Miocene Calcareous Nannofossils from the Mut Basin, southern Turkey

A detailed study of Miocene calcareous nannofossils using light and scanning electron microscope techniques has been undertaken on sections from the Cifciler, Mut and Silifke regions of the Mut Basin, southern Turkey. Age determinations are based upon a combination of previously published zonal schemes. Forty-one species are recorded; a new combination, Pontosphaera segmenta is also introduced.


PREVIOUS WORK
The Mut Marl Formation has been studied previously for its foraminifera by different workers. Akarsu (1 960) studied the geology of the Mut Basin and identified rocks ranging in age from Palaeozoic to Quaternary. He paid particular attention to the Miocene strata, which cover 90% of the basin. The limestone sequence was assigned an Early Miocene age on the presence of the foraminifera1 species Archais malabaricus (Carter) while the laterally equivalent marls were regarded as Middle Miocene on macrofossil evidence. It is noteworthy that Adams (1970) has subsequently assigned a Middle Miocene age, Letter Stage Lower Tf (for Taberina ("Archais") malabaricus (Carter). Further contributions to the knowledge of the biostratigraphy and micropalaeontology of Tertiary basins in southern Turkey, including the Mut Basin, were made by Bizon et a1 (1974). On the basis of foraminifera, these workers suggested an Early-Middle Miocene (Upper Burdigalian -Lower Langhian) age for the Mut Marl Formation. In 1975, Sezer defined three formations in the Mut Basin and described the lateral facies changes between the Ortakoy Formation, Mut Marl Formation and Mut Limestone Formation. He divided the rocks into the following four zones based on planktonic foraminifera: Orbulina universa zone, Orbulina suturalis zone, Praeorbulina zone, and Globigerinoides sicanus zone, which indicate an Early-Middle Miocene age.
The Medetsiz Member of the Silifke Formation was studied by Bizon et al. (1 974) and Gokten (1 976). Bizon et al. (1974) suggested a late Middle Miocene (Serravalian) age for this member on the basis of the presence of Globorotaliu mayeri Cushman & Ellis and Globorotaliu praemenardii (Cushmann & Ellis). The former has a range of N9-Nl3 and the latter N9-Nl2 which would indicate that the formation has an age within the N9-N12 zones of Blow (1969Blow ( , 1979, Langhian and not Serravallian as quoted by Bizon et al. (1974). Gokten (1976)   STUDIED SECTIONS Samples were collected from three separate sections in the Cifciler, Mut and Silifke areas of the Mut Basin, the locations of which are indicated in Fig. 2.

Cifciler section
Twenty-nine samples were collected for calcareous nannofossil examination from the marl at the locality described by Sezer (1975). Thirty-four species of calcareous nannofossils are recognised and their ranges and relative abundance are recorded in Fig. 3.
The species are moderately well preserved and many of them show signs of overgrowth. Samples from this section contain calcareous nannofossil assemblages with a relatively low species diversity. Helicosphaera carteri, (Wallich) Kamptner, 1954, H . ampliaperta Wilcoxon, 1967 andSphenolithus hetermorphus Deflandre, 1953 are the biostratigraphically impwtant species recovered from this section. Apart from the above mentioned forms, Coccolithuspelagicus (Wallich) Schiller, 1930 and Reticulofenestra pseudoumbilica (Gartner) Gartner, 1969 are recorded commonly throughout the studied section.
Pontosphaera japonica (Takayama) Nishida, 1971 and Homozygosphaera tholifera (Kamptner) Halldal & Markali, 1955 display older stratigraphical ranges than previously reported. Syracosphaera mediterranea Lohmann, 1902 is found in the Early Miocene and was also reported from the Early Miocene by Baldi-Beke In this section, from top to bottom, the following zones are recognised: Sphenolithus heteromorphus zone, Helicosphaera ampliaperta zone and Helicosphaera carteri zone.

Mut section
Fourteen samples were collected from a section within the Mut Marl Formation and examined for their calcareous nannofossil content. Thirty species are recognised and the relative abundance of the species and their stratigraphic ranges are given in Fig. 4.
Overall abundance and diversity of calcareous nannofossils increase towards the top of the studied section. The following are the most common species, of which the first three are found throughout the sampled material: Coccolithus pelagicus (Wallich) Deflandre, 1953. The following zones are recognised in the Early Miocene: Helicosphaera ampliaperta zone and Helicosphaera carteri zone.

