Basin Research - Volume 25, Issue 5, 2013

In this study, we use seismic reflection, well and core data to investigate the role that basin physiography and sediment routing systems played on the distribution, geometry and stratigraphic architecture of Upper Cretaceous submarine fans (SF) offshore Norway. The Late Cretaceous Møre‐Trøndelag margin of western Norway was characterised by steep submarine slopes (gradient of ~0.3°–3°). Mudstones dominate the Upper Cretaceous slope succession, although a few regionally extensive, sandstone‐dominated units are developed. We focus on the most regionally extensive sandstone unit, which is of Late Turonian‐to‐Early Coniacian age. Mapping and visualisation of 2D and 3D seismic reflection data and analysis of well data indicates that the sandstone unit comprises a total of 11 SF, which were fed by sand‐rich sediment gravity flows routed through multiple upper slope canyons. Based on the internal organisation of seismic facies, four fan types have been identified: (i) Type Ia fans, which are characterised by <10 erosional channel complexes at their bases and aggradational to landward‐stepping lobes in their upper parts; (ii) Type Ib fans, which are characterised by >10 erosional channel complexes at their bases and aggradational to landward‐stepping lobe and mass‐transport deposits near the fan apex in their upper parts; (iii) Type II fans, which are dominated by aggradational lobe deposits; and (iv) Type III fans, which are dominated by a single channel complex that passes downdip into a small terminal lobe. The different fan types are interpreted to reflect variable stratigraphic responses to source proximity and basin physiography, which is principally related to the degree of local fault reactivation and differential compaction. This variability highlights the diversity of fan types that may occur over short distances along continental margins, and demonstrates the importance of local controls in understanding the internal stratigraphic variability that may be present in deep‐marine successions.

The composition, volume and stratigraphic organisation of submarine fan systems deposited along continental margins are expected to reflect the landscape from which the sediment was derived. During the Late Cretaceous, the Møre‐Trøndelag margin, Norwegian North Sea was dominated by the deposition of deep‐marine fines; the emplacement of 11 sand‐rich submarine fan systems occurred only during a c. 3 Myr period in the Turonian‐Coniacian. The systems were fed by sediment that was routed through submarine canyons incised into the basin margin; the canyons are underlain by angular unconformities and are interpreted to have resulted from tectonically induced changes in slope physiography and erosion by gravity flows. The areal extent of the onshore drainage catchments that supplied sediment to the fans has been estimated based on scaling relationships derived from modern source‐to‐sink systems. The results of our study suggest that the Turonian fans were sourced by drainage catchments that were up to ca.3600 km², extending more than ca.100 km inland from the palaeo‐shoreline. The estimated inboard catchment extent correlates with the innermost structures of a large, long‐lived, basement‐involved, normal fault complex. On the basis of our analysis, we conclude that increased sediment supply to the Turonian fan systems reflects tectonic rejuvenation of the landscape, rather than eustatic sea‐level or climate fluctuations. The duration of fan deposition is thus interpreted to reflect the ‘relaxation time’ of the landscape following tectonic perturbation, and fan system retrogradation and abandonment is interpreted to reflect the eventual depletion of the onshore sediment source. We demonstrate that a better understanding of the stratigraphic variability in deepwater depositional systems can be gained by taking a complete source‐to‐sink view of ancient sediment dispersal systems.

Ultra‐large rift basins, which may represent palaeo‐propagating rift tips ahead of continental rupture, provide an opportunity to study the processes that cause continental lithosphere thinning and rupture at an intermediate stage. One such rift basin is the Faroe‐Shetland Basin (FSB) on the north‐east Atlantic margin. To determine the mode and timing of thinning of the FSB, we have quantified apparent upper crustal β‐factors (stretching factors) from fault heaves and apparent whole‐lithosphere β‐factors by flexural backstripping and decompaction. These observations are compared with models of rift basin formation to determine the mode and timing of thinning of the FSB. We find that the Late Jurassic to Late Palaeocene (pre‐Atlantic) history of the FSB can be explained by a Jurassic to Cretaceous depth‐uniform lithosphere thinning event with a β‐factor of ~1.3 followed by a Late Palaeocene transient regional uplift of 450–550 m. However, post‐Palaeocene subsidence in the FSB of more than 1.9 km indicates that a Palaeocene rift with a β‐factor of more than 1.4 occurred, but there is only minor Palaeocene or post‐Palaeocene faulting (upper crustal β‐factors of less than 1.1). The subsidence is too localized within the FSB to be caused by a regional mantle anomaly. To resolve the β‐factor discrepancy, we propose that the lithospheric mantle and lower crust experienced a greater degree of thinning than the upper crust. Syn‐breakup volcanism within the FSB suggests that depth‐dependent thinning was synchronous with continental breakup at the adjacent Faroes and Møre margins. We suggest that depth‐dependent continental lithospheric thinning can result from small‐scale convection that thins the lithosphere along multiple offset axes prior to continental rupture, leaving a failed breakup basin once seafloor spreading begins. This study provides insight into the structure and formation of a generic global class of ultra‐large rift basins formed by failed continental breakup.

