Us, Muhammed Sami; Tekin, Erdoğan; Akgün, Funda; Kayseri-Özer, Mine Sezgül; Varol, Baki Erdoğan

This study presents an integrated sedimentological, microfacies, and palynological analyses of the Late Eocene–?Early Oligocene (Priabonian–?Rupelian) Akçapınar Formation, exposed along the Soğanlı Stream in the Intra-Pontide Belt of the Western Black Sea region, Turkey. The formation, which overlies the evaporitic Pürçükören Formation and locally the Soğanlı Formation, records deposition in restricted shallow-marine to a lagoonal setting during a phase of significant tectonic and climatic reorganization. Detailed field mapping and measured stratigraphic sections, supported by petrographic, XRD, and SEM analyses, reveal mud-supported textures, limited faunal diversity, and thin-shelled gastropods, consistent with low-energy, brackish conditions. Palynological assemblages, identified here for the first time, refine the age constraints and document freshwater influence, whereas mineralogical data indicate alternating arid (smectite-rich) and humid (chlorite–illite-rich) intervals. Microfacies patterns (Mf1–Mf4) and lithofacies associations (Lf1–Lf8) were synthesized into three-dimensional depositional models, illustrating progressive basin restriction, episodic subaerial exposure, and evaporite precipitation. The multi-proxy approach, integrating sedimentology, microfacies, palynology, and mineralogy, refined the depositional model of the Akçapınar Formation, revealing facies heterogeneity driven by the interplay of tectonically induced basin isolation, relative sea-level fluctuations, and paleoclimatic oscillations during the Eocene–Oligocene transition, and providing new insights into the paleogeographic evolution of the northern Neo-Tethys during the final stages of its closure.

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Us, Muhammed Sami

The gypsum member of the Balpayam Formation (GMoBF) in the Pülümür Kırmızıköprü Basin (PKB), Eastern Anatolia, records a complex evaporitic system shaped by episodic tectonism, volcanism, and fluctuating hydrological conditions. Stratigraphic logging, facies analysis, and systematic sampling from outcrops and quarries enabled a detailed assessment of the evaporite succession. Petrographic data reveal pervasive secondary gypsum textures, including porphyroblastic, alabastrine, laminated, brecciated, and satin-spar fabrics preserving relics of primary anhydrite and calcite. XRD and FIB-SEM-EDS analyses identify gypsum, anhydrite, celestine, dolomite, calcite, clay minerals, and minor siliciclastic, clarifying diagenetic pathways. Diagenesis initiated with early calcite and aragonite precipitation, followed by replacement by primary anhydrite and gypsum under elevated Mg2+/Ca2+ ratios and shallow burial. Later hydration, dehydration, and rehydration cycles produced secondary gypsum with distinctive microtextures and micro-hydration channels. The PKB reflects a dual depositional system: a shallow, low-energy, restricted lagoon dominated by massive-laminated gypsum, stromatolitic textures, and organic-rich layers, and a comparatively deeper open marine setting with laminated-banded gypsum and transported gypsum arenite-rudite facies. Chicken-wire gypsum and anhydrite nodules indicate synsedimentary to early diagenetic formation under hypersaline conditions. A schematic depositional model constrains the temporal and spatial evolution of diagenetic processes, highlighting the interaction among evaporite deposition, tectonic activity, and environmental fluctuations in the southern Neo-Tethys Ocean of Eastern Anatolia.

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