Brand, Uwe; Logan, A.; Bitner, M. A.; Griesshaber, Erika; Azmy, K.; Buhl, D.
What is the ideal proxy of Palaeozoic seawater chemistry?
In: Memoirs of the Association of Australasian Palaeontologists, No. 41: pp. 9-24
Full text not available from 'Open Access LMU'.
The chemistry of many biogenic allochems and whole rock is used as a proxy of original seawater chemistry during the geological past. Common Palaeozoic proxies are brachiopods, conodonts, and whole rocks. Brachiopods may secrete low-Mg calcite shells; conodonts consist of francolite, a carbonate fluorapatite; and whole rock is usually diagenetic low-Mg calcite altered from different original carbonate mineralogy. Stratigraphic uncertainty of specimens from isolated successions remains a serious impediment to accurate age assignment and in modelling events of the ancient hydrosphere. Furthermore, diagenesis is the great nemesis of these allochems and whole rocks, and in many instances they are not preserved in their original composition. Thus, the chemical composition of many of these proxies instead of being representative of the original and ambient seawater reflects the composition of the diagenetic fluid and character of the diagenetic microenvironment such as the water/rock ratio. Consequently, the best proxy is not necessarily the most abundant material, nor the most readily available (i.e. in outcrop or museums), nor the one supported exclusively by hypothetical concepts. Instead, the best proxy is the one that has passed the most screening tests, and in addition, is stratigraphically well constrained and provides results reflecting the natural variation of the ambient oceanographic environment.