T81 Deep-Time Carbon Cycles, Redox Changes, and the Evolution of the Biosphere I

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

SEDIMENTARY MAGNESITE FORMATION THROUGH TEMPERATURE AND PH FLUCTUATIONS

Paper number: T81-11
Program: Technical Sessions
Time: 3:50 PM – 4:05 PM

Authors

Abstract

Incorporating magnesium into the carbonate structure is difficult at low temperatures. However, Veitsch-type anhydrous magnesites (MgCO3) are found in evaporative environments without the typical hydrothermal conditions associated with magnesite formation. To address the disconnect, this study refined a temperature and pH cycling method to achieve up to 91 mol% MgCO3 of (Mg,Ca)CO3 carbonates without exceeding 40 °C. Individual parameters were tested to develop a novel simultaneous growth and replacement mechanism for magnesite formation. The experimental conditions ideal for magnesite growth match very well with an evaporative/lagoonal/playa geologic setting: small thermal mass for daily temperature swings, algal mass for pH control, and a solution highly concentrated in Mg2+ with high Mg:Ca ratios. Additionally, this study suggests the inclusion of dissolved silica in the system may play an important, but previously unacknowledged, catalytic role in the development of magnesium bearing carbonates. Finally, a high mol% MgCO3 carbonate precursor, such as the one produced in this study, is needed for the diagenetic alteration towards pure magnesite.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-355106

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