Diachronous pattern of Milankovitch cyclicity in late Albian pelagic marlstones of the North German Basin

Abstract

The occurrence, correlation and preservation of high-frequency cyclicity has been studied in pelagic marlstones across an epicontinental basin. Wavelet analysis has been used for detection and extraction of stationary periodicity, and gradual, random and abrupt sedimentary changes from gamma-ray and carbonate content data in three Upper Albian successions in the North German Basin. The sections represent the basin center, a salt diapir edge, and a submarine swell. The mean sedimentation rate varies from 11 cm/ka in the basin center to 0.8 cm/ka on the submarine Pompeckj swell, respectively. The major periodicity of 0.7–13 m most likely represents Milankovitch-cycles of ∼100 ka eccentricity. The length of major periodicity of each section depends on sedimentation rate and ranges from 0.7 to 13 m. Up to 15 periodic sedimentary cycles are embedded in a transgressive–regressive cycle from ∼101.5 to 99 Ma. Regional correlation indicates that preservation of periodic sedimentation shifts diachronously throughout the North German Basin. Periodic cyclicity does not occur during the early transgressive phase and across regional sequence boundaries in early late Albian. The preservation of periodic cyclicity shifts diachronously according due to the preservation of undisturbed pelagic sedimentation. The degree of disturbances in sedimentation limits the preservation of periodicity more than the mean sedimentation rate. Undisturbed sedimentation started in the basin center at higher subsidence in an early stage transgression. On the other side, increased terrigeneous supply during regression favored the preservation of periodic sedimentation for longer time along the more off-shore submarine Pompeckj swell. Other high-frequency Milankovitch cycles (i.e. obliquity, precession) are more sensitive to disturbances and less preserved than eccentricity cycles.