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deposited as Saudi Arabia rapidly drifted to the arid southern At approximately similar distances from the equatorial Euler GSA TODAY | www.geosociety.org/gsatoday
tropics (Fig. 2). This rapid source-to-seal succession allowed the pole but on the other side of Gondwana, the oil-producing
actual reservoirs to be located in the intervening porous bioclastic Neuqén Basin of Argentina provides an example of a source-reser-
limestones of the Arab Formation (Daraei et al., 2014). Similar voir-seal plate-motion stratigraphy involving transits across the
scenarios can be envisaged for other correlative systems involving boundary between the (austral) temperate humid belt and the
the Tuwaiq-Hanifa sources and Hith anhydrite seal in neigh- tropical arid belt (Fig. 1). There, Early–Middle Jurassic and latest
boring Bahrain, Quatar, and the UAE (Alsharhan and Nairn, Jurassic–earliest Cretaceous marine shale source rocks (Los Molles
1997; Alsharhan and Magara, 1994; Al-Suwaidi et al., 2000), and Vaca Muerta formations) are separated by an intervening evap-
whereas more to the north in central Iran, sedimentation switched oritic unit (Auquilco Formation) of Oxfordian–Kimmeridgian
from mid-latitude coal-bearing to tropical evaporitic during the (Late Jurassic) age, whereas the overlying Cretaceous rocks are
Jurassic polar shift (Mattei et al., 2014). mainly continental (e.g., Howell et al., 2005; Palma et al., 2007;
Boyer et al., 2011). A paleolatitude curve calculated for the Neuqén
The ensuing progression of paleolatitudes after the Jurassic Basin (Fig. 3, upper panel; Table 1) shows that the Neuqén Basin
polar shift that culminated at the 145 Ma cusp shows that Ghawar dwelled at paleolatitudes higher than ~35°S (temperate humid
drifted back, albeit more slowly, across the ITCZ from the arid belt) during practically the entire Mesozoic and Cenozoic except
tropics of the southern hemisphere to the arid tropics of the for a single northward incursion to ~30°S at 145 Ma, the culmi-
northern hemisphere during the Cretaceous–Paleogene (Fig. 2). nating cusp of the Jurassic polar shift. This brief incursion toward
This provided a second time window in the Cretaceous for the a presumably more arid environment broadly coincided (within
formation of oil that is indeed also widespread in the Persian Gulf the error resolution of the available biostratigraphic dating of the
region. For example, most of Iran’s oil reserves situated in the Neuqén Basin sequence) with deposition of the Auquilco evapo-
Persian Gulf (within ~400 km from Ghawar) are also sourced in rites that seal the underlying Los Molles marine shales (Fig. 3,
Cretaceous rocks (e.g., Albian Kazhdumi Formation, Cenomanian upper panel).
Ahmadi Member of the Sarvak Formation, Late Cretaceous Gurpi
Formation; Bordenave and Burwood, 1995; Mashhadi and When our plate-motion stratigraphy operates in reverse
Rabbani, 2015) that formed at or close to the ITCZ and were mode—the transit occurring from the arid tropics into productive
sealed by the Miocene Gachsaran evaporites (Soleimani and equatorial or mid-latitude humid belts—the resulting layercake
Bahadori, 2015). sequence does not conspire positively for sealing oil. In these
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