Did phosphorus derived from the weathering of large igneous provinces fertilize the Neoproterozoic ocean?

Abstract

Primary productivity and organic carbon burial rates in the Precambrian were highly sensitive to fluxes of phosphorus (P) from the weathering of continental crust. Large igneous provinces (LIPs)-containing substantial P and highly susceptible to chemical weathering-occurred regularly during the breakup of the Rodinia supercontinent, and flood basalts probably covered 3.7-7.4 3 10 6 km 2 at a time when a lowlatitude continental configuration expedited weathering. Assuming chemical weathering liberated much of the P contained in the flood basalts, an estimated 1-4 3 10 17 mol of biologically available P entered the ocean from LIPs between 900 and 500 Ma. Especially, voluminous LIP magmatism began at 850 Ma and culminated with the Franklin Province at 720 Ma, after which an estimated bioavailable P flux from flood basalts of 1-5 3 10 9 mol/yr may have been sustained for millions of years, elevating primary production and organic carbon burial rates. P enrichment of LIP magmas prior to eruption could have contributed to efficient reactive P delivery to the ocean: liquid-crystal fractionation beneath thick cratonic lithosphere and the incorporation of metasomatic P potentially enriched Neoproterozoic LIP magmas more than anytime previously. Thus, a unique convergence of tectonic conditions-supercontinent breakup, voluminous mafic volcanism containing abundant P, and a low-latitude continental configuration-may have facilitated an unprecedented flux of bioavailable P to the ocean that was capable of triggering oxidation of the oceanatmosphere system and enabling accelerated biologic diversification.

Timing and tempo of the Great Oxidation Event

“…Examples include supercraton-or supercontinent-size continental landmasses that were capped by continental flood basalts, incipient rifting and/or breakup, and rapid transit to low latitudes. All of these factors enhanced chemical weathering of juvenile basaltic material and greatly increased the flux of biolimiting nutrients to depositional basins, thus leading to a biotic response of higher organic carbon burial (40,50) as well as deposition of giant iron and manganese deposits. It seems likely that these similar scenarios are not coincidental but that the critical factors (assembly of large landmasses, LIPs, incipient rifting, and relief enhancement-all resulting in a lithospheric mass anomaly and movement to low latitudes, high rates of organic carbon burial, surface oxygenation, and Snowball Earth glaciations) are mechanistically linked.…”

Trace elements at the intersection of marine biological and geochemical evolution

“…However, several studies have used Phanerozoic ironstones and hydrothermal exhalites to extend the record from the Precambrian to the modern (e.g., Konhauser et al, 2009;2015;Partin et al, 2013a;Robbins et al, 2013;Swanner et al, 2014). Such hydrothermal deposits provide an opportunity to test experimental and hypothesized partitioning scenarios for trace elements onto IF-but only to a limited extent.…”

“…Abiogenic cherts are predominantly formed in the Precambrian due to high marine silica concentrations in the absence of a biological sink (Siever, 1992;Maliva et al, 2005). Several mechanisms have been proposed for the primary formation of abiogenic Precambrian cherts, including direct precipitation of amorphous silica from seawater (Siever, 1992;Maliva et al, 2005) and more recently sedimentation of sand-sized silica granules (Stefurak et al, 2014;2015).…”

“…Furthermore, they identified a large influx of P into the oceans coincident with the end of global Neoproterozoic glaciations. More recently, it has been argued that the Neoproterozoic influx of P to the oceans may instead be directly attributed to the weathering of large igneous provinces (LIPs) (Horton, 2015). This idea is based on compiled P…”

“…5) was also observed in a compilation of Mo concentrations in synsedimentary to early diagenetic pyrite through time . In the pyrite record, Large et al (2014;2015) identify the Mo increase in the Neoproterozoic at ~660 Ma. This boundary has since been pushed back to ca.…”