Stratigraphical signatures of glacier activity, marine processes and a possible tsunami in the Leirfjorden fjord‐valley system, north Norway

Abstract

An integrated interpretation of on‐ and offshore stratigraphical records at Leirfjorden, north Norway, reveals new aspects of the area's palaeoenvironmental history. The study is based on marine sparker data and well‐exposed sections on land that were analysed for their sediment facies, mineralogy and fossil assemblages. Existing research and new radiocarbon dates provide a chronological framework for the interpretation. The late Younger Dryas Nordli substage type locality in the Leirfjorden catchment is revised and found to reflect local glacial activity, maybe a collapse of stagnant ice rather than glacier advance, while late Younger Dryas to Preboreal glacier re‐advances south of Leirfjorden and near Ranfjorden are here named the Bardal substage. The stratigraphical record includes pre‐Younger Dryas, valley‐crossing, glacial striae and old till with provenance of resistant bedrock typical of more elevated mountain areas. It differs from younger till units representing topographically controlled glacier movement. Part of the Leirfjorden fjord‐valley system is located between the main glacial and fluvial drainage paths affecting the sediment supply. As a result, highstand deposits are indistinct and fluvial sediments form only a minor part of the forced‐regressive systems tract. Instead, the valley fill overlying till and subtill sediments is dominated by the deglacial transgressive tract and a forced‐regressive systems tract with composite marine deposits and various marine erosion surfaces. A special event bed is interpreted as a possible tsunami deposit caused by seismicity and/or mass‐wasting in the fjord following glacier retreat. The study highlights the stratigraphical complexity of interconnected fjord and sound systems in a low accretion setting.

Marine mine tailings disposal at Lillebukt, Stjernsundet, North Norway: distribution, sedimentary processes and depositional impacts

“…Although the time of onset of erosion is unknown, in the depressions along the foot of the Stjernsundet Moraine and along the southern margin of Stjernsundet, erosion appears to be an ongoing process. Similar erosional features along steep slopes (at the seabed and buried in the stratigraphy) have been observed in many Norwegian fjords (e.g., Bøe et al, 2003;Hansen et al, 2018) and are interpreted to be related to changes in fjord circulation following changes in glacier positions/meltwater discharge, river discharge, and tidal and oceanographic circulation.…”

“…Unit D and underlying strata onlap the Stjernsundet Moraine and are assumed to be of glacimarine origin. Similar, alternating units of stratified and homogeneous sediments occur above glacial deposits in most Norwegian fjords (e.g., Bøe et al, 2003Bøe et al, , 2004bHansen et al, 2018) where their accumulated thickness may reach hundreds of metres. The hummocky appearance and varying thickness of Unit C suggests that this is a mass movement deposit.…”

Deglacial patterns and ice-sheet dynamics in the fjords of southern Nordland, Norway

“…1; Andersen et al, 1982). Marginal moraines related to the event have been traced onshore (Andersen et al, 1981;Hansen et al, 2018), whilst large submarine icemarginal deposits have been identified and mapped in the outer parts of the fjords (Andersen et al, 1982;Lyså et al, 2004). Bargel (2003) mapped end moraines and ice-marginal features in the outer Tosenfjord region (Fig.…”