Geochemical Evidence on the Source of Silica and Depositional Setting of the Diatomites in the Ağın (Elazığ, Turkey)

Abstract

The Upper Oligocene-Lower Miocene Alibonca Formation retains an essential record of intricate relationships among carbonate platform evolution, volcanic-sedimentary inflow, and high-purity silica deposition. This study examines the stratigraphic structure, paleoenvironmental development, and industrial viability of the A & gbreve;& imath;n diatomite deposits using comprehensive sedimentological, mineralogical, and geochemical investigations. Stratigraphic evidence indicates that the formation commenced with Early Miocene alluvial fan and shallow restricted marine sub-basin sedimentation prior to evolving into a significant marine incursion. This marine phase created a resilient carbonate platform structure consisting of reef-core, fore-reef, and back-reef sub-environments. Simultaneously, vigorous regional synsedimentary volcanism introduced high-flux silica pulses into the basin, acting as a major catalyst for diatom proliferation and high biological productivity within a restricted sub-basin setting. Geochemical analyses indicate that these bright white, diatomite deposits formed in conjunction with potassium-rich clays in a relatively deep, low-energy, and confined sub-basin of the Alibonca Sea. The high concentration of bulk SiO2 and low trace element baselines are consistent with a high-purity deposional system and a low total rare earth element (Sigma REE) abundance. However, their relatively high Al2O3 and K2O contents indicate significant volcanic and terrigenous detrital input together with authigenic clay mineral formation during diatomite deposition, classifying the deposits as clay-bearing (argillaceous) diatomites rather than exceptionally pure diatomites. Chemical Index of Alteration (CIA) values indicate moderate continental chemical weathering under mostly hot and humid paleoclimatic conditions. The rapid terrestrial runoff and nutrient influx stimulated significant diatom growth before the ultimate late Early Miocene marine regression, transforming the area into a subaerial, volcanically influenced terrestrial environment. The A & gbreve;& imath;n deposits exemplify intra-platform marine silica sinks, demonstrating how tectonic-magmatic influences can surpass typical carbonate factory conditions to provide economically valuable biogenic mineral resources.