Marisia - Maros Megyei Múzeum Évkönyve 32/1. (2012)
Paleontology and mineralogy
Fiorina DIACONU In the Danube - Motru area was identified the five main paleobiotopes (Fig. 1) that formed the coal-generating swamps from Oltenia during the Pliocene. 1. The marginal zone — The Sequoia Forest is a marginal biotope dominated of the forests with S. abietina, Pinus sp. G. europaeus, Cedrus and Sciadopitys. 2. The seasonally flooded zone - The deciduous forests is the biotope in the central part of the coal-generating swamps, with herbaceous vegetation dominated by Carex species, various Pandanus species and probably Myrica lignitum bushes. In same seasonal flooded areas, in a more advanced stage of vegetation, hygrophyte deciduous forests with multi-plant assemblages dominated by B. tiliaefolium or various Salix species installed. Salix associations were probably related to the outside biotope and Myrica lignitum, Alnus sp., Liquidambar europaeum, Carya aquatica type., Juglans barbui, probably Nyssa and Acer tricusp idatum. 3. The almost permanently covered by water zone — The swamp forest Glyptostrobus is a biotope absolute dominated by G. europaeus assemblages, with B. tiliaefolium, Taxodium dubium, Nyssa. This plant community was characterized by the presence of a discontinuous bed of ferns, especially Osmunda regalis. Sometimes the distance between trees reached several meters allowing installing the beds of Phragmites and even meshes water with Stratiotes dacicus. 4. The permanently covered by water zone (< 2 m) — The swamp with Phragmites and Pandanus was a biotope permanently covered with water, from a few centimeters to 2 m in depth, dominated by Phragmites oeningensis plant assemblage with: Typha latissima, Pandanus div. sp., Sparganium sp. and occasionally other species. 5. The permanently covered by water zone (> 3 m) — The swamp with aquatic plants was dominated by assemblages with: Stratiotes dacicus, Nelumbo protospeciosa, Nymphaea luteum, N. alba, Ceratophyllum demersum and Potamogeton div. sp. Each of the plant communities (phytocoenoses, associations) led to a distinct coal facies with specific environmental factors, forming different lithotypes [15, 20]. The Sequoia forest led to form the xylitic coal with many roots which; unfortunately, because of their marginal position these roots were eroded. The coal facies of the grassy swamps with Carex, Pandanus and Myrica, and all the forest swamps with hygrophyte deciduous woods formed the detritic coals, but poor xylitic coal in small quantity. The swampy forests with Glyptostrobus generated lithotypes as: coal xylitic and xylite, these two being genetically related. Ticleanu’s [14, 15] researches showed that more than 80% of the fossil wood passed into xylite derived from Glyptostrobus europaeus, one of the trees that make an important contribution to the establishment of parental vegetal material of the coal from Oltenia. The swamps with reed (Phragmites, Pandanus and Typha) were much extended when the coal seam IV formed, generating the detritic coal and very little weak xylitic coal. The detritic coal is the most widespread lithotype in the coals from Oltenia. The associations with aquatic plants, depending on their density and the input of suspended clayey minerals formed detritic coals, clayey coals and coal clay. The changes in water depth due to the changes of the rate of subsidence or flooding, caused alternations in time of the phytocoenoses and formation of the genetic series reported [4] in Husnicioara open pit. 178
