Tectonic Control Research Articles

The southern Wyoming Laramide basin: implications for long-term tectonic control on uplift and subsidence

ABSTRACTAn evolving tectonic setting during the Late Cretaceous and Paleocene drove the dramatic transformation of southern Wyoming from a broad marine shelf setting to a series of lacustrine basins. Early dominant control of depositional patterns by flexural tectonics gave way to control by dynamic topography and Laramide-style deformation. The southern Wyoming region demonstrates how progressive partitioning by Laramide movements exerted increasingly dominant control on regional depositional patterns. It did this by creating a long-lived, Laramide uplift-bounded fluvial catchment and basin largely controlled by Laramide-driven subsidence. The Rock Springs and Rawlins uplifts underpinned the basin and exerted their influence in the subsurface. Episodes of Laramide-driven subsidence produced a series of embayments, including the large Rusty–Allen Ridge embayment and the very large deepwater Lewis embayment. The degree of eustatic control in the region would have been greatest at short time scales in the low coastal–shallow-marine settings, causing shoreline oscillations. Several long transgressive episodes followed relatively punctuated progradational periods of coastal-plain construction when supply was generally high from the thrust belt and surrounding uplifts. Laramide activity in the Paleocene led to enclosure of the fluvial basin and the development of a series of smaller marine embayments that mark the end of influence in the region by open and coastal marine processes.

Morphotectonic and morphostructural investigation in northwestern Minas Gerais State, Brazil: a lineament mapping assessment

This study aimed to investigate whether linear natural features are associated with structural or tectonic control of landforms and current drainage patterns in northwestern Minas Gerais State (Southeastern Brazil). To answer this question, more than 1,700 lineaments were manually mapped in a broader area encompassing the Paracatu and Urucuia River catchments. One satellite image scene (Operational Land Imager/Landsat-8), three different digital elevation models (Shuttle Radar Topography Mission, Advanced Spaceborne Thermal Emission and Reflection Radiometer-Global digital elevation model, and Advanced Land Observing Satellite-Phased Array L-band Synthetic Aperture Radar), and digitised analogical maps (geologic and topographic maps) were used to draw linear geometric features representing the lineament population. The resulting vector databases were integrated in a Geographic Information System for quantitative and spatial analyses, which resulted in two main trending lineament sets: NNW-SSE and NE-SW. Subsequent field assessments revealed that numerous lineaments from the first set were correlated to the formerly Upper Precambrian reverse and strike-slip faults. The second set were correlated to NE-SW normal faults derived from the Mesozoic-Cenozoic tectonic event following the breakup of Gondwana. These datasets contribute to a better understanding of the regional-, sub-regional-, and catchment-scale features underlying the structural control of the drainage network arrangement and pattern, which present long straight channels and are interrupted by anomalous and prominent bends that strictly fit major structural directions.

Morphology, seismic stratigraphy, and tectonic control of the Yitong submarine canyons – fan apron system in the northern South China Sea

Submarine fans are ubiquitous in modern deep-water environments. Such systems reported in the literature are largely fed by shelf-indented canyons receiving ample fluvial or longshore drift sediment inputs, whereas those nourished by slope-confined canyons far away from terrigenous sediment sources remain poorly understood. Herein, we report such a system, the Yitong submarine canyons – fan apron system (YCFS), from the northern South China Sea. This system was studied using multibeam bathymetric and two-dimensional multichannel seismic data, combined with geological constraints from nearby International Ocean Discovery Program drilling sites. YCFS consists of approximately 12 submarine canyons confined in the lower continental slope of >1200 m water depth, which feed a fan apron in the connecting abyssal plain. The canyons are erosion-dominated, as evidenced by their V-shaped cross-sections with up to 708 m deep incisions. Canyon infillings comprise mass transport deposits and turbidites, and interfluves exhibit features such as landslides, creep-typed sediment waves, and gullies, indicating the canyons and interfluves are dominated by mass transport and turbidity-current processes. The fan apron is generally depositional, in which channels and channel-levee complexes, turbidite lobes, and mass transport deposits comprise the main depositional elements. In the canyon-to-fan transitions, supercritical turbidity current features and bedforms, including plunge pools and connected sediment mounds, cyclic steps, and antidunes, are developed, which are linked to the deceleration and hydraulic-jump effects of the high-velocity turbidity currents shedding off the canyons. Seismic stratigraphic analysis revealed that YCFS was initiated in Late Miocene. The formation and maintenance of YCFS are linked to the long-term existence of an upslope margin-parallel basement high. The latter could have maintained a steep slope condition (up to 6.5°) that favors the development of canyons and supercritical turbidity currents. Because of the blocking effect of the basement high, YCFS receives limited supply of the shallow-water sediments.

