Pleistocene stratigraphy and glacial history of the central part of Denmark
Authors: Nielsen Michael Houmark 
Published: August 2021

The Pleistocene deposits of Denmark are largely composed of two major facies that interfinger with each other: 1) tills, and 2) waterlaid outwash material. The two facies are occasionally interbedded with inter­glacial or interstadial deposits.
By applying lithostratigraphy combined with structural analysis in open exposures, a glacial stratigraphy of the Pleistocene has been established, and the glacial history interpreted. Only till units are classified lithostratifically because of their high regional consistency compared to waterlaid outwash deposits. Cor­relation of till units is based on three basic properties: lithology, stratigraphic position and associated gla­ciotectonic boundaries.
Lithic characteristics, some of which have local value whilst others indicate regional properties, include data on local glacier flow directions from fabric analyses and the contents of provenance dependent com­positional features, the latter may provide information on the long range path of glaciers. Fine gravel ana­lyses and stone counts demonstrate, that distinct stratigraphical relationships exist between tills rich and poor in quartz as well as between tills of Fennoscandian and Baltic provenance primarily indicated by the quantities of Paleozoic limestone clasts. The contests of re-deposited Quaternary foraminifera primarily serve as lithic characteristica and secondly as a guide line to estimate the possible age of a till unit.
Bounding relations between till units are studied with special emphasis on glaciotectonic unconfor­maties. They not only serve as supreme marker horizons on a regional scale, but they also supply high rank information on the local direction of glacier movement. Analysis of glaciotectonic structures often constitutes the implement by which the stratigraphy of a dislocated glacial sequence can be recognized.
Using a combined set of glacial-stratigraphic methods, about 200 selected localities in the central part of Denmark have been investigated over the past ten years.
Studies at eight principal localities and two key localities, some of which are classical exposures, provide the foundation for a litho-stratigraphic model for the till units.
The Elsterian glaciaiton is represented by three till units (S0NDER VISSING TILL, PALSGARD TILL, SNOGH0J TILL) of Norwegian, Middle Swedish and Baltic provenance respectively. The Saalian comprise three till units (TRELDE NIES TILL, ASHOVED TILL, LILLEBJELT TILL), the two former are of Fennoscandian provenance and the latter of Baltic provenance; deposited in the above mentioned order by icesheets from the north, the north east and from the east respectively. The Weichselian is build up of six till units, the oldest of which (RISTINGE KLINT TILL) was most probably deposited later than 36800 BP. This Baltic till is followed by three tills of Fennoscandian provenance (KATTEGAT TIL:i.,, MID DANISH TILL, NORTH SJ,ELLAND TILL) deposited respectively from the north, the northeast, and the east. The two youngest Weichselian till units are of Baltic provenance (EAST JYLLAND TILL, BJELTHAV TILL) and they were deposited from south-easterly directions before 13500 BP.
Till beds are erected into formal lithostratigraphic units of Formation rank and they are extended to cover extraregional till units, correlation is based on stratigraphic position, lithology and boundaries.
The following glacial history can be outlined.
During the Elsterian the S0nder Vissing till, the Palsgard till and the Snoghl'lj till were deposited by three glacial advances probably in the chronological order as mentioned above. During the Holsteinian in­terglacial, marl and diatomite were deposited in lake basins in the central part of the region.
The Saalian glaciation was initiated with the deposition of outwash material by southerly to southwest­erly directed meltwater streams and succeeded by an ice-stream from southern Norway, which deposited the Trelde Nres Till. After deposition of this till, interstadial conditions prevailed, and outwash material was deposited by westward flowing meltwater streams. This interstadial phase was followed by the second Saalian glacial advance during which the Ashoved Till was laid down by an ice-sheet from Middle Sweden. Prior to the last Saalian glacial phase, outwash material was deposited by generally westward flowing melt­water streams, that probably emerged from the Palaeobaltic ice. This latter deposited the Lillebrelt Till and invaded the country from the western part of the Baltic.
During the Eemian, lake sediments were formed in kettle bogs on the surface of the Lillebrelt Till, while at the same time, marine sediments were deposits in the southern and northern part of the examined re­gion.
Tundra vegetation developed in a dry polar climate characterize the Early- and the larger part of the Middle Weichselian. Interstadial deposits with an age of about 36800 BP were formed on Sejerl'l - prob­ably prior to the Old Baltic ice advance, which in the southern and eastern part of the region deposited
he Ristinge Klint Till from the Baltic. The Old Baltic advance was succeeded by the Norwegian advance which came from southern Norway crossing the Kattegat depression and deposited the Kattegat TIU in the northern part of the region. After deposition of the previously mentioned two till units, interstadial condi• tions re-occurred and meltwater streams transported outwash material northward into the Kattegat basin.
A change in meltwater palaeocurrent direction towards the west indicates the approach of the Main Weichselian advance. This advance crossed Middle Sweden and deposited the Mid Danish Till, and it probably reached its maximum extension along the Main Stationary Line at around 20000 BP. A read• vance during the general retreat of the Main Weichselian icestream crossed Fyn from the NE, and outwash streams were generally directed towards the north until a younger re-advance from easterly directions de­posited the North Sjrelland Till in the eastern part of Denmark. This re-advance may have occupied the northeastern part of Denmark and Kattegat before giving way to the transgression of the Younger Yoldia Sea, which was initiated about 15000 BP in Vendsyssel. Whilst this transgression was progressing the Main Weichselian ice sheet retreated to a probable position along the Swedish west coast. Northward flowing meltwater streams prevailed, at this time, in the central Danish region, until the Young Baltic icesheet ad• vanced from the Baltic depression and deposited the East Jylland Till. This advance formed the East Jyl• land ice border line, probably around 14000 BP. During the East Jylland advance, northward directed drainage patterns prevailed in the northern part of the region, whereas outwash material was deposited by westward flowing streams in southern Jylland.
The East Jylland ice sheet retreated to a position south-east of the examined region before the Brelthav re-advance deposited the Brelthav Till. Still supplied from the Baltic this readvance reached the classical Odsherred ice marginal zone of Northwest Sjrelland and gave rise to the final molding of the ice marginal hills of North Sams0 and the archshaped shoals in Storebrelt.
During the Weichselian, the Saalian, and probably also the Elsterian, the direction of the majority of ice sheet advance that invaded Denmark changed in a "clockwise" manner. During each glacial, an initial ad­vance from the north was succeeded by one from northeast ending up with one from the east and south· east. The change in direction of advance is accompanied by a corresponding change in the provena􀁁ce de­pendent elements of the till units. Hence, the "clockwise" pattern established for the Danish region can reflect a fundamental trend in the dynamic evolution of consecutive Scandinavian ice sheets. The present study therefore, may provide important guide lines for future attempts to establish more detailed the• oretical glaciological models for the dynamics of these former Scandinavian ice sheets.