Mehedinti Plateau: The Zăton-Bulba Karst System

Abstract

In the central part of the Mehedinţi Plateau, west of the Nadanova-Baia de Aramă tectonic corridor, Zăton and Ponoarele depressions, along with Bridge’s and Bulba caves form a karst system developed in Mesozoic limestones. The Zăton Lake hosted by a karst marginal depression is located on Precambrian granitoides rocks, with its northeastern part in Mesozoic limestones. Dry for most part of the year, the lake fills after heavy rains or snow melting and is drained along the subterranean galleries of Bulba Cave (5360 m long). When the Zăton Lake is full, the water level rises and flow through the Bridge’s Cave, flooding a large sector of the cave, forming a pond hydrodynamically connected to the Zăton Lake. Once the lake level recedes or dries out, the underground pond disappears. During years with heavy rainfall, a second temporary lake forms within the Ponoarele endorheic depression, which also drains along the underground network of the Bulba Cave. The Bridge’s Cave, 734 m in length, presents an underground network consisting of dry galleries, galleries temporarily invaded by rising waters from below, and underlying—only partly accessible—galleries with perennial flow. Vertical shafts connect the passages with perennial flows, to overlying galleries. Bulba Cave is the local base level, which control the evolution of the entire karst system. In the central sector of the dry galleries, calcite draperies, soda straw, and candlestick stalagmites are common. Both caves host bat colonies, represented by the species: Rhinolophus ferrumequinum, Rh. hipposideros, Rh. blasii, Miniopterus schreibersii, and Myotis dasycneme.