TY - JOUR

T1 - Response of salt structures to ice-sheet loading

T2 - Implications for ice-marginal and subglacial processes

AU - Lang, Jörg

AU - Hampel, Andrea

AU - Brandes, Christian

AU - Winsemann, Jutta

N1 - Funding information: Financial support by the Niedersächsisches Ministerium für Wissenschaft und Kultur (MWK) (11.2-76202-17-3/09) is gratefully acknowledged (PRO Niedersachsen Project No. 11.2-76202-17-3/09). T. Li, G. Maniatis and H. Turpeinen are thanked for their help with ABAQUS. F. Busch is thanked for GIS work. We appreciate constructive reviews by M. Albertz and J. Lee, which greatly helped to improve our manuscript.

PY - 2014/10/1

Y1 - 2014/10/1

N2 - During the past decades the effect of glacioisostatic adjustment has received much attention. However, the response of salt structures to ice-sheet loading and unloading is poorly understood. Our study aims to test conceptual models of the interaction between ice-sheet loading and salt structures by finite-element modelling. The results are discussed with regard to their implications for ice-marginal and subglacial processes. Our models consist of 2D plane-strain cross-sections, which represent simplified geological cross-sections from the Central European Basin System. The model layers represent (i) sedimentary rocks of elastoplastic rheology, (ii) a viscoelastic diapir and layer of salt and (iii) an elastoplastic basement. On top of the model, a temporarily variable pressure simulates the advance and retreat of an ice sheet. The durations of the individual loading phases were defined to resemble the durations of the Pleistocene ice advances in northern central Europe. The geometry and rheology of the model layers and the magnitude, spatial distribution and timing of ice-sheet loading were systematically varied to detect the controlling factors. All simulations indicate that salt structures respond to ice-sheet loading. An ice advance towards the diapir causes salt flow from the source layer below the ice sheet towards the diapir, resulting in an uplift of up to+4m. The diapir continues to rise as long as the load is applied to the source layer but not to the crest of the diapir. When the diapir is transgressed by the ice sheet the diapir is pushed down (up to-36m) as long as load is applied to the crest of the diapir. During and after ice unloading large parts of the displacement are compensated by a reversal of the salt flow. Plastic deformation of the overburden is restricted to the area immediately above the salt diapir. The displacements after unloading range between-3.1 and+2.7m. Larger displacements are observed in models with deep-rooted diapirs, thicker ice sheets, longer duration of the loading phase, thicker salt source layers and lower viscosity of the salt. The rise or fall of diapirs triggered or amplified by ice-sheet loading are likely to affect glacigenic deformation, erosion and deposition above the diapir and within the rim synclines. Ice-load induced uplift in front of an ice sheet will provide favourable conditions for the formation of push moraines, for example by creating a topographic obstacle and inclining potential detachments. Subglacial subsidence of salt structures will enhance erosion by providing a preferential drainage pathway and fracturing of the overburden of the salt structure and thereby contribute to the incision of tunnel valleys. However, the resulting displacements are probably too low to have a marked effect on the advance or retreat pattern of the ice sheets.

AB - During the past decades the effect of glacioisostatic adjustment has received much attention. However, the response of salt structures to ice-sheet loading and unloading is poorly understood. Our study aims to test conceptual models of the interaction between ice-sheet loading and salt structures by finite-element modelling. The results are discussed with regard to their implications for ice-marginal and subglacial processes. Our models consist of 2D plane-strain cross-sections, which represent simplified geological cross-sections from the Central European Basin System. The model layers represent (i) sedimentary rocks of elastoplastic rheology, (ii) a viscoelastic diapir and layer of salt and (iii) an elastoplastic basement. On top of the model, a temporarily variable pressure simulates the advance and retreat of an ice sheet. The durations of the individual loading phases were defined to resemble the durations of the Pleistocene ice advances in northern central Europe. The geometry and rheology of the model layers and the magnitude, spatial distribution and timing of ice-sheet loading were systematically varied to detect the controlling factors. All simulations indicate that salt structures respond to ice-sheet loading. An ice advance towards the diapir causes salt flow from the source layer below the ice sheet towards the diapir, resulting in an uplift of up to+4m. The diapir continues to rise as long as the load is applied to the source layer but not to the crest of the diapir. When the diapir is transgressed by the ice sheet the diapir is pushed down (up to-36m) as long as load is applied to the crest of the diapir. During and after ice unloading large parts of the displacement are compensated by a reversal of the salt flow. Plastic deformation of the overburden is restricted to the area immediately above the salt diapir. The displacements after unloading range between-3.1 and+2.7m. Larger displacements are observed in models with deep-rooted diapirs, thicker ice sheets, longer duration of the loading phase, thicker salt source layers and lower viscosity of the salt. The rise or fall of diapirs triggered or amplified by ice-sheet loading are likely to affect glacigenic deformation, erosion and deposition above the diapir and within the rim synclines. Ice-load induced uplift in front of an ice sheet will provide favourable conditions for the formation of push moraines, for example by creating a topographic obstacle and inclining potential detachments. Subglacial subsidence of salt structures will enhance erosion by providing a preferential drainage pathway and fracturing of the overburden of the salt structure and thereby contribute to the incision of tunnel valleys. However, the resulting displacements are probably too low to have a marked effect on the advance or retreat pattern of the ice sheets.

KW - Central European Basin System

KW - Finite-element modelling

KW - Ice-sheet loading

KW - Salt structures

UR - http://www.scopus.com/inward/record.url?scp=84907334533&partnerID=8YFLogxK

U2 - 10.1016/j.quascirev.2014.07.022

DO - 10.1016/j.quascirev.2014.07.022

M3 - Article

AN - SCOPUS:84907334533

VL - 101

SP - 217

EP - 233

JO - Quaternary science reviews

JF - Quaternary science reviews

SN - 0277-3791

ER -