Moutaz A. Al-Dabbas, Salih Muhammad Awadh & Ayad Abed Zaid
الملخص الانجليزي
The Euphrates Formation (Lower Miocene) in the
Central Iraq consists mainly of shallow marine carbonates.
Two hundred ten samples were collected from 21 wells (1E to
21ED) at Bahar Najaf area, and 18 samples were collected at
Wadi Asadi in Baghdadi area, from Euphrates Formation.
Four microfacies are identified, namely mudstone,
wackestone, packstone, and rare grainstone with ten
submicrofacies. The allochems in the Euphrates Formation
are dominated by bioclasts. Peloids, ooids, and intraclasts are
less abundant. The common fossils in the Euphrates
Formation are miliolids, algae, ostracods, Miogypsina, and
abundant shells of pelecypods and gastropods. Calcite and
dolomite are the predominant mineral components of the
Euphrates Formation. The carbonates of the Euphrates
Formation have been affected by a variety of diagenetic processes
such as micritization, dissolution, neomorphism, cementation,
stylolitization, dolomitization, dedolomitization,
and silicification. The Euphrates Formation was deposited in
open to restricted platforms which indicated lagoonal environment
with warm and restricted open circulation. In fact,
prevalence and abundance of micrite provide an evidence of a
shallow marine of low-energy environment and, in some
places, may be approaching to be stagnant environment. The
average of CaO in Najaf area (51.5 %) is slightly lower than
that in Baghdadi area (53.3 %), which was reflected in calcite
content found being 91 % in Najaf and 94 % in Baghdadi.
Dolomite and gypsum appeared as minor minerals beside
calcite, so low concentration of MgO (0.83 % in Najaf;
0.63 in Baghdadi) and SO3 (0.55 % in Najaf; 0.53 % in
Baghdadi) was reflected information of small amounts of
dolomite (2 % in Najaf; 1.6 % in Baghdadi) and gypsum
(0.7 % in Najaf and 0.6 in Baghdadi) in the Euphrates
Formation. The insoluble residue in Najaf area (4.37 %) is
relatively higher than that in Baghdadi area (1.9 %),
indicating that the Euphrates Formation in Najaf Area
has deposited in an environment closer to the shoreline.
Concentrations of the trace elements Sr, Mn, and Fe
which support the conclusion that reminds the Euphrates
Formation had been deposited in a shallow marine environment
of quiet energy, with the likelihood that the
shoreline was the nearest to Najaf rather than to Baghdadi.
صالح محمد عوض | Salih Muhammad Awadh | 11392