River Systems
Types (Fig. 9.7, p. 275)
a. Straight - uncommon
b. Anastomizing special type of meandering river
c. Meandering
d. Braided
Continental Fluvial: Braided Rivers Facies (Fig. 9.9, p.
277)
= lower (shorter) sinuosity (channel length to valley length)
a. distal alluvial fans, glacial outwash plains, mountainous
river reaches
b. abundant sediments
c. rapid large sporadic variations in water discharge
d. little vegetation
e. most common in pre-Devonian (before well-developed plants)
Continental Fluvial: Meandering River Facies (Fig. 9.13,
p. 280)
= confined to single channel, higher sinuosity
a. often downstream of braided streams
b. less sediment load, less variation in discharge
Hydrology (Fig. 9.14, p. 281)
a. low flow conditions
maximum velocity at concave outer parts of meander
b. high flow conditions
maximum velocity at convex inner parts of meander
c. lateral shifting sets up helical flow
erodes outer meander and deposits at inner edge of meander
Morphology and Composition (Fig. 9.13, p. 280)
a. channel - imbricated gravel lag deposits
b. point bars - upward fining, plane lamination into dunes into
ripples
c. natural levees - outer meander wall tops
d. floodbasin and Oxbow-lakes - thin muds in shallow lakes behind
levee
e. crevasse-splay - graded Bouma-like depsoits
Vertical Successions (Fig. 9.15, p. 283)
a. generally strong upward fining trends from lateral facies shifts
b. hydrologic shifts can also cause reversed grading
c. coarse basal channel lag gravels
d. parallel -laminated to trough crossbedding (dunes) sands
e. ripple cross-laminated sands
f. alternating sand and muds overbank and levee deposits
g. produce shoe-string sand bodies (Fig. 10.14, p. 318)
Continental: Eolian Facies
Environments
a. occur primarily in arid 10 - 30o latitude belts
b. dune fields = arid desert regions carpeted by windblown sands
sand seas (Ergs) = areas > 125 km2
c. coastal areas = linear dune systems tracting beach migration
d. suspended eolian sediments = < 0.05 mm diameter
e. saltation and traction = > 0.05 mm diameter
Vertical Successions (Fig. 9.21, p. 289) - only crossbedding
is preserved
a. first-order surfaces - cut other structures, migration of
large draas, water table
b. second-order surfaces - at angles between first-order surfaces,
lee or slip faces
c. third-order surfaces - bound bundles of laminae, wind fluctuation
erosion/depo
Compositions
a. well rounded
b. well sorted
c. thick crossbedding sets
d. high-angle crossbedding (up to 32o)
Ancient Examples
a. Cenozoic of the Colorado Plateau
Navajo, Entrada and the dropping sealevel source
b. often difficult to distinguish from subaqueous sands