Biological response to Milankovitch forcing during the Late Albian (Kirchrode I borehole, northwestern Germany)

Abstract

We studied the biological response to orbital forcing in marine Upper Albian sediments recovered from the 245 m-long Kirchrode I borehole in the Lower Saxony basin in northwestern Germany. Results from quantitative analysis of planktonic and benthic foraminifera, of calcareous nannofossils, and radiolaria were used for this study. Spectral analysis in the depth domain indicates for the high sedimentation rate part of the Upper Albian dominant periods with wavelengths of 10–13 m, 5–6 m, and 2–3 m, which we interpret to represent the biological response to orbital forcing in the Milankovitch frequency bands eccentricity, obliquity, and precession, respectively. In addition, a low amplitude 40–50 m cycle was found, which would represent the long-term eccentricity variation of roughly 400 ka. Microfossil cyclicity does not change significantly within the whole core indicating sedimentation rates of 11–12 cm/ka on an average, with variations between 3.5 and 13 ka). Microfossils show greater variability in their abundance changes than the physical and chemical parameters and also greater power in the higher-frequency bands (obliquity and precession). While most of the planktonic foraminifer species studied are dominated by variations in the obliquity, most benthic foraminifer species show an additional strong influence of precession. These differences in the cyclicity of the abundance changes are interpreted as reflecting a stronger influence of low latitude water in the deep waters of the Late Albian Lower Saxony basin than in the shallow waters. This basin was part of a wide, ‘Boreal’ epicontinental sea, which was connected to the Tethys to the south via the Polish strait and via the Paris basin, and which was connected with the North Atlantic and Arctic to the north. In analogy to results from analysis of data from the Late Neogene, strong effects of precession interpreted as being more characteristic for changes/influences triggered in the low latitudes and those of obliquity to be more characteristic for influences from the high latitudes. The presence of a relatively strong eccentricity cycle, not only in the compound parameters, but also in the abundance changes of single species during the Late Albian means that there must have been a non-linear response to orbital forcing and internal feedbacks.