An Approach to Paleoclimatic Conditions for Devonian (Upper Lochkovian and Middle Givetian) Ironstone Formation, NW Anatolian Carbonate Platform
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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). 22 YILMAZ et al. / Turkish J Earth Sci In this study, we provide preliminary