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The morphology of a river and its channel belt is in part the product of ecological, hydrological and tectonic processes shaping the terrestrial landscape. River morphology is critical for understanding their physical evolution through time, and in predicting the future behavior of rivers and floods. To date, there is no global-scale, quantitative study of the morphology of rivers and their channel belt deposits. Based on a pattern recognition algorithm, we can calculate that the global surface area of channel belts, at an approximate 1 km resolution, is estimated at 30.5 x 105 km2, seven times larger than the extent of river channels. We find that 52% of river channels have a more braided planform morphology with the remaining 48% being more meandering. The new global river morphology (GRM) map and datasets allows new ways to study river morphology and to improve analysis of flood mitigation, freshwater resources management, and ecosystem accounting.

The growth of faults and folds in basins formed under transtension has been less studied than that in their extensional counterparts. In this study, we capitalize on 3D seismic reflection data to investigate the evolution of faults and folds that evolved coevally during suborthogonal partitioned extension and shortening, respectively, in the Sørvestsnaget Basin, Western Barents Sea. We use quantitative techniques to constrain the distribution of normal fault throw, shortening accommodated by folds and thrusts, and stratigraphic thickness variations, to analyse the relative temporal and spatial evolution of faults and folds. Our results show that normal faults display a similar evolution to those occurring in extensional basins, where they grew by lateral- and dip-linkage of individual fault segments as well as upward propagation. Notably, we show that shortening-related fold growth affected the fault growth patterns, skewing their throw distributions, and shifting the location of accommodation away from the evolving folds. Thus, fold amplification caused lateral migration of normal fault hanging-wall depocentres. Our results shed new light on fault-and-fold growth processes in transtensional basins and contribute to an improved understanding of the structural evolution of basins forming along sheared continental margins, which has economic implications for sheared-margin basins targeted for hydrocarbon exploration.

Some potentially attractive reservoirs, containing anomalously thick (10s to a few 100 m), cross-stratified sandstone, have been locally encountered within both the classic regressive (lower Brent) and the transgressive (upper Brent) segments of the Brent Delta. Three documented cases of these sandstone bodies are re-examined. They are internally dominated by simple or compound dunes, and typified by two types of deepening-upward succession, recording a retrogradational or transgressive shoreline history. Type I is expressed as a single estuarine succession changing upwards from erosive, coarse-grained channelized deposits into outer estuary tidal bar deposits. The estuary is underlain and overlain by deltaic deposits. Type II lacks significant basal river deposits but is composed by stacked mixed-energy and tide-dominated estuarine deposits. It is underlain by deltaic deposits and overlain by open marine sediments. Considering the structural evolution in the northern North Sea basin, we suggest (as did some earlier researchers) that these sandstone bodies were local, but sometimes broad transgressive estuaries, formed at any time during large-scale Brent Delta growth and decay. The estuary generation was likely triggered by fluvial incision coupled with active faulting, producing variable accommodation embayments, where tidal currents became focused and deposition became transgressive. The spatial variations of the interpreted estuary deposits were linked with variable, fault-generated accommodation. The relatively simple, lower Brent estuarine units were created by short-lived, fault activity in places, whereas the complex, stacked upper-Brent estuarine units were likely a result of more long-lived, punctuated fault-induced subsidence leading into the northern North Sea main rifting stage. The thick cross-stratified units potentially accumulated in the hangingwall of large bounding faults.

Spatio-temporal analysis of basins formed along sheared margins has received much less attention than those formed along orthogonally extended margins. Knowledge about the structural evolution of such basins is important for petroleum exploration but there has been a lack of studies that document these based on 3D seismic reflection data. In this study, we demonstrate how partitioning of strain during deformation of the central and southern part of the Sørvestsnaget Basin along the Senja Shear Margin, Norwegian Barents Sea, facilitated coeval shortening and extension. This is achieved through quantitative analysis of syn-kinematic growth strata using 3D seismic data. Our results show that during Cenozoic extensional faulting, folds and thrusts developed coevally and orthogonal to sub-orthogonal to normal faults. We attribute this strain partitioning to be a result of the right-lateral oblique plate motions along the margin. Rotation of fold hinge-lines and indications of hinge-parallel extension indicate that the dominating deformation mechanism in the central and southern Sørvestsnaget Basin during opening along the Senja Shear Margin was transtensional. We also argue that interpretation of shortening structures attributed to inversion along the margin should consider that partitioning of strain may result in shortening structures that are coeval with extensional faults and not a result of a separate compressional phase. publishedVersion

