The clay mineralogy of the Recent surface sediments from the Cilicia Basin, northeastern Mediterranean

Marine Geology, 26 (1978) M51--M58

M51

© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

L e t t e r Section THE CLAY MINERALOGY OF THE RECENT SURFACE SEDIMENTS FROM THE CILICIA BASIN, NORTHEASTERN MEDITERRANEAN

H.F, SHAW

Department of Geology, Imperial College, London (Great Britain) (Received July 19, 1977; revised and accepted November 14, 1977)

ABSTRACT Shaw, H.F., 1978. The clay mineralogy of the Recent surface sediments from the Cilicia Basin, northeastern Mediterranean. Mar. Geol., 26: M51--M58. The mineralogy of the clay fractions of 98 surface sediment samples from the Cilicia Basin, northeastern Mediterranean, have been determined by X-ray diffraction analysis. Illite and smectite are the major clay-mineral phases with minor amounts of kaolinite, chlorite and serpentine in all the samples analysed. Maps of the distributions of illite, smectite and chlorite are presented and from these, four clay-mineral provinces, with characteristic clay assemblages, have been defined. The main sources of the clay sediments into the Cilicia Basin are from the river systems draining the coasts of southern Turkey and northwestern Cyprus, though there may also be some influx of clay material from outside the Basin to the south.

INTRODUCTION

The CiliciaBasin lies between Cyprus and the southern coast of Turkey, flanked by the Taurus Mountains to the north and the Kyrenia Mountains to the south (Fig. 1). The surface sediments of the CiliciaBasin are mainly composed of mudgrade material (Folk's Classification, 1954) and in the central part of the Basin the surface sediments consist of more than 50% <~2 ~ m material. Consequently, for the majority of the surface sediments, the clay minerals are amongst the principal mineralogical phases. The main suppliers of fluvialdetritus into the basin are the perennial rivers draining the Turkish coast represented by the rivers of the Seyhan Delta complex and the Goksu. In addition to these rivers,the short seasonal rivers draining the Turkish and Cyprus coasts m a y also provide appreciable amounts of sediment when they flow in winter and spring (Evans, 1971).

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SAMPLING AND ANALYTICAL PROCEDURES

The surface sediments were sampled at 98 locations during the late summer/ early autumn of 1972 and 1974 on board the Natural Environment Research Council ship R.R.S. "Shackleton". Samples of clay sediments from the rivers and coastal regions (collected by Dr. G. Evans, Imperial College) were also selected for clay-mineral analysis. The < 2 pm fractions were separated from the whole-sediment samples and orientated specimens of the clay fractions were prepared using a suction -onto-ceramic-tile method (Shaw, 1972) for X-ray analysis. To completely differentiate all the clay-mineral phases present, X-ray analyses were carried out on (1) the air-dried specimens, (2) after gtyceration, (3) after heating for one hour at 400°C, and (4) after heating for one hour at 550°C. The analyses were made using a Philips powder diffractometer employing Mn-filtered FeK~ radiation with a scanning speed of 1/~o20 per minute. N

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Fig. 1. Bathymetry and regional framework of the Cilicia Basin.

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MISIS

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M53

The relative proportions of the clay minerals identified, i.e., illite, smectite, kaolinite, chlorite and serpentine, were estimated by comparing the weighted intensities (peak areas) of the basal reflections of the different clay minerals after glyceration of the specimen. The reflections and intensities used are: 17 A reflection for smectite, 4 times the 10 A reflection for illite and 2 times the 7 A reflection for kaolinite, chlorite and serpentine. To determine the relative proportions of the latter three minerals, the relative intensities of their 002 (3.57 A), 004 (3.54 A) and 002 (3.66 A) reflections, respectively, were compared. R E S U L T S A N D DISCUSSION

In all the samples analysed, illite, smectite, kaolinite, chlorite and serpentine were detected in varying amounts. Distribution maps for smectite, illite and chlorite are shown in Figs. 2--4. Illite and smectite are the major phases, varying from < 2 0 % to > 6 0 % in each case with a strong antipathetic relationship so that areas of high smectite content are areas of low illite content and vice versa. Kaolinite and chlorite are only present in minor amounts of 5--10% whilst serpentine is usually only in the order of 1--2%. 32"E 37°N

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Fig. 2. Percentage smectite in the clay fractions of the surface sediments.

