Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
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150<br />
ADVANCES IN PALAEOICHTHYOLOGY<br />
This work is important to clarify the Wood Bay Formation subdivision. It is presently<br />
different for geologists, using the stratigraphic <strong>un</strong>its, <strong>and</strong> palaeontologists who use the<br />
biostratigraphic <strong>un</strong>its.<br />
Brief history<br />
A Wood Bay Formation stratigraphy was first proposed by Føyn <strong>and</strong> Heintz (1943).<br />
They divided the formation into three divisions (Kapp Kjeldsen, Lykta, <strong>and</strong> Stjørdalen)<br />
mainly based on the differing suites of pteraspidiforms.<br />
Friend (1961) confirmed these divisions for the Woodfjord area. He tried to characterise<br />
them from a geological point of view based on colour, grain size, <strong>and</strong> alternations of beds.<br />
However, he replaced the Lykta name by Keltiefjellet. At the same time Friend proposed another<br />
geological scale for the Dicksonfjord-Austfjord region where he described two different <strong>un</strong>its:<br />
the Austfjord S<strong>and</strong>stone <strong>and</strong> Dicksonfjord S<strong>and</strong>stone (Friend 1961, p. 90-92).<br />
Friend et al. (1966) pointed out that the previous geological considerations for the<br />
Woodfjord area were <strong>un</strong>satisfactory. They came back to the concept of fa<strong>un</strong>al divisions,<br />
redefining them on the basis of their content of pteraspidiforms <strong>and</strong> placoderms. They<br />
also revised the lithostratigraphic <strong>un</strong>its from the Dicksonfjord-Austfjord area <strong>and</strong><br />
renamed them as members (Friend et al. 1966, p. 61). Finally, they proposed possible<br />
stratigraphic correlations between the Woodfjord <strong>and</strong> Austfjord-Dicksonfjord regions,<br />
without any fa<strong>un</strong>al considerations.<br />
The last revision of the biostratigraphy of the Wood Bay Formation was done by Goujet<br />
(1984). He enhanced it with the introduction of a new basal fa<strong>un</strong>al division, the Sigurdfjellet,<br />
characterised by its peculiar but at that time <strong>un</strong>described fa<strong>un</strong>al content.<br />
Since the first subdivision of the Wood Bay Formation by Føyn <strong>and</strong> Heintz (1943),<br />
the ranges of the pteraspidiforms have been used as data for differentiation of the<br />
divisions. This choice is dictated by their ab<strong>un</strong>dance in terms of specimens <strong>and</strong> their<br />
easy recognition in the field outcrops (Føyn <strong>and</strong> Heintz 1943; Heintz 1962, 1967).<br />
Moreover their diversity is sufficient to characterise the divisions with successions of<br />
the different species (Pernegre 2002, 2003, <strong>and</strong> <strong>un</strong>published revision of the genus<br />
Gigantaspis).<br />
The other known fa<strong>un</strong>a possess less value for such a work due to the high diversity of forms,<br />
as for e.g. the osteostracans: 16 genera with 40 described species (Janvier 1985). Moreover,<br />
each taxon is only represented by a restricted number of specimens (often one specimen only),<br />
so it is impossible to establish precise range extensions. The placoderms are well represented<br />
(Heintz 1929; Goujet 1973, 1984) in terms of occurrence <strong>and</strong> specimens available, but many<br />
forms remain <strong>un</strong>described <strong>and</strong> others should be redescribed. At the same time, no global<br />
biostratigraphic works have been done with the placoderms. Therefore, our biostratigraphic<br />
correlations are mainly based, as for preceding authors, on the pteraspidiform associations.