Colour origin of red sandstone beds within the Hüdai Formation (Early Cambrian), Aydıncık (Mersin), southern Turkey

Turkish Journal of Earth Sciences Turkish J Earth Sci (2013) 22: 563-573 © TÜBİTAK doi:10.3906/yer-1208-1 http://journals.tubitak.gov.tr/earth/ Research Article Colour origin of red sandstone beds within the Hüdai Formation (Early Cambrian), Aydıncık (Mersin), southern Turkey 1, 2 Muhsin EREN * Selahattin KADİR Department of Geological Engineering, Faculty of Engineering, Mersin University, Mersin, Turkey 2 Department of Geological Engineering, Faculty of Engineering, Eskişehir Osmangazi University, Eskişehir, Turkey 1 Received: 06.08.2012 Accepted: 28.02.2013 Published Online: 13.06.2013 Printed: 12.07.2013 Abstract: The basal part of the Hüdai Formation (Early Cambrian) in the Aydıncık (Mersin) area comprises red sandstone beds at different stratigraphic levels, showing ripple cross-lamination. These beds were deposited in the middle to lower part of an intertidal flat environment. Bedding-parallel reddening and its cyclic character suggest syn-sedimentary or early diagenetic red colouration in a marine environment. Both X-ray diffraction and petrographic analyses indicate that the red sandstones are composed of predominantly K-feldspar and quartz grains and an illite matrix. These are dominantly arkosic wacke. A small amount of hematite (<5 wt.%) is present in all the samples, which gives a red colour to the whole rock. Scanning electron microscopy images show that hematite pigment appears as spherical and rod-shaped particles in sizes of 1 µm or less disseminated on the grains and in the matrix. Considering their size and morphology, the hematite particles can be interpreted as fossil bacteria, indicating a bacterially induced precipitation, probably from seawater. A 2-step biomineralisation process could explain iron oxidation during early diagenesis in an intertidal environment: (a) trapping of iron (Fe2+) on the bacterial cell wall with oxidation by bacterial activity; (b) inorganic precipitation followed early-stage bacterial nucleation sites resulting in crystal growth. The Fe2+ for reddening is provided by an intrastratal alteration of the iron-bearing minerals. Key words: Arkosic wacke, colour origin, early diagenesis, biomineralisation, Early Cambrian, Hüdai Formation, intertidal red bed 1. Introduction The term “red beds” usually refers to strata of reddishcoloured sedimentary rocks, which are commonly sandstone, shale, and limestone. They are formed in various depositional environments, including marine and nonmarine environments, and are common in all parts of the stratigraphic record (Van Houten, 1973). The red colour is due to the presence of finely dispersed hematite pigment (Fe2O3). The origin of the hematite pigment in red beds is controversial and has been discussed in many papers (Van Houten, 1968, 1973; Einsele, 1992). There are mainly 2 contrasting hypotheses to explain the origin of hematite pigment (Franke and Paul, 1980; Turner, 1980; Pye, 1983; Einsele, 1992; Friedman et al., 1992). One hypothesis contends that the hematite is detritally derived from lateritic soils (e.g., Krynine, 1949; Folk, 1976), and the other hypothesis suggests that the hematite forms authigenetically after deposition by the alteration of ironbearing detrital grains (e.g., Walker, 1967; Eren and Kadir, 1999). More recently, in the second hypothesis, a microbial origin was proposed for the hematite pigment in carbonate rocks (see Mamet et al., 1997; Preat et al., 1999, 2000; * Correspondence: Boulvain et al., 2001; Della Porta et al., 2003; Mamet and Preat, 2006). However, there is no available information regarding a microbial origin of hematite pigment in clastic sedimentary rocks. Most of the knowledge on this subject comes from synthesised microbial (especially bacterial) iron oxidation (e.g., Ehrenreich and Widdel, 1994; Konhauser, 1998; Kapler et al., 2005; Benzerara et al., 2008; Fredrickson and Zachara, 2008; Miot et al., 2009). This paper investigates the origin of hematite pigment in the red sandstone beds of the Hüdai Formation (Early Cambrian) and provides for the first time evidence for a microbial origin of the red colour in clastic sedimentary rocks. 2. Geological setting The study area is located within the Aydıncık (Mersin) district, which is known as a part of the central Taurides in southern Turkey (Figure 1; Eren et al., 2007). In the Aydıncık area, a thick sedimentary package ranging in age from the Infra-Cambrian to Recent is present (Figure 2; Koç, 1996; Koç et al., 1997; Eren et al., 2002, 2007). The lower part of this sequence consists of Palaeozoic 563 EREN and KADİR / Turkish J Earth Sci 32° 28° 36° 40° 44° N B LAC K S EA İstanbul Kars NAFZ 40° Kayseri N ER ES ST D EA U R I FZ EA TA Aladağ . . . . . Konya . Bolkar M.. . . . . . . . . . Adana . . . . . .. . . CENTRAL . .. . . . .. . . . . TAURIDES . . . . . . . .. . . . . . . Alanya . . .. . Mersin . .. .... . .. . . . .. . . . . . . MEDITERRANEAN SEA Erzincan Bitli s su Diyarbakır ture zone 250 km 0 Am ano Beydağ ı . ik M Geayvak k Kırk ult Fa N R E ES Muğla ST D E RI W U TA Ece m Fau iş lt İzmir a Munzur ns Mountai sM . AEGEAN SEA ANKARA Aydıncık 36° TARSUS MERSİN MUT GÖKSU RIVER ERDEMLİ N R AL VE GÜLNAR RI GAZİPAŞA AM OS SİLİFKE ANAMUR Scale AYDINCIK STUDY AREA b TAŞUCU 0 10 20 30 km MEDITERRANEAN SEA Figure 1. a) Schematic map illustrating the Tauride Orogenic Belt in Turkey and its subdivisions (Eren et al., 2007), NAFZ = North Anatolian Fault Zone, EAFZ = East Anatolian Fault Zone. Study area marked with a square. b) Detailed location map of the study area. sedimentary/metasedimentary (low-grade metamorphic) units that were deposited at the northern margin of northeastern Gondwana, describing a preopening period of the Neotethys Ocean (Özgül, 1983; Wehrmann et al., 2010). The Hüdai Formation (Early Cambrian) and its equivalent sedimentary rocks of predominantly cross-bedded quartzarenites (the Feke Formation) represent the basal part of the Palaeozoic units in the Tauride Belt and are interpreted as beach deposits (Dean and Özgül, 1994; Göncüoğlu, 1995; Kozlu and Göncüoğlu, 1995; Göncüoğlu and Kozlu, 2000). Details of the sedimentary and stratigraphic characteristics of the Hüdai Formation in the Aydıncık area have been provided by Eren and Öner (2000). In the study area, sedimentary rocks of the Hüdai Formation are typically exposed in a cliff near the shoreline and also at Çıra Tepe (hill), where the Hüdai Formation conformably overlies the Sipahili Formation (Infra-Cambrian) at the 564 coastal area and is conformably overlain by the Çaltepe Formation (Lower to Middle Cambrian) (Figure 2; Koç, 1996; Koç et al., 1997; Eren and Öner, 2000). The thickness of the formation is approximately 830 m (Figure 3). In the vertical sequence, the formation represents 3 different parts. The basal part of the formation consists of a rhythmic alternation of a cream-beige, horizontally laminated sandstone (predominantly qu (...truncated)