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Fig. 4. Percentage chlorite and percentage serpentine in the clay fractions of the surface sediments.

M55

From visual examination of the distribution maps of the various clay minerals, four regions with characteristic clay-mineral assemblages can be defined (Fig. 5). These regions resemble the geochemical provinces defined from the geochemical data of the bulk sediment samples (Shaw and Bush, 1978). The boundaries between the four regions are not of course rigidly defined and the provinces grade one into the other. Southern Turkish coast Region

Along the southern Turkish coast westwards from the Goksu Delta, the clay-mineral assemblage of the nearshore sediments is characterised by relatively low smectite and high illite contents, and with increasing distance from the coast the smectite content increases whilst that of illite decreases. Analyses of a few samples of coastal soils and river clays from this part of the Turkish coast show the following average composition for the clay fractions: 40--45% smectite, 45% illite, 5--10% kaolinite and 5% chlorite. The offshore sediments are thus generally richer in illite and poorer in smectite than the immediately adjacent coastal-plain sediments. The distribution patterns of illite and smectite suggest that there is differential settling, in zones parallel to the coast, of the clay-grade sediments that 32°E

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ASSEMBLAGES

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Fig. 5. Clay-mineral provinces of the surface sediments in the Cilicia Basin.

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M56 originate locally from the rivers and, to a lesser extent, from coastal erosion of this part of the Turkish coast. Such differential settling would cause the illite to settle out more quickly and in higher proportions nearer the coast than the smectite, due to difference in particle size and flocculation rates. Further evidence of local sources for the clay material in this coastal region is found in the far west where the seasonal rivers drain the metamorphic chlorite schists of the Alanya Massif. There is an increase in the proportion of chlorite in the clay fraction of the sediments off this part of the coast, indicating a direct source from the Massif.

Seyhan Delta Region Analyses of flood-plain and fluvial deposits from the Seyhan Delta show them to contain an average of 40% smectite, 45--50% illite, 5% kaolinite and 5--10% chlorite. A profile from the m o u t h of the Seyhan to the edge of the shelf shows a general tendency for the smectite content to increase while the illite content decreases, presumably as a result of differential settling. However, the clearly defined region of high smectite (> 55%) and low illite {<:35%) contents may not simply reflect differential settling of clay minerals from the Seyhan because of its extension southwards to the edge of the Cilicia Basin. The distribution of samples does not allow a southern boundary of this smectite enriched region to be defined and an influx of smectite-rich clays from the south cannot be discounted (Fig. 2). Venkatarathnam and Ryan (1971) proposed that the Nile clays could be dispersed northwards parallel to the Levant coast and into the Cilicia Basin. However, Nit and Nathan (1973) concluded that north of Cyprus the Nile could no longer be considered as a principal source of fine-grained sediment. Shaw and Bush (1978) noted a region of sandier sediments on the edge of the shelf off the Seyhan enriched in Cr and Ni, that they suggested might be relict deposits. These sediments also have a characteristic clay mineralogy with higher proportions of illite, chlorite and serpentine, and lower smectite contents than the surrounding sediments. The clay-mineral assemblage and the presence of enhanced serpentine in particular confirms that these sediments must be associated with basic--ultrabasic source rocks as suggested by Shaw and Bush (1978). Along the Turkish coast from the Goksu Delta to the m o u t h of the Seyhan the clay assemblages of the adjacent coastal sediments axe characterised by enriched chlorite contents. This implies a local source of material from the short seasonal rivers draining this part of the coast with the chlorite originating from the ultrabasic rocks cropping out in their drainage areas.

