Climatic and tectonic controls on ferroan dolomite formation : insights into Early Miocene anoxia in the Mediterranean Sea (il-Blata, Malta)

Abstract

Records from the Miocene il-Blata section in Malta offer insights into the depositional environments of the Central Mediterranean following an Early Miocene restriction of the Mesopotamian Seaway (c. 20 Ma). Inorganic and organic stable carbon isotope values suggest relatively steady depositional environments, whereas authigenic iron dolomite abundances exhibiting substantial (Formula presented.) 18O and (Formula presented.) 13C variations at a sequence scale indicate dynamic sedimentation conditions leading to differential diagenesis. Petrographically, the dolomitic levels exhibit matrix-selective dolomitization, occasional silicification and phosphatization, and textural indicators pointing to subsurface microbial influences. These features collectively point to complex shallow burial diagenesis. In addition, the presence of framboidal pyrite and gypsum infilling foraminiferal chambers, along with the absence of large planktonic foraminifera, suggests the development of palaeoenvironmental stress imposed by a density-stratified water column affecting the pore waters. Towards the top of the studied succession, a shift from organic to siliceous deposits reflects water column perturbations possibly linked to changes in oceanic circulation associated with a temporary re-opening of the Mesopotamian Seaway. This study not only underscores the hydrochemical controls exerted by North African terrigenous fluxes over the Mediterranean, but also highlights the intricate interplay between shifting depositional environments and shallow burial diagenetic processes in shaping the geochemical and textural fabrics of authigenic mineral assemblages.