| Author||D. Burger|
|Title||Palynology of uppermost Jurassic and lowermost Cretaceous strata in the Eastern Netherlands|
|Journal||Leidse Geologische Mededelingen|
|Abstract||The present investigation is a systematical treatment of the sporomorphs from strata at the Jurassic-Cretaceous boundary in the eastern Netherlands Twente area, and an attempt to apply palynology to detailed stratigraphical study, by making use of quantitative pollen analyses. The rock samples used have been derived from two drilled sections in the eastern Netherlands, each of them representing the uppermost Jurassic and lowermost Cretaceous. The sediments are part of the sequence belonging to the Mesozoic Lower Saxon Basin; they contain the so-called ”Wealden” beds, the age of which is not exactly known. Two pollen diagrams were composed from the analyses and show major pollen fluctuations, which are most probably to be regarded as a consequence of long-range oscillations of vegetational belts near the western border of the Lower Saxon Basin.|
The purpose of the investigation has been to establish the time-stratigraphical position of the ”Wealden” more precisely and furthermore, to establish major quantitative frequency changes in the pollen flora at the Jurassic-Cretaceous boundary. For this purpose the diagrams have been divided into nine pollen zones R to Z, based on first and last occurrence of sporomorph species. The ”Wealden” section contains nearly three zones (V to X).
Recent correlation in several European stratigraphical sequences, based on ostracods, have shown that the Jurassic-Cretaceous boundary in the Dutch-German stratigraphy may be located between the base of the Serpulite and the upper limit of ostracod zone ”Wealden” 4, with strong indications that it might even be placed in a much less extended interval, ranging from the uppermost Serpulite to the base of ostracod zone ”Wealden” 2, that is to say from the base of pollen zone V to the base of pollen zone W.
The present investigation in the field of palynology takes also into consideration the rhythmic fluctuations, shown in the pollen diagrams from the eastern Netherlands. Similar fluctuations were recorded in the pollen flora from Maastrichtian and Paleocene strata in Colombia, South America. They are attributed to regular oscillations of the climate at timeintervals of approximately 2.3 million years and 7 million years. These rhythmic fluctuations were also recorded in the sedimentary history of the Eastern Cordillera in Colombia during the Cretaceous; they are assumed to originate from regular sea-level oscillations, taking place synchronously with the Cretaceous ages at time-intervals of around 7 million years.
Applying this theoretical time-scale to the pollen diagrams from the eastern Netherlands, it might be possible to attribute the rhythmic oscillations, shown in the Dutch pollen flora, to time-intervals of approximately 2.3 million years. In this case the Berriasian occupies 3 cycles immediately underneath the Valanginian, that is to say the pollen zones X and W, and possibly also zone V. The Jurassic-Cretaceous boundary might then be located at the base of zone W or the base of zone V. This agrees with a major change in the quantitative and qualitative composition of the pollen flora, and with the results of the correlation based on ostracods.
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