Preservation models of ophiuroids in epicontinental basins: Examples from a new Devonian echinoderm Lagerstätte from Brazil

How does rapid burial work? New insights from experiments with echinoderms

“…These processes may be frequent on many continental slopes, but are incompatible with the shallow, low-gradient environment of most epicontinental seas. In turn, although storm disturbance is common in shallower seas, fossil preservation under these conditions is hampered by constant proximal reworking and the low rate and thickness of distal beds (Jelby et al 2020;Fraga & Vega 2022). Even an exceptional burial by tempestites on the middle shelf must be treated with caution because, in the absence of numbing agents, the chance of successful escape remains high among free-living organisms.…”

“…Thus, the rapid burial of the seafloor by an extrabasinal turbidite may help to quickly immobilize entire communities of echinoderms, delaying the development of escape attempts due to the limited osmoregulation of these invertebrates. Unlike intrabasinal turbidites, the numbing by fresh water is the major limiting factor in burial by hyperpycnal flows and may favour the preservation of live specimens even in thinner beds (Fraga & Vega 2022).…”

“…An important case occurs in epicontinental basins, where tempestites are considered the main burial agent of articulated invertebrates (Lewis 1980;Brett & Baird 1986;Speyer & Brett 1988;Brett et al 1997;Ausich 2021), even in the absence of direct sedimentological evidence of storm influence. However, although storm waves also can produce potential burial events, they carry a paradox: post-depositional reworking is high in proximal sandy tempestites, while the frequency and thickness of beds are limited in distal muddy tempestites, narrowing the fossilization potential in both depositional scenarios (Fraga & Vega 2022).…”

“…These events can generate long-duration hyperpycnal flows capable of transferring large loads of freshwater-rich sediments to distal regions beyond the storm wave base, sometimes hundreds of kilometres from the river mouth (Mulder et al 2003;Mulder & Chapron 2011;Zavala et al 2011;Zavala & Arcuri 2016;Zavala 2020). Considering that fresh water is an anaesthetic for echinoderms (Saldanha 1972;Hendler et al 1995), these hyperpycnal flows may have the potential for mass immobilization of live specimens, favouring preservation under thinner burial beds (Fraga & Vega 2022).…”

“…Considering that fresh water is an anaesthetic for echinoderms (Saldanha 1972; Hendler et al . 1995), these hyperpycnal flows may have the potential for mass immobilization of live specimens, favouring preservation under thinner burial beds (Fraga & Vega 2022).…”