ARHIVELE OLTENIEI - Universitatea din Craiova

The genetic control factors of the lignite types from western Oltenia 367The limnic basins can be large when they are low, as it is the case ofOltenia basin, or small, according to the size of the depression as well, whenthey are high, intermountain, as it is Comăneşti basin. There predominate thetelematic and shallow submerged environments, which influence the quantityand the quality of the coals. The limnic coal-generating marshes installed inlacustrine, fluvial, and, more rarely, in fluvial-deltaic depositing systems.The paleogeographic factor influenced the formation, development, andevolution of coal-generating marshes. The geographical location of a marsh ascompared to the continent and the sea is determinant for the types of vegetalassociations, for the marsh water features and for the quality of the organicsediment 3 .In Oltenia, there can be noticed lignite beds with regional extension, asthe V bed, which geographically can be considered as formed on a littoral plain,at the shore of the Pliocene lake, where water increased constantly andequivalently to the rate the marginal marsh was covered as the shore of this lakegradually advanced.Unlike the lignite beds formed in such conditions, there appear otherbeds, especially on the western side of the basin, which cover small surfaces andare mostly elongated, suggesting their formation in a fluvial domain due to theirtransformation in a marsh.It is the case of the II and III lignite beds located west of the Motru andof some intercalations of lignite located above the V bed, which cannot becorrelated.Within Motru-Rovinari coal field, as well as in the area of the lignitePliocene deposits located south of the alignment Strehaia-Filiaşi-Craiova, thepaleogeographical factor favourable to the formation of the lignite beds,especially in the formation of Motru-Jiu, was the presence of a plain relief,which allowed the extension of the coal-generating marsh regime on large areas.These marshes could rapidly be covered by water, as the level of thePliocene lake and their supply with psammitic-psefitic material through marshydeltas increased.The sedimentation stages present in the evolution of the Pliocene coalfield from Oltenia are characteristic to an accumulation plain and they comprise:the telematic phases, when subsidence was low and equal to the accumulation ofthe vegetal parental material; the lacustrine phases, achieved as subsidenceincreased, which led to the accumulation of certain predominantly clayishdeposits and the fluvial phases, when the areas located outside the basin rosemore rapidly, erosion strengthened and the hydrographical system carried largequantities of psammites.3 P. Enciu, I. Andreescu, Stratigraphy of the Pliocene-Pleistocene deposits in the southwesternpart of the Dacic Basin (Jiu – Desnăţui Sector), in “Dări de Seamă”, Institute of Geologyand Geophysics, tome 74/4, Bucureşti, 1990, p. 141-156.