Organic geochemistry (Rock-Eval) and maturation rank of the Garumnian coal in the Central Pyrenees (Spain)

Maturity and source rock potential of coal and organic matter-rich levels in the Tremp Formation in Berga, Tremp and Ager (Central Pyrenees) are analyzed by optical and geochemical techniques. The organic matter has a humic constitution, and is mainly included in a carbonatic rock matrix. The average vitrinite reflectance were found between 0.35 and 0.45%, corresponding to organic-rich levels and coal levels, respectively; these values are characteristic of a low maturity. This parameter shows a good correlation with fluorescence colors, calorific value higher than 24 MJ/kg wet sample without ashes, mineral matter diagenesis and average Tmax (430°), and it indicates that the range of maturity fits the immature diagenetic state bordering maturity, near to the oil window. Composition and maturity of organic and inorganic matter are similar in the Berga, Tremp and Ager areas. The three areas were part of a single basin located to the north, corresponding the Ager zone to the distal environment episode and thus, paleoenvironments were similar in all the studied zones. These materials suffered a low-grade transformation, consequence of a low lithostatic pressure. So, the Garumnian Tremp Formation coal may be classified as sub-bituminous, corresponding to a low rank of maturity.