 |
| Titel |
Revisiting diagenesis on the Ontong-Java Plateau: evidence for authigenic crust precipitation in Globortalia tumida |
| VerfasserIn |
Elizabeth Read, Oscar Branson, Simon Redfern, Christoph Rau, Henry Elderfield |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112663
|
| Publikation (Nr.) |
 EGU/EGU2015-12829.pdf |
|
|
|
|
|
| Zusammenfassung |
| Foraminifera hold the key to the past climate of the Earth. They can be retrieved from core
tops of sea floor sediments, allowing the record to extend back many thousands to millions
of years. The time lag between the foraminifera formation, deposition, and the
routine analysis can therefore be very long. The sites from which foraminifera
are collected and cored experience different physicochemical conditions to those
which they were formed and deposited in. The samples used in this study are from
the Ontong-Java Plateau, west equatorial Pacific, and were studied in Brown and
Elderfield, 1996. Synchrotron X-ray computed tomography (sXCT) and electron
micro-probe analyses were carried out on samples collected from different core top
depths, chosen to span the lysocline in the area, in order to re-asses the character and
extent of diagenetic alteration. Previous work on Globorotalia tumida collected
in the area (Brown and Elderfield, 1996) found that high-Mg calcite of the test is
preferentially dissolved, leading to significantly reduced whole test Mg/Ca and
Sr/Ca.
Dissolution of high-Mg calcite was directly observed using the sXCT, confirming
previous work of Brown and Elderfield, 1996. In addition to this, the sXCT also
exposed a thickening of external test walls with increasing core top depth, with further
chemically and structurally distinct calcite present outside the periphery of the
test. Electron micro-probe analyses revealed this new calcitic material to have a
generally lower trace element composition that the original calcitic test. This suggests a
dissolution of the internal high-Mg calcite, as well as diagenetic precipitation of calcite
external to the test, generally lower in trace elements. This leads to the proposal of a
closed-loop dissolution-precipitation model, which may be able to account for the
phenomena and trends observed. This demonstrates the impact of two simultaneous
diagenetic aleration processes, with notable impacts on resulting paleoproxy signals. |
|
|
|
|
|
|