Sarmatian aragonite sediments in North-eastern Bulgaria - origin and diagenesis

Abstract

Unconsolidated aragonite sediments of Bessarabian – Chersonian age (Middle – Late Sarmatian), are established for the first time in the Topola Formation (North-Eastern Bulgaria). The aragonite crystals amount to 85-95% of the rock volume, and are considered as a product of chemical precipitation. The term “aragonitites” is proposed for the unconsolidated aragonite sediments. Aragonitites predominate over the consolidated carbonate rocks (micritic limestones and dolomites) in the studied sections. Clay interbeds are also identified. The deposition of the primary aragonite muds took place in a small shallow bay, opened to the south-southeast, in condition of arid climate. Periodic lithification of a part of the aragonite muds proceeded as a result of neomorphic processes – aragonite transformation to low-magnesian calcite, recrystallization of calcite to coarser one, and further dolomitization. An attempt is made to prove that lithification had place under submarine and brackish conditions.