155 Early Cretaceous core and cuttings samples from 15 northeast Libyan wells have been dated, mainly on the basis of dinoflagellate cyst assemblages although stratigraphically important spore and pollen taxa have also been used when dinocysts are rare, absent or not age diagnostic. Spores and pollens have also helped with palaeoenvironmental reconstructions. Six distinct associations that are both stratigraphically and palaeoenvironmentally controlled are identified; these range from Hauterivian to early Cenomanian age. ? late Hauterivian to ? middle Barremian assemblages (IA) are dominated by dinoflagellate cysts thought to indicate lower than normal marine salinities, namely Cyclonephelium hystrix, Muderongia simplex microperforata, and Systematophora spp. Barremian assemblages (IB) are characterised by the presence of Aptea anaphrissa, and those from the early to late middle Aptian (II) by several other species of Aptea, especially A. securigera and the pollen Afropollis operculatus. An inner to middle shelf, pre-Vraconian Albian association (IIIA) comprises numerous morphologically varied dinoflagellate cysts including several species of each of the genera Coronifera, Oligosphaeridium, Spiniferites and Subtilisphaera notably S.terrula, and S.deformans/S.perlucida, whereas near-shore deposits of approximately the same age (IIIB) contain fewer cysts, more miospores and some megaspores. Both reflect a regression of the sea in the region prior to a major Late Cretaceous transgression, the early stages of which are indicated by two Vraconian-early Cenomanian associations (IVA and IVB). These consist of numerous chorate and proximochorate dinoflagellate cysts including Cyclonephelium, Dinopterygium, Florentinia, Oligosphaeridium, Spiniferites, Palaeohystrichophora infusorioides and Subtilisphaera cheit. Generic and species diversity is however higher in IVA, implying deposition in more open marine conditions than assemblages identified as IVB, which contain larger numbers of miospores. The complexities of intergeneric and intra- and interspecific morphological variation are described and illustrated for several taxonomic groups, including Aptea, Coronifera, Cyclonephelium, Dinopterygium, Florentinia, Kiokansium, Occisucysta, Oligosphaeridium, Palaeohystrichophora, Protoellipsodinium, Subtilisphaera and Xiphophoridium. Several possible synonymies at both generic and specific levels are suggested, and 10 informal species and three varieties of Florentinia berran are described.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:383579 |
| Date | January 1987 |
| Creators | Uwins, Philippa Joanne Rashleigh |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU010065 |
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