Universidade Federal do Rio Grande do Sul, Instituto de Geocièncias, Av. Bento Gonçalves, 9500, Porto Alegre, RS, 91500, Brazil.
Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia
Article first published online: 14 JUN 2006
Volume 41, Issue 6, pages 1253–1272, December 1994
How to Cite
MORAD, S., ISMAIL, H. N. B., DE ROS, L. F., AL-AASM, I. S. and SERRHINI, N.-E. (1994), Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia. Sedimentology, 41: 1253–1272. doi: 10.1111/j.1365-3091.1994.tb01452.x
- Issue published online: 14 JUN 2006
- Article first published online: 14 JUN 2006
- Manuscript received 21 October 1993; revision accepted 27 May 1994
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 12C isotope (δ13CPDB= - 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.