EAG

Home

  • Program

    The Goldschmidt2020 program

  • Venue

    All about the venue and city

  • Registration

    Details of how to register to attend the conference and/or submit an abstract

  • Exhibition

    Information for and about exhibitors and sponsors

  • My Goldschmidt

    My program, purchases, connections, etc.

Home

Program

Events

  • Sponsor Seminars

  • Training Events

    These are scheduled events to help delegates test out the tools and platform we will be using for the Q&A and other events at the conference.

  • Workshops

    Our workshop program provides training and teaching in topics across geochemistry and related fields. We are currently liaising with the workshop organisers to ascertain if any workshops can become virtual. Any updates will be added to this page.

Locations

  • Conference Locations

    Location of the convention center and social events

  • Hotels

    The hotels are no longer available to book at the special rates agreed by the conference. Should you wish to cancel or change your hotel reservation please see the details below.

Information

Present your work

Attend

Exhibition

Sponsorships

My Goldschmidt

Role functions

Abstract Details

Transient Ocean Oxygenation at 850Ma Recorded in δ98Mo of Microbial Carbonates

O'Sullivan E, Nägler T, Wille M, Kamber B & Turner E

O'Sullivan E, Nägler T, Wille M, Kamber B & Turner E (2020) Goldschmidt Abstracts, 2020 1968

Sorry, the PDF cannot be displayed on your browser.

Download abstract

The author has not provided any additional details.

09f: Room 3, View in program

Edel O'Sullivan
Thomas Nägler
Martin Wille View all 3 abstracts at Goldschmidt2020
Balz Samuel Kamber View all 6 abstracts at Goldschmidt2020
Elizabeth Turner

Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.

Submitted by Kun Zhang on
Can you specify your method of extracting Mo isotope signals from carbonate rocks? Do you think it is possible that the differences of Mo isotope values between carbonate rocks and shales are derived from experiments? Thanks!
Thank you for your question! I did not have time to explain this in my talk. The method I used was bulk digestion. After petrographic examination of the microbialites, I did not see any signs of Fe or Mn oxides, and XRD analysis showed that it was pretty much pure calcite with minor dolomite and quartz, and some organic matter (1-2%TOC range max, graphite). So I used an overnight hot HCl digestion on powdered sample, to leach all of the Mo from any remaining insolubles (none was obvious apart from graphite), and I then did a separate analysis of the same powder for major elements, trace elements and TOC so that I could monitor the Mo content of bulk rock vs Al content etc. My idea was that I would model and correct for detrital contamination. Unfortunately my models didn't work at all! I then repeated many of the samples and found that there were huge differences in Mo content and isotope composition despite being thoroughly milled (by hand to avoid contamination). I conclude that there is a mixture of different contaminants that may not have been visible under a microscope. I then tried to use these repeated samples to model the end members of the individual samples, as the direction of alteration to the composition was always roughly in the same direction. I found that the some of the pure carbonate end member calculations converged on around 1.8 permil or higher at a lower Mo content, but the second end member had a very high range of compositions, so it was likely a mixture of several sources. This is pretty rough work, I haven't had the time to work on it any more. The important point was that the Mo isotopes are always shifted towards lighter isotopes. I am not aware of a mechanism that favours concentration of heavy isotopes in the solid phase. Therefore the isotopically heaviest sample is the closest to coeval seawater, but is likely s minimum estimate. As for the shales, I do not trust the data due to the trace element characteristics, even though they agree well with previous estimates of proterozoic ocean water. As there has been evidence of an offset between euxinic black shale and overlying seawater in the black sea and in various other cases, I don't doubt the offset that I see between the black shales and the microbialites. My next step is to try a reductive dissolution of the microbialites to isolate the pure carbonate signature, and to analyse more black shales for Mo isotope compositions as well as Fe speciation, to better understand the environment. If you have any other questions, or if you have any suggestions, I welcome further email correspondence!

Sign in to ask a question.

Geochemical Society, an organization registered in USA. Address: 5241 Broad Branch Road, NW Washington, DC 20015-1305.
Tel: +44 1223 852663. Email: helpdesk@goldschmidt.info

Goldschmidt® is a registered trademark of the Geochemical Society and of the European Association of Geochemistry

Conference management and website by White Iron Conferences

Main photograph © Kenneth Rubin