The Kregnes moraine in Gauldalen, west-central Norway: anatomy of a Younger Dryas proglacial delta in a palaeofjord basin

The Kregnes "moraine" ridge in Gauldalen, a north-bending valley south of T rondheim, is a Gilbert-type delta formed at a Younger Dryas glacier terminu s. The gravelly delta consists of a north-dipping foreset, 150 m thick, com prised of turbidites, debrisflow beds and debrisfall deposits. The bottomse t consists of turbiditic sand and mud layers. The topset, 2-3 m thick, is a braided-river alluvium with local beach deposits, matching the marine limi t of 175 m a.s.l. The fjord-wide delta front had an extent of 3 km and prog raded over a distance of 1,5 km, in probably less than 100 years, with the delta toe climbing by 50 m against the basin's rapidly aggrading muddy floo r. The delta advanced through the alternating episodes of its toe aggradati on and progradation, related to the increases and decreases of the delta-sl ope gradient. Slope steepening led to intense sediment sloughing by chutes and occasional large-scale failures. The fjord's wave fetch was low and the wave base no deeper than 1.5-2 mi but strong storm waves occasionally rewo rked the delta front to a depth of 6 m. Glacitectonic deformation was limit ed to the system's upfjord end. Allostratigraphic analysis suggests that th e proglacial system commenced its development as an ice-contact submarine f an that was deformed, quickly aggraded to the sea surface and turned into a n ice-contact delta, which further evolved into the large glaciofluvial del ta. The Kregnes ridge represents an episode of the ice-front re-advance due to climatic deterioration and is tentatively correlated with the Hoklingen substage.