Eolianite and coquinite as evidence of MIS 6 and 5, NW Black Sea coast,
Turkey
Ahmet Evren Erginal
a,⇑, Nafiye Güneç Kıyak
b, Hamit Haluk Selim
c, Mustafa Bozcu
d,
Muhammed Zeynel Öztürk
e, Yunus Levent Ekinci
f, Alper Demirci
g, Elmas Kırcı Elmas
h, Tug˘ba Öztürk
b,
Çag˘lar Çakır
i, Mustafa Karabıyıkog˘lu
aa
Ardahan University, Department of Geography, 75000 Ardahan, Turkey
b
Isßık University, Faculty of Arts and Sciences, Department of Physics, 34460 Istanbul, Turkey
c
Istanbul Commerce University, Department of Jewellery Engineering, 34378 Istanbul, Turkey
d
Çanakkale Onsekiz Mart University, Department of Geological Engineering, 17000 Çanakkale, Turkey
eÖmer Halisdemir University, Department of Geography, Nigde 51240, Turkey f
Bitlis Eren University, Department of Archaeology, 13000 Bitlis, Turkey
g
Bitlis Eren University, Department of Geophysical Engineering, 13000 Bitlis, Turkey
h
Istanbul University, Institute of Marine Sciences and Management, 34116 Istanbul, Turkey
i
Atatürk University, Department of Geography, 25030 Erzurum, Turkey
a r t i c l e i n f o
Article history:
Received 13 September 2015 Revised 7 January 2017 Accepted 25 January 2017 Available online 10 February 2017 Keywords: Eolianite Coquinite Sea level Late Pleistocene Black Sea Turkey
a b s t r a c t
This paper discusses the implications of a lowstand carbonate eolianite and overlying transgressive sequence of coquinite at Sßile on the Turkish Black Sea coast based on composition, depositional charac-teristics and optical age estimations. The cross-bedded eolianite is a mixed ooid quartz grainstone in composition, yielding a depositional age matching MIS 6. It formed at the backshore of the paleobeach with the supply of sediment the from the beach face and offering insights into the drift of mixed shallow marine carbonates and siliciclastics together with radial ooids by onshore winds from a subaerially exposed high- to low-energy ooid shoals and oolitic sand complexes which developed parallel to the shoreline on the shallow shelf margin. During this lowstand, a low-relief dune retaining a record of opposing paleowind directions than that of prevalent northeasterly winds of today appears to have been lithified to form dune rock (aeolinite) under drier conditions compared to the present. Coinciding with MIS 5e, shallow marine coquina beds resting unconformably on the eolianite indicate the occurrence of the Mediterranean transgression during the last interglacial, as confirmed by benthic foraminifera within the high-salinity tolerant coquina shells.
Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction
The Black Sea exhibits a relatively complicated sea-level history during the Quaternary. Available evidence on secular trends in its level and the magnitude of fluctuations of this anoxic inland water body during the glacial and succeeding interglacial periods remains somewhat incompatible with global oceans (Algan et al., 2007). Sedimentological and paleontological records have asserted that the Black Sea’s water budget has been largely independent of the global sea level (Chepalyga, 1984), causing differences in hydrological and faunal characteristics. The hydrological connec-tion with the Caspian Sea via the Manych-Kuma Depression and
the Mediterranean through the Turkish Straits System determined the level of the Black Sea during the Pleistocene (Svitoch et al., 2000). Previous data from key sections of the Kerch and Taman peninsulas revealed the importance of the Black Sea basin with regard to climastratigraphic reconstructions (Zubakov, 1988); explaining the repeated phases of salinization and freshening owing to invasions by Mediterranean and Caspian waters.
Badertscher et al. (2011), for instance, suggested that a connection between the Black Sea and Mediterranean was established at least twelve times over the past 670 ka. Further time-based variations in the Black Sea from early Pleistocene up to recent years were discussed bySvitoch et al. (2000).
The Late Pleistocene history of the Black Sea includes the Karangatian, Tarkhankutian and Flandrian transgressions as well as the New Euxinian regression (Yanina, 2014). When Late
http://dx.doi.org/10.1016/j.aeolia.2017.01.004
1875-9637/Ó 2017 Elsevier B.V. All rights reserved.
⇑ Corresponding author.
E-mail address:aerginal@gmail.com(A.E. Erginal).
Contents lists available atScienceDirect
Aeolian Research
Pleistocene levels of the Black Sea are considered, available data have attested to ?dramatic changes in the salinity and level of the Black Sea after the Karangatian transgression, coinciding with so-called Eemian (Mikulinian) interglacial. During this interglacial of long duration between 120–125 ka and 85–90 ka (Federov, 1988), with much higher salinity compared to that of today, changes in water chemistry were first manifested by the establish-ment of mollusk fauna similar to the present (Nevesskaya, 1965) with a rise in sea level up to 7 m. The higher salinity (30‰) is con-genial with the subsistence of saltwater clams and subtropical dia-tom species (Zhuze et al., 1980; Yanina, 2014) due to further inflows from the Mediterranean. This transgressive period is con-firmed by230Th/234U age data obtained from marine shells at the Taman Peninsula and Kerch Strait, yielding ages of around 125 ka (Arslanov, 1993). This warm interglacial period is known to have been followed by the post-Karangatian regression that occurred between 72 and 45 kyr BP and then by the Sourozhian (a later syn-onym of Tarkhankutian) transgression, represented by sea levels of
60 m and 10 ± 1 m, respectively (Chepalyga, 1984).
In addition to the above data from sections of the northern Black Sea coast, albeit limited, age estimations have also been pro-vided from marine terrace deposits and eolianites on Turkey’s Black Sea coast. Electron Spin Resonance (ESR) dating results from such deposits lying at seven different elevations between 3 m and 260 m on the eastern Black Sea coast of Turkey affirmed different ages ranging between 5.141 ± 0.294 ka and 407.998 ± 67.475 ka (Keskin et al., 2011), including marine isotope stage (MIS) 5e (124.8 ± 26.0 ka). Recent data obtained by Optically Stimulated Luminescence (OSL) dating of similar deposits on the Sinop Penin-sula at the northern margin of the Central Anatolian Plateau revealed ages of 125, 190, 400 and 570 ka, corresponding to MIS stages 5e, 7a, 11 and 15, respectively (Yildirim et al., 2013). These estimations correspond to a long depositional period spanning from the late Chaudian to early Uzunlarian to the Karangatian interglacial (Zubakov, 1988) when middle to Late Pleistocene ana-logues for the Caucasian Black Sea coast are considered. Optical ages dated to around MIS 5e (Erginal et al., 2013a; Polymeris et al., 2012) have also been obtained from firmly-cemented lami-nated carbonate eolianites on the northwest Black Sea coast, con-stituting a terrestrial-sourced equivalent in deposition age to the above-stated marine terrace deposits.
