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Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia
Author(s) -
MORAD S.,
ISMAIL H. N. BEN,
ROS L. F.,
ALAASM I. S.,
SERRHINI NE.
Publication year - 1994
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.1365-3091.1994.tb01452.x
Subject(s) - geology , siderite , diagenesis , geochemistry , meteoric water , ankerite , feldspar , illite , anhydrite , quartz , cementation (geology) , clastic rock , mineralogy , kaolinite , sedimentary rock , clay minerals , calcite , paleontology , cement , gypsum , hydrothermal circulation , archaeology , history
The fluvial Triassic reservoir subarkoses and arkoses (2409·5–2519·45 m) of the El Borma oilfield, southern Tunisia, were subjected to cementation by haematite, anatase, infiltrated clays, kaolinite and K‐feldspar at shallow burial depths from meteoric waters. Subsequently, basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths, magnesian siderite, minor ferroan magnesite and anhydrite. The enrichment of siderite in 12 C isotope (δ 13 C PDB = ‐ 14·5 to ‐ 9‰) results from derivation of carbon from the thermal decarboxylation of organic matter. During further burial, the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred, followed by the formation of microcrystalline K‐feldspar and quartz, chlorite and illite, prior to the emplacement of oil. Present day formation waters are Na‐Ca‐Cl brines evolved by the evaporation of seawater and water/mineral interaction and are in equilibrium with the deep burial (≤ 3·1 km) minerals. These waters are suggested to be derived from the underlying Silurian and Devonian dolomitic mudstones.