Description: For establishment of adequate environmental, oceanographic and climatic reconstructions based on fossil dinoflagellate cysts associations detailed information on selective transport and preservation is required. Here we present a comparison of export rain of dinoflagellate cysts with cyst associations in different intermediate nepheloid layers in the water column, the bottom nepheloid layer and surface sediments collected along two onshore-offshore transects off Cape Blanc (NW Africa) during active upwelling in November 2015. Highest cyst export production took place at the rim of a newly formed upwelling eddy/filament. Lateral transport of cysts up to 130 km off the shelf break was observed in a nepheloid layer varying in depth of 600 - 1300 m (shelf break - deep ocean) and in the bottom nepheloid layer. No indication of lateral transport could be documented in a second intermediate nepheloid layer deeper in the water column as well as in the more offshore part of the bottom nepheloid layer. The effects of lateral transport as registered from the water column was not reflected in underlying sediments. Selective degradation altering the cyst associations was not observed in the water column but the surface sediment cyst association differed considerable from that of the nepholoid layers and the upper water column. Comparison with long term sediment trap time series of cyst production in the region indicate that the surface samples are modified predominantly by species specific post depositional degradation rather than inter-annual variation in transport and/or production of cysts.

Description: Assessment of selective preservation is of prime importance for the interpretation of proxies. Zonneveld et al. (1997) demonstrated strong selective changes in dinocyst assemblages as a result of aerobic degradation in the MAP F-turbidite. Based on two sets of 3 samples only, this did not allow much further differentiation. The present study relates palynological with geochemical changes at the transition from anoxic to oxic conditions in MAP turbidites with a high, 0.5-1 cm resolution. We now can understand why the geochemical processes already modify the peridinioid component of the dinoflagellate assemblage in the anoxic zone below the oxidation front, and why they lead to increasing cyst concentrations for some species close to the front. We demonstrate how taxon-specific differences in cyst degradation lead to successive dominance of Brigantedinium, Spiniferites and Impagidinium when degradation proceeds. We show the importance of knowledge of selective preservation by interpreting the assemblages with and without taking this process into account.

Description: Small, organic-walled microfossils were usually attributed to the general term ‘hystrichospheres’ until the early 1960’s. After the discovery that many of these ‘hystrichospheres’ displayed morphological characteristics that are specific for dinoflagellates namely having a cingulum, a sulcus, an operculum and a para-tabulation, Evitt (1963) created the new term ‘acritarchs’ to classify all the remaining forms of unknown biological affinity and separate these from dinocysts. The acritarchs therefore include various kinds of organisms that have been affiliated to animal remains, fossil spores of various groups, and to several classes of (green) algae, including the prasinophycean, zygnematophycean or chlorophycean groups, for example. Although of unknown biological affinities by definition, many Palaeozoic acritarchs, in particular taxa from the Ordovician, Silurian and Devonian, have been compared morphologically to dinoflagellates. Such morphotypes have therefore been considered to be the resting cysts of phytoplankton since many years. The diversity of (planktonic) dinocyst-like taxa strongly increases in the late Cambrian, triggering probably the onset of the ‘Ordovician plankton revolution.’ These acritarchs are virtually impossible to differentiate from dinocysts, showing often the same process morphology (see Kröck et al., this conference). Furthermore, their palaeoecological distribution patterns, following inshore-offshore trends, is identical to those of dinoflagellates. Also, their biogeographical distribution is comparable to that of modern dinoflagellate taxa. We consider that some Palaeozoic acritarchs might therefore have been produced by dinoflagellate-like species, although they do not display all morphological criteria necessary to be recognized as a dinoflagellate cyst.