COAL-BALL ARCHIVE OF PENNSYLVANIAN-AGE TROPICAL PEAT-FORMATION PROCESSES

Widespread peat formation in a tropical environment requires high soil moisture levels, attainable almost exclusively through nearly year round rainfall in excess of evapotranspiration – humid to perhumid climate. This results in acidic, oligotrophic conditions that inhibit microorganismal activity (organic-matter degradation), and reduce fire frequency. Based on modern peat analogues, there are three active layers to any peat-accumulating environment: top litter layer, underlain by acrotelm (active water table fluctuation), and bottom catotelm (stable water-table). Only 10-20% of standing net primary productivity may reach the catotelm, indicative of enormous amounts of organic matter degradation. Pennsylvanian age coal balls (peat stages of coal preserved by early diagenetic permineralization) are snapshots of the peat forming process, demonstrating multiple biological, chemical, and physical processes operative contemporaneously in the litter-to-catotelm transformation. These processes include organic matter degradation and associated collapse of plant organs and tissues, rooting, and leaching. Peat permineralization at different stages reveals a continuum of fibric, hemic, and possibly sapric fabrics. Decay is ubiquitous and has a taxonomically detectable, differential effect on litter. For example, lycopsid periderm, often mistaken for wood, was the most decay-resistant tissue, nearly immune to root penetration, surviving when virtually all else was degraded. Evidence of rooting is quite common in the coal balls: lycopsid stigmarian systems are the most prominent roots in Lower and Middle Pennsylvanian peats, and tree-fern roots are the most common in the Late Pennsylvanian. Both could penetrate to and possibly into the catotelm, due to internal air chambers within the roots. Some peats were weakly rooted to unrooted, suggesting permineralization in early stages of degradation and of the peat formation process. Collapse and compression of plant material was highly differential, a function of organ and tissue type, and degree of decay, but is evident at all stages. Understanding these peat forming processes, timing and inter-relation, is essential for utilizing coal balls to reconstruct original environments of deposition and the standing peat-swamp ecosystem.