Contrary to the vast amount of evidence from MIS 5e (Karanga-tian) and 7 (Uzunlarian) marine sequences around the Kerch Strait area north of the Black Sea coast as well as the south Georgia sea-board (Jaoshvili et al., 2010), existing knowledge regarding envi-ronmental conditions immediately before the Mikulino, or at the transition period from MIS 6 glacial to MIS 5, is greatly limited. Questioning the contention by Grigor’yev et al. (1985) about a gradual transition from Uzunlarian to Karangatian beds on the Bul-garian and Ukrainian coasts,Federov (1988)underlined the proba-ble existence of a regression due to the gap between these interglacial deposits. Separating Karangatian from Uzunlarian, Chelyadintsevo clays with freshwater mollusks in the Azov-Kerch area can also be considered as suggestive of deposition in a fresh-ened environment (Zubakov, 1988). Linked to the Dnieper (Saalian) glaciation at between 180 ka and 140 ka (Colleoni et al., 2009), gla-cial deposits left by the ice sheet to the north of the East European Plain preceding the Mikulino Interglacial also provide a continental equivalent of the regressive period MIS 6.
Considering the limited geological evidence from the Black Sea coast, environmental conditions during the MIS 6 glacial and at the transition stage from MIS 6 penultimate glacial into MIS 5e inter-glacial are as yet little known. In this study, we present dune rock, eolianite sensu stricto, and coquinite as possible evidence of alter-nating lowstand and highstand deposits suggestive of MIS 6 to MIS 5e respectively on the western Black Sea coast of Turkey.
The studied outcrops are the first records in respect of the co-existence of such beach (foreshore) and back-beach (backshore) deposits along the Black Sea coast. Our data offer multiple insights into paleoclimatic factors that favored eolian deposition, mainly by onshore-directed northerly paleowinds and subsequent carbonate cementation under drier conditions together with the inflow of Mediterranean fauna into the Black Sea.
2. Study area
The studied beds of eolianite and coquinite collocate as out-crops emerging along a 30 m-wide beach on the northwest Black Sea coast of Turkey (Fig. 1). Backed by low ridges of recent hum-mocky coastal foredunes, both outcrops extend along a sandy beach. The well- indurated eolianite with an exposed thickness of 1.5 m backs onto and underlies tightly cemented coquina beds. The 80 cm-thick coquinite beds, having a maximum width of 30 m, are exposed for about 150 m along the foreshore. The basement rock unit is not observed along the shore. Based on long-term cli-matic data from Sßile Meteorology Station about 12 km from the study area, the region receives annual precipitation of around 749 mm, much of which falls during the winter season. The annual average temperature is 13.6°C. Northeast winds predominate throughout the year.
3. Methods
3.1. Sampling and analyses
Four samples were extracted, each 20 cm_diameter blocks, from fresh exposures for dating and analysis, three from the eolianite and one from the coquinite. The embedded detrital grains of quartz were extracted from the inner parts of these 20 cm-diameter blocks of both outcrops that are well-preserved in their vertical sections.
Quantitative element analyses of the finer materials filling inter-grain pore spaces within the eolianites and interstitial spaces of tightly-packed bivalvia fragments of coquinite were made using Energy Dispersive X-ray Spectroscopy (EDX-Bruker AXS XFlash). Interior parts of the cemented materials were scanned using Scan-ning Electron Microscopy (SEM-ZEISS EVO 50 EP) to examine the micro-fabrics of the samples. Total carbonate content was mea-sured using a Scheibler calcimeter (Schlichting and Blume, 1966).
For the micro-paleontological investigation, 10 g of sub-sampled sediments were treated with 10% H2O2 for 24 h then wet-sieved through a 63
l
m sieve. The residue was dried in air and the benthic foraminifera fauna was identified and counted in the sediment fraction above the 63l
m sieve. Due to poor preserva-tion of the foraminifera fauna from the coquinite samples, approx-imately 70 g of the spare sub-samples were re-examined and some differences in the diversity of benthic foraminifera were found. To assess the possible contribution of stable isotopes of oxygen (18O/16O) and carbon (13C/12C) to a paleo-environmental interpre-tation of the coquinite shells and connective carbonate cement within the eolianites, stable isotope measurements were carried out in the Laboratory of Isotope Geochemistry at the University of Arizona. Analytical precision (1r
) values were 0.06 and 0.09 for d13C and d18O, respectively. 3.2. Geoelectrical measurements
Subsurface imaging was also carried out using Electrical Resistivity Tomography (ERT) to determine the thickness and subsurface geometry of the eolianite and debris of shell-laden coquina, which has proved useful in studying the subsurface
nature of beachrock (David et al., 2009), coquinite (Erginal et al., 2012) and eolianites (Erginal et al., 2013) elsewhere. Three coastline-parallel ERT transects were measured (Fig. 2). The first tomogram (ERT1) was taken along the wave swash-backswash zone where coquinite beds are widely exposed. The second tomo-gram (ERT2) was obtained from the transition zone between the sandy beach and incipient foredunes in order to monitor the land-ward extension of coquinite beds under the beach sands. A third transect (ERT3) was taken from the foredune area at the back to identify any resistivity difference between the eolianites and coquinite.
The apparent resistivity data acquisition for each profile was carried out using a GF ARES multi-electrode system, with 21 elec-trodes spaced at 5.5 m intervals along a total length of 110 m. Dipole-dipole electrode configuration was used for 9 different data levels with dipoles of 5.5 and 11 m, and unit dipole separations of 1, 2, 3, 4, 5, 6, 2.5 and 3.5 m. RES2DINV software package was used to invert the apparent resistivities to construct a subsurface resis-tivity model. The tomographic inversion algorithm was based on the smoothness-constrained least-squares method (Sasaki, 1992) implemented by a quasi-Newton optimization technique (Loke and Barker, 1996). The Finite Element method was used for
calculation of theoretical apparent resistivity data in the inversion process. We chose geoelectrical models at the iteration, after which the root mean square (RMS) error did not change significantly. The two-dimensional inversion process produced geoelectrical models with RMS errors of 4.5%, 7.8% and 1.7% for ERT1, ERT2 and ERT3 data, respectively, at the end of the sixth iteration.
