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extent, only a very subdued hairpin around the Jurassic–
Cretaceous boundary. For example, according to paleolatitudes
computed using the widely cited Torsvik et al. (2012) APW path
(Fig. 2, black triangles with vertical error bars across critical
interval 180–150 Ma), Ghawar was located in the center of the
ITCZ only during the Late Triassic and Early Jurassic; a transit
from the oil-generating ITCZ to the seal-generating austral trop-
ical arid belt is evident, but according to their APW path, it would
have occurred in the Early–Middle Jurassic and therefore cannot
readily explain the observed source-to-seal systems of the Persian
Gulf. However, soon afterward in the Cretaceous, paleolatitudes
from virtually all modern APW paths come into close agreement
and can equally explain the Cretaceous source-to-seal oil systems
in the Persian Gulf region (Fig. 2).
Torsvik et al. (2012) recognized that the Jurassic “spike” and
associated features seen in the Kent and Irving (2010) APW path
differ strongly from their and other published APW paths (e.g.,
Besse and Courtillot, 2002). They attributed the differences as
largely an artifact of aliasing from the low number of input poles
deemed reliable by Kent and Irving (2010). We believe that the
retention of often poorly dated (±10 m.y. or more) or otherwise
potentially biased paleomagnetic data, especially of earlier vintage
for which, moreover, no direct assessment of sedimentary inclina-
tion error is available (e.g., Jura Blue Limestone sediments of
Switzerland, Sub-Tatric and Krakow Upland sediments of Poland,
Tunisia Upper Jurassic sediments, Rio Grande do Norte dikes of
Brazil), is likely to attenuate the full expression of important
features of APW, such as the Jurassic polar shift (see Kent and
Irving, 2010, for a discussion).
CONCLUSIONS
In this paper, we show how APW paths based on stricter accep-
tance criteria can lead to an interesting reconciliation between
paleolatitudes, generalized zonal climate belts, and the generation
and sealing of the Late Jurassic Persian Gulf oil. Of course, not all
oil formed and was sealed in the plate-motion–mediated manner
we describe for Ghawar, as a notable example. Other oil systems
like Neuqén and the Gulf of Mexico, where Jurassic latitudinal
changes were smaller, may be controlled by other factors operating
at more local basin scales (orography, coastal upwelling, high
riverine nutrient supply) or more strongly depend on the different
levels of details of the climate models adopted (e.g., Manabe and
Bryan, 1985; Sellwood and Valdes, 2006; Huber and Caballero,
2011). Nevertheless, relevant aspects of the basic zonal climate
model we adopted, which assumes a simple geography and very
different pCO2 levels (Manabe and Bryan, 1985), seems to be
confirmed by more comprehensive analyses of Hadley circulation
showing that since the Last Glacial Maximum, mean ITCZ shifts
are likely to be within 1° latitude from the equator (McGee et al.,
2014). And local basin controls must still operate in the context of
latitudinal-dependent factors that paleomagnetic poles are well-
suited to constrain.
We acknowledge that there could exist specific (and thus inevi-
tably rare) combinations of local variables that could explain the
occurrence of organic matter-rich deposits at tropical latitudes,
where aridity would be normally expected, or marine evaporites on
the equator, where precipitation exceeding evaporation is the (zonal)
norm, but in general, it is hard to deny that the most potent venues
to generate extensive and persistent marine evaporites are the arid
tropics (e.g., present day Red Sea, Abu Dhabi) rather than the humid GSA TODAY | www.geosociety.org/gsatoday
equator. Orography is known to perturb zonal circulation patterns,
but considering the wide spatial distribution and tight temporal
coupling between source and seal rock formation in the Late Jurassic
of the Persian Gulf, one would expect a major orographic perturba-
tion to rise (or disappear) in a few million years, shifting the para-
digm from rapid horizontal plate motion, for which we have direct
paleomagnetic evidence, to rapid vertical crustal motion, for which
there is no evidence at least in the Persian Gulf.
Our plate-motion scenario of the Arabian passive continental
margin (where organic matter could be efficiently buried in sedi-
ments) crossing the ITCZ of high nutrient availability and organic
matter productivity and rapidly drifting into the anhydritic seal-
forming tropics seems to explain some of the key factors that
contributed to the world’s Jurassic hydrocarbon richness, espe-
cially in the Persian Gulf, home of the world’s largest oil field at
Ghawar (Alsharhan and Nairn, 1997; Sorkhabi, 2010). Notably, a
reduced timing between source and seal formation as predicted by
our plate stratigraphy model reduces the uncertainties related to
oil maturation and migration relative to timing of trap formation:
Oil can migrate virtually any time after organic matter deposition
and maturation and still be efficiently trapped by the early-in-
place evaporitic seal lying immediately above.
In conclusion, our plate tectonic model for the genesis and
sealing of Late Jurassic oil, especially in the Persian Gulf, should
be considered a promising first-order model that will require
further tests and elaboration by means of finely dated, global
plate-motion scenarios. These will in turn be obtained by means
of a further improved inventory of well-dated and inclination
flattening-free paleomagnetic data as well as paleoclimate models
of paleogeographies cast in the appropriate latitudinal reference
frame according to the geocentric axial dipole model.
ACKNOWLEDGMENTS
The editor and three anonymous reviewers are thanked for insightful
comments on an earlier version of this manuscript. This is Lamont-Doherty
Earth Observatory contribution #8049.
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