MACERAL DISTRIBUTION IN GARUMNIAN COALS AND PALEOENVIRONMENTAL IMPLICATIONS IN THE CENTRAL PYRENEES, SPAIN

The organic content of Garumnian coals in the central Pyrenees of Spai n is heterogeneous and is formed of plant fragments, with the fossil r emains of botanic structures and secondary products resulting from the rmal and biochemical transformation of macerals. The maceral compositi on of the three areas studied, Berga, Tremp and Ager, is similar. The Berga and Tremp zones include an upward decrease in organic materials and the top sequence is significantly richer in inorganic sediments. I n contrast, in the Ager zone only one level with organic matter is pre sent. The organic matter of the Tremp Formation is humic and five resi nite groups have also been characterized. The mineral phases determine d, mainly carbonates, appear closely associated with macerals, infilli ng cell lumens or replacing cell walls, and in layers within the organ ic matter. The maturity and source rock potential of the organic rich beds were investigated using reflected light and fluorescence microsco py. The results are compared with other maturity parameters (Rock-Eval , calorific value and diagenetic mineral matter). The vitrinite reflec tance (R(o) 0.35-0.45) and the maximum temperature (430-degrees-C) are low and homogeneous in the different areas. These values indicate tha t the rank of the samples corresponds to an immature diagenetic state close to the lower oil window and allows classification of this coal a s subbituminous. The relationship between inorganic and organic phases indicates low-grade transformation as a consequence of a low lithosta tic pressure. The macerals indicate that the coal-forming peat was dep osited in a predominantly forest-moor swamp environment. The liptinite assemblage suggests a subtropical and damp climate during peat deposi tion. The amount of organic matter decreases upwards within the sedime ntary sequences analyzed. Palaeoenvironments were similar in the three areas, which could originally have been part of the same basin.