The Lower Cretaceous is of wide geographical distribution in Bulgaria, mainly in the northern and southwestern part of the country. Marine deposits predominate, with exception of the most northeastern part of the country, where paralic and continental deposits occur. The main part of the Lower Cretaceous sediments were deposited in shelf environments, and a small part of them – in moderately deep-water (epibathial) ones.
The shelf sediments consist of conglomerates, gritstones, various sandstones, marls and different types of limestones. In the lower (Berriasian-Valanginian) part of the series, as well as in the Uppermost Barremian-Middle Aptian, flysch and flyschoid (flysch-like) clastic sediments were formed in deeper-water environments. Pelagic limestones alternating with marls (in the Western Fore-Balkan and partly in South-West Bulgaria) were developed, too, and typical catastrophic sediments (debrites, tempestites, sediments with hummocky-cross stratified bedding) – in the boundary Jurassic-Cretaceous beds. These sediments are also observed in several higher stratigraphic levels (Upper Valanginan, Upper Barremian-Aptian). At the beginning of the Late Barremian (up to the Early Aptian) a considerable build-up of large carbonate platforms of Urgonian type associated with terrigenous sediments in the Northern Fore-Balkan band commenced. The Lower Cretaceous sediments are grouped (united) into nine sediment associations, each of them integrating with the main lithostratigraphic successions and facial types.