New interglacial deposits from Copenhagen, Denmark: marine Isotope Stage 7

Abstract

During a pre‐site survey and construction of a new metro route and station in Copenhagen, fossiliferous organic‐rich sediments were encountered. This paper reports on multidisciplinary investigations of these organic sediments, which occurred beneath a sediment succession with a lower till, glacifluvial sand and gravel, an upper till and glacifluvial sand. The organic sediments were underlain by glacifluvial sand and gravel. The organic‐rich sediments, which were up to 0.5 m thick, accumulated in a low‐energy environment, possibly an oxbow lake. They were rich in plant fossils, which included warmth‐demanding trees and other species, such as Najas minor, indicating slightly higher summer temperatures than at present. Freshwater shells were also frequent. Bithynia opercula allowed the sediments to be put into an aminostratigraphical framework. The amino acid racemization (AAR) ratios indicate that the organic sediments formed during Marine Isotope Stage 7 (MIS 7), which is consistent with optically stimulated luminescence dating that gave ages of 206 and 248 ka from the underlying minerogenic deposit. The assemblages from Trianglen are similar to interglacial deposits from the former Free Port (1.4 km away) in Copenhagen, except that Corbicula and Pisidium clessini were not found at Trianglen. The presence of these bivalves at the Free Port and the ostracod Scottia tumida at Trianglen indicates a pre‐Eemian age. AAR data from archived Bithynia opercula from the Free Port were almost identical to those from Trianglen, indicating that the two sites are contemporary. We suggest the Trianglen interglacial be used as a local name for the MIS 7 interglacial deposits in Copenhagen. MIS 7 deposits have rarely been documented from the region, but MIS 7 deposits may have been mistaken for other ages. The use of AAR ratios in Bithynia opercula has a great potential for correlation of interglacial non‐marine deposits in mainland northern Europe.

A new Middle Pleistocene interglacial occurrence from Ejby, Sjælland, Denmark

“…Based on amino acid analyses, the occurrence was correlated with Holsteinian deposits in NW Germany www.geusbulletin.org (Miller & Mangerud 1985). Another interglacial deposit from Røsnaes, near Skambaeks Mølle (Madsen et al 1908), may be of the same As mentioned earlier, interglacial non-marine deposits referred to MIS 7 are known from the former Free Port in Copenhagen and nearby Trianglen (Bennike et al 2019; location in Fig. 1).…”

“…It has a wide geographical range, but it does not grow in Arctic regions. Achenes of Z. palustris have previously been reported from interglacial deposits in Denmark by Hartz (1909) and Bennike et al (2019).…”

“…It occurred in north-western Europe during the Early and Middle Pleistocene, whereas it was absent during the Last Interglacial. In Denmark, it has been found in interglacial deposits from the former Free Port in Copenhagen (Johansen 1904), a deposit nowadays referred to MIS 7 (Bennike et al 2019). The species has also been reported from an interglacial deposit at Førslevgaard in southern Sjaelland (Johansen 1904; location in Fig.…”

“…Despite more than a century of investigations, parts of the Quaternary stratigraphy of Denmark with their fragmented record of deposits remain ambiguous. Known interglacial occurrences include the Cromerian complex (the Harreskovian, marine isotope stage [MIS] 19), the Holsteinian (MIS 11C), the Trelde Klint interglacial (MIS 11), the Trianglen interglacial (MIS 7), the Eemian (MIS 5e) and the current interglacial, the Holocene (Kuneš et al 2013;Odgaard et al 2016;Bennike et al 2019;Candy et al 2021). Moreover, several deposits of unknown age have been described (Andersen 1967).…”

“…1). Shells of the bivalve Corbicula were noted in one of the samples; this species indicates a Middle Pleistocene interglacial age (Meijer & Preece 2000;Bennike et al 2019), and since such occurrences are rare in Denmark, we decided to conduct analyses of macrofossils. This data article puts the new occurrence on record and provides details of the macrofossil analysis of the sample.…”