The intermontane Quebrada de Humahuaca Basin (Humahuaca Basin) in the Eastern Cordillera of the southern Central Andes of NW Argentina (23°–24°S) records the evolution of a formerly contiguous foreland‐basin setting to an intermontane depositional environment during the late stages of Cenozoic Andean mountain building. This basin has been and continues to be subject to shortening and surface uplift, which has resulted in the establishment of an orographic barrier for easterly sourced moisture‐bearing winds along its eastern margin, followed by leeward aridification. We present new U–Pb zircon ages and palaeocurrent reconstructions suggesting that from at least 6 Ma until 4.2 Ma, the Humahuaca Basin was an integral part of a largely contiguous depositional system that became progressively decoupled from the foreland as deformation migrated eastward. The Humahuaca Basin experienced multiple cycles of severed hydrological conditions and subsequent re‐captured drainage, fluvial connectivity with the foreland and sediment evacuation. Depositional and structural relationships among faults, regional unconformities and deformed landforms reveal a general pattern of intrabasin deformation that appears to be associated with different cycles of alluviation and basin excavation in which deformation is focused on basin‐internal structures during or subsequent to phases of large‐scale sediment removal.

Two end‐member models have been proposed for the Paleogene Andean foreland: a simple W‐E migrating foreland model and a broken‐foreland model. We present new stratigraphic, sedimentological and structural data from the Paleogene Quebrada de los Colorados (QLC) Formation, in the Eastern Cordillera, with which to test these two different models. Basin‐wide unconformities, growthstrata and changes in provenance indicate deposition of the QLC Formation in a tectonically active basin. Both west‐ and east‐vergent structures, rooted in the basement, controlled the deposition and distribution of the QLC Formation from the Middle Eocene to the Early Miocene. The provenance analysis indicates that the main source areas were basement blocks, like the Paleozoic Oire Eruptive Complex, uplifted during Paleogene shortening, and that delimits the eastern boundary of the present‐day intraorogenic Puna plateau. A comparison of the QLC sedimentary basin‐fill pattern with those of adjacent Paleogene basins in the Puna plateau and in the Santa Bárbara System highlights the presence of discrete depozones. These reflect the early compartmentalization of the foreland, rather than a stepwise advance of the deformation front of a thrust belt. The early Tertiary foreland of the southern central Andes is represented by a ca. 250‐km‐wide area comprising several deformation zones (Arizaro, Macón, Copalayo and Calchaquí) in which doubly vergent or asymmetric structures, rooted in the basement, were generated. Hence, classical foreland model is difficult to apply in this Paleogene basin; and our data and interpretation agree with a broken‐foreland model.

In the mid‐Cretaceous Lasarte sub‐basin (LSB) [northeastern Basque‐Cantabrian Basin (BCB)] contemporaneous and syn‐depositional thin‐ and thick‐skinned extensional tectonics occur due to the presence of a ductile detachment layer that decoupled the extension. Despite the interest in extension modes of rift basins bearing intra‐stratal detachment layers, complex cases remain poorly understood. In the LSB, field results based on mapping, stratigraphic, sedimentological and structural data show the relationship between growth strata and tectonic structures. Syn‐depositional extensional listric faults and associated folds and faults have been identified in the supra‐detachment thin‐skinned system. But stratigraphic data also indicate the activation of sub‐detachment thick‐skinned extensional faults coeval with the development of the thin‐skinned system. The tectono‐sedimentary evolution of the LSB, since the Late Aptian until the earliest Late Albian, has been interpreted based on thin‐ and thick‐skinned extensional growth structures, which are fossilized by post‐extensional strata. The development of the thin‐skinned system is attributed to the presence of a ductile detachment layer (Upper Triassic Keuper facies) which decoupled the extension from deeper sub‐detachment basement‐involved faulting under a regional extensional/transtensional regime.