Abstract
The Karadere area to the east of Safranbolu in NW Anatolia is one of the very few localities in Turkey where the contact between the Cadomian basement and the Lower Palaeozoic transgressive succession is well exposed. The Ordovician graptolite Rhabdinopora flabelliformis (Eichwald) ssp. was found in the basal part of the Bakacak Formation, indicating an Early to early Late Tremadocian age for the beginning of the Palaeozoic transgression in the Zonguldak terrane. A few metres above this occurrence, another horizon contains Paradelograptus cf. antiquus (T. S. Hall), which mainly ranges into the Late Tremadocian. Higher up in the Ordovician succession, a new graptolite bed confirms an early Darriwilian (Dw1) age for the middle part of the Karadere Formation with the occurrence of the biozonal index Levisograptus austrodentatus (Harris & Keble) and the first record of Tetragraptus cor (Strandmark) in the area. The palaeobiogeographic distribution of these Karadere fossils is in agreement with a peri-Gondwanan affinity of the Zonguldak Terrane of the Pontides, NW Anatolia, during the Early-Middle Ordovician.
Highlights
In contrast to the relatively well documented Ordovician successions known from the SE Anatolian Gondwanan Autochthon and the Tauride-Anatolide units (e.g. Ghienne et al 2010 and references therein), fossil data from the Lower and Middle Ordovician rocks are relatively scarce in the Istanbul and Zonguldak terranes of NW Anatolia (e.g. Yanev et al 2006; Bozkaya et al 2012)
The purpose of this article is to report new biostratigraphic data from the Ordovician of the Bakacak and Karadere formations in the Zonguldak Terrane (Karadere generalized section and Incüves measured section representing its lower part), not recognized in previous studies but of interest for correlation with the Istanbul Terrane in the west and with the Taurides Gondwanan succession in the south. They confirm the record of Tremadocian deposits at the base of the Palaeozoic sequence and of Middle Ordovician beds that include the index graptolite for the basal Darriwilian Stage
The deposition of the graptolitebearing dark shales until the Late Tremadocian or the earliest Floian was followed by a regression that is recorded by red–brown fluvial clastics in the upper part of the Bakacak Formation
Summary
In contrast to the relatively well documented Ordovician successions known from the SE Anatolian Gondwanan Autochthon and the Tauride-Anatolide units (e.g. Ghienne et al 2010 and references therein), fossil data from the Lower and Middle Ordovician rocks are relatively scarce in the Istanbul and Zonguldak terranes of NW Anatolia (e.g. Yanev et al 2006; Bozkaya et al 2012). The purpose of this article is to report new biostratigraphic data from the Ordovician of the Bakacak and Karadere formations in the Zonguldak Terrane (Karadere generalized section and Incüves measured section representing its lower part), not recognized in previous studies but of interest for correlation with the Istanbul Terrane in the west and with the Taurides Gondwanan succession in the south.
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