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

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 12to 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.

Ordovician ironstone of the Iberian margin: Coastal upwelling, ocean anoxia and Palaeozoic biodiversity

“…In contrast to this traditional view of ironstone accumulation, which relies on a continental source of Fe (Van Houten and Bhattacharyya, 1982;Young, 1989;Bhattacharyya and Crerar, 1993;Van Houten, 2000;Robb, 2005;Yilmaz et al, 2015), lithofacies associations suggest that Fe was also supplied through coastal upwelling (Figures 10 and 11). The organic-rich nature and occurrence of synsedimentary Fe and Mg silicates, francolite and framboidal pyrite in offshore lithofacies (Facies 5-8) imply deposition near an upwelling front (Glenn et al, 1994;Pufahl and Groat, 2017) and development of a distal ironstone factory.…”

“…Unlike the earlier iron formation, Palaeozoic ironstone also commonly co-occurs with sedimentary phosphorite (Petránek, 1991;Todd et al, 2019), an upwelling-related biochemical sediment containing >18 wt% P 2 O 5 (Glenn et al, 1994;Pufahl and Groat, 2017). Precise causes remain unclear, but several studies imply that a greenhouse climate and related intensification of chemical weathering may have been important for increasing the delivery of Fe and P to the ocean (Van Houten and Bhattacharyya, 1982;Föllmi, 1996;Robb, 2005;Yilmaz et al, 2015;Pufahl and Groat, 2017). Thus, understanding the apparent relationship between climate, periods of ocean anoxia, biological evolution and episodes of ironstone accumulation may provide new insight into the unique conditions that permitted the Lazarus-like return of widespread Fe deposition that was so common in the Precambrian.…”

Middle Ordovician Upwelling-Related Ironstone of North Wales: Coated Grains, Ocean Chemistry, and Biological Evolution

“…What is different about ironstone from the Welsh Basin is the ubiquity of large, coated Fe grains. An upwelled source of Fe contrasts the more traditional view of ironstone deposition that relies on a greenhouse climate and increased chemical weathering for the delivery of continentally derived Fe to the shelf (Van Houten and Bhattacharyya, 1982;Young, 1989Young, , 1992Van Houten, 2000;Yilmaz et al, 2015).…”

Notes on beyrichiacean ostracodes from the Early Devonian of NW Turkey andtheir palaeobiogeographical relations

“…fragilis and these faunas indicate a Lochkovian age (Yalçın and Wilde, 2009). Conodont taxa have been determined in the beyrichiacean-bearing levels of the Kabalakdere Section (Boncheva et al 2009;Yılmaz et al 2015) and dated as Lochkovian to Pragian.…”

“…The aim of this research is to give an overview of the beyrichiacean ostracodes and to analyse their records from the İstanbul region, north-western Turkey, to help establish international biostratigraphical and palaeogeographical correlations. Kaya, 1973;Aydın et al, 1987;Okay, 1989;Derman and Özçelik, 1993;Göncüoğlu et al, 1997Göncüoğlu et al, , 2003Görür et al, 1997;Göncüoğlu and Kozur, 1999;Gedik and Önalan, 2001;Gedik et al, 2005;Yanev et al, 2006;Boncheva et al, 2009;Yalçın and Yılmaz, 2010;Özgül, 2012;Yılmaz et al, 2015). The thick Palaeozoic sedimentary successions of the Pontides contain unmetamorphosed Devonian rocks.…”