Late Cretaceous and Paleocene marine diatom floras

The aims of this study were to assess the palaeoenvironmental and biostratigraphic potential of Late Cretaceous and Palaeocene diatoms and to create a useable taxonomy capable of being applied to any Upper Cretaceous or Palaeocene site studied. Samples and slides were studied from 9 diatomaceous sites. The published count data from a further 11 diatomaceous sites were also studied. The taxonomic information from 96 published papers was collected and placed into a card index system and a computer database. Each species reference, including its illustration, was cross-referenced against every other species in the database and its holotype illustration. In addition, extensive light microscope and scanning electron microscope work was performed on individually picked problem species. As a result of this work, 510 diatom species were considered to be taxonomically valid for Upper Cretaceous and Palaeocene assemblages. These form the basis of the taxonomy section of this study, which was itself used to identify diatom species whilst quantatively counting slides. The count data, including the published data sets, were analysed using principle components analysis and cluster analysis the results of which suggested that the samples could be grouped into 32 clusters. The relationship between these clusters was further explored by the cross-comparison of species abundance and composition within each cluster against all other clusters. This suggested that the 32 clusters could be placed into 7 broad groups. The results of this statistical analysis was used as part of the assessment of the potential for Late Cretaceous and Palaeocene diatoms as palaeoenvironmental indicators. A comparison of the distribution of the known Cretaceous and Palaeocene diatomites with modem diatomaceous oozes suggests that a comparable distribution pattern may have existed in the past. Late Cretaceous and Palaeocene diatom genera with modem representatives, it was found that using the number of benthonic species relative to meroplanktonic species could be used to distinguish shallow palaeowater depth diatom assemblages from deeper water ones. Little evidence was found of a change in diatom distribution with increasing or decreasing palaeolatitude, although Arctic Basin cores may show diatom assemblages that had adapted to a very high palaeolatitudinal existence. An examination of the statistical groupings of samples indicated that there may have been diatom palaeobiogeographical provinces in existence in the Late Cretaceous and Palaeocene. The Late Cretaceous had 4 possible palaeobiogeographic provinces, whilst the Palaeocene possibly had 2. An assessment of Upper Cretaceous and Palaeocene diatoms was made for their bosratigraphic, potenia. The ranges for 169 species were plotted out, 88 of which are possibly useful as markers from the Campanian to the lower Eocene and a preliminary biostratigraphy with 11 zones was recognised. This biostratigraphy was tested on a number of previously undated diatomaceous samples from the Upper Cretaceous, Palaeocene and Eocene. A study was made of the diatoms' reaction to the Cretaceous/Tertiary Boundary Event. An estimate of overall diatom survival across the Cretaceous/Tertiary boundary was put at 37.5%. Benthonic genera were found to have a higher extinction rate than meroplanktonic genera, suggesting that resting spores may have aided the survival of selected genera across the Cretaceous/Tertiary boundary. The results of this study suggests that there is potential for diatoms to be used as palaeoenvironmental and biostratigraphic indicators in the Late Cretaceous and Palaeocene although their application is currently limited.