Middle Triassic to Upper Jurassic
Palynofacies
, Paleoenvironment, Source Rock Potential and Organic Thermal
Maturity of Radiometric-dated Sequence, Qatar - Arabian Gulf
By
Mohamed Ismail Ibrahim1, Hamad A. Al-Saad2, Suzan E. Kholeif3
(1) Alexandria University, Alexandria, Egypt (2) Qatar University, Doha, Qatar (3) Institute of Oceanograpgy and Fisheries, Alexandria, Egypt
Strontium isotope analysis
(87Sr/86Sr ratio) have been conducted on core
samples representing, from top to base, the Hanifa, Araej, Izhara, Hamlah and
Gulailah formations, onshore Qatar. They gave an overall age range from 157.80Ma
to 233.30Ma, Oxfordian to Ladinian.
Deposition of the Gulailah and lower Hamlah formations (Ladinian-Norian) were
took place in a lacustrine environment. The middle Hamlah Formation may have
been deposited in shallow, normal marine environment, whilst the upper part was
deposited in a hypersaline environment. A mixture of kerogen
type II-III, oil
and gas-prone is inferred for the Gulailah-basal Hamlah formations (TOC higher
than 0.3%).
Kerogen
type IV, inert material is suggested for the upper Hamlah
Formation. Thermal alteration index (TAI) is ranged from 3- to 3+, interpreted
as peak oil to onset gas generation.
The Izhara, Araej and Hanifa formations are dominated with marine
microplankton, dated early Hettangian to Oxfordian. They were deposited under
shallow marine environment grading from oxic, dysoxic to anoxic shelf
respectively. The organic matter is almost exclusively of marine algal origin.
Izhara Formation is mature to over mature of kerogen
type III-IV, gas-prone to
inert material. Mature
kerogen
type II-III (oil and gas-prone material) is
deduced for the Lower and Upper Araej, while the stylolitic limestone of the
Uwainat Member has weak source. Mature
kerogen
type I-II, highly oil-prone, is
possible for the black limestone Hanifa Formation. It is considered as the
prolific petroleum source rock for the underlying and overlying reservoirs of
the Uwainat (Bathonian) and the Arab “D” (Kimmeridgian) respectively.