Palaeoecology and plant succession in a borehole through the Rhynie cherts, Lower Old Red Sandstone, Scotland

A cored borehole through the Early Devonian Rhynie cherts at Rhynie, Aberdeenshire, NE Scotland, has revealed 53 chert beds in 35.41 m of core. The cherts originated as sinters deposited by hot-spring activity. Chert comprises 4.20 m of the cored succession, with the thickest bed, representing a single silicification event, being 0.31 m thick and the thickest composite chert (comprising six beds) 0.76 m thick. Average chert bed thickness is 80 mm. Forty-five plant-bearing chert beds are interbedded with sandstones, mudstones and shales. The sediments were deposited on an alluvial plain with local lakes, the area being periodically affected by hot-spring activity. Plants initially colonized both subaerial sand and sinter surfaces. Rhynia gwynne-vaughanii and Horneophyton lignieri commonly form the basal parts of the profiles with subsequent colonization by other genera. Rhynia is commonly found in life position above originally sandy substrates, and Horneophyton above sinter surfaces. The composition of the Rhynie vegetation is compared with coeval assemblages and, on the basis of current knowledge, it is concluded that there is no unequivocal evidence that the plants were adapted to life in the stressed environments in the immediate vicinity of hot springs.