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Stable isotope evidence for the origin of diagenetic carbonate minerals from the Lower Jurassic Inmar Formation, southern Israel
Author(s) -
AYALON AVNER,
LONGSTAFFE FRED J.
Publication year - 1995
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.1365-3091.1995.tb01275.x
Subject(s) - diagenesis , geology , dolomite , dolomitization , siderite , ankerite , calcite , carbonate , geochemistry , isotopes of oxygen , petrography , carbonate minerals , paleontology , mineralogy , facies , chemistry , organic chemistry , structural basin
The oxygen isotope compositions of diagenetic carbonate minerals from the Lower Jurassic Inmar Formation, southern Israel, have been used to identify porewater types during diagenesis. Changes in porewater composition can be related to major geological events within southern Israel. In particular, saline brines played an important role in late (Pliocene‐Pleistocene) dolomitization of these rocks. Diagenetic carbonates included early siderite (δ 18 O SMOW =+24.4 to +26.5‰δ 13 C PDB =−1.1 to +0.8‰), late dolomite, ferroan dolomite and ankerite (δ 18 O SMOW =+18.4 to +25.8‰; δ 13 C PDB =−2.1 to +0.2‰), and calcite (δ 18 O SMOW =+21.3 to +32.6‰; δ 13 C PDB =−4.2 to + 3.2‰). The petrographic and isotopic results suggest that siderite formed early in the diagenetic history at shallow depths. The dolomitic phases formed at greater depths late in diagenesis. Crystallization of secondary calcite spans early to late diagenesis, consistent with its large range in isotopic values. A strong negative correlation exists between burial depth (temperature) and the oxygen isotopic compositions of the dolomitic cements. In addition, the δ 18 O values of the dolomitic phases in the northern Negev and Judea Mountains are in isotopic equilibrium with present formation waters. This behaviour suggests that formation of secondary dolomite post‐dates the tectonic activity responsible for the present relief of southern Israel (Upper Miocene to Pliocene) and that the dolomite crystallized from present formation waters. Such is not the case in the Central Negev. In that locality, present formation waters have much lower salinities and δ 18 O values, indicating invasion of freshwater, and are out of isotopic equilibrium with secondary dolomite. Recharge of the Inmar Formation by meteoric water in the Central Negev occurred in the Pleistocene, and halted formation of dolomite.