Origin of Coal
Coal is formed from the compression and alteration of partly decomposed peat. Peat forms from the accumulation of partially decomposed plant materials under generally wet conditions having a restricted supply of oxygen. Such conditions exist in environments called mires which can be classified as limnic or paralic. Limnic coal deposits are inferred to have resulted from peat that formed in mires isolated from marine conditions in slowly subsiding basins. In contrast, paralic deposits resulted from peat mires which had a hydrological connection with the sea at the time of peat formation.
The composition of peat depends on the the type of plants that grew in the mire, nutrient availability, climatic conditions, level of the water table, and the pH and Eh conditions of the mire. Any organic part of the mire ecosystem may be preserved in some way in the peat, including large trees, herbaceous shrubs, grasses, aquatic plants, and the microorganisms that break down the organic material. Differences between coals of different geologic periods are, in part, due to differences in the dominant plant groups from those times.
Figures & Tables
This volume of the “Atlas of Coal Geology” provides 393 images on various subject matters related to coal deposits and coal resource utilization. The supporting text provides an introductory overview of coal exploration, mining, and coalbed methane (CBM) development, followed by discussions on various megascopic aspects of coal geology (microscopic aspects are covered in Volume 2). Because of the vast subject matter, many generalities had to be made in the text. References are included to guide those interested to more detailed discussions. All citations within the document are linked to the detailed reference list for this volume. The overriding theme for this publication is that a picture is worth a thousand words.