The Chibanian stratum, which dates back to the Chiba period, is located along the Yoro River in Ichihara City, Chiba Prefecture. At the bottom left is a golden spike that marks the boundary between eras. The color-coded stakes on the right mark the boundaries of geological formations, indicating that the Earth's magnetic field was reversing.
The Chibanian, more widely known as Middle Pleistocene (its previous informal name), is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period.[4] The Chibanian name was officially ratified in January 2020. It is currently estimated to span the time between 0.770 Ma (770,000 years ago) and 0.129 Ma (129,000 years ago), also expressed as 770–126 ka. It includes the transition in palaeoanthropology from the Lower to the Middle Paleolithic over 300 ka.
The term Middle Pleistocene was in use as a provisional or "quasi-formal" designation by the International Union of Geological Sciences (IUGS). While the three lowest ages of the Pleistocene, the Gelasian, Calabrian and Chibanian have been officially defined, the Late Pleistocene has yet to be formally defined.[8]
^Cohen, K. M.; Finney, S. C.; Gibbard, P. L.; Fan, J.-X. (January 2020). "International Chronostratigraphic Chart"(PDF). International Commission on Stratigraphy. Retrieved 23 February 2020.
^Cohen, K. M.; Finney, S. C.; Gibbard, P. L.; Fan, J.-X. (January 2020). "International Chronostratigraphic Chart"(PDF). International Commission on Stratigraphy. Retrieved 23 February 2020.