T11 Oxygen and Ecosystems from the Proterozoic to the Paleozoic

Sunday, 22 October 2017
8:00 AM - 12:00 PM
Room 607

THE EMERGENCE OF SHALLOW BIOTURBATION DURING THE EDIACARAN: INFLUENCE ON P BURIAL MECHANISMS

Paper number: T11-9
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

Over geological timescales, phosphorus (P) is generally considered the ultimate limiting nutrient for O2 production via organic carbon burial. Our current understanding of P burial mechanisms throughout the Proterozoic largely relies on modelling approaches. These hypothesize that the emergence of shallow bioturbation in the Ediacaran Period (630 – 542 Ma) exerted a strong influence on organic P fixation in sediments. To empirically address this proposal, an adapted version of the P speciation “SEDEX” method for ancient sediments has been applied to the Kel’tminskaya-1 drillcore from the southern Timan region of Northern Russia. This succession spans the Cryogenian-Ediacaran Periods (715 – 542 Ma) and previous studies1 of iron speciation from this site document the evolution of deep ocean redox from ferruginous to oxic, as well as the transition of life from protistan assemblages to bilaterian animals.

The geochemical results presented here both agree with previous modelling evidence as well as provide a deeper insight into P burial mechanisms during this time. Following the advent of shallow bioturbation and the onset of oxic conditions, P buried in Fe-bound and magnetite phases become significant, but minor sinks. With the increasing stability of an oxic water column as evidenced by iron speciation, P is primarily retained in authigenic phases. This corroborates with prior redox interpretations, as a larger proportion of organic-P is trapped in sediments underlying oxic bottom waters, where it can subsequently form authigenic-P.

This is the first geochemical record to support the idea that the emergence of shallow bioturbation had a profound impact on P burial mechanisms by authigenic P becoming the main P sink. This study also highlights the sensitivity of feedbacks operating between the evolution of life and ocean redox during the Ediacaran.

1Johnston et al. (2012) Late Ediacaran redox stability and metazoan evolution. Earth and Planetary Science Letters. 335–336,pp.25–35.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-296790

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