Waalian interglacial
{{Short description|Interglacial period of the Early Pleistocene}}
The Waalian interglacial ({{langx|de|Waal-Warmzeit}} or Waal-Interglazial) Zagwijn, W.H., 1960. Aspects of the Pliocene and Early Pleistocene vegetation in the Netherlands. Mededelingen Geologische Stichting, Serie C-III-l, 5: 178 pp. or Waalian Stage was an interglacial period of the Early Pleistocene in north-west Europe. It was preceded by the Eburonian Stage and succeeded by the Menapian Stage. It coincides with part of the much longer Beestonian stage in Britain.{{cite web|url=https://data.bgs.ac.uk/id/Geochronology/Division/BW|title=Waalian Stage|publisher=British Geological Survey|accessdate=28 November 2021}} It is variously dated by different authorities. Oxford Reference gives 1.3 to 0.9 million years ago{{cite web|url=https://www.oxfordreference.com/view/10.1093/oi/authority.20110803120307676|title=Waalian|publisher=Oxford Reference|accessdate=28 November 2021}} and the British Geological Survey 1.6 to 1.36 million years ago. However, the 2020 chart of the international authority on stratigraphic dating, the International Commission on Stratigraphy shows it as c. 1.6 to 1.4 million years ago.{{cite web|url=https://stratigraphy.org/ICSchart/QuaternaryChart1.jpg|title=Global chronostratigraphical correlation table for the last 2.7 million years v. 2020b|publisher=International Commission on Stratigraphy |accessdate=28 November 2021}} It is distinct from other Pleistocene periods in its complexity, vegetational composition, and vegetational succession.
Its name is derived from a major branch of the Rhine delta, the Waal.
Distinguishing features
Unlike later interglacial periods, the Waalian Interglacial had at least one period of permafrost conditions, making it a "complex stage".{{Cite journal |last=Zagwijn |first=Waldo H. |date=1992-01-01 |title=The beginning of the Ice Age in Europe and its major subdivisions |url=https://dx.doi.org/10.1016/0277-3791%2892%2990015-Z |journal=Quaternary Science Reviews |language=en |volume=11 |issue=5 |pages=583–591 |doi=10.1016/0277-3791(92)90015-Z |bibcode=1992QSRv...11..583Z |issn=0277-3791|url-access=subscription }} It has been proposed that the Waalian Interglacial was composed of three phases: a temperate phase, a cool phase, and another temperate phase.{{Cite journal |date=1962-01-09 |title=Vegetational history of the Early Pleistocene of the Royal Society Borehole at Ludham, Norfolk |url=https://royalsocietypublishing.org/doi/10.1098/rspb.1962.0011 |journal=Proceedings of the Royal Society of London. Series B. Biological Sciences |language=en |volume=155 |issue=960 |pages=437–453 |doi=10.1098/rspb.1962.0011 |bibcode=1962RSPSB.155..437W |issn=0080-4649 |last1=West |first1=R. G. |s2cid=128467486 |url-access=subscription }}{{Cite journal |last=Zagwijn |first=W.H |date=1957 |title=Vegetation, climate and time-correlations in the Early Pleistocene of Europe |journal=Geologie en Mijnbouw |series=New Series|volume=19 |pages=233–244}} The Waalian Interglacial is also distinct from later interglacial periods in that the migration of tree species during this period did not follow a clear pattern of succession (i.e., most of the species that were present at the end of the Waalian were there at the beginning). In addition, though earlier research indicated that the forest species assemblage of the Waalian period mirrored that of the Tiglian, more recent research into pollen records show that there was a marked decrease in the number of arboreal taxa from earlier Pleistocene periods.{{Cite journal |last1=Hahne |first1=Jürgen |last2=Ellwanger |first2=Dietrich |last3=Stritzke |first3=Rüdiger |date=2009-04-01 |title=Evidence for a Waalian thermomer pollen record from the research borehole Heidelberg UniNord, Upper Rhine Graben, Baden-Württemberg |url=https://egqsj.copernicus.org/articles/57/403/2009/ |journal=E&G Quaternary Science Journal |language=en |volume=57 |issue=3/4 |pages=403–410 |doi=10.3285/eg.57.3-4.7 |issn=2199-9090|hdl=11858/00-1735-0000-0001-B9E6-4 |hdl-access=free |doi-access=free }} Common arboreal taxa from the Waalian period included Tsuga, Eucommia, Celtis, and Pterocarya.