Zoophycos Massalongo, 1855

Uchman, Alfred & Wetzel, Andreas, 2024, Sequestrichnia - an ethological category of marine trace fossils recording the collection and stowage of nutritional material within burrows, Comptes Rendus Palevol 23 (22), pp. 325-338 : 328

Ichnogenus Zoophycos Massalongo, 1855

( Fig. 1 )

Zoophycos represents a regularly to irregularly coiled, simple to complex lobate spreite burrow that has shown changes in shape, size, and geometry through the Phanerozoic (e.g. Seilacher 1977b; later refined by Chamberlain 2000 and Zhang et al. 2015). For most Zoophycos older than the late Mesozoic, different ways of spreite production and behaviour are possible, including fodinichnial behaviour (e.g. Olivero & Gaillard 1996). In contrast, for Late Cretaceous to modern Zoophycos , sequestrichnial behaviour of the producers appears to be common. These are outlined here.

Evidence for sequestration of sediment on the seafloor is given by the colour of the spreite fill in combination with enlarged organic carbon values. The spreite consists of alternating lamellae containing host sediment and material likely sequestered on the seafloor and transferred downward; pellets may occur in both types of lamellae ( Fig. 1 ). The sequestered sediment is commonly darker in greenish-grey host sediment or grey in reddish host sediment. In both cases, the organic carbon content of the spreite fill is higher than that of the host sediment; for example, the black spreite material of Paleocene Zoophycos (Gurnigel Flysch; Seligraben/Gurnigelbad, Switzerland) contains 1.1-1.7% Corg compared to 0.5-0.7% Corg in the green host sediment (see Wetzel & Uchman 1998: fig. 1d, e). In the Eocene of Arnakatxa Headland near Bilbao, 0.3-0.7% Corg occurs in grey spreite material and <0.1% Corg in red limestone lutite alternations. However, in deep oceanic settings, also lighter material deposited during periods of enhanced nannoplankton productivity can be transferred downward ( Fig. 1A ). Other tracers, e.g. volcanic ash, also record a downward sediment transfer (e.g. Kotake 1991). For Pleistocene and Holocene Zoophycos , chronometric age data record a sequestration of surface material as the spreite fill is generally younger than the host sediment (e.g. Löwemark & Werner 2001; Leuschner et al. 2002; Küssner et al. 2018). In well-dated sediments, Zoophycos appears to be produced when environmental conditions switch to a starved sedimentation regime ( Küssner et al. 2018) or during times of enhanced seasonality (e.g. Löwemark et al. 2006; Wetzel et al. 2011; Dorador et al. 2016).

The Zoophycos producer stows the sequestered material commonly in the form of mud lamellae or pellets in the spreite. Pellets, however, occur in both host and sequestered sediment, suggesting that they could have provided “seed” microbes housed in the gut to the spreite “bioreactor” ( Fig. 1C ). Therefore, a priming scenario appears realistic, in particular as subsequent lamellae overlap previous ones, indicating partial reworking and utilization of the spreite fill by the tracemaker ( Fig. 1D ). Since Zoophycos represents very likely a lifetime burrow of its producer (e.g. Wetzel & Werner 1980), the worm-like tracemaker probably took advantage of priming on a time scale of months to years.

Figures

FIG. 1. — Sequestered and downward-transferred material in Zoophycos Massalongo,1855: A, black mud and white nannofossil ooze displaced for> 26 (black arrows) and> 23 cm (white arrows) downward, respectively, as indicated by colour and composition of sediment (Institute of Geological Sciences Kiel, Germany, core 16867-3; 2.2°S, 5.1°E, 3894 m water depth, mid Atlantic; 16.56-16.99 m core depth); B, sequestered organic-rich grey sediment filling Zoophycos spreite (white arrows) produced in red pelagic mud (Maastrichtian, Zumaia, Spain); C, homogeneous and pelleted sequestered sediment alternating with host sediment in Zoophycos spreite; inset (C’) showing pellets occurring in both sequestered sediment (green arrows) and host sediment (yellow arrows) (DSDP Leg 93, Site 605, Core 16-4, 59.5-66.5 cm core depth; for details see Wetzel 1987); D, truncation of lamellae (marked with red stippled lines) in Zoophycos spreite in horizontal section, indicating reworking of previously emplaced material (Paleogene, Zumaia, Spain). Scale bars: 1 cm.