ABSTRACT

The Missourian Dalton "coal" crops out in northern Texas near Mineral Wells and is a bed within the Wolf Mountain Shale member of the Grafford Formation, Canyon Series. Technically a carbonaceous shale because of its high (70%) ash concentration, the origin of this coal is controversial. The high clastic content and lack of a rooted underburden suggest that the Dalton formed by accumulation of plant debris at the head of a small bay or lagoon. However, coal balls at the top of the seam contain large pieces of wood and roots. These deposits, consisting of the Marrattialean fern Psaronius, the seed fern Medullosa, and the gymnosperm Cordaites, may represent a rooted peat.

As shown below, the most important palnomorphs in the Dalton are Laevigatosporites sp., Cyclogranisporites orbicularis, Punctatatosporites sp., and Endosporites globiformis. The gymnosperms and seed ferns, although fairly abundant in the coal balls, are underrepresented in the palynomorph counts. Variation among coal samples and coal and shale samples is slight, although a reciprocal arrangement between Laevigatosporites sp. and C. orbicularis is noticeable. This lake of sequential variability is uncommon in modern peats and other Late Pennsylvanian coals into which much of the palynomorph input has been local and may represent plant successional stages. The Dalton "diagram" is more similar to those of lagoonal sequences, and consequently we believe that most of the Dalton coal is a detrital deposit.

Figure DALTON COAL Upper Pennsylvanian

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