Changes

The upper left diagram of [[:file:M31F17.jpg|Figure 2]] illustrates schematically the process of a bifurcated channel. In the cross sections on this panel, the three major units illustrated include lower prodelta clays, overlain by alternating silt and sand units of the distal bar, and uppermost, distributary-mouth-bar sands. As the diagram shows, distributary-mouth-bar sands form a nearly continuous sand body extending laterally large distances.

The upper left diagram of [[:file:M31F17.jpg|Figure 2]] illustrates schematically the process of a bifurcated channel. In the cross sections on this panel, the three major units illustrated include lower prodelta clays, overlain by alternating silt and sand units of the distal bar, and uppermost, distributary-mouth-bar sands. As the diagram shows, distributary-mouth-bar sands form a nearly continuous sand body extending laterally large distances.

The upper right-hand diagram shows the most common vertical sequence within the distributary-mouth-bar deposits and some of its characteristics. The unit generally displays a coarsening-upward sequence in which depositional dips are extremely low, rarely exceeding 1° except in areas where slump deposits result in high angles within the mass-moved sediment. [[:file:M31F18.jpg|Figure 3A and B]] illustrates some of the characteristic structures found within the lowermost units of prodelta clays. Parallel, colored clay laminations, thin graded silt and silty clay parallel laminations, bioturbation (generally confined to the clay laminations), and slump structures are common within the prodelta deposits. Microfaunal remains generally indicate marine deposition, and diversity of species is generally quite high, indicating an open, inner to outer shelf depositional environment. These deposits display most of the characteristics of normal marine shelf deposits and are differentiated only by their rate of accumulation.

The upper right-hand diagram shows the most common vertical sequence within the distributary-mouth-bar deposits and some of its characteristics. The unit generally displays a coarsening-upward sequence in which depositional dips are extremely low, rarely exceeding 1° except in areas where slump deposits result in high angles within the mass-moved sediment. [[:file:M31F18.jpg|Figure 3A and B]] illustrates some of the characteristic structures found within the lowermost units of prodelta clays. Parallel, colored clay laminations, thin graded silt and silty clay parallel laminations, [[bioturbation]] (generally confined to the clay laminations), and slump structures are common within the prodelta deposits. Microfaunal remains generally indicate marine deposition, and diversity of species is generally quite high, indicating an open, inner to outer shelf depositional environment. These deposits display most of the characteristics of normal marine shelf deposits and are differentiated only by their rate of accumulation.

For a given length of time, prodelta deposits are thicker (because of high sedimentation) than an equivalent section of normal marine shelf deposits. Rapid deposition often results in slightly lower amounts of bioturbation and deposits displaying excess pore fluid pressures. Graded bedding zones are sometimes present in the prodelta deposits, but are rarely found in normal marine shelf deposits. X-ray radiography of the cores reveals that many of the parallel laminations are defined either by inclusions of diagenetic origin or extremely slight differences in textural characteristics. Because of the high rates of deposition normally associated with prodelta deposits, intense bioturbation is usually confined only to the lowermost parts of the deposit, where it grades downward into norma open-marine shelf environments, that often show intense bioturbation.

For a given length of time, prodelta deposits are thicker (because of high sedimentation) than an equivalent section of normal marine shelf deposits. Rapid deposition often results in slightly lower amounts of bioturbation and deposits displaying excess pore fluid pressures. Graded bedding zones are sometimes present in the prodelta deposits, but are rarely found in normal marine shelf deposits. X-ray radiography of the cores reveals that many of the parallel laminations are defined either by inclusions of diagenetic origin or extremely slight differences in textural characteristics. Because of the high rates of deposition normally associated with prodelta deposits, intense bioturbation is usually confined only to the lowermost parts of the deposit, where it grades downward into norma open-marine shelf environments, that often show intense bioturbation.