Abstrakt
Twenty-eight channel samples with a cumulative thickness of about 4m collected from three sections of the Maghara main coal seam in the middle Jurassic Safa Formation have been studied for their lithotype and maceral compositions to reconstruct the character of peat swamp, its hydrological regime and the predominating type of vegetation. Dominantly vitrinite composition of coal and extremely low fire- and oxidation-borne inertinite content, together with high Gelification Indices imply predomination of waterlogged anoxic conditions in the precursing mire with water tables mostly above the peat surface throughout most of the time during peat swamp formation.
Increases in collotelinite contents and Tissue Preservation Index up the section, followed by a reversal trend in upper third of the coal section, further accompanied by a reversal trend in collodetrinite, liptodetrinite, alginite, sporinite and clay contents records a transition from dominately limnotelmatic and limnic at the lower part to dominately limnotelmatic with increase telmatic condition achieved in the middle part of coal. At the upper part of coal seam an opposite trend marks the return to limnic and limnotelmatic conditions in the final phases of peat swamp history and its subsequent inundation.
The proportion of arborescent (mostly coniferous) and herbaceous vegetation varied throughout the section of the coal with tendency of increasing density of arborescent vegetation to the middle part of the coal seam section. The intercalation of coal in shallow marine strata implies that peat swamp precursor formed in a coastal setting, probably on delta plain or lagoon.
Its formation was controlled by water table changes driven by sea level fluctuations that created an accommodation space necessary for preservation of peat.