3.3. Radiocarbon dating
For a pre-assessment of the age of the coquinite shells, two bulk samples of bivalvia rich in Mytilus sp. were tested using conven-tional radiocarbon dating at BETA Limited, Miami, USA. Dating was carried out from bulk samples of equal-sized fragments of bivalvia packed very closely to each other. Two samples weighing 50–60 g were analyzed, which provided ample carbon for finite age determination. For the dating, two samples were extracted from the 80 cm and 10 cm levels of a typical vertical section.
3.4. Luminescence measurements
Optically Stimulated Luminescence (OSL) dating was applied to the embedded quartz minerals within the cemented beds.
Fig. 1. Location map of study area.
3.4.1. Sampling, sample preparation and OSL analyses
Eolianite samples for Optically Stimulated Luminescence (OSL) dating were collected in small block portions. The samples were taken from exposures at different intervals where the natural land surface was several meters above the sample point, thereby influ-encing the contribution of cosmic rays to the environmental radi-ation dose rate.
Sample preparation and OSL measurements were performed under subdued red light in the laboratory. For luminescence anal-ysis, the hard outer surface of the eolianite samples was removed with chisel to eliminate the light-subjected portions. The inner part was crushed in a mortar and grains of 90–180
l
m were separated under wet conditions. To separate the quartz grains from other mineralogical components of the sediments, standard procedures were used. The grains were cleaned first with 10% HCl to remove the carbonate fraction then with 10% H2O2for removal of organic components and finally HF of 40% for 40 min. for etching was undertaken to eliminate the alpha contribution to the dose rate, followed by a final bath of 10% HCl, respectively. The purity of the quartz grains was tested by the absence of IRSL signals during infrared stimulation. The purified quartz was spread as a mono-layer over 10 mm-diameter aluminum discs using Silkospray sili-cone oil. All luminescence measurements were performed with an automated Risø TL/OSL reader, model TL/OSL-DA-15, equipped with an internal90Sr/90Y beta source (0.097 Gy s 1as calibrated using the calibration quartz provided by Risoe Lab), blue light emitting diodes (LEDs) (470 nm, 40 mW cm 2) and IR LEDs (880 nm, 135 mW cm 2). Luminescence signals were detected using an EMI 9635QA photomultiplier tube fitted with 7.5 mm-thickness Hoya U-340 filters (Bøtter-Jensen, 1997).OSL analyses were undertaken in the Luminescence and Archeometry Laboratory at Isik University in Istanbul. An equiva-lent dose to the artificial radiation dose providing the same amount of luminescence as the natural environmental dose of each sample was determined by comparing the luminescence growth curves for the unbleached and bleached aliquots, using the conven-tional single-aliquot regenerative-dose protocol (OSL-SAR). This is based on a comparison of the natural OSL signal with regenerative OSL signals produced by known doses (Murray and Mejdahl, 1999; Murray and Wintle, 2000).
3.4.2. OSL-SAR protocol and growth curve
The protocol has six cycles. In the first cycle, a natural aliquot was first preheated at 260°C for 10 s and then recorded with blue
light stimulation at 125°C for 40 s to obtain the natural OSL signal (L0). Possible sensitivity changes in the OSL signal were monitored and corrected using a small test dose of 10 Gy delivered to the same aliquot prior to heating to 190°C. Then the test dose OSL sig-nal (T0) was measured to obtain a sensitivity-corrected natural sig-nal (L0/T0). For the next three cycles, following the same sequence of treatments as in the first cycle, three known laboratory doses were applied to the same bleached aliquot to obtain regenerated OSL signals (Li, i = 1,2,3). Then, the corresponding test dose OSL sig-nal (Ti) was recorded as in the first cycle after a reduction to 190°C and sensitivity-corrected OSL signals (Li/Ti, i = 1,2,3) were obtained. Then a growth curve was constructed using the corrected dose points obtained; the dose points fit well with the exponential func-tion for all samples (Fig. 3). The corrected natural signal (L0/T0) was interpolated onto the growth curve to obtain the accumulated dose De, which was measured before saturation.
In addition to the sensitivity correction, a zero dose was given as an internal test for reliability of the OSL measurements to observe the bleach ability of the OSL signal (recuperation), which is usually expected to be below 5% of the natural signal. Then, a regenerative dose was obtained equal to the first regeneration dose given to the same aliquot to monitor the sensitivity change in OSL signals of the same dose recorded at two different cycles (recycling ratio). This was close to unity, as expected. Recuperated values are generally below the upper suggested limit of 5% of natural signal. All values obtained were acceptable.
3.4.3. OSL ages
The experiments indicated that the quartz used for OSL analysis was sensitive to both dose and light exposure, yielding very bright OSL signals per unit dose. Therefore, the OSL-SAR protocol pro-duced reliable results when applied to quartz grains extracted from the eolianite samples. All dose–response curves were fitted using a saturating exponential, as seen inFig. 3for representative sample L2.5. An open diamond indicates the corrected natural dose point on the growth curve, interpolated onto the horizontal axis to obtain the equivalent dose De. Dose recovery experiments (Murray and Wintle, 2003) performed on a representative sample of L2.2 showed that the doses given were close to the measured Defor the chosen sample, indicating that the measurement proce-dure used in this study was able to recover laboratory doses.
Dose rates required for age estimation were obtained from con-centrations of the major radioactive isotopes of the uranium and thorium series and of potassium (Olley et al., 1996; Prescott and
Hutton, 1988, 1994), concentrations of which were measured at Acme Analytical Laboratories (Vancouver) Ltd. in Canada using mass spectrometer. The carbonate fraction and moisture content affecting dose rate evaluation were also taken into account. The luminescence age, equivalent dose and environmental dose rate obtained for each sample are shown inTable 1. The OSL ages from each sample were in good correlation with the stratigraphy.
