An Approach to Paleoclimatic Conditions for Devonian (Upper Lochkovian and Middle Givetian) Ironstone Formation, NW Anatolian Carbonate Platform

Home , Ferizli, Givetian

Turkish Journal of Earth Sciences Turkish J Earth Sci (2015) 24: 21-38 http://journals.tubitak.gov.tr/earth/ © TÜBİTAK Research Article doi:10.3906/yer-1406-7

An approach to paleoclimatic conditions for Devonian (upper Lochkovian and middle Givetian) ironstone formation, NW Anatolian carbonate platform

1, 1 2 2 İsmail Ömer YILMAZ *, M. Cemal GÖNCÜOĞLU , Dilek Gülnur DEMİRAY , İbrahim GEDİK 1 Department of Geological Engineering, Middle East Technical University, Ankara, Turkey 2 General Directorate of Mineral Research and Exploration (MTA) of Turkey, Ankara, Turkey

Received: 10.06.2014 Accepted: 10.11.2014 Published Online: 02.01.2015 Printed: 30.01.2015

Abstract: Lower-middle Devonian iron-bearing successions were studied along 2 measured stratigraphic sections in the Çamdağ region of NW Anatolia. Ironstones in the upper part of the Fındıklı Formation in Kabalakdere are characterized by alternating red and green mudstones and sandstones at the bottom, followed by a series of dolomite, dolomitic limestone with oolitic ironstones, and chamositic mudstones at the top. Conodonts from these carbonates indicate the delta–pesavis zones of the late Lochkovian. The 12- to 45-m-thick Ferizli Formation unconformably overlies the Fındıklı Formation with a quartz-arenite succession at the bottom. The formation comprises alternating red, iron-rich limestones and dolomitic limestones, where iron-rich bioclastic grainstones are more dominant than iron-rich oolitic grainstones. The dolomitic limestones in this succession mark the ensensis and hemiansatus zones of the middle Givetian age. Mineralogically, the carbonates are dominated by goethitized and chamositized fossil fragments and chamositic oolites. In the oolitic facies, the oolites are made up of iron-bearing carbonates/iron, the bioclast of micritized/ironized brachiopods, and crinoids, whereas the matrix includes goethite, brown iron-silicates, chamosite, sideritic oolites, quartz clasts, and brachiopods. Partial iron precipitation within microborings or precipitation along the spine holes on echinoid grains is observed in the bioclastic grainstone/ biosparite facies. Iron peloids are also recognized in the grainstone facies. Iron precipitation could be explained as precipitation of transported and dissolved iron from a terrestrial environment under wet/subtropical climate conditions within oxidizing and increased pH conditions, or as dissolved iron transported by upwelling currents over the shelves and precipitated under an oxidizing environment. The cyclic occurrence of primary iron in a marine carbonate environment and its extensive distribution over large areas indicates that a controlling mechanism for iron-rich carbonates and mudstones could be related to the cooperation of climate, sea level, and oceanographic changes in the middle Givetian. During the late Lochkovian, the same or very similar controlling factors might have operated, where the alternation of red mudstones can be explained by lateral facies changes or changes in terrestrial/nutrient influx.

Key words: Middle Givetian, upper Lochkovian, Çamdağ area, NW Turkey, sedimentology, ironstones, iron-rich limestones, paleoclimate

1. Introduction explained some possible origins of the red pigmentation Iron-rich limestones have been studied on a broad of hematite in the Pragian Slivenee Limestone, Czech geographic and temporal scale in the world (e.g., Dreesen, Republic, by ferric bacteria, where distinct bacteria types 1989; Young, 1989; Young and Taylor, 1989; Ferretti, 2005; can precipitate iron in mainly oxic environments with low Brett et al., 2012; Ferretti et al., 2012; McLaughlin et al., or high pH conditions and even in interfaces between 2012). However, their origin is still under discussion. Preat anoxic and oxic environments. Bulvain et al. (2001) stated et al. (2008) indicated a contribution of iron bacteria in that the precipitation of iron is mainly related to the Devonian carbonates in hemipelagic and outer shelf contribution of an endobiotic microbial community and environments in Morocco. Kearsley (1989) made a network of bacteria/fungi. Microbial precipitation of iron primary approach for a possible mode of occurrence of continued during mound development, where they were ooids in terms of mineralogy and tried to classify different bathed by water impoverished in oxygen. ooids into some classes and subclasses. Each mineralogical On the other hand, Sturesson et al. (2000) emphasized association may have a different origin and might even the formation of iron ooids as a rapid process and the have been modified by diagenesis. Mamet and Boulvain origin of ooids was mostly associated with the chemical (1990) reported the presence of iron-rich microborings precipitation of cryptocrystalline iron oxyhydroxides from the “Griottes” facies in Spain. Mamet et al. (1997) by seawater enriched with Fe, Al, and Si by volcanic * Correspondence: [email protected] 21 YILMAZ et al. / Turkish J Earth Sci

