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The Hemse Group is one of the least understood stratigraphic units of the Silurian sequence of Gotland, Sweden. New results from airborne transient electromagnetic (ATEM) measurements in combinatio...

Based on the Tingskullen drillcore, we present the first continuous carbon isotope stratigraphy from the Lower–Middle Ordovician “orthoceratite limestone” of Oland, Sweden. The extremely condensed Tremadocian and Floian stages include large gaps as well as the Ceratopyge Regressive Event and the widespread Evae transgression accompanied by prominent shifts in the δ 13C record. The Dapingian and Darriwilian stages are characterised by low sedimentation rates and a relatively complete sedimentary record. A total of 99 whole-rock samples were analysed for carbon isotope geochemistry from the Ordovician part of the succession (46 m thick). The most striking anomaly detected is the middle Darriwilian isotope carbon excursion (MDICE) that appears unusually well developed and complete for the region, and thus forms an important proxy for intercontinental correlation of the succession.

This paper reports on the geochemistry of the mid-Silurian Grotlingbo Bentonite, a ca. 0.1–0.4-m-thick and regionally important bentonite bed in Sweden and the East Baltic area. A series of eight samples, spaced by 5 cm, were taken from the Hunninge-1 drillcore in Gotland, Sweden, and were analysed in order to establish the vertical element composition and variation in the bentonite. The results show that the Gotlingbo Bentonite originates from one source magma and from one single eruption. The lowermost 0.1–0.15 m of the bentonite (compacted) was deposited from air-transport fall-out, whereas the upper portions have been reworked in a shallow-marine environment and re-deposited. Vertical differences in Ti and Zr within the Grotlingbo Bentonite mean that regional correlation of the bed may need several samples at each locality to be reliable.

Zircon grains extracted from three sedimentary units within the Caledonian Lower Allochthon in Jamtland, central Sweden, were investigated for provenance studies using LA-ICP-MS. 207 Pb/ 206 Pb ages fall into the intervals: 3.1-1.7 Ga (Ronnofors Conglomerate), 3.2-1.4 Ga (Ede Quartzite), and 2.6-1.1 Ga (Kyrkas Quartzite). The age distribution of the Ronnofors and Kyrkas units vary sufficiently to suggest different source areas. The Ede Quartzite constitutes a mixture of the Kyrkas and Ronnofors provenance groups. The zircon age spectrum of the Kyrkas Quartzite reflects the typical age group present in the Jamtland basin in late Ordovician. In comparison, most zircon grains from the Ronnofors Conglomerate were derived from a local source, and only a small portion of these grains is characteristic for the basin. The Ede Quartzite contains a mixture of the typical basinal and, to a lesser extent, locally derived material. The variation in age distribution between the Ede and Kyrkas Quartzites reflects differ- ent dominating source areas. Tectonic activities along a shear zone (a continuation of SEDZ), which runs through the Ede and Kyrkas areas may be responsible for the noted differences in source areas. A deriva- tion from older sedimentary rocks to the present west-southwest and/or the Southwest Scandinavian Domain is suggested for the younger parts (