4. Results and discussion
4.1. Composition and depositional characteristics of the eolianite Located about 20 m back from the present shoreline, the eolian-ite layers covered by modern climbing dune sands are characteris-tically composed of moderately- to well-sorted, medium- to coarse-grained sandstones with well-developed tabular-planar and wedge-planar cross-beds dipping in opposite directions (Fig. 4a–c).
Field observations demonstrated that the cross-stratified sets, albeit of very limited areal and vertical extent, are bounded by sharply defined horizontal or gently-inclined planar bounding sur-faces, representing changes in the dune growth. Low-angle cross– beds with thin, uniform, gently inclined (<100) foreset laminae constitute the main part of the succession. These may represent deposition resulting from climbing translatent strata formed by migrating wind ripples (Hunter 1977a,b; Kocurek and Dott, 1981). Tabular-planar cross-stratified sets with steeply dipping (>100) foreset laminae are also present, though not common. They are considered to have been formed by avalanching processes or grain flows of non-cohesive sands on the active slip faces of the dune (Hunter 1977a,b;Kocurek and Dott, 1981). Both in tabular-and wedge-shaped cross-beds there are several deformational fea-tures in the form of irregular folds (Fig. 4c). These chaotically-disturbed overlying beds might be considered to have been formed pene-contemporaneously by aerially-limited sand flows in wet conditions after heavy rains (Bigarella, 1972; McKee and Bigarella, 1972) or snow melts.
The overall sedimentary features of these units represent depo-sition on the crest of a transverse sand dune with a very subdued topographic relief characterized by gently inclined windward (stoss side) and relatively steep downwind (lee face) slopes. Evenly deposited plane-parallel horizontal beds represent interdune deposits probably developed in an area of flat sand sheets. On the other hand, main dip directions measured from the foresets indicate southeast, northwest, southwest and northeast-directed paleowinds.
The calcimetric analyses reveal that the beds contain high cal-cium carbonate of between 50% and 75%. Sand-sized components predominate (65%) with very fine and fine gravels constituting about 34% and the remainder consisting of very fine sands, silt and clay. EDX data from the lowermost sample reveals the exis-tence of various elements in descending order of O > C > Fe > Si > Ca > Al > Mg > Na > K.
Table 1
OSL age, equivalent dose and environmental dose rate obtained for each sample.
Lab Code Sample type Depth Age Dose (n)*
Dose rate U Th K CaCO3
(cm) (ka) (Gy) (Gy/ka) ppm ppm % %
L2.1 Eolianite 80 177.9 ± 14.5 75.15 ± 3.00 8 0.42 ± 0.03 0.5 1.4 0.07 41.7 L2.2 Coquinite 10 127.4 ± 9.3 60.07 ± 1.81 8 0.47 ± 0.03 0.5 1.0 0.07 44.1 L2.3 Coquinite 10 128.1 ± 11.9 63.22 ± 4.29 5 0.49 ± 0.03 0.5 1.0 0.07 44.1 L2.4 Eolianite 80 187.5 ± 21.2 70.01 ± 5.82 7 0.37 ± 0.03 0.5 1.0 0.04 49.1 L2.5 Eolianite 15 163.3 ± 13.0 64.70 ± 2.80 8 0.40 ± 0.03 0.5 0.7 0.03 76.4 * n: Number of aliquots.
Fig. 4. Views of eolianite with sampling points. (a) Large scale tabular- and wedge-shaped cross-beds with high-to low-angle foreset laminations. Hammer indicates scale; (b) Close-up of tabular-planar cross-bedding with steeply dipping foreset laminae representing deposition on active slip face of dune through grain flows. Pen indicates scale; (c) Irregularly-folded coarse-grained sandstone beds interbedded with massive coarse sandstone comprising a few disarticulated shells. Note vertical burrow to left of lens cap.
Thin sections also showed abundant spherical ooids with nuclei made up of various mineral fragments such as quartz, epidote and rutile. The calcite concretions have thicknesses ranging from 50
l
m to 250l
m, which is equal to or thicker than the nucleus in ooids of the last interglacial deposits in the Mediterranean (Bardaji et al., 2009). Amalgamated with spar calcite cement, the ooids have diameters between 500l
m and 1 mm that present a tangentially-oriented structure derived from the paleobeach, sug-gesting a high-energy agitated depositional environment. The common broken forms of ooids suggest physical deformation by waves or winds during transportation and deposition, which is confirmed by the presence of fragments of shallow marine shells within the eolianite sands. The predominance of meniscus cement is also indicative of meteoric cementation after deposition of dune components.4.2. Composition and depositional characteristics of the coquinite The studied cemented beachrock is a coquinite, being a syn-onym of well- indurated coquina (Bissell and Chilingar, 1967), rich in debris of packed disarticulated and abraded bivalvia fragments, including Cardium sp., Mytilus sp., Mytilaster sp., Ostrea edulis, Chlayms opercularis and Anomia ephippium inhabiting the bottom sands. These species are indicative of a well-circulated and oxy-genated, warm shallow water depositional environment with proper nutrient levels (Wilson, 1975; Flügel et al., 2010). Coquinite beds at Sßile extend along a 40 m-wide sandy beach with a sprin-kling of disarticulated shell debris comprising Donacilla cornea, Donax trunculus, Mytilus galloprovencialis, Venus gallina and Car-dium glaucum. These cross-bedded formations are about 100 m-long and cemented by calcium carbonate. Bedding measurements showed the existence of beds aligned NW-SE and NE-SW with low to high dip angles inclined towards the northeast and south-east between 3° and 18° (Fig. 5).
Thin sections showed that the post-depositional diagenesis dominated by meniscus cementation under meteoric conditions occurred after subaerial exposure similar to examples found else-where (Dockal, 1995a,b). This is confirmed by our stable isotope measurements. d13C (‰PDB) results obtained from the bulk car-bonates of four coquinite samples yielded values from 8 to 5
for the lowermost and from 5.6 to 4.6 for the topmost samples. The d18O (‰PDB) values of the same samples also revealed deple-tion with light isotopes, which vary from 7.7 to 8.6 and 7 to 9.2, respectively. These results suggest that the connective car-bonate of the coquinite might have been freshened with light iso-topes by meteoric waters during the diagenetic period.
