Piperock ichnofabrics from western Henan, China: spatial distribution pattern and environmental controls on middle Cambrian carbonates

The middle Cambrian (Miaolingian Series, Wuliuan Stage) Mantou Formation Member III in the Dengfeng area, western Henan, China provides an opportunity to explore the relationship between suspension feeders and sedimentary substrates in the early Phanerozoic hydrodynamic high-energy environment. Its strata record abundant vertical burrows in the easily migrated carbonate sediments of calcarenitic shoals or oolitic beaches. Three types of piperock ichnofabrics are identified: Skolithos ichnofabric, Arenicolites ichnofabric and Skolithos-Arenicolites ichnofabric. Bedding plane expressions of these ichnofabrics show that there is a spatial distribution pattern dominated by segregated distribution between individual burrows; this pattern is shown to be genuine through nearest neighbor and spatial point process analyses. These characteristics not only indicate that burrows were constructed by contemporaneous suspension feeders, but also reflect the selection and adaptation of suspension feeders to strong hydrodynamics and mobile substrates. In addition, the interspecific competition caused by the heterogeneity of nutrients is one of the determinants of the spatial distribution pattern of vertical burrows. As ecosystem engineers, these suspension feeders significantly transform landforms, create pressure gradients and accelerate geochemical cycles, which may further promote biodiversity in benthic organisms.

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