Plate Tectonic Reorganization Research Articles

The Davis Strait proto-microcontinent: The role of plate tectonic reorganization in continental cleaving

A prolonged period of rifting and seafloor spreading between Greenland and North America formed the Labrador Sea and Baffin Bay oceanic basins, connected by the Davis Strait. However, disagreement exists regarding the exact plate motions between Greenland and Canada as well as the tectonic evolution of the Davis Strait, with previous models unable to explain the origin of anomalously thick continental crust within the seaway. Here, we present a new plate tectonic reconstruction of Greenland’s separation from Canada, constrained by a new comprehensive set of mid-ocean ridge (MOR) and transform fault lineaments identified using free-air, vertical gradient, and filtered directional gradient maps from the Sandwell and Smith gravity data. Furthermore, the reinterpretation of seismic reflection data offshore West Greenland, along with a new combined crustal thickness model, identifies an isolated terrane of relatively thick (19–24 km) continental crust that was separated from Greenland during a newly recognised phase of E-W extension along West Greenland’s margin. We interpret this continental block as an incompletely rifted microcontinent, which we term the Davis Strait proto-microcontinent. Our reconstruction suggests release of the protomicrocontinent coincided with a change in the spreading orientation from ∼ 58 to 49 Myr and was induced by transpression along a NE-SW trending transform margin that joined the Labrador Sea and Baffin Bay, prior to development of the Ungava Fracture Zone (UFZ). The location of this transform margin is constrained using our crustal thickness model, which demonstrates a sharp NE-SW trending continent-ocean transition across the North Saglek basin. We term this structure the Pre-Ungava Transform Margin (Pre-UTM), which accommodated early NE-SW motion between Greenland and Canada. Our identified mechanism of microcontinent formation may be widely applicable to other microcontinents around the globe, and further study is merited to understand the role of plate motion changes and transpression in microcontinent calving.

Prolonged post-orogenic extension in the southeastern Canadian Cordillera: Miocene reactivation of the Columbia River Fault

Post-orogenic extension in the southeastern Canadian Cordillera manifested in the form of metamorphic core complexes exhumed during the Paleocene–Eocene, but new thermochronology data suggest this interval may be longer. The Columbia River Fault is a brittle-ductile normal fault bounding the eastern margin of the Monashee Complex, southeastern British Columbia. Vertical motions along this fault are investigated here using apatite fission-track and (U-Th)/He thermochronology and samples from two elevation profiles. Apatite fission track ages range from 29.3 to 17.7 Ma, and apatite (U-Th)/He ages range from 26.6 to 7.0 Ma. Inverse thermal history modeling of these profiles suggests the footwall underwent rapid cooling between 18 and 16 Ma, whereas the hanging wall experienced more protracted cooling since 40 Ma, with two small cooling pulses at 20 and 10 Ma. These new data suggest the Columbia River Fault was reactivated in the early Miocene and continued to exhume the Monashee Complex an additional ∼2 km. Combining all thermochronology data from the region suggests three phases of accelerated cooling in the Monashee Complex; 1) Eocene (56–40 Ma); 2) Miocene (20–16 Ma); and 3) Pliocene to recent. Thermal history modeling of thermochronometric data reported from elevation profiles from across the wider region of the southern Canadian Cordillera find early Miocene cooling phases contemporaneous with that seen along the Columbia River Fault. This widespread exhumation coincides with early Miocene plate tectonic reorganization of the Pacific-North American margin which resulted in increased transtension in northwestern North America. We propose that the early Miocene reactivation of the Columbia River Fault is a splay fault associated with dextral strike slip faulting along the Rocky Mountain Trench, driven by an increase in transtensional stresses along the Pacific-North American plate boundary. Building on earlier models, pre-existing gravitational instabilities in the southeastern Canadian Cordillera aided in lateral extension of the upper crust along unstable inherited structures throughout the Shuswap Metamorphic Core Complex

Seismic Structure of the Caroline Plateau‐Yap Trench Collision Zone

AbstractCollision of oceanic plateaus with trenches has played a key role in the continental growth and plate tectonic reorganizations throughout the Earth's history. However, the understanding of collision between an initially rifted plateau with a trench is still deficient. Here we conduct the first seismic tomography and receiver function analyses in the Yap subduction zone, western Pacific Ocean, where the initially rifted Caroline Plateau is colliding with the Yap Trench. Our results reveal horizontal and overturned slabs south and north of the Sorol Trough, respectively, which may be caused by slab breakoff followed by underplating and eastward mantle flow with ultra‐slow convergence. The distinct slab morphologies could be responsible for the short‐lived arc volcanism (11‐7 Ma), horst‐graben structures, different Bouguer gravity anomalies and stress regimes in the Yap subduction zone. The overturned slab may cause the incoming plateau to be stretched to facilitate the initial plateau subduction.

