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In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW–SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with east–west to NE–SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems. [ABSTRACT FROM AUTHOR]

We present new geophysical observations of the Mull Dyke Swarm in the Southern North Sea. Two- and three-dimensional seismic reflection and aeromagnetic data were used to map the dykes. The three main dyke groups recognized onshore (Cleveland, Blyth and Hawick–Acklington) are found to extend to varying distances into the North Sea, crossing a number of major crustal-scale fault zones and domain boundaries, with almost no reorientation. The Blyth Dyke Group extends furthest, for a distance of 672 km from the source on Mull. The seismic data show extensive development of pit chain craters above the upper tips of these dykes, which can be approximately dated to the late Paleocene from the ages of crater fills. Volumetric estimates are made of the intrusive volumes associated with each group, ranging from 90 to 202 km3. These three main axes of intrusion probably formed in different intrusive events within a c. 1 myr period, from 59 to 58 Ma, during magnetic chron C26R. [ABSTRACT FROM AUTHOR]

Navarino Island is located in the southernmost part of the Fuegian Andes, south of the Beagle Channel. Its geological record documents the complex tectonic history of Tierra del Fuego, which includes the opening and closure of the Rocas Verdes basin, Cordillera arc collision and subsequent subduction processes. The geology of the island is mostly composed of the Cretaceous Yahgán Formation, a marine metasedimentary sequence, which is intruded by diverse plutons that are mostly exposed on the northwestern tip of the island. We herein present a new dataset that shows the presence of three Cretaceous–earliest Paleocene magmatic suites of active margin magmatism emplaced during the early stage of the Fuegian Andes, which are referred to as (1) the Dientes de Navarino Microdioritic Sills, a suite of pre-tectonic microdioritic sills that formed at c. 101–97 Ma; (2) the Castores Plutonic Complex, a series of pre- to syntectonic gabbroic to tonalitic plutons emplaced at c. 90–87 Ma, and (3) the Samantha Monzonites, a suite of isolated monzonitic to monzodioritic post-tectonic plutons that formed at c. 66–65 Ma. These distinct magmatic episodes are recognized by field observations, geological mapping, petrography and whole-rock geochemistry integrated with amphibole and biotite 40Ar/39Ar and U–Pb LA-ICP-MS. The geochemical compositions of these rocks are consistent with a continental arc setting that existed during the interval c. 101–65 Ma. Whereas the three pulses spatially overlap in Navarino Island, the arc magmatism shows a migration (or expansion) throughout the Late Cretaceous. The locus of the arc then migrates at c. 68–66 Ma towards the SW. We suggest that this trenchward migration at c. 68–66 Ma may be associated with a change in the subduction angle. The three Cretaceous–earliest Paleocene plutonic pulses recorded in Navarino Island formed during the early stages of development of the Fuegian Andes, and are pre-, syn- and post-tectonic with respect to a major compressional event caused by the collision and obduction of the back-arc Rocas Verdes oceanic floor. Supplementary material: A detailed dataset is available at https://doi.org/10.6084/m9.figshare.c.6675416 [ABSTRACT FROM AUTHOR]

This study focuses on new clumped isotope data from concretionary calcite cements in the Middle Jurassic Valtos Sandstone Formation (Great Estuarine Group) of the Inner Hebrides. Clumped isotopes show that concretion cementation began at 45 ± 6°C increasing to temperatures in excess of 70°C before cooling slightly to 57 ± 7°C at the concretion margin. In the early stages of cementation, calculated δ 18OFLUID values were c. −12‰ VSMOW, identical to an estimate of Paleocene Hebridean meteoric water based on hydrothermal reactions close to Paleocene igneous centres. These δ 18OFLUID values imply that concretion cementation started in the Paleocene probably during the earliest stages of phreato-magmatic effusive igneous activity. As the concretion grew, temperature changes were accompanied by progressively evolving δ 18OFLUID compositions up to +2.1 ± 1.1‰ VMOW. These evolving δ 18OFLUID compositions were caused by isotope exchange reactions between 18O-rich lithologies and hot basinal fluids migrating upward along faults. This fluid flow was driven by progressive crustal loading from the thickening Paleocene lava pile, which also caused sandstone compaction. Published radiometric dates that constrain the emplacement time of the Skye Lava Group, and its subsequent rapid erosion, suggest that concretion formation and final compaction was completed in no more than 2.6 myr, far more rapidly than modelled previously. Initial concretion growth that predates development of volcanic topography shows that the strongly negative compositions of Hebridean Paleocene meteoric water are mainly of latitudinal rather than orographic origin. Supplementary material: Clumped isotope data correction and uncertainties, sample details and additional figures are available at https://doi.org/10.6084/m9.figshare.c.6459860 [ABSTRACT FROM AUTHOR]

The Paleocene–Eocene Thermal Maximum (PETM) has previously been recorded in marine density flow sedimentary rocks of the Forties Member, Sele Formation, North Sea Basin. Two cored well sections with existing δ 13C records were analysed for their total palynofloras. Using statistically defined microplankton groups and diversity data, the Sele Formation Unit S1 depositional sequence and its maximum flooding surface was identified in both wells. This highlighted that deposition of the Forties Fan complex began significantly earlier than the inception of the PETM in the proximal fan area. Palynofloras from the Central and West Axial fairways of the Forties Fan have previously been used to indicate increased rainfall, erosion and onset of Forties Fan deposition at the PETM inception. However, winterwet floodplain communities typify the coeval East Axial Fairway, whereas the dominance of swamp-derived communities in the West and Central Axial Fairway sediments reflects source palaeogeography overriding the regional winterwet climate signal. Palynofloras reflecting regional increased seasonality and lower moisture availability increase immediately before the PETM CIE onset, but reflect climate warming over the hyperthermal. However, there is no correlation between Forties Fan initiation and the PETM. NE Atlantic margin basin flank uplift in response to synrift volcanism is indicated as the driving mechanism behind Forties Fan inception. Supplementary material: Raw data, DCA graphs for microplankton, pollen and spore data and δ 13C data for well 22/6-1 are available at https://doi.org/10.6084/m9.figshare.c.6080873 [ABSTRACT FROM AUTHOR]

The break-up of Gondwana resulted in extension of New Zealand continental crust during the Cretaceous-- Paleocene. Offshore the geometry and rift history arewell imaged by new regional mapping of a large seismic reflection dataset, tied to wells, used here to document the Cretaceous--Paleocene (c. 105 -- 55 Ma) evolution of the greater Taranaki Basin region. Two temporally distinct phases of rifting have been recognized in the region, and record Gondwana break-up. The first (Zealandia rift phase) produced half-grabens trending NW to WNW during the mid-Cretaceous (c. 105 -- 83 Ma). These rift basins predate, and are parallel to, Tasman Sea spreading centres. They record distributed stretching of northern Zealandia prior to the onset of seafloor spreading in the Tasman Sea. A short period (c. 83 - 80 Ma) of uplift and erosion followed, possibly representing a break-up unconformity, with erosion in southern Taranaki Basin and deposition of the 'Taranaki Delta' sequence in Deepwater Taranaki. The second, West Coast-Taranaki rift phase produced north- to NE-trending extensional half-grabens in the shelfal Taranaki Basin during the latest Cretaceous-Paleocene (c. 80-- 55 Ma). This rift was narrow (<150 km wide), orthogonal to Zealandia phase rifting, affected mainly western Zealandia and did not progress to full break-up. [ABSTRACT FROM AUTHOR]

Detrital zircon U-Pb laser ablation inductively coupled plasma mass spectrometry age data for Paleocene and Eocene sandstones from the Central Tertiary Basin on Spitsbergen, Arctic Norway are used to investigate provenance and to test the filling history of the basin in response to the evolving Eurekan orogeny. The zircon age data from 16 analysed samples allow us to distinguish five sources. The zircon age populations of the Paleocene Firkanten and Basilika formations have a distinct Uralide signature (c. 275 Ma) and are interpreted to represent four mixtures of reworked Late Triassic, Jurassic and older sandstones affected by Early Cretaceous volcanism. The zircon age population of the Eocene Battfjellet Formation lacks Uralide- and Early Cretaceous-aged zircons and is dominated by Proterozoic and Archaean zircons indicating sourcing from Middle Triassic and older rocks. The data support models implying a marked shift from easterly to westerly source areas during the evolution of the basin in response to the evolving Eurekan orogeny. The population of Cretaceous-aged zircons indicates that volcanism in the High Arctic Large Igneous Province took place during two separate events at 80-100 and 118-150 Ma, thus supporting previous models for Cretaceous volcanic activity in the High Arctic. [ABSTRACT FROM AUTHOR]

The article presents a comment to Loseth and colleagues' study on the physical processes of injection, extrusion and depletion of sand in the North Sea. Topics discussed include reasons behind the sand being extrusive according to Loseth and a study from Rundberg and Eidvin, reasons for suggesting Paleocene and Eocene deep marine sands as source of Oligocene sands and the erosion at the top Hordaland Group Unconformity.

Mass-balance calculations indicate that a massive amount of d13C-depleted carbon was released into the early Danian atmosphere in volumes comparable with the younger Paleocene-Eocene Thermal Maximum (PETM). This Danian hyperthermal event (the Dan-C2) has been documented from the fill of the Boltysh meteorite crater, Ukraine. Palynofloras recovered from the Boltysh crater fill show a trend from mesic forest to savannah ecosystem dominance on a millennial scale across the hyperthermal inception with no abrupt compositional shift. This longer-term trend is overprinted by moisture availability oscillations reflecting orbital forcing. Forcing is not directly tracked by the oscillations, which are composed of mesic forest and savannah palynofloras separated by rapid critical transitions. The absence of an ecological collapse at the Dan-C2 indicates that plant ecosystems experienced dominant forcing from orbital cyclicity, rather than a stochastic temperature rise. [ABSTRACT FROM AUTHOR]

The Palaeocene-Eocene Thermal Maximum (PETM) interval at the Wadi Nukhul section (Sinai, Egypt) is represented by a 10 cm thick condensed clay-rich layer corresponding to the NP9a-NP9b nannofossil subzone boundary. The Wadi Nukhul Palaeocene-Eocene boundary (PEB) is characterized by (1) an abrupt negative excursion in carbonate and organic carbon isotope ratios (-6‰ in δ13Ccarb and -2‰ δ13Corg), (2) an abrupt persistent negative shift in organic nitrogen isotope values (δ15Norg), (3) a significant increase in phosphorus concentrations just above the carbon isotope excursion, (4) a decrease in carbonate content and significant increase in kaolinite and (5) high vanadium and low manganese contents coincident with the occurrence of framboidal pyrite. The abrupt correlative isotopic excursions of δ13Ccarb, δ13Corg and δ15N suggest that the lowermost part of the PETM is missing. The decrease in carbonate content indicates dilution by high detrital input triggered by acid weathering and carbonate dissolution in response to increased atmospheric CO2 resulting from the oxidation of methane. The sudden increase in kaolinite content reflects a short-lived change to humid conditions. The δ15N values close to 0‰ above the PEB suggest a bloom of N2-fixing cyanobacteria. Increased bacterial activity may be either the cause or the result of the anoxia locally associated with the PETM. [ABSTRACT FROM AUTHOR]

The Kap Washington Group volcanic sequence is exposed on the north coast of Greenland. The sequence was erupted in a continental rift setting during the opening of the Arctic Ocean and provides important geological constraints on the timing of this event. In this study we present the first isotope dilution thermal ionization mass spectrometry U-Pb zircon ages from 10 samples of trachytic to rhyolitic composition. Samples from Lockwood Island (n = 4) gave concordant ages between 67.2 ± 0.5 and 61.0 ± 0.3 Ma (2±). Lavas from Kap Kane (n = 5) yielded concordant ages between 70.5 ± 0.3 and 69.7 ± 0.2 Ma. An ignimbrite from the Kap Washington peninsula yielded a concordant age of 68.5 ± 0.3 Ma. The Kap Washington Group sequence and similar occurrences on Ellesmere Island record a prolonged period of continental rift volcanism lasting from 92 to 58 Ma. We propose that this volcanism occurred along the margins of a nascent Eurasia Basin undergoing east-west extension linked to rifting in the Labrador Sea-Baffin Bay system. [ABSTRACT FROM AUTHOR]