Evaluation of the effect of diagenetic cements on element/Ca ratios in aragonitic Early Miocene (~16 Ma) Caribbean corals: Implications for 'deep-time' palaeoenvironmental reconstructions. / Griffiths, Naomi.

2015. 210 p.

Research output: ThesisDoctoral Thesis

Unpublished

Documents

Abstract

The skeletons of scleractinian corals incorporate elemental and isotopic signatures that reflect ambient seawater conditions during the time of coral growth and thus represent important geochemical archives for palaeoenvironmental reconstruction. Most previous studies have focussed on Holocene and Late Pleistocene corals however attention has recently turned towards probing pre-Pleistocene records. This thesis examines for the first time the skeletal preservation and geochemistry of ~16 Ma old corals from the southern Caribbean. Early Miocene corals from the Paraguaná Peninsula, northern Venezuela and modern specimens from Florida and Bermuda were investigated. X-ray diffraction analyses showed 1-2% calcite contamination in the fossil specimens. Light and electron microscopy revealed regions of excellent preservation juxtaposed with zones in-filled by several generations of aragonite and calcite cements in both fossil and modern corals. Brucite cements were confined to the modern coral specimens while pyrite, dolomite and hydrocarbon residues were noted in the fossil samples. Endolithic macro- and micro-boring activity was evident in both modern and fossil coral samples. Targeted laser ablation depth profile analyses showed increased Sr/Ca and decreased Mg/Ca ratios in aragonite cements compared to the values recorded in primary skeletal aragonite. For calcite cements these trends were reversed. B/Ca ratios were lower in both aragonite and calcite cements compared to primary aragonite. Estimates of the effect of 1% contamination by aragonite cements on Sr/Ca, Mg/Ca, B/Ca and U/Ca -based temperature reconstructions for the fossil corals produced anomalies of -1.2oC, -0.2oC, +0.3oC and -0.1oC respectively. Similar percentage calcite cement contamination produced temperature anomalies of +1.7oC, +2.7oC, +0.3oC and -0.1oC. Highly elevated and depleted Ba/Ca signatures were found in aragonite and calcite cements respectively, therefore care has to be exercised when reconstructing past flood or upwelling events from fossil corals. Targeted spatially-resolved analysis of well-preserved Early Miocene corals may yield reliable ‘deep-time’ palaeo-proxy information.
Original languageEnglish
QualificationPh.D.
Awarding Institution
Supervisors/Advisors
Award date1 Mar 2015
Publication statusUnpublished - 2015
This open access research output is licenced under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

ID: 24137153