Intercalibration of Boreal and Tethyan timescales: the magneto-biostratigraphy of the Middle Triassic and the latest Early Triassic from Spitsbergen, Arctic Norway

An integrated bio-magnetostratigraphic study of the latest Early Triassic to the upper parts of the Middle Triassic, at Milne Edwardsfjellet in central Spitsbergen, Svalbard, allows a detailed correlation of Boreal and Tethyan biostratigraphies. The biostratigraphy consists of ammonoid and palynomorph zonations, supported by conodonts, through some 234 m of succession in two adjacent sections. The magnetostratigraphy consists of ten substantive normal–reverse polarity chrons defined by sampling at 150 stratigraphic levels. The magnetization is carried by magnetite and an unidentified magnetic sulphide, and is difficult to fully separate from a strong present-day like magnetization. The bio-magnetostratigraphy from the late Olenekian (Vendomdalen Member) is supplemented by data from nearby Vikinghøgda. The early and mid-Anisian has a high sedimentation rate, comprising over half the ca. 140-m thickness of the Botneheia Formation, whereas the late Anisian and lower Ladinian is condensed into about 20 m. The two latest Boreal Ladinian ammonoid zones are absent due to erosional truncation below the Tschermakfjellet Formation. Correlation to Tethyan bio-magnetostratigraphies shows the traditional base of the Boreal Anisian (base of G. taimyrensis Zone) precedes the base Anisian (using here definitions based on the Desli Caira section in Romania). The Boreal upper Anisian G. rotelliforme and F. nevadanus ammonoid zones correlate to most of the Tethyan Pelsonian and Illyrian substages. The base Ladinian defined in the Tethyan global boundary stratotype and point (GSSP) is closely equivalent to the traditional base of the Boreal Ladinian at the I. oleshkoi Zone. The latest Olenekian to early Anisian magnetic polarity timescale is refined using the Spitsbergen data

Geology and palynology of the Triassic succession of Bjørnøya

The Triassic succession of Bjørnøya (200 m) comprises the Lower Triassic Urd Formation (65 m) of the Sassendalen Group, and the Middle and Upper Triassic Skuld Formation (135 m) of the Kapp Toscana Group. These units are separated by a condensed '.'Middle Triassic sequence represented by a phosphatic remainé conglomerate (0.2m). The Urd Formation consists of grey to dark grey shales with yellow weathering dolomitic beds and nodules. Palynology indicates the oldest beds to be Diencrian; ammonoid faunas in the middle and upper part of the formation arc of Smithian age. The organic content (c. 1 %) includes kerogen of land and marine origin, reflecting a shallow marine depositional environment. The Skuld Formation is dominated by grey shales with red weathering siderite nodules. There are minor coarsening upwards sequences; the highest bed exposed is a 20 m thick, very fine-grained sandstone. Palynomorphs indicate a late Ladinian age for the lower part of the formation, and macrofossils and palynomorphs indicate Ladinian to Carnian ages for the upper part. Sedimentary structures, a sparse marine fauna and microplankton indicate deposition in a shallow marine environment. The organic residues contain dominantly terrestrially derived kerogen

Palynostratigraphic reassessment of the Late Devonian of Bjørnøya, Svalbard

A comprehensive study of the Late Devonian palynostratigraphy of Bjørnøya, Svalbard Archipelago is presented.A total of 61 samples collected from 10 outcrops located along the eastern coast of the island were analyzed forpalynology yielding a mid- to latest Famennian age. A reassessment of the existing palynostratigraphy of the UrsaSandstone Unit of the Røedvika Formation was undertaken. As no independent age control exists for this succes-sion, the palynological assemblages were correlated to well-calibrated palynological zonations from the Easternand Western Europe. The middle to upper part of the Vesalstranda Member and the Kapp Levin Member wereassigned a mid- to late Famennian age (CVa to VF biozones), and the middle to lower-upper part of the TunheimMember was dated as latest Famennian in age (LL to LN biozones). For thefirst time, a palynological age wasassignedto the upperpart ofthe KappLevin Member. Correlation with other Arctic areas show close resemblanceto Late Devonian assemblages from Europe and the Arctic region. However, differences in the stratigraphicalranges of several taxa were identified. In terms of Late Devonian paleophytogeographic provinces the miosporeassemblages are assigned to the Northern EuroamericanCornispora varicornataRealm for the mid-Famennian. Amore cosmopolitan trend was recognized for the latest Famennian (Strunian), with assemblages including abun-dantRetispora lepidophyta. The paleobotanical affinities of the palynomorphs reveal aflora of lycopods andprogymnosperms occupying this area during the Late Devonian, withRetispora lepidophytabecoming a commonelement in the latest Famennian.Portuguese Foundation for Science and Technology: UIDP/00350/2020info:eu-repo/semantics/publishedVersio

Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis

International audienceOne of the most important carbon cycle perturbations following the end-Permian mass extinction event straddles the Smithian-Spathian boundary (SSB) (Olenekian, Early Triassic). This anomaly is characterized by a prominent positive carbon isotope excursion known from Tethyan marine rocks. Its global signifi cance is established here by a new high paleolatitude record (Spitsbergen). Paleontological evidence, such as Boreal palynological data (Barents Sea, Norway) and global patterns of ammonoid distribution, indicates a synchronous major change in terrestrial and marine ecosystems near the SSB. The reestablishment of highly diverse plant ecosystems, including the rise of woody gymnosperms and decline of the formerly dominating lycopods, is interpreted as an effect of a major climate change. This hypothesis is supported by modeling of ammonoid paleobiogeography, the distribution patterns of which are interpreted as a proxy for sea surface temperatures (SST). The latest Smithian thus appears to have been a time of a warm and equable climate as expressed by an almost fl at pole to equator SST gradient. In contrast, the steep Spathian SST gradient suggests latitudinally differentiated climatic conditions. We propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end-Smithian CO2 injection. The SSB event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end-Permian biotic crisis