Palynological analyses in the laminated sediment of Lake Holzmaar (Eifel, Germany): duration of Lateglacial and Preboreal biozones

The laminated sediment of Lake Holzmaar (Germany) has provided a continuous varve chronology for the last 3500 varve years (vy) and beyond that a floa ting varve chronology back to more than 22500 vy BP. This chronology in cal endar years, in combination with palynology, enables us to determine the ti ming. and the magnitude of Lateglacial and Early Holocene environmental cha nges on land (from 13838 to 10930 vy BP). The palynological diagram has a m ean time resolution of 27 vy between samples. This paper establishes for th e first time the biozonation for Lake Holzmaar below the Leacher see Tephra . Fifteen pollen subzones grouped in four biozones are defined by cluster a nalysis. After a period disturbed by microturbidites, only a parr of the Be lling is present. Three cold periods have been evidenced by pollen analyses : the Older Dryas (96-vy-long), the Younger Dryas (654-vy-long) and the Ram melbeek phase (237-vy-long). The Allerod (883-vy-long) is bipartite with a first Betula-dominated period followed by a Pinus-dominated one. The Younge r Dryas is also bipartite, with first a decrease of winter temperatures alo ng with a change to a more continental climate. It is followed by a drier p hase with a second decrease in temperatures. probably this time also affect ing summer temperatures. The Preboreal is 702-yr-long. The duration of most phases corresponds to published records, except for that of the Younger Dr yas. Cluster and rare-of-change analyses indicate a sharp change in the ter restrial vegetation assemblages that may be caused by a sedimentary hiatus of erosive origin during this cold and dry period. As a result the chronolo gy of Holzmaar has to be revised most likely below the middle of the Younge r Dryas. Comparison with the varve record of Meerfelder Maar, a neighbour m aar lake, suggests adding 320 vy below 12025 vy.