Detailed observations on the Rannoch Formation in several deep Viking Graben wells indicate that the ‘classical’ wave-dominated Brent delta-front shows coupled storm–tide processes. The tidal signals are of three types: I): alternations of thick cross-laminated sandstone and thin mud-draped sandstone, whereby double mud drapes are prominent but discretely distributed, II): a few tidal bundles within bottomsets and foresets of up to 10 cm-thick sets cross-strata, and III): dm-thick heterolithic lamination showing multiple, well-organized sand–mud couplets. During progradation of the Brent Delta, the Rannoch shoreline system passed upward from 1) a succession dominated by clean-water, storm-event sets and cosets frequently and preferentially interbedded with type I tidal beds, and occasional types II and III tidal deposits, toward 2) very clean storm-event beds less frequently separated by types II and III tidal beds, and then into 3) a thin interval showing muddier storm-event beds mainly alternating with type II tidal beds. It is likely that those variations in preservation bias of storm and tidal beds in each facies succession result from combined effects of 1) the frequency and duration of storms; 2) river discharge; and 3) the absolute and relative strength of tides. Tidal deposits are interpreted as inter-storm, fair-weather deposits, occurred preferentially in longer intermittent fair-weather condition and periods of lower river discharge, and well-pronounced in the distal-reach of delta-front. The formation and preservation of tidal signals between storm beds, indicate that the studied Rannoch Formation was most likely a storm-dominated, tide-influenced delta front 1) near the mouth of a large Brent river, where a significant tidal prism and high tidal range might be expected, and 2) in a setting where there were relatively high sedimentation rates associated with high local subsidence rates, so that the storm waves did not completely rework the inter-storm deposits. The documentation of the unconventional Rannoch Formation contributes to our understanding of mixed-energy coastal systems.

The evolution of depositional systems in multiphase rifts is influenced by the selective reactivation of faults between subsequent rift phases. The Middle Jurassic to Palaeocene tectonic history of the Lofoten margin, a segment of the North Atlantic rift system, is characterised by three distinct rift phases separated by long (>20 Myr) inter-rift periods. The initial rift phase comprised a distinct fault initiation and linkage stage, whereas the later rift phases were characterised by selective reactivation of previously linked through-going faults which resulted in immediate rift climax. Using 2-D and 3-D seismic reflection data in conjunction with shallow core data we present a 100 Myr record of shallow to deep marine depositional environments that includes deltaic clinoform packages, slope aprons and turbidite fans. The rapid re-establishment of major faults during the later rift phases impacts on drainage systems and sediment supply. Firstly, the immediate localisation of strain and accumulation of displacement on few faults results in pronounced footwall uplift and possible fault block rotation along those faults, which makes it more likely for any antecedent fault-transverse depositional systems to become reversed. Secondly, any antecedent axially-sourced depositional systems that are inherited from the foregoing rift phase(s) are likely to be sustained after reactivation because such axial systems have already been directed around fault tips. Hence, the immediate localisation of strain through selective reactivation in the later rift phases restricts fault-transverse sediment supply more than axial sediment supply, which is likely to be a key aspect of the tectonosedimentary evolution of multiphase rifts.

This case study addresses fault reactivation and linkage between distinct extensional episodes with variable stretching direction. Using 2-D and 3-D seismic reflection data we demonstrate how the Vesterdjupet Fault Zone, one of the basin-bounding normal fault zones of the Lofoten margin (north Norway), evolved over c. 150 Myr as part of the North Atlantic rift. This fault zone is composed of NNE-SSW- and NE-SW-striking segments that exhibit a zigzag geometry. The structure formed during Late Jurassic and Early Cretaceous rifting from selective reactivation and linkage of Triassic faults. A rotation of the overall stress field has previously been invoked to have taken place between the Triassic and Jurassic rift episodes along the Lofoten margin. A comparison to recent physical analogue models of non-coaxial extension reveals that this suggested change in least principal stress for the Lofoten margin may best explain the zigzag-style linkage of the Triassic faults, although alternative models cannot be ruled out. This study underlines the prediction from physical models that the location and orientation of early phase normal faults can play a pivotal role in the evolution of subsequent faults systems in multi-rift systems. acceptedVersion

