The Bolsovian to Cantabrian sediments in the Dobrudzha Coal Field are about 800 m thick. They were deposited in a depression bounded to the east, south and west by active synsedimentary faults. Most of the succession is coal-bearing clay- and siltstones, including occasional lacustrine deposits with fresh water faunas (molluscs and ostracods). Basin-wide sandstone intervals are associated with two periods of erosion and non-sequence. There are also localized sandstone bodies with vitrinized plant remains associated with the basin-margin faults. Conglomerates are only thin and rarely developed, and pebbles are only rarely found in the sandstones. There are only three basin-wide coals (m5 at the middle Makdonka Formation, n1 at the base of the Krupen formation and p3 in the middle Gurkovo Formation) representing times of diminished influx of clastic sediment, and thus of reduced movement along the basin-margin faults. Based on the depth of the erosive down-cutting, it is estimated that the elevation of the basin was at least 180 m above sea-level. The area surrounding the basin is supposed to be an alluvial plain covered with vegetation and swamps. The dense vegetation cover suggests periods of high precipitation, whereas dry conditions with active weathering are most probable during deposition of the Velkovo Formation. Volcanic activity occurred near to the depression, perhaps related to the boundary faults. In the stratigraphically highest part of the succession (the Kabalak Member), volcaniclastics are the main component of the detritic sediments. The basin eventually inverted to become a horst around which Permian sediments were deposited.

The Dobrudzha Coalfield in northeast Bulgaria has coal-bearing deposits ranging from latest Namurian to early Stephanian age (late Bashkirian to Moscovian age). Palynology of the coals in the upper Makedonka, Krupen and Gurkovo formations has been used to identify major changes in the vegetation during late Westphalian and early Stephanian times. The palynomorphs were grouped in two different ways (according to general morphotype and according to parent plant group) and stratigraphical trends in the two sets of groups used to identify vegetation change through the succession. Detrended Correspondence Analysis was also used to identify ecological relationships between the palynofloras. In the upper Makedonka and Krupen formations, lycophyte spores mostly comprise 15–25 % of the palynofloras in the thicker seams, but in the thinner coals they can represent up to 55 %. Of the other plant groups, ferns are the most abundant, representing 31–69 % in the thicker seams, 12–41 % in the thinner seams. This suggests that the arborescent lycophytes were mainly restricted to pioneer vegetation in these upland areas, and were replaced by ferns as the peat substrates became better developed, suggesting better-drained conditions. The thinner seams also have a noticeable component of sphenophyll spores, indicating significant areas of open conditions allowing colonization by these scrambling plants. In the Gurkovo Formation coals, lycophytes form an even smaller part of the palynological spectra, usually less than 10 % and in only one sample just over 25 %; fern spores make up 43–57 % of the palynofloras. This is in contrast to the palynofloras reported from contemporaneous clastic deposits in South Wales, most of which consist mostly of 34–60 % lycophyte spores and 14–34 % fern spores. Even more marked is the difference from the contemporaneous coals formed in lowland settings in the USA, which have mostly > 50 % lycophyte spores. This evidence suggests that the timing of the decline in abundance of arborescent lycophytes varied according to elevation above sea-level. In lowland coastal settings, the lycophytes remained dominant until middle–late Cantabrian times, but in more inland areas they were progressively replaced mainly by arborescent ferns during late Westphalian times.