processes. Van Houten and Hou (1990) and, more recently, alternations related to variations in atmospheric CO2 levels Ferretti et al. (2012 and references therein) analyzed and partially correlated to eustatic sea level and aragonite– the stratigraphic and paleogeographic distribution of calcite ocean phases must also be tested in terms of TSFs. Paleozoic oolitic ironstones. Ebbighausen et al. (2007) Therefore, local or global causes of ironstones can also be reported the presence of mixed neritic–pelagic facies of considered for interbasinal correlations. the volcaniclastic hematitic ironstones in the Rhennish In NW Turkey, Devonian iron ooids were recognized Massif, Germany, in the Givetian. Extensive ironstone for the first time by de Wijkerslooth and Kleinsorge (1959). formations formed during the lower and upper Devonian Kipman (1974) performed the first mineralogical work on were reported from Central Europe, Northwest Africa, the the oolitic iron formations in this area and evaluated the South Russian platform, and South China (e.g., see Ferretti, occurrence as a sedimentary iron ore deposit. More recent 2005 and references therein). In these occurrences, the work was carried out mainly in a regional geological context ironstone was mainly associated with carbonate-detrital (e.g., Derman, 1997; Gedik and Önalan, 2001; Göncüoğlu successions deposited most commonly in the detritic et al., 2004; Boncheva et al., 2009) without emphasizing nearshore environment and mainly associated with major these formations. In the Çamdağ area, these studies have cratonic flooding conditions. shown the presence of a tectonostratigraphic unit that It is also possible to see a collaboration of fungi and completely differs in its Silurian-Devonian interval from algae in the forming of the iron ooids. Ferretti (2005) the typical “Paleozoic of İstanbul” of Görür et al. (1997). studied the ooidal and laminated ironstones of the Silurian Despite the striking differences in the lithostratigraphy, age from the Carnic Alps of Austria and noted the presence the most critical divergence is the occurrence of iron of magnetite coatings formed by fossil fungi in the form of ooid formations alongside the regional Middle Devonian microstromatolite-like features. Bacterial contribution is unconformity (Boncheva et al., 2009; Bozkaya et al., 2012). also possible to see as chamositic coating layers. Therefore, In the Central and Eastern Taurides, no iron-rich it was stated that the collaboration of bacteria and fungi Devonian successions were reported (e.g., Wehrmann et contributed to the iron ooids in that part of the Silurian in al., 2010). This may indicate that iron-rich deposits mostly the Carnic Alps. belong to the İstanbul-Zonguldak Composite Terrane, Brett et al. (2012) stated the importance of time-specific which is considered as the eastern continuation of the aspects of facies (TSFs) and their importance in terms central European terranes during the middle Devonian of global events and basinal variations. They imply that (e.g., Dojen et al., 2005). TSFs can be confined to single basins or are widely global. Our detailed fieldwork (Göncüoğlu et al., 2008) on Recognition of these facies can play an important role in these iron ooid occurrences along 2 different sections understanding the global changes. Controlling factors for in the Kabalakdere (90 m) and Ferizli (13.45 m) areas TSFs can be stated as abrupt changes in redox conditions in Çamdağ, NW Anatolia (Figure 1), revealed 2 distinct and early diagenetic mineralization, sedimentary sequences of formations that also differ in depositional condensation, abrupt sea level change, altered climate features. From these, the relatively younger main body in and paleoceanography, biotic evolution, and extinction. Ferizli comprises 11 separate centimeter-thick bands of According to the explanations of Brett et al. (2012), iron- oolitic/dolomitic limestones and oolitic ironstones. Recent rich red- to reddish-colored limestones/ironstones can field studies (Göncüoğlu et al., 2008) in the northern also be seen as one of the subjects of the TSF. However, central Pontides in the Bartın, Eflani, and Karadere areas it was also stated that the relationship of large-scale facies (Figure 1) have shown the continuation of these formations changes and major cycles such as icehouse–greenhouse towards the east for more than 300 km.

Figure 1. Location and geological map of the studied regions (modified from Sachanski et al., 2010).

