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- Title
Recrystallization of dolomite: evidence from the Monterey Formation (Miocene), California.
- Authors
Malone, Mitchell J.; Baker, Paul A.; Burns, Stephen J.
- Abstract
Dolomites from the upper calcareous-siliceous member of the Miocene Monterey Formation exposed west of Santa Barabara, California, were analysed for geochemical, isotopic and crystallographic variation. The data clearly document the progressive recrystallization of dolomite during burial diagenesis in marine pore fluids. Recrystallization is recognized by the following compositional and crystallographic variations. Dolomites have decreasing δ[SUP18]O and δ[SUP13]C compositions, decreasing Sr contents and increasing Mg contents with increasing burial depths and temperatures from east to west in the study area. δ[SUP18]O values vary from 5˙3%[SUB0] in the east to -5˙5%[SUB0] PDB in the west and are interpreted to reflect the greater extent and higher temperature of dolomite recrystallization in the west. δ[SUP13]C values correlate with δ[SUP18]O and decrease from 13˙6%[SUB0] in the east to -8˙7%[SUB0] PDB in the west. Sr concentrations correlate positively with δ[SUP18]O values and decrease from a mean of 750 ppm in the east to a mean of 250 ppm in the west. Mo% MgCO[SUB3] values inversely correlate with δ[SUP18]O values and increase from a minimum of 41˙0 in the east to a maximum of 51˙4 in the west. Rietveld refinement of powder X-ray diffraction data indicate that the more recrystallized dolomites have more contracted unit cells and increased cation ordering. The fraction of the Ca sites in the dolomites that are occupied by Ca atoms increases slightly with the approach to stoichiometry. The fraction of the Mg sites occupied by Mg atoms strongly correlates with mol% MgCO[SUB3]. Even in early diagnetic, non-stoichiometric dolomites, there is little substitution of Mg in Ca sites. During recrystallization, the amount of Mg substituing for Ca in Ca sites decreases even further. Most of the disorder in the least recrystallized, non-stoichiometric dolomites is related to substitution of excess Ca on...
- Subjects
DOLOMITE; RECRYSTALLIZATION (Geology)
- Publication
Sedimentology, 1994, Vol 41, Issue 6, p1223
- ISSN
0037-0746
- Publication type
Article
- DOI
10.1111/j.1365-3091.1994.tb01450.x