The impact of deep-tier burrow systems in sediment mixing and ecosystem engineering in early Cambrian carbonate settings

Abstract

Bioturbation plays a substantial role in sediment oxygen concentration, chemical cycling, regeneration of nutrients, microbial activity, and the rate of organic matter decomposition in modern oceans. In addition, bioturbators are ecosystem engineers which promote the presence of some organisms, while precluding others. However, the impact of bioturbation in deep time remains controversial and limited sediment mixing has been indicated for early Paleozoic seas. Our understanding of the actual impact of bioturbation early in the Phanerozoic has been hampered by the lack of detailed analysis of the functional significance of specific burrow architectures. Integration of ichnologic and sedimentologic evidence from North China shows that deep-tier Thalassinoides mazes occur in lower Cambrian nearshore carbonate sediments, leading to intense disruption of the primary fabric. Comparison with modern studies suggest that some of the effects of this style of Cambrian bioturbation may have included promotion of nitrogen and ammonium fluxes across the sediment-water interface, average deepening of the redox discontinuity surface, expansion of aerobic bacteria, and increase in the rate of organic matter decomposition and the regeneration of nutrients. Our study suggests that early Cambrian sediment mixing in carbonate settings may have been more significant than assumed in previous models.

Ichnology of the Winnipeg Formation, southeast Saskatchewan: a glimpse into the marine infaunal ecology of the Great Ordovician Biodiversification Event

“…; Zhang et al . ). Thalassinoides is a facies‐crossing ichnotaxon, commonly found in oxygenated marine environments and soft and firm sediments (Ekdale et al .…”

“…Thalassinoides is interpreted as a feeding structure. Post-Palaeozoic examples are produced by decapod crustaceans, but other tracemakers have been suggested for Palaeozoic examples (Myrow 1995;Carmona et al 2004;Zhang et al 2017b). Thalassinoides is a facies-crossing ichnotaxon, commonly found in oxygenated marine environments and soft and firm sediments (Ekdale et al 1984;Schlirf 2000;Rodr ıguez-Tovar et al 2008).…”

“…The timing of appearance of the mixed layer in the geological record is still debatable (e.g. Zhang et al 2017b). Although originally regarded as first occurring in the Ordovician (e.g.…”

Quantifying carbonate sediment mixing across a formational boundary, an example from the Late Pleistocene Miami Limestone

“…A main focus of most downward mixing, however, has been through processes related to biological activities, mainly bioturbation while sediment is still unconsolidated (Bianco, ; Droser, Jensen, & Gehling, ; Frey, ; Kennedy, ; Seilacher, ; Teal, Bulling, Parker, & Solan, ; Zhang et al, ). Bioturbation structures can be held open by mud‐packed burrow linings or partial cementation, and sediment then infills open burrows (Tedesco & Wanless, ; Wanless, Tedesco, & Tyrrell, ; Warme, ).…”

“…In some sedimentary strata, downward movement of sediment from an overlying bed is relatively easy to distinguish by the presence of distinct sediment types (Bromley, ; Frey, ; Zhang et al, ). In some cases, however, especially limestone where sediment colour or composition is similar, mixing of different sediments can be much more difficult to recognize.…”