The Blytt–Sernander classification, or sequence, is a series of North European climatic periods or phases based on the study of Danish peat bogs by Axel Blytt (1876) and Rutger Sernander (1908). The classification was incorporated into a sequence of pollen zones later defined by Lennart von Post, one of the founders of palynology.
Layers of peat were first noticed by Heinrich Dau in 1829.[1] A prize was offered by the Royal Danish Academy of Sciences and Letters to anyone who could explain them. Blytt hypothesized that the darker layers were deposited in drier times and lighter in moister times, applying his terms Atlantic (warm, moist) and Boreal (cool, dry). In 1926 C. A. Weber[2] noticed the sharp boundary horizons, or Grenzhorizonte, in German peat, which matched Blytt's classification. Sernander defined the subboreal and subatlantic periods, as well as the late glacial periods. Other scientists have since added other information.
The classification was devised before the development of more accurate dating methods, such as C-14 dating and oxygen isotope ratio cycles. Geologists working in different regions are studying sea levels, peat bogs, and ice core samples by a variety of methods, intending to further verify, and refine the Blytt–Sernander sequence. They find a general correspondence across Eurasia and North America.
The fluctuations of climatic change are more complex than Blytt–Sernander periodizations can identify. For example, recent peat core samples at Roskilde Fjord and Lake Kornerup in Denmark identified 40 to 62 distinguishable layers of pollen, respectively.[3] However, no universally accepted replacement model has been proposed.
Today the Blytt–Sernander sequence has been substantiated by a wide variety of scientific dating methods, mainly radiocarbon dates obtained from peat. Earlier radiocarbon dates were often left uncalibrated; that is, they were derived by assuming a constant concentration of atmospheric radiocarbon. The atmospheric radiocarbon concentration has varied over time and thus radiocarbon dates need to be calibrated.
La clasificación de Blytt-Sernander se ha utilizado como marco temporal para las culturas arqueológicas de Europa y América . Algunos han llegado incluso a identificar etapas de la tecnología en el norte de Europa con períodos específicos; sin embargo, este enfoque es una simplificación excesiva que generalmente no se acepta. No hay ninguna razón, por ejemplo, por la que los europeos del norte debieran dejar de usar bronce y comenzar a usar hierro abruptamente en el límite inferior del subatlántico en el año 600 a.C. En el cálido período atlántico , Dinamarca estuvo ocupada por culturas mesolíticas , más que neolíticas , a pesar de la evidencia climática. Además, las etapas tecnológicas varían ampliamente a nivel mundial.
Las fases del Pleistoceno y las fechas calibradas aproximadas (ver arriba) son:
Las fases del Holoceno son:
Algunos géneros o especies de plantas marcadoras estudiadas en turba son
Aparece más esfagno en los períodos húmedos. Los períodos secos presentan más tocones de árboles, de abedules y pinos.