Southern and Central Basin Region The clay assemblage of this region shows little variation and is characterised

M57 by similar proportions of illite and smectite (35--45%), a b o u t 10% kaolinite, 5% chlorite and 1--2% serpentine. There is little or no variation in the clay mineral compositions in the vicinity of the coast of northern Cyprus. This implies that there is little or no input of fine-grained sediment from the northern coast of Cyprus, and is supported b y the geochemical evidence of Shaw and Bush {1978). The clay assemblage of the Southern and Central Basin Region suggests the accumulation of fine-grained sediment transported westwards by the Mediterranean gyre from the Seyhan Delta and possibly outside the Basin from the south, and also sediment transported from the immediately adjacent Turkish coast. MORPHOU

BAY REGION

The sediments of this region are characterised by a clay-mineral assemblage that is significantly enriched in smectite. The highest smectite contents occur in and around Khrysokhou Bay, where seasonal rivers draining the volcanics to the south of the Troodos Massif enter the sea. The weathering of these volcanics should provide a ready source of smectite and this is confirmed by the presence of local bentonite deposits and available analyses of the river deposits show high smectite contents. In the Morphou Bay Region the smectite contents tend to decrease with distance from the shore, in contrast to the pattern observed off the southern Turkish coast and off the Seyhan Delta where differential settling is given as the explanation for increasing smectite contents with distance from the shore. A similar pattern of decreasing smectite contents with distance from shore is also observed off the Nile and along the Levant coast (Venkatarathnam and Ryan, 1971; Nir and Nathan, 1973) where the clay assemblage is also dominated by 60--70% smectite. It would thus appear that when the clay source is dominated by smectite the effects of differential settling are less apparent than when the clay source material is composed of a more equal distribution of the various clay minerals. CONCLUSIONS The clay mineral assemblages suggest that the main sources of clay sediment in the Basin are from the rivers of the Seyhan Delta, the Goksu and the seasonal rivers of the southern Turkish coast, and also from the northwestern coast of Cyprus via the seasonal rivers draining the T r o o d o s Massif. There is also the possibility that some clay material originates from sources outside the Basin although it is unlikely that this is from as far away as the Nile. Further work is needed to define the nature and relative importance of any influx of material from outside the Basin, b u t the principal sources of the clay sediments are thought to lie within or be from the margins of the Basin.

M58 ACKNOWLEDGEMENTS The author would like to thank Dr. G. Evans for his advice in the writing of this paper, Mr. R. Curtis for his help in carrying out the mineralogical analyses and to Mary Pugh for her help in drafting the figures. Financial support from the Natural Environment Research Council and the assistance of the Masters and crews of R.R.S. "Shackleton" during the 1972 and 1974 cruises, are gratefully acknowledged. The writer also wishes to thank the Governments of Turkey and Cyprus for permission to work in their territorial waters and particularly to Dr. Alpan of M.T.A. for his help and co-operation. REFERENCES Evans, G., 1971. The Recent sedimentation of Turkey and the adjacent Mediterranean and Black Seas: a review. In: A.S. Campbell (Editor), Geology and History of Turkey. Petroleum Exploration Society of Libya, pp. 385--406. Folk, R.L., 1954. The distinction between grain size and mineral composition in sedimentary rocks. J. Geol., 62: 344--359. Nir, Y. and Nathan Y., 1973. Mineral clay assemblages in Recent sediments of the Levantine Basin, Mediterranean Sea. Bull. Groupe F. Argiles, 24: 187--195. Shaw, H.F., 1972. The preparation of orientated clay mineral specimens for X-ray diffraction analysis by a suction-onto-ceramic-tilemethod. Clay Miner., 9 (3): 349--350. Shaw, H.F. and Bush, P.R., 1978. The mineralogy and geochemistry of the Recent surface sediments of the CiliciaBasin, N.E. Mediterranean. Mar. Geol., in press. Venkatarathnam, K. and Ryan, W.B.F., 1971. Dispersal patterns of clay minerals in the sediments of the eastern Mediterranean Sea. Mar. Geol., 11: 261--282.