrhenian side of Calabria (southern Italy) (Grasso et al., 1996); Caltanissetta basin (Sicily) (Grasso and Pedley, 1989; Pedley and Grasso, 1994), Malta (Russo and Bossio, 1976), Gulf of Gabes (Bonaduce et al., 1992), Crete (Sissingh, 1972; Meulenkamp, 1979; Meulenkamp et al., 1979; ten Veen and Postma, 1999a; Delrieu et al., 2004; Cosentino et al., 2004; Brachert et al., 2006; Tsaparas and Dermitzakis, 2005). Anyway, papers dealing with ostracods associated with coral reefs are numerous only in the western Mediterranean area (Bonaduce et al., 1992; Bosellini et al., 2001, 2002; Bossio et al., 1996; Conesa and Babinot, 1999; Russo and Bossio, 1976) and concern Late Tortonian and, above all, Early Messinian coral reef complexes, while from the eastern Mediterranean area, and particularly from Crete, only the Tortonian section of Drosi (central Crete) provided very few ostracod valves (Sissingh, 1972). In this paper, the ostracod assemblages associated with ten coral reef complexes cropping out in the Messara Plain (central Crete) between the villages of Gergeri and Raptis have been analysed and compared with the coral reef ostracod assemblages known from the western Mediterranean. Moreover, the comparison of the Gergeri–Raptis ostracod assemblages with those coming from the silty levels intercalated among the coral reef complexes lead to depict the palaeoenvironmental evolution of the Gergeri–Raptis succession. Finally, the age of the studied coral reef complexes has been provided, integrating the biostratigraphical data inferred from calcareous nannoplankton and ostracods. 2. Geological setting and sample location Crete and the Aegean Sea lie in the back-arc area of the active hellenic subduction zone (AHSZ),(Fassoulas, 1999). In particular, Crete belongs to the outer-arc domain of the AHSZ, which,
starting from either Late Middle Miocene (i.e. Serravallian, ten Veen and Meijer, 1998; Fassoulas, 2001) or Late Miocene (i.e. Early Tortonian, ten Veen and Postma, 1999b; Meulenkamp et al., 1994), was affected by extensional tectonics. This tectonic activity gave rise to the formation of several fault-bounded sedimentary basins, which controlled the Neogene basin fill in the area. The Iraklion basin is the widest Neogene basin in Crete. It is characterised by two branches with different orientations: (1) a N–S oriented northern branch (northern Iraklion basin) and (2) an E–W oriented southern branch (southern Iraklion basin or the Messara basin) (Fig. 1). In the Messara basin, Neogene deposits rest unconformably upon a pre-Neogene nappe pile, which was stacked during Paleogene–Early Neogene times, as the result of Alpine compressional processes linked to the AHSZ. The pre-Neogene nappe pile of central Crete crops out both on the northern (Psiloritis Mts.) and southern margins (Asteroussia Mts.) of the Messara basin, where it is characterised by the occurrence of: (1) the Ophiolites nappe; (2) the Asteroussia nappe, (3) the Pindos nappe, (4) the Gavrovo nappe and (5) the Plattenkalk nappe (Fassoulas, 1999, 2001). The Neogene succession of the Messara basin, (Fig. 2) starts with continental deposits of a braided fluvial system, consisting mainly of conglomerates and sandstones (Viannos Fm.). Nearby the Gergeri village, the uppermost portion of the Viannos Fm. consists of alternations of coarse-grained channelized deposits and fine-grained alluvial plain sediments with hydromorphic soils. The early marine incursion in the western part of the Messara basin is recorded at the base of the Ambelouzos Fm. (Meulenkamp et al., 1979), which in the Gergeri–Raptis area starts with fan delta conglomerates alternating with sandy shallow-marine deposits with coral reef complexes (Fig. 2). These coral reef complexes developed in a predominantly siliciclastic depositional system. They start with subspherical colonies of Siderastrea and Tarbellastraea, together with Porites in massive colonies and some columnar morphs. As a consequence of relative sea-level changes above this first bioherm, at least nine low-diversity coral reefs have been developed in a mixed sedimentation system with marked partitioning in the siliciclastic and carbonate deposition (Fig. 3). These later reefs are mainly characterised by branching Porites colonies and are cyclically separated by coarse-grained fan delta deposits.
