Interpreting syndepositional sediment remobilization and deformation beneath submarine gravity flows; a kinematic boundary layer approach

Robert W. H. Butler,Joris T. Eggenhuisen,Peter Haughton,William D. McCaffrey

doi:10.1144/jgs2014-150

Abstract

Turbidite sandstones and related deposits commonly contain deformation structures and remobilized sediment that might have resulted from post-depositional modification such as downslope creep (e.g. slumping) or density-driven loading by overlying deposits. However, we consider that deformation can occur during the passage of turbidity currents that exerted shear stress on their substrates (whether entirely pre-existing strata, sediment deposited by earlier parts of the flow itself or some combination of these). Criteria are outlined here, to avoid confusion with products of other mechanisms (e.g. slumping or later tectonics), which establish the synchronicity between the passage of overriding flows and deformation of their substrates. This underpins a new analytical framework for tracking the relationship between deformation, deposition and the transit of the causal turbidity current, through the concept of kinematic boundary layers. Case study examples are drawn from outcrop (Miocene of New Zealand, and Apennines of Italy) and subsurface examples (Britannia Sandstone, Cretaceous, UK Continental Shelf). Example structures include asymmetric flame structures, convolute lamination, some debritic units and injection complexes, together with slurry and mixed slurry facies. These structures may provide insight into the rheology and dynamics of submarine flows and their substrates, and have implications for the development of subsurface turbidite reservoirs.

Highlights

Turbidite sandstones and related deposits commonly contain deformation structures and remobilized sediment that might have resulted from post-depositional modification such as downslope creep or density-driven loading by overlying deposits
As McClelland et al (2011) pointed out, many synsedimentary structures can be misinterpreted as the products of subsequent tectonics where found in metasedimentary successions within mountain belts
Understanding and recognizing these structures is important to those seeking to unravel orogenic structure. These syndepositional structures may provide clues to the rheology and dynamics of submarine flows and their substrates during deposition, and their distribution in sandstones within sedimentary basins can affect the performance of hydrocarbon reservoirs

Summary

Introduction

Turbidite sandstones and related deposits commonly contain deformation structures and remobilized sediment that might have resulted from post-depositional modification such as downslope creep (e.g. slumping) or density-driven loading by overlying deposits. To avoid confusion with products of other mechanisms (e.g. slumping or later tectonics), which establish the synchronicity between the passage of overriding flows and deformation of their substrates This underpins a new analytical framework for tracking the relationship between deformation, deposition and the transit of the causal turbidity current, through the concept of kinematic boundary layers. Turbidites and related deposits can contain deformation structures that are interpreted as having formed prior to lithification Such soft-sediment deformation can include the products of slumping and sliding Here we lay out criteria for establishing the temporal relationships between deformation and turbidity currents (i.e. subaqueous particulate density currents; in the broad sense, as used by Kneller & Buckee 2000) These inform a framework for analysing soft-sediment deformation structures, with specific reference to three case studies. It is common to find that the flame structures are asymmetric and are entrained into the overlying

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Discussion

Conclusion