Structural evolution and sediment entrainment in mass-transport complexes: outcrop studies from Italy

R W H Butler, W D McCaffrey

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Mass-transport complexes (MTCs) form a significant component of many deep marine clastic successions. Here, studies of outcrop examples of MTCs from the Italian Apennines indicate that material can be entrained across both the upper and lower boundaries of a mass flow. The studied MTCs all incorporate debrite–turbidite couplets. Growth stratal geometries in the overlying turbidite sandstones indicate that turbidite deposition occurred synchronously with internal deformation within substrate debris flows. The turbidite stratal patterns and the internal structure of the debrites jointly indicate that at least the later stages of MTC emplacement were ordered, involving coherent creep. This process can generate unexpected sand-on-sand juxtapositions across otherwise low-permeability debritic horizons. Entrainment of substrate material across the lower debris-flow boundary occurred by thrusting, although this deformation can have initiated before the arrival of the further-travelled debris flow itself. The outcrop examples are thus characterized by composite deformation and depositional histories, such that different parts of composite MTCs can have experienced radically different amounts of displacement. The ordered creeping deformation recognized at outcrop may, however, be under-recognized in seismic examples, where internal deformation and associated growth stratal geometries are less easy to study.
Original languageEnglish
Pages (from-to)617-631
Number of pages15
JournalJournal of the Geological Society
Volume167
Issue number3
DOIs
Publication statusPublished - May 2010

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mass transport
entrainment
outcrop
turbidite
debris flow
sediment
geometry
substrate
sand
low flow
creep
emplacement
sandstone
permeability
history
material

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Structural evolution and sediment entrainment in mass-transport complexes : outcrop studies from Italy. / Butler, R W H; McCaffrey, W D.

In: Journal of the Geological Society , Vol. 167, No. 3, 05.2010, p. 617-631.

Research output: Contribution to journalArticle

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AB - Mass-transport complexes (MTCs) form a significant component of many deep marine clastic successions. Here, studies of outcrop examples of MTCs from the Italian Apennines indicate that material can be entrained across both the upper and lower boundaries of a mass flow. The studied MTCs all incorporate debrite–turbidite couplets. Growth stratal geometries in the overlying turbidite sandstones indicate that turbidite deposition occurred synchronously with internal deformation within substrate debris flows. The turbidite stratal patterns and the internal structure of the debrites jointly indicate that at least the later stages of MTC emplacement were ordered, involving coherent creep. This process can generate unexpected sand-on-sand juxtapositions across otherwise low-permeability debritic horizons. Entrainment of substrate material across the lower debris-flow boundary occurred by thrusting, although this deformation can have initiated before the arrival of the further-travelled debris flow itself. The outcrop examples are thus characterized by composite deformation and depositional histories, such that different parts of composite MTCs can have experienced radically different amounts of displacement. The ordered creeping deformation recognized at outcrop may, however, be under-recognized in seismic examples, where internal deformation and associated growth stratal geometries are less easy to study.

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