Page 318 - Carbonate Platforms Facies, Sequences, and Evolution

of
the
The
area,
sheets
nappes
Hawasina
telescoped
tectonic
redeposited
nation (Fig.
Arabian
distal nappe,
thrust-faulted
four mappable
Sumeini Group
2).
Qumayrah form
(hanging
Mayhah Fm
a
passive
apparently
over
This
flanks indicate lateral
wall
limestone
carbonate
sub-units
Complex (and
displacement
one locality; Watts, 1985).
Wadi Qumayrah study area
STRATIGRAPHY
basinal
is
represent
which
the
and
continental
two major thrust sheets,
structure
ANALY SIS
cut-offs).
and
can
AND
is
passes
Semail
be
known,
margin
Structure of the Wadis Qumayrah area
different
and associated rocks
platform (Fig.
part
of
termed the
1).
cated the structure of these deformed rocks.
ramp margins of the
FACIES
a
parts
which
continental
divided
upward
because
Ophiolite
of
structural detachment at the base of the Jurassic­
out-of-sequence thrust-faulting has further compli­
Mayhah Fm marks the return to carbonate sedimen­
major structural high or culmi­
a
eastern
thrust faults locally place the Mayhah Fm over the
and western na p pes, are each comprised of Mayhah
Cretaceous slope sequence. The front of each nappe
is marked by a major thrust fault, and the plunging
These
fine-grained calcilutite and madstone (Figs 3 & 5).
of
Out-of-sequence
Fm and Qumayrah Fm rocks. Neither the nature of
thrust
the basement upon which it formed nor the amount
and slope sediments of the Sumeini Group. Younger
part of the sequence, the Middle to Upper Jurassic
have
(Watts, 1985). The lower
A Member of the Mayhah Fm, begins with coarse
been tectonically stacked and shortened. The most
Semail Ophiolite (ocean crust?) was
sediments of the allochthonous Hawasina Complex
rise
near Wadi
thin beds of chert-clast breccia of the C Member,
As Judi culmination of Searle (1984). In the study
tectonic window beneath the Semail Ophiolite, the
large
were progressively emplaced over
at
the Valanginian to Cenomanian D Member of the
are key marker horizons. Thin-bedded calcilutite of
Locally, an interval of bedded chert, the Tithonian
to Valanginian B Member of the Mayhah Fm, and
Qumayrah Fm were mapped and described in the
into
into
tation whereas slumps and calcirudite in the upper
Several lithologic units within the Mayhah Fm and
of
and
distal
Thick
the
distinct
cluding
whereas
bedding
Major
between
Siliceous
relatively
upper part.
importantly
the
the
and
(Figs 3 & 7).
Eastern na ppe
in
At the base,
Arabian carbonate platform margin
intervals
intraclastic
coralline
of
proximal
uppermost
eastern nappe (Fig.
sediments
base-of-slope
differences
eastern
foraminifera
calcarenite sub-units.
eastern
interbeds
Numerous
in
of
and
upper
calcirudite and megabreccia
calcarenite,
interpreting
limestone.
apron
beds
nappe
the
madstone comprise the 'shaly
redeposited
slope
of the Oman continental margin.
the
lain by synorogenic megabreccias.
The
of orange
western
Nautiloculina
stratigraphy
Upper
unit
deposits
calcareous
interval',
represents
is
Jurassic-Cretaceous
tectonic
nappes
of calcirudite,
calcilutite
no
circularis
(Fig.
shale,
deposits (Fig.
in
sedimentation at the platform margin and are over­
Megabreccias and other distinct markers allow cor­
clasts of fossiliferous shallow-marine limestone in­
the thick-bedded lower oolite sub­
part indicate rejuvenation/steepening of the slope.
6).
295
Cretaceous
Qumayrah Fm indicate major changes in patterns of
documented
nappe and occur at Jebel Sumeini, the type locality
B Member chert, the thin-bedded calcilutites of the
relation between nappes. The western nappe lacks
cherts of the B Member that characterize the eastern
history,
Lower A Member, Mayhah Formation- calcarenite,
upper A and D Members cannot be distinguished,
so the upper part of the succession in the western
shortening. In the Jurassic part, several stratigraphic
differences suggest that the western nappe represents
indicate
different depositional settings and possible tectonic
relatively
7)
Aspects of each lithologic unit figure
carbonate) sediment form a stratigraphic succession
bedded
calciclastic (coarse
palaeogeography and palaeoceanography of this part
nappe is simply referred to as the upper Mayhah Fm
unit is primarily composed of ooids and has graded
(Watts & Garrison, 1986). Without the intervening
8) consists of the lower oolite
calcarenite, 'shaly interval', megabreccia and upper
in the
of four mappable sub-units The A Member in the
oolitic
older
a
than middle-late Jurassic based upon the presence
commonly contain slope-derived blocks and lesser
and
the middle
sub-unit of the lower A Member. Beds of calcirudite