'IRAQ AND THE PERSIAN GULF' [‎392v] (787/862)

6i6
STRATIGRAPHY
Age
Lower Miocene
and Oligocene
Eocene
Upper Cre
taceous
Middle Cre
taceous
Formation
Red grit, sandstone, and silt in north-east
passing laterally into thick and thin-
bedded foraminiferal limestones, the
Kalhur or Ana or Euphrates limestone.
Restricted to troughs and absent over
certain ridges. Thickness varies from o to
550 feet. Anhydrite locally in thin bands
near the base, and some conglomerates
fringing ancient banks.
Miliola, Lepidocyclina, and other foramini-
fera and calcareous algae.
Yellow and red chert grit in the north
east, passing into dark grey silty shales
with thin sandstone ribs to the south
west. Local conglomerates of chert
pebbles occur. The whole series resem
bles European flysch. Up to 3,000 feet
thick.
Nummulitic massive and banded lime
stones occur interbedded with marls and
cover some of the flysch and replace part
of it. They give way to Globigerina marls
near the centre of the basin. About 1,000
feet thick. West of the basin chalky
marls with some beds of flint occur.
About 350 feet thick.
Nummulites, Globigerina, and Operculina
libica in the west. Laterite at the base in
the western desert.
Grey conglomerate, red and grey sand
stones, grey shales and reef limestones
with rudists and Loftusia rest on light grey
and green marls in the north-east; in all
more than 5,000 feet thick, thinning
rapidly in both directions from this
maximum.
Thin sandstones, shales, and thin lime
stone ribs occur to the south-west and
pass to Globigerina marls and argillaceous
limestones in the foothills. Thickness is
rather regular at about 800 feet.
Shelly sandy limestone and sandstones
with Loftusia occur interbedded with sand
stones and shales west of the Euphrates
making a thickness of about 100 feet.
Some chalky limestone developed in the
western desert.
Two types of limestone deposits occur in
the north-east; one is massive and dolo-
mitic with Orbitolina and occasional reefs
of oysters, rudists, and Gasteropods; the
other is thin-bedded and argillaceous
with some shaly partings. It contains
Ammonites and Globigerina. These two
facies change suddenly from north-west
to south-east.
Remarks
Steep coast lay to the
north-east with a trough
in front. It rose south
west to a narrow ridge at
Sadid.
Westwards there was a
flooded shelf like the
Bahamas bank at the
present day.
From a steep shore on the
north-east a trough sank
to 3,000 feet near the
course of the Tigris but
was bounded by a ridge
at Sadid. The nearly
flat sea floor to the west
retained a depth of about
300 feet of water on it
for about 200 miles,
though it gradually shal
lowed farther west.
The coarse sediments
showing rapid variation
in thickness reflect
mountain building to the
north-east and north.
The shallow marine
sandstones with Loftusia
and rudists are wide
spread but thin over the
western platform.
Open sea conditions over
a wide area with deposi
tion modified by a large
distant river’s discharge.