This study investigates the depositional architecture of turbidite lobes from the Southern Laga Basin (Lower Messinian, Central Apennines) and the external controls on its development. Physical stratigraphy and facies analysis of a 1700 m thick stratigraphic interval enabled us to unravel the hierarchical partitioning of lobes and compare the internal organisation of four units of different age and degree of topographic confinement. A four-fold hierarchy of depositional bodies recording short and long term variations in sediment input to lobes was recognized and includes: i) event beds, composed of sandstone-mud cap couplets deposited by single turbidity currents: ii) single lobes, comprised of few m thick bed sets with variable degree of amalgamation; iii) lobe sets, consisting of few ten of m thick stacks of single lobes that are typically depocentre-wide and iv) lobe complexes, representing high rank units of greater internal complexity. Field mapping of channel-lobe transition sectors and onlap terminations of lobes highlighted a significant stratigraphic change in size and morphology of the receiving basin topography which mainly resulted from sediment filling and onlapping of basinal slopes. The lobe depocentre evolved from an initial funnel-shaped trough of an approximate area of ?150 km2 to a wider morphology reaching a maximum area of over 500 km2, which suggest a notably more confined setting for the two older lobe complexes. Comparison of external shape and internal organisation of lobe sandbodies from the studied complexes points out how this different degree of confinement resulted in development of two main depositional architectures: i) sheet-like confined lobes, comprised of laterally contained sandbodies that in the axial part of the depocentre show flat geometry and little internal variability in facies partitioning and degree of amalgamation and ii) semi-confined lobes with a 'jigsaw' architecture, internally comprised of shingled to compensational patterns of building blocks with lobate to more complex planform and highly variable facies partitioning. The architecture of confined lobes is interpreted as having resulted from flow containment of incoming turbidity currents by lateral basinal slopes and deposition under confined accommodation space whereas that of semi-confined lobes would record deposition from freely expanding turbidity currents in a wider depocentre allowing for lateral migration of depositional lobes. The different architecture of confined vs. semi-confine lobes has important implications for the hydrocarbon industry as it results in significantly dissimilar structures of permeability and connectivity.

Existing facies models of tide-dominated deltas largely omit fine-grained, mud-rich successions. Sedimentary facies and sequence stratigraphic analysis of the exceptionally well-preserved Late Eocene Dir Abu Lifa Member (Western Desert, Egypt) aims to bridge this gap. The succession was deposited in a structurally controlled, shallow, macrotidal embayment and deposition was supplemented by fluvial processes but lacked wave influence. The succession contains two stacked, progradational parasequence sets bounded by regionally extensive flooding surfaces. Within this succession two main genetic elements are identified: non-channelized tidal bars and tidal channels. Non-channelized tidal bars comprise coarsening-upward sandbodies, including large, downcurrent-dipping accretion surfaces, sometimes capped by palaeosols indicating emergence. Tidal channels are preserved as single-storey and multilateral bodies filled by: (i) laterally migrating, elongate tidal bars (inclined heterolithic strata, 5 to 25 m thick); (ii) forward-facing lobate bars (sigmoidal heterolithic strata, up to 10 m thick); (iii) side bars displaying oblique to vertical accretion (4 to 7 m thick); or (iv) vertically-accreting mud (1 to 4 m thick). Palaeocurrent data show that channels were swept by bidirectional tidal currents and typically were mutually evasive. Along-strike variability defines a similar large-scale architecture in both parasequence sets: a deeply scoured channel belt characterized by widespread inclined heterolithic strata is eroded from the parasequence-set top, and flanked by stacked, non-channelized tidal bars and smaller channelized bodies. The tide-dominated delta is characterized by: (i) the regressive stratigraphic context; (ii) net-progradational stratigraphic architecture within the succession; (iii) the absence of upward deepening trends and tidal ravinement surfaces; and (iv) architectural relations that demonstrate contemporaneous tidal distributary channel infill and tidal bar accretion at the delta front. The detailed facies analysis of this fine-grained, tide-dominated deltaic succession expands the range of depositional models available for the evaluation of ancient tidal successions, which are currently biased towards transgressive, valley-confined estuarine and coarser grained deltaic depositional systems.

