GeoResources - Palynology of Limestone-Marlstone Alternations


	Palynology of Limestone-Marlstone Alternations
	Abstract





	Scientists Hartmut Jäger, GeoResources and University of Heidelberg Paulo Fernandes, University of the Algarve, Faro, Portugal Axel Munnecke, University of Erlangen

	Abstract It is an ongoing debate about the origin of limestone-marl alternations. On one side it is interpreted as product of primary differences in the sediment input, linked to high frequency cyclicity in the depositional system. On the other side it is seen as secondary effect due to diagentic differentiation of primary homogenous deposits, leading to a totally different model for the depositional system. Therefore the origin of these alternations is essential for all further interpretations of the depositional system and palynofacies analysis provides important information for this interpretation. Palynofacies analysis was done in limestone-marl alternations of the lower Turonian in the Sergipe Basin (NE-Brasil), representing outer platform to slope deposits. In the middle part of the section a lithological change is observed, starting with thin bioclastic limestones at the base and followed by high amounts of plant fragments restricted to the marlstone beds. Palynofacies analysis was focused on this interval and one interval from the lower part of the section without plant fragments. Samples from the interval with plant fragments show a highly terrestrial palynofacies, dominated by (mostly degraded) phytoclasts and AOM, minor proportions of dinocysts and foraminiferal test linings and rarely poorly preserved sporomorphs and leiospheres. Palynofacies shows a significant difference between limestones and marlstones. Marlstones are clearly dominated by phytoclasts and AOM, whereas limestones show less phytoclasts, but more marine palynomorphs. These significant differences in terrestrial input between marlstones and limestones give clear evidence for primary differences in limestone and marlstone deposition in this interval. Samples from the lower interval show a clearly marine palynofacies, dominated by dinocysts and minor amounts of AOM and foraminiferal test linings. Palynofacies of limestones and marlstones shows similar differences as above, but less significant, caused by a generally minor terrestrial input in this interval. Palynofacies confirms the previous model of the primary origin of limestone-marl alternations in the Upper Cretaceous of the Sergipe basin due to differences in terrestrial run off controlled by climatic chnages. Marlstones represent times of high terrestrial run off linked to wet climates, whereas limestones represent low terrestrial run off during dry climates. The change to high terrestrial input in the middle of the succession is explained by migration towards the coastline due to a fall in relative sea-level. The abrupt change gives evidence, that this was linked to tectonic activity. Therefore additional to the climatic control the depositional environment is influenced by tectonically induced changes.

	Presentations & Publications XII. International Palynological Congress, Bonn, 2008 19. Lateinamerika Kolloquium, Potsdam, 2005

	Funding Organizations GeoResources