FEST: 'Precambrian (and Pleistocene?) Milankovitch'


Friday Earth Sciences Talk by Dr Frits Hilgen

Astronomical (Milankovitch) climate forcing is omnipresent in the Phanerozoic (last 540 million years of Earth history), being equally responsible for Quaternary and Carboniferous ice ages, the deposition of organic-rich layers like black shales and sapropels, and the migration and evolution of species, including that of our own. However, much less is known about the same forcing mechanism in the Precambrian (first 80% of Earth history), while we know that it must have been operative at that time as well. This is particularly interesting as at that time System Earth was fundamentally different than today (or in the Phanerozoic).

Here I will summarize the findings of two PhDs, Margriet Lantink and Bianca Spiering. More than half a year ago Margriet successfully defended her thesis on Milankovitch cycles in ~2.5 billion year (Ga) old Banded Iron Formations (BIFs); among others she was able to determine the Earth-Moon distance and Length of Day, based on the cycle thickness ratio of the precession and eccentricity related variations in BIFs. In addition, she showed that the precession related cycle reflects redox cyclicity possibly linked to cyanobacterial blooms, which resulted in the production of free oxygen just prior to the Great Oxidation Event at 2.4 Ga. By contrast, Bianca recently started with her thesis on Milankovitch cycles in the Ediacaran of Namibia, just prior to the Cambrian explosion of life. Her first aim is to establish a cyclostratigraphic framework based on the available sequences and prove that these sequences are astronomically induced and, if so, reconstruct the key processes involved and determine the relation with changing redox conditions, and the distribution and possibly evolution of early complex life. If time is left, I will spend some time on the remarkable story of potential astronomical climate forcing recorded in the classical fossil hominid-bearing succession of the Sangiran dome in Indonesia, as part of a third PhD thesis, namely that of my son Sander.

With the Friday Earth Sciences Talks (FEST) we intend to bring the departments of Earth Sciences and Physical Geography together. The aim is to present (mostly) Utrecht-based Earth Sciences in an accessible way in order i) to stay familiar with each other’s work across disciplines and ii) to help (in particular MSc.) students in their orientation on possible graduation specialisations and future careers. Alumni are also invited.

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