Rheological and tectonic modeling of salt provinces

The effects of benthic organisms on the physical properties of granular substrata are well documented The range of effects has been presented in H B Moore (1931, 1939), Schwartz (1932), Dapples (1942), D G Moore and Scruton (1957), McMaster (1967), Rhoads (1974), Rowe (1974), Powell (1974), Richards and Park (1976), Myers (1977a,b), Self and Jumars (1978), Lee and Swartz (1980), and Carney (1981) These papers relate the effects of benthic species to changes in grain size, sorting, fabric, water content, compaction, shear strength, and bottom stability Those autecologic parameters that appear to be most highly correlated with physical modifications of sediments include: method of feeding, feeding selectivity, feeding level relative to the sediment—water interface, degree of mobility, organism size and population density, burrowing depth, and, if the organism is a tube dweller, the density, spacing, and length of tubes

The Effects of Marine Benthos on Physical Properties of Sediments

Turbidite muds in cores from the outer Scotian continental margin, off eastern Canada, contain abundant thin silt laminae. Graded laminated units are recognized in parts of this sequence. These represent single depositional events, and show a regular decrease in modal grain size and thickness of the silt laminae through the unit. A similar fining trend is shown by both silt and mud layers over hundreds of kilometres downslope. Textural analysis of individual laminae allows the construction of a dynamically consistent physical model for transport and sorting in muddy turbidity currents. Hydraulic sorting aggregates finer material to the top and tail regions of a large turbidity flow which then overspills its channel banks. Downslope lateral sorting occurs with preferential deposition of coarser silt grains and larger mud flocs. Depositional sorting by increased shear in the boundary layer separates clay flocs from silt grains and results in a regular mud/silt lamination. Estimates can be made of the physical parameters of the turbidity flows involved. They are a minimum of several hundreds of metres thick, have low concentrations (of the order of 10−3 or 2500 mg 1−1), and move downslope at velocities of 10-20 cm s−1. A 5 mm thick, coarse silt lamina takes about 10 h to deposit, and the subsequent mud layer ‘blankets’ very rapidly over this. A complete unit is deposited in 2-6 days which is the time it takes for the turbidity flow to pass a particular point. These thick, dilute, low-velocity flows are significantly different from the ‘classical’ turbidity current. However, there is mounting evidence in support of the new concept from laboratory observations and direct field measurements.

A physical model for the transport and sorting of fine‐grained sediment by turbidity currents

Contourites: Their recognition in modern and ancient sediments

The stability of tidal flats in Venice Lagoon—the results of in-situ measurements using two benthic, annular flumes

On experimentally deposited kaolinite, illite, and Ca-bentonite consolidated under their own load or by additional vertical pressure, the progress of compaction in relation to excess pore water pressure, mass physical properties, gravitational mass movements in a tilted tank, and erodibility under running water in a flume were studied. The very low consolidated sediments near the mud/water interface do not obey the generally used theory in soil mechanics. They show a different, non-linear relationship between void ratio or water content and depth below the sedimentary surface on the one hand, or effective overburden pressure and shear strength on the other. The same is true of other physical properties such as permeability, which changes considerably with depth and time of consolidation.



High sedimentation rates on slopes induce shallow sediment flow, whereas at low rates and critical slope angles different types of slope failures including the breaking up of water-rich sediment into sharp boundered blocks are observed.



Flume studies on soft clay muds show three different types of erosion: continuously suspending, discontinuous erosion of crumbs or shreds, and wavy deformation of the clay surface with disintegration of particles from the crests. The critical tractive stress depends not only on clay type, void ratio, and shear strength, but significantly also on the ‘geologic history’of the clay (i.e. deposition from thin suspension or dense slurry, fabric, consolidation and swelling generating minute inhomogeneities etc.).



The experiments may lead to a better understanding of all mechanical processe's including pore-water flow taking place near or not far below the sediment/ water interface.

Mass physical properties, sliding and erodibility of experimentally deposited and differently consolidated clayey muds (Approach, equipment, and first results)

G. Einsele

Papers

Mass physical properties, sliding and erodibility of experimentally deposited and differently consolidated clayey muds (Approach, equipment, and first results)