Abstract. Inverted structures provide traps for petroleum
exploration, typically four-way structural closures. As to the degree of
inversion, based on a large number of worldwide examples seen in various
basins, the most preferred petroleum exploration targets are mild to
moderate inversion structures, defined by the location of the null points.
In these instances, the closures have a relatively small vertical amplitude but are simple in a map-view sense and well imaged on seismic reflection data.
Also, the closures typically cluster above the extensional depocenters which
tend to contain source rocks providing petroleum charge during and after the
inversion. Cases for strong or total inversion are generally not that common
and typically are not considered as ideal exploration prospects, mostly due
to breaching and seismic imaging challenges associated with the trap(s)
formed early on in the process of inversion. Also, migration may become
tortuous due to the structural complexity or the source rock units may be
uplifted above the hydrocarbon generation window, effectively terminating the
charge once the inversion has occurred. Cases of inversion tectonics can be grouped into two main modes. A structure
develops in Mode I inversion if the syn-rift succession in the preexisting
extensional basin unit is thicker than its post-rift cover including the
pre- and syn-inversion part of it. In contrast, a structure evolves in Mode
II inversion if the opposite syn- versus post-rift sequence thickness ratio
can be observed. These two modes have different impacts on the petroleum
system elements in any given inversion structure. Mode I inversion tends to develop in failed intracontinental rifts and
proximal passive margins, and Mode II structures are associated with back-arc
basins and distal parts of passive margins. For any particular structure the evidence for inversion is typically
provided by subsurface data sets such as reflection seismic and well data.
However, in many cases the deeper segments of the structure are either
poorly imaged by the seismic data and/or have not been penetrated by
exploration wells. In these cases the interpretation in terms of inversion
has to rely on the regional understanding of the basin evolution with
evidence for an early phase of crustal extension by normal faulting.
Referee comments on the paper “Inversion tectonics: a brief petroleum industry perspective” by Gábor Tari et al.
