Holmiid trilobites from the lower Cambrian of the Digermulen Peninsula, Arctic Norway

• Lower Cambrian holmiid olenelloids are used for biozonation of lower Cambrian (Series 2) strata in Baltoscandia. About a dozen species have been named since the description of Holmia kjerulfi (Linnarsson, 1868), but except for the classical area in Mjøsa, Norway, the species traditionally occur in small numbers, are variably preserved, occur at one or a few localities only and usually with only one taxon present. Definitions of the biozones are therefore still problematic. One level in the lower Cambrian Duolbasgáissá Formation of the Digermulen Peninsula, Arctic Norway, has yielded more than 50 new specimens of holmiids, preliminarily assigned to Elliptocephala n. sp. and Kjerulfia n. sp. Acritarchs indicate the Heliosphaeridium dissimilare–Skagia ciliosa acritarch Zone which corresponds to the traditional Holmia kjerulfi Assemblage Zone. Elliptocephala n. sp. is known from about a dozen specimens. It is characterized by very long palpebral lobes, a parallel-sided glabella, a short anterior glabellar lobe and short genal spines. A node is developed on the occipital ring. Semi-complete specimens show up to 10 thoracic segments, but the full number of thoracic segments and the pygidium is unknown. The slightly older E. lundgreni (Moberg, 1892), known from the Schmidtiellus mickwitzi Zone of southern Sweden, differs in the proportions of the glabella, the length of the palpebral lobes and definition of the cephalic border. Both H. mobergi and H. sulcata from Sweden show similarities to Elliptocephala n. sp. in the weakly developed lateral border with an effaced anterior border furrow. Nikolaisen & Henningsmoen (1987) described Kjerulfia lata Kiær, 1917 from two fragmentary specimens from this locality in Digermulen. More than 20 new specimens from this site shows that the species differs from Kjerulfia lata from the type area in southern Norway in proportions and features of the glabella, the width of the genal field and the possession of a stout and high spine on the occipital ring, and it is tentatively assigned to Kjerulfia n. sp. The material from the Digermulen Peninsula adds to the diversity of the Baltoscandian holmiids and is tightly constrained stratigraphically.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Annan geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Other Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Digermulen

Cambrian

Holmia

Kjerulfia

Baltoscandia

dissimilare-ciliosa Zone

Earth Science with specialization in Historical Geology and Palaeontology

Geovetenskap med inriktning mot historisk geologi och paleontologi

Publikations- och innehållstyp

ref (ämneskategori)

kon (ämneskategori)