Marine Diagenesis of Shallow Marine Lime-Mud Sediments: Insights from δO ¹⁸ and δC ¹³ Data

Abstract

Shallow marine lime-mud sediments of the Ste. Genevieve Formation (Mississippian), in part of the Illinois Basin, underwent at least three diagenetic changes: (i) local dolomitization in seawater or a brine, producing dolostone having average deltaC(13) of +2.5 per mille and deltaO(18) of +1.9 per mille (versus PDB-1); (ii) more usually cementation of unreplaced CaCO(3), in intrasediment seawater, yielding isotopically marine lime mudstone mainly composed of calcite, 4-micron or finer, with deltaO(18) of from -1 to +1 per mille; (iii) later partial alteration of CaCO(3), in permeable dolomitic rocks, by isotopically "lighter" waters, to calcite with an estimated deltaO(18) of -10 per mille or less. Isotope data appraised by petrographic analysis thus suggest "submarine" cementation of these carbonates in shallow marine conditions.

Isotopic studies on the palaeoecology and diagenesis of the Great Estuarine Series (Jurassic) of Scotland

“…Carbonates formed during early diagenesis should be in oxygen isotopic equilibrium with depositional waters (Choquette 1968). As we have shown, most depositional waters ranged from dO 18 = o to slightly negative, with indications of insolated water (dO 16 positive) in a few horizons.…”

“…Secondly, diagenetic alteration can take place during deep burial, and the increased temperature associated with this also causes a lowering of the 0 1 8 / 0 1 6 ratio in the carbonate. Although the situation is complex, isotopic evidence combined with petrographic studies can help to distinguish early-from late-precipitated carbonate cements (Choquette 1968).…”

“…More recently, the diagenesis of carbonates has been studied isotopically (Gross 1964;Choquette 1968). There has been some confusion concerning the relative importance of depositional and diagenetic factors influencing the isotopic composition of carbonates.…”

Oxygen and carbon isotopes in Jordanian phosphorites and associated fossils

“…8. , but the alteration of carbonate after deposition makes such interpretation uncertain (Choquette, 1968). Shemesh et al (1988) found that d 18 O CO 3 , like d 18 O p , decreases with increasing age.…”

Sea-Level Research

“…Many authors have studied isotope ratios 16 0/ 18 0 and 12 0/ 13 0 in carbonate minerals as indicative of sedimentary and diagenetic environments (Craig, 1953;Friedman, 1964;Land, 1967Land, , 1970Choquette, 1968;Land & Epstein, 1970;Hudson, 1975;Magaritz, 1983). 18 0 and I'C are indeed enriched in marine waters compared with non-marine waters owing to fractionation during evaporation and precipitation in equilibrium with the atmosphere.…”