Biogenic chert and the Ordovician silica cycle

Assessing the Potential of Sponges (Porifera) as Indicators of Ocean Dissolved Si Concentrations

“…Both transitions are ascribed to biological innovations-the first to the evolution of silicification by radiolarians and sponges, and the second to the expansion of diatoms-and therefore biology's progressive ability to remove dSi from seawater. Superimposed on this long-term decline in ocean dSi, transient excursions in the ocean dSi inventory have been proposed in response to periods of extensive volcanism (particularly the emplacement of large igneous provinces, LIPs) (Ritterbush et al, 2014Kidder and Tomescu, 2016), or orogenesis (e.g., Cermeño et al, 2015). One of the lines of evidence supporting these interpretations is a change in the sedimentary facies associated with sponges in the rock or sediment record (e.g., Kidder and Tomescu, 2016).…”

“…The evolution of the ocean Si cycle has received attention for many decades (e.g., Maliva et al, 1989;Kidder and Tomescu, 2016). The prevailing narrative (Maliva et al, 1989;Siever, 1991;Kidder and Tomescu, 2016) argues for two particularly important events.…”

“…The prevailing narrative (Maliva et al, 1989;Siever, 1991;Kidder and Tomescu, 2016) argues for two particularly important events. The first is a transition from a Precambrian ocean saturated with respect to dSi to a slightly undersaturated Mesozoic ocean.…”

“…Superimposed on this long-term decline in ocean dSi, transient excursions in the ocean dSi inventory have been proposed in response to periods of extensive volcanism (particularly the emplacement of large igneous provinces, LIPs) (Ritterbush et al, 2014Kidder and Tomescu, 2016), or orogenesis (e.g., Cermeño et al, 2015). One of the lines of evidence supporting these interpretations is a change in the sedimentary facies associated with sponges in the rock or sediment record (e.g., Kidder and Tomescu, 2016). The link between sponge abundances/distributions and dSi stems from the implicit assumption that siliceous sponges are unable to thrive at low dSi (e.g., Ritterbush et al, 2015;Kidder and Tomescu, 2016).…”

“…One of the lines of evidence supporting these interpretations is a change in the sedimentary facies associated with sponges in the rock or sediment record (e.g., Kidder and Tomescu, 2016). The link between sponge abundances/distributions and dSi stems from the implicit assumption that siliceous sponges are unable to thrive at low dSi (e.g., Ritterbush et al, 2015;Kidder and Tomescu, 2016). Kidder and Tomescu (2016), for example, interpret an Ordovician retreat in sponges from lagoonal depositional environments toward deeper, shelf settings, as reflecting radiolarian driven dSi depletion of the surface ocean.…”