Jan Ove R. Ebbestad

Attempted predation and shell repair in Middle and Upper Ordovician gastropods from Sweden

Repaired shell injuries are reported in 11 specimens including six genera and eight species of gastropods from the upper Middle Ordovician (Caradoc) Kullsberg Limestone and the Upper Ordovician (Ashgill) Boda Limestone, Siljan district, Sweden. The specim

New Ordovician-Silurian drill cores from the Siljan impact structure in central Sweden: an integral part of the Swedish Deep Drilling Program

New drill cores from the largest known impact structure in Europe, the relict of the Siljan meteorite crater, provide new possibilities to reconstruct Early Palaeozoic marine environments and ecosystems, and to document changes in sedimentary facies, sea level and palaeoclimate in Baltoscandia. The impact crater is an important target of the project “Concentric Impact Structures in the Palaeozoic” within the framework of the “Swedish Deep Drilling Program”. Two core sections, Mora 001 and Solberga 1, have been analysed. The sedimentary successions of these core sections include strata of late Tremadocian through late Wenlock ages. Our preliminary studies show not only that several of the classical Palaeozoic units of Sweden are represented in the area, but also that other significantly different facies are preserved in the Siljan district. An erosional unconformity representing a substantial hiatus occurs between Middle Ordovician limestone and a Llandovery-Wenlock (Silurian) shale succession in the western part of the Siljan structure and suggests an extended period of uplift and erosion. This may be related to forebulge migration due to flexural loading by the Caledonian thrust sheet to the west. Thus, this part of Sweden, previously regarded as a stable cratonic area, presumably was affected by the Caledonian collision between Baltica and Laurentia.

Biochronology of the autochthonous Lower Cambrian in the Laisvall–Storuman area, Swedish Caledonides

New records of phytoplankton (acritarchs). ichnofossils and olenellid trilobites have been studied from the autochthonous upper Neoproterozoic-Lower Cambrian successions along the Caledonian Thrust Front in the Laisvall-Storuman region of northern Sweden.

Multiple attempted predation in the Middle Ordovician gastropod Bucania gracillima

Abstract Repaired shell injuries, resulting from multiple non-lethal predatory attacks are reported in the bellerophontid gastropod Bucania gracillima Koken, 1896, from the upper Middle Ordovician of Sweden. The described specimen shows four distinct, ontogenetically separate, attacks on the body whorl, each of which resulted in shell breakage and subsequent shell repair. All but one of the attacks are concentrated along the dorsal emargination, with large portions of the shell being removed in the three major episodes of breakage. Irregular growth of the dorsal carina and on the lateral areas associated with the attacks, shows that the mantle itself was damaged. The predator, however, is unknown.

Concentric impact structures in the Palaeozoic of Sweden – the Lockne and Siljan craters

The Ordovician age Lockne and Devonian Siljan craters are two of the largest impact structures in northern Europe. Both formed in targets with a thick, low-strength upper layer. This target configuration is known to generate concentric crater structures with an outer, shallow crater in the low-strength layer, surrounding a central, deeper crater in the more resistant substrate. The concentric craters of Lockne and Siljan are excellent models for studies of similar concentric craters on Earth and elsewhere in the Solar system. Several structural issues remain, and drilling through the craters within the Swedish Deep Drilling Program intends to address the following: the extent of the craters with respect to the time of impact; the effects of cratering on the basement; and the role of basement structure for the crater formation. A problem for the Lockne crater is the relation to the Caledonian orogeny and the lateral extension of the ejecta blanket – the rim is interrupted by a radial depression that has been interpreted both as primary and secondary, tectonically induced. A second feature to study is the deeper and older (1.82–1.80 Ga) NNW–SSE shear zones that cut the basement. In the Siljan area the development of mega block associations comprising the infilling of the graben is disputed. The blocks may either be formed by sagging of peripheral parts of the fault blocks or alternatively by major radial movement involving kilometre long transport.

Burlingiid trilobites from Norway, with a discussion of their affinities and relationships

Four Middle and Upper Cambrian burlingiid trilobites from the Oslo Region, Norway, are described including Burlingia angusta sp. nov. from the Ptychagnostus punctuosus Zone and Schmalenseeia athrotryphe sp. nov. from the lower part of the Lejopyge laevigata Zone. New complete material previously attributed to Schmalenseeia jagoi Whittington is assigned to Burlingia. Cladistic analysis supports the genera Burlingia and Schmalenseeia as currently understood, including the placement of the controversial middle Middle Cambrian Schmalenseeia acutangula Westergard in Schmalenseeia, even though it lacks typical characters of the genus such as the median ridge on the preglabellar field. The analysis also supports burlingiid monophyly, and suggests that Schmalenseeia was derived from a broadly Burlingia–like ancestor, with S. acutangula displaying how the transition may have occurred. The broader relationships of Burlingia remain obscure, although similarities between burlingiids and the arthropod Kleptothule from the Early Cambrian Sirius Passet fauna are discussed: these include overall form, lack of functional hinges in the thorax, and details of the cephalic region. It is unclear whether these similarities represent general progenetic features, are functional convergences or, less likely, represent a genuine relationship.

Shell repair following failed predation in two Upper Ordovician brachiopods from central Sweden

Abstract Shell repair is reported in two dorsal valves of the brachiopod Strophomena? arachnoidea Lindström, 1880 from the lower Ashgill Fjäcka Formation of the Siljan district, Dalarna. The most severe case displays a large wedge-shaped injury that cuts back about half the length of the animal. Substantial damage to the growing edge of the mantle resulted in malformation of the repaired area. The outline of the injury on the second specimen is also wedge-shaped, but of much less extent and with little disturbance of the subsequent growth pattern. Both injuries are interpreted as resulting from failed predation, with cephalopods being the most likely aggressors.

Bucaniid gastropods from the Upper Ordovician of Baltica, with a discussion of the Bucaniinae

Bucaniid gastropods from the Upper Ordovician of Baltica, with a discussion of the Bucaniinae

Paragastropoda, Tergomya and Gastropoda (Mollusca) from the Upper Ordovician Dalby Limestone, Sweden

Abstract A fauna of 12 species of paragastropods, tergomyans and gastropods is described from the Upper Ordovician (Kukruse Stage to Idavare substage) Dalby Limestone of Tvären, Lockne, and Fjäcka (Sweden), presenting a higher diversity than previously recognized. The presence of Mimospira, Laeogyra, Sarkanella epelys n. sp. indicates a strong faunal connection with Bohemia, Czech Republic. Sarkanella is reported from outside Bohemia for the first time. Bucania erratica n. sp. represents one of the earliest records of the genus in Baltoscandia. A single case of shell repair from failed predation is recorded in this species. Synonyms for Eccyliopterus princeps Remelé and E. regularis Remelé are proposed. The significance of Laeogyra, Eccyliopterus, and Deaechospira for regional correlation within the Upper Ordovician of Baltoscandia is confirmed.

Terminal Ordovician stratigraphy of the Siljan district, Sweden

Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive δ13C excursions are identified (from bottom) – the Moe, an unnamed excursion, Paroveja and Hirnantian Carbon Isotope Excursion (HICE). The δ13C values through the Boda Limestone are 1–2‰ higher than usual in Baltica, only the values for the HICE remains within what is expected. Background values increase from 1.5‰ in the bottom of the core of the Boda Limestone up to 3‰ in the top of it. The HICE is identified in five of eight sections and the main peak falls according to inferred correlation within the Metabolograptus persculptus Biozone, at or close to the Hindella beds in the Upper Boda Member. The late Katian (Pirgu) age of Holorhynchus in the Siljan district is clear and its co-occurrence with the chitinozoan Belonechitina gamachiana in Estonia supports a Katian age for this zone. The base of the Ozarkodina hassi Biozone may occur within units B–C of the Upper Boda Member and in the upper part of the Loka Formation and most likely is correlated with the M. persculptus Biozone. The Hirnantia–Dalmanitina faunas reported from the lowermost part of the Loka Formation and units B–D of the Upper Boda Member seem to range through all the Hirnantian, but detailed morphological studies allow to distinguish an older ( = extraordinarius) and a younger ( = persculptus) fauna.