The elusive subchron C13r.1n: a tie point for the Eocene-Oligocene Transition.

The Eocene-Oligocene Transition (EOT) marks one of the most profound climatic shifts in Earth’s history, as recorded by deep-sea isotope data. This interval is characterized by global cooling and the onset of modern icehouse conditions, making it a focal point of paleoclimate research. Understanding the expression of the EOT globally as well as its regional variability requires the correlation of disparate records over the globe. To achieve this magnetostratigraphic data is key to provide the necessary independent age constrains.

Detailed magnetostratigraphic records embracing the EOT have at times revealed the presence of very short magnetostratigraphic intervals within chron C13r. Some have interpreted these small-scale features as true geomagnetic reversals that could correspond to cryptochrons or even subchrons. Worth noting is the record in Leg 73, Site 522 (Tauxe et al., 1984), where a subchron was identified in the uppermost part of C13r, at the approximate location of the E/O boundary. Other sections around the globe have yielded records of lower resolution that could record this same event (Miller et al, 1993). On the other hand, several studies of varying resolution in the Rupelian GSSP at Massignano (Italy), yielded contrasting results. While the early study of Bice and Montanary (1988) revealed a single-sample normal polarity interval close to the E/O boundary, the higher resolution study of Lanci et al. (1996) did not reveal such an event.

Here we present a review of earlier magnetostratigraphic records and new revisited ones embracing the EOT, from marine and continental sedimentary successions and around the globe (Tramoy et al, 2016; Valero et al., 2015; Huber et al., 2019). They show compelling evidence for the occurrence of a normal subchron, namely C13r.1n, at very short distance to the E/O boundary, and that is worth included in the Geomagnetic Polarity Time Scale. Recognition of C13r.1n provides a new anchor point to calibrate records of the EOT at finer resolution.

References

Bice, D.M. and Montanari A., 1988. Magnetic Stratigraphy of the Massignano section across the Eocene-Oligocene boundary. In: Premoli Silva, I., et al. (Eds.), The Eocene-Oligocene Boundary in the March-Umbria Basin (Italy). IUGS International Commission on Stratigraphy, Subcommission on Paleogene Stratigraphy, pp. 111-117.

Huber, B.T et al., (2019). Site U1514. In Hobbs, R.W., Huber, B.T., Bogus, K.A., and the Expedition 369 Scientists, Australia Cretaceous Climate and Tectonics. Proceedings of the International Ocean Discovery Program, 369: College Station, Texas.

Lanci, L., et al. (1996). Magnetostratigraphy of the Eocene/Oligocene boundary in a short drill-core. Earth and Planetary Science Letters, 143(1–4), 37–48.

Miller, K. G., et al. (1993). Integrated late Eocene-Oligocene Stratigraphy of the Alabama coastal plain: Correlation of hiatuses and stratal surfaces to glacioeustatic lowerings. Paleoceanography, 8(2), 313–331.

Tauxe, L., et al. (1984). Magnetostratigraphy of Leg 73 sediments. Initial Reports DSDP, 73, 609–621.

Tramoy, R., et al. (2016). Stepwise palaeoclimate change across the Eocene-Oligocene transition recorded in continental NW Europe by mineralogical assemblages and δ15Norg (Rennes Basin, France). Terra Nova, 28(3), 212–220.

Valero, L. et al. (2015). Linking sedimentation rates and large-scale architecture for facies prediction in non-marine basins. (Paleogene, Almazán Basin, Spain). Basin Research, 1–20.