Reassessment of sediments and trace fossils from old red sandstone (Lower Devonian) of Dunure, Scotland, described by John Smith (1909)

Abstract

In 1909 John Smith, a Scottish naturalist and geologist, described 23 «genera and 51 «species of trace fossils from small patches of sediment associated with andesite lava flows at Dunure, Ayrshire. He interpreted the traces as evidece of a diverse invertebrate fauna which inhabited small pools and fissures in the lava surface between eruptions. Smith's collection (c 300 specimens) was presented to the British Geological Survey, Edinburg but has remained largely unstudied. Re-examination of the Smith collection shows that it came from 3 separate localities which differ in composition of the ichnofaunas, associated sediments and sedimentary structures. Arthropod trackways dominate the ichnofauna occurring in laminated siltstone frequently with ripple marks and foam marks suggesting formation in shallow lacustrine conditions. Preservational and behavioral analysis of trace fossils reveals about 10 valid ichnogenera of locomotion and swimming trackways, resting traces, feeding trails but few burrows. Presence of early terrestrial arthropods traces is uncertain. Palaeoecological interpretation is of ephemeral lakes in distal braid-plain situation subject to subsurface invasion of andesite lava producing fluidization and deformation of wet sediment. The Dunure ichnocoenosis shows unique diversity of Devonian arthropod trace fossils.