Cladichnus D'Alessandro & Bromley 1987

Ichnogenus Cladichnus D’Alessandro & Bromley, 1987 The Cladichnus burrow (Cretaceous-Eocene) consists of primary successively branched and radiating tubes, which contain a meniscate fill. These traces are preferentially constructed in anoxic sediments. New branches are produced roughly at the same level as previous ones, implying that appropriate conditions for stowing were encountered by the producer. In contrast, new branches constructed below or above may target stronger or weaker reducing conditions or represent a response to the downward or upward migration of the redox boundary. Collection and transfer of surface material is recorded by the tubes’ fill that was analyzed in detail for the ichnospecies Cladichnus parallelum Wetzel & Uchman, 2013, which contains 0.8% Corg and 0.3% CaCO 3 compared to 0.3% Corg and 64% CaCO 3 in the host sediment Cretaceous in age (Wetzel & Uchman 2013). The fill of the branches is interpreted to indicate priming that provided microbes (or their metabolic products) as an additional subsurface food source (cf. Mayer et al. 2001; van Nugteren et al. 2009). Most likely, the trace producer ingested a considerable proportion of the filling material before emplacing the final, now meniscate fill. The arrangement of the branches has further implications. Branches at a level above the previous ones could allow utilization of upstreaming pore water, probably carrying nutritious compounds. Alternatively, a shift of the redox boundary may have caused the construction of new levels of open burrows.