Original paper

A coastal forest swamp dominated by Omphalophloios C. D. White, in the Autunian (uppermost Stephanian) of Puertollano, south-central Spain

Wagner, Robert H.; Álvarez-Vázquez, Carmen


The geological history of the Puertollano coal and oil shale field shows two successive intervals with significantly different palaeogeographic connotations. Borehole and mine evidence shows the first interval to be characterised by a deeply incised palaeovalley and local, explosive volcanism (volcanic plug and tuffs). Later, an alluvial plain became established over a large area, with a mild palaeotopography. Volcanic ash bands in the lower part of a 500 m thick succession of coal-bearing strata with intercalated oil shale horizons show lingering volcanism of more remote origin. Coal seam III provides the main focus of the present paper. It contains two intercalated volcanic ash bands, the lower one of which shows evidence of in situ Omphalophloios tree bases and subaerial parts representing a swamp environment that may have been (slightly) brackish, and that follows upon a freshwater swamp with Sigillaria. The Omphalophloios swamp is found interspersed with areas colonised by pecopterid tree ferns and their undergrowth of small ferns (e.g. Senftenbergia). These presumably corresponded to slightly more elevated parts of the swamp area. The general swamp area also contained patches of open water and was probably crossed by water courses bordered by Calamites (with Asterophyllites foliage). The coastal swamp with Omphalophloios and Pecopteris (tree fern) stands (with only limited intermingling on intermediate ground) suffered the effect of high winds preceding the volcanic eruption with ash fall. Fully mature, partly disarticulated fertile apices of Omphalophloios were torn off, as were entire fronds from the tree ferns. These large plant fragments were laid down on top of the first ashes of the eruption, which buoyed up the partly degraded forest litter (mainly woody parts) deposited in what appears to be a small depth of water. The dispersal strategy of Omphalophloios is discussed, as is the possibility that the fertile apex of this small tree was regenerated at successive stages of growth. A reconstruction is presented of this monopodial tree with occasional bifurcation of the heterosporous fertile apex. Several specimens are figured of a very large collection from a single locality.