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In this study, we provide preliminary data on the early and crinoid-rich carbonates yielded Ozarkodina to middle Devonian ironstones from NW Anatolia by remscheidensis remscheidensis Ziegler, Ozarkodina masara using sedimentological, stratigraphical, and mineralogical Schönlaub, and Ozarkodina typica denkmanni Ziegler, methods to understand their modes of genesis and to indicating the postwoschmidti Zone of early Lochkovian interpret for the first time their formation in a broad age. The overlying limestone–mudstone intercalation with paleoclimatological and paleoceanographic framework. the first oolitic ironstone band found in this interval is late Lochkovian in age and will be described in detail in 2. Geological setting Section 3. The Devonian successions under investigation belong The Middle Devonian regional transgressional event, to the Zonguldak Terrane of the İstanbul-Zonguldak restricted to the Zonguldak Terrane, marks the onset Composite Terrane (Göncüoğlu et al., 1997; Göncüoğlu, of a new cycle represented by the Ferizli and Yılanlı 2010) in the western Pontides in NW Turkey. It is Formations, respectively. The transgression starts in considered as a Gondwana-derived continental microplate both the Kabalakdere and Ferizli sections with white and that was attached to southeastern Moesia prior to the reddish quartz-arenites with red and green mudstones Variscan closure of the Rheic Ocean (e.g., Göncüoğlu, and sandstones followed by a series of dolomite, dolomitic 1997; Yanev et al., 2006). limestone with oolitic ironstones, and chamositic The Paleozoic rocks in the Zonguldak Terrane mudstones (Ironstone Member of Kipman, 1974). outcrop along an E-W trending belt (Figure 1) stretching Conodont findings in the first limestone bands beneath from Çamdağ in the NW to the Devrekani-Çatak and the ironstones indicate the ensensis and hemiansatus zones Safranbolu-Karadere area in the NE (Göncüoğlu et of the middle Givetian (Boncheva et al., 2009). In the al., 2004). Along this belt, an almost complete lowest Ferizli Section, the thickness of this unit may reach up to Ordovician (Lakova et al., 2006) to lower Devonian 45 m and it is mined locally for iron ore. The overlying siliciclastic succession with carbonate intercalations marly limestones, nodular limestones, and dolomitic unconformably covers a Late Neoproterozoic to Cambrian limestones (Manastır Member of the Yılanlı Formation) crystalline basement (Dean et al., 2000). Middle Devonian are characterized by an abundance of corals, bryozoans, clastics overlie them unconformably. Locally, the clastics brachiopods, bivalves, and echinoids. overlie the anchimetamorphic middle Silurian (Wenlock) The oolitic ironstone-bearing interval extends towards black shales with an angular unconformity (e.g., Bozkaya the east to Bartın-İnkumu and to the Çatak and Karadere et al., 2012), indicating a period of uplifting and erosion. areas (Figure 1) to the northeast of Safranbolu in the In the Çamdağ area, within an E-W trending anticline, central Pontides, where the stratigraphy is almost the same the Ordovician-Lower Devonian part of the Zonguldak as in the Çamdağ area. Terrane has the most complete succession (Gedik and Önalan, 2001), including the Ordovician Kurtköy and 3. Lithostratigraphy and biostratigraphy Aydos Formations, the Silurian-Lower Devonian Fındıklı 3.1. Lithostratigraphy Formation, the Middle Devonian Ferizli Formation, and Two sections have been measured in detail in the Çamdağ the Upper Devonian to Lower Carboniferous Yılanlı area: the Kabalakdere and the Ferizli sections to the N and Formation (Figure 2). NE of Adapazarı, respectively. The Kurtköy and Aydos formations are characterized 3.1.1. Kabalakdere Section by fluvial sediments followed by ?Lower Ordovician The total thickness of the section is about 70 m, of which shallow-marine quartz-arenites. The earliest fossiliferous only the lower 16.45 m was sampled in detail. Overall, the sediments in the overlying Fındıklı Formation are measured part of the section is dominated by bioclastic Darriwilian in age (Boncheva et al., 2009). The lower part limestones in the first 12 m. The lower part includes gray of the Fındıklı Formation comprises a thick siliciclastic pebbly limestone and grades into gray algal and bioclastic unit with graptolitic black shale intercalations. These were limestone with echinoid and brachiopod fragments dated in detail by acritarchs and graptolites (Sachanski (Figure 3). Upwards follow gray cross-laminated bioclastic et al., 2010) to the middle-upper Silurian. The upper limestones rich in brachiopod fragments. The upper parts of the graptolitic shales are rich in Orthoceras part of the lower calcareous interval is characterized by limestones with conodonts of late Silurian (Pridolian) age gray-pinkish nodular dolomitic limestones. Within these (Kozlu et al., 2002). The fossil-free black shale-siltstone bioclastic limestones, there is an iron-rich limestone interval between the Orthoceras limestones and the interval 4 m from the bottom. Iron-rich limestones include brachiopod-rich sandstone–limestone alternation may iron-rich ooids, pellets, and bioclasts as grains and are mark the Silurian-Devonian boundary. The overlying cemented by sparry calcite. Towards the middle part of the succession with sandstones, mudstones, and brachiopod- Kabalakdere Section, the limestone facies are overlain by

23 YILMAZ et al. / Turkish J Earth Sci . Se q Stage Ag e Series Main System 360 T R

365 Famennian 04-133 370 04-132 PPER

04-131 U 375 08-13 06-22 06-08 Ferizli Fm . 08-06,07 Frasnian 380 04-136 10 m

06-21 385 04-130A 0 06-19, 20 07-09,11 Givetian 08-05 E 390 IDDL M Eifelian 04-130B 395

400 DEVONIAN Emsian

405 OW ER L

Pragian 410

Lochkovian 415

Aydos Fm. Ludfordian W 420 LO UD

Gorstian L 25 m Homerian 425 LOCK

Sheinwoodian EN 0 W

Kurtköy Fm . 430

acritarch Telychian Y ER brachiopods 435

Aeronian SILURIAN

bivalves LANDOV L 440 conodonts Rhuddanian corals crinoids marly limestone Fault sandy limestone nautiloids Olo itic ironstone microvertebrate dolomite graptolites Nodules macroflora

Figure 2. Generalized stratigraphic column of the Devonian succession exposed in the Çamdağ region (modified from Boncheva et al., 2009). The numbers to the right of the geological section refer to the paleontological samples taken. The last column on the figure shows the main sequences (Main Seq.) with transgressive (T) and regressive (R) tracts.