From coastline to backshore, the visible maximum width of these landward and seaward-dipping cross-beds is about 30 m. Nevertheless, submerged beds and single blocks are followed up to 10 m offshore and terminate at about 1 m below the current sea-level. Taken to clarify the thickness and extension of coquinite beds under the loose beach sands, three coastline-parallel resistiv-ity tomograms, together with measured apparent resistivresistiv-ity pseudo-sections obtained using the two-dimensional inversion process, are shown in Fig. 6a–f, respectively. ERT1, taken along the wave swash zone where coquinite beds are widely exposed, showed a large resistivity range varying between 1 and 900 O-m (Fig. 6b). Relatively high resistivity values throughout this transect indicate that the exposed blocks are protrusions of a body of coqui-nite buried under the beach sands. On the other hand, lower values (<5 O-m) well define saturation of the beach material by sea-water. The thickness of the beach material appears to be about 9–10 m and it covers resistive (>500 O-m) rugged bedrock at the bottom. ERT2 (Fig. 6d), obtained 13 m back from ERT1, showed very similar subsurface patterns and revealed a landward extension of the coquinite beds under the beach sands. However, the underlying eolianite is not apparent in terms of contrast in ERT sections due to its similarity in resistivity with the coquinite.
Field observations showed that the exposed coquinite layers are composed of tightly cemented tabular planar cross-beds with a total thickness of 0.8 m. The main trend of the beds is parallel to the NE-SW trending coastline with the exception of local changes. Despite lacking consistency in both azimuth trends and dip direc-tions due to short-distance changes in bedding structure, four sets of cross-beds were determined at a few typical sections from bot-tom to top, separated from each other by nearly horizontal planes (Fig. 5).
The lowermost set is composed of slightly seaward-inclined (average: 2°) laminae. Grain size measurements showed that it is composed predominantly (83%) of fine, medium and coarse sands
of which medium sand prevails. Very coarse sands and very fine gravels account for about 14%. The rest comprise very fine sands and a mixture of silt and clay. Albeit in broken form, various ben-thic foraminifera were identified in this bottom level, such as Ammonia parkinsoniana, A. tepida, Ammonia sp., Elphidium sp., Hay-nesina sp., and Polymorphina sp.
This 10-cm-thick bottom layer, which becomes submerged dur-ing high tides, passes upward into foresets with a thickness of 20 cm, prograding towards the sea at higher angles ranging between 15-20°. The third unit is about 20 cm thick and composed of low-angle (15°) laminae, again dipping seaward. This level is rather open due to sea-wave erosion in many sections and passes upward into the thickest (about 60 cm) topmost bed comprising foresets with landward-inclined beds up to 20°. This is somewhat different in terms of grain size distribution, consisting of a silt and clay mixture (20%), sand grains ranging in size between very fine and very coarse (77%), and a small amount (3%) of very fine gravels. Various species of foraminifera exist within this top level, includ-ing E. crispum, Ammonia sp., A. compacta, A. parkinsoniana, A. tepida,
Ammonia spp., E. macellum, E. cf. Pulvereum, Elphidium spp., Hay-nesina sp., Quinqueloculina sp., Porosononoin subgranosum, and Por-osononoin sp.
4.3. Implications for paleocoastal environment during MIS 6
OSL age estimations revealed that the deposition ages of the eolian quartz sands vary between 187,5 ± 21,2 and 163,3 ± 13 on the back-beach and are 177,9 ± 14,5 under the coquinite layers near the coastline, implying that the studied sequence is a low-stand or glacial-age eolianite. Suggesting dune accretion during the MIS 6 glacial period, such eolianite sands together with their carbonate fills are known to be representative of eolian reworking or deflation. In other words, they are attributed to carbonate-laden diachronous dune deposits derived from the exposed coastal shelf with high- to low-energy ooid shoals and oolitic sand complexes (Bebout et al., 1991; Rankey and Reeder, 2011), which was invaded during the preceding MIS 7 interglacial and was the main source for reworking by onshore winds (Abegg et al., 2001; Brooke,
2001). The areal extent of the exposed continental shelf of the Black Sea during the lowstand of this penultimate glaciation, which was lower than -100 m (Winguth et al., 2000), was large enough to supply sediment and amalgamating calcium carbonate.
When considered from this point of view, the existence of such well-indurated dune sands together with very abundant ooids sug-gestive of marine provenance along the Black Sea coast poses a conflict considering the temperate oceanic climate of the Black Sea coasts, dominated at present by high and regularly distributed rainfall, cool (<20°) sea water and low evaporation all year round. Thus, it is logical to assume that drier and windier conditions might have been effective during the deposition and ensuing cementation of dune sands by the incorporated carbonates, as reported from several coastal sites elsewhere (Bigarella, 1972; Ward, 1973; Bowler, 1986; Zhou et al., 1994). The lack of rhizoliths and paleosol within the low-relief eolianite indicates that the dune sand accretion by onshore and offshore winds following lithifica-tion formed sets of tabular to planar cross-beds that were perpet-ual and formed inappropriate conditions for development of soils and dune plants. The relatively cooler temperatures during MIS 6 compared to other glacial periods might also have been favorable for eolianite formation (Masson-Delmotte et al., 2010).
4.4. Implications for paleocoastal environment during MIS 5e The above-stated characteristics of the seaward and landward inclined tabular planar cross-beds of the coquinite are indicative of deposition along a wave-dominated high-energy beach (foreshore-backshore) environment: the seaward dipping beds represent deposition by swash-backswash flow, whereas landward dipping tabular planar cross beds represent deposition generated by landward migration of foreshore ridges and /or formation of storm-induced washover fans.
For the deposition age of the overlying coquina beds, AMS radiocarbon dating from the cemented bivalvia shells revealed cal-ibrated age ranges of 30,610 to 30,250 and 26,950 to 26,250 years BP for the lowermost and topmost samples, respectively. Based on available data provided by Russian researchers compiled by Yanko-Hombach (2007), these ages coincide with the Surozhian era, which occurred at 40–25 kyr BP. At 31 kyr BP of this highstand, the Mediterranean waters were connected with the Black Sea (Chepalyga, 2002), as evidenced by low-salinity-tolerant mollusks, such as Cerastoderma edule, Bittium reticulatum, etc. (Chepalyga, 1995). Amongst other evidence regarding this transgressive event, when the level of the Black Sea was about 30 m compared to pre-sent, there were submerged coastal bars on the northwestern and Romanian shelves and a quantity of Mediterranean foraminifera (Yanko-Hombach, 2007), as well as a co-mixture of Mediterranean mollusca with those from the Caspian Sea (Nevesskaya and Nevessky, 1961).
