Long-eccentricity control on Paleocene sea-level cycles

Long-eccentricity control on Paleocene sea-level cycles

van Ginneken, S.

Molengraaff Fonds

2017

It has been proposed that 400-kyr eccentricity is the driving force behind 4th order sea-level cycles in sequence stratigraphy during greenhouse times. However, this suggestion, which is mostly based on spectral peak ratios in the depth domain, is hard to verify due to lack of reliable age control with a resolution higher than or similar to the observed cycles. To tackle this issue, we applied an integrated stratigraphic approach to the lower Paleocene “Slope Section” of the Ludlow Member (Fort Union Formation) in North Dakota (USA). This coal-bearing succession of fluvio-deltaic to coastal sediments contains two distinct brackish-water marine tongues of the Cannonball Member. Our magnetostratigraphy allows the identification of magnetochrons C29n, C28r and C28n, while spectral analysis of proxy records (lightness, grain size) reveals the presence of a 100-kyr cycle in the coals. The previously observed continuity of the coals, that do not laterally pass into major fluvial sandstones, suggests an allogenic control of this cycle. Next, bandpass filtering combined with the well-constrained C29n/C28r reversal as tie point was used to correlate the coal cycles to the astronomical tuned deep marine Zumaia section in Spain. The preferred correlation results in astronomical ages of 64.805 Mya for the Boyce Tongue and of 64.425 Mya for the Three V Tongue, thus approximately 400-kyr apart. This implies that the tongues are possibly related via relaxation of the hydrological cycle too long 400-kyr eccentricity and formed at the transition from an eccentricity maximum to minimum coeval to eustatic high-stand paleovalley facies in upstream Montana.

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Utrecht University

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