Mitlehner, Alexander Gideon; (1995) The occurrence and preservation of diatoms in the Palaeogene of the North Sea Basin. Doctoral thesis (Ph.D), UCL (University College London).

Preview

Text The_occurrence_and_preservatio.pdf Download (17MB) | Preview

Abstract

The often widespread occurrence of diatoms in the marine sediments of the North Sea Palaeogene has long been recognised. They occur in abundance through a number of intervals where calcareous microfossils are absent (due to palaeoenvironmental conditions and subsequent dissolution). However, poor preservation has previously impeded the taxonomic identification of these diatom assemblages, with most specimens occurring as pyritised inner moulds (steinkerns). This study has involved the first detailed description of these assemblages, which was achieved through the use of electron microscopy combined with comparisons with well-preserved specimens, and a survey of original species descriptions held in the Natural History Museum. These techniques have enabled the identification of a total of 79 species, 40 of which have not previously been formally described in pyritised form. Material analysed in this study (including samples from exploration wells and coeval onshore sections around the North Sea Basin) has led to the recognition of a number of diatom events which broadly form three major assemblages through the North Sea Palaeocene sequence. The lowermost is the most diverse, occurring within the volcaniclastic Sele and Balder formations and their onshore equivalents around the Paleocene/Eocene boundary interval. The relationship of abundant diatomaceous deposits to vulcanicity during this interval is discussed, together with other factors (including increased nutrient levels) encouraging the proliferation of diatoms. A later, less diverse assemblage in the mid Eocene includes more cosmopolitan species; above this is a distinctive Oligocene to mid Miocene assemblage. The state of preservation of diatom assemblages varies markedly around the North Sea Basin; this has been discussed and microprobe analyses conducted. A number of taxonomic revisions of previously published species (both pyritised and non-pyritised) have also been carried out, including translations of descriptions into English (and their emendment where necessary). A new genus, Cylindrospira (consisting of two species, C. simsi and C. homanni) is described which has no living representatives, but has features found in both extinct and extant genera. It is palaeoenvironmentally significant, occurring in a brackish facies of the Fur Formation diatomite, age-equivalent to one of the main diatomaceous intervals in the North Sea. Prior to this study, only fully marine diatoms had been documented from the Paleocene. Existing microfossil zonation schemes for the North Sea Palaeogene have been refined, by integrating diatom events with those of stratigraphically well-defined fossil groups such as foraminifera and silicoflagellates. This has ebabled their correlation with other sections, and an improved understanding of palaeocirculation changes through the North Sea Palaeogene.

Download activity - last month

Export as XMLCSVJSON

Download activity - last 12 months

Export as XMLCSVJSON

Downloads by country - last 12 months

Export as JSONCSVXML

Archive Staff Only

View Item