On the other hand, if it is assumed that the Black Sea was nearly 30 m lower at that time, the present position of the coquinite beds could only be explained by tectonic uplift after deposition of coquinite components. In such a case, the coquinite could have been raised about 1 mm 1, which appears unreasonable given the lack of any tectonic-induced evidence throughout the coastal zone. Another assumption might be that the Black Sea reached a level equal to the present, as evidenced by the thickness and diage-netic characteristics of the coquinite. Thus, at this stage, it can be presupposed that when the Black Sea was in connection with the Mediterranean via the Bosphorus at that time, the loose coquina materials might have accumulated in the studied beach face (fore-shore) zone, which is very close (about 20 km) to this waterway. Nevertheless, it must be stated that recent data (Çag˘atay et al., 2009) from the Marmara Sea are not supportive of that connection
but rather a propound disconnection during the period spanning MIS 4 to MIS 2.
The two OSL ages (127.4 ± 9.3 ka and 128.1 ± 11.9 ka) obtained from the detrital quartz grains embedded within the coquina shells showed, on the other hand, a much older period, coinciding with the last interglacial, during which it has been suggested that the sea-level was 6–8 m above the present level (Federov, 1978; Chepalyga, 1984; Svitoch et al., 2000). The alternating foresets with opposite directions from bottom to top can be attributed to depo-sition by swash-backwash and storm-originated currents that might have dominated along the cemented coquina beach at the pre-cementation stage. Confirming the connection with the Mediterranean Sea at this stage, as demonstrated by increasing Sr/Caostracods and U/Caostracods values at 128.1 ± 0.7 ka BP (Wegwerth et al., 2014), microscopic examination of the coarse grain-shelly sand (with abundant mollusk shells) and finer sand parts of the cemented coquinite revealed the occurrence of poor benthic foraminiferal assemblages in terms of diversity, repre-sented mainly by Elphidium and Ammonia species. Haynesina anglica, Haynesina sp., Polymorphina sp., Cribroelphidium sp. and Porosononoin sp. are found in small amounts. The presence of E. ponticum and H. anglica within the assemblages is typical of Pleis-tocene sediments in the Black Sea and their occurrence in the Gulf of Izmit (Marmara Sea) has been attributed to the connection between the Black Sea and Mediterranean during Pleistocene (Meriç et al., 1995). Thus the coquinite sequence could be consid-ered as a unique record in relation to the presence of cemented MIS 5e deposits throughout the Black Sea coast together with MIS 5e eolianites, previously recognized to the further west (Erginal et al., 2013a), which is, however, missing in the study area. Even though the coquinite beds could be considered as a thin succession for the MIS 5e deposits, its present thickness, considering the pro-posed tectonic stability of the coast, could be due to removal to a large extent by high-energy waves prevalent in the area.
5. Conclusions
The studied coastal deposits bear witness to the paleocoastal environment during the Late Pleistocene penultimate lowstand and highstands on the west Black Sea coast of Turkey. The collocat-ing ooid-rich lowstand eolianite and overlycollocat-ing transgressive sequence of coquinite with mixed benthic foraminiferal assem-blage, typical of the Mediterranean, provide data for paleocoastal dynamics during MIS 6 and 5e, respectively, but reveal a long non-depositional period between them. The ERT-derived images of resistivity proved useful in manifesting the subsurface extent of the studied coastal outcrops.
Acknowledgements
The first author wishes to thank the Scientific and Technological Research Council of Turkey (TÜB_ITAK) (project number: 113Y418) and Turkish Academy of Sciences (TÜBA) for financial support. Gra-ham H. Lee is thanked for proof-reading the text. Mustafa Avcıog˘lu is thanked for assisting with the field work. Critical reviews by anonymous referees contributed much for the improvement of the paper.
References
Abegg, F.E., Loope, D., Harris, P.M., 2001. Carbonate aeolionites: depositional models and diagenesis. In: Abegg, F.E., Harris, P.M., Loope, D.B. (Eds.), Modern and Ancient Carbonate Aeolionites: Sedimentology, Sequence Stratigraphy, and Diagenesis. SEPM Spec. Publ., vol. 71, pp. 17–30.
Algan, O., Ergin, M., Keskin, Sß., Gökasßan, E., Alpar, B., Ongan, D., Kırcı-Elmas, E., 2007. Sea level changes during the late Pleistocene-Holocene on the southern shelves of the Black Sea. In: Yanko-Hombach, V., Gilbert, A.S., Panin, N., Dolukhanov, P.
M. (Eds.), 1980, The Black Sea Flood Question: Changes in Coastline, Climate, and Human Settlement. Springer, Dordrecht, The Netherlands, pp. 603–631.
Arslanov, Kh.A., 1993. Late Pleistocene geochronology of European Russia. Radiocarbon 35 (3), 421–427.
Badertscher, S., Fleitmann, D., Cheng, H., Edwards, R.L., Göktürk, O.M., Zumbühl, A., Leuenberger, M., Tüysüz, O., 2011. Pleistocene water intrusions from the Mediterranean and Caspian seas into the Black Sea. Nat. Geosci. 4, 236–239.
Bardaji, T., Goy, J.L., Zazo, C., Hillaire-Marcel, C., Dabrio, C.J., Cabero, A., Ghaleb, B., Silva, P.G., Lario, J., 2009. Sea level and climate changes during OIS 5e in the Western Mediterranean. Geomorphology 104, 22–37.
Bebout, D.G., Major, R.P., Tyler, N., Harris, P.M. and Kerans, C., 1991, Platform-edge, shallow-marine, ooid grainstone shoals, Joulters Cays, Bahamas: A modern analog of carbonate hydrocarbon reservoirs, in coastal depositional systems in the Gulf of Mexico, Quaternary framework and environmental issues: Gulf Coast Section SEPM Foundation. In: 12th Annual Research Conference, Program and Abstracts, pp. 26–29.
