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Cyst formation, sedimentation, and preservation: factors affecting dinoflagellate assemblages in recent sediments from Trondheimsfjord, Norway
Dale, B. (1976). Cyst formation, sedimentation, and preservation: factors affecting dinoflagellate assemblages in recent sediments from Trondheimsfjord, Norway. Rev. Palaeobot. Palynol. 22(1): 39-60. https://dx.doi.org/10.1016/0034-6667(76)90010-5
In: Review of Palaeobotany and Palynology. Elsevier: Tokyo; Oxford; Lausanne; New York; Shannon; London; Amsterdam. ISSN 0034-6667; e-ISSN 1879-0615
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| Trefwoorden |
Analysis > Sediment analysis
Classification > Taxonomy
Environmental factors
Fossils
Palaeo studies > Palaeontology
Palynology
Sedimentation
Dinoflagellata [WoRMS]; Gonyaulax Diesing, 1866 [WoRMS]
Marien/Kust |
| Abstract |
Plankton records and 25 samples of recent sediment from Trondheimsfjord and the adjoining shelf were studied to investigate production, sedimentation, and preservation of cysts, as factors which influence the eventual composition of dinoflagellate cyst assemblages. All sediment samples were examined for dinoflagellate cysts using routine semiquantitative palynological procedures. In addition, fjord sediments were subjected to a limited sediment analysis, and, for 3 samples, results from preparations both with and without acid treatments were compared. For the 1st time, cyst assemblages from Recent sediments were directly compared with extensive plankton records from overlying waters. Results indicate that {approx} 20% of the 55 locally recorded dinoflagellate spp contribute cysts to bottom sediments. Once formed, cysts behave as fine silt particles in the sedimentary regime, increasing in abundance as the percentage abundance of fine sediment increases, usually with increased water depth. Cyst-forming spp are almost entirely restricted to a few genera, particularly Gonyaulax and Peridinium, within the order Peridiniales. For some groups, reasonably good correspondence was found between percentage abundances of dinoflagellates in plankton and their cysts in sediment, though plankton records covering at least 5yr were required to establish this. G. grindleyi Reinecke (Von Stosch 1969) appeared to be consistently overrepresented by cysts in sediment relative to available plankton evidence; possible explanations are suggested. At least 30% of the cyst spp present, including most Peridinium spp, were eliminated, or rendered unreliable for semiquantitative palynology, by application of routine palynological preparation treatments. Such cysts may provide useful, non-quantitative, palynological information from Recent and possibly Quaternary sediments, but their persistence would seem unlikely. Thus, factors of preservation probably further restrict the dinoflagellate fossil record. Cyst assemblages from Trondheimsfjord are comparable with those previously recorded from the northeastern coast of USA, and from Scotland and northeastern England. Fjord assemblages are dominated by small, simple, spinose cysts which would be regarded as acritarchs if culture experiments had not proved that they are dinoflagellate cysts. Much potential biogeographic and palaeoenvironmental information was included within the less abundant spp. Attention is drawn to the role which future culture experiments may be expected to play in helping to resolve taxonomic difficulties currently affecting dinoflagellate studies. Palynological significance of results from the present study is discussed especially with reference to recent work by Von Stosch which strongly suggests that cysts may be hypnozygotes formed routinely in sexual cycles of dinoflagellates. |
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