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Kabalakdere section

16.45 m

Pinkish laminated mudstone/shale 6 Gray pinkish nodular dolomitic limestone 5 4 Gray cross - laminated bioclastic limestone 3 Gray algal and bioclastic limestone Gray pebbly bioclastic limestone 2 Gray - red iron rich algal limestone Brachiopod fragments Echinoid fragments

1 Siliciclastic pebble Cross lamination

0 m Figure 3. Stratigraphic details of the Kabalakdere Section. The numbers 1 to 10 correspond to sample numbers and the symbols correspond to conodont fossils. (GPS coordinates: bottom: 40°55′31.43″N, 30°33′03.58″E, top: 40°55′31.35″N, 30°33′03.78″E).

25 YILMAZ et al. / Turkish J Earth Sci cross-bedded bioclast-rich siliciclastics with an alternation limonite-rich mudstones at the bottom. In the middle of pinkish quartz-rich sandstones and mudstones overlain part, thicker iron-rich gray to red limestones occur and by laminated pinkish mudstones. In the upper part of the display thick-bedded crinoid- and brachiopod- rich cross- Kabalakdere Section, an iron-rich dolomitic limestone laminated bioclastic facies alternating with thin-bedded succession including an alternation of mudstones and gray to yellow iron-rich mudstones. An alternation of dolomitic limestones is present. This iron-rich limestone- thicker red iron-rich mudstone and thin-bedded limestone dolomitic limestone interval at the top of the Kabalakdere characterizes the top of the section. The 5.45-m-thick section corresponds to the succession at the Ferizli interval with bioclastic-rich gray to red limestones in the Section (Figure 4). On the basis of its lithostratigraphy, it middle part of the Ferizli Section was sampled and studied can be correlated with coeval successions in the western in detail. Zonguldak Terrane (e.g., Bozkaya et al., 2012). The 3.2. Biostratigraphy limestone facies recognized in this latter section may The biostratigraphy of the measured sections has been display lateral facies changes over long distances and may established according to conodont determinations as be replaced by the reefal limestone facies, which is the shown in Figures 5a and 5b. Large numbers of samples topmost unit in the Kabalakdere Section (Figure 3). were collected in field campaigns in 2004, 2006, 2007, and 3.1.2. Ferizli Section 2008. The locations of productive samples are shown in This measured part of the Ferizli section is 13.45 m in Figure 2. Mostly, acritarch, bivalve, coral, echinoderm, and thickness (Figure 4) and is composed of an alternation brachiopod fragments were identified, but they proved not of gray to red iron-rich limestones and yellow to cream to be useful for biostratigraphic assignment.

5.45 m Ferizli Section 12 11

13.45 m 10

9 Alternation of red iron rich mudstone 8 and thin-bedded limestone 7

6 5 4 3 2 Gray to red iron rich thick bedded limestones 1

0 m

Gray - red iron rich algal and bioclastic limestone Yellow to cream limonite rich Gray - red iron rich clayey limestone mudstones Brownish/reddish - yellow iron rich mudstone/shale Intensively altered grey - red iron rich limestone Gray to red iron rich thick bedded Brachiopod fragments limestones Echinoid fragments

0 m Cross lamination Figure 4. Stratigraphic details of the Ferizli Section. The numbers 1 to 12 correspond to sample numbers. (GPS coordinates: bottom: 40°58′04.25″N, 30°46′00.06E″, top: 40°58′05.03″N, 30°46′00.20″E).

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Figure 5a. Conodont taxa determined in the Fındıklı Formation in the Kabalakdere Section. 1–3, 8: Pelekysgnathus serratus serratus Jentzsch, delta Zone, late Lochkovian. 1: Upper view, 06-19, 170×. 2: Upper view, 06-19, 140×. 3: Lateral view, 06-19, 170×. 8: Lateral view, 07-09, 312×. 4: Icriodus cf. angustoides alcoleae Carls, delta–pesavis Zone, late Lochkovian, upper view, 06-20, 130×. 5: Icriodus angustoides alcoleae Carls, delta–pesavis Zone, late Lochkovian, upper view, 06-20, 200×. 6: Icriodus cf. angustoides castilianus Carls, delta Zone and pesavis Zone, late Lochkovian, upper view, 06-20, 150×. 7: Icriodus cf. angustoides angustoides Carls & Gandl from pesavis Zone, late Lochkovian to sulcatus Zone and kindlei Zone, middle Pragian, upper view, 06-20, 180×. 9: Peleksygnathodus serratus elongatus Carls & Gandl., late Lochkovian, lateral view, 07-09, 248×. 10–13: Peleksgnathodus cf. serratus Jentzsch, late Lochkovian. 10: Lateral view, 07-11, 253×. 11: Lateral view, 07-11, 287×, late Lochkovian. 12: Lateral view, 07-11, 253×. 13: Lateral view, 07-11, 287×. 14: Icriodus postwoshmidti Mashkova, late Lochkovian, upper view, 07-11, 409×. 15–19: Pelekysgnathus serratus quadarramensis Valenzuala-Rios, transition to Icriodus angustoides alcoleae Carls delta Zone to pesavis Zone, late Lochkovian. 15: Upper view, 08-05, 120×. 16: Upper view, 08-05, 140×. 17: Upper view, 08-05, 180×. 18: Upper view, 08-05, 200×. 19. Lateral view, 08-05, 150×.