Thermochronologic constraints on the origin of the Great Unconformity

The origin of the phenomenon known as the Great Unconformity has been a fundamental yet unresolved problem in the geosciences for over a century. Recent hypotheses advocate either global continental exhumation averaging 3 to 5 km during Cryogenian (717 to 635 Ma) snowball Earth glaciations or, alternatively, diachronous episodic exhumation throughout the Neoproterozoic (1,000 to 540 Ma) due to plate tectonic reorganization from supercontinent assembly and breakup. To test these hypotheses, the temporal patterns of Neoproterozoic thermal histories were evaluated for four North American locations using previously published medium- to low-temperature thermochronology and geologic information. We present inverse time-temperature simulations within a Bayesian modeling framework that record a consistent signal of relatively rapid, high-magnitude cooling of ∼120 to 200 °C interpreted as erosional exhumation of upper crustal basement during the Cryogenian. These models imply widespread, synchronous cooling consistent with at least ∼3 to 5 km of unroofing during snowball Earth glaciations, but also demonstrate that plate tectonic drivers, with the potential to cause both exhumation and burial, may have significantly influenced the thermal history in regions that were undergoing deformation concomitant with glaciation. In the cratonic interior, however, glaciation remains the only plausible mechanism that satisfies the required timing, magnitude, and broad spatial pattern of continental erosion revealed by our thermochronological inversions. To obtain a full picture of the extent and synchroneity of such erosional exhumation, studies on stable cratonic crust below the Great Unconformity must be repeated on all continents.

Trøndelag Platform and Halten–Dønna Terraces Composite Tectono-Sedimentary Element, Norwegian Rifted Margin, Norwegian Sea

Abstract The Trøndelag Platform and Halten–Dønna Terraces occupy a central part of the Norwegian Sea rifted continental margin off the mid-Norway coast. The margin is expected to hold 4500 Mboe of undiscovered oil equivalents and represents an economically important Arctic province. The geological evolution of the area is closely linked to processes involving the Caledonian Orogeny and subsequent plate tectonic reorganizations, multiphase rifting, continental drift and glaciations across the northern hemisphere. In this chapter we review the geology of the Trøndelag Platform and Halten–Dønna Terraces Composite Tectono-Sedimentary Element based on published data and results of Equinor ASA in-house studies. Three new structural elements are defined for the first time: the Leka fault complex, the Vikna high and the Sula basin.

Detrital zircon uranium-lead geochronology of the Schoonover Sequence (Golconda Allochthon, Nevada): Alternative paleogeography of the Havallah-Schoonover Basin with implications for Antler-SLaB-Sonoma orogenesis

Detrital zircon UPb data (N = 3; n = 713) from the Lower Mississippian Schoonover Sequence support an alternative two-source provenance model for Carboniferous strata of the Golconda Allochthon that may have significant implications for late Paleozoic paleogeography and tectonism along the western margin of Laurentia. Existing models invoke derivation of quartzofeldspathic material within Schoonover-Havallah strata by erosion of the Roberts Mountain Allochthon coupled with simultaneous derivation of the volcanic component from the offshore Eastern Klamath-Northern Sierra arcs. Deposition of these two components occurred in a parautochthonous extensional basin that formed between the latest Devonian to Early Mississippian Antler and Permo-Triassic Sonoma compressional orogenies. In our alternative model, the quartzofeldspathic component of the ca. 350 Ma Schoonover Sequence was derived by erosion of Canadian passive margin strata and metamorphic equivalents exposed north of the submerged Peace River Arch; volcanic contributions were derived from the Yukon-Tanana Arc. This model implies that deposition of strata comprising the Roberts Mountain and Golconda allochthons occurred in transient, transtensional marine basins formed within a sinistral transcurrent plate boundary; local plate tectonic reorganization ended deposition in a given basin, followed by southward tectonic translation of basin strata.In this alternative model, the Antler and the Sonoma orogenies represent tectonic bookends of a single, ca. 100-Myr-long sinistral transcurrent orogeny. Continuous sinistral transcurrent deformation along the jagged western edge of Laurentia produced local stress variations that accommodated deposition in transtensional basins while deformation and translation of basin strata occurred along transpressional fault strands. A protuberance in the continent's rifted edge formed a barrier to continued southward transport along the inner edge of the transcurrent plate boundary, forcing far-traveled strata to sequentially pile up and form the Roberts Mountain and Golconda allochthons. Between allochthon emplacement, the focus of sinistral deformation stepped outboard within the broad Southwestern Laurentian Borderland (SLaB). The relative tectonic quiescence permitted local deposition of overlap and successor strata above the Roberts Mountain but below the subsequently overlying Golconda Allochthon; these strata record, however, multiple unconformities and deformation events indicating that deformation across the broad SLaB region continued between the Antler and Sonoma orogenies.

Indo-Atlantic plate accelerations around the Cretaceous-Paleogene boundary: A time-scale error, not a plume-push signal

AbstractIt has been suggested that plume arrival at the base of the lithosphere introduces a push force that overwhelms the balance of torques driving plate circuits, leading to plate-tectonic reorganizations. Among the most compelling evidence in support of a “plume-push” mechanism is the apparent coincidence between eruption of the Deccan flood basalts around 67–64 Ma and a short-lived increase in Indian (and decrease in African) plate speed. Using existing and newly calculated high-resolution plate-motion models, we show that plate divergence rates briefly increased throughout the Indo-Atlantic circuit, contrary to the expected effects of plume-push. We propose that this circuit-wide spike in divergence rates is best explained as the artifact of a magnetic reversal time-scale error around the much studied Cretaceous-Tertiary boundary, and that the period spanning chrons C29–C28 lasted 70% longer than currently assumed. Corrected for this error, the residual long-term patterns of Indo-Atlantic plate motions and accompanying plate-tectonic reorganization are explicable in terms of maturation of the circuit’s spreading ridges, without invoking a significant plume-push force.

The Jan Mayen microplate complex and the Wilson cycle

AbstractThe opening of the North Atlantic region was one of the most important geodynamic events that shaped the present day passive margins of Europe, Greenland and North America. Although well-studied, much remains to be understood about the evolution of the North Atlantic, including the role of the Jan Mayen microplate complex. Geophysical data provide an image of the crustal structure of this microplate and enable a detailed reconstruction of the rifting and spreading history. However, the mechanisms that cause the separation of microplates between conjugate margins are still poorly understood. We assemble recent models of rifting and passive margin formation in the North Atlantic and discuss possible scenarios that may have led to the formation of the Jan Mayen microplate complex. This event was probably triggered by regional plate tectonic reorganizations rejuvenating inherited structures. The axis of rifting and continental break-up and the width of the Jan Mayen microplate complex were controlled by old Caledonian fossil subduction/suture zones. Its length is related to east–west-oriented deformation and fracture zones, possibly linked to rheological heterogeneities inherited from the pre-existing Precambrian terrane boundaries.

Relict basin closure and crustal shortening budgets during continental collision: An example from Caucasus sediment provenance

Comparison of plate convergence with the timing and magnitude of upper-crustal shortening in collisional orogens indicates both shortening deficits (200-1700 km) and significant (10-40%) plate deceleration during collision, the cause(s) for which remain debated. The Greater Caucasus Mountains, which result from post-collisional Cenozoic closure of a relict Mesozoic back-arc basin on the northern margin of the Arabia-Eurasia collision zone, help reconcile these debates. Here we use U-Pb detrital zircon provenance data and the regional geology of the Caucasus to investigate the width of the now-consumed Mesozoic back-arc basin and its closure history. The provenance data record distinct southern and northern provenance domains that persisted until at least the Miocene. Maximum basin width was likely ~350-400 km. We propose that closure of the back-arc basin initiated at ~35 Ma, coincident with initial (soft) Arabia-Eurasia collision along the Bitlis-Zagros suture, eventually leading to ~5 Ma (hard) collision between the Lesser Caucasus arc and the Scythian platform to form the Greater Caucasus Mountains. Final basin closure triggered deceleration of plate convergence and tectonic reorganization throughout the collision. Post-collisional subduction of such small (102-103 km wide) relict ocean basins can account for both shortening deficits and delays in plate deceleration by accommodating convergence via subduction/underthrusting, although such shortening is easily missed if it occurs along structures hidden within flysch/slate belts. Relict-basin closure is likely typical in continental collisions in which the colliding margins are either irregularly shaped or rimmed by extensive back-arc basins and fringing arcs, such as those in the modern South Pacific.

Pre-salt to salt stratigraphic architecture in a rift basin: insights from a basin-scale study of the Gulf of Suez (Egypt)

We propose a basin-scale (∼300 × 100 km) study of the pre-salt to salt sedimentary fill from the Suez rift based on outcrop and subsurface data. This study is a new synthesis of existing and newly acquired data using an integrated approach with (1) basin-scale synthesis of the structural framework, (2) stratigraphic architecture characterization of the entire Suez rift using sequence stratigraphy concepts, (3) lithologic maps reconstruction and interpretation, (4) isopach/depocenter maps interpolation to quantify sedimentary volumes, and (5) quantification of the sediment supply, mean carbonate and evaporite accumulation rates, and their integration into the rift dynamic. The Gulf of Suez is ca. 300-km-long and up to 80-km-wide rift structure, resulting from the late Oligocene to early Miocene rifting of the African and Arabian plates. The stratigraphic architecture has recorded five main stages of rift evolution, from rift initiation to finally tectonic quiescence characterized by salt deposits. Rift initiation (ca. 1–4 Myr duration): the Suez rift was initiated at the end of the Oligocene along the NNW-SSE trend of the Red Sea with evidences of active volcanism. Continental to lacustrine deposits only occurred in isolated depocenters. Sediment supply was relatively low. Rift widening (ca. 3 Myr duration): the rift propagated from south to north (Aquitanian), with first marine incursions from the Mediterranean Sea. The rift was subdivided into numerous depocenters controlled by active faults. Sedimentation was characterized by small carbonate platforms and associated sabkha deposits to the south and shallow open marine condition to the north with mixed sedimentation organized into an overall transgressive trend. Rift climax (ca. 5 Myr duration): the rift was then flooded during Burdigalian times recording the connection between the Mediterranean Sea and the Red Sea. The faults were gradually connected and reliefs on the rift shoulders were high as evidenced by a strong increase of the uplift/subsidence rates and sediment supply. Three main depocenters were then individualized across the rift and correspond to the Darag, Central, and Southern basins. Sedimentation was characterized by very large Gilbert-type deltas along the eastern margin and associated submarine fans and turbidite systems along the basin axis. Isolated carbonate platforms and reefs mainly occurred in the Southern basin and along tilted block crests. Late syn-rift to rift narrowing (ca. 4 Myr duration): during the Langhian, the basin recorded several falls of relative sea level and bathymetry in the rift axis was progressively reduced. The former reliefs induced during the rift climax were quickly destroyed as evidenced by the drastic drop in sediment supply. Stratigraphic reconstruction indicates that the Central basin was restricted during lowstand period; meanwhile, open marine conditions prevailed to the north and south of the Suez rift. The Central basin, Zaafarana, and Morgan accommodation zones thus acted as a major divide between the Mediterranean Sea and the Red Sea. During Serravalian times, the Suez rift also recorded several disconnections between the Mediterranean and Red seas as evidenced by massive evaporites in major fault-controlled depocenters. The Suez rift was occasionally characterized by N–S paleogeographic gradient with restricted setting to the north and open marine setting to the south (Red Sea). Tectonic quiescence to latest syn-rift (ca. 7 Myr duration): the Tortonian was then characterized by the deposition of very thick salt series (>1000 m) which recorded a period of maximum restriction for the Suez rift. The basin was still subdivided into several sub-basins bounded by major faults. The basin with a N-S paleogeographic gradient was totally and permanently disconnected from the Mediterranean Sea and connected to open marine condition via the Red Sea. The Messinian was also characterized by a thick salt series, but the evaporite typology and sedimentary systems distribution suggest a more humid climate than during Tortonian times. Pre-salt to salt transition was not sharp and lasted for ca. 4 Myr (Langhian-Serravalian). It was initiated as the result of the combined effect of (1) climatic changes with aridization and low water input from the catchments and (2) rift dynamic induced by plate tectonic reorganization that controlled the interplay between sea level and accommodation zones constituting sills.

