Catastrophic deposits in the Bulgarian Lower Cretaceous

Catastrophic sediments are formed under the influence of sharp and short-term natural phenomena – earthquakes, tsunami, hurricanes, storms, submarine slumps, continuous torrential rains etc. They could be caused by different reasons (relief and land dynamics, shelf and continental slope, sharp climatic changes, impact and orbital influences etc.) which have outside (allocyclic) character in respect to the deposition. These deposits are named catastrophic because they are a result of the very short-term phenomena (Ager, 1974, 1993; Einsele, 1991; Seilacher, 1991). 
   The sediments discussed are genetically and dynamically determined and characterized in diverse Lower Cretaceous cross sections in Bulgaria. The basic types of catastrophic deposits in the Bulgarian Lower Cretaceous record are: debrites and diamictites with chaotic structure, very thick extensive debrites, as well as tempestites and beds with hummocky cross stratification (HCS). Specific event deposits are so called fluxoturbidites, whose origin is connected to the combination between turbiditic curents and significant submarine slumping. Generally these are thick-bedded deposits with slightly expressed graded stratification, often with chaotic structure and practically without any marks on the lower bed surface of the sand beds.
   The following types of catasttophic deposits were established in the Lower Cretaceous sections in the region of the Central and Eastern Balkan: 1) mass debris flow deposits - debrites and diamictites (or mixtites); 2) tempestites; 3) sediments with hummocky-cross-stratified bedding; 4) submarine slumps and slumping. Their formation is conditioned by the specificy of the palaeogeographic environment...