Facies character and evolution of a mixed carbonate–siliciclastic shelf: Upper Triassic–Lower Jurassic succession in the eastern Northern Calcareous Alps (Stumpfmauer, Austria)

Western Tethys sedimentary successions constitute fundamental archives of Late Triassic–Early Jurassic environmental, carbonate production and tectonic changes. During the Late Triassic, the Northern Calcareous Alps (Austria) belonged to the Western Tethys passive margin, characterised by the deposition of the early-dolomitized peritidal Hauptdolomit (Norian) adjacent basinward to the Dachstein carbonate shelf and passing upward to the mixed carbonate–siliciclastic Kössen Formation (Upper Norian–Rhaetian). The Kössen Fm. was subdivided into the lower shallow-water Hochalm Member and the upper Eiberg Member, accumulated in an intraplatform basin coeval to shallow-water carbonates (Upper Rhaetian Limestone). The Eiberg Mb. and overlying Jurassic strata were extensively studied as a continuous marine record across the Triassic/Jurassic boundary. In contrast, shallow-water successions, time-equivalent to the Eiberg Mb. and Upper Rhaetian Limestone, located North of the Eiberg Basin, are poorly investigated. This study focusses on the approximately 350 m thick Norian to Lower Jurassic succession cropping out in the eastern Northern Calcareous Alps (Stumpfmauer). The 32 distinguished lithofacies compose seven, vertically superimposed, sedimentary units (A–G), belonging to the Hochalm Mb. of the Kössen Fm. (Unit A peritidal cyclothems, Unit B claystone/marlstone with fossiliferous beds, Unit C coral boundstone to floatstone), Upper Rhaetian Limestone (Unit D subtidal cyclothems with claystone), shallow-water carbonate strata transitional to Lower Jurassic (Unit E ooidal coated grain peloidal grainstone with basal transgressive lag, Unit F bivalve-rich, microbialite and oncoidal lithofacies, previously attributed to the Upper Rhaetian Limestone) and Hettangian–Sinemurian Kalksburg Fm. (Unit G cross-laminated coated grain peloidal grainstone with quartz and chert). The detailed lithofacies characterisation presented in this study contributes to the knowledge on the Northern Calcareous Alps stratigraphy and depositional environments across the Triassic/Jurassic boundary. The identified sedimentary units can be framed in the evolution of Western Tethys and share similarities with depositional systems from the Western Carpathians, Transdanubian Range, Southern Alps and Dinarides suggesting coherent sedimentary response and environmental, climate and tectonic controls in different palaeogeographic domains.

The control of collisional tectonics over valley morphology: the case of the largest glacier in the European Alps

AbstractUnderstanding how bedrock properties influence the valley‐forming processes of Alpine landscapes is an outstanding challenge. A multi‐methodological approach was used to uniformly quantify fault frequency, orientation, and rock hardness of crystalline basement rocks to evaluate their impact on the erosional processes that shaped the valley of the Aletsch Glacier, Switzerland. We show how variations in fault frequency and orientations, imposed by the inherited collisional framework of the area, controls the local erodibility of the valley, affecting both hillslopes and channel erosion processes. Our results highlight how tectonic preconditioning exerts a first‐order control on the efficiency of erosion in the mountain chain, elucidating an integral link between deep‐seated collisional dynamics and surface‐based mountain shaping. Moreover, our results express the importance of a uniform, quantitative characterization of bedrock properties to comprehend the interaction and variability of erosional processes and hazards distributed within the valley systems.

