The Idre marginal moraine – an anchorpoint for Middle and Late Weichselian ice sheet chronology

We here report the results of luminescence and cosmogenic exposure dating of the Idre marginal moraine, located in the southern Scandinavian Mountains. This particular moraine is targeted because it is morphologically distinct and marks the margin of a former ice sheet. The till in the moraine contains erratics that provide strong evidence of flow from an ice sheet centred over Norway. The area immediately outside the moraine margin is an older residual soil. Luminescence ages of three samples taken from a sand lense within the moraine indicate that it formed at around 55 ka, during the early warm part of Marine Isotope Stage (MIS) 3. Median exposure ages (10Be) of ten samples from boulders embedded in the surface till indicate that about 30 ka of ice-free time have elapsed since formation of the moraine. The difference between the age of the ridge and the duration of exposure provides a measure of the time of ice-cover in the ice sheet core area. Previous research indicates that final deglaciation of the site occurred at approximately 10 ka ago, which in combination with our results implies that the area around the Idre marginal moraine was ice free for ca. 20 ka, i.e. from around 55 ka to around 35 ka. Thereafter, the area was glaciated and the marginal moraine was covered by the Late Weichselian ice sheet for around 25 ka without experiencing any significant erosion or morphological destruction. While earlier studies have already pointed towards MIS 3 ice free conditions in northern and central Sweden, this study contributes a measurement-based duration estimate for the MIS 3 interstadial

Deglaciation of Fennoscandia

To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating. This 25 is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every 1000 years between 22 and 13 cal kyr BP and every hundred years between 11.6 and final ice decay after 9.7 cal kyr BP. Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins. For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin. Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas. For example, we locate the LGM extent of the ice sheet in northwestern Russia further east than previously suggested and conclude that it occurred at a later time than the rest of the ice sheet, at around 17-15 cal kyr BP, and propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages. Retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet, with the lowest rates on the high-elevation and maritime Norwegian margin. Retreat rates compared to the climatic information provided by the Greenland ice core record show a general correspondence between retreat rate and climatic forcing, although a close match between retreat rate and climate is unlikely because of other controls, such as topography and marine versus terrestrial margins. Overall, the time slice reconstructions of Fennoscandian Ice Sheet deglaciation from 22 to 9.7 cal kyr BP provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the Fennoscandian Ice Sheet, and are an important resource for testing and refining ice sheet models

Utvärdering av den underkambriska litostratigrafin på Österlen, södra Sverige

Den underkambriska lagerföljden i Skandinavien domineras av ljusa, marint avsatta sandstenar och når i Skåne en mäktighet av 120 m. Dess omfattande blottningsgrad har gjort den intressant för olika geologiska undersökningar. På Österlen i sydöstra Skåne är underkambrium blottad vid kusten och i nedlagda stenbrott utanför Simrishamn. Försöken att stratigrafiskt dela in den underkambriska lagerföljden har varit många och varierande vilket lett till osäkerhet. Berggrundsavsnitt med olika stratigrafiska lägen har t.ex. benämnts med samma namn av olika författare. Syftet med detta arbete är att göra en utvärdering av tidigare stratigrafiska indelningar och ge förslag till en ny reviderad litostratigrafi vilken följer de rekommendationer som föreslagits av International Subcommission on Stratigraphic Classification (ISSC). Förutom litteraturstudier har också nya sedimentologiska och petrografiska undersökningar genomförts på Österlen. Resultaten visar att den litostratigrafiska indelning som föreslagits av bl.a. Ahlberg 1984 och som innebär att underkambrium delas in i fyra formationer är den mest korrekta. För att litostratigrafin skall följa ISSCs förslag bättre föreslås dock flera komplement samt en ändring till korrekta, formella formationsnamn. De fyra formationerna, från äldsta till yngsta, skulle därvid namnges "Hardeberga Formation", "Norretorp Formation", "Rispebjerg Formation" och "Gislöv Formation". Däremot bör den indelning i led av "Hardeberga Formation" som gjorts av Hamberg 1990 betraktas som informell och enheterna ej benämnas led.The Lower Cambrian sedimentary succession in Scandinavia is dominated by shallow marine sandstones. In Scania, southern Sweden, this succession is about 120 m thick. Outcrops mainly comprise shore cliffs and abandoned quarries, primarily near the Simrishamn area. Several authors have subdivided this succession stratigraphically by different standards, which has led to confusion and the need for a review of the stratigraphy. For example, units with different stratigraphical position have been given identical names by different authors. The purpose of this study is to evaluate previous stratratigraphical work and to suggest a new litostratigraphical subdivision in agreement with the recommendations proposed by the International Subcommission on Stratigraphic Classification (ISSC). The data used include previous authors publications as well as material from new petrographical and lithofacies investigations. The study shows that the subdivision by Ahlberg (1984), which subdivides the Lower Cambrian succession into four formations, is the hitherto most appropriate one. However, several complements and changes with respect to formal nomenclature are herein suggested to conform with ISSC recommendations. Accordingly, the Lower Cambrian subdivision should include four formations, from the oldest to the youngest the "Hardeberga Formation", the "Norretorp Formation", the "Rispebjerg Formation" and the "Gislöv Formation". Further, the previous subdivision of the "Hardeberga Formation" into members should according to ISSC recommendations include clearly informal unit names rather than member names