ORBITAL CONTROL ON THE ORIGIN AND PRESERVATION OF LOFER CYCLICITY IN THE LATE TRIASSIC DACHSTEIN PLATFORM

The Upper Triassic Dachstein Limestone is an archetypal example of platform carbonate formation that consists of peritidal-subtidal Lofer cycles. However, despite a long history of study, their allocyclic vs autocyclic origin remains controversial. Using modern cyclostratigraphic methodology, here we revisit the archive data of the Dachstein Limestone in core Po‑89 from the Transdanubian Range, Hungary. Analysis of high-resolution time series of the Lofer facies types, color, greyscale, and lithology revealed several spectral peaks that are identified with the Milankovitch cycles. The Lofer cycles correspond to a robust peak with a period of 3.6 m that is the expression of precession cycles with a period 21.65 kyr. The sedimentary rate is 16.5 cm/kyr, thus the studied core section represents 2.5 Myr. Our model of cyclic carbonate deposition suggests that aquifer- and limno-eustasy were the most likely drivers of cyclic sea level changes. Differences in the depositional processes and preservation of the Lofer cycles led to variations in their completeness that is also orbitally controlled and responds primarily to long eccentricity forcing. We detected several sub-Milankovitch cycles, of which the 13.5, 7, 5, 3.4, 2.4, and 1.48 kyr cycles are the most prominent. Our results are in good agreement with other studies of Upper Triassic Lofer cyclic successions. The similarities in the thickness of individual Lofer cycles, the periods of all identified cycles, and the sedimentary rates suggest common allocyclic processes. Our findings provide evidence for the orbital forcing of carbonate sedimentation in the Late Triassic Dachstein platform system.