Putative arthropod trace fossils from the Orcadian Basin at Achanarras Quarry (Middle Devonian of Scotland)

Abstract

Achanarras Quarry, Caithness, Scotland displays a diverse fossil fish fauna that is presumed to have inhabited shallow-lacustrine environments present in the Orcadian Basin during the Early to Middle Devonian. Although Achanarras Quarry itself exposes deep-lacustrine facies, the ecology of their depositional environment remains unknown, in stark contrast to the detailed environmental reconstructions available for the lake margin. I report putative arthropod trace fossils from Achanarras Quarry that are tentatively interpreted as having been formed in a deep-lake environment. Transport of doomed pioneers from the thriving shallow-water ecosystems by turbidite flows is discussed as a possible scenario for their formation. The infrequent and ephemeral intrusions of animals into the deep waters of Lake Orcadie fit the broader narrative of the colonization of deep-lake ecosystems after the Devonian. These interpretations of deep-lacustrine trace fossils from Achanarras, along with their place within the narrative of lake ecosystem evolution, are made cautiously, however, given the paucity of the specimens and the uncertainty surrounding their sedimentary setting.