Eolian deposits
•
•
•
•
•
Coarse grained, cross bedded dunes (high angle, 20-30° dip, well sorted, rounded, frosted quartz)
Desert pavement (deflation lag)
Provide important climate information (wind strength, direction, aridity)
Excellent reservoirs for groundwater, oil
Fine grained Loess
High angle, Tabular-Planar Cross-Stratification
Wedge-planar and
Tabular-planar Cross-Bedding
Terrestrial fossils in Eolian sequences
•
•
•
•
•
Check interdune sequences
Trackways
Vertebrates
Microfossils in ephemeral lakes
Root casts, insect burrows.
Eolian facies models
•
•
•
•
•
•
Lithologies follow no orderly sequence (random)
Associated with aluvial fans, and playa lake deposits.
sand sheets
ephemeral stream deposits
dune deposits
Mudcracked shales may be present
Example: Navajo SS part of an ancient, massive
desert
Correlative Units
• Nugget SS in Wyoming
• Aztec SS California and Nevada
• 100’s of meters thick in places
Coastal (Marginal Marine) Environments
•
•
•
•
Deltas
Tidal flats
Barrier complexes
Lagoons and marshes
The
Sedimentary Cycle
The delta at a glance
•
•
•
Name coined by Greek Historian Herodotus (c. 490 B.C.)
Fertile environments
Reservoirs for oil, gas, and coal deposits
Deltaic depositional environments
• Delta plain
• Floodplains
• Swamps and marshes
• beach complex
• Delta front
• Platform
• Mouth bars
• Prodelta
• Marine transition
(Hemipelagic)
Deltaic
Depositional
Environments
Delta or River mouth Bar Genesis
•
•
Coarse material deposited as river plume disperses
Position depends on zone of mixing between plume and sea water
Time-transgressive deposition
Depositional geometry is analogous to the point bar sequence but with spatial scales of 10-1000’s of km rather than
meters!
Delta classification of Galloway
 River dominated
- Fluvial currents
 Tide dominated
- Tidal current
 Wave dominated
- Longshore or coastal currents
 Many deltas have transitional characteristics
Examples of modern delta geometry
River dominated deltas
• e.g. Mississippi
•
•
•
•
Major R. discharge
Abundant sediment supply
Bird’s foot delta
Switching of major distributary during progradation
Progradation
of the
Bird’s foot delta:
a 3D process
Wave (Current) Dominated Delta
•
•
•
•
•
e.g. Sao Franciso, Brazil; Rhone, France
Waves, long shore, and coastal currents redistribute alluvial sediments
Arcuate (arc shaped)
Thick sheet sands
Lack mouth bars
•
•
•
•
•
e.g. Ganges-Brahmaputra or Mekong River deltas
Redistribution of alluvial sediment by bidirectional tides
Tidal flats and channels
Tidal bars and islands parallel to tidal current flow
Lack mouth bars
Tide-dominated delta
Deltaic facies model
•
•
•
•
•
•
Coarsening upward sequence
Prodelta silt/clay
Distributary bar sands
Overbank silt/clay and coal
Abundant cross-bedding in sands
Sequence may be interupted by crevasse splay deposits
Example: Deltas of the Appalachians
•
•
•
•
•
Pennsylvanian Age
Mapped in OH, PA, WV, and KY
Sedimentation from ancient appalachians toward inland seas of OH, PA
Variety of deltaic environs with coarsening upward sequences, soft deformation features
Abundant coal deposits
Allegaheny Formation Cross-section
•
•
•
Coarsening upward sequences associated with deltaic progradation
Finning upward sequences within individual distributary channels
Transition from terrestrial to marine deposits on spatial scale of 10’s of km
Delta classification of Galloway
• River dominated
• Tide (Current) dominated
• Wave dominated
• Many deltas have transitional characteristics
Alluvial Fan or Delta?
Similarities:
Differences: