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Physical modelling of bedrock brecciation by ice segregation in permafrost

Author

Listed:
  • J. B. Murton
  • J.‐P. Coutard
  • J.‐P. Lautridou
  • J.‐C. Ozouf
  • D. A. Robinson
  • R. B. G. Williams

Abstract

The lower half of a large block of moist chalk was maintained at subzero temperatures while the upper half was cyclically frozen and thawed, simulating 19 seasonal temperature cycles in an active layer above permafrost. During the experiment, the rock surface heaved vertically by at least 34.7 mm. Sixty‐one percent of the heave occurred during freezing periods, and is attributed primarily to ice segregation accompanying upward freezing from the permafrost table during the early stages of simulated winters. Thirty‐nine percent of the heave occurred during thawing periods, and is attributed to ice segregation in the frozen rock beneath the thaw front during the mid to late stages of simulated summers. By the end of the experiment, the middle horizon of the chalk, representing the upper part of the simulated permafrost and the basal part of the active layer, had become strongly brecciated and rich in segregated ice. The style of brecciation has similarities with that in perennially‐frozen limestone, sandstone and shale in Svalbard and Canada, and chalk frozen during Quaternary cold stages in France and England. These similarities suggest that ice segregation during perennial and seasonal freezing is an important process of weathering and coarse‐sediment supply in areas of frost‐susceptible bedrock. Copyright © 2001 John Wiley & Sons, Ltd. La moitié inférieure d'un gros bloc de craie humide a été maintenue à des températures inférieures à zéro degré (maintien d'un pergélisol) pendant que sa moitié supérieure était soumise alternativement au gel et au dégel, simulant ainsi 19 cycles saisonniers dans la couche active. Pendant l'expérience, la surface de la roche s'est soulevée verticalement de 34,7 mm. Soixante et un % du gonflement a été acquis pendant les périodes de gel simulant les hivers et attribué essentiellement à la ségrégation de glace accompagnant un gel à partir du sommet du pergélisol au début de ces périodes. Trente neuf % du gonflement a été enregistré pendant le milieu et la fin des périodes de dégel simulant les étés. Ceci est considéré comme le résultat de regels en‐dessous du niveau atteint par le front de dégel. A la fin de l'expérience, la partie médiane du bloc, correspondant au sommet du pergélisol et à la base de la couche active, est apparue très fragmentée et riche en glace de ségrégation. Le type de fragmentation offre des aspects semblables à ceux qu'on observe dans les calcaires, grès et schistes gelés en permanence du Svalbard et du Canada et les craies soumises aux gels des stades froids du Quaternaire en France et en Angleterre. Cela suggère que la ségrégation de la glace pendant les périodes de gel permanent ou saisonnier est un important processus de fragmentation des roches et de fourniture de sédiments grossiers dans les régions où les roches sont sensibles au gel. Copyright © 2001 John Wiley & Sons, Ltd.

Suggested Citation

  • J. B. Murton & J.‐P. Coutard & J.‐P. Lautridou & J.‐C. Ozouf & D. A. Robinson & R. B. G. Williams, 2001. "Physical modelling of bedrock brecciation by ice segregation in permafrost," Permafrost and Periglacial Processes, John Wiley & Sons, vol. 12(3), pages 255-266, September.
  • Handle: RePEc:wly:perpro:v:12:y:2001:i:3:p:255-266
    DOI: 10.1002/ppp.390
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