T144 Toward Unravelling the Dolomite Problem: New Approaches and Novel Perspectives

Tuesday, 11 October 2022
8:00 AM - 12:00 PM
503

EVOLUTION OF EARTH’S SURFICIAL MG CYCLES IN THE PAST 2 BILLION YEARS: A TALE FROM DOLOSTONES

Paper number: T144-10
Program: Technical Sessions
Time: 10:10 AM – 10:30 AM

Authors

Abstract

The surficial cycling of Mg is directly coupled with the global cycle of carbon, a predominant control of Earth’s climate. How global surficial Mg cycle has changed through geological history, however, has been elusive. Magnesium isotope signatures of seawater (δ26Mgsw) track the balance between silicates and carbonates as sources and sinks of Mg in the oceans. Here, we reconstructed the δ26Mgsw record for the ancient oceans using marine halite fluid inclusions and sedimentary dolostones. The two independent archives yielded consistent evolutionary trends of δ26Mgsw for the past 450 million years, and the dolostone records extend the δ26Mgsw curve to 2 billion years ago. The data show that δ26Mgsw decreased, with fluctuations, by over 1‰ from the late Paleoproterozoic to the present time, and the periods of low δ26Mgsw coincided with ice ages in the Phanerozoic. Mass balance calculations based on this record reveal that the proportion of Mg sequestered as dolomite in the total Mg outflux from the oceans was significantly greater than the proportion of Mg sourced from carbonate in the total Mg delivered to the oceans in the Proterozoic, but since then, the gap between the two decreased to a modern value of around zero. This points to a secular decay in the net CO2 sequestration efficiency by surficial Mg cycles in the past 2 billion years, which was caused by long-term changes in dolostone weathering and precipitation intensities. Our work underlines the indispensable role of dolostones in regulating Earth’s climate on geologic time scales.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-381681

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.