Revised late Cenozoic foraminifer biostratigraphy of the Eskiköy Formation (Aksu Basin), SW Turkey and its paleoenvironmental conditions

Highlights

• Pleistocene bioevent marker planktic and benthic foraminifers were identified.

• The sedimentation of the Aksu Basin in southwestern Turkey did not end in the Late Pliocene but continued during the Calabrian.

• The Aksu Basin marks a period of low temperatures and lowered sea-level stands during the Calabrian.

Abstract

The Aksu Basin, near Antalya, is an important area from many aspects of the geology as it hosts the youngest marine deposits of the western Taurides in southwestern Turkey. These marine deposits play an important role in revealing the response of the Eastern Mediterranean coasts to the post-Zanclean transgression following the Messinian Salinity Crisis and provide a chronological record for detailing the late Cenozoic regional tectonic and sedimentary features. Therefore, biostratigraphic reconstruction of this basin is essential to enhance our understanding of the late Cenozoic evolution of the region and the response of the Eastern Mediterranean realm to climatic shifts. Here, we present an updated foraminifer biostratigraphy of the topmost part of the Eskiköy Formation in the Aksu Basin, a member of the Neogene Antalya basins. The studied Kargı section, located in the northern part of the Aksu Basin, contains planktic foraminifer species such as Neogloboquadrina pachyderma, Globigerinoides tenellus, Globigerinoides obliquus obliquus, and Globoturborotalita rubescens, and benthic foraminifers Bulimina marginata and Saidovina karreriana. These species are important bioevent markers in the Mediterranean Region. Accordingly, we update the stratigraphic range of the Eskiköy Formation found in southwestern Turkey extending it to the Pleistocene falling in MPle1a Neogloboquadrina spp. sx Interval Subzone, more specifically between 1.54 and 1.36 Ma, which previously was considered to be of Pliocene age. This age interval is also in agreement with the previous studies that reported Calabrian-Chibanian aged marine deposits in the Mut Basin, southern Turkey.

Introduction

Foraminifer biostratigraphy constitutes the basis of comparison and in-depth investigation of marine sedimentary basins as it provides age correlation between the rock units (BouDagher-Fadel, 2013). The Eastern Mediterranean Region, given its particular geodynamic and sedimentary evolution registering important events, such as the Messinian Salinity Crisis (MSC) and the Zanclean flooding, has been intensively investigated by researchers for its sedimentary basins. The Neogene MSC as a major regression and the Zanclean flooding as a major transgression, marking the end of the Miocene and start of the Pliocene, were first reported by Hsü et al., 1973, Hsü et al., 1977, Hsü et al., 1978 based on findings from offshore studies conducted in a vast area ranging from the Western to the Eastern Mediterranean Sea (DSDP Leg 13). In this concept, the Neogene Antalya basins, namely the Aksu, Köprü, and Manavgat basins, have been of interest to researchers since the 1910s because of their rich tectonic complexities and well-exposed structural and sedimentary features (e.g., Penck, 1918; Altınlı, 1944; Chaput and Darkot, 1953; Brunn et al., 1970, Brunn et al., 1971; Poisson, 1977; Gutnic et al., 1979; Şenel, 1997; Robertson and Woodcock, 1982). Its Miocene (bio-)stratigraphy and evolution were extensively studied by several researchers (e.g., Bizon et al., 1974; Varol, 1982; Akay et al., 1985; Poisson, 1977, 1983, 1984; Karabıyıkoğlu et al., 2000, Karabıyıkoğlu et al., 2005; Üner et al., 2011) and Flecker et al., 1995, Flecker et al., 2005 complemented these studies with detailed Miocene facies analysis and Sr isotope stratigraphy (Flecker et al., 1998). Pliocene-Quaternary characteristics of the Antalya basins were investigated by Glover (1995), Glover and Robertson (1998a), and Poisson et al., 2003a, Poisson et al., 2003b, Poisson et al., 2011. Combined Neogene-Quaternary sedimentary and tectonic evolution of the Antalya basins were documented by Çiner et al. (2008) and Üner et al., 2015, Üner et al., 2018. The Mut and Adana basins of the same age interval in the neighboring localities in the further east (Mersin and Adana districts, respectively) were studied by Yıldız et al. (2003), Cipollari et al. (2012), Cosentino et al. (2012), Schildgen et al. (2012), Faranda et al. (2013), Radeff et al. (2016), and Öğretmen et al., 2018a, Öğretmen et al., 2018b who revised the late Cenozoic biostratigraphy and geodynamical mechanisms of the region.

