Dissolution and recrystallization in modern shelf carbonates: evidence from pore water and solid phase chemistry

Abstract

We present an overview of geochemical data from pore waters and solid phases that clarify earliest diagenetic processes affecting modern, shallow marine carbonate sediments. Acids produced by organic matter decomposition react rapidly with metastable carbonate minerals in pore waters to produce extensive syndepositional dissolution and recrystallization. Stoichiometric relations among pore water solutes suggest that dissolution is related to oxidation of H 2 S which can accumulate in these low-Fe sediments. Sulphide oxidation likely occurs by enhanced diffusion of O 2 mediated by sulphide-oxidizing bacteria which colonize oxic/anoxic interfaces invaginating these intensely bioturbated sediments. Buffering of pore water stable isotopic compositions towards values of bulk sediment and rapid 45 Ca exchange rates during sediment incubations demonstrate that carbonate recrystallization is a significant process. Comparison of average biogenic carbonate production rates with estimated rates of dissolution and recrystallization suggests that over half the gross production is dissolved and/or recrystallized. Thus isotopic and elemental composition of carbonate minerals can experience significant alteration during earliest burial driven by chemical exchange 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.

Carbon mineralization and carbonate preservation in modern cold-water coral reef sediments on the Norwegian shelf

“…Depending on the magnitude of sulfate reduction and the initial value of pore-water pH, the accumulation of sulfide and DIC in the pore-water may decrease the pH below carbonate saturation, which may lead to carbonate dissolution (Ben-Yaakov, 1973;Gardner, 1973). The oxidation of hydrogen sulfide strongly enhances this process (Walter and Burton, 1990;Walter et al, 1993). Sulfate reduction linked to carbonate dissolution accounts for significant carbonate losses at modern platform carbonate sediments off Florida and at Tahitian warm-water coral reefs (Ku et al, 1999;Tribble, 1993;Walter et al, 1993;Walter and Burton, 1990).…”

“…The oxidation of hydrogen sulfide strongly enhances this process (Walter and Burton, 1990;Walter et al, 1993). Sulfate reduction linked to carbonate dissolution accounts for significant carbonate losses at modern platform carbonate sediments off Florida and at Tahitian warm-water coral reefs (Ku et al, 1999;Tribble, 1993;Walter et al, 1993;Walter and Burton, 1990). However, if a sufficient pool of reactive iron minerals is present in the sediment, dissolved sulfide reduces ferric iron and precipitates as iron-monosulfides (FeS), intermediate ironsulfide species, and pyrite (Afonso and Stumm, 1992;Berner, 1984;Morse et al, 1992;Pyzik and Sommer, 1981;Rickard and Luther, 2007;Wilkin and Barnes, 1996).…”

“…Boudreau and Canfield, 1993;Ku et al, 1999;Walter et al, 1993;Walter and Burton, 1990) have shown that the relationship between sulfate reduction, hydrogen sulfide oxidation and iron-sulfide mineral formation can drive carbonate dissolution and precipitation in shallow marine sediments. Best et al (2007) noted that shell preservation of bivalve shells is enhanced in siliciclastic sediments compared to carbonate dominated sediments.…”

Controls on porosity preservation within a Jurassic oolitic reservoir complex, UAE

“…At such an early stage in the burial history, prior to compaction and hydrocarbon emplacement, the only fluid that would have been available, therefore, would be seawater. Modern seawater is supersaturated with respect to aragonite, but dissolution can occur in the shallow subsurface as a result of microbial respiration and organic matter oxidation and bacterial sulphate reduction (Walter et al, 1993). During the Jurassic, the Mg/Ca ratio of seawater decreased and by the late Jurassic was probably calcitic (Hardie, 1996).…”

Diagenesis makes the impossible come true: intersecting beds in calcareous turbidites

“…The interbeds, in contrast, at the same time have been subject to dissolution of calcium carbonate and were being compacted by increasing sediment loading (Ricken 1986;Munnecke and Samtleben 1996;Westphal et al 2000). Differential diagenesis is initiated by changes in pore-water chemistry caused by microbially mediated decay of organic matter (Raiswell 1987(Raiswell , 1988Walter and Burton 1990;Canfield and Raiswell 1991;Walter et al 1993) which takes place in defined depth intervals, causing the resulting diagenetic patterns to develop parallel to the sea floor, and thereby in most cases also parallel to the sedimentary layers. According to Munnecke and Samtleben (1996) and Westphal et al (2000Westphal et al ( , 2008a, the carbonate cement in calcareous rhythmites such as limestone-marl alternations that fills the pore space of the (later) limestones derives from selective dissolution of aragonite in the non-cemented layers (marls).…”