Sedimentology and Stratigraphy of Bekhme Formation (Upper Cretaceous) in Selected Sections in Kurdistan Region-Iraq

Abstract thumbnail of Dilshad Omer Ali

This thesis incorporates a study of stratigraphy and sedimentology
of the Bekhme Formation in selected areas of the Iraqi Kurdistan region.
The Bekhme Formation belongs to the Late Campanian-Early
Masstrichtian cycle. At least eight sections were visited in the area
extending from 36015`00“; long. 44030`00“ to lat. 37000`00“; long.
42045`00“ but two sections were described and sampled. The first section
is taken at the northern edge of the Bekhma Gorge, at the western bank
of the Great Zab River and 160 samples were collected from this sec􀆟on.
The second is Khanzad sec􀆟on, which is 6.5 km southeast of Harir Town
and 45 samples were collected from this sec􀆟on. A total of 175 thin
sections prepared and stained with Alizarin Red S.
In this study the Bekhme Formation was divided, in the field, into
four units depending on lithology, bedding and fossils. These units are:
Basal Conglomerate Unit (B1), Dolomitic Calcarenite Unit (B2), Bedded
Dolomitic Limestone Unit (B3) and Massive Dolomitic Limestone (B4).
Petrographic studies revealed the presence of six microfacies: lime
mudstone facies, wackestone facies, packstone facies, grainstone facies,
rudstone facies and framestone facies. Combined field observation, fossil
content, microfacies and diagenetic changes aided in establishing four
facies associations. These facies associations are: Basal conglomerate
(palimpsest), Forereef, Reef and Backreef. Accordingly it is suggested that
deposition of the Bekhme Formation took place in isolated platform, in
many respects similar to that of the Bahama Bank.

The formation was affected by intensive diagenetic processes such
as compaction, dissolution, cementation, neomorphism, micritization,
dolomitization, silicification and stylolitization. In cementation diagnostic
types of cement blocky cement, granular cement, drusy cement, syntaxial
(rim) cement and Dog tooth cement and in dolomitization diagnostic
fabrics of dolomite which were sieve mosaic, suture mosaic, fogged
mosaic and saddle textures and build the model of dolomitization which
was mixing zone model.
Field and laboratory investigations revealed that the Bekhme
Formation differs from the Aqra Formation, especially their fossil content
for example Globotruncana gr. Stuarti and Rugoglobigerinidae genera are
presence in Bekhme Formation but absence in Aqra Formation and
Loftusia and Actionella are presence in Aqra Formation but absence in
Bekhme Formation.
In addition to in places when Shiranish Formation appear above
massive limestone then this massive limestone is Bekhme Formation not
Aqra Formation. It is therefore recommended here to separate both
formations from each other and not combine them as some authors have

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