Abstract Analyses of high-resolution multibeam and sub-bottom profiling data, acquired during marine geological field cruises between 2017 and 2019 in the eastern Gulf of Finland (Baltic Sea), enabled the detailed mapping of Quaternary deposits, and revealed diverse submerged glacial and post-glacial landforms (e.g. streamlined moraine ridges, large retreat moraine ridges, De Geer moraines and kettle holes). The morphology of these glacial features provides evidence of the ice-sheet retreat direction and rate throughout the deglaciation of the region, which occurred between 13.8 and 13.3 ka BP (Pandivere­­–Neva Stage) and 12.25 ka BP (Salpausselkä I Stage). Analysis of sub-bottom profiling, supported by piston long-core sampling, indicates periods of bottom erosion/non-deposition during the Holocene caused by relative water-level regressions. Significant negative relief features are also observed in the area for the first time. These linear and curved V-shaped furrows are several kilometres long and 5 m deep, and are tentatively ascribed to bottom current and gas-seepage processes.

Abstract The spatial distribution of polar lakes is governed by the lithology and structure of the geological units, whereas their shape and size is modified by later fluctuations of the polar ice sheet and glacier movements. Polar lakes are the downwards integrator of the sediment action in their catchment areas. Bathymetric profiles of some proglacial, land-locked and epi-shelf lakes spread across the Schirmacher Oasis were obtained during the austral winter period of 2008 using ground-penetrating radar (GPR) to understand their evolution through space and time. Morphometric characteristics of these lakes show different depth ratios and they have different surface areas and volume proportions with depth. This study shows that the largest land-locked lake, L-49, appears to have been formed by the fusion of three sub-basins. Some of the proglacial lakes which are becoming detached from the polar ice sheet, such as lake P-11, are kettle lakes. Water from the polar ice-sheet melt has been accumulating at these lake basins, but no further aggradation processes have affected them. Some of the larger lakes such as lakes L-27, L-49 and P-9 are reworked lakes which evolved during a phase of glacial advancement and were later modified during another advancement phase. The other larger lakes such as lake E-14, E-15 and L-75 are very deep and were produced by the glacial activity associated with some weak structural fabric.

Single-step, laser-fusion 40 Ar/ 39 Ar ages of single muscovite grains with an automated micro-extraction system is a precise and relatively rapid way of analyzing large numbers of grains. This study used >500 muscovite grains from a late Wisconsinan sandy loess from eastern Long Island, New York, in order to evaluate the potential of Ar-Ar ages of single grain muscovite as a provenance tool for loess. The samples for dating were from a 2.7 m core of sediments from a small kettle hole in Wildwood State Park on the north shore of Long Island. These eolian deposits consist of a bimodal distribution of poorly sorted medium silt and medium sand that are buff colored, homogeneous, and unstratified. Long Island is a good place to test this approach, because the 40 Ar/ 39 Ar and K/Ar ages for muscovite in the potential bedrock sources to the north in New England vary systematically from ca. 450 Ma in the west to ca. 200 Ma in the east. The majority of muscovite ages in the loess range from 250 to 400 Ma, and muscovite age populations along the core show a change in proportion of muscovite input from the different provenances in New England. The results of this study confirm that using 40 Ar/ 39 Ar ages of a large number of single muscovite grains is a good method for examining the provenance of muscovite in loess, and thus understanding processes that produce loess.

The temperate Laurentide Ice Sheet exhibited a grounded calving front as it retreated across coastal Maine about 14,000 to 12,500 B.P. The terminus resembled a modern tidewater glacier as the ice retreated through 0 to 80-m-deep water in the isostatically depressed region. Many areas of coastal Maine exhibit structural features that affect Holocene coastal landforms. In southwestern Maine, these northeast-southwest–trending strike valleys and ridges formerly exerted strong control on glacial retreat rates and deposition along the ice margin. Deposition of small DeGeer-type moraines and larger, stratified, subaqueous moraines/fans occurred where structural ridges slowed ice retreat. As ice retreat continued landward into even shallower water, the retreat rate was slowed by structural ridges, and deposition prograded to sea level, producing ice-contact beheaded deltas. In some areas, bedrock ridges underlie Gilbert-type deltas, while in other situations, ridges protruded above sea level as hills or islands. Eskers connected to the proximal sides of the deltas indicate that ridges deflected subglacial water to the surface in these locations.