Tectonic controls on the ecosystem of the Mara River basin, East Africa, from geomorphological and spectral index analysis

Abstract. Tectonic activity impacts the environment; therefore, identifying the influence of active faulting on environmental factors, such as soil development and vegetation growth patterns, is valuable in better understanding ecosystem functions. Here, we illustrate how tectonic activity and the lithology of bedrock influence temporal and spatial patterns of vegetation and soil parameters in a fault-controlled river basin. The Mara River basin lies in a region of previously unrecognised active normal faulting, dominated by the Utimbara and Isuria faults, resulting in areas of relative uplift, subsidence and tilting. Faulting leads to spatially variable erosion and soil formation rates as well as disruption and modification of drainage systems. On a small scale, steep escarpments cast shade and provide shelter. All of these factors might be expected to exert controls on ecosystem dynamics on a range of lengths and timescales. Here, we investigate tectonic controls on ecological processes in the Mara River basin using TanDEM-X and Sentinel-2 data. We use high-resolution digital elevation models (DEMs) to map the Utimbara and Isuria faults and to measure the height of the escarpments (up to 400 m) along the length of the faults. Total fault offset can be estimated by correlating Neogene phonolite lavas (thought to be 3.5–4.5 Myr old) on either side of the faults. If the age is correct, slip rates can be estimated to be on the order of 0.1 mm yr−1. Analysis of DEMs also reveals the presence of recent earthquake scarps in the hanging-wall sediments of the main faults and extensive alluvial fan formation on the hanging wall. Low mountain front sinuosity values and the presence of steep escarpments also suggest recent activity. Drainage is displaced across the fault traces, and, in one area, it is possible to map the lateral channel migration of the Mara River due to hanging-wall tilting. We used a 5-year normalised difference vegetation index (NDVI) time series, the clay mineral ratio (CMR) and a moisture stress index (MSI) to investigate spatiotemporal vegetation patterns and soil formation. Whilst lithology does exert some control, as expected, we observed that the downthrown hanging wall of the faults, especially directly adjacent to the escarpment, is consistently associated with a higher degree of vegetation, wetland formation and clay distribution. Analysis of spectral indices shows that the overall spatial pattern of vegetation cover is seasonally low in the flat plains and perennially high in the vicinity of more complex, tectonically influenced structures. The NDVI highlights several locations with permanently healthy vegetation along the escarpment which extend downslope for several kilometres. Our study shows that in the Mara River basin, active normal faulting is an important stabiliser of vegetation growth patterns, likely caused by favourable hydrological and pedological conditions along the escarpments; tectonic activity has a direct beneficial influence on ecological processes in this climatically sensitive region.

Controls on evaporite facies distribution during the early phases of the Zechstein Basin development (Zechstein 1, Upper Permian): Implications from the marginal part of the basin in SW Poland

Amongst the least understood issues in the giant evaporite basin evolution is their early development. Here, we use a unique set of archival data from the Fore-Sudetic Homocline in SW Poland to investigate the controls on evaporite facies distribution in the marginal part of the Zechstein Basin after the Zechstein Sea transgression (Upper Permian, Z1 cycle). Based on integrated data from boreholes, subsurface mining survey and seismic profiling we constructed a 3D structural model, which showed that the carbonate, sulphate and chloride facies boundaries originally extended W–E, irrespective of the fault patterns in the basement. The thickness distribution for the Zechstein Limestone (Ca1), Lower Anhydrite (A1d) and Upper Anhydrite (A1g) evidences carbonate and sulphate platform development in respective evaporitic phases. Although the sea bathymetry and progressive seawater evaporation were the main factors responsible for the northward progradation of the evaporite facies, the relief over the sulphate platforms implies a significant influence of sea currents on the sulphate deposition. The channelised circulation of variably saturated seawater decreased the overall accumulation rate in the channels and promoted the high-and-trough topography development over the platforms. The Upper Anhydrite (A1d) top relief was evened by the Oldest Halite (Na1) rocksalt deposition. Prior to the Zechstein Limestone (Ca1) deposition, the distribution of clastic facies was mostly restrained by the dune relief inherited after the aeolian sedimentation in the Rotliegend. This old relief partly influenced also the Zechstein Limestone (Ca1) carbonate thickness and subfacies distribution and was eventually buried by the Lower Anhydrite (A1d) sulphates. There is no evidence on tectonic controls on evaporite depositional patterns throughout the Z1 cycle in the studied area.

