Portal de Periódicos da CAPES

Fossiliferous boulders of Lower Cambrian phosphoritic sandstone in southwestern Finland

1983; Geological Society of Finland; Volume: 55; Issue: 2 Linguagem: Inglês

10.17741/bgsf/55.2.001

1799-4632

Jyrki J. Lehtovaara, R. Tynni,

Geology and Paleoclimatology Research

The paper deals with fossiliferous sandstone boulders from three localities in southwestern Finland.The largest of the boulders was found on the west coast west of Olkiluoto.It is conglomeratic with an abundance of worn remains of lingulid and obolellid brachiopod valves.Its rock type is made up of a relatively coarse, bimodal quartz sandstone containing a few phosphoritic siltstone fragments.The main part is sandy and practically free of glauconite, which is more common in the phosphoritic fragments.A few of the phosphoritic pieces are tubular in form having phosphorite enriched in an outer ring and a one-grain-thick outermost crust of quartz.They may be worn remains of Hyolithellus micans.Some of the brachiopod shells contain small calcitic globules in a carbonaceous phosphorite matrix.Tasmanites sp. is one of the few preserved forms of the Acritarch genera.According to the fossils, the sandstone dates to the upper part of the Lower Cambrian, corresponding to the Lingulid sandstone facies in Västergötland, which in turn corresponds to the Holmia kjerulfi-group Zone in southern Scandinavia.Mineralogically and petrologically, too, the rock could be derived from such lithostratigraphical units.Sandstones of the same age have not been reported previously from Finland.The present boulders would seem to derive from the bottom of the Bothnian Sea.Although smaller and not so conglomeratic the boulders from Säkylä and Uusikaupunki are fossiliferous.The fossil fragments in the boulder from Pyhäjärvi, Säkylä, are probably remains of the brachiopod Mickwitzia, and thus refer to a Lower Cambrian stratum still older than the former.The worn brachiopod fragments in the boulder from North Viisastenkari, Uusikaupunki, did not allow the boulder to be dated more accurately within the Lower Cambrian.