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Participation of fresh water in chert diagenesis: evidence from oxygen isotopes and boron α‐track mapping
Author(s) -
KOLODNY YEHOSHUA,
TARABOULOS ALBERT,
FRIESLANDER URI
Publication year - 1980
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1980.tb01180.x
Subject(s) - evaporite , geology , diagenesis , breccia , matrix (chemical analysis) , sedimentary rock , geochemistry , boron , clastic rock , mineralogy , subaerial , isotopes of oxygen , paleontology , chemistry , organic chemistry , chromatography
Sedimentary chert breccias are the product of two stages of silicification: one which produced ‘fragments’, the other, during which the ‘matrix’ crystallized. Fragments and matrix of twenty‐five breccias from the Senonian Mishash Formation in Southern Israel were separated and analysed for δ 18 O in quartz. The matrix is significantly depleted in 18 O in comparison with fragments (δ 18 O of fragments ranges between +29.4 and +34.7‰, for matrix the range is +21.1–32.6‰). Boron has been mapped in the same rocks using the 10 B(n, α) 7 Li reaction and α‐track etching. Fragments are significantly enriched in boron in comparison to the matrix. The correspondence between boron maps and rock texture is perfect. These results when combined with Steinitz's (1977) report of evaporites and evaporite ghosts in the same rocks are interpreted as indicating two different environments of chert diagenesis: a first, normal marine to hypersaline stage during which the microquartz in fragments crystallized, and a second stage of matrix chertification which in most cases occurred when fresh water was interacting with the crystallizing sediment. These conclusions are corroborated by isotopic analysis of carbonates which coexist with the cherts, as well as stratigraphical and palaeontological analysis.