Biostratigraphy and paleoenvironments of the Oligocene succession(İhsaniye Formation) at Karaburun (NW Turkey)

Abstract

The biostratigraphy and paleoenvironments of the İhsaniye Formation exposed at Karaburun in northwest Turkey is described based upon the study of abundant and well-preserved foraminifera, calcareous nannofossils and palynomorphs. The studied succession is Early Oligocene in age, with calcareous nannofossil zones upper NP21 (Subzone CNO1) to lower NP23 (Subzone CNO3) and planktonic foraminifera zones O1 (~P18) and O2 (~P19) represented, and palynological assemblages suggestive of zones D13 to D14a. Based on these new data, a revised interpretation of the stratigraphic succession is presented. Deposition was controlled by a now inverted normal fault, with deposition of older stratigraphy (upper NP21 to NP22) restricted to the original hanging wall. During NP23, deposition commenced on the footwall, resulting in progressive onlap of an exposed Eocene reefal limestone (Soğucak Formation). Three primary sedimentary facies are present: marls with thin calcareous siltstones, marls with synsedimentary slumps and debris flows, and coarse pebbly sandstones. The coarse pebbly sandstones were deposited in a fan-delta/shoreface paleoenvironment and represent the initial phase of onlap during biozone NP23 onto a rocky shoreline on the footwall side of the fault. The marl-dominated facies represent deposition in outer shelf-upper bathyal environments. The succession demonstrates evidence for a near-end Eocene relative sea-level fall. Changes in the abundance of planktonic foraminifera and the onlap onto the footwall demonstrate maximum subsequent transgression within NP23. This reflects eustasy rather than Paratethyan relative sea-level. No interpretation of sea-water salinity reduction can be made for the sediments deposited during biozone NP23 in the studied sections, although this is noted in coeval sediments in parts of Paratethys (the "Solenovian Event"). Together with the open marine nature of the diverse and abundant fossil assemblages, it is suggested that deposition of the Karaburun section was strongly influenced by a connection to the global ocean, via the Çatalca Gap, as suggested in a recent study.

Late Eocene to Early Oligocene palynostratigraphy of the Western Black Sea, Eastern Paratethys

“…Marl, siltstone, and sandstone dominate this section with thin layers of limestone present towards the top (Figure 3). This section has been demonstrated by Simmons et al (2020) to represent more complete Early Oligocene stratigraphy at Karaburun with nannoplankton biozones NP21-NP23 supported by planktonic foraminifera (Biozones O1-O2). Our limited number of samples appear to lie within the upper part of this age range (Assemblage Zone D).…”

“…Seven samples were collected from the Karaburun (1) section (GPS coordinates: 41°20′51″61N, 28°40′47″71E) ( Figure 2). This section, on Cape Karaburun, features well-known outcrops that encompass the Eocene-Oligocene succession on the Thracian coast of the Western Black Sea (Less et al, 2011;Okay et al, 2019; the "Footwall Section" described by Simmons et al, 2020). The Karaburun (1) section is about 140 m thick and comprises conglomerate, sandstone, calcareous sandstone, siltstone, mudstone, marl, silty marl, shale, and bioclastic limestone.…”

“…The Upper Eocene shallow marine limestones of the Soğucak Formation at the base are unconformably overlain by the Lower Oligocene Ceylan Formation composed of shallow marine calcareous sandstone, siltstone, conglomerate, and deeper marine marls. Okay et al (2019) and Simmons et al (2020) used the local term "İhsaniye Formation" for this rock unit based on its distinctive lithological character. We prefer the term "Ceylan Formation" to permit ready correlation with the stratigraphy of the adjacent Thrace Basin.…”

Microfossil assemblages (diatoms, calcareous nannofossils, and silicoflagellates), paleoenvironment, and hydrocarbon source rock potential of the Oligocene Ruslar Formation at Karadere, Bulgaria

“…Within this context, it is important to note that the "Solenovian event" is probably missing at Karaburun along the Turkish Black Sea coast (İhsaniye Formation, Simmons et al, 2020;Tulan et al, 2020), located about 185 km SSE of Karadere. This may indicate that a connection between the Paratethys and the Mediterranean Sea remained open at the southwestern edge of the Black Sea.…”

The stratigraphy of the Oligocene-lower Miocene deposits of southern Ukraine

“…Follow-up studies should address many other important aspects of this key sequence in the Black Sea region, such as the context of basin evolution with the associated paleogeographic changes, sequence stratigraphy, and petroleum geology, just to name a few. For this kind of more specialized future studies, we consider the other papers in this special issue as useful templates (e.g., Okay et al, 2020;Simmons et al, 2020;Tulan et al, 2020).…”