File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎63v] (141/522)

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Graiel. —High level gravels occur at heights of from 50 to 150 feet above the river level. The
gravel has a hard calcareous cement and probably belongs to a drainage system much older than the
present one.
Alluvium. —Recent alluvium of the Tigris obscures the beds in the eastern part of the area.
SEEPAGES.
4. Large seepages occur in three places in the area examined—
{a) In the valley just east of the wells, the oil appears to seep out from a green shale,
which is full of gypsum crystals ; gas and sulphur water also present. No sign of salt
water.
(b) About 400 yards, N.-W. of the post in a valley. The seepages are large and a con
siderable quantity of gas comes up ; sulphur water is also present.
(c) In the River Tigris from the post to about 300 yards N.-E. of it. Here the same green
marl with gypsum crystals crops out below gypsum.
A small isolated seepage occurs about 1,200 yards north of the post. A seepage is said to occur
near Qishlah, about 9 miles W.-N.-W. of the oil wells.
Sulphur. —Much sulphur occurs in the eastern part of the area ; it is associated with all the
seepages. Sulphur gas is liberated in an area about 400 yards south of the wells, where it comes up
through gypsum. To the North-West of the wells near the junction of the Upper and Lower Ears a
considerable stream of water heavily charged with sulphur flows out of a cavern in gypsum. The
gas is so strong that birds become poisoned by it and fall in the water when they become coated
with sulphur.
GEOLOGICAL STRUCTURE.
5. The hills of Qaiyarah (Jebel Qaiyarah) which run from the West to within about 1^ miles
of the Tigris, owe their presence and form to the existence of an anticline. This anticline conforms
very closely to the shape of the hills, and the river has cut through the hills where the anticline
plunges to the east. The axis of the anticline, shewn on the map as a red “ dash and dot ” line does
not run straight, but starting from the west end, it runs first N.-W.—S.-E., then W.-N.-W.—E.-S.-E.
and then again turns N.-W.—S.-E. The crest of the anticline is at a point about l\ miles west from
the Well No. 7 and here the hills also reach their highest altitude (some 400 feet above the river).
From the crest eastward the axis plunges to the east uniformly at an angle of about 2 degrees.
Westward it plunges at first steeply (10—12 degrees), then flattening out to 2—3 degrees, and still
further to the west becoming horizontal..
In general it can be said that the anticline is regular in shape, but the N.-E. flank dips somewhat
steeper than the S.-W. flank. As. will be seen from the map and sections the beds of the Lower
Ears dip gently at an angle which does not usually exceed 5 degrees until the junction of the Upper
and Lower Ears is approached, then the dip steepens to as much as 30 degrees. On the S.-W.
flaflk the junction is not sharp as the dip appears to get less and also the country is much obscured
by wash. The Limestone band A is one of the most useful horizons to map as it is easily traced.
On the crest of the anticline there is a small subsidiary dome or semi-dome ; this is best seen
in the sections. The dip, which is not more than 4 degrees on the higher parts of the flanks,
suddenly increases to 10—12 degrees, causing the Limestone band A to crop out again on top of the
high ridge, called by us Plateau Hill.
We have thus a very elongated dome, on the crest of which is a small subsidiary dome. The
extent of this structure is difficult to measure, but the breadth taken as far as the junction of the
Upper and Lower Ears varies from 3,500 yards to over 6,000 yards. The length of the anticlinal
structure is probably some 10—11 miles of which we have followed it about 7 miles. Owing to
transport difficulties it was not possible to carry out examination further in a westerly direction, but
from the form of the ground it is probable that the anticline rises to another crest further to the
north-west in the direction of Qishlah.
Still further in the same direction another range of hills, which run approximately east and
west, probably marks another anticline. It is hoped that the examination of this area will be
possible, later on.
TECTONICS OF THE AREA.
6. With our very limited knowledge of the geology of this country, it is impossible to come to
any definite conclusions as to the movements which have determined the structure of the area.
The following points, however, are considered of interest :—
The most important earth movement, which has determined the present structure, was one
which occurred after the deposition of the Upper Ears Beds ; this was of the nature of a thrust
from the north-east and had the effect of causing a series of folds the axes of which were N.-W.—S.-E.
This is noted by Messrs. Busk & Mayo in their paper on “ The Geology of the Persian Oil Fields,”
Jour. Inst. Petroleum Technologists, December, 1918. This movement came in early Pliocene
times and the deposition of the Pliocene Beds—the Bakhtiari Beds of Persia went on con
temporaneously. Fo this movement the Anticline of Qaiyarah owes its origin and its orientation
conforms in general with the general strike. No Pliocene deposits of the nature of the Bakhtiari
Beds were seen by us, but there is strong evidence of a movement at a period later than the Pliocene
one. The fact of the occurrence of Coral limestone capping hills and on ledges in valleys, shews
clearly that the area has been subjected to depression and elevation at some period subsequent to
the denudation of the Upper Ears. We believe that the coral was deposited during a period of

File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎63v] (141/522)

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