Biostratigraphy of planktic Foraminifera from the Maastrichtian white chalk of Sweden
Titel:
Biostratigraphy of planktic Foraminifera from the Maastrichtian white chalk of Sweden
Auteur:
Malmgren, Bjorn A.
Verschenen in:
GFF
Paginering:
Jaargang 103 (1982) nr. 3 pagina's 357-375
Jaar:
1982-01-15
Inhoud:
Three bore-hole cores (30-200 m long) from the latest Cretaceous chalk of southern Sweden (Limhamn area, Skåne) have been analyzed for planktic Foraminifera. The sequences are referable to the Upper Maastrichtian (Nephrolithus frequens coccolith Zone). Planktic foraminiferal assemblages, mostly dominated by Heterohelix striata and Globigerinelloides multispina, are of a typical high-latitude (Boreal) character. Rugoglobigerina rugosa and the Pseudotextularia elegans-Racemiguembelina fructicosa complex are occasionally abundant. The P. elegans-R. fructicosa complex is abundant in the uppermost parts of the sequences; this increase has been suggested by other workers to represent a climatically related migration from the Tethys. Other taxa are all rare (Hedbergella monmouthensis, Praeglobotruncana havanensis, Guembelitria cretacea, Heterohelix glabrans, Globigerinelloides sp., and Globotruncana sp.). The proportions between the two dominating species, G. multispina and H. striata, change systematically with time (towards increase in H. striata), and it is suggested that this represents a response to the shallowing of the Danish Embayment at the end of the Cretaceous reported by other workers. Four subzones are established within the H. striata-G. multispina Zone spanning the entire sequences: the R. rugosa Subzone II (lowermost), the R. rugosa-R. rugosa Interval-Subzone, the R. rugosa Subzone I, and the P. elegans-R. fructicosa Subzone (uppermost). The R. rugosa subzones are distinguished by different G. multispinal H. striata ratios (> 1 in Subzone II and < 1 in Subzone I). The P. elegans-R. fructicosa Subzone can be correlated with the latest Maastrichtian Belemnella casimirovensis belemnite Zone, but the other subzones may be local.
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