| Mezdren Formation | |
| Type: | Geological formation |
| Period: | Campanian |
| Prilithology: | Limestone |
| Region: | Shumen Province |
| Coordinates: | 43.15°N 26.53°W |
| Unitof: | Eastern Fore-Balkan Zone |
| Underlies: | Kaylaka Formation |
The Mezdren Formation is a Late Cretaceous (Campanian) geologic formation located within Bisserna Cave, Shumen, Bulgaria.[1]