Changes

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In the absence of high tidal range and extremely strong marine energy, the distributary channel pattern is often one of seaward bifurcation ([[:file:M31F16.jpg|Figure 1]]). Because of this bifurcating channel pattern, the distributary-mouth bars at each of the river mouths often merge and form a near-continuous sand strip around the entire periphery of the delta. Shallow offshore slopes and low wave and tide action favor this type of distributary pattern, and turbulent diffusion within the water mass becomes restricted to the horizontal. Bottom friction plays a major role in causing effluent deceleration and expansion. Initially a broad, arcuate radial bar will form at the mouth. However, as deposition on the bar continues, natural subaqueous levees will develop beneath the lateral boundaries of the expanding effluent, where velocity gradients are generally steepest. Development of subaqueous levees tends to inhibit further increases in effluent expansion, so that with continuing bar accretion continuity can no longer be maintained simply by increasing effluent width. As the central part of the bar grows upward, channelization develops along the threads of maximum turbulence, which tend to follow the subaqueous levee. This process results in formation of a bifurcating channel, which has a triangular middle ground shoal separating diverging channel arms. This type of channel pattern is well displayed in the high-altitude photograph shown as [[:file:M31F16.jpg|Figure 1]].

In the absence of high tidal range and extremely strong marine energy, the distributary channel pattern is often one of seaward [[bifurcation]] ([[:file:M31F16.jpg|Figure 1]]). Because of this bifurcating channel pattern, the distributary-mouth bars at each of the river mouths often merge and form a near-continuous sand strip around the entire periphery of the delta. Shallow offshore slopes and low wave and tide action favor this type of distributary pattern, and turbulent diffusion within the water mass becomes restricted to the horizontal. Bottom friction plays a major role in causing effluent deceleration and expansion. Initially a broad, arcuate radial bar will form at the mouth. However, as deposition on the bar continues, natural subaqueous levees will develop beneath the lateral boundaries of the expanding effluent, where velocity gradients are generally steepest. Development of subaqueous levees tends to inhibit further increases in effluent expansion, so that with continuing bar accretion continuity can no longer be maintained simply by increasing effluent width. As the central part of the bar grows upward, channelization develops along the threads of maximum turbulence, which tend to follow the subaqueous levee. This process results in formation of a bifurcating channel, which has a triangular middle ground shoal separating diverging channel arms. This type of channel pattern is well displayed in the high-altitude photograph shown as [[:file:M31F16.jpg|Figure 1]].

[[file:M31F18.jpg|thumb|500px|{{figure number|3}}Cores of distributary-mouth bar sequence. Diameter of cores is 13 cm (5 in.). A. Smooth, gray, partially laminated clays of the prodelta deposits. B. Steeply dipping sand-silt laminations characteristic of block slumping often found in the prodelta environment. C. Small lenticular laminations and graded parallel silt laminations common near the top of the prodelta environment. D. Alternating sand, silt, and silty clay laminations in the lower part of the distal bar environment. E. Well-developed parallel silt and sand laminations showing graded bedding and small-scale ripple laminations common in the distal bar deposits. F. Lenticular sand laminations representing "starved current ripples" and small-scale ripple laminations common in the transition zone between the distal bar and distributary-mouth bar. G. Slump structure common near the shear plane in a distributary-mouth bar sequence that has mass-moved seaward. H. Cross laminations common in the distributary-mouth bar sands. The dark material is transported organic debris. I. Large-scale cross laminations common near the top part of the distributary-mouth bar deposits. The dark material is transported organic debris. J. Alternating silty sand and clay layers common to the small overbank splays that cap the distributary-mouth bar deposits.<ref name=Colemanetal_1981 />]]

[[file:M31F18.jpg|thumb|500px|{{figure number|3}}Cores of distributary-mouth bar sequence. Diameter of cores is 13 cm (5 in.). A. Smooth, gray, partially laminated clays of the prodelta deposits. B. Steeply dipping sand-silt laminations characteristic of block slumping often found in the prodelta environment. C. Small lenticular laminations and graded parallel silt laminations common near the top of the prodelta environment. D. Alternating sand, silt, and silty clay laminations in the lower part of the distal bar environment. E. Well-developed parallel silt and sand laminations showing graded bedding and small-scale ripple laminations common in the distal bar deposits. F. Lenticular sand laminations representing "starved current ripples" and small-scale ripple laminations common in the transition zone between the distal bar and distributary-mouth bar. G. Slump structure common near the shear plane in a distributary-mouth bar sequence that has mass-moved seaward. H. Cross laminations common in the distributary-mouth bar sands. The dark material is transported organic debris. I. Large-scale cross laminations common near the top part of the distributary-mouth bar deposits. The dark material is transported organic debris. J. Alternating silty sand and clay layers common to the small overbank splays that cap the distributary-mouth bar deposits.<ref name=Colemanetal_1981 />]]