Judith Totman Parrish1
(1) University of Arizona, Tucson, AZ
Abstract: Paleoclimate and coal
Climate interpretations of coal are implicit in the literature, but the terms "wet" and "dry" usually apply to the position of the water table rather than climate. Whether peat—the precursor to coal—forms depends on (1) exclusion of clastic sediments, (2) interplay of changes in groundwater level and accumulation of organic matter, which directly affects (3) the balance between plant productivity or organic input and decay, and (4) supply of nutrients. Climate plays an important role in both groundwater level and production and decay of organic matter. However, groundwater level is also influenced by sea level and tectonics, as are the rate and volume of clastic influx.
A number of models have been put forth linking peat formation with sea-level change, particularly sea-level rise, or tectonics. Peat accumulation requires a delicate balance between peat accumulation rates and the rates of formation of accommodation space. Within a mire, a comparably delicate balance exists between production and decay of organic matter. In relatively well-drained areas or dry climates, peat can form only where mean annual temperatures are low and decay is therefore inhibited. In contrast, peat can form in wet climates at any mean annual temperature.
With the exception of coal derived from raised mires, it is difficult to separate climate from sea level and tectonics in determining the origin of any particular sequence of coal beds. Some aspects of coal-bed chemistry may be helpful. Placing coal beds in their overall stratigraphic and paleogeographic contexts also can narrow the possible interpretations.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana