Tectonic Pulses Research Articles

Sedimentology and biostratigraphy of the Biancone Limestone Formation of the Tolmin Basin (Southern Alps, NW Slovenia)

The Tolmin Basin constitutes the western part of the Slovenian Basin, a large Mesozoic interplatform basin that was bounded to the north by the Julian Carbonate Platform and to the south by the Dinaric Carbonate Platform. Today, it is found along the structural boundary between the Southern Alps and the External Dinarides in northwestern Slovenia. After the drowning of the Julian Carbonate Platform, the Tolmin Basin was dominated by pelagic deposits, namely the Toarcian marlstones (Perbla Formation), the Aalenian to lower Tithonian siliceous limestones and radiolarites (Tolmin Formation), and the upper Tithonian to the Berriasian Biancone Limestone Formation. In this study, a basin-scale sedimentary evolution and calpionellid biostratigraphy of the latter is presented. The Biancone Limestone Formation is a calpionellid-bearing pelagic limestone typical of all deepened segments of the Adria microplate in this time interval. It is generally monotonous but shows considerable vertical and lateral variations. The lower boundary with radiolarites is sharp, revealing a pronounced and rapid overturn in pelagic sedimentation. The lower Berriasian slumps indicate a tectonic pulse. Rare beds of resedimented limestones, assigned to the middle Berriasian, are similar in composition to those intercalated in the underlying radiolarites. They thus show that the factors that led to a significant shift in pelagic sedimentation had little or no effect on shallow-marine carbonate production. In the upper Berriasian, an increase in clay content is evident in the formation, which is explained by the uplift and erosion of the propagating thrust belt in the Neotethys area, superimposed by humidification.

Cenozoic morphotectonic evolution of the eastern edge of Paraná Sedimentary Basin, southern Brazil

The Paraná Sedimentary Basin (PSB) is one of the most important geotectonic structures on the South American continent and its tectono-sedimentary evolution has been widely investigated, especially during the Paleozoic and Mesozoic. However, the post-rift Cenozoic dynamics need further studies to fully understand its evolution. Hence, this research aims to add data and interpretations regarding the morphostructural features inherent in the Cenozoic tectonic framework, especially in the south/southeast region of Brazil. Here, we explore the Cenozoic processes of tectonic reactivation of preexisting structural features, as well as the neoformation of structural features, considering that Mesozoic sedimentary and volcanic strata of the Serra Geral Group in the Paraná Basin were deformed by Cenozoic joints and faults. For this purpose, structural and geomorphological (morphometric) analyses were used in the Itararé and Cinzas rivers catchments, on the eastern edge of the PSB. The study area is part of the Ponta Grossa Arch domain, in the northeast of Paraná state and southwest of São Paulo state. The structural data collected, when associated with the morphometric analyses (qualitative and quantitative), were compatible, showing the influence of tectonic structuring on the geomorphological framework of the investigated watersheds, resulting in the morphotectonic compartmentalization of the surveyed area. Alterations to the topographic surface, asymmetry patterns in the watersheds, disturbances in the longitudinal river profiles and anomalies in the drainage network patterns are the result of reactivation of ancient NE-SW and NW-SE faults in the crystalline basement and present in the units that fill the sedimentary basin, as well as new families of faults, mainly in N–S and E-W direction. The structural analysis supported the determination of the Cenozoic paleostress fields, defined from the analysis of the fault population, spatial arrangement and through statistical and mechanical treatment of the kinematic structural data. The results of the paleostress tensors indicate a landscape evolution associated with at least four tectonic pulses, which compressive SHmax values are oriented in NE-SW, N–S, NW-SE and E-W directions, respectively. These are in agreement with the main regional scientific studies in southern and southeastern Brazil, which involve tectonic events from the Upper Cretaceous and Paleogene, advancing into the Neogene and up to at least the Pleistocene.

Extrapolation Paleostress Orientations Deduced from Joints Analyses at Spi Rais and West Part of Chai Gara Anticlines, Duhok Area, Kurdistan Region, Iraq

Spi Rais anticline (East part of major Bekhair anticline) and western part of Chia Gara anticline were chosen to study joint paths. They are located within the highly folded zone of the western zagros fold and thrust belt, Iraqi segment. These anticlines arranged in an en-echelon pattern and they expose rocks range in age from Late Cretaceous to Late Miocene. The Late Cretaceous (Campanian – Maastrichtian) succession represented by Bekhme and Shiranish Formations. The lithologies of these rocks are competent and consist of limestone, dolomitic limestone and marly limestone whichare favorable to joint development. Different types of joints were developed in such rocks due to stresses resulted from collision between Arabian and Eurasian (Turkish and Iranian) plates. The joint sets and systems are the most abundant fractures in the rocks of the study area. The chronological relationships of the joints refer that the area had witnessed multiple tectonic pulses in the form of compressional and extensional stresses. The stereonet and the Win – Tensor programs were used to plot the attitudes of joints and deduce their paleostresss orientations. Furthermore, the orientations of deduced paleostresses were plotted onto geological map of investigated area and simulated as paleo trajectories as well. The deduced paleostress direction responsible for folding in traverse 1 was (356° - 195°), in traverse 2 (330° - 168°) and in traverse 3 (353°- 163°).

Disentangling orbital, sub-orbital, and tectonic signatures from lacustrine sediments developed upon a half-graben (Lake Ifrah Basin, Northwest Africa): Insights into lowest-rank T-R sequences in low accommodation basins

Lacustrine settings constitute a unique environment that preserves detailed expressions of allocyclic signals such as those of climate and tectonics. Possible decryption of these signatures stems from careful scrutiny of the sedimentation dynamics (temporary base-level variations), lake-level fluctuations (accommodation), and resulting strata bounding surfaces that are used to build a conventional sequence stratigraphic framework. However, due to discrepancies between marine, to which this approach has been initially dedicated, and lacustrine settings (especially regarding the physical scale), deciphering climate from tectonic forcing becomes unwieldy in such interior basins. The present work deals with this challenge and provides insights from a case study where lacustrine sedimentation occurs on a tectonically active half-graben within a key climate region (Lake Ifrah, Northwest Africa). We conducted conventional sedimentological and high-resolution sequence-stratigraphic analyses, integrated with palaeolimnological proxies (geochemical elements and ostracod species). Up to five facies models (accounting for lithological domination, wind-driven energy, and lake-level state) and three lowest rank T-R sequences, deposited since the Marine Isotope Stage-3 (MIS-3), have been identified. Periods with sustained high lake levels appear to be mainly precession-paced (as during MIS-3 and the Early Holocene), although the role of obliquity is shown to influence the hydrological budget as well. Furthermore, sedimentation dynamics are shown to respond to millennial timescale climate variability associated with North Atlantic cooling events (Dansgaard-Oeschger stadials, Heinrich Events) and, interestingly, to enhanced Saharan winds during the deglacial period. On the other hand, tectonism had a rather instantaneous effect on lake level and sedimentation. Two tectonic pulses marking instantaneous differential hanging-wall subsidence have triggered a sharp drop in relative lake level, hence conditioning a forced regression.We highlight the importance of the conventional high-resolution sequence stratigraphy in shaping our understanding of the cyclic interplay between orbital/sub-orbital and tectonic forcings, so as the resulting sedimentation dynamics and lake-level cycles in lacustrine settings. We stress the role of the forced regression concept and associated systems tract and bounding surfaces, as well as the importance of using ostracods and geochemical proxies to trace transgressions and cryptic surfaces with sequence-stratigraphic significance, such as the maximum flooding surface, in lacustrine settings.

Late Permian-Triassic sedimentary evolution of the Southern Adriatic area based on wells and cores analysis

Rock samples from two cores within the Triassic interval of the Puglia 1 well, were studied to reveal the sedimentary facies and diagenesis. The Core 1 (5.048–5.056 m deep) is characterized by laminated dolomudstones with thinly microbial laminae alternated to lenticular/tabular shaped anhydrite crystal levels, suggesting an intertidal/sabkha-type environment. The Core 2 (6.067–6.075 m deep), shows coarse-grained crystalline massive dolomite with remnants of oolites and shell fragments, suggesting a marginal shallow-water setting. Dolomitization is ubiquitous and occurred early after the deposition through the circulation of high saline dolomitizing fluids under general reducing conditions. The early-dolomitization preserved the dolomites from major burial diagenetic transformations, permitting only the ordering and the development of xenotopic textures in the dolomite crystals (aging). Primary anhydrite crystals were lately affected at least by one burial hydration-dehydration cycle, whereas fracture-filling anhydrite is a later-stage diagenetic product of circulating sulphate-rich fluids. Moreover, the integration of Puglia 1 well data with other six exploration wells and a seismic line allowed a possible reconstruction of the Permian-Triassic sedimentary evolution of the Southern Adriatic area. During Permian continental/coastal lagoon settings developed, while in the Ladinian, after a generalized subaerial exposure and an erosional phase, the extensional tectonic inputs linked to Tethys rifting brought to a relative sea-level rise and to the formation of carbonate shelves in NW-SE oriented tectonic depressions. During Carnian-early Norian a further extensional tectonic pulse coupled with a relative sea-level drop, led to the formation of NW-SE elongated intrashelf basin with a consequent enhancement of salinity and settlement of evaporative conditions. This triggered a massive evaporite deposition during the Norian, that filled the basinal areas. Lastly, in the late Norian-Rhaetian a marked relative sea-level rise, restored the connections with open-sea and shifted the evaporite deposition up to the shallowest parts of the basins that previously remained under subaerial conditions.

Sedimentary record of the “Austrian” tectonic pulse around the Aptian–Albian boundary in SE France, and abroad

A tectonically-controlled forced regression occurred on the western margin of the French subalpine basin around the Aptian–Albian boundary. It nearly emptied the western part of the Vocontian Trough during the early and middle Albian. A compressional pulse associated with vertical movements along the Cevennes fault row and its satellites is inferred. This forced regression is correlated with an inverse transgressive trend, both in the Paris Basin and the northern subalpine chains. The black shales of the early Aptian OAE1a and Albian OAE1b of the Vocontian Trough succession occur within opposite regional sea level trends, transgressive for the former, regressive for the latter. The inferred tectonic pulse is also recorded on a broader scale from literature data. The overall picture also shows outphasings in relative sea level changes on a large scale, likely controlled by tectonics. Une régression forcée d’origine tectonique s’est produite sur la marge occidentale de la mer subalpine au passage Aptien–Albien. Elle a vidangé presque complètement la partie ouest de la fosse vocontienne pendant l’Albien inférieur et moyen. Une pulsation tectonique en régime compressif associée à des mouvements verticaux est suggérée le long du couloir de failles cévenol et satellites. La régression forcée est corrélée avec une tendance inverse transgressive dans le Bassin de Paris et dans les Chaines Subalpines nord. Les black shales vocontiens des événements anoxiques océaniques globaux OAE1a (Aptien) et OAE1b (Albien) s’inscrivent dans des tendances opposées en termes de variations du niveau marin relatif, largement transgressive pour le premier, fortement régressive pour le second. La pulsation tectonique déduite se manifeste à plus grande échelle d’après les données de la bibliographie. Elle est également responsable des déphasages constatés dans les variations locales du niveau marin à grande échelle.

The Mesozoic West and Central Africa Rift System (WCARS) and the older Kandi Shear Zone (KSZ): Rifting and tectonics of North Africa and South America and fragmentation of Gondwana based on geophysical investigations

Intra- and trans-continental tectonic lineaments and tectonic structures cutting Africa and Gondwana have long been identified by many authors. These structures were initially identified from topography, coast lines and geological data but more recently from remote sensing and geophysical data. Here gravity and aeromagnetic data for Africa and South America have been used to identify, track and model these structures at depth within the crust/upper mantle. The two structures investigated are the West and Central African Rift System (WCARS) and the Kandi Shear Zone (KSZ). WCARSthe nature and spatial extent of the WCARS have been identified using gravity data. In its simplest form, the WCARS consists of a set of strike-slip shear zones linked to extensional rift basins that can be traced as continuous structures from the Atlantic coast of Nigeria to southern Algeria and from the coast of Cameroon to Kenya. The rift system developed as a set of discrete tectonic pulses throughout the Mesozoic at the same time as the Central, South and Equatorial Atlantic Oceans developed into a single unified spreading centre. Each tectonic pulse had a different basin response due to the changing orientation of the plate tectonic controlled displacement field. The African rift basins formed by crustal extension involving brittle failure and ductile flow of the upper and lower crust respectively, resulting in the isostatic subsidence of the surface and rapid infilling of the basins with mainly continental derived sediments. Gravity and seismological studies support this crustal basin model originally proposed by McKenzie. This contribution shows that the evolution of the WCARS is clearly linked to the oceanic plate tectonic processes. New analysis of the fracture zone geometry in the Central Atlantic shows that these rift pulses involving crustal extension, strike-slip faulting, stratigraphic unconformities and short episodes of crustal contraction e.g. Santonian and Maastrichtian events, which can be identified and correlated with changes in the azimuth of the fracture zone geometry. KSZThe second, shorter part of the paper uses predominantly aeromagnetic data to track the KSZ from the Atlantic coast of Benin north into central Algeria before splaying out beneath the Saharan Platform. To the south the KSZ is shown, prior to the formation of the Equatorial Atlantic, to link with the Trans-Brazilian Lineament but its continuation south of Brazil still remain highly speculative.Finally, this review raises new insights and questions that are ideal for future research topics, both in developing the analytic methodologies and their application to other continental scale datasets.

Late Cretaceous evolution of chemical weathering at the northeastern South American margin inferred from mineralogy and Hf-Nd isotopes

The origin of the global temperature decrease that initiated the last greenhouse-icehouse transition about 90 million years ago still remains debated. Among the potential processes driving long-term climate evolution over million-year timescales, this study investigates the possible impact of the uplift-weathering connection on the late Cretaceous atmospheric CO2 drawdown and associated cooling.We analysed a marine sediment record from the Demerara margin, using Nd and Hf isotopes in clay-size detrital fractions (ΔɛHf(t)clay) together with bulk and clay mineralogy and major element abundances to reconstruct the evolution of tectonic uplift and chemical weathering intensity in northeastern South America during the late Cretaceous. Our data indicate that silicate weathering intensified on the northeastern South American margin during the middle Campanian and the Maastrichtian, concomitant with an uplift phase of the Guiana craton. We propose that the tectonic pulse highlighted by apatite fission track data, argon/argon dating and primary silicate mineral evolution, was accompanied by an accelerated chemical weathering, which presumably acted as a sink for atmospheric CO2. By contrast, during the earlier late Turonian to early Campanian, period of relative tectonic quiescence, climate most likely acted as the main driver controlling the evolution of chemical weathering intensity. The main phase of enhanced weathering induced by the uplift of the northeastern South American margin occurred during the Campanian, thereby postdating the onset of global seawater temperature decrease (late Turonian). By inference, this regional event is unlikely to have triggered late Cretaceous cooling but it may have acted as an additional factor stabilizing colder climate conditions at that time.

An exceptional sedimentary record of initial rifting on the East African Plateau in the Miocene: Lessons from depositional cyclicity and palaeoenvironmental proxies

AbstractKnowledge about the initial tectonic and depositional dynamics, as well as the influence of early rifting on climate and environmental evolution remains speculative to a large extent, because sediments are usually deeply buried. Within the East African Rift System, inversion tectonics uplifted a few of these successions to the surface hence presenting rare windows into the pre‐rift depositional history. One such example, an exceptional 700 m long and up to 60 m high fresh road cut provided the opportunity to study in detail initial rift successions of the southern Albertine Rift (Western Uganda). This focusses on the basal and poorly known Middle to Late Miocene in order to unravel the climatic, environmental, hydrological and tectonic evolution of the initial Albertine Rift. A large and robust multi‐proxy dataset was gathered comprising 169 m of stratigraphic thickness, which spans from 14.5 to 4.9 Ma according to a revised lithostratigraphic model. Fieldwork comprised logging of the sedimentary record, spectral gamma ray, magnetic susceptibility and 2D wall mapping with photomosaics. Additionally, the sections were sampled for bulk mineral and clay mineral analysis. The succession exposes a suite of lithofacies and architectural elements detailing the evolution of a fluvio‐lacustrine system. Five depositional environments were identified which show an overall back‐stepping trend from an alluvial plain to a delta plain and finally palustrine/shallow lacustrine conditions. Mesoscale base‐level cycles, preservation potential of architectural elements, and stacking pattern exhibit limited accommodation space. However, it increases over time. This overall trend indicates increasing tectonic subsidence, which can be explained by flexural downwarp within the pre‐rift phase and in the upper part grading into fault‐controlled crustal extension of the syn‐rift phase, which more and more disrupted a large‐scale river system. From the Middle Miocene up to the early Pliocene, this study revealed that palaeoclimate trends become marked by increasing and more fluctuating Th concentrations, loss of feldspar, intercalated lenses of hydroxosulphate minerals, and a shift from smectite‐dominated to kaolinite‐dominated clays. These signals are all interpreted as detrital except for the hydroxosulphates, and they mirror the increasing intensity of chemical weathering and stripping of soils in the catchment. A trend towards increasing humidity is supported by an increase in lacustrine sediment facies and a lake‐level rise. Nevertheless, intercalation of hydroxosulphate, ferricretes and pedogenised horizons prove ongoing seasonality and dry intervals. Finally, based on a revised stratigraphic model a sequence stratigraphic correlation of the outcrop's depositional cycles with basin‐scale cycles is presented. According to these cycles, transition from the pre‐rift to the syn‐rift stage is marked by an unconformity and a tectonic pulse in the latest Miocene. However, the response of fluvial supply, the depositional system as well as climate conditions are less punctuated and characterised by gradual trends and temporal delays. The long pre‐rift phase (ca 10 Myr) and the gradual transition to the syn‐rift phase is in accordance with the active rifting model, which is based on thermal thinning of the lithosphere by asthenospheric upwelling.

