Calcareous dinoflagellates — an introduction to basics, long-term variation and applicability.
03 May 2002, Oslo (Norway).
Dinoflagellates are unicellular organisms which represent a major part of the marine phytoplankton communities. If cysts are formed during the lifecycle of the dinoflagellates, different substances, besides cellulose, can be used to shape the wall. These substances, for example sporopollenin-related material or calcite, can be fossilised. "Calcispheres", which are quite common in Mesozoic and Cenozoic marine sediments (e.g., "Thoracosphaera"-bloom in the lowermost Danian NP1 zone), are mainly formed of calcareous dinoflagellate cysts. Although calcareous dinoflagellates exist at least since the Late Triassic, little is known about this enigmatic group of organisms. Since the first description of fossil calcareous dinoflagellates, some investigators have especially focused their studies on systematics and taxonomy. The evolution of the organisms and their applicability for palaeoenvironmental reconstructions or stratigraphic purposes has more recently been addressed.
In the past few years, numerous studies on Quaternary calcareous dinoflagellates have proven evidence that the organisms can be used for palaeoceanographic and palaeoclimatic reconstructions. Additionally, studies on the long-term evolution of calcareous dinoflagellate associations have shown that modifications are closely connected to changing environmental conditions in the course of Cenozoic climate change. Recent investigations of Cretaceous strata indicate that calcareous dinoflagellates can provide essential information for a better understanding of the architecture of sedimentary cycles. Their possible usability for cyclic and sequence stratigraphy should therefore be verified in future studies. Overall, calcareous dinoflagellates clearly reflect changes in the environmental conditions. Thus, the application of ecological data on calcareous dinoflagellates to the reconstruction of past ecosystems and their succession might lead the development of a reliable ecostratigraphy.
Although many scientists believe individual calcareous dinoflagellate species to have a rather long stratigraphic range, others use them for biostratigraphy. For instance, an integrated zonation based on calcareous dinoflagellates and calpionellids exists for the Jurassic and Cretaceous of the Carpathian Mountains and is widely accepted and used by scientists in eastern and south-eastern Europe.
All recent studies on calcareous dinoflagellates illustrate that the organisms can provide important and unique palaeoenvironmental and -oceanographic information over a broad range of geological time scales. The successful application of calcareous dinoflagellates for stratigraphy is promising, however, it is still in its infancy and should be further exploited in future research.