Fault-controlled barite veins of the eastern Anti-Atlas (Ougnat, Morocco), a far-field effect of the Central Atlantic opening? Structural analysis and metallogenic implications

Tectonic and micro-tectonic studies at different scales are of primary importance in a modern metallogenic investigation. In the Ougnat massif of the eastern Anti-Atlas belt (Morocco), the barite ore deposit is hosted within mafic to felsic rocks of the Ediacaran Saghro and Ouarzazate groups together with their folded Paleozoic cover. Here, we provide for the first time new field-based data on the tectonic control of barite mineralization, and their relation with regional tectonic events. The mineralization occurs in brittle-ductile structures as a vein-type system, mainly hosted within NE-SW to E-W and NW-SE strike-slip-normal faults. Economic orebodies spread frequently along the Precambrian-Cambrian contact zone thus acting as open conduits for mineralized fluid flow. The geometry of hosted barite sigmoidal lenses corresponds to “pull-apart” or “tension gashes” openings, commonly arranged en echelon arrays along the bearing transcrustal faults. The occurrence of predominant massive and breccia internal texture implies a tectonic-mineralizing collapse process in an extensional tectonic context. Kinematic pattern, directional distribution and host-rock age relationship point to a syntectonic barite control probably occurred during the NW-SE Atlantic rifting, as already attributed to similar deposits in the neighboring Ougarta and Atlas-Meseta domains.The barite ore is quantitatively and qualitatively more preserved in competent host rocks than those with ductile behavior, thus offering a useful hint for further barite exploration in this part of the Anti-Atlas fold and thrust belt.

Orogens and detritus: unravelling the Mesoproterozoic tectonic geography of northern Australia through coupled detrital thermo- and geo-chronometers

This study presents detrital muscovite 40Ar/39Ar data from the Mesoproterozoic Roper Group and overlying informally named successions, in the Beetaloo Sub-basin, northern Australia. Detrital muscovite chronology reveals tectono-thermal processes within source regions and provides new constraints on the basin provenance, revising previous interpretations based on detrital zircon data. Detrital thermo- and geochronology, together demonstrate three main periods when the basin paleogeography was altered that correspond to the evolving tectonic history of the North Australia Craton (NAC) through the Mesoproterozoic. The first is characterised by an increased sediment contribution from source regions that lay along the eastern margin of Proterozoic Australia. These source regions are interpreted to have formed the uplifted rift-shoulders between Proterozoic Australia and Laurentia at ca 1.45 Ga. After that, sediments derived from eastern Proterozoic Australia sources become less voluminous up-section. The youngest analysed formation from the Roper Group, the Kyalla Formation, was predominately from sources to the south of the basin, representing another modification of basin geography. This is interpreted to result from the closure/subduction of the Mirning Ocean as the West Australian Craton (WAC) approached and collided with the NAC, resulting in an uplift of the southern margin of the NAC, at ca 1.35–1.31 Ga. The uppermost Mesoproterozoic to lower Neoproterozoic sandstone successions that overlie the Roper Group were derived from the Musgrave Province. Coupled detrital zircon and muscovite data imply a rapid cooling at ca 1.20–1.15 Ga that is interpreted to reflect syn-orogenic exhumation during the Musgrave Orogeny. Furthermore, data from the Beetaloo Sub-basin suggest that the changed basin tectonic settings reshaped basin geography and result in distinctive detrital zircon and muscovite geochronology records. In this study, we used the detrital U–Pb zircon and muscovite 40Ar/39Ar age data from the Beetaloo Sub-basin and a range of other basins deposited in different tectonic environments, including the convergent, collisional and extensional settings, to reconstruct the basin tectonic geography and illustrate various tectonic controls on basin formation in different tectonic backgrounds. KEY POINTS Detrital muscovite 40Ar/39Ar data provide thermochronological constraints on basin provenance, complementing previous interpretations based on detrital zircon data. Spatial and temporal variation of provenance reconstructs the basin tectonic geography, reflecting the Mesoproterozoic tectonic history of the North Australia Craton. Coupled thermo- and geochronology constrain tectonic settings of basin deposition.

Chapter 2. Sequence stratigraphic concepts and methodologies

Abstract This chapter reviews sequence stratigraphic concepts and methodologies and presents an approach that is most applicable to the North Sea Jurassic, based on the concept of genetic sequence stratigraphy. The concept of depositional sequences, comprising rock units bounded by unconformities, has been developed from the late nineteenth century up to the present day. Many different studies have been carried out on North Sea Jurassic sequence stratigraphy, from the early 1980s to the present day and involving a range of different approaches. Many authors have adopted the J sequence approach that was first published in the early 1990s; however, a number of alternative North Sea Jurassic sequence schemes have also been described. A close relationship existed between tectonics and sequence boundary development, particularly during the Middle–Late Jurassic in the North Sea region. Several of the major unconformities that are known to be of regional extent can be directly related to significant tectonic phases. Other sequence boundaries, for which a tectonic control is not evident, for example, particularly in the Early Jurassic, were potentially driven by glacio-eustatic cycles, which may have been controlled by orbital forcing cycles.