Volcano‐Tectonic Evolution of the Christiana‐Santorini‐Kolumbo Rift Zone

AbstractLocated on the Hellenic Arc, the Christiana‐Santorini‐Kolumbo (CSK) rift zone represents one of the most active and hazardous volcano‐tectonic systems in the Mediterranean. Although this rift zone has been intensively studied, its tectonic evolution and the interplay of volcanism and tectonism are still poorly understood. In this study, we use high‐resolution reflection seismic imagery to reconstruct the opening of the rift basins. For the first time, we relate the activity of individual faults with the activity of specific volcanic centers in space and time. Our analysis shows a pre‐volcanic NNE‐SSW‐oriented paleo basin underneath the CSK volcanoes, representing a transfer zone between Pliocene ESE‐WNW‐oriented basins, which was overprinted by a NE‐SW‐oriented tectonic regime hosting Late Pliocene volcanism that initiated at the Christiana Volcano. All subsequent volcanoes evolved parallel to this trend. Two major Pleistocene tectonic pulses preceded fundamental changes in the volcanism of the CSK rift including the occurrence of widespread small‐scale volcanic centers followed by focusing of activity at Santorini with increasing explosivity. The observed correlation between changes in the tectonic system and the magmatism of the CSK volcanoes suggests a deep‐seated tectonic control of the volcanic plumbing system. In turn, our analysis reveals the absence of large‐scale faults in basin segments affected by volcanism indicating a secondary feedback mechanism on the tectonic system. A comparison with the evolution of the neighboring Kos‐Nisyros‐Yali volcanic field zone and Rhodos highlights concurrent regional volcano‐tectonic changes, suggesting a potential arc‐wide scale of the observed volcano‐tectonic interplay.

Soft-sediment deformation structures recognised in a reverse-drag associated with normal faulting (Lake Ifrah, Northwest Africa): Palaeoseismic assessment and neotectonic implications

Reverse-drags in extensional settings are emblematic structures that may provide imprints of (neo)tectonic pulses, and even evidence of palaeoseismic activity. The direct pieces of evidence of (neo)tectonic activity therein are mostly reported to be subsidiary grabens, synthetic and antithetic normal faults, and/or bed-parallel slips that brittlely deform newly deposited soft-sediments, therefor being classified as soft-sediment deformation structures (SSDSs). Liquidization-induced SSDSs are, reasonably, likely to occur in such tectonically active settings as well. Nonetheless, both SSDSs types have not gained enough interest from structural geologist and sedimentologist communities. We hereby address this gap by investigating brittle and liquidization-induced SSDSs from late Pleistocene-Holocene fluvio-lacustrine beds (Lake Ifrah, northern Morocco). Sedimentation and deformation occur upon a reverse-drag anticline connected to a master normal fault that borders a half-graben structure (Ifrah sub-basin) superimposed on a master basin (Ifrah Basin), itself connected to a major strike-slip fault (the Tizi n'Tretten Fault, TTF). Liquidization-induced SSDSs involve load structures and water-escape structures, whereas brittle deformations encompass shrinkage cracks, subsidiary grabens, neptunian dykes, and bed-parallel slip (BPS) and associated domino-style faults. The deformation mechanism for both SSDS types involves either loss of strength upon liquidization (load structures and water-escape structures) or an increase in applied (internal or external) shear (shrinkage cracks, faults). Facies analysis and conventional trigger assessment allowed deciphering endogenic from exogenic triggers for deformation. Liquidization has been inferred to be seismic-triggered whereby the deformed beds are considered seismites. While BPS deformed brittlely late Pleistocene deposits (probably Marine Isotope Stage 3, MIS-3) and subsidiary grabens and neptunian dykes involve Middle Holocene sediments, they are considered to be linked to two flexural-slip events of the reverse-drag during MIS-3? and the Middle Holocene, respectively.Scaling relationships between the structural entities of the hanging-wall-master fault-footwall system allowed estimation of the subsidence due to hanging-wall collapses, and thereby the initiation of the Ifrah sub-basin (at least since 260 kyr). The rhomboidal-shaped master basin was suggested to belong to a dilational quadrant of the associated strike-slip fault, the TTF, at a tip-damage region. Accordingly, we highlight structural isolation of a segment of the TTF that is synchronous with the Ifrah Basin initiation.

Paleoenvironmental redox evolution of Ediacaran-Cambrian restricted seas in the core of West Gondwana: Insights from trace-metal geochemistry and stratigraphy of the Bambuí Group, east Brazil

The sedimentary evolution of the Bambuí foreland basin system in the interior of West Gondwana is marked by periods of connection and isolation from the global ocean during the late Neoproterozoic and early Paleozoic. To understand the link between these periods and seawater redox conditions, we present an integrated study of trace-metal geochemistry and stratigraphy of the carbonate-siliciclastic rocks from the two lowermost second order transgressive-regressive sequences of the Bambuí Group, east Brazil. The basal 2nd-order sequence trace-metal pattern shows a progressive decrease of mass fractions of Co, Cr, Ni, Cu, Mo, U, V, Zn, and Cd, concomitant with a progressive decrease of Al and Fe contents and Mo/TOC ratios. Among all these elements, only Cd, Mo and U mass fractions seem to be less or not affected by detrital influence, so they can be used as reliable redox proxies for the paleoenvironmental analysis of the studied Bambuí strata. Moreover, normalization to aluminum shows a progressive increase of trace-metal enrichments for Cd and Mo in the order of 0.1–10 times and for U in the order of 1–100 times, accompanied by a progressive increase of organic carbon content upward section. These changes in sedimentary trace-metal patterns provide evidence for the chemical evolution of basinal deep-waters, whose conditions changed progressively from suboxic-anoxic to anoxic-euxinic at the basal transgressive-regressive sequence. We suggest that the paleomarine system represented by the basal Bambuí Group has probably evolved as an intracontinental silled basin recording changes in seawater chemistry associated with redox variations and restricted hydrographic conditions. Sedimentary trace-metal patterns indicate that Bambuí epeiric sea was initially in communication with open ocean followed by the marine restriction during the transgressive and regressive cycles, respectively. This resulted in a long deepwater residence time and chemical evolution of deep watermass as a response to tectonic pulses and consequent sea-level variations during the restricted stage. Under anoxic-euxinic conditions of seawater, trace metals scarcity and micronutrient fixation limitation would have impacted nitrate bioavailability, preventing the evolution of early benthic metazoans in the Bambuí paleomarine system during the late Ediacaran and early Cambrian.

Late Miocene evolution of the eastern Deep Algarve basin: Interaction of bottom currents and gravitational processes in a foredeep setting

Foreland basins are normally dominated by turbidite deposits in the early stages of their evolution. In this work, we show evidences of bottom current influence in the Algarve basin, which evolved as a foredeep basin of the Betic-Rif orogeny, during which the paleo-Mediterranean Outflow Water (MOW) was active through the Betic and Rifian corridors. Seismic interpretation identified four stages of sedimentary evolution (Stages I-IV) in the eastern domain of the Deep Algarve basin. Stages I and II correspond to the Late Miocene contourite depositional system during the late Tortonian to early Messinian, interrupted by the emplacement of the allochthonous unit of the Gulf of Cádiz. Bottom currents reworked the initial turbiditic sediments in the eastern Deep Algarve basin, as the downstream continuation of the Guadalquivir sands turbidite system, forming contourite drifts prior to the severe weakening or cessation of the paleo-MOW around mid-Messinian. Stages III and IV represent the evolution of the turbidite system with a lack of bottom current influence, through the downstream translation and lateral migration of meandering submarine channels, and their subsequent abandonment, during the late Messinian. The Tortonian to Messinian evolution of bottom current is modulated by the water-mass exchange between the Mediterranean and the Atlantic due to the shallowing of gateway sills and subsequent restriction of the paleo-MOW through the Betic and Rifian gateways around ∼6.4 Ma. Tectonic and glacioeustatic changes related to the orbital forcing exerted control over both the turbidite and contourite depositional systems, where tectonic pulses of about 400-kyr dictated their large-scale morphosedimentary evolution and interactions.

How sensitive are intraplate inherited structures? Insight from the Cévennes Fault System (Languedoc, SE France)

ABSTRACTDeformation in intraplate domains is usually considered as a consequence of tectonic events at plate boundaries. Nevertheless, the occurrence of intraplate earthquakes such as the recent Le Teil event in the south of France along the Cévennes Fault System (CFS), on 11 November 2019, Mw = 4.9, questions whether this far-field deformation only occurs during tectonic pulses at plate boundaries, or if it corresponds to low-intensity but regional continuous deformation through time. To address this question, we have coupled U–Pb geochronology of fault-related calcites with structural analysis along a major fault system (the CFS) in the South-East Basin, France. We evidence (1) an Albian activity of the CFS and (2) a continuous compressional activity of the CFS and satellite structures during the whole Eocene and probably during the Late Cretaceous – Palaeocene, including periods (e.g. Lutetian) usually considered as phases of tectonic quiescence. We thus demonstrate that the tectonic reactivation of this intraplate fault system is not restricted to periods of high rates of deformation at plate boundaries.