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Figure 5b. Conodont taxa determined in the Ferizli Formation. 1: Polygnathus dubius Hinde, hermanni Zone, Givetian, upper view, 06-22, 264×. 2: Icriodus subterminus Youngquist, hermanni Zone, Givetian, upper view, 06-22, 264×. 3–4: Icriodus cf. obliquimarginatus Bischoff & Ziegler, from hemiansatus Zone to ansatus Zone, early Givetian. 3: Upper view, 08-06 160×. 4. Upper view, 08-07, 220×. 5–7: Icriodus cf. brevis Stauffer, Givetian. 5: Lateral view, 08-08, 170×. 6: Upper view, 08-13, 130×. 7: Upper view, 08-13, 170×. 8–11: Icriodus brevis Stauffer, Givetian. 8: Upper view, 07-13, 299×. 9: Upper view, 07-13, 426×. 10: Upper view, 07-13, 299×. 11: Upper view, 06-07, 426×.

3.2.1. Fındıklı Formation 3.2.2. Ferizli Formation A late Lochkovian age was assigned by the conodont The Ferizli Formation overlies the Findikli Formation samples obtained from the limestone with brachiopods. in the studied sections (Figure 2). At the bottom of the The identified conodonts are Pelekygnathus serratus formation, red sandstones alternate with brachiopod- serratus Jentzsch, Peleksygnathodus serratus elongatus bearing red mudstones. The overlying part includes Carls & Gandl, Icriodus cf. angustoides alcoleae Carls alternating red siltstones and red mudstones with large (Figures 3 and 5a). The limestones with brachiopods brachiopods and gray micritic limestones. This lower intercalate with iron ooids in the upper part of the Findikli part of the formation (Figure 4) provided the following conodont species: Polygnathus dubius Hinde, Icriodus Formation. The samples within the iron ooid interval expanses (Branson & Mehl), Icriodus obliquimarginatus have these documented conodont species: Icriodus Bischoff & Ziegler, and Icriodus brevis Stauffer (Figure cf. angustoides angustoides Carls & Gandl, Icriodus cf. 5b). This assemblage is indicative of the middle Givetian angustoides castilianus Carls, Icriodus angustoides alcoleae (varcus-hermanni zones) age. The overlying part includes Carls, Icriodus steinachensis Al-Rawi, and Icriodus iron-rich oolites alternating with calcarenites and postwoschmidti Mashkova. A latest Lochkovian age dolomites/dolomitic limestones. (pesavis Zone) was also assigned (Figure 5a). One sample included conodonts (Icriodus cf. angustoides angustoides 4. Sedimentology Carls & Gandl) with a wider age range including the Despite the difference in their ages, very similar microfacies pesavis Zone (late Lochkovian) to the sulcatus and kindlei and components are observed in the Kabalakdere and zones (middle Pragian) Ferizli sections. A bioclastic and ooidal grainstone/

