Marginal Marine Environments
• A mix of continental and marine processes
• Importance
– Economics - oil and gas
– Paleontology
• Types - deltas, beachs, barrier islands, lagoons, tidal flats
Marginal Marine Environments
• Very diverse and very dynamic
• Major Factors -
– Tectonic Setting
– Climate
– Rates and type of S/L change
Deltaic Environments
• Wedge shaped deposit on the margin of a body of water
• Alluvial - river or fan delta
• Non-alluvial - volcanic
Deltaic Environments
• Deposition => distributary channels
• Delta Growth => channel migration and progradation
• Best developed in passive margin settings
Deltaic Environments
• Parts = 1) Prodelta, 2) Delta front, 3) Delta plain
• Progradation/relative regression
Deltaic Environments
• Major types of river deltas
– Fluvial dominated
– Wave dominated
– Tidal dominated
Deltaic Environments
• Fluvial dominated deltas
• Velocity of flow decreases as stream enters standing body of water.
• Density differences can control the dispersal of sediments
– Homopycnal, hyperpycnal, hypopycnal
– Bouancy
• Mississippi = birds-foot delta
Deltaic Environments
• Tidal-dominated deltas
• Tidal currents stronger than river input
• Linear tidal ridges
• Ganges
Deltaic Environments
• Wave dominated deltas
• Wave processes stronger than river input
• Seasonal - storms
• Barrier beach ridges
• Sao Francisco
Deltaic Sedimentation
• Upper Delta Plain
– Fluvial features
– wetlands
• Lower Delta Plain
– Tidal influence
– Saltwater marsh
– Distributary channels - bay fill
• Subaqueous Delta Plain
- Subtidal
- Sheet sands
Deltaic Sedimentation
• Subaqueous Delta Processes
• Gravity flow
• Soft sediment deformation
• Overpressure tectonics
– Growth faults
Deltaic Deposits
• Recoginition
• Geometry (Seismic Reflection)
– Delta to wedge-shaped
• Lateral facies relationships
– W/I delta part
– Proximal to distal trends
Deltaic Deposits
• vertical facies relationships
– Coarsening upward
– Cyclic facies (autocyclic)
• Sedimentary structures and fossil
– Soft sediment deformation
– Proximal to distal trendsDeltaic Deposits
• Ancient Examples
• Carboniferous of North America and Europe
• Wilcox and Frio - GOM