Paleoenvironmental conditions of Puertollano coals (Spain):: petrological and geochemical study

In the present work, petrographic, geochemical and mineralogical data have been combined with results from prior paleobotanical studies in order to determine the sedimentary and postsedimentary diagenetic factors responsible for the physicochemical properties of coal seams and associated sediments from the Puertollano Stephanian coal basin. Although the coal seams (4) originated under similar lacustrine conditions, the highest coal seams (1 and 1bis) show higher production/preservation of structured tissues (telinite and collotelinite) than the lowest coal seams (2 and 3) where destruction of the cell tissues (collodetrinite) is predominant. Differences in degree of preservation as a result of changes in the environmental sedimentary conditions in the water table (pH, redox) may explain the different maceral distribution. This feature may also be due to the increase in degree of humification from the highest seams (1 and 1 bis) to the lowest seams (2 and 3). However, the gentle thermal maturation undergone by these Stephanian coals only produced a slight modification in the physicochemical properties of the organic matter. In general, alkaline synsedimentary conditions could be deduced from the dominance of organic sulphur with respect to pyritic sulphur. Reducing conditions for seam I, Ibis and 2 and more oxidant conditions for seam 3 can be deduced from maceral, sulphur and carbonate distribution. Other diagenetic processes involved organic and inorganic sediments. For example, a kaolinitisation process with a different intensity for the early diagenetic stages suggests the occurrence of leaching processes, which affected both organic and inorganic sediments. (C) 1999 Elsevier Science B.V. All rights reserved.