Bigarella, J.J., 1972. Eolian environments: their characteristics, recognition, and importance. In: Rigby, J.K., Hamblin, W.K. (Eds.), Recognition of Ancient Sedimentary Environments: Soc. Econ. Paleontologists Mineralogists Spec. Pub., vol. 16, pp. 12–62.
Bissell, H.J., Chilingar, G.V., 1967. Classification of sedimentary carbonate rocks. In: Chilingar, G.V., Bissell, H.J., Fairbridge, R.W. (Eds.), Carbonate rocks: Origin, Occurrence and Classification: Developments in Sedimentology. Elsevier, 9A, New York, pp. 87–168.
Bøtter-Jensen, L., 1997. Luminescence techniques: instrumentation and methods. Radiat. Meas. 17, 749–768.
Bowler, J.M., 1986. Spatial variability and hydrologic evolution of Australian lake basins: analogue for Pleistocene hydrologic change and evaporite formations. Paleogeogr. Paleoclimatol. Paleoecol. 54, 21–41.
Brooke, B., 2001. The distribution of carbonate aeolionite. Earth Sci. Rev. 55, 135– 164.
Çag˘atay, M.N., Eris, K., Ryan, W.B.F., Sancar, U., Polonia, A., Akcer, S., Biltekin, D., Gasperini, L., Gorur, N., Lericolais, G., Bard, E., 2009. Late Pleistocene-Holocene evolution of the northern shelf of the Sea of Marmara. Mar. Geol. 265, 87–100. Chepalyga, A.L., 1984. Inland sea basins. In: Late Quaternary Environments of the Soviet Union. Velichko, A.A., Wright, Jr., H.E., Barnowsky, C.W. (Eds.). University of Minnesota Press, English edition, Minneapolis, pp. 229–247.
Chepalyga, A.L., 1995. Pliyo-Pleyistosen Karadeniz havzaları ve bunların Akdeniz ile iliskileri. In: Meriç, E. (Ed.), _Izmit Körfezi Kuvaterner _Istifi. Istanbul, pp. 303–311 (in Turkish).
Chepalyga, A.L., 2002. Chernoe more [Black Sea]. In: Velichko, A.A. (Ed.), Dinamika landshaftnykh komponentov i vnutrennikh morskikh basseinov Severnoi Evrazii za poslednie 130 000 let [Dynamics of Terrestrial Landscape Components and Inner Marine Basins of Northern Eurasia during the Last 130,000 Years]. GEOS, Moscow, pp. 170–182 (in Russian).
Colleoni, F., Krinner, G., Jakobsson, M., Peyaud, V., Ritz, C., 2009. Influence of regional parameters on the surface mass balance of the Eurasian ice sheet during the peak Saalian (140 kya). Global Planet. Change 68, 132–148.
David, P., Panagiotis, T., Konstantinos, A., 2009. Electrical resistivity tomography mapping of beachrocks: application to the island of Thassos (N. Greece). Environ. Earth Sci. 59, 233–240.
Dockal, J.A., 1995a. Documentation and evaluation of radiocarbon dates from the ‘‘Cape Fear Coquina” (Late Pleistocene) of Snows Cut, New Hanover County, North Carolina. Southeast. Geol. 35, 169–186.
Dockal, J.A., 1995b. Evaluation of an Apparent Late Pleistocene (25–40 ka BP) Sea level high stand: an artifact of a greatly enhanced cosmic ray flux of60 ka BP. J. Coastal Res. 11, 623–636.
Erginal, A.E., Ekinci, Y.L., Demirci, A., Elmas, E.K., Kaya, H., 2012. First note on Holocene coquinite on Thrace (Black Sea) coast of Turkey. Sed. Geol. 267–268, 55–62.
Erginal, A.E., Kiyak, N.G., Ekinci, Y.L., Demirci, A., Ertek, A., Canel, T., 2013. Age, composition and paleoenvironmental significance of a late Pleistocene eolianite from the western Black Sea coast of Turkey. Quat. Int. 296, 168–175.
Erginal, A.E., Ekinci, Y.L., Demirci, A., Avcıog˘lu, M., Öztürk, M.Z., Türkesß, M., Yig˘itbas, E., 2013. Depositional characteristics of carbonate-cemented fossil eolian sand dunes: Bozcaada Island, Turkey. J. Coastal Res. 29 (1), 78–85.
Federov, P., 1978. Ponto-Caspian Pleistocene. Bulletin of the Geological Institute of the Academy of Sciences of USSR, 310, pp. 31–43 (in Russian).
Federov, P.V., 1988. The problem of changes in the level of the Black Sea during the Pleistocene. Int. Geol. Rev. 30, 635–641.
Flügel, E., 2010. Microfacies of Carbonate Rocks: Analysis, Interpretation and Application. Springer, pp. 242–244. ISBN 978-3-642-03795-5.
Grigor’yev, A.V., Scevchenko, A.I., Shopov, V.L., 1985. Korrelyatsiya chetvertichnykh otlozheniy chernomorskogo shelfa i poberezh’ya Bolgarii i Ukrainy [Correlation of the Quaternary Deposits of the Black Sea Shelf of Bulgaria and Ukraine], Academy of Science, Kiev, preprint 85–29 (in Russian).
Hunter, R.E., 1977a. Basic types of stratification in small eolian dunes. Sedimentology 24, 361–387.
Hunter, R.E., 1977b. Terminology of cross-stratified sedimentary layers and climbing-ripple structures. J. Sediment. Res. 47 (2), 697–706.
Jaoshvili, G., Popkhadze, L., Tvalchrelidze, M., 2010. Lithostratigraphy of the Pleistocene deposits of Georgian sector of the Black Sea. Scientific Annals of the School of Geology, Aristotle University of Thessaloniki. Proceedings of the XIX CBGA Congress, Thessaloniki, Greece, Special vol. 99, pp. 457–461.
Keskin, S., Pedoja, K., Bektasß, O., 2011. Coastal uplift along the eastern Black Sea coast: new marine terrace data from eastern Pontides, Trabzon (Turkey) and a review. J. Coastal Res. 27 (6A), 63–73.
Kocurek, G., Dott, H.R., 1981. Distinction and uses of stratification types in the interpretation of eolian dunes. J. Sediment. Res. 51 (2), 579–595.
