A review of O, C, Sr and S isotope trends for the entire Phanerozoic shows
that the present-day values of isotope signals are similar to those at the
Proterozoic termination. The sharp rise in Sr-87/Sr-86 since similar to 65
Ma has been attributed to an uplift and subsequent metamorphism and erosion
associated with the Himalayas and Tibet. This orogenic evolution has been
postulated to have influenced the global organic and inorganic carbon cycle
s and climate as well. A similar large-scale orogeny, the Pan-African event
, also dominated the Neoproterozoic (Vendian) times, and the similarity of
modern and Neoproterozoic isotope values for seawater may therefore have ha
d a comparable tectonic cause. In this contribution, we present the results
of a numerical model of the coupled C-alkalinity-S-Sr cycles suggesting th
at the early Paleozoic (from early Cambrian to late Devonian) evolution of
Sr, O, C and S seawater isotope signals could have been the consequence of
progressive oxidation of a large reduced carbon reservoir exhumed during th
e Pan-African orogeny. The delta O-18 measured in brachiopod shells is used
as a forcing of the model, postulating that any change in the oxygen isoto
pic composition of seawater is the result of a disequilibrium in the organi
c carbon subcycle through the coupling of the oxygen isotopic and carbon cy
cles. The calculated delta C-13, Sr-87/Sr-86 and delta S-34 are in good agr
eement with the data, as is the reasonable calculated history for atmospher
ic pCO(2) and its relation to global climate. (C) 2001 Elsevier Science B.V
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