28 YILMAZ et al. / Turkish J Earth Sci packstone (Figures 6a and 6b) is observed at the base of the Scanning electron microscope (SEM) analysis section. Echinoid/brachiopod packstones are observed as indicated that iron primarily precipitated in the holes/ a fitted texture (Figure 6c) towards the lower middle part empty places of the shell structures of the biogenic grains of the section as observed in the Ferizli Section. Towards in samples of both sections. In back-scattered images, the upper part of the section, iron content decreases and metallic content can easily be seen as bright reflections on bryozoan- and brachiopod-bearing grainstone/packstone the shells/grains (Figure 9a). Iron/iron-bearing minerals can be observed (Figure 6d). At the top, cross-bedded can be seen as mainly concentrated on the shell structures quartz-rich fine sandstone/siltstones (Figure 6e) overlie (Figures 9b–9d) and are never seen as disseminated within the limestone with a sharp and unconformable contact. the matrix/cements. Finally, pinkish laminated mudstones/shales lie above the During or just after the precipitation of iron as infill dolomitic limestones that cover the cross-bedded quartz- material during oxidizing/suboxic conditions, there was a rich sandstones/siltstones. period of anoxic/semianoxic conditions in the sediment In the Ferizli Section, iron-rich limestones mainly water contact or within the sediment. The presence of display biopel/biosparite and grainstone microfacies pyrite framboids smaller than 10 µm within the same (Figures 7b, 7c, and 7e). Alternating mudstones in the sample (Figure 9e) indicates that anoxic conditions Ferizli Section display clay and iron-rich silty mudstone took place at least for a short while, which is enough to facies (Figure 7a). Bioclasts are rarely observed in this develop pyrite framboids. In the same sample taken from mudstone facies. However, brachiopod and echinoderm the lower level of the Kabalakdere section, spherical grains are abundantly present in both the Ferizli and iron-bearing carbonate minerals have been identified Kabalakdere sections. according to energy-dispersive X-ray spectroscopy (EDX) The iron-rich ooids display a cortex (ranging between measurements (Figures 10 and 11). Their origin and mode 10 and 200 µm) totally composed of iron lamination of formation is not clear; however, a bacterial/fungal (single lamina vary from 1 to 10 µm in thickness and can contribution can be suggested on the basis of the shape, be composed of iron/iron carbonates) (Figures 7b and 7c). size, and composition of the carbonate crystals. Nuclei can be various fragments (such as iron peloids, In previous studies, Kipman (1974) identified bioclasts, and quartz grains), but iron grains can also be goethitized and chamositized fossil fragments and seen as nuclei. One of the most abundant iron-rich types chamositic oolites in Devonian limestones in the Çamdağ of grains are bioclasts that display microboring features area. He recognized that the oolitic ore includes goethite, infilled by iron and have iron infilling in their microporous brown iron-silicates, chamosite, sideritic oolites, quartz structure, where the original shell composition is not clasts, and brachiopods. Bozkaya et al. (2012) also identified replaced (Figure 7d). Iron-rich pellets (ranging between notable amounts of goethite in a Lower Devonian sample 50 and 200 µm) are generally ellipsoidal and well rounded (IZP-84) from the Çamdağ area in their X-ray diffraction (Figure 7e). Iron mineralization could not be observed (XRD) studies. replacing the matrix or cement. However, iron could be In this study, XRD measurements have been carried seen in the primary pore spaces between the grains to some out on the samples of reddish and grayish-greenish iron- degree. There was no indication of iron mineralization rich limestones within the Kabalakdere section. The results being a secondary formation. indicate the presence of some goethite? and hematite in Iron-rich bioclastic facies display lateral pinch-outs the reddish limestones and chlorite (chamosite) and illite in iron-rich mudstones in some outcrops in the Ferizli can be detected in the greenish-grayish samples (Figures Section. The contacts between mudstones and iron-rich 12a and 12b). limestones are sharp and cyclic alternations can clearly be seen (Figures 8a–8c). Bioclastic accumulations are fully 5. Interpretations for paleoceanographic and iron infilled and are generally composed of macrofragments paleoclimatic conditions of brachiopods, crinoids, and echinoids (Figure 8d). The studied iron-rich facies suggests that depositional Bioclastic accumulations display random positions within conditions were mainly shallow marine, carbonate-mixed, bed. Therefore, strong current/storm conditions may have agitated, and relatively warm water. The presence of iron disordered their positions. At the top of the Ferizli Section, has been observed as microborings on the bioclasts, the limestones get thinner and the iron-rich mudstones iron coatings around whole bioclasts and quartz grains, thicken, displaying cyclic alternations (Figure 8e). Over iron ooids, oncoids, and infillings within pores of algae/ the iron-rich succession, light gray-beige coral, bryozoan, bryozoans/brachiopods. Iron minerals could not be brachiopod, and other macrofossils bearing calcareous observed replacing/impregnating the matrix or cement. successions occur without any iron content (Figures 8f Therefore, iron must have been synchronously precipitated and 8g). during or just after the sedimentation and possibly the

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a b

c d

B c

Figure 6. Photomicrographs of the main microfacies types determined in the Kabalakdere Section. Scale corresponds to 100 µm. a) Iron-rich bioclastic peloidal grainstone (sample 1, C = calcite, green solid arrow = iron peloids, red arrow = bioclast with iron infilling, b) iron-rich bioclastic peloidal grainstone with iron coated grains (C = calcite, green arrow = iron-coated grain, red solid arrow = iron peloid), c) iron-rich bioclastic packstone with fitted texture (sample 4, B = bioclast, red arrow = calcite), d) bioclastic packstone without iron content (sample 5, Br = bryozoan, C = calcite), e) quartz-rich siltstone to very fine sandstone (sample 9, C = calcite, red arrow = quartz).

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a b

c c d

Pl Bc

c e Figure 7. Photomicrographs of the main microfacies types determined in the Ferizli Section. The black/yellow bar is a 100-µm-long scale. a) Iron-rich mudstone (sample 3), b) iron-rich bioclastic/ooidal grainstone (sample 4, red solid arrow = iron ooid, green arrow = bioclast with iron infilling, yellow arrow = iron peloid, C = sparry calcite cement), c) iron ooid (C = sparry calcite cement, green arrow = bioclast with iron infilling, Nc = nuclei, lm = laminae), d) iron-rich fitted bioclastic packstone (sample 8, C = sparry calcite, Bc = bioclast), e) iron-rich bioclastic peloidal grainstone (sample 10, C = sparry calcite, Bc = iron infilled bioclast, Pl = iron peloid).

