The kinematics of ancient tidewater ice margins: criteria for recognition from grounding-line moraines

Abstract

Modern studies indicate that the kinematic behaviour of tidewater glaciers is a crucial part of ice-sheet dynamics. A similar relationship may be expected for ancient ice sheets, but can the kinematics of ancient tidewater ice margins be recognized? The paper addresses this methodological issue by pointing to the high-resolution stratigraphic record of marine moraines, thus far little explored. On the basis of a series of case studies, a range of field criteria are proposed for the recognition of short-term grounding-line movement and possible oscillations in moraine outcrop sections. The method combines allostratigraphic mapping and architectural facies analysis of the moraine sedimentary units formed during glacier advance, subaqueous stillstand and eventual subaerial stillstand, with recognition of the successive ice-contact surfaces. The stacking architecture of the sedimentary units and their ice-contact bounding surfaces reveal the time-distance trajectory of the grounding-line positions. It is also possible to recognize changes in the mode and rate of subglacial sediment delivery, as well as fluctuations in the ice flux and meltwater discharge. This methodology invites detailed studies of marine moraines. Systematic case studies on a regional scale may provide new information on the behaviour of tidewater ice margins and lead to unprecedented insights into the dynamics of ancient ice sheets.

A Neoproterozoic ice advance sequence, Sperry Wash, California

“…‐5). Ice‐marginal fans typically build‐up steep slopes (Powell, ; Lønne, ; Lønne & Nemec, ,b), promoting sediment gravity flow remobilization downslope on both the ice‐proximal and ice‐distal fan margins. This process is thought to account for the preservation of slump folds verging perpendicular to the principal palaeoflow orientation recorded throughout the remainder of the succession (Fig.…”

Late Quaternary sedimentation and permafrost development in a Svalbard fjord‐valley, Norwegian high Arctic

“…The corresponding glacial lowstand systems tract (GLST) would be represented by the grounding‐line moraine or shelf‐edge submarine outwash apron formed at a distant seaward location ( cf . Lønne & Nemec, ). It is further worth pointing to the variable role of the individual controlling factors at the successive stages of fjord‐valley infilling.…”

“…It is further worth pointing to the variable role of the individual controlling factors at the successive stages of fjord‐valley infilling. At stage GRST, the accommodation space plays a crucial role in the subglacial environment – where it reaches a minimum – while both the accommodation and sediment supply are at their maximum at the glacier terminus, where a thick grounding‐line moraine forms (Nemec et al ., ; Lønne et al ., ; Lønne & Nemec, ). The Adventdalen ice stream was probably a tributary to the Isfjorden ice‐drainage system (Fig.…”

“…Dalrymple et al ., , ; Gobo et al ., ). However, the pattern in glacial fjord‐valleys differs markedly from non‐glacial norms by the involvement of a tidewater glacier, with its asymmetrical dynamics of relatively slow advance and rapid retreat (Benn et al ., ; Lønne & Nemec, ) and with the related wave of paraglacial sediment yield (Church & Ryder, ; Ballantyne, ). The present study expounds on this issue with implications for the sequence stratigraphy of fjord‐valley infilling.…”

Protracted active surge phase in the high arctic (svalbard): dynamic development and morphological impact

“…Subglacial sediments would favor fast ice flow and proglacial sediment ridges must have formed in front of the advancing terminus. However, glaciers have a limited ability to push sediments into frontal ridges (Bennett ) and, as the accumulations are overrun, they tend to recycle with low preservation potential, depending on basin depth and glacier thickness (Lønne ; Lønne and Nemec 2011a, 2011b). The thrusting caused by the high ice flux is the most important process along the confined marine basin, which transports debris into the ice (Alley et al .…”