File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎190v] (403/522)

4
(9) The Bakhtiari Series.—Thv Upper Pars Group passes up into the
Bakhtiari Series showing all stages between continuous conformable deposition
and the most striking unconformity, according to whether diastrophism was
comparatively quiescent or very marked in the particular locality during
Bakhtiari times. The strata often exhibit in themselves the phenomena of
unconformity and overlap, which shows that they were laid down under condi
tions of contemporaneous orogenic movement.
From the foregoing it will readily be recognised that the thickness of this
series must be an exceedingly variable quantity, and in fact from the enormous
thickness of 14,000 feet which Anglo-Persian Oil Company Geologists have
found near the Maidan-i-Naftun oilfield, it may vary to a mere insignificant
capping only.
The Bakhtiari rocks of North-East Mesopotamia fall naturally into two
divisions, a lower or arenaceous group, and an upper conglomeratic group.
The Lower Bakhtiari Group is not easily distinguished from the Upper
Ears Group, it, however, exhibits occasional pebbly grits and conglomeratic
bands, the latter formed mainly of Asmari Limestone pebbles and boulders.
Bands of detrital gypsum may be found, and even secondary oil was once
discovered by the author, i.e., oil derived like the gypsum from Lower Ears
rocks outcropping at the time and sealed in the Bahhtiari beds. As above
intimated the Lower Bakhtiari strata consist essentially of regularly occurring
sandstones with intercalated clay shales, the whole being of a dark red color.
The Upper Bakhtiari Group is formed typically of a coarse conglomerate
of boulders and pebbles of Asmari Limestone, at times somewhat loosely
cemented together in a pebbly calcareous matrix, and at times firmly cemented
together by a solid calcareous matrix forming an extremely rigid rock. Although
by far the most important constituents of the Upper Bakhtiaris are Asmari
Limestone derivatives, a quite noticeable number of sub-angular red chert
fragments are also contained.
The rigidity of these rocks, when brought by earth flexures into juxtaposition
with the non-resistant Lower Ears beds, has been a determining factor in the
tectonics of large areas of Persia. They have not played a part of such primary
importance in North-East Mesopotamia because here the Lower Ears rocks are
for the most part buried too deeply and are also outside the region of complex
folding.
{10) The Koweit Series. —This series, so named from its development at
Eloweit, where it was first examined by Anglo-Persian Oil Company Geologists,
is of shallow marine origin. It extends from Koweit to Hit but has not so far
been observed East of the Tigris. It consists of gypseous clays, sands and
gypseous sandy clays, green, brown, blue, yellow and mottled clays with thin
bands of gypsum and occasional bands of very friable sandstone, the whole being
but little compacted. Shell beds were found 7 miles South-East of Abu Jir,
and near Hit on the opposite side of the Euphrates ; the fossils collected were
pecten and other lamellibranchiata in poor condition, but they nevertheless
suffice to leave no doubt that their age is of late Tertiary or Recent.
From Nafatah, near Ramadi, on the Euphrates a striking lithological
change sets in. Down stream from this point beds of gypsum more than 4
inches thick were nowhere observed, but at N afatah a gypseous clay, within a
mile or less, varies laterally into a bed of gypsum (selenite) 5 feet thick. From
here to Hit and beyond this increased gypsum content is maintained, while at
the latter place the gypsum beds are anything up to 12 feet thick, with local
impregnations of bitumen, the bitumen having of course migrated from the
Asmari Limestone below. This change would easily be accounted for by sand
or mud banks protecting a large lagoon sufficiently long for concentration and
chemical precipitation of the gypsum.
The Koweit Series at Hit, as everywhere else where it has been observed, is
lying horizontal on the disconformably horizontal Asmari Limestone beneath
and here comprises not more than 100 feet of strata, No sign of earth move
meat, apart from general uplift, has been seen.

File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎190v] (403/522)

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File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎190v] (403/522)

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