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a e

CLm f m

Lm Lm

c b g Figure 8. Field views of the outcrops of the iron-rich facies recognized in the Ferizli area. a) Outcrop view of the alternation of iron-rich limestones and mudstones within an open iron mine in the Ferizli area (the white bar is about 1 m in length), b) close-up view of the alternation of iron-rich limestone and mudstones at the lower part of the Ferizli Section (lm = cross laminated bioclastic limestone, m = mudstone, the white bar is about 1 m in length), c) close-up view of the contact between the iron-rich mudstone and the limestone indicated by a white box in b with a coin for scale, d) close-up view of the iron-rich bioclastic limestone (bioclasts are mainly brachiopod and crinoid fragments) with a coin for scale, e) field view of the upper part of the section dominated by iron-rich mudstone, f) field view of the contact between the coral-bearing limestones and the underlying iron-rich succession (Fe = iron-rich level, CLm = coral-bearing limestone), g) a close-up view of the limestone in f with a coin for scale. relationship between the bioclasts and the iron bacteria Iron infilling/emplacement on biogenic constituents could be related to the presence of organic matter and could be explained as biogenically induced precipitation microenvironments. (bacterial origin: Mamet and Préat, 2006; Preat et al., Generally, cross-laminated calcareous siltstone/fine 2008) of transported dissolved iron from the terrestrial sandstone facies display very little or no iron component in environment due to increased weathering conditions the Kabalakdere Section. This may be related to a siliciclastic under a wet/subtropical climate. These conditions could influx into the basin changing the Eh-pH conditions and create oxidizing and increased pH conditions on shelves. disturbing the conditions of the iron-oxidizing bacteria/ In addition, dissolved iron could be transported by fungi. However, there also has been no iron observed in upwelling currents over the shelves and precipitated under some samples of bioclastic grainstone facies. This may be an “oxidizing” environment in relation to global sea level interpreted as a change in the water chemistry (CO2 content, fluctuations (e.g., Becker and Kirchgasser, 2007). Eh-pH, temperature, etc.) without siliciclastic influx and McLaughlin et al. (2012) stated that during a sea-level can be related to the cooperation of paleoenvironmental drop, reducing conditions may surround the shallow and paleoceanographic changes such as sudden changes in basin margins and widespread ironstones and ankeritic evaporation, fresh water influx, upwelling currents rich in carbonates can be deposited along the margin in alternating nutrients, and turnover of surface oceanic currents. sequence with pyritic shales, resulting in fluctuating redox

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Figure 9. SEM images of samples in the Ferizli and Kabalakdere sections. a) Back-scattered SEM image of the bioclastic ooidal grainstone in the Ferizli section (sample 4, C = calcite, yellow arrow = echinoderm fragment), b) close-up view of an echinoderm fragment infilled by iron in a back-scattered SEM image of the bioclastic ooidal grainstone in b (sample 4, C = calcite, yellow arrow = echinoderm fragment), c) details of iron infilling within pores of echinoderm spines in the SEM image in b (sample 4, C = calcite, yellow arrow = iron infilling), d) details of iron infilling within pores of echinoderm spines in the SEM image in b (C = calcite wall, FeC = iron/iron calcite infilling), e) SEM image of bioclastic packstone/grainstone in the Kabalakdere Section (sample 2, C = calcite, P = pyrite framboid, arrow = spherical iron calcite mineralization grown within a pyrite framboid whole), f) close-up SEM view of the spherical iron calcite mineral in e.

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Figure 10. EDX measurement results obtained from the SEM view of sample 2 from the Kabalakdere Section (Figure 9e). conditions. Consistent deposition of ironstones at certain below the surface or in an anoxic shallow water column, time intervals may indicate the presence of dominant a short-term precipitation of pyrite minerals took place. marine redox conditions, but can also be affected by large- Van Houten and Hou (1990) indicated the deposition scale sea-level changes. of Paleozoic oolitic ironstones mainly in relation to major The type of climate could not be very clearly identified cratonic flooding conditions in a detritic nearshore for the iron precipitation in the upper Lochkovian and environment in the Lower and Upper Devonian in middle Givetian in this study. Joachimski et al. (2009) Middle Europe, Northwest Africa, the South Russian indicated the lower–middle Givetian was characterized platform, and South China. In addition to this, Ogg et by cooler temperatures of about 20–22 °C and the upper al. (2008) indicated that global large-scale Paleozoic sea- Lochkovian by warm tropical temperatures of around 30 level records demonstrated a transgressive phase both in °C using a global isotope data set. If this global record is the late Lochkovian and the middle Givetian. Boncheva considered in interpretations, it can be concluded that the et al. (2009) also mentioned the presence of large-scale iron was not influenced by temperature but might have transgressive conditions in the Lochkovian and middle been affected by fresh water/clay or nutrient influx. In both Givetian (Figure 2). Therefore, it can be interpreted that a sections, iron-rich facies were generally observed in high- sea-level rise or transgressive conditions might have also energy conditions. A random ordering of macrofossil contributed to the formation of the iron-rich facies in the fragments was clearly apparent; even the lateral pinch- Çamdağ area. out feature of the high-energy facies within the mudstone Although the iron-rich facies were deposited in facies displays current/storm control in the background as different ages and in different climates, the microfacies, shaping the features of the facies. textures, and compositions are quite similar in both The presence of pyrite framboids synchronously ages. Therefore, it can be suggested that the depositional in the iron-rich limestones may indicate that oxygen- conditions were nearly the same, at least at these locations. poor conditions existed during or just after deposition. However, pyrites and irons are recorded in the same high- 6. Discussion energy bioclastic facies. This relationship can roughly be Two measured sections have been studied in detail, interpreted as sudden stormy conditions followed by low- exposing the Fındıklı and Ferizli Formations in the energy, stagnant, and oxygen-poor conditions. During Kabalakdere and Ferizli areas, respectively, in the Çamdağ stagnant conditions at the sediment-water interface just region (NW Anatolia) of the Zonguldak Terrane.

