J A Trotter
The ubiquity and biostratigraphic significance
of conodonts underscore their potential importance for geochemical
studies, especially as potential recorders of past oceanic composition,
with the aim to better reconstruct and understand palaeoenvironmental
change during the Palaeozoic and early Mesozoic. They have great
potential to help define the processes that were operating in
palaeoceans, both regionally and globally, particularly in the
context of bio- and geo-events, and thus the driving forces that
determine the evolution of life. Understanding extinction events
and the processes controlling life during Earth history has immediate
implications for present and future life on Earth.
Despite the increasing focus on conodont apatite
for such studies, their reliability as proxies of ambient seawater
chemistry has been questioned by the geochemistry and palaeontology
communities due to issues of data reproducibility and internal
consistency, and is therefore yet to be effectively demonstrated.
Chemical systematics of marine biogenic apatite in general is
not well understood due to the lack of rigorous and systematic
investigations to address potential diagenetic effects. Studies
to date incorporate many assumptions on the integrity of conodont
tissues and are based on
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bulk specimens of which details regarding
taxonomy and morphology are generally lacking, yet are likely
to have significant implications for the integrity of data generated.
Detailed and high resolution geochemical studies are therefore
required to determine the significance of such variables (including
histology) that have been thusfar overlooked, to address these
critical issues of sample and data integrity.
This study aims to determine the suitability
of conodont apatite as a recorder of ambient seawater chemistry
and the criteria to discriminate primary geochemical signatures
from secondary effects and background noise. A multi-proxy approach
of trace element and isotope geochemisty using an array of high-resolution
instrumentation are being applied to key intervals through the
Ordovician and Early Silurian to identify potential relationships
between climate cycles, tectonics, fluxes in ambient seawater
chemistry and the biosphere. Initial work has produced continuous,
high-resolution chemical profiles of different components within
single conodont elements using in-situ laser ablation ICPMS.
Systematic variations in the chemistry of the component tissues
have been recognised and related to conodont ultrastructure (SEM),
and have significant implications for the integrity of conodont
tissues and sampling strategies for further conodont geochemical
studies. Current work is also utilising Transmission Electron
Microscopy, Laser Raman Spectroscopy, Electron and Ion Micropobes
and MC-ICPMS, targeting specific tissues to assess their chemical
and isotopic heterogeneity, preserved textures, and relative
susceptibility to diagenesis.
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