Geology and Depositional Characteristics of Early-Middle Miocene Fossil Woods (Central Türkiye)

The Galatian Volcanic Complex (GVC), also known as the Kızılcahamam Volcanics, extends over extensive areas of northwestern Central Anatolia, Türkiye. It exhibits lateral transitions into, and occasionally fills, the adjacent Neogene basins of Çankırı-Çorum, Kazan, Beypazarı, and Çayırhan. The transitional zones between the volcanic deposits and the sedimentary basin fills host silicified wood fossils that occur as distinct, localized horizons. This study investigates the geological context and depositional characteristics of these fossil woods across seven distinct localities. The fossilized remains are observed in stratified, scattered, or tightly packed configurations within sedimentary and fine-grained pyroclastic host rocks. Stratified assemblages suggest in situ fossilization, whereas scattered and packed occurrences indicate post-depositional transport and reworking. Notably, the sedimentary and pyroclastic host rocks enclosing these fossil horizons have also undergone pervasive silicification. Much like the fossil woods themselves, these silicified host rocks largely retain their original depositional textures. Silicification, primarily occurring via permineralization, represents a major post-eruptive diagenetic phase in the region. This process affected not only the botanical remains but also extensive sedimentary successions, including the up to 250-m-thick Akpınar Formation within the Çayırhan and Beypazarı basins. Field observations and analytical investigations indicate that high-temperature, silica-saturated geothermal fluids drove this widespread silicification. These geothermal systems were continuously sustained and recharged by active regional tectonism. Furthermore, this hydrothermal activity persists to the present day, albeit at a reduced intensity.