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Figure 11. EDX measurement results obtained from the SEM view of sample 2 from the Kabalakdere Section (Figure 9f).

The Kabalakdere Section is mostly composed of iron- the Ferizli Section. The cyclic occurrence of primary iron rich bioclastic limestones of late Lochkovian age. The in the marine carbonate environment and an extensive Ferizli Section mostly displays an alternation of iron-rich distribution over large areas suggest that the controlling bioclastic limestones and mudstones of middle Givetian mechanism for iron-rich carbonates and mudstones could age. be related to the cooperation of climate, sea level, and Sedimentological and SEM analysis indicated that iron oceanographic changes in both the Lochkovian and the precipitation took place within microborings or along middle Givetian. In the upper Lochkovian, the absence of the spine holes of echinoderm grains in the bioclastic alternation of red mudstones can be explained by lateral grainstone facies. Iron was also involved in the ooid facies changes, the absence of terrestrial influx, and/or formation and can be observed as concentric laminae and nutrient influx in that time. Therefore, the same or very nuclei or involved in peloids. Iron could not be observed similar controlling factors might have operated in these as replacing the sparry cement; therefore, the occurrence time intervals. of iron is not related to late diagenesis. According to paleotemperature studies (Joachimski et In addition to previous studies (e.g., Kipman, 1974; al., 2009), the lower to middle Givetian was characterized Bozkaya et al., 2012; Ferretti et al., 2012) indicating the by cooler temperatures and the upper Lochkovian by presence of goethitized and chamositized fossil fragments warm tropical temperatures. In both intervals, the same and chamositic oolites in the Devonian limestones of the iron-rich facies were identified in the Çamdağ area. This Çamdağ area, our XRD analysis indicated the presence of indicates that iron was not controlled by temperature but goethite and hematite in the reddish samples and chlorite it may have been affected by fresh water/clay or nutrient (chamosite) and illite in the greenish-grayish samples of influx. The high-energy iron-rich facies display a random the Kabalakdere Section. ordering of macrofossil fragments, including even a lateral Iron precipitation could be explained as precipitation of pinch-out feature within the mudstone facies. This may transported dissolved iron from the terrestrial environment imply that current or storm controls were a background under a wet/subtropical climate within oxidizing and influence in collaboration with iron transportation/ increased pH conditions, or dissolved iron transported precipitation and chemical/production conditions on the by upwelling currents over the shelves and precipitated carbonate shelf of the Çamdağ area. under an oxidizing environment. The alternation of iron- Consequently, this study carried out on the Kabalakdere rich limestones and mudstones indicates a cyclic nature in and Ferizli areas in the Çamdağ region (NW Anatolia)

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Figure 12. XRD graphs of samples from the Kabalakdere Section: a) sample K1, b) sample K4. demonstrated the presence of iron-rich bioclastic Bulgaria and NW Anatolia: Implications for the tectonic- limestones of late Lochkovian age and the alternation of paleogeographic evolution of NW Gondwana”. We would iron-rich bioclastic limestones and mudstones of middle like to thank the General Directorate of Mineral Research Givetian age. The precipitation of iron-rich carbonates and and Exploration (MTA) of Turkey for its logistic support mudstones was related to the collaboration of paleoclimatic during the fieldwork. Dr I Boncheva is acknowledged for and paleoceanographic conditions and was possibly her supervision of the conodont study of the third author. affected by sea-level changes over large areas even though Dr O Bozkaya (Sivas) is acknowledged for his contribution the literature shows that temperatures varied significantly to the XRF analyses. The SEM images were taken in the during the late Lochkovian and middle Givetian ages. METU Central Laboratories. This study was carried Acknowledgments out in the laboratories of the Department of Geological This study was initiated by the members (Drs I Boncheva, Engineering, Middle East Technical University, Ankara, I Lakova, N Özgül, S Yanev, V Sachanski, C Okuyucu, and Turkey, and MTA, Ankara, Turkey. The constructive E Timur) of a TÜBİTAK-BAS joint project (YDABAG- comments of A Ferretti (Modena) and an anonymous 102Y157) on “Correlation of the Paleozoic terranes in reviewer are gratefully acknowledged.

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