New data on Maastrichtian fishes of the ‘Haţeg Island’

Some discoveries from the continental deposits of the paleogeographic landmass named the ?Ha?eg Island? complete the fossil record of the Maastrichtian fish fauna of Europe. Teeth belonging to the Lonchidiidae and three morphotypes of Teleostei indet. are reported herein, from the uppermost Cretaceous continental formations cropping out in the Ha?eg and Transylvanian sedimentary basins of Romania. These fishes document a terrestrial realm, where various aquatic environments occurred ca. 70 Ma ago, immediately after the ?Laramian? (latest Cretaceous) tectonic pulse. It is important to note the presence of a brackish water shark, reported for the first time in the Maastrichtian deposits of Romania. This advance in research argues for a higher Cretaceous fish diversity in Transylvania than previously suggested. Therefore, the ecology of the ancient vertebrate communities is better documented with elements unknown so far.

Interpretation of Depositional Environment of Fusulinid Bearing Middle Permian Succession of Bolula and Khaja Ghar Formation, Bamian Zone, Central Afghanistan

The study area belongs to the north Afghanistan having complex tectonic setting, because of separation of the Afghanistan plate from Pangea in Early Permian and its subsequent northward journey and collision with Eurasian plate. The rock exposed in the area belongs to Paleozoic, Mesozoic to Quaternary with Proterozoic basement. Particularly the Permian succession of Afghanistan is rich in fusulinids (larger foraminifera), is age diagnostic, provides strong biostratigraphic tool for the Permian deposits, and has paleobiogeographic applications. The Bamian zone of north Afghanistan has good exposure to Middle Permian and is designated as Bolula and Khaja Ghar Formation is undertaken in this study. The Bolula Formation overlies the greenschist and basalts, composed mainly of carbonate rocks (Dolostone and limestone), having massive limestone, with some quartz and secondary calcite vein in the succession. The intermittent siliciclastic wedges within the carbonate succession are identified as input within the platform with tectonic pulses in the hinterland. Bolula and Khaja Ghar succession is divided into 8 lithofacies ( Facies A to H) and 6 carbonate Facies viz. Sparry calcites limestone, Micritic limestone, Fossiliferous limestones (Biomicrite), Peloidal limestone (Fecal pellets), Interlaminated micritic and sparite limestone, and sandy limestone (micritic). The Bolula and Khaja Ghar Formation in the Bamian area have deposited in a shallow marine shelf environment because of predominance of carbonate rocks and presence of shallow-water marine fossils including fusulinids, small benthic foraminifera, algae, bivalve, brachiopods fragments, corals and bryozoans, etc. In the Bamian zone the unconformity between Upper Carboniferous and Lower Permian; indicates extensive gap in sedimentation, traceable to many parts of Afghanistan as unconformity or tectonic contact is considered here as sequence boundary.

Factors controlling the geometry of travertine mounds: Insights from Heinitang (China)

AbstractTravertine mounds are common spring‐constructed landforms with highly variable geometries, but factors controlling their development have not yet been fully understood. To investigate processes linked with their lateral and vertical growth, this study investigated travertine mounds at Heinitang (China) and compared them with typical mounds around the world. Calcium concentration variation modelling and height evaluation of travertine mounds were also performed. The lateral extent of travertine mounds was found to be mainly controlled by Ca2+ and concentrations and water discharge: relatively small metre‐scale mounds, like those from Heinitang, are largely the products of Ca2+‐deficiency (<150 mg L−1, commonly <100 mg L−1) or ‐deficiency (<500 mg L−1) springs with low discharges (<0.1 L s−1), whereas springs with higher Ca2+ and concentrations and discharges give rise to the formation of wider mounds. Additional factors affecting mound lateral development include infiltration, evaporation, micro‐organisms, water cooling, CO2 degassing and flow paths. Height of travertine mounds cannot be simply considered to represent the piezometric surface, because the vertical growth of travertine mounds is also influenced by the water table change triggered by tectonic pulses and climate fluctuations, and the closing of conduits induced by self‐sealing. The extinction of travertine mounds at Heinitang is, for example, probably caused by the water table lowering triggered by earthquakes or climate drying after 4 kyr bp. These findings offer new inputs for the better understanding of factors controlling travertine mound development and might assist in the reconstruction of fluid properties, hydrodynamics, tectonics and climate fluctuations in fossil geothermal systems with travertine mounds.

Allogenic and autogenic controls on facies and stratigraphic architecture of the Lower Jurassic Mashabba Formation, Gebel Al-Maghara, North Sinai, Egypt

