Continental Deposits
• General Characteristics
– Color, geometry, paleontology, lithology and associations
• Major Types
– Fluvial/alluvial, eolian, lacustrine, glacial
• Importance
– Economics
– Paleontology
Fluvial Environments
• Most important agent of transport
• Characteristics
– Gradient, discharge, sediment supply and type, setting (climate and
tectonics)
• Types
– Alluvial fans, braided streams, meandering streams
– A continuum
Fluvial Environments
• Alluvial Fans
• Modern Fans - fans of sediment that originate in mountain ranges that
spread out across valleys
• Abrupt gradient change - fault block mountains
• Arid to semiarid regions
• Precip. = an event
Fluvial Environments
• Alluvial Fans - characteristics of modern fans
• Debris Flow versus Fluvial (braided) dominated
• Fanhead = course grained debris flows
• Midfan = debris flow, channel, and sheetflood
– Sieve deposits
• Distal fan = sheetflood
• Proximal to distal fining
Fluvial Facies
• Alluvial Fans - ancient deposits
• Lobate and wedge-shaped geometries
• Sparse fossils
• Radial paleocurrents
• Distal fining
• Proximal termination
• Examples:
– Penn. - Perm - Fountain Formation
– Precambrian - Van Horn
Fluvial Environments
• Streams - Braided - environmental characteristics
• Many low-sinuosity channels separated by bars & islands
• Why do they form?
• Bed load streams
Fluvial Environments
• Streams - Braided - environmental characteristics
• Gravel-rich to sand dominated downstream
• Associated with humid alluvial fans
• Bar forms
– Longitudinal, transverse, lateral
• Gravel and sand
Fluvial Facies
• Streams - Braided - ancient deposits
• Highly variable
• Lateral and vertical accretion
• Proximal = cgl., distal = sheetflood sandstones
• Fining upward sections
Fluvial Facies
• Streams - Braided - ancient deposits
• Geometries
• Sheet or wedge shape sheet cgls. - sandstone
• Examples:
– Westwater Canyon Mbr. - Morrison
– Ivishak - Prudoe Bay
Fluvial Environments
• Streams - meandering streams - environments
• Sinuous single channels
• Low gradients - fine sediment load (mixed and suspended)
• Moderate to high discharge
• Periods of increased flow = erosion and deposition
• End in delta systems
Fluvial Environments
• Outward building point bar, cutbank, natural levee, cut-off meanders
• Why would seasonal high flow result in the greatest amount of erosion
and deposition?
• Straight-line helical/transverse spiral flow
• Lateral and downstream migration of meanders
Fluvial Environments
• 4 major depositional settings
• Channel => channel-lag, imbricated gravel, mud clasts, bone and plant
fragments
• Point bar - fining upward, large to small-scale x-beds upward
• Natural-levee - over cutbank, ripple laminated sands and mud
• Floodbasin - suspended sediments, crevasse splay
• Lateral and vertical accretion
Fluvial Facies
• Red; plant and vertebrate fossils; downstream fining
• Vertical Succession of Facies
• Gravel lag
• Point bar sandstone - fining upward & x-bedded
• Floodbasin - siltstones and shales - pedogenic development
• Cyclic repitition of facies - autocyclic
Fluvial Facies
• Geometries
• Linear sand bodies - shoestring sands - within sh & sltstone
• Ancient Examples
• Old Red Sandstone (Devonian)
• Tertiary of the Colorado Plateau
• Parts of the Morrison
• Mesaverde Group