Porttipahta end moraine in Finnish Lapland is constrained to Early Weichselian (MIS 5d, Herning stadial)

Abstract

Litho- and chronostratigraphy of the Early Weichselian time period, or Marine Isotope Stages (MIS) 5e-5a, is insufficiently established in Northern Fennoscandia and still more ambiguous is the regional-scale distribution of the corresponding end moraines. We applied Light Detection And Ranging Digital Elevation Models (LiDAR DEMs), electromagnetic (EM) sedimentary anisotropy (orientation) and ground penetrating radar (GPR) to reveal till-covered landforms diagnostic to the Early Weichselian phase(s) in Finnish Lapland. Morphometric and geophysical data revealed that sands and gravels of the Porttipahta end moraine were deposited from the north-northwest and are overlain by one diamicton (till) unit deposited from the southwest and most likely being correlative to the Late Weichselian (MIS 2). Sub-till OSL-ages yielded 91 ± 19, 96 ± 14, 100 ± 16 and 120 ± 26 ka, thus correlative with the MIS 5c interstadial (Brørup). The Porttipahta end moraine deposited during the deglaciation of the Early Weichselian 5d stadial (Herning).The NW-SE oriented till-covered eskers and rock drumlins in the area suggest Late Saalian (MIS 6) phase. Southwest of the Porttipahta area the end moraine complex is deformed by earthquake(s) attributable to glacial isostatic adjustment (GIA) probably during the MIS 5d phase. The morphological appearance is similar to Veiki moraine in Norrbotten, Sweden, and high-resolution LiDAR DEMs emphasize that both landforms exhibit a minute erosion by the later stadials. It remains unresolved, if the Porttipahta end moraine represents the maximum extent of the MIS 5d or if it represents a recessional stage.