Chapter 8. Controls on North Sea Jurassic–lowermost Cretaceous sequence development

Abstract Of 40 recognized Jurassic–earliest Cretaceous sequence boundaries or surfaces, 21 are considered to have had a primary tectonic control on their generation, particularly during the Bathonian–Berriasian interval of synrift-dominated tectonism. These boundaries include the intra-J22 sequence boundary, the base J36, the base J54, the base J55, the intra-J56 transgressive surface, the base J62, the base J63, the base J64, the base J71, the base J73 and the top J76 (‘Base Cretaceous’). In the study area, these events all occurred within a marine setting and none can be unequivocally matched to times of subaerial exposure or coastal onlap. Ten Jurassic sequence surfaces appear to have had a primary eustatic control on their generation, some of which are also associated with the deposition of major marine source-rock facies, including the base J18 and the base J74.

Miocene to Quaternary geodynamic evolution of the southern section of the Burdur-Fethiye Shear Zone and its offshore continuation, eastern Mediterranean

The main interrelated structures of the eastern Mediterranean are shaped by the complex tectonic regimes including active subduction, uplift, and progressive counterclockwise rotation. The Hellenic Arc, the Anaximander Mountains, the Western Taurides, the extensional western Anatolian graben, the Burdur-Fethiye Shear Zone and the Rhodes Basin are these structures located in one of the most tectonically active regions. The Burdur-Fethiye Shear Zone is a 75- to 90- km wide and 300-km-long transtensional left-lateral shear zone developed during the formation of the Aegean back-arc extensional system and the thrusting of Western Taurides. In this study, fault kinematic analysis, and DEM and earthquake data characterize the tectonic controls of the southern section of the Burdur-Fethiye Shear Zone. The high-quality multibeam bathymetry data, their processing and interpretation with the onshore structures and an integrated interpretation with multichannel seismic profiles allowed the geodynamic evolution of the Burdur-Fethiye Shear Zone, Rhodes Basin and environs to be evaluated. Despite the heated debates regarding the presence of the zone, the latest offshore data reveals again that the continuation of the subduction transform edge propagator (STEP) fault between the Hellenic and Cyprus arcs comes into play as the Burdur-Fethiye Shear Zone on land.

Island formation adjacent to a large-scale slope failure in Central Peru: The Nazca Ridge subducted relief hypothesis

Vertical tectonics and mass wasting activity along convergent margins are geodynamic processes commonly associated with the subduction of oceanic plate structures. At the Central Peruvian margin, the connection of the small Hormigas de Afuera Islands (HAI) (12°S) with a large-scale slope failure suggests the surficial expression of the subducted relief of the Nazca Ridge. This hypothesis is supported by the idea that the Tuamotu Ridge relief on the Pacific Plate is the analog of the subducted roughness of the Nazca Ridge based on their mirror-image location relative to the East Pacific Rise. Here, we use bathymetry, multichannel seismic data, subbottom profiling data and published findings to analyze the massive slope collapse near the HAI. At the shelf break, the HAI reflect uplift of the metamorphic basement and mark a N-S transition between post-Pliocene onlapping sediments and seafloor erosion of an uplifted, tectonically deformed sequence. W of the shelf break, the HAI scar is a trench-parallel, two-horseshoe-shaped escarpment in the upper slope (1300 m high and 1690 km2 area) that has lost mass with a total volume of 810 km3. Within this large escarpment, two cliffs show differences in size, seafloor morphology, and basement uplift. An embayment at the base of the HAI scar aligns with a downslope mass of 285 km3 volume in the middle slope. A bathymetric bulge of 800 m height characterizes the toe of this mass deposit. When the HAI are projected onto the Tuamotu Ridge northeastern flank, a seamount-shaped platform-like feature of 12,000 km3 is found. Our study area coincides with the well-known and highly coupled segment of the Central Peru subduction, which suggests an association with the history of large megathrust earthquakes in this area such as the great 1746 MW 8.8 Callao-Lima earthquake. Based on these findings, we postulate that the formation and spatial association of the small HAI with the HAI mass wasting result from the tectonic control imposed by the subducted roughness of the Nazca Ridge.

