Geology Reference
In-Depth Information
Basinward (~ north)
Shelf margin (ca.109.5 Ma)
Ramp margin (ca.108 Ma)
6
4
5
7
8
9
3
Upper
Shu'a
iba
Mid.&
lower
Shu'a
iba
2
1
Porous carbonate (i.e. coral-rudist buildups and their debris)
100 km
Low-porosity carbonate (deeper-water)
Persian Gulf
25
0
N
Shale
Gulf of Oman
Sequence boundary
Facies boundary
Muscat
Bu Hasa
Sequence number (placed near upper boundary)
1
Safah
23
0
54
0
56
0
58
0
Fig. 13.
Schematic section of Shu'aiba Formation (Aptian), Bu Hasa Field, Abu Dhabi. After Fitchen (1997), modifi ed.
Tropical carbonate platform (algae, foraminifera, rudist-coral biostromes) progrades into a shallow cratonic basin where
argillaceous sediments accumulate. During early progradation (units 1-6), slopes steepen and each sequence has recogniz-
able topset beds - the units constitute a highstand systems tract. During late stage of progradation (units 7-9), slopes fl at-
ten, sequences step down and lack topset beds - the units form a falling-stage systems tract (called 'late highstand tract' by
Fitchen, 1997). Rate of fall estimated as 15-20
m yr, based on age dates and thicknesses in Fitchen (1997, Fig. 32).
South
North
11 km
150
7
56
45
10
36
15
18
3
1
Nahr
Umr
Upper
Shu'aiba
Middle
Shu'aiba
F
F
F
L
Shu'aiba A
100 km
Upper Shu'aiba lithologies
Packstone-grainstone + biostromes
Wackestone-packstone
Argillaceous basin sediments
Persian Gulf
25
o
N
Gulf of Oman
Mus
c
at
Bu Hasa
M
iddle Shu'aiba
Safah
23
o
Exposure unconformity at top Middle Shu'aiba
Middle Shu'aiba shelf margin
54
o
E
56
o
58
o
Fig. 14.
Cross-section of Shu'aiba Formation of Safah Field, Oman, based on correlation of wells (well numbers shown
above section). After Boote & Mou, (2003), modifi ed. Section is fl attened on an Eocene datum to remove Miocene deforma-
tion. Depositional evolution is very similar to Bu Hasa Field (Fig. 13). Lower Shu'aiba lacks signifi cant depositional relief;
middle-Shu'aiba deposits evolve from ramp to rimmed platform (with rudists, and coral biostromes). After signifi cant
sea-level fall, upper Shu'aiba deposition starts with a lowstand systems tract (L) that abuts against the mid-Shu'aiba slope;
subsequently, the systems aggrades. The fi nal stage of deposition consists of three downstepping limestone tongues (F)
that form an FST.
