Role of sediment in speleogenesis; sedimentation and paragenesis

Abstract

6Although the effects of sedimentation in caves have been recognised for many years, its role in 7 speleogenesis is frequently overlooked. Influxes of sediment into a cave system fundamentally alters 8 the way cave passages develop, either by alluviation in a vadose environment, forcing lateral 9 corrosion and the development of notches, or upwards dissolution in a phreatic environment through a 10 process known as paragenesis. Sediment influxes affect the hydrological functioning of a karst aquifer 11 by changing the way conduits behave and subsequently develop both in plan and long section. 12Here we give an overview of the mechanisms of cave sedimentation and describe how the process of 13 alluviation and paragenesis affect speleogenesis. A characteristic suite of meso-and micro-scale 14 dissolutional features can be used to recognise paragenetic development, which is reviewed here. In a 15 vadose environment these include alluvial notches, whilst in a phreatic environment, half tubes, 16 anastomoses and pendants, bedrock fins and paragenetic dissolution ramps result. Using these to 17 identify phases of sedimentation and paragenesis is crucial for reconstructing denudation chronologies 18 from cave deposits. We suggest that sedimentation and paragenesis is most likely to occur in certain 19 geomorphological situations, such as ice marginal and periglacial environments, beneath thick 20 residual soils and where rivers can transport fluvial sediment into a cave, either via stream sinks or 21 back-flooding. 22

Simulation of 3D karst conduits with an object-distance based method integrating geological knowledge

“…Thus, conduit irregularities are not symmetrical and, moreover, their variations do not range between the same extrema ( figure 11). Such differences between conduit ceiling, floor and/or sides can be noticed in several conduits, such as in the Abracurrie Main Chamber, Nullarbor, Australia [James et al, 2012] or in the Clearwater Cave, Gunung Mulu, Sarawak [Farrant and Smart, 2011]. To model a smooth trench floor, for instance, we propose to separate the grid in two areas: the first one contains the vertical trench planes -with eventually an extension around the planes to avoid trench side protuberances to develop below the trench floor when using very high perturbations, and the second one the rest of the grid.…”

“…Modelling sediments could also be interesting considering their impact on fluid flows and on speleogenesis [Farrant and Smart, 2011]. Finally, the entire methodology could be adapted to other underground processes, such as hydrothermal alteration, or be used to study the usefulness and applicability of the method in sinkhole prevention.…”

“…According to various authors, the groundwater table has a major influence on conduit development [e.g., Jameson, 1985, Ford and Williams, 2007, Farrant and Smart, 2011, Jaillet et al, 2011. In the phreatic zone, corresponding to the saturated zone below the water table, the inception features are the most influential factor upon the resulting shapes .…”

“…Horizontal dissolution notches are less common. They develop at the water-table interface when conduits are partially flooded and water level variationsa are small enough to favour a lateral incision [e.g., Lauritzen and Lundberg, 2000, Ford and Williams, 2007, Farrant and Smart, 2011. Geometrically speaking, notches have a rounder aspect than shapes linked to inception features ( figure 4.3).…”

Natural variations in calcite dissolution rates in streams: Controls, implications, and open questions

“…While mechanical erosion dominates channel incision in low-solubility lithologies, dissolution may make nonnegligible contributions to channel incision in carbonate terrains [e.g., Springer et al, 2003], which outcrop on 15% of the Earth's ice-free surface [Ford and Williams, 2007].…”