TITLE:
Stratigraphic Correlation between Subsurface Maastrichtian Digma Formation and Safra Unit from Outcrop Sections, Western Desert of Iraq
AUTHORS:
Ibrahim Q. Mohammed, Fadhil A. Lawa
KEYWORDS:
Maastrichtian, Digma Formation, Safra Unit, Western Iraq
JOURNAL NAME:
International Journal of Geosciences,
Vol.8 No.9,
September
29,
2017
ABSTRACT: In this work we try to clarify, and correlate between two Maastrichtian aged
units, namely Digma and Safra Units from selected sections in western desert of
Iraq. Taking in consideration the stratigraphic code of NASCENT (2005), and
the results of previous studies, nine criteria have been used for the correlation,
as follow: 1- From lithostratigraphic point of view, Digma Formation (Fm.)
mostly composed of dark grey to blackish gray, uniform Carbonates-dominated
facies, while Safra unit is characterized by light yellowish brown mixed phosphatic-
siliceous-siliciclastics and carbonates facies. 2- Digma Fm. is characterized
by Benthonic foraminifera assemblages (Bulimmina sp., Siphogerinoides
sp. & Bolivinoides sp. ), while Safra phosphatic unit is flourished by macrofossils
assemblages and vertebrates (Oyster, fish teeth’s and bones). 3- The upper and
lower boundaries of the Digma Fm. are conformable, and vice versa for Safra
Unit. 4- Illite/Semctite mixed layers-Illite clays assemblage and Glauconitic are
predominates in Digma Fm., while Sepiolite-palygorskite-Montmorillonite, are
common in Safra Unit, without any Glauconitic mineralization. 5- Digma Fm.
slightly influenced by neomorphism and micritization. On other hand, Safra facies
extremely influenced by phosphatization, silicification, dolomitization, and
neomorphism and carbonate-silica replacement of the original evaporate minerals.
6- The predominated foraminiferal wackestone and mudstone microfacies,
within Digma facies associations, mostly indicate deep trough marine condition
(Anah Graben). The mixed phosphatic-carbonates (Oyster coquina band)
and siliciclastics facies, (occasionally cross laminated), mostly deposited in shallower
water depth, on the Arabian platform and distal steepened ramp towards
Rutba flanks. 7- Sequence boundary of type one and three is bounded the Safra
Unit respectively from upper and lower parts. 8- Continuously deposited Sequence
was detected from the parasequences of the Safra facies, and across Maastrichtian/Danian boundary (Trafawi Unit). 9- The paleo-configuration of
the basin almost influenced by the reactivity of the Anah basement faults started
in the Late Campanian, and combined by shallowing upwards sequences. The
conclusion is that, Digma facies can be considered as local facial changes of the
Shiranish Formation, while Safra unit can be considered as a lower Member of
(L. Maastrichtian-Danian) Jeed Formation, which is coincides with the whole
stratigraphic frame work of the Mediterranean segments of the Tethyan phosphatic
realm.