Risto A. Kumpulainen

Field data from recent geological mapping over a major part of the north-central Scandinavian Caledonides combined with published information give a detailed view of early Cambrian basin successions, comprising the Gärdsjön formation (Gf; Jämtland supergroup) in the Lower Allochthon and autochthonous equivalents (Dividal Group). The Gf comprises ten units of sandstone and siltstone or mudstone (Gf I—X, > 300 m thick). Green siltstones with red layers (Gf VI, c. 521 to 519 Ma) and green–grey siltstones at the top (Gf X, c. 516.5 to 513.5 Ma) are regional key horizons. Gf V, VI, VII, IX, and X deposition may be related to eustatic events. Restoration of Caledonian shortening reveals a major “Hornavan-Vattudal basin” (HVB; > 330 km NW–SE, > 400 km NE-SW) between the Grong–Olden culmination in the S and the Akkajaure–Tysfjord culmination in the N. Published zircon ages imply the latter separated the HVB from those shed from the Timan orogen in the N. The eastern basin margin straddles the present Caledonian erosional margin. Basement highs identified here within the Nasafjället, Bångonåive, and Børgefjellet “basement” windows define the western margin. They separate the HVB from the outer shelf towards the Iapetus Ocean in the W. The onset of sedimentation is time-related with E–W extension at c. 544–534 Ma. NNE–SSW-directed extension occurs after c. 518 Ma, perhaps related with Timan late-orogenic extension. The HVB is distinctly younger (c. 535–513.5 Ma) than Rodinia break-up and Iapetus ocean formation (> 550 Ma), comparable with post-rift basins in inner parts of modern passive margins. Graphical Abstract

The Ottfjället Dyke Swarm (ODS) is a prominent component of the Ediacaran mafic magmatism associated with opening of the Iapetus ocean, and hosted in the Särv Nappe, Middle Allochthon of the Scandinavian Caledonides. A U-Pb baddeleyite age of 596.3 ± 1.5 Ma for a thick, well preserved, plagioclase-phyric dolerite dyke in Härjedalen, Sweden, dates emplacement of the swarm. The age represents a robust, inheritance-free reference age for variably deformed and metamorphosed tholeiitic dykes in sandstone-dominated sequences of the lower part of the Middle Allochthon, representing the proximal, rifted Baltoscandian margin preceding the opening of Iapetus. The new age is within the narrow time span between 610 and 595 Ma defined by the most reliable age estimates for mafic dykes in structurally higher nappes (upper part of Middle Allochthon), representing the distal margin during the opening of Iapetus. The Ottfjället Dyke Swarm cuts the Tossåsfjället Group succession, which includes sabkha-related carbonate platform and diamictite couples, one of several correlated Neoproterozoic glaciogenic successions in Scandinavia. The intrusion age of ca. 596 Ma therefore sets a minimum age for the glaciogenic successions. It implies that Neoproterozoic glaciations in Scandinavia predate the ca. 580 Ma Gaskiers glaciation event and are probably part of the ca. 635 Ma Marinoan “Snowball-Earth”-type glaciation.

This guide provides recommendations on how to introduce formal names for geological units, specifically lithostratigraphic, chronostratigraphic, biostratigraphic, lithodemic, tectonic and tectonostratigraphic units, as well as for other geological features such as deformational structures and bedrock landforms. The recommendations apply to Swedish geology but are crafted to harmonize with international practice in geological nomenclature.

All geoscientists working with the geology of Sweden are invited to join a common effort to review Swedish geological nomenclature and the naming of geological units and other features. A new guide, the Guide for geological nomenclature in Sweden, provides advice for this review process. The Geological Survey of Sweden will set up a new open and freely accessible database for geological names, and a dedicated name committee with mandate to formally approve proposed names will supervise the naming process. The success of this vital long-term commitment will depend on active participation of the geoscientific community at large.

Trace fossils Broomichnium cf. fliri, Glaciichnium cf. liebegastensis, Planolites isp., ?Undichna isp. and ?Warvichnium ulbrichi have been recognised in early Holocene glacial varved clays near Vittinge, west of Uppsala, Sweden. They are referred to different arthropods and fishes that periodically colonised the lake floor and were important components of the ecosystem. The trace fossils are typical of the Glaciichnium ichnocoenosis within the Mermia ichnofacies, which suggests less stressful conditions in Vittinge than in many other Quaternary varved clays in Europe typified by the Cochlichnus ichnocoenosis.

This issue of the GFF is dedicated to Professor Maurits Lindström on the occasion of his 75th birthday by students, colleagues, and friends in recognition of his profound impact on the Science of Geology as researcher and teacher during more than half a century.