Oriented clusters of the deep-sea trace fossil Tubulichnium rectum in the Eocene flysch of the Pindos foreland basin, western Greece

The trace fossil Tubulichnium rectum, probably produced by a soft-bodied wormlike animal, normally consists of a single tube lined with organic-rich pellets, which were stored as a food resource during periods of scarcity (ethological category: sequestrichnia). On a large sandstone bedding surface in the Eocene flysch of western Greece, this trace fossil occurs in fan-shaped clusters oriented almost perpendicular to the direction of sand transport within the host bed. This unusual configuration, documented here for the first time, is attributed to specific palaeoenvironmental conditions in this part of the deep-sea fan depositional system, where the periodic supply of organic matter and the prevailing current direction remained stable over extended periods. The formation of these clusters reflects an adaptive response to changes in flow direction. The near-perpendicular alignment of the tubes to the current may have reduced ventilation, thereby delaying the oxygenation of the stored organic matter within the pellets.