Predicting the hydrodynamics, morphology and evolution of ancient deltaic successions requires the evaluation of the three-dimensional depositional process regime based on sedimentary facies analysis. This has been applied to a core-based subsurface facies analysis of a mixed-energy, clastic coastal-deltaic succession in the Lower-to-Middle Jurassic of the Halten Terrace, offshore mid-Norway. Three genetically related successions with a total thickness of 100–300 m and a total duration of 12.5 Myr comprising eight facies associations record two initial progradational phases and a final aggradational phase. The progradational phases (I and II) consist of coarsening upward successions that pass from prodelta and offshore mudstones (FA1), through delta front and mouth bar sandstones (FA2) and into erosionally based fluvial- (FA3) and marine-influenced (FA4) channel fills. The two progradational phases are interpreted as fluvial- and wave-dominated, tide-influenced deltas. The aggradational phase (III) consists of distributary channel fills (FA3 and FA4), tide-dominated channels (FA5), intertidal to subtidal heterolithic fine-grained sandstones (FA6) and coals (FA7). The aggradational phase displays more complex facies relationships and a wider range of environments, including (1) mixed tide- and fluvial-dominated, wave-influenced deltas, (2) non-deltaic shorelines (tidal channels, tidal flats and vegetated swamps), and (3) lower shoreface deposits (FA8). The progradational to aggradational evolution of this coastal succession is represented by an overall upward decrease in grain size, decrease in fluvial influence and increase in tidal influence. This evolution is attributed to an allogenic increase in the rate of accommodation space generation relative to sediment supply due to tectonic activity of the rift basin. In addition, during progradation, there was also an autogenic increase in sediment storage on the coastal plain, resulting in a gradual autoretreat of the depositional system. This is manifested in the subsequent aggradation of the system, when coarse-grained sandstones were trapped in proximal locations, while only finer grained sediment reached the coastline, where it was readily reworked by tidal and wave processes.

The facies characteristics and stratigraphic architectures of ancient mixed, wave- and tide-influenced deltas are poorly documented, despite the abundance of analogous modern shorelines. This paper presents the first facies analysis and stratigraphic-architectural characterization of the distal part of the Cretaceous lower Sego Sandstone (Book Cliffs, Colorado, U.S.A.), whose correlative proximal part is arguably the most comprehensively documented example of ancient deltaic strata that exhibit evidence for the activity of tides and waves. The distal lower Sego Sandstone consists of tide-dominated and wave-dominated deposits arranged within four regressive–transgressive tongues bounded by flooding surfaces. The proximal part of each regressive–transgressive tongue contains tide- dominated sandstones that sharply to erosionally overlie, and laterally interfinger with, wave-dominated deposits in the distal part of the tongue. Tide-dominated sandstones are fine to medium grained, and comprise wavy bedded and cross-bedded sandstones with abundant mud drapes, reactivation surfaces, and bidirectional, ebb- and flood-tide-directed paleocurrents. They define active tidal distributary channel-fill and nonchannelized tidal-bar deposits of similar lithologic character, which represent the proximal part of the delta front. Abandoned tidal distributary channel fills comprise intensely bioturbated mudstones. The outer, paleoseaward parts of tidal bars contain direct evidence for mixed tide and wave influence in the form of hummocky cross-stratified, very fine-grained sandstone beds intercalated with cross-bedded, fine- to medium-grained sandstones containing tidal indicators. These deposits locally pass paleoseaward into low-angle and hummocky cross-stratified sandstones with grain size and texture similar to tidal-bar deposits, implying reworking by storm waves. Wave-dominated deposits consist of coarsening-upward successions of mudstone and hummocky cross-stratified sandstone beds that represent the distal part of the delta front. Localized rhythmic variations in the wavelength of hummocky cross-stratification in some deposits may record tidal modulation of water depth and storm-wave velocities. These facies components and their architectural arrangement suggest that tides and waves operated together throughout deposition of the “lower Sego Delta,” but that tide-dominated and wave-dominated deposits were spatially partitioned into the proximal and distal parts of each regressive–transgressive tongue. Thus, tides and waves were effective in transporting and reworking sediment in different water-depth ranges and at different geographic locations. Mixed tide- and wave-influenced deposits are generally preserved only at the down-dip pinchout of regressive–transgressive tongues, because they are removed by tidal scour during delta progradation in more proximal locations. The spatial partitioning of time-equivalent tide-dominated and wave-dominated deposits is readily explained in a single depositional model, which requires the interpretation of neither sequence boundaries nor temporal changes in process regime across the sharp-to-erosional juxtaposition of tide-dominated sandstones above wave-dominated deposits in a regressive–transgressive tongue.

