Sedimentary Environments
SEDIMENTARY ENVIRONMENTS
REGIONS OF SEDIMENT ACCUMULATION:
A. Continental/Terrigenous/Non-Marine
B. Transitional (shoreline)
C. Marine
CONTINENTAL/TERRIGENOUS/NON-MARINE ENVIRONMENTS
a. Alluvial Fans - cone-shaped deposits of coarse stream sediments, sheet flood deposits, and debris flows that form where a narrow canyon stream suddenly disgorges into a flat valley.
TECTONIC SETTING: rifting continental grabens, foreland basins, collisional overthrust mountain belts, or other highlands undergoing rapid uplift; associated with meandering fluvial valleys and playa lakes
GEOMETRY: wedge-shaped and limited in lateral extent from only a few tens of meters to kilometers
TYPICAL SEQUENCE/ SEDIMENTOLOGY: coarsening upward sequence; fining upward sequence during decay of the fan
FOSSILS: rare because of high oxidation, high-energy flood waters and coarse cgl
b. Fluvial/River systems
Braided fluvial system
TECTONIC SETTING: upper reaches of alluvial plains; assoc. with downdropping basins because they require an upland to provide the coarse material and high stream gradient
GEOMETRY: elongate, fairly straight, lenticular or sheetlike sand bodies grade laterally into finer deposits of an alluvial plain
TYPICAL SEQUENCE/SEDIMENTOLOGY: fining upward sequence; occasional cross-beds; gravel, sand, very little silt and mud
FOSSILS: root casts and burrows
Meandering fluvial system
TECTONIC SETTING: low parts of the craton; preserved in downdropping basins or in aggrading coastal sequences; grade downstream into the deltaic system and upstream into a braided system
GEOMETRY: long, ribbon-like bodies of sand (“shoestring sands”) within a thick sequence of shales
TYPICAL SEQUENCE/SEDIMENTOLOGY: fining upward sequence; cross-beds; more fine- grained components than braided rivers
FOSSILS: organic matter and fossil wood, land vertebrates and invertebrates, freshwater molluscs
c. Lacustrine (lakes)
A lake is
REGIONS OF SEDIMENT ACCUMULATION:
A. Continental/Terrigenous/Non-Marine
B. Transitional (shoreline)
C. Marine
CONTINENTAL/TERRIGENOUS/NON-MARINE ENVIRONMENTS
a. Alluvial Fans - cone-shaped deposits of coarse stream sediments, sheet flood deposits, and debris flows that form where a narrow canyon stream suddenly disgorges into a flat valley.
TECTONIC SETTING: rifting continental grabens, foreland basins, collisional overthrust mountain belts, or other highlands undