Upper Cambrian trilobite faunas and biostratigraphy at Kakeled on Kinnekulle, Västergötland, Sweden

University essay from Lunds universitet/Geologiska institutionen

Abstract: Upper Cambrian strata are well exposed in an old quarry at Kakeled on south-western Kinnekulle, south-central Sweden. The exposures consist of finely laminated alum shale with lenses and beds of dark grey limestone (stinkstone or orsten), and a few thin layers of sandstone. A 6.20 m thick section in the central part of the quarry has been measured and sampled in order to establish the succession of trilobite species. This section extends from the lower-middle part of the Agnostus pisiformis Zone into the Peltura scarabaeoides Zone. A 150 cm thick stinkstone bed ("The Great Stinkstone Bed") occurs in the Olenus/Homagnostus obesus Zone and in the upper part of the A. pisiformis Zone. It comprises a lower part measuring 30 cm and an upper part measuring 120 cm. These are separated by a thin (10 cm) bed of alum shale. Above "The Great Stinkstone Bed" nine additional stinkstone beds, with thicknesses varying from 10 to 55 cm, are present. Fossils are usually preserved only in the stinkstones, but in the A. pisiformis Zone trilobites can be found in both the shales and the stinkstones. The A. pisiformis Zone is dominated almost entirely by the zonal index, which occurs in abundance. A. pisiformis occurs throughout the A. pisiformis Zone and ranges up into the Olenus gibbosus Subzone. Nearly all specimens of A. pisiformis are disarticulated. The orientation of cephala and pygidia of A. pisiformis were measured on four shale surfaces and one stinkstone bedding plane. The majority of the shields were deposited with the convex side up and showed a preferred orientation, suggesting that their positions were affected by currents. The orientation of the shields generally indicates a current direction roughly towards the present north. Above the A. pisiformis Zone the section comprises the Olenus/Homagnostus obesus Zone (30 cm), the upper part of the Parabolina spinulosa Zone (5 cm), the Peltura minor Zone (105 cm), and the Peltura scarabaeoides Zone (260 cm). The Leptoplastus and Protopeltura praecursor Zones are missing. The Olenus/H. obesus Zone is represented only by the O. gibbosus and O. wahlenbergi Subzones, whereas the O. truncatus, O. attenuatus, O. dentatus, and O. scanicus Subzones are missing.

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