Stable isotopes, chemistry and petrology of carbonate concretions (Mishash formation, Israel)

Eytan Sass*, Yehoshua Kolodny

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

39 Scopus citations

Abstract

Carbonate concretions of variable sizes occur in the upper member of the Senonian (Upper Cretaceous) Mishash formation in Israel. Eight concretions and their surrounding country rocks were examined in the field, in thin sections and by X-rays. The isotopic composition of carbon and oxygen in the carbonates, the amount of acid insoluble residue, as well as the concentrations of P2O5, Ca, Mg, Sr and Fe were determined. Other concretions and country rocks were analyzed for oxygen and carbon isotopes only. The concretions are composed of almost pure, microsparitic calcite, whereas the country rocks are porcellanitic-phosphoritic chalks. Compared with the surrounding rocks, the concretions are strongly enriched in 12C and are depeleted in insoluble residue, P2O5, SiO2, Fe, Sr and Mg. It is postulated that the concretions were formed by addition of CaCO3 to sites of anaerobic decomposition of organic matter, while CaCO3 was mobilized in the surrounding sediments, in which aerobic decomposition of organic matter prevailed. Several consequences of this model are considered, concerning the quantitative volume changes, as well as the distribution of SiO2 and Mg between concretions and country rocks.

Original languageEnglish
Pages (from-to)261-286
Number of pages26
JournalChemical Geology
Volume10
Issue number4
DOIs
StatePublished - Dec 1972

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