Lm. Walter et al., DISSOLUTION AND RECRYSTALLIZATION IN MODERN SHELF CARBONATES - EVIDENCE FROM PORE-WATER AND SOLID-PHASE CHEMISTRY, Philosophical transactions-Royal Society of London. Physical sciences and engineering, 344(1670), 1993, pp. 27-36
We present an overview of geochemical data from pore waters and solid
phases that clarify earliest diagenetic processes affecting modern, sh
allow marine carbonate sediments. Acids produced by organic matter dec
omposition react rapidly with metastable carbonate minerals in pore wa
ters to produce extensive syndepositional dissolution and recrystalliz
ation. Stoichiometric relations among pore water solutes suggest that
dissolution is related to oxidation of H2S which can accumulate in the
se low-Fe sediments. Sulphide oxidation likely occurs by enhanced diff
usion of O2 mediated by sulphide-oxidizing bacteria which colonize oxi
c/anoxic interfaces invaginating these intensely bioturbated sediments
. Buffering of pore water stable isotopic compositions towards values
of bulk sediment and rapid Ca-45 exchange rates during sediment incuba
tions demonstrate that carbonate recrystallization is a significant pr
ocess. Comparison of average biogenic carbonate production rates with
estimated rates of dissolution and recrystallization suggests that ove
r half the gross production is dissolved and/or recrystallized. Thus i
sotopic and elemental composition of carbonate minerals can experience
significant alteration during earliest burial driven by chemical exch
ange among carbonate minerals and decomposing organic matter. Temporal
shifts in palaeo-ocean carbon isotope composition inferred from bulk-
rocks may be seriously compromised by facies-dependent differences in
dissolution and recrystallization rates.