Ancient plate kinematics derived from the deformation pattern of continental crust: Paleo- and Neo-Tethys opening coeval with prolonged Gondwana–Laurussia convergence

The formation and destruction of supercontinents requires prolonged convergent tectonics between particular plates, followed by intra-continental extension during subsequent breakup stages. A specific feature of the Late Paleozoic supercontinent Pangea is the prolonged and diachronous formation of the collisional belts of the Rheic suture zone coeval with recurrent continental breakup and subsequent formation of the mid-ocean ridge systems of the Paleo- and Neo-Tethys oceans at the Devonian and Permian margins of the Gondwana plate, respectively. To decide whether these processes are causally related or not, it is necessary to accurately reconstruct the plate motion of Gondwana relative to Laurussia. Here we propose that the strain pattern preserved in the continental crust can be used for the reconstruction of ancient plate kinematics. We present Euler pole locations for the three fundamental stages of the Late Paleozoic assembly of Pangea and closure of the Rheic Ocean: (I) Early Devonian (ca. 400Ma) collisional tectonics affected Gondwana at the Armorican Spur north of western Africa and at the promontory of the South China block/Australia of eastern Gondwana, resulting in the Variscan and the Qinling orogenies, respectively. The Euler pole of the rotational axis between Gondwana and Laurussia is positioned east of Gondwana close to Australia. (II) Continued subduction of the western Rheic Ocean initiates the clockwise rotation of Gondwana that is responsible for the separation of the South China block from Gondwana and the opening of Paleo-Tethys during the Late Devonian. The position of the rotational axis north of Africa reveals a shift of the Euler pole to the west. (III) The terminal closure of the Rheic Ocean resulted in the final tectonics of the Alleghanides, the Mauritanides and the Ouachita–Sonora–Marathon belt, occurred after the cessation of the Variscan orogeny in Central Europe, and is coeval with the formation of the Central European Extensional Province and the opening of Neo-Tethys at ca. 300Ma. The Euler pole for the final closure of the Rheic Ocean is positioned near Oslo (Laurussia). Thus, the concomitant formation of convergent and divergent plate boundaries during the assembly of Pangea is due to the relocation of the particular rotational axis. From a geodynamic point of view, coupled collisional (western Pangea) and extensional tectonics (eastern Pangea) due to plate tectonic reorganization is fully explained by slab pull and ridge push forces.

Transient Cenozoic tectonic stages in the southern margin of the Caribbean plate: U-Th/He thermochronological constraints from Eocene plutonic rocks in the Santa Marta massif and Serranía de Jarara, northern Colombia

We use U-Th/(He) zircon and apatite thermochronology and Al in hornblende geobarometry from Eocene granitoids of the Sierra Nevada de Santa Marta and Guajira uplifted massifs in northern Colombia to elucidate the exhumation history of the northern South America continental margin and its bearing to Cenozoic Caribbean– South American plate interactions. Aluminium in hornblende geobarometry from the Eocene Santa Marta batholith yields pressures between 4.9±0.6kbar and 6.4±0.6kbar, which indicate that at least, 14.7-19.2km of unroofing took place since 56-50Ma in the northwestern Sierra Nevada de Santa Marta. In the Guajira Peninsula, calculated pressures for the Eocene Parashi stock are 2.3±0.6kbar and 3±0.6kbar. Stratigraphic considerations pertaining to Oligocene conglomerates from the Guajira area suggest that 6.9-9km of crust was lost between 50Ma and ca. 26Ma. U-Th/He zircon and apatite thermochronology from granitoids in the Sierra Nevada de Santa Marta shows the existence of major exhumation events in the Late Eocene (ca. 45-40Ma), Late Oligocene (ca. 25Ma) and Miocene (ca. 15Ma). The Guajira region records the Late Eocene to Early Oligocene (35-25Ma) event, but it lacks evidence for the Miocene exhumation phase. These differences reflect isolation of the Guajira region from the Sierra Nevada de Santa Marta and the Andean chain due to extensive block rotation and transtensional tectonics that affected the region during post-Eocene times. The post-Eocene events correlate in time with an increased convergence rate and the frontal approach of North and South America. It is suggested that the two major tectonic mechanisms that govern exhumation in these Caribbean massifs are: 1) subduction of the Caribbean plate, and 2) post Eocene changes in plate convergence obliquity and rates that caused the South American continental margin blocks to override the Caribbean plate. Temporal correlation with other Caribbean and Northern Andean events allows to resolve the regional Cenozoic plate tectonic reorganizations experienced by the South American, Caribbean and Pacific plates at a regional scale

