Sources of data

Data on mire vegetation come from two principal sources, coal-ball macrofossils and pollen-spore microfossils. Coal balls are carbonate concretions that contain structurally pre

Fig. 1. Coal-balls in situ; Herrin No. 6 Coal Member, Carbondale Formation, late Westphalian D age; Old Ben Coal Company, No. 24 Mine, near Benton, Illinois. Coal balls are light-coloured material within the darker coal. Coal ball layers are extracted and analysed quantitatively, providing a partial record of vegetational change on the site through the time of peat accumulation.

Fig. 1. Coal-balls in situ; Herrin No. 6 Coal Member, Carbondale Formation, late Westphalian D age; Old Ben Coal Company, No. 24 Mine, near Benton, Illinois. Coal balls are light-coloured material within the darker coal. Coal ball layers are extracted and analysed quantitatively, providing a partial record of vegetational change on the site through the time of peat accumulation.

served peat stages of the coal and that occur within coal seams (Phillips et al. 1976; DeMaris et al. 1983; Scott & Rex 1985). Coal balls preserve part of the original litter of the mire forest, often in exceptional anatomical detail. They occur in layers or aggregates (Fig. 1) and can replace much of the thickness of a coal seam, providing the basis for quantitative analysis of vegetational change during the history of peat accumulation (Phillips et al. 1977). Coals usually contain abundant pollen and spore microfossils, produced by plants of the mire vegetation. Incremental sampling of a coal seam can reveal fine-scale details of the history of peat accumulation, particularly when the more abundant microfossils can be linked to parent plants (e.g. Mahaffy 1985; Willard 1993).

Most of our analysis and inference is based on coal-ball data of two types, profile and random sample. Profiles of coal balls are collected in situ; relative position of coal-ball layers within the coal bed is noted, which permits recovery of the original zonation of the plant litter (Fig. 1). Random samples of coal balls are collected from one locality without respect to the position of coal balls in the coal bed. Consequently, they represent the average composition of the per-mineralized peat at the collection site. A coal-bed summary can be obtained from a profile by averaging the composition of individual coal-ball zones. Palynological and compression fossil data are presented and discussed where appropriate, and in order to amplify coal-ball patterns. There are critical gaps in the coal-ball record, particularly in the early Stephanian, immediately following the extinctions at the end of the Westphalian, and palynological data are of particular importance in this interval. The coal-ball data base used in this analysis is described in Phillips et al. (1985), with some additions of coals from the Westphalian A and B of the United States (Winston & Phillips 1991; unpublished). Palynological data are mostly from Peppers (1985). Compression-impression species ranges are from Gillespie & Pfefferkorn (1979).

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