Stalked crinoids: From skeleton to sediment

ABSTRACT Stalked crinoids were dominant producers of carbonate skeletal sediment during the Paleozoic. Prolific growth and post-mortem disarticulation of their endoskeletons formed widespread sedimentary rocks composed almost entirely of crinoidal debris. These “encrinites” hold key insights into the evolution of life on Earth and serve as important paleoclimate and paleoecological indicators. Despite the significance of stalked crinoids as sediment producers, the nature and hydrodynamic properties of their transported skeletal products remain enigmatic. Yet, such insights are essential to reconstructing sediment dispersal patterns, especially where encrinites form hydrocarbon reservoirs. This work identifies five various crinoid skeletal elements generated through simulated biological disarticulation of a modern stalked crinoid using bleach-bath experiments. A single animal produced more than 135,000 particles with grain sizes from fine sand to fine pebbles and shapes ranging from discoids to rods. These findings were upscaled to a local crinoid depositional environment under the assumption of log-normal distribution of crinoid body size in the carbonate factory, which produced a log-normal grain-size distribution of the skeletal elements. These results provide insights for more accurate sediment-transport modeling and sedimentological interpretations of the globally significant encrinite depositional record.