Environmental Engineering Reference
In-Depth Information
Chapter 20
Slopes
Stephen M. Hubbard, * ,1 James A. MacEachern and Kerrie L. Bann
*Department of Geoscience, University of Calgary, Calgary, Canada, Department of Earth
Sciences, Simon Fraser University, Burnaby, Canada, Ichnofacies Analysis Inc., Calgary, Canada
1 Corresponding author: e-mail: shubbard@ucalgary.ca
1. INTRODUCTION
Deposits of the continental slope, and of other slopes associated with high-relief
basin margins, contain the record of sedimentological processes critical to the
understanding of sediment transport from continents into deep-sea basins. In
many instances, slopes can be considered primarily as zones of sedimentary
bypass, wherein coarse-grained sediment derived from the continent is funneled
through conduits such as submarine canyons, ultimately accumulating as subma-
rine fans on the basin-floor ( Fig. 1 ). Extensive and regular mass-wasting events
also play key roles in sediment remobilization and bypass on slopes. On many
margins, contour currents are also significant, and help to shape the seascape.
It is important to recognize that slopes can be as diverse as many better-
documented depositional realms (e.g., marginal-marine settings, or basin-floors)
and that, in many instances, accretion of slopes by widespread suspension settling
of fine-grained particulate debris constitutes the dominant process.
Due to their prevalence as zones of sedimentary bypass or of suspended
sediment settling, deposits of slopes are commonly dominated by fine-grained
sediment. Major erosion surfaces that are excavated into fine-grained substrata
and subsequently overlain by fine-grained material, are subtle, but may com-
prise the only record of high-energy processes responsible for the transport
of sands and gravels across this depositional setting. In many instances then,
slope regimes do not host extensive coarse-grained sedimentary accumulations,
and this, in turn, has dictated the quality and abundance of data available for
their study in two ways: slope deposits (1) have been traditionally under-
represented in drill cores acquired for hydrocarbon exploration because they
were typically considered to lack significant reservoir potential until the last
two decades; and (2) are commonly poorly exposed in outcrop, owing to their
recessive weathering character. By contrast, the deposits of more broadly sand-
prone sedimentary environments of continental shelf or basin-floor affinity
were often more extensively drilled or are better exposed in outcrop. For these
 
 
 
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