Cyclical alternations of sandstone and mudstone at a variety of length-scales cause significant permeability variations in tidal sandstone reservoirs, which makes them difficult to characterize and model. In this study, the geometry and distribution of small- and intermediate-scale tidal heterogeneities and their influence on fluid flow have been investigated using an outcrop analogue from the Eocene Dir Abu Lifa Member (Western Desert, Egypt). The key challenge in modelling such heterogeneities is to accurately reproduce their three-dimensional architecture. We use a novel, surface-based modeling approach, which honours the geometry of geological surfaces and therefore the contacts between laminae, beds and facies units. The technique used in this study directly reproduces three-dimensional surfaces using a purely geometrical approach. Statistical datasets of the distribution, length and continuity of mud drapes and associated geometrical parameters have been collated from high-resolution outcrop photomontages and associated measurements. The modelling algorithm, in conjunction with the quantitative outcrop data, has been used to generate generic three-dimensional models of heterolithic tidal sand bodies. The models are suitable for direct use in flow simulation studies and are currently being applied to characterize the effective reservoir properties and predict fluid flow behaviour in subsurface tidal sandstone reservoirs.

Marine rift basins represent a continuum ranging from mixed nonmarine/marine through shallow marine to deep marine, or from partly emergent through partly submergent to completely submergent basin types. These rift basin types have strongly variable synrift sedimentary architectures because of temporal changes in relative sea level, accommodation creation, and sediment supply throughout the rift cycle. Accommodation changes are controlled mainly by local basin-floor rotation, basinwide background subsidence, and, to a lesser degree, by eustatic changes. Sediment supply determines how much of the accommodation is filled and in what manner, and is controlled by the distance to the main hinterland areas, and the size and sediment- yield potential of any local fault-block source area. Marine siliciclastic synrift successions, whether dominantly shallow or deep marine in nature, are classified in terms of sediment supply as overfilled, balanced, underfilled, and starved. Sediment-overfilled and sediment-balanced infill types are characterized by a threefold sandstone-mudstone- sandstone synrift sediment-infill motif; the sediment-underfilled type is represented by a two-fold conglomerate-sandstone-mudstone motif; and the sediment-starved type commonly is represented by a one-fold mudstone motif. The sequential development, linked depositional systems, and stratigraphic signatures of the early synrift, the rift climax, and the late synrift to early postrift stages vary significantly between these rift basin infill types, as do the tectonic significance (timing of initiation and duration) of stratal surfaces, such as footwall unconformities, nondepositional hiatuses, and marine condensed sections. The construction of the fourfold rift basin infill classification scheme provides a first basis and a strong tool for predicting the distribution and geometry of synrift reservoir and source rock types, despite the inherent variability of the marine synrift infills.

Numerous authors recognized the importance of variations in stretching rates for basin stratigraphy, and several subdivisions of the rift stage into phases were proposed, based on variations in the rate of extension (e.g. Prosser, 1993; Nottvedt et at., 1995; Ravnas and Bondevik, 1996).

A threefold subdivision of the syn-rift infill of extensional half-grabens, relating distinct lithologies and stratigraphic signatures to the temporal rift development was proposed by Prosser (1993). Subsequently Ravnas and co-workers (1994) have argued that a bipartite subdivision is developed more commonly in underfilled and sediment starved rift-basins. The Jack of late syn-rift sandstone cappings is attributed to low sediment supply despite low rates of tectonic subsidence and rotation. These two models can be seen as end-members in a series of syn-rift architectural patterns present in the middle Jurassic-lowermost Cretaceous of the northern North Sea.

The Mesozoic evolution of the northern North Sea has been subject to a lot of research already, and the general rift-basin development is fairly well known (e.g. Badley et.al., 1988; Gabrielsen et.al., 1990). Two periods of rifting are observed, the first one in the Late Permian and Early Triassic, the second one starting in the Early Bathonian (Late Jurassic). The aim of this study is to increase the understanding of the tectonic history of the Eastern part of the northern Viking Graben, i.e. the Oseberg and Brage area, during and after deposition of the Brent Group sediments. We used a numerical model, describing crustal deformation in a faulted region.

Upper Jurassic marine syn-rift successions from the onshore Lusitanian Basin (Portugal) and Helmsdal Boulder Beds (Scotland) and the offshore Oseberg-Brage, Brae and Visund fields (Viking Graben) have been studied.