The growth of a mountain belt forced by base-level fall: Tectonics and surface processes during the evolution of the Alborz Mountains, N Iran

The idea that climatically modulated erosion may impact orogenic processes has challenged geoscientists for decades. Although modeling studies and physical calculations have provided a solid theoretical basis supporting this interaction, to date, field-based work has produced inconclusive results. The central–western Alborz Mountains in the northern sectors of the Arabia–Eurasia collision zone constitute a promising area to explore these potential feedbacks. This region is characterized by asymmetric precipitation superimposed on an orogen with a history of spatiotemporal changes in exhumation rates, deformation patterns, and prolonged, km-scale base-level changes. Our analysis suggests that despite the existence of a strong climatic gradient at least since 17.5 Ma, the early orogenic evolution (from ∼36 to 9–6 Ma) was characterized by decoupled orographic precipitation and tectonics. In particular, faster exhumation and sedimentation along the more arid southern orogenic flank point to a north-directed accretionary flux and underthrusting of Central Iran. Conversely, from ∼6 to 3 Ma, erosion rates along the northern orogenic flank became higher than those in the south, where they dropped to minimum values. This change occurred during a ∼3-Myr-long, km-scale base-level lowering event in the Caspian Sea. We speculate that mass redistribution processes along the northern flank of the Alborz and presumably across all mountain belts adjacent to the South Caspian Basin and more stable areas of the Eurasian plate increased the sediment load in the basin and ultimately led to the underthrusting of the Caspian Basin beneath the Alborz Mountains. This underthrusting in turn triggered a new phase of northward orogenic expansion, transformed the wetter northern flank into a new pro-wedge, and led to the establishment of apparent steady-state conditions along the northern orogenic flank (i.e., rock uplift equal to erosion rates). Conversely, the southern mountain front became the retro-wedge and experienced limited tectonic activity. These observations overall raise the possibility that mass-distribution processes during a pronounced erosion phase driven by base-level changes may have contributed to the inferred regional plate-tectonic reorganization of the northern Arabia–Eurasia collision during the last ∼5 Ma.

Diversity dynamics of Early and Middle Jurassic brachiopods in the Getic and Danubian tectonic units of eastern Serbia: Regional versus global patterns

Quantitative assessment of regional diversity patterns reveals trajectories of faunal development on the basin scale and helps to understand its dependence on palaeoenvironmental changes, global-scale biotic evolution, and major events in the history of the Earth. A total of 86 species, 50 genera, 18 families, and 9 superfamilies of Early and Middle Jurassic brachiopods are established in the Getic and Danubian tectonic units of eastern Serbia. Compilation of their stratigraphic ranges allows analysis of their total diversity, number of appearances and disappearances, and turnovers. In both units, brachiopods radiated rapidly in the Early Pliensbachian. Then, their diversity declined, and these fossils disappeared. A new radiation took place in the Late Bajocian, and brachiopods remained diverse until the end of the Bathonian. They disappeared before the Callovian in the Getic Unit and in the Early Callovian in the Danubian Unit. The Early Pliensbachian radiation was significantly stronger than the Late Bajocian at the level of species; the strength of these radiations was more or less comparable at higher taxonomic levels. The strength of turnovers among brachiopods differed through geological time. The composition of the Middle Jurassic brachiopod assemblages was more or less stable. Regional shoreline shifts, basin depth changes, palaeobiogeographical changes, and plate tectonic re-organizations were possible controls on regional patterns of brachiopod diversity dynamics. However, the latter also reflects some diversity patterns documented globally and in some other regions (the Bakony Mountains, the Swiss Jura Mountains, and the Northern Caucasus).

Regional variations in the structure of the Permian Zechstein 3 intrasalt stringer in the northern Netherlands: 3D seismic interpretation and implications for salt tectonic evolution

The late Permian Zechstein evaporites in the northern Netherlands were exceptionally well imaged in [Formula: see text] of prestack depth migration 3D seismic data. Seismic reflections of a 30–150-m-thick Zechstein 3 anhydrite-carbonate stringer, which was encased in thick layers of rock salt, provided an unparalleled, basin-scale view of the 3D internal structure of a giant salt basin. Seismic data were used to map the regional variation of the intrasalt stringer to analyze its role in deformation styles and salt flow as well as its interaction with the sub- and suprasalt sediments. From our interpretation of the stringer, the salt layers, and the encasing sediments, three regional structural stringer styles can be defined and were analyzed in the context of regional salt kinematics. Our results revealed that the current stringer initially formed a continuous sheet of anhydrite and carbonate, embedded in salt of varying thickness. After the onset of syndepositional gravitational gliding of some of the salt masses and passive salt diapirism triggered by differential loading in the Triassic in other areas, salt flow caused rupture and folding of the stringer on a wide range of scales. The thickness and deformation degree of the individual salt layers controlled the development of regionally distinctive styles of intrasalt structures. Although deformation of the salt and the embedded stringer stopped early on morphologic highs, the basinal areas experienced phases of later activation or reactivation of salt structures and sedimentary basins. This was especially the case during the Late Cretaceous to Early Tertiary plate tectonic reorganization in the Central European plate, causing three-dimensionally complex intrasalt structures observable today.

Late Ordovician cooling event: Evidence from the Siberian Craton

The Upper Ordovician of the Tungus Basin on the Siberian Platform is represented by cool-water carbonates. Onset of cool-water conditions starts at the Darriwilian, and it is associated with widespread phosphatization, especially in the Volginian, Kirensko-Kudrinian and Chertovskian regional stages (mid-Darriwilian–lower Sandbian). The shift from tropical-type to temperate-type carbonates was preceded by destruction of the warm-water “carbonate factory” and a large input of siliciclastic material (Baykit Sandstone) during the Vikhorevian and Mukteian regional stages (lower to mid-Darriwilian). Wide distribution of temperate-type carbonates across the Siberian Platform, located in the low latitudes in the Ordovician time, can be explained by upwelling of cold oceanic waters and their penetration into epicontinental seas. The same situation was recorded for the Upper Ordovician of the North American Platform. Newly discovered K-bentonite beds in the uppermost Sandbian–Katian of the Tungus Basin are also associated with cool-water carbonates. The K-bentonite beds point to extensive volcanism on or near the western (in present-day orientation) margin of the Siberian Craton in the Late Ordovician time. Timing of the volcanism is surprisingly close to the period of volcanic activity of the Taconic Arc near the margin of Laurentia. Both upwelling and volcanism seem to be activated by the same plate-tectonic reorganization, and both these processes seem to play an important role in a global, later Ordovician cooling terminated by the Hirnantian glaciation.

New insights into peri-Gondwana paleogeography and the Gondwana super-fan system from detrital zircon U–Pb ages

We present a synopsis of detrital zircon U–Pb ages of sandstones from North Africa and neighboring Israel and Jordan, which allows us to identify zones with characteristic sediment provenance along the northern Gondwana margin (in present-day coordinates) in Cambrian–Ordovician times, and helps us to unravel the peri-Gondwana jigsaw puzzle. A special feature of the early Paleozoic cover sequence of North Africa is the eastward increase of 1.1–0.95Ga detrital zircons, which become ubiquitous in the early Paleozoic sandstones of the Saharan Metacraton. Detrital zircons aged about 2.7–2.5, 2.15–1.75 and 0.75–0.53Ga are also present. Early Paleozoic sandstones with similar provenance are known from peri-Gondwana terranes in the Eastern and Western Mediterranean and from NW Iberia. These terranes need not be transported from western Gondwana (Amazonia) as suggested previously. They were likely located to the north of the Saharan Metacraton during the early Paleozoic before they rifted off from Gondwana. Furthermore, we recognize an increase, as stratigraphic ages get younger, of ca. 1.0Ga detrital zircons at some point between the Late Cambrian and late Middle Ordovician. We speculate that this might be linked to far-field tectonics and regional uplift in central Gondwana related to plate-tectonic reorganization along the Gondwana margin, leading to erosion of ca. 1.0Ga basement and country rocks of the Transgondwanan supermountain and fluvial dispersal of detritus toward the Gondwana margin.

A Miocene tectonic inversion in the Ionian Sea (central Mediterranean): Evidence from multichannel seismic data

It is widely accepted that the Central and Eastern Mediterranean are remnants of the Neo-Tethys. However, the orientation and timing of spreading of this domain remain controversial. Here, we present time migrated and pre-stack depth migrated NW-SE oriented Archimede (1997) lines together with the PrisMed01 (1993) profile to constrain the evolution of the Ionian basin. Our interpretation allows us to identify a large-scale set of SW-NE striking reverse faults beneath the Ionian Abyssal Plain. These primarily NW vergent faults are characterized by a spacing comprised between 10 to 20 km and a dip ranging from 60 to 65{degree sign}. Following very recent paleogeographic reconstructions, we propose that the set of N{degree sign}55 features initially formed as normal faults during the NW-SE trending seafloor spreading of the Ionian basin after its late Triassic-early Jurassic rifting. Based on geometric comparisons with the intraplate deformation observed beneath the Central Indian Ocean, we show that the inherited oceanic normal faults were reactivated under compression as reverse faults. Well-developed Tortonian syntectonic basins developed NW of the major faults and the base of the Messinian evaporites (Mobile Unit) is slightly folded by the activity of the faults. We show that 3-4 km of total shortening occurs over a 80 km wide area beneath the Ionian Abyssal Plain, resulting in a bulk shortening of 3.5-5 %. We propose a link between the Tortonian-early Messinian inversion of the fault pattern and a plate tectonic reorganization prior to the main phase of back-arc opening of the Tyrrhenian domain.

Paleoenvironmental changes across the Eocene-Oligocene boundary: insights from the Central-Carpathian Paleogene Basin

Paleoenvironmental changes across the Eocene-Oligocene boundary: insights from the Central-Carpathian Paleogene Basin The sedimentary sequence of the Central-Carpathian Paleogene Basin provides proxy records of climatic changes related to cooling events at the Eocene/Oligocene boundary (TEE). In this basin, climatic deterioration is inferred from the demise of the carbonate platform and oligotrophic benthic biota in the SBZ19 and from the last species of warm-water planktonic foraminifers in the E14 Zone. Upper Eocene formations already indicate warm-temperate to cool-temperate productivity and nutrient-enriched conditions (Bryozoan Marls, Globigerina Marls). Rapid cooling during the earliest Oligocene (Oi-1 event) led to a temperature drop (~11 °C), humidity, fresh water influx and continental runoff, water mass stratification, bottom water anoxia, eutrofication, estuarine circulation and upwelling, carbonate depletion, sapropelitic and biosiliceous deposition, H2S intoxication and mass faunal mortality, and also other characteristics of Black Sea-type basins. Tectonoeustatic events with the interference of TA 4.4 sea-level fall and the Pyrenean phase caused basin isolation at the beginning of the Paratethys. The Early Oligocene stage of Paratethyan isolation is indicated by a stagnant regime, low tide influence, endemic fauna development, widespread anoxia and precipitation of manganese deposits. The episodic rise in the sea-level, less humid conditions and renewed circulation is marked by calcareous productivity, nannoplankton blooms and the appearance of planktic pteropods and re-oxygenation. Paleogeographic differentiation of the Carpatho-Pannonian Paleogene basins resulted from plate-tectonic reorganization during the Alpine orogenesis.

Piston core record of Late Paleogene (31 Ma) to recent seafloor hydrothermal activity in the Southwest Pacific Basin

A large diameter piston core containing 8.35 m of metalliferous sediment has been recovered from a small abyssal valley in the remote Southwest Pacific Basin (31° 42.194′S, 143° 30° 331′W; 5082 m water depth), providing unique insight into hydrothermal activity and eolian sedimentation there since the early Oligocene. A combination of fish‐teeth Sr‐isotope stratigraphy and INAA geochemical data reveals an exponentially decreasing hydrothermal flux 31 Ma to the present. Although hydrothermal sedimentation related to seafloor spreading explains this trend, a complex history of late Eocene/early Oligocene ridge jumps, propagating rifts and plate tectonic reorganization of South Pacific seafloor could have also played a role. A possible hiatus in deposition, as recorded by changes in core composition just below 2 m depth, is beyond the resolution of the fish teeth Sr isotope dating method employed here; however, the timing of this interval may be coincident with extinction of the Pacific‐Farallon Ridge at ∼20 Ma. A low flux eolian component accumulating at this site shows an increase relative to the hydrothermal component above 2 m depth, consistent with dust‐generating continental sources far to the west (Australia/New Zealand). This is the first long‐term paleoceanographic record obtained from within the South Pacific “bare zone” (Rea et al., 2006), an anomalous region where Pacific seafloor has largely escaped sediment accumulation since the Late Cretaceous.