Hostname: page-component-78c5997874-lj6df Total loading time: 0 Render date: 2024-11-17T18:22:46.356Z Has data issue: false hasContentIssue false
  • English
  • Français

Intrusive and extrusive (micro)melange couplets as distal effects of tidal pumping by a marine ice sheet

Published online by Cambridge University Press:  01 May 2009

C. J. Talbot  and
V. Von Brunn
C. J. Talbot
Affiliation:
Institute of Geology, University of Uppsala, Box 555, S-751 22 Uppsala, Sweden
V. Von Brunn
Affiliation:
Department of Geology, University of Natal, P.O. Box 375, Pietermaritzburg 3200, South Africa
Get access Rights & Permissions [Opens in a new window]

Abstract

Microscopic soft-sediment deformation structures in a 30 × 25 × 12 mm hand specimen of glaciogenic silty mudstone from the Permo-Carboniferous Dwyka Formation of northern Natal in South Africa are illustrated by serial sections. The processes these structures imply are interpreted using palinspastically restored sections and isopachytes reconstructed from them. The sedimentation of silts, muds, and microrhythmites is found to have been punctuated by episodes of hydraulic activity which resulted in thirteen bodies with the mixed fabrics of micromelanges. These are divisible into five melange types: (1) subconcordant intrusive; (2) disconcordant intrusive; (3) subconcordant extrusive; (4) near-surface with asymmetric internal structures, and (5) conformable near-surface with internal structures symmetric about the palaeovertical.

Remarkable similarities between isopachs for pairs of micromelanges at different levels in the specimen suggest that intrusive melanges at depth fed contemporaneous extrusive melanges on the sea floor. Each couplet of melanges with matched isopachs is linked by faults which are interpreted as having acted as hydraulic vents despite only parts of them being infilled by intrusive melange. A significant proportion of the succession could consist of sediment recycled from depth by hydraulic extrusion. Repeated hydraulic intrusions along, and extrusions from, the same disturbed interface suggest that this interface acted as the distal leaking end of one of the hydraulic sills recently described by von Brunn & Talbot (1986). Pulses of pressurized water were transmitted through a prograding marine slope of quickclay by the tidal pumping of a marine ice sheet periodically grounding upslope.

The results of this analysis are extrapolated to processes operative in subduction complexes. All four fabrics described from large-scale hydraulic melanges in modern and ancient accretionary prisms are matched on a much smaller scale in our sample from a proglacial submarine slope. Dismemberment by faults is the only fabric element described from accretionary complexes which is missing from the micro-analogues described here.

Type
Articles
Information
Geological Magazine , Volume 124 , Issue 6 , November 1987 , pp. 513 - 525
Copyright
Copyright © Cambridge University Press 1987

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Allen, J. R. L. 1985. Principles of Physical Sedimentology. London: Allen & Unwin, 272 pp.Google Scholar
Archer, J. B. 1984. Clastic intrusions in deep-sea fan deposits of the Rosroe Formation, lower Ordovician, Western Ireland. Journal of Sedimentary Petrology 54, 1197–1205.Google Scholar
Barber, A. J., Tjokrosapoetro, S. & Charlton, T. R. in press. Wrench faults, shale diapirs, mud volcanoes and melanges in accretionary complexes. American Association of Petroleum Geologists Bulletin.Google Scholar
Bentley, S. P. & Smalley, I. J. 1978. Interparticle cementation in Canadian post-glacial clays, and the problem of high sensitivity. Sedimentology 25, 297–302.CrossRefGoogle Scholar
Cowan, D. S. 1985. Structural styles in Mesozoic and Cenozoic melanges in the western Cordillera of North America. Geological Society of America Bulletin 96, 451–62.2.0.CO;2>CrossRefGoogle Scholar
Dixon, J. M. & Simpson, D. G. 1987. Centrifuged modelling of laccolith intrusion. Journal of Structural Geology 9, 87–103.CrossRefGoogle Scholar
Roberts, J. L. 1970. The intrusion of magma into brittle rocks. In Mechanisms of Igneous Intrusions (eds. Newall, G. Rast, N.), pp. 287–338. Liverpool: Gallery Press.Google Scholar
Torrance, J. K. 1983. Towards a general model of quick clay development. Sedimentology 30, 547–55.CrossRefGoogle Scholar
von Brunn, V. & Talbot, C. J. 1986. Intrusive clastic sheets and their subglacial deformation in the Dwyka Formation in Northern Natal, South Africa. Journal of Sedimentary Petrology 56, 35–44.Google Scholar