Neil Hodgson

Temporal and spatial evolution of deepwater fold thrust belts: Implications for quantifying strain imbalance

Deepwater fold and thrust belts (DWFTBs) occur in a large number of active and passive continental margins, and their occurrence play an important role in controlling the structural configuration and stratigraphic evolution of margins. Although DWFTBs that are located on passive margins are a coupled system, in which updip extension is linked to downdip contraction, many studies have established a significant imbalance between these two domains in favor of net extensional strain. We have sequentially restored a series of parallel sections from the Orange Basin, South Africa, to quantify the amount of extension and contraction along a single collapse system. We found there to be a constant shortfall in the amount of contraction relative to extension in these features, which allowed us to quantify the lateral compaction of the margin as 5%. We also established a temporal model for the development and growth of thin shale detachment gravity collapse structures on passive margins. This model had implications not only for the kinematic and geometric evolution of these systems but also on the geomechanical process involved, in particular the accommodation of strain through compactional processes rather than discrete faulting.

Interaction of crustal heterogeneity and lithospheric processes in determining passive margin architecture on the southern Namibian margin

Abstract The influence of pre-rift crustal heterogeneity and structure on the evolution of a continental rift and its subsequent passive margin is explored. The absence of thick Aptian salts in the Namibian South Atlantic allows imaging of sufficient resolution to distinguish different pre-rift basement seismic facies. Aspects of the pre-rift basement geometry were characterized and compared with the geometries of the Cretaceous rift basin structure and with subsequent post-rift margin architectural elements. Half-graben depocentres migrated westwards within the continental synrift phase at the same time as basin-bounding faults became established as hard-linked arrays with lengths of c. 100 km. The rift–drift transition phase, marked by seaward-dipping reflectors, gave way to the early post-rift progradation of clastic sediments off the Namibian coast. In the Late Cretaceous, these shelf clastic sediments were much thicker in the south, reflecting the dominance of the newly formed Orange River catchment as the main entry point for sediments on the South African–Namibian margin. Tertiary clastic sediments largely bypassed the pre-existing shelf area, revealing a marked basinwards shift in sedimentation. The thickness of post-rift megasequences does not vary simply according to the location of synrift half-graben and thinned continental crust. Instead, the Namibian margin exemplifies a margin influenced by a complex interplay of crustal thinning, pre-rift basement heterogeneity, volcanic bodies and transient dynamic uplift events on the evolution of lithospheric strain and depositional architecture.

Inversion structures in a foreland domain: Seismic examples from the Italian Adriatic Sea

AbstractPositive structural inversion within foreland domains ahead of thrust belts can create structures with significant hydrocarbon potential in mature and underexplored areas. Within this context, the Adriatic region represents a well-established hydrocarbon province constituting a foreland domain bounded by the Apennines, Southern Alps, and Dinaric fold-and-thrust belts. Newly reprocessed regional 2D seismic data and a renewed exploration interest in the area motivate a reappraisal of the regional structure and stratigraphy of the deformed Central Adriatic region of Italy (i.e., the Mid-Adriatic Ridge). Here, we developed and discussed examples of inversion structures that have different structural styles. The structural interpretations displayed on time-to-depth converted profiles had been validated by 2D structural-kinematic balancing and forward modeling. Our aim was to better define the geometry, style, and timing of the analyzed inversion-related folds. Positive inversion structures appeared loc...

The missing piece of the South Atlantic jigsaw: when continental break-up ignores crustal heterogeneity

Abstract Crustal heterogeneity is considered to play a critical role in the position of continental break-up, yet this can only be demonstrated when a fully constrained pre-break-up configuration of both conjugate margins is achievable. Limitations in our understanding of the pre-break-up crustal structure in the offshore region of many margins preclude this. In the southern South Atlantic, which is an archetypal conjugate margin, this can be achieved because of the high confidence in plate reconstruction. Prior to addressing the role of crustal heterogeneity, two questions have to be addressed: first, what is the location of the regionally extensive Gondwanan Orogeny that remains enigmatic in the Orange Basin, offshore South Africa; and, second, although it has been established that the Argentinian Colorado rift basin has an east–west trend perpendicular to the Orange Basin and Atlantic spreading, where is the western continuation of this east–west trend? We present here a revised structural model for the southern South Atlantic by identifying the South African fold belt offshore. The fold belt trend changes from north–south to east–west offshore and correlates directly with the restored Colorado Basin. The Colorado–Orange rifts form a tripartite system with the Namibian Gariep Belt, which we call the Garies Triple Junction. All three rift branches were active during the break-up of Gondwana, but during the Atlantic rift phase the Colorado Basin failed while the other two branches continued to rift, defining the present day location of the South Atlantic. In addressing these two outstanding questions, this study challenges the premise that crustal heterogeneity controls the position of continental break-up because seafloor spreading demonstrably cross-cuts the pre-existing crustal heterogeneity. Furthermore, we highlight the importance of differentiating between early rift evolution and subsequent rifting that occurs immediately prior to seafloor spreading.

Exploration revival from multi-vintage diverse source dataset - bay of Biscay

Introduction It is now commonly accepted that the only way to unlock new hydrocarbon provinces is by investing in modern methods of seismic acquisition and processing. However, new data is not always available and in some areas may be prohibitively difficult to acquire. Fortunately the legacy of seismic acquisition over the last 50 years provides a resource base we can re-examine. Data that is often forgotten and overlooked can be re-processed using modern techniques to provide new insight into frontier geology.