A catastrophically buried stand of calamitean sphenopsids and sigillarian lycopsids is reported from the Middle Pennsylvanian of southwestern Indiana, in the Illinois Basin. The plants were exposed in the highwall of a small surface mine and were rooted in a thin bed of coal (peat), thus representing a flooded and buried swamp surface. Coarse, floodborne silts and sands buried the forest to a depth of <3 m or more, before further incursions of water and sediment truncated the deposit. The rocks are part of the Staunton Formation. Taking up >250 linear meters of exposed highwall surface, the vegetation appears to have been a patchwork of calamitean thickets, with stems perhaps as tall as 3-5 m, within which scattered, but much larger, emergent Sigillaria trees grew, possibly reaching heights of 10-15 m. No ground cover was observed, nor were foliage or reproductive organs attributable to the dominant plants found. The growth of this vegetation in a peat-forming swamp indicates conditions of high water availability, likely in a humid, high-rainfall climate. This kind of plant assemblage, however, cannot be characterized as a rain forest, given that it consisted of medium-height thickets of horsetails with scattered, emergent, and polelike, giant lycopsids, thus lacking a closed upper canopy and possibly only partially shading the ground. Copyright ?? 2009, SEPM (Society for Sedimentary Geology).
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Catastrophically buried middle Pennsylvanian sigillaria and calamitean sphenopsids from Indiana, USA: What kind of vegetation was this?