New constraints on the Messinian salinity crisis from the north-eastern Ibiza island event records

In order to better constrain the chronology of the Messinian Salinity Crisis (MSC) onland and to provide new observations on the stratigraphic position of the Messinian erosional surface as well as evidence for continentalization, we have studied the Mio-Pleistocene succession of the island of Ibiza, ideally located in a strategic position between the peripheral Messinian basins of south-eastern Spain and the MSC-related gypsum of the Palma Basin (Mallorca).Five lithological units are identified and compared with those known from the island of Mallorca. The equivalent of the “reef” unit, mainly Tortonian in age, is composed of median to inner ramp facies. It is overlain by coastal alluvial fans set up under extensive tectonic control, and then by a carbonate unit rich in oolites and microbialites attributed to the Terminal Carbonate Complex (TCC) of Messinian age. The overlying red clays fossilizing paleosols express a continentalization phase at the end of the Miocene. This regressive episode is evidenced by karstification and erosion incising the pre-crisis units and shaping valleys connected to submarine canyons. The erosion surface is linked to the acme of the MSC, a major sea-level fall, and is then sealed by Pliocene coastal calcarenites or by Pleistocene eolianites. The emptying of the basin led to a global collapse, which is recorded on all the slope domains of the Mediterranean margins. We document this collapse for the first time onland by syn-MSC gravity events such as mudflows, upwelling of geothermal fluids under pressure and soft deformation of the TCC. The interweaving of these phenomena of multiple origin (baselevel decrease, climate change, geothermal activity, sediment transfer) contributes to the onland/offshore reshaping of the Mediterranean margins during the major environmental changes of the Messinian salinity crisis.

Earth observation approach for targeting stratiform deposit of manganese in central India

The stratiform manganese deposits, hosted within the Sausar Group of rocks, in Madhya Pradesh state of India, has undergone polyphase deformation and metamorphism. The region is an enterprising geosite to understand the lithological and tectonic control on manganese mineralization. We have carried out a conjugate remote sensing based analysis using Visible, Near Infrared and Short Wave Infrared bands (VIS-NIR-SWIR) of optical imagery from multiple sensors supplemented with analysis of L-band microwave data over the Balaghat district of Madhya Pradesh to delineate prospective areas for manganese exploration, supported by the lab and field-based evidence.The enhanced image products (i.e.band ratios, principal components) and spectral anomaly map derived from Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) and Sentinel-2B multispectral bands are used to delineate the lithological contrast of the host rock and indicate key locales of mineralization. The geological structures interpreted using the merged product of Advanced Land Observation Satellite Phased Array L-band SAR (ALOS PALSAR −1), Landsat 8 PC bands (2 & 3) and the processed Horizontal Gradient Magnitude (HGM) from advanced satellite gravity model (EIGEN-6C4), illustrates the structural control on the mineralization. The petrological details derived from the host rock samples shows microstructures like micro-folding, foliations, quartz grain elongation etc., thus representing the microscale deformations within the rock units occurring in the area.The lab-based spectral signatures of manganese-bearing host rock was resampled to image spectra and spectral anomaly map using ConstrainedEnergyMinimization(CEM), which shows good correlation with the existing mine locations.The information from remote sensing and lab analysis has been integrated thematically using the knowledge-based Weighted Sum Method (WSM) with existing mine locations as the training dataset. The derived mineral prospect map indicates several new areas of manganese prospectivity which can serve as a guide for detailed future explorations in the region .

