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A Novel Plate Tectonic Scenario for the Genesis and Sealing
of Some Major Mesozoic Oil Fields
GSA TODAY | DECEMBER 2016 Giovanni Muttoni, Dipartimento di Scienze della Terra ‘Ardito Desio,’
Università degli Studi di Milano, via Mangiagalli 34, I-20133 Milan,
Italy, giovanni.muttoni1@unimi.it; and Dennis V. Kent, Earth and
Planetary Sciences, Rutgers University, Piscataway, New Jersey
08854, USA, and Lamont-Doherty Earth Observatory of Columbia
University, Palisades, New York 10964, USA
ABSTRACT
Recent research reveals evidence of a major event of global plate
motion during the Jurassic, with a magnitude and tempo hitherto
not fully appreciated. Yet, its legacy persists today as the potent
Jurassic source-reservoir-seal oil systems in the Persian Gulf region.
We suggest that these formed as a consequence of a sweeping
tectonic movement whereby Arabia drifted rapidly from the oil-
forming Intertropical Convergence Zone along the equator to the
arid tropics of the southern hemisphere with rapid deposition of
relatively uncemented carbonate reservoirs and anhydrite seals, all
during as little as 15 m.y. in the Late Jurassic. The Ghawar super-
giant oil field of Saudi Arabia was one of the results. Rapid latitu-
dinal change may have influenced the development of some
source-reservoir-seal oil systems elsewhere as well.
INTRODUCTION
Ghawar is the world’s largest oil field, a supergiant that accounts
for ~60% of Saudi Arabia’s crude production (Al-Anazi, 2007).
The source rocks at Ghawar are marine muds and carbonates of the
Tuwaiq Mountain and Hanifa formations (Alsharhan and Nairn,
1997) deposited in the Callovian-Oxfordian stages of the Late
Jurassic (Al-Husseini, 2009) between 166 and 157 Ma (time scale of
Cohen et al., 2013). The reservoirs are located in overlying bioclastic axial dipole (GAD). According to the GAD hypothesis, paleomag-
limestones of the Kimmeridgian (Late Jurassic; 157–151 Ma) Arab
Formation that are sealed by anhydrites of the Tithonian (Late
Jurassic; 152–145 Ma) Hith Formation (Alsharhan and Nairn, 1997;
Al-Husseini, 2009).
This closely packed layercake stratigraphy with source and
reservoir rocks sealed upsection with anhydrites makes Ghawar
and similar supergiant oil fields of the Persian Gulf a dreamland
for oil exploitation essentially because it minimizes the variables
associated with oil maturation and migration that are by far the
most difficult to forecast in oil assessment protocols. At the same
time, these hydrocarbon provinces constitute a paleogeographic
conundrum. Organic matter that eventually transforms into oil
and gas with burial and maturation can originate in abundance
in sedimentary basins along the Intertropical Convergence Zone
(ITCZ), which straddles about ±5° from the equator (Manabe and
Bryan, 1985; Kent and Muttoni, 2013; McGee et al., 2014) due to
high levels of nutrients upwelled from deep waters or in run-off
from adjoining continents onto shelf areas. And indeed,
GSA Today, v. 26, no. 12, doi: 10.1130/GSATG289A.1.
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protracted residence along the equator is the commonly accepted
explanation for the origin of the shelf-facies Jurassic oil in the
Persian Gulf (Al-Awwad and Collins, 2013). However, carbonate
sands for a reservoir and especially an anhydritic seal are more
likely formed at tropical latitudes (~5–30°) where evaporation
exceeds precipitation even under highly variable atmospheric
pCO2 levels (Manabe and Bryan, 1985). So it seems that to form a
winning temporal sequence of source-reservoir-seal rock units,
Arabia (= Persian Gulf region) needs to cross the ITCZ (deposi-
tion of Callovian-Oxfordian source rocks) and into the tropical
arid belt (deposition of Kimmeridgian reservoir and especially
Tithonian seal) in less than 15 m.y. within the Late Jurassic.
Recent research shows the existence of a major event of global
plate (or even whole-mantle) motion during the Jurassic that was
hitherto unknown to the earth science community and can be
referred to as the Jurassic polar shift (Kent and Irving, 2010;
Muttoni et al., 2013; Kent et al., 2015). When the Jurassic polar
shift is taken into account to describe global paleogeography, the
rapid trans-zonal plate motion that produced the source-reser-
voir-seal sequence at Ghawar and elsewhere in the world can be
adequately explained.
JURASSIC POLAR SHIFT
The recent discovery of the Jurassic polar shift was made from
paleomagnetic studies that provide a means to track the motion
of tectonic plates relative to Earth’s spin axis. Under favorable
conditions, the remanent magnetization of rocks records ancient
geomagnetic field directions, which when averaged over several
thousands of years, closely correspond to those of a geocentric
netic directions of similar age from localities on a rigid tectonic
plate should give the same paleomagnetic pole and hence the loca-
tion of that plate with respect to the geographic axis or, equiva-
lently, parallels of latitude. A temporal sequence of paleopoles or
an apparent polar wander (APW) path is a convenient way to
represent the motion of a tectonic plate with respect to the rota-
tion axis (e.g., Creer and Irving, 2012). Relative motions between
tectonic plates (usually their continental proxies) are detected by
systematic differences in their respective APW paths (e.g., Van der
Voo, 1990). It is also possible that Earth’s entire crust and mantle
rotated with respect to the spin axis, a still poorly understood
phenomenon referred to as True Polar Wander (TPW) (e.g.,
Goldreich and Toomre, 1969). In either case—APW or TPW—
the included continents experience an effective rotation about a
Euler pole that involves a systematic change in latitude according
to the GAD hypothesis.
The Jurassic polar shift largely derives from the recognition of a
distinct set of paleomagnetic poles deemed reliable from three