Long-periodic variations in the Earth's obliquity and their relation to third-order eustatic cycles and late Neogene glaciations

Evolutive spectra of four high-resolution climatic proxy records reveal that the spectral power in the obliquity frequency band increases during five well-defined intervals in the last 5.3 million years. These intervals correspond to periods of high-amplitude variations in the tilt (obliquity) of the Earth's axis, connected with a 1.2 myr cycle, and to sea-level lowstands of third-order eustatic cycles in the Haq et al. (1987) curve. This implies that the development of major Plio-Pleistocene glaciations proceeded episodically and that third-order cycles are glacio-eustatically controlled. In (at least) two of these intervals sinistrally-coiled neogloboquadrinids entered the Mediterranean at times of glacial periods. One interval starts around 2.8 Ma and is characterized by the first occurrence of N. atlantica (s). Another interval begins at the Plio-Pleistocene boundary around 1.8 Ma and is characterized by the common occurrence of sinistrally-coiled N. pachyderma. Also during the late Miocene third-order cycles correlate well with the 1.2 myr cycle of obliquity. A significant drop in the third-order eustatic curve starting at the Tortonian-Messinian boundary, for instance, coincides with a period of high-amplitude variations in the obliquity time series connected with the 1.2 myr cycle. (C) 1997 INQUA/Elsevier Science Ltd.