Changes

Near the base of the infilled channel, often erratic and contorted clay layers are concentrated as clast within the sand body ([[:file:M31F14v2.jpg|Figure 7A]]). Within the deposited sands themselves, contorted structures are very common. Slump-type structures, distorted bedding, clay infills, and occasionally fairly persistent layers of organic trash sandwiched between sand layers are also common. [[:file:M31F14v2.jpg|Figure 7B]] illustrates some of the contorted bedding probably associated with localized slumps within a channel-fill deposit. Silts and silty clays that are deposited in the central part of the channel fill often display thin silty and sandy layers that intercalate with highly burrowed clays. Most commonly the sandy laminations display extremely sharp upper and lower surfaces ([[:file:M31F14v2.jpg|Figure 7C]]). Convolute laminations and other types of distorted bedding such as flow rolls, ball and pillow structures, etc. ([[:file:M31F14v2.jpg|Figure 7D]]), are common within the sand bodies. The uppermost part of the fill consists primarily of organic-rich clays ([[:file:M31F14v2.jpg|Figure 7E]]) that generally show intense root burrowing. Occasionally, thin seams of shell debris and silt-infilled animal burrows can be detected.

Near the base of the infilled channel, often erratic and contorted clay layers are concentrated as clast within the sand body ([[:file:M31F14v2.jpg|Figure 7A]]). Within the deposited sands themselves, contorted structures are very common. Slump-type structures, distorted bedding, clay infills, and occasionally fairly persistent layers of organic trash sandwiched between sand layers are also common. [[:file:M31F14v2.jpg|Figure 7B]] illustrates some of the contorted bedding probably associated with localized slumps within a channel-fill deposit. Silts and silty clays that are deposited in the central part of the channel fill often display thin silty and sandy layers that intercalate with highly burrowed clays. Most commonly the sandy laminations display extremely sharp upper and lower surfaces ([[:file:M31F14v2.jpg|Figure 7C]]). Convolute laminations and other types of distorted bedding such as flow rolls, ball and pillow structures, etc. ([[:file:M31F14v2.jpg|Figure 7D]]), are common within the sand bodies. The uppermost part of the fill consists primarily of organic-rich clays ([[:file:M31F14v2.jpg|Figure 7E]]) that generally show intense root burrowing. Occasionally, thin seams of shell debris and silt-infilled animal burrows can be detected.

Although grain size has a general tendency to show a fining-upward sequence within any one sandy unit, in some deposits there is virtually no change in grain size. Dip angles can also be extremely erratic, resulting primarily from the large number of disturbed and distorted structures found within the channel-fill deposits. Undoubtedly, the rapidity of the infilling process and extremely high porewater content of the clays and silts are responsible for the large amount of distorted bedding.

Although grain size has a general tendency to show a fining-upward sequence within any one sandy unit, in some deposits there is virtually no change in grain size. [[Dip]] angles can also be extremely erratic, resulting primarily from the large number of disturbed and distorted structures found within the channel-fill deposits. Undoubtedly, the rapidity of the infilling process and extremely high porewater content of the clays and silts are responsible for the large amount of distorted bedding.

[[:file:M31F15.jpg|Figure 8]] is a continuously cored boring through an old distributary channel that existed off Southwest Pass, Mississippi River delta, in the early 1800s. The channel on old maps was approximately 9 to 10 m deep and about 100 to 110 m wide. The base of the channel in the cored boring is identified by the letter A and occurs at a depth below mean sea level of 10.5 m. The clays directly below this scour plane, where burrowing is present, contain marine microfaunal remains. Just above the scour surface is a sand approximately 1 m thick. It contains fairly [[Core_description#Maturity|well-sorted]] fine- to medium-grained sands displaying small-scale current structures. Organic trash and other debris are common along the bedding planes.

[[:file:M31F15.jpg|Figure 8]] is a continuously cored boring through an old distributary channel that existed off Southwest Pass, Mississippi River delta, in the early 1800s. The channel on old maps was approximately 9 to 10 m deep and about 100 to 110 m wide. The base of the channel in the cored boring is identified by the letter A and occurs at a depth below mean sea level of 10.5 m. The clays directly below this scour plane, where burrowing is present, contain marine microfaunal remains. Just above the scour surface is a sand approximately 1 m thick. It contains fairly [[Core_description#Maturity|well-sorted]] fine- to medium-grained sands displaying small-scale current structures. Organic trash and other debris are common along the bedding planes.