Upper Triassic Peritidal Limestones from the Konyava Mountain, SW Bulgaria

Abstract

Four microfacies are distinguished in the section of Tran Formation exposed near Viden peak. The bioclastic wackestones at the base are defined as low-energy, shallow subtidal sediments. The laminated mudstones were deposited in the intertidal/supratidal zone of a tidal flat where fine-grained carbonate was mainly accumulated by tidal currents along with some in-situ microbially induced precipitation. The mudstones with root casts and the massive mudstones are interpreted as deposits in intertidal/supratidal ponds and supratidal marsh (palustrine) areas where alternating wetting and drying periods locally favoured desiccation and pedogenesis with vegetation development. The interbedding of laminites with non-laminated mudstones was likely controlled by a combination of autogenic and allogenic processes. The ambient waters did not reach hypersalinity for early dolomitization because the landward part of the restricted peritidal setting was influenced by freshwater input under semi-arid climatic conditions. Another hypothesis presumes that the sedimentation occurred in a coastal wetland with influence of both freshwater and seawater. However, the peritidal interpretation is preferred herein because it more adequately explains the general depositional environment. The carbonate succession indicates an upward-shallowing trend and was formed during the final regressive phase of Triassic platform development in Carnian–Norian times.