Tectonostratigraphic evolution of the Helleh Paleo-high (NW Persian Gulf): Insights from 2D and 3D restoration methods

Abstract

Seismic and well data, restored cross sections and surfaces, as well as non-seismic data were utilized to reconstruct the tectonostratigraphic evolution of the Helleh Paleo-high, a gentle, elongated, N-NE trending structure in the Iranian sector of NW Persian Gulf. Based on Bouguer gravity anomaly and basement depth maps, the southeastern margin of the Helleh Paleo-high is defined by the Bushehr Fault, a NE-SW trending deep-seated fault which contributed to the deposition of thicker late Precambrian-early Cambrian Hormuz Salt to the SE. There is also a significant increase in thickness of the Late Devonian to latest Triassic succession in the southeastern block of this fault, a feature which is interpreted as evidence for syn-depositional fault activity.After a period of relative tectonic quiescence during the Jurassic and Early Cretaceous, the Helleh Paleo-high became emerged and eroded from the Cenomanian to Maastrichtian-early Paleocene. Uplift and erosion continued until the early Miocene, but at lower rates compared to the Late Cretaceous. The repeated reactivations of the Bushehr Fault together with the remobilization of the Hormuz Salt in the core area of the Helleh Paleo-high could have contributed to these phases of amplified erosion.In the early Miocene, the peripheral loading related to the southward advance of the Zagros Fold and Thrust Belt resulted in the establishment of the Zagros foredeep basin. This event exerted a NE downward tilting on the Helleh Paleo-high. The progressive tilting continued during the middle Miocene when the structure attained its maximum extent as a 4-way closure. The latest Miocene- Pleistocene was a critical period in the structural history of the Helleh Paleo-high when the final stage of Zagros foredeep basin evolution tilted the structure to such a degree that all pre-existing structural reliefs in the post- Upper Triassic reservoir units were completely destroyed. In fact, the Helleh Paleo-high is an example of a damaged hydrocarbon trap due to recent tectonic tilting.