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.
TheMiddle Pleistocene, also known by itsICS official name ofChibanian, is anage in the internationalgeologic timescale or astage inchronostratigraphy, being a division of thePleistocene Epoch within the ongoingQuaternary Period.[3] The Chibanian name was officially ratified in January 2020. It is currently estimated to span the time between 0.7741Ma (774,100 years ago) and 0.129 Ma (129,000 years ago), also expressed as 774.1–129 ka.[1][4] It includes the transition inpalaeoanthropology from theLower to theMiddle Paleolithic over 300 ka.
The term Middle Pleistocene was in use as a provisional or "quasi-formal" designation by theInternational Union of Geological Sciences (IUGS). While the three lowest ages of the Pleistocene, theGelasian, Calabrian and Chibanian have been officially defined, theLate Pleistocene has yet to be formally defined.[7]
TheInternational Union of Geological Sciences (IUGS) had previously proposed replacement of the Middle Pleistocene by an Ionian Age based on strata found in Italy. In November 2017, however, the Chibanian (based on strata at a site inChiba Prefecture, Japan) replaced the Ionian as the Subcommission on Quaternary Stratigraphy's preferred GSSP proposal for the age that should replace the Middle Pleistocene sub-epoch.[8] The "Chibanian" name was ratified by the IUGS in January 2020.[3]
By early Middle Pleistocene, theMid-Pleistocene Transition had changed theglacial cycles from an average 41,000 yearperiodicity present during most of the Early Pleistocene to a 100,000 year periodicity,[9] with the glacial cycles becoming asymmetric, having longglacial periods punctuated by short warminterglacial periods.[10] Millennial-scale climatic variability continued to be highly sensitive to precession and obliquity cycles.[11]
In central Italy, the climate became noticeably more arid from 600 ka to 400 ka.[12]
The late Middle Pleistocene was a time of regional aridification in theLevant, with a shallow lake covering what is now the Shishan Marsh drying and developing into a marsh.[13]
Eastern Africa's hydroclimate was governed primarily by orbital precession, although modulated significantly by the 100 kyr eccentricity cycle.[14]
The Early-Middle Pleistocene boundary saw the migration of true horses out of North America and intoEurasia.[16] Also around this time, the European mammoth speciesMammuthus meridionalis became extinct and was replaced by the Asian speciesMammuthus trogontherii (the steppe mammoth). This was coincident with the migration of the elephant genusPalaeoloxodon out of Africa and into Eurasia, including the first appearance of species like the Europeanstraight-tusked elephant (Palaeoloxodon antiquus).[17] With the extinction ofSinomastodon in East Asia at the Early-Middle Pleistocene boundary,gomphotheres became completely extinct inAfro-Eurasia,[18][19] but continued to persist in the Americas into the Late Pleistocene.[19] There was a major extinction of carnivorous mammals in Europe around the Early-Middle Pleistocene transition, including the giant hyenaPachycrocuta.[20] The mid-late Middle Pleistocene saw the emergence of thewoolly mammoth (Mammuthus primigenius), and its replacement ofMammuthus trogontherii, with the replacement ofM. trogontherii in Europe by woolly mammoths being complete by around 200,000 years ago.[17][21] The last member of thenotoungulate familyMesotheriidae,Mesotherium, has its last records around 220,000 years ago, leavingToxodontidae as the sole family of notoungulates to persist into the Late Pleistocene.[22] During the late Middle Pleistocene, around 195,000–135,000 years ago, thesteppe bison (the ancestor of the modernAmerican bison) migrated across theBering land bridge into North America, marking the beginning of theRancholabrean faunal stage.[23] Around 500,000 years ago, the last members of the largely European aquatic frog genusPalaeobatrachus and by extension the familyPalaeobatrachidae became extinct.[24]
After analyzing 2,496 remains ofCastor fiber (Eurasian beaver) andTrogontherium cuvieri found atBilzingsleben in Germany, a team of scientists concluded that, around 400 ka, hominids in the area hunted and exploitedbeavers. They may have been targeted for their meat (based on cut marks on the bones) and skin.[27]
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