Tectonostratigraphic analysis of the syn-rift infill in the Drava Basin, southwestern Pannonian Basin System

The Drava Basin in the SW Pannonian Basin System (PBS) was initially formed by passive rifting with accompanying sedimentary infill. Although this has been the subject of much previous work, an account of tectonic control has been lacking. Based on cores, wire logging, and seismic data, the tectonostratigraphic interpretation, depositional systems, and control on depositional systems of the syn-rift infill of the eastern part of the Drava Basin were studied. The rifting phase is characterised by the formation of half-grabens, grabens, a sag, and supradetachment basin structures with structural ramp and structural highs. The syn-rift infill can be divided into second-order tectonostratigraphic sequences corresponding to the early and late rift stages. The second-order sequences are further subdivided into third-order tectonostratigraphic sequences formed in response to higher-order tectonic events associated with local rift migration. In contrast to the early-stage structures, the late-stage rift structures are primarily controlled by extensional detachments that represent parts of the Drava Rift Fault System (DRFS). The early syn-rift is characterised by continental deposition through alluvial fans, fan deltas, and lacustrine environments. The late syn-rift stage is characterised by marine deposition in shallow water, fan deltas, and submarine slope-aprons, with deep marine sedimentation and intense volcanic activity. The ramp, basin slopes, and fault scarp slopes represent the major sediment transport pathways involved in the formation of alluvial fans, fan deltas, or submarine slope-aprons. Basinal sedimentation and major depocenters are located within synforms formed by structural lows in the geometry of extensional detachments. This study gives an example of syn-rift tectonic control for the SW part of the PBS and the influence of detachment geometry on basin fill. We have presented an approach based on 3D seismostratigraphic interpretation of tectonostratigraphic sequences, and the correlation of seismic facies with depositional environments developed in a back-arc setting.

Frontal wedge variations and controls of submarine landslides in the Negros–Sulu Trench System, Philippines

Frontal wedge characteristics provide clues to the efficiency of the overriding slab for large displacement during megathrust and upper-plate earthquakes, whereas submarine landslides along active margins may trigger or amplify tsunamis. The lack of clear precursors of submarine failures poses difficulty in monitoring and providing real-time alert warning systems. With that, delineating submarine features along active margins, their spatial distribution, and controls provide valuable information in identifying regions susceptible to large submarine landslides and tsunami hazard assessments. In this study, we performed terrain and morphometric analyses on 20 m resolution bathymetry data to map submarine landslides, submarine canyons, and lineaments in the forearc margin of the Negros–Sulu Trench System in the Philippines. Lineaments are distributed mainly along the frontal wedge, where previous seismic surveys revealed that the mapped ridges are morphotectonic expressions of thrusted sediments. The morphological variations of the four frontal wedge segments were attributed to heterogeneous sediment influx, convergence rates, and subduction processes. More than 1,200 submarine landslides and their morphometric parameters were delineated, and exploratory spatial analyses indicate clustering and underlying controls. The tendencies of prolate submarine landslides (high L/W) to significantly cluster along submarine canyons while oblate morphologies (low L/W) along the frontal wedge reflect the different environments and geomorphological conditions to form these contrasting shapes. Ubiquitous small submarine landslides are mainly controlled by submarine canyon systems at relatively shallow depths of <2 km, where high sediment influx from inland sources preconditions instability. Large submarine landslides (>0.5 km3), on the other hand, are significantly most clustered where the Cagayan Ridge seamount collides and subsequently subducts beneath the northernmost frontal wedge. This suggests the dominant role of seamount subduction and related tectonic processes causing slope steepening to mainly induce large submarine landslides. This study unveiled how submarine landslides vary morphologically depending on their spatial, geomorphological, and tectonic controls in the active margin. This new information provides clues in identifying offshore areas susceptible to large submarine landslides that may induce damaging tsunamis in the Negros–Sulu Trench System as well as in other active margins of similar underlying controls.

Tectonic control on travertine and silica sinter deposition in oceanic transform-fault setting: the case of the Lýsuskarð volcano-geothermal area, Snæfellsnes Peninsula, Iceland

