Sub-Milankovitch Cycles Established from High-Resolution Logs and Robust Chronostratigraphic Tuning: An Example from a Miocene Sedimentary Sequence in the Vienna Basin
Paulissen, Wieske 1; Luthi, Stefan M.1
(1) Department of Geotechnolgy, Delft University of Technology, Delft, Netherlands.
Through an integrated stratigraphic approach a high-resolution chronostratigraphic record has been established that takes into account variations in sedimentation rates and temporal gaps caused by unconformities and faulting in a research borehole in the Vienna Basin. This chronostratigraphic record was used to investigate the possible presence of orbital, millennial and centennial periodicities. The sedimentary sequence covers Middle to Late Miocene shallow marine, fluvio-deltaic and lacustrine shales, silt- and sandstones deposited during the transition from a pull-apart basin to the final infill in a compressional regime. Spectral analysis was performed on gamma ray logs and high-resolution electrical borehole images using three different analytical methods over six suitable intervals where continuous and constant sedimentation was identified. The significant periods were found to closely match the orbital cycles of precession, obliquity and short eccentricity, providing a solid basis for the analysis of potential sub-Milankovitch cycles. Moreover the very high vertical resolution of electrical borehole images allowed for the recognition of millennial- to centennial scale cycles, for example a sedimentation rate of 0.25 m/kyr represents 40 years with an FMI resolution of 1 cm.
The significant frequencies encountered at the millennial- to centennial-scale fell for 75% within a relatively narrow time period of 0.25 to 5 kyr, with a concentration of peaks between 1 to 2 kyr (29%) and 500 to 800 yrs (17%). These periodicities relate closely to the millennial- (Dansgaard-Oeschger and Bond cycles) and centennial-scale climate cycles documented from the Quaternary. It is suggested that the high-frequency cycles observed in the Miocene of the Vienna Basin represent differences in grain size related to cyclic variations in regional precipitation. Through this integrated stratigraphic methodology our findings suggest that the infill of this Paratethyan basin can be seen as the result of three superposed processes, i.e. regional tectonism modulated by orbital influences and an additional component at the millennial- to centennial-scale.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.