Loke, M.H., Barker, R.D., 1996. Rapid least-squares inversion of apparent resistivity pseudosections using a quasi-Newton method. Geophys. Prospect. 44, 131–152.
Masson-Delmotte, V., Stenni, B., Pol, K., Braconnot, P., Cattani, O., Falourd, S., Kageyama, M., Jouzel, J., Landais, A., Minster, B., Krinner, G., Johnsen, S., Röthlisberger, R., Chappellaz, J., Hansen, J., Mikolajewicz, U., Otto-Bliesner, B., 2010. EPICA Dome C record of glacial and interglacial intensities. Quat. Sci. Rev. 29 (1–2), 113–128.
McKee, E.D., Bigarella, J.J., 1972. Deformational structures in Brazilian coastal dunes. J. Sediment. Res. 42, 670–681.
Meriç, E., Yanko, V., Avsßar, N., 1995. _Izmit Körfezi (Hersek Burnu-Kaba Burun) Kuvaterner istifinin Foraminifer Faunası. In: Meriç, E. (Ed.), Izmit Körfezi Kuvaterner Istifi. Deniz Harp Okulu Komutanlıg˘ı Basımevi, _Izmit, pp. 105–151 (in Turkish).
Murray, A.S., Mejdahl, V., 1999. Comparison of regenerative-dose single-aliquot and multiple-aliquot (SARA) protocols using heated quartz from archaeological sites. Quat. Sci. Rev. (Quat. Geochronol.) 18, 223–229.
Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiat. Meas. 32, 57–73.
Murray, A.S., Wintle, A.G., 2003. The single aliquot regenerative dose protocol: potential for improvements in reliability. Radiat. Meas. 37 (2003), 377–381.
Nevesskaya, L.A., 1965. Pozdnechetvertichnye Dvustvorchatye Molluski Chernogo Morya, Ikh Sistematika I Ekologiya [Late Quaternary Mollusks of the Black Sea, Their Systematics and Ecology]. Academy of Science of the USSR, Moscow (in Russian).
Nevesskaya, L.A., Nevessky, E.N., 1961. O sootnoshenii karangatskikh i
novoevksinskikh sloev v pribrezhnykh raionakh Chernogo moria [Correlation between the Karangatian and Neoeuxinian layers in littoral regions of the Black Sea]. Doklady Akademii Nauk SSSR 137, 934–937.
Olley, J.M., Murray, A.S., Robert, R.G., 1996. The effects of disequilibria in the uranium and thorium decay chain on burial dose rates in fluvial sediments. Quat. Sci. Rev. 15, 751–760.
Polymeris, G.S., Erginal, A.E., Kiyak, N.G., 2012. A comparative morphology, compositional as well as TL study of Bozcaada (Tenedos) and Sßile aeolianites, Turkey. Mediterr. Archaeol. Archaeometry 12 (2), 117–131.
Prescott, J.R., Hutton, J.T., 1988. Cosmic ray and gamma ray dosimetry for TL and ESR. Nucl. Tracks Radiat. Meas. 14, 223–227.
Prescott, J.R., Hutton, J.T., 1994. Cosmic ray contribution to dose rates for luminescence and ESR dating: large depths and long-term time variations. Radiat. Meas. 23, 497–500.
Rankey, E.C., Reeder, S.L., 2011. Holocene oolitic marine sand complexes of the Bahamas. J. Sediment. Res. 81, 97–117.
Sasaki, Y., 1992. Resolution of resistivity tomography inferred from numerical simulation. Geophys. Prospect. 40, 453–464.
Schlichting, E., Blume, E., 1966. Bodenkundliches Practicum. Verlag paul Parey, Hamburg un Berlin.
Svitoch, A.A., Selivanov, A.O., Yanina, T.A., 2000. Paleohydrology of the Black Sea Pleistocene basins. Water Resour. 27, 594–603.
Ward, W.C., 1973. Influence of climate on the early diagenesis of carbonate eolianites. Geology 1, 171–174.
Wegwerth, A., Dellwig, O., Kaiser, J., Ménot, G., Bard, E., Shumilovskikh, L., Schnetger, B., Kleinhanns, I.C., Wille, M., Arz, H.W., 2014. Meltwater events and the Mediterranean reconnection at the Saalian-Eemian transition in the Black Sea, Earth Planet. Sci. Lett. 404, 124–135.
Wilson, J.L., 1975. Carbonate Facies in Geologic History. Springer-Verlag, Berlin, p. 65.
Winguth, C., Wong, H.K., Panin, N., Dinu, C., Georgescu, P., Ungureanu, G., Krugliakov, V.V., Podshuveit, V., 2000. Upper Quaternary water level history and sedimentation in the northwestern Black Sea. Mar. Geol. 167, 127–146.
Yanina, T., 2014. Ponto-Caspian region: environmental consequences of climate change during the Late Pleistocene. Quat. Int. 345, 88–99.
Yanko-Hombach, V., 2007. Controversy over Noah’s Flood in the Black Sea: geological and foraminiferal evidence from the shelf. In: Yanko-Hombach, V., Gilbert, A.S., Panin, N., Dolukhanov, P. (Eds.), The Black Sea Flood Question: Changes in Coastline, Climate, and Human Settlement. Springer, Dordrecht, The Netherlands, pp. 149–203.
Yildirim, C., Melnick, D., Ballato, P., Schildgen, T.F., Echtler, H., Erginal, A.E., Kıyak, N. G., Strecker, M.R., 2013. Differential uplift along the northern margin of the central anatolian plateau: inferences from marine terraces. Quat. Sci. Rev. 81, 12–28.
Zhou, L., Williams, M., Peterson, J.A., 1994. Late Quaternary aeolianites, paleosols and depositional environments on the Nepean Peninsula, Victoria, Australia. Quat. Sci. Rev. 13, 225–239.
Zhuze, A.P., Koreneva, E.V., Mukhina, V.V., 1980. Paleogeography of the Black Sea on the data of diatom investigation and spores and pollen analyses of the deepwater deposits. Geological History of the Black Sea on the Results of Deepwater Drilling, Nauka, Moscow, pp. 77–86.
Zubakov, V.A., 1988. Climatostratigraphic scheme of the Black Sea Pleistocene and its correlation with the oxygen-isotope scale and glacial events. Quat. Res. 29, 1–24.
