Bioturbation of Thalassinoides from the Lower Cambrian Zhushadong Formation of Dengfeng area, Henan Province, North China

Abstract

Bioturbation plays a critical role in sediment mixing and biogeochemical cycling between sediment and seawater. An abundance of bioturbation structures, dominated by Thalassinoides, occurs in carbonate rocks of the Cambrian Series 2 Zhushadong Formation in the Dengfeng area of western Henan Province, North China. Determination of elemental geochemistry can help to establish the influence of burrowing activities on sediment biogeochemical cycling, especially on changes in oxygen concentration and nutrient regeneration. Results show that there is a dramatic difference in the bioturbation intensity between the bioturbated limestone and laminated dolostone of the Zhushadong Formation in terms of productivity proxies (Baex, Cu, Ni, Sr/Ca) and redox proxies (V/Cr, V/Sc, Ni/Co). These changes may be related to the presence of Thalassinoides bioturbators, which alter the particle size and permeability of sediments, while also increase the oxygen concentration and capacity for nutrient regeneration. Comparison with modern studies shows that the sediment mixing and reworking induced by Thalassinoides bioturbators significantly changed the primary physical and chemical characteristics of the Cambrian sediment, triggering the substrate revolution and promoting biogeochemical cycling between sediment and seawater.

A new approach for investigating spatial relationships of ichnofossils: a case study of Ediacaran–Cambrian animal traces

“…Shibantan ichnofossils document extensive trails, resting or dwelling traces, undermat mining for oxygen and/or food (Xiao et al 2019), and putative trackways of bilaterian animals with paired appendages (Xiao et al 2021). Beddingplane bioturbation intensity reaches 20%-40% (Meyer et al 2014), comparable to some pretrilobite Cambrian carbonates (Dornbos et al 2004), although lower than the maximum observed for post-trilobite Cambrian carbonates (Fan et al 2021). These ichnofossils are interpreted as recording the activity of organisms burrowing in and out of microbial mats, likely mining for oxygen and/or food (Xiao et al 2019), which we refer to broadly as "resources," and may have been spatially heterogeneous (Darroch et al 2021) and temporally dynamic in Ediacaran oceans (Wood et al 2015).…”