File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎126v] (267/522)

The dominant factor in the tectonics of the country was the thrust from the N.E. in late
Pliocene times, which has determined the trend of the hills of Persia and which in this country
has caused the rocks to have been folded into a series of anticlines all having a general N.W.-S.E.
trike.
It would be expected that the S.W. limbs of the anticlines would be steeper than the N.E.
limbs ; this is the case in the anticlines in the Southern part of the area. But in the Qaiyarah
anticline it is not noticeable, the two flanks being symmetrical, with a slight tendency for the N.E.
flank to be a little steeper. Still further north the N.E. limb of the Mishraq anticline is in general
steeper than the S.W. limb.
In the Mishraq-Araij area a new factor appears, which we do not yet understand ; cross folds
apparently on an E.-W. or E.N.E-W.S.W. axis have been mapped and these complicate the general
N.W.-S.E. structure. Some trace of this direction of folding was observed in the Qaiyarah anticline.
It seems to us likely that the country has been affected by a thrust from the north, probably prior
to the N.W.-S.E. folding. We hope to get evidence for this soon.
(6) GEOLOGICAL STRUCTURE OF THE ANTICLINAL AREAS.
A detailed description of the geological structure of the country examined is dealt with below
under the six headings given in the last Chapter.
I. Jabal Ham kin and Jabal Makhul.
A brief note on the general' structure of the J, Hamrin was given in Geological Report No 2.
This ra^ge is one of the most conspicuous physical features of Mesopotamia, as it runs as
an unbroken line of hills rising to 800—1,000 feet above the plain, for more than 100 miles. The
part dealt with in this report extends from a little east of the Tigris to Tulul-el-Baqq about 12
miles W.S.W. of Sharqat.
The hills are composed of beds of the Lower Ears series, gypsum, marls and limestone bands.
The junction with the Upper Ears beds is everywhere a sharp one and comes where the hills
flatten out to the plain.
Structure .—The hills are formed of an anticlinal fold and their height and shape is dependent
directly on the geological structure. The Lower Ears beds come out from under the Upper Ears
at the foot of the hill with a dip varying from vertical to .30 deg. then gradually flatten forming an
arch the flat portion of which is from 1,000—1,200 yards across. In most places the middle part of
the hill slope is a dip slope of a limestone band.
The axis of the anticline is not straight (see map 1 inch scale) but has several changes of trend.
East of the Tigris it runs W.N.W., but at the river turns sharply N.W.; near Ain Dibbs it turns
N.N.W. and forms a sigmoidal curve, after which it runs N.W. as far as Tulul-el-Baqq. To the
west of that place the range appears to continue in the same direction as a well defined line of
hills which is marked on the map as J. Qutr.
The axis does not remain horizontal but pitches frequently forming crest maxima and minima.
In the portion of the range east of the Tigris, Dr. Pascoe notes two crest maxima, one about 2)>
miles W.N.W. of Ain Nukhailah and another about 9 miles east of Fathah. In the river two
small domes of Lower Ears beds are seen ; they are not more than 500 yards in diameter and their
structure is beautifully shown by concentric rings of limestone and gypsum cropping out in the
river. The.rocks of the domes are soaked in oil, a considerable quantity of which seeps out into
the river. Thus at the point which is a crest minimum the lowest beds yet seen of the Lower Ears
crop out. As this section will be examined in detail shortly, no more will be said about it now.
From Fathah north westward the axis rises at an angle of 5 degs., but soon flattens and remains
horizontal for about 12 miles, after which it rises to a crest maximum near Ain Dibbs. It then falls
and rises again forming another crest maximum about 2 miles S.E. of Bilalij. From here the axis
falls at a very small angle to Tulul-el-Baqq and to the N.W. of that place it probably rises again.
In general the south west limb is steeper then the north east limb. East of Fathah the S.W.
limb is steeply folded at the junction with the Upper Ears and in places overturned. At Fathah the
fold is more gentle and the maximum dip found was 30 degs., whilst the N.W. dips of 70—80 degs..
are found. This is what would be expected to result from the sharp twist of the anticlinal axis.
The fact that the river has cut through here is interesting and similar phenomena have been noted
in the Qaiyarah and Mishraq anticlines.
Further to the N.W. the anticline becomes more symmetrical the dip at the junction on the S.W.
limb decreasing: near Ain Dibbs the maximum dip is 50 degs. and opposite Bilalij it has fallen to
to about 30 degs. Still further to the N.W. no steeper dips than 30 degs. were seen.
Prospects :—
{a) Presence of oil bearing beds. —The Lower Ears series is considered to be the oil bearing
formation. v It forms the anticline and only some 600 feet are exposed. Oil bearing beds are ex
posed at Fathah and a considerable quantity of oil seeps out there.
(b) Cap-Rock .—Up to the present we have no reliable information on the thickness of the
Lower Ears in this area, but we believe the nature of the beds in the upper parts of the series is
suitable as a cap rock. Except at Fathah, only 400 feet of the series is exposed.
(c) Geological Structure .—The anticlinal fold is of such a nature as would, in our opinion, be
favourable for the accumulation of oil. There are a number of -well, defined crest maxima, which
may be considered as elongated subsidiary domes on the anticline and these points would be
favourable for a test.
On these grounds therefore, the whole of the part of the J. Hamrin and J. Makhul covered by
this report can be looked upon as favourable territory. The detailed examination at Fathah will
add to our knowledge of this anticline and may alter our views on the prospects of obtaining pro
duction from it.