Silifke section
Eleven samples were collected from a section within the Medetsiz Member of the Silifke Formation and examined for their calcareous nannofossils. The samples from this section provided fairly well preserved assemblages of calcareous nannofossils which exhibit relatively low species diversity. The stratigraphic distributions of the species, many of which are long-ranging, are shown in Fig. 5 .

ZONATION SCHEME
The zonation scheme proposed in this study utilises previously described zones. A correlation between the previously published zonation and the present scheme is given in Fig. 6.
Helicosphaera carteri Zone Edwards, 1971 emend. Varol (1983) (non Okada & Bukry, 1980) Definition. The base of this zone is not recognised in this study; the top of this zone is recognised by the first occurrence of Sphenolithus heteromorphus Deflandre, 1953. Age. Early Miocene. Common species. Helicosphaera carteri, (Wallich) Kamptner, 1954, H. ampliuperta Bramlette & Wilcoxon, 1967, Coccolithus pelagicus (Wallich) Martini, 1965 and Sphenolithus belemnos Bramlette & Wilcoxon, 1967 are absent in the Early Miocene of southern Turkey ; it is also reported as being very rare or absent in S.E. Asia. Varol (1983) found it necessary to combine the Discoaster druggi subzone (CNla) and the Sphenolithus belemnos zone (CN2) of Okada & Bukry (1980). This zone is equivalent to 'the "Unnamed Neogene Zone" of Edwards (1971). However, in his study Edwards primarily marked the upper limit of this zone by the evolutionary appearance of Discoaster divaricatus Hay (in Hay et al., 1967) and the evolutionary appearance of Sphenolithus heteromorphus Deflandre, 1953 is used secondarily. Varol (1983) used only the evolutionary appearance of Sphenolithus heteromorphus Deflandre, 1953, which is cosmopolitan and solution resistant. The Helicosphaera kamptneri Zone of Chi (1979) corresponds to the lower part of the present zone. Zones NN2-NN3 of Martini (1971) are also approximately equivalent to the H . carteri zone. The first occurrence of Discoaster pugnosa Hoj jatzadeh 1978, Rhabdosphaera clavigera Murray & Blackman, 1898 and Syracosphaera mediterranea Lohmann, 1902 were observed in this zone. Localities. Mut and Cifciler sections.  Kamptner 1954, Coccolithus pelagicus (Wallich) Schiller 1930 Remarks. Homozygosphaera thofifera (Kamptner) Halldal and Markali 1955 first appears within this zone. Locality. Cifciler Section. Chi, 1979 Definition. The base and top of this zone were not recognised in this study. Age. Middle Miocene.   Martini (1971) and zone CN5a of Okada & Bukry (1980). Discoaster kugleri Martini & Bramlette, 1963 and Discoaster exilis Martini & Bramlette, 1963 are absent from the studied material whereas C. Jloridanus is commonly present and easily applicable to the Mut Basin. Bukry (1975) also used the nominate species as a second marker to define the same boundary in the absence ofDiscoaster kugleri Martini & Bramlette, 1963.

REMARKS ON PRESERVATION AND PALAEOECOLOGY
Palaeoecological control and preservational conditions are the two main factors which affect both species diversity and abundance of calcareous nannofossil assemblages. It is always, however, very difficult to determine whether palaeoecological control, preservational conditions or a combination of both were responsible for species diversity and abundance.
In the present study, all studied sections contained moderately well preserved calcareous nannofossils. Certain species, however, are slightly more affected in the Cifciler Section than in the Mut and Silifke sections by preservational conditions. Some specimens of Braarudosphaera bigelowi (Gran & Braarud) Deflandre, 1947 from the Cifciler Section, for example, are strongly etched which other displays overgrowths. In all sections, Discoasters and the central part of Coccolithus pelagicus (Wallich) Schiller, 1930 (Wallich) Schiller, 1930 and Reticulofenestra pseudoumbilica (Gartner) Gartner, 1969 are common in all sections.
Warm water indicators present in the studied section include Helicosphaera carteri (Wallich) Kamptner, 1954, Rhabdosphaera clavigera Murray & Blackman, 1898, Pontosphaera spp. and Scyphosphaera spp. of which Helicosphaera carteri (Wallich) Kamptner, 1954 is especially common. Supportive evidence for the presence of warm water is provided by the presence of coral reefs along the edge of the basins.