ABSTRACT Deposition of terrestrial carbonate (i.e. travertine) and silica sinter in geothermal areas is always closely linked to the presence of relevant crustal structures which enhance the permeability in the upper crust favouring the upflow of fluids to the surface. Most travertine deposits are originated by geothermal fluids stored within carbonate reservoirs in continental crust, and their morphology and areal distribution provide useful information on geometry, kinematics, and age of faults which control the fluid flow. In this paper, we focus on the tectonic control on a travertine depositional system, associated with silica sinter, developing in oceanic crust, in the Lýsuskarð volcano-geothermal area on the Snæfellsnes Peninsula, West Iceland. The presence of HCO3 and Ca in the geothermal fluids is related to chemical-physical processes linked to fluid–rock interaction that occurs in the geothermal reservoir made up of tholeiitic basalt, by fluids enriched in CO2 of deep origin (i.e. magmatic). Travertine deposits consist of mounds and slopes, which are still in formation and overlie the silica sinter deposits. Both sinter and travertine deposits derive from thermal springs aligned according to two trends: NNE-SSW and WNW-ESE. This evidence suggests the occurrence of buried, permeable, and thus active faults, which control the circulation of fluids containing HCO3 and Ca. Faults are near parallel to those which define the rift systems and transform zones in Iceland, and probably comprise the still active sector of the abandoned transform zone that, starting with the Snæfellsnes Peninsula, interrupts eastward the northern continuation of the western and eastern rift-zones in the south-central Iceland. In this setting, we refer, for the first time, travertine and silica sinter deposition to an oceanic active crustal structure.

Fault growth and orthogonal shortening in transtensional supradetachment basins: Insights from the ‘Old Red’ of western Norway

AbstractFor basins that evolve adjacent to large‐magnitude normal faults, tectonic controls on sedimentation involve isostatic back rotation of an exhuming footwall and, commonly, the evolution of kilometre‐scale extension‐parallel folds. Based on observations from classic localities in western Norway, we propose a three‐stage evolution scenario for transtensional supradetachment basins where the basins become progressively re‐arranged because of core complex exhumation and subsequent orthogonal shortening. Extension‐parallel transverse synclines initially form due to a normal displacement gradient, but when displacements accumulate beyond a certain magnitude, the hanging wall increasingly responds to core complex exhumation and the original depocentre, formed close to the original area of maximum displacement, will become inverted and dismembered above the core complex. Two new synclinal depocentres will develop along the flanks. Because these synclines form by extensional fault growth rather than by shortening, they will be associated with widening of the basin and onlap onto basement at high angles to the maximum elongation trend with overall grain‐size decrease and retrogradational stacking patterns. Further, because these synclines grow away from the evolving core complex, sedimentary units will become asymmetrically distributed inside each syncline in such a way that the oldest deposits in the syncline will be preserved on the flank most proximal to the core complex. In transtensional environments, a third evolutionary stage may involve constrictional strain where extension‐parallel folds and reverse faults produced by orthogonal shortening enhance or interact with other structures. Ultimately, initial extensional sub‐basins may become warped across extension‐parallel folds. Hanging wall deformation will be manifested in shifting accommodation patterns, with depocentres that generally migrate in the direction of the detachment fault. Accommodation patterns initially related to megafault growth may conceptually evolve into depocentres controlled by orthogonal shortening.

Plate tectonic control of strontium concentration in Phanerozoic and Neoproterozoic seawater: Evidence from fluid inclusions in marine halite

Chemical analyses of 1371 fluid inclusions in 131 halite samples with marine 87Sr/86Sr values were used to reconstruct the strontium concentrations [Sr]SW of Phanerozoic and Neoproterozoic seawater. [Sr]SW varied seven-fold and oscillated twice between high- and low-Sr concentrations over the past 550 million years (Myr), in rhythm with Ca-rich and SO4-poor paleoseawater intervals and calcite-aragonite seas. Variations in the [Sr]/[Ca]SW ratio from fluid inclusions were not significant over the past ∼270 Myr, and are within ±3 µmol/mmol of the modern [Sr]/[Ca]SW ratio of ∼8.5 µmol/mmol. These results agree with the [Sr]/[Ca]SW ratios obtained from fossil corals, benthic foraminifera, brachiopods, belemnites, and rudists. [Sr]/[Ca]SW in the early and middle Paleozoic was ∼2 times the modern [Sr]/[Ca]SW ratio. A major shift of the [Sr]/[Ca]SW ratio in the late Permian coincided with the initial rifting of the Pangean supercontinent. Seawater 87Sr/86Sr ratios plotted against 1/[Sr]SW show two distinct linear correlations: negative correlation from 515 to 252 Ma and positive correlation from 150 to 0 Ma, suggesting different controls on the global Sr cycle between these intervals. The negative correlation coincides with the long-term assembly of Pangea in the Paleozoic (∼500–250 Ma). The positive correlation from 150 to 0 Ma parallels the break-up of Pangea and the decrease of mid-ocean ridge (MOR) hydrothermal fluid flux and subduction zone length in the Mesozoic and Cenozoic.