C. Faranda et al. / Revue de micropaléontologie 51 (2008) 287–308
289
Fig. 1. Geological sketch map of Crete, showing the distribution of the Neogene deposits and the pre-Neogene nappe pile. Fig. 1. Carte g´eologique sch´ematique de la Cr`ete avec la localisation des d´epˆots n´eog`enes et pr´en´eog`enes.
The Gergeri–Raptis coral reef complexes are covered by fineto medium-grained Late Miocene shelf deposits with molluscs, scaphopods, ostracods, sponge spicules, calcareous nannofossils, planktonic and benthonic foraminifers (Fig. 2, Samples KR61–63). These deposits represent the result of a flooding in the Messara basin, which gave rise to the first deepening of the marine environment in central–southern Crete. Above these deeper marine deposits, Heterostegina-bearing sandstones indicate a relative sea-level fall with the occurrence of an extensive coastal shallow-marine environment in the whole Messara basin and also on Gavdos Island (Tsaparas and Dermitzakis, 2005). A second flooding event in the Messara basin is recorded just above the Heterostegina sandstones with the deposition of marls containing sapropel levels. In Crete, these deeper marine deposits show a well-developed precessional cyclicity and encompass the Tortonian/Messinian (T/M) boundary (Hilgen et al., 1995; Krijgsman et al., 1995). In the Panasos-Ag. Varvara area (Fig. 3c), the T/M boundary has been placed in the upper part of an interval with fine- to medium-grained sandstones, which corresponds to the Ambelouzos–Varvara transition. Frydas (2004) used the FCO of Amaurolithus delicatus to fix this boundary. Further up section, the Agia Varvara Fm. is characterised by laminated marls that contain intercalations of biogenic and terrigenous turbidites, shallow-marine sandstones and carbonates with in situ Porites reefs (ten Veen and Postma, 1999a; Delrieu et al., 2004). A further increase in depth in the Messara basin is recorded by the deposition of Lower Messinian tripolaceous marls, which in some places pass up section into the evaporites connected with the Messinian salinity crisis of the Mediterranean basin. Mainly re-sedimented gypsum deposits are resting unconformably above the Lower Messinian tripolaceous marls in the Messara basin. As in the whole Mediterranean basin, the end of the Messinian stage is characterised by the occurrence of the
well-known Lago-Mare biofacies. In the Messara basin, it consists of fine- to coarse-grained deposits containing Paratethyan ostracod assemblages (Cosentino et al., 2005). The angular unconformities within the postevaporitic deposits of the Messara basin (Fig. 2), which also characterises the Messinian/Zanclean transition in the southern Iraklion basin should be related to late Messinian tectonic activity. 3. Material and methods The Gergeri–Raptis coral reef complexes have been sampled in detail for micropaleontological analyses (Fig. 3): five samples (KR65, 66, 67, 68 and 69) come from the sandy silts beneath the lowermost coral reef complex, ten samples (GE35, RA03, 04, 07, 11, 14, 15, 21, 23, 25) come from clayey lenses dispersed within the different coral reef complexes, nine samples (RA09, 26, 27–33) are from the silty levels interposed among the coral reef complexes, two samples (RA36 and 37) are from the upper silts heteropic to the uppermost coral reef complex, and four samples come from the silty clays that overlie the uppermost coral reef (KR61–63) and from the Heterostegina sandstones (KR64) (Fig. 2). Samples for ostracod analyses were soaked with a 5% H2 O2 solution, washed over a 0.063 mm mesh sieve and dried. When possible, up to 300 ostracod specimens were collected from each sample. Their frequencies have been normalised to 10 g of dry sieved sample material and on the obtained frequency matrix the community structure analysis (Margalef, Shannon and equitability indexes) and cluster analysis were performed (supplementary Table 1). Statistical analyses have been carried out using the software package PAST - PAleontological STatistics (version 1.53) (Hammer et al., 2001). For the calcareous nannoplankton analyses, smear slides were prepared from unprocessed sediment and were analysed with light microscope techniques at 1000× magnification. A semiquantitative study was performed, based on the follow-
290
C. Faranda et al. / Revue de micropaléontologie 51 (2008) 287–308
Fig. 2. Neogene composite section of the Messara basin with location of Samples KR61–64. Fig. 2. Coupe g´eologique sch´ematique des d´epˆots n´eog`enes du bassin de Messara avec la localisation des e´ chantillons KR61–64.
ing abundance categories: A = abundant (>10 specimens per field of view), C = common (1–10 specimens per field of view), F = frequent (1 specimen per field of view), R = rare (
