Jonas Björck

Correlation of Swedish glacial varves with the Greenland (GRIP) oxygen isotope record

A mean varve thickness curve has been constructed for a part of the Swedish varve chronology from the northwestern Baltic proper. The mean varve thickness curve has been correlated with the delta(1 ...

Climate oscillations and tephrochronology in eastern middle Sweden during the last glacial–interglacial transition

ABSTRACT: Two sequences spanning the last glacial–interglacial transition in southern O¨ stergo¨t-land, eastern middle Sweden have been investigated for high-resolution vegetation change andtephrochronology. Organic carbon and pollen analysis indicates that the Younger Dryas–Pre-boreal climatic transition was characterised by at least one well-defined oscillation or possiblytwo shorter climatic oscillations. The Vedde Ash (ca. 12000 GRIP yr BP or ca. 10300 14 CyrBP) has been identified at both sites, significantly increasing the known distribution of thismarker horizon. In addition, a previously unrecorded rhyolitic tephra of Icelandic origin hasbeen identified at ca. 9000 14 C yr BP. The expansion of Corylus into southern O¨ stergo¨tland isestimated to be ca. 9400 14 C yr BP. Copyright 1999 John Wiley & Sons, Ltd. KEYWORDS: Preboreal oscillation; lacustrine records; Vedde Ash; last glacial–interglacial transition; expan-sion of Corylus . Introduction The last glacial–interglacial transition (15–10 k cal. yr BP)was a period characterised by a succession of rapid, extremeclimatic oscillations throughout the North Atlantic. The eventstratigraphy recently proposed by Bjo¨rck

An event stratigraphy for the Last Glacial–Holocene transition in eastern middle Sweden: results from investigations of varved clay and terrestrial sequences

This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the tim ...

Early Holocene deglaciation chronology in Västergötland and Närke, southern Sweden — biostratigraphy, clay varve, 14C and calendar year chronology

This thesis outlines an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. Events are short-lived occurrences that have left traces in the geological record and w ...

The Aller⊘d-Younger Dryas pollen zone boundary in an 800-year varve chronology from southeastern Sweden

Abstract This is the first pollen stratigraphical investigation of late Weichselian deposits in the area which was situated close to the late Weichselian Fennoscandian ice sheet margin and the Baltic Ice Lake shore during the Aller⊘d-Younger Dryas climatic transition. Pollen analyses were carried out on varved clay sequences, covering a time span of 350 years of an AMS radiocarbon-dated 800-year varve chronology, and on two lacustrine sequences. The Aller⊘d-Younger Dryas pollen zone boundary has been defined at the local varve year 2000. The pollen zone boundary coincides with an apparent drop of AMS radiocarbon ages from c. 11,000 to 10,800-10,600 14C years BP. The Aller⊘d, Younger Dryas, and Preboreal climatic events are distinguished in the pollen records of the lacustrine sites. Pollen and macrofossil evidence and AMS radiocarbon dates at these sites indicate that the area was deglaciated during the Aller⊘d. Soon after the deglaciation Betula pendula/pubescens immigrated. At the Aller⊘d/Younger Dryas ...

The isolation age and history of Lake Sågsjön, Stockholm, based on different dating techniques

Abstract Laminated sediments from Lake Sågsjön, situated east of Stockholm, were used to study the last 1000 years history of the lake. A combination of 14C dated (AMS) terrestrial macrofossils and annually laminated sediments were used, together with diatom stratigraphy, to determine the age of the isolation from the Baltic Sea. The laminae were counted using greyscale analysis and studied in detail by thin sections. Three new pair of laminae were formed between 1993 and 1996, indicating that the laminae are annually formed as varves. This is further supported by studies of thin sections, which reveal organic and minerogenic layers reflecting summer algae bloom and spring flood, respectively. Two of the 14C dated macrofossils are interpreted as redeposited wheras the calibrated ages received from two leaf fragments are believed to represent the age of sediment deposition. According to the varve counting, Lake Sågsjön (2.0 m a.s.1.) was isolated from the Baltic Sea between AD 1500 and 1600. The two radiocarbon dated leafs give an isolation age between AD 1150 and 1400. Compared to the 14C dates, the laminae based chronology yields too young ages, which indicates that the deposition of the laminae was not continuous. Shortly after the isolation the rate of sediment accumulation increases, which most probably is an effect of increased erosion when the catchment area was partly brought under cultivation.