The Lower Jurassic Mashabba Formation crops out in the core of the doubly plunging Al-Maghara anticline, North Sinai, Egypt. It represents a marine to terrestrial succession deposited within a rift basin associated with the opening of the Neotethys. Despite being one of the best and the only exposed Lower Jurassic strata in Egypt, its sedimentological and sequence stratigraphic framework has not been addressed yet. The formation is subdivided informally into a lower and upper member with different depositional settings and sequence stratigraphic framework. The sedimentary facies of the lower member include shallow-marine, fluvial, tidal flat and incised valley fill deposits. In contrast, the upper member consists of strata with limited lateral extension including fossiliferous lagoonal limestones alternating with burrowed deltaic sandstones. The lower member contains three incomplete sequences (SQ1-SQ3). The depositional framework shows transgressive middle shoreface to offshore transition deposits sharply overlain by forced regressive upper shoreface sandstones (SQ1), lowstand fluvial to transgressive tidal flat and shallow subtidal sandy limestones (SQ2), and lowstand to transgressive incised valley fills and shallow subtidal sandy limestones (SQ3). In contrast, the upper member consists of eight coarsening-up depositional cycles bounded by marine flooding surfaces. The cycles are classified as carbonate-dominated, siliciclastic-dominated, and mixed siliciclastic-carbonate. The strata record rapid changes in accommodation space. The unpredictable facies stacking pattern, the remarkable rapid facies changes, and chaotic stratigraphic architecture suggest an interplay between allogenic and autogenic processes. Particularly syndepositional tectonic pulses and occasional eustatic sea-level changes controlled the rate and trends of accommodation space, the shoreline morphology, the amount and direction of siliciclastic sediment input and rapid switching and abandonment of delta systems.

U–Pb dating of middle Eocene–Pliocene multiple tectonic pulses in the Alpine foreland

Abstract. Foreland fold-and-thrust belts (FTBs) record long-lived tectono-sedimentary activity, from passive margin sedimentation, flexuring, and further evolution into wedge accretion ahead of an advancing orogen. Therefore, dating fault activity is fundamental for plate movement reconstruction, resource exploration, and earthquake hazard assessment. Here, we report U–Pb ages of syn-tectonic calcite mineralizations from four thrusts and three tear faults sampled at the regional scale across the Jura fold-and-thrust belt in the northwestern Alpine foreland (eastern France). Three regional tectonic phases are recognized in the middle Eocene–Pliocene interval: (1) pre-orogenic faulting at 48.4±1.5 and 44.7±2.6 Ma associated with the far-field effect of the Alpine or Pyrenean compression, (2) syn-orogenic thrusting at 11.4±1.1, 10.6±0.5, 9.7±1.4, 9.6±0.3, and 7.5±1.1 Ma associated with the formation of the Jura fold-and-thrust belt with possible in-sequence thrust propagation, and (3) syn-orogenic tear faulting at 10.5±0.4, 9.1±6.5, 5.7±4.7, and at 4.8±1.7 Ma including the reactivation of a pre-orogenic fault at 3.9±2.9 Ma. Previously unknown faulting events at 48.4±1.5 and 44.7±2.6 Ma predate the reported late Eocene age for tectonic activity onset in the Alpine foreland by ∼10 Myr. In addition, we date the previously inferred reactivation of pre-orogenic strike-slip faults as tear faults during Jura imbrication. The U–Pb ages document a minimal time frame for the evolution of the Jura FTB wedge by possible in-sequence thrust imbrication above the low-friction basal decollement consisting of evaporites.

Paleoseismological evidence for historical ruptures along the Meduno Thrust (eastern Southern Alps, NE Italy).

We carried out new geological, morphotectonic, geophysical and paleoseismological investigations on the Meduno Thrust that belongs to the Pliocene-Quaternary front of the eastern Southern Alps in Friuli (NE Italy). The study area is located in the Carnic Prealps, where a series of alluvial terraces, linked to both climatic and tectonic pulses characterises the lower reach of the Meduna Valley. In correspondence of the oblique ramp of the Meduno Thrust, the Late Pleistocene Rivalunga terrace shows a set of scarps perpendicular to the Meduno valley, often modified by human activity. In order to reconstruct the tectonic setting of the area and identify the location for digging paleoseismological trenches, integrated geophysical investigations including electrical resistivity tomography, seismic refraction and reflection, ground penetrating radar and surface wave analyses (HVSR, ReMi and MASW), were carried out across the scarps of the Rivalunga terrace. Geophysical surveys pinpointed that in correspondence of the oblique ramp, stress is accommodated by a transpressive thrust system involving all the seismo-stratigraphic horizons apart from the ploughed soil. Trenching illustrated the Meduno Thrust movements during Late Pleistocene-Holocene. Trenches exhibited both shear planes and extrados fracturing, showing deformed alluvial and colluvial units. 14C datings of the colluvial units show that the most recent fault movements occurred after 1360 CE and 1670 CE. The age of the deformed stratigraphic units compared with the earthquakes listed in current catalogues, suggests that the 1776 earthquake (Mw 5.8, Io = 8–9 MCS) could represent the last seismic event linked to the Meduno thrust activity. This study provided new quantitative constraints improving seismic hazard assessment for Carnic prealpine area.