Introduction
Stratigraphic column of Saudi Arabia is composed of several lithologies that were
deposited in different depositional environments. Paleozoic section is dominated by
clastics and sandstone, whereas Mesozoic and Cenozoic are mostly dominated by
carbonates. Depositional environments were affected by many factors through out the
geologic time including: paleo-latitude, global sea level change, and regional tectonic
activities. This report describes the outcrop of the formations that were visited by Saudi
Aramco crow on October 2003. It will focus on two parts: Paleozoic and Jurassic.
Paleozoic section includes: Pre-Khuff Unconformity, Unayzah Fm., Pre-Unayzah
Unconformity, Qalibah Fm., and Sarah Fm. The Jurassic section includes: Hith Fm., Arab
Fm., Jubaila Fm., Hanifa Fm, Tuwaiq Mountains Fm., and Dhruma Fm.
Paleozoic Stratigraphy
Saq Formation
The Saq sandstone is descried by Powers as a vertically and laterally uniform succession
of white , gray , and brown ,cross-bedded sandstone from Jabal Saq, the type area. In
most places the base of the formation consists of coarse-grained , poorly sorted , pebbly
sandstone , but locally a basal conglomerate less that a meter thick is present . the sand
stone was deposited in numerous interlocking channels , with each channel deposit being
characterized by microocongromerate at the base and containing scattered quartz pebbles
about 1 cm in diameter .
Risha Member
Risha member represents approximately the lower half of the Saq sandstone . It consists
almost entirely of sandstone . the member unconformably overlies a peneplaned surface
of Proterozoic basement rocks , although locally , at Jabla al Isbaah.
Sajir Member
In contrast to the Risha member , the Sajir member of the Saq sandstone consists of
siltstone in addition to sandstone . the member is 355 m thick at Wadi al Wasiah and 310
m thick north of Wadi at Turmus . the uppermost 65 m of the Sajir member consist of
brown to beige , fine-grained sandstone in inclined and graded beds , intercalated with
red and brown , micaceous , bioturbated siltstone. The saq sandstone contains substantial
amounts of extensively reworked tourmaline and less aboundant zircon and rutile , of
these heavy detrital minerals ,rutile is more common in the Sajir member than in the
risha member .
Qasim Formation
The qasim formation generally corresponds to the lower informal units of the tabuk
formation defined by Powers and others (1966).
The qasim formation crops out in the northeastern corner of the Jabla Habashi quadrangle
, where it forms a regular succession of southwest-facing cuestas trending approximately
northwest and locally intersected by ridges aligned north or northwest . The basal part of
the formation conformably overlies the Saq Sandstone , and the uppermost part is absent
in places due to erosion during deposition of the overlying zarqa and Sarah formations .
Qasim formation includes four informal members defined in the Qasim region and they
are : Hanadir , Kahfah ,Ra’an and Quwarah member
Hanadir member
The Hanadir member is the basal argillaceous part of the Qasim formation . it forms the
first Qasim formation cuesta in the jabal Habashi quadrangle . the thickness of the
member is approximately 25 m throughout the quadrangle . the member apparently
conformably overlies silicified , ferruginized and blackened Saq sandstone , and is
conformably overlain by sandstone and siltstone of the Kahfah member .
Kahfah member
The Kahfah member defined from the locality north of the jabal Habashi quadrangle . It
crops out over a width of about 12 km, between the , major cuestas of the Hanadir and
ra;an members and forms small cuestas a meter to several meters high. The Kahfah
member at the latitude of Wadi al Makhrim is 110.5 m thick , increasing in thickness
southeastward to reach 163 m immediately to the east of the quadragle . It conformably
overlies the Hanadir member and is locally overlain by the Ra’an member , elsewhere it
is channeled by the zarqa and sarah formation . The member is divided into two lithologic
assemblages . the lower assemblage is predominantly composed of fine-grained , fairly
laminated sandstone interspersed with clayey and silty layers . It has an aggregate
thickness of about 55 m.
Ra’an member
The Ra’an member of the Qasim formation was named after Ar Ra’an in the Jabal
Habashi quadrangle. The member is predominantly composed of clay and conformably
overlies the Kahfah member, but is complete only at Ar Ra’an where the Quwarah
member conformably overlies it. On the cuesta at Khashm ar Ra’n the member comprises
at the base, 3 m of gray and dark-red finely laminated silty clay interspersed with beds of
brown micaceous siltstone containing graptolites. This is overlain by 27 m of greenish
gypsiferous clay, capped by 9.5 m of gray silty clay and fine-grained bioturbated , clayey
sandstone in beds about a centimeter thick .
Quwarah member
The Quwarah member is the sandy and clayey sequence conformably overlying the Ra’an
member in the Jabal Habashi quadrangle. The basal beige, fine-grainded bedded
sandstone of the quwarah member forms the upper part fo the Kahsm ar Ra’n cuesta. The
top of the succession is channeled by the Zarqa formation and is absent in several parts of
the quadrangle.
Qalibah Formation
Qalibah formation consists of two members. The first member from the bottom is
Qusaiba member which is a very well known source rock in the Arabian platform. Its
general lithology is shale with some stringer of sandstone. The other member is
Sharawra. Its lithology is shale in general.
Khuff Formation
The khuff formation is formally defined by Steineke and others (1958). The type section
for the formation in the Ad Dawadmi quadrangle and divided it informally into the
Huqayl, Duhaysan, Midhnab and Khartam members.
The general lithology of Khuff Formation shows alternation between carbonate and
evaporite. This alternation might be due to the fluctuation of sea level that caused the
change in depositional environments between deep marine and restricted lagoons.
Unayzah Formation
The Unayzah member lies disconformably on the pre-Khuff paleosuface and begins a
conformable succession that continues to the late Triassic Minjur Sandstone A more
complete section that the type section of the member given by Delfour and others (1982)
near Khuff where it displays a maximum thickness of about 70 m and comprises the
following facies from top to bottom:
4. a carbonate assemblage of beige laminated dolomite and bioturbated and bioclastic
clayey dolomite
3. Alternating gray claystone with gypsiferous intervals and green dolomitic claystone .
the upper part displays intervals of fine-grained sandstone containing ligneous debris and
ripple marks
2. conglomeratic sandstone and medium-grained, slightly consolidated sandstone
channeled into unit 1
1. Green and purplish-red very pedogenized claystone
Jurassic Stratigraphy
Dhruma Formation
Tuwaiq Mountains Formation
Hanifa Formation
Jubaila Formation
Arab Formation
Hith Formation
Sulaiy Formation
Conclusion