In this study, we focus on the Aksu Basin among the Neogene Antalya basins. It is situated on the Mediterranean coast of Turkey, bordered by the Beydağları Carbonate Platform to the west and its eastern margin is underlain by the Aksu Thrust (Fig. 1a) (Poisson et al., 2011). The Aksu Basin, being in a complex tectonic setting, plays an important role as it hosts key marine successions to unlock the chronostratigraphy of the tectonic and sedimentary events in the Eastern Mediterranean coastal areas. Many important studies were conducted to unearth the age relationships of the sedimentary formations of the Aksu Basin through foraminiferal (Bizon et al., 1974; Poisson, 1977; Glover, 1995; Glover and Robertson, 1998a) and nannoplankton biostratigraphy (Varol, 1982; Akay et al., 1985; Poisson et al., 2003a, Poisson et al., 2003b, Poisson et al., 2011). These studies are based on the foraminiferal biozonations of Iaccarino (1985) and calcareous nannoplankton biozonations of Martini (1971), Okada and Bukry (1980), and Perch-Nielsen (1985) dating the youngest marine deposits as the Early-Late Pliocene within the foraminiferal Globorotalia puncticulata-G. margaritae Zone and nannoplakton NN15 and NN16 zones. However, biostratigraphic zonations of the Mediterranean Region have been revised through paleomagnetic and astronomical calibrations, and several new foraminiferal and nannoplankton datum events have been recognized which aid in more refined age model reconstructions (Rio et al., 1990; Lourens et al., 1992, Lourens et al., 1996a, Lourens et al., 1996b, Lourens et al., 1998, Lourens et al., 2004; Raffi, 2002; Raffi et al., 2006; Iaccarino et al., 2007; Cita et al., 2008; Anthonissen and Ogg, 2012; Lirer et al., 2019). For example, the biozonations of Iaccarino (1985) did not include the sinistral coiling Neogloboquadrina pachyderma whose first occurrence marks the Pleistocene at 1.79 Ma (i.e., Lourens et al., 1996a, Lourens et al., 1996b, Lourens et al., 1998, Lourens et al., 2004; Iaccarino et al., 2007; Lirer et al., 2019). Similarly, in 1993, Raffi et al. have introduced four new nannoplankton datum events within the Early Pleistocene based on the size groups of Gephyrocapsa. Furthermore, the Pliocene-Pleistocene boundary has been redefined from ca. 1.8 to 2.6 Ma (Gibbard et al., 2010) and thus many Late Pliocene deposits today correspond to the Early Pleistocene. Therefore, revising the biostratigraphy of the Antalya basins will contribute to many important recent studies which considered and were built on the older versions of biostratigraphic schemes (e.g., Poisson et al., 2011; Koşun, 2012; Üner et al., 2015, Üner et al., 2018; Koç et al., 2016; Doğan et al., 2019; Şiş et al., 2020; Wasoo et al., 2020; Gürbüz et al., 2021; Wasoo and Koç, 2021 among others).

Here, we present the initial study of high-resolution foraminifer biostratigraphy revisions of the Antalya basins. We aim to contribute to the Quaternary geology and paleoclimate reconstructions of the region providing missing information about the depositional history of the Eastern Mediterranean coastal zones.