Calcareous ooid formation in clay-dominated, transgressive environment: Dacian Basin, Upper Neogene (Romania)

Abstract

In this paper the genesis of the Jitia de Jos calcareous oolite (Upper Meotian, Eastern Carpathians, Romania) and its appearance as an intercalation in the Upper Meotian clay-dominated deposits are explained using the Bahama ooid model.  According to our hypothesis, the Jitia de Jos ooids accumulated upon an isolated shallow-water platform bordered by deeper water. Under these conditions, strong shallow-water currents removed the suspended clayey material from the ooid platform, while the clayey-silty sediments accumulated in the deeper water surrounding the elevated relief. This hypothesis explains the hydrodynamic difference between the oolitic wave ripples (formed in high energy shallow water) and the fine-grained sandstone, Meotian-Pontian wave ripples (shaped in deeper water, by lower-energy waves). The genesis of the Jitia de Jos oolite was also controlled by the hydrochemical changes that occurred during the initial phase of the Upper Meotian – Lower Pontian transgression.