Taphonomy of fossil plants from the Viséan of East Kirkton, West Lothian, Scotland

Abstract

Plant fossils are a common and important element in the East Kirkton biota of Brigantian (late Visean age). The most important taxa are preserved as compressions or anatomically preserved as permineralisations. The basis of the quantitative study of the flora and the distribution of individual plant species was the trenched section excavated for the East Kirkton Project. The largest diversity of compressions have been recorded from loose blocks. In the trenched section, the uppermost ashes contain only lycopsid compressions including Stigmaria. Nodules in the underlying shales yield mainly lycopsid leaf and sporophyll compressions. The uppermost limestones (Units 39-52) contain drifted fragments of pteridosperm fronds mainly Sphenopteridium crassum, S. pachyrrhachis, Spathulopteris obovata and Adiantites antiquus. Permineralised Lyginorachis spp. occur at this level. Large permineralised woody gymnosperm axes have been found loose (including Pitus, 50 cm in diameter). Permineralised axes, mainly reworked, including the gymnosperms Bilignea, Eristophyton, Stanwoodia and possibly Protopitys, have been found in Units 72-88. Poorly preserved permineralised lycopsids are rare, but include Lepidophloios. Loose chert blocks contain root mats of permineralised Stigmaria, together with Lepidocarpon, the sphenopsid Archaeocalamites and the fern Botryopteris. Similar material is found in Unit 83 of the Limestone sequence. Unit 82, the black shale containing many of the articulated vertebrates, contains predominantly pteridosperm frond and pinnule material including Spathulopteris obovata. The distinctive changes in the flora from the base to the top of the trenched sequence reflect mainly ecological and taphonomic controls upon plant distribution and preservation. Evidence suggests a close relationship between climate, fire, erosion, deposition and vegetation type through the sequence and a climatic change, from a drier to a wetter environment, is suggested at the top of the East Kirkton Limestone sequence.