Cardiff University | Prifysgol Caerdydd ORCA
Online Research @ Cardiff 
WelshClear Cookie - decide language by browser settings

Microstructural and geochemical perspectives on planktic foraminiferal preservation: “Glassy” versus “Frosty”

Sexton, Phillip Francis, Wilson, Paul A. and Pearson, Paul Nicholas ORCID: https://orcid.org/0000-0003-4628-9818 2006. Microstructural and geochemical perspectives on planktic foraminiferal preservation: “Glassy” versus “Frosty”. Geochemistry, Geophysics, Geosystems 7 (12) , Q12P19. 10.1029/2006GC001291

[thumbnail of Sexton 2006.pdf]
Preview
PDF - Published Version
Download (3MB) | Preview

Abstract

In recent years it has become apparent that the “cool tropic paradox” of Paleogene and Cretaceous “greenhouse” climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor, yielding artificially high δ 18O values. Because the Mg/Ca compositions of foraminiferal and inorganic calcite are thought to be quite different, Mg/Ca measurements should be a sensitive way of monitoring diagenetic alteration. Here we examine the extent of diagenetic alteration of Eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical (δ 18O and Mg/Ca) analyses. We compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation: those that appear “frosty” under reflected light and those that appear “glassy.” Microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale, while δ 18O analyses document consistently higher δ 18O (and therefore lower paleotemperatures) in this material. Yet we find that δ 18O offsets between species in these frosty foraminiferal assemblages appear to be generally preserved, suggesting that frosty foraminifera remain valuable for generating relatively short (approximately ≤1 Myr) paleoceanographic time series that do not demand absolute estimates of paleotemperature. We also find that the observed increase in Mg/Ca for planktic foraminifera exhibiting diagenetic alteration (compared to glassy taphonomies) is far smaller than would be expected from the addition of inorganic calcite based on laboratory-derived Mg2+ partition coefficients. Our findings imply that a much lower Mg2+ partition coefficient controls inorganic calcite formation in deep sea sedimentary sections, in accordance with the findings of Baker et al. (1982).

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Additional Information: Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/1525-2027/ (accessed 20/02/2014).
Publisher: American Geophysical Union.
ISSN: 1525-2027
Date of First Compliant Deposit: 30 March 2016
Last Modified: 13 May 2023 12:35
URI: https://orca.cardiff.ac.uk/id/eprint/1358

Citation Data

Cited 190 times in Scopus. View in Scopus. Powered By Scopus® Data

Actions (repository staff only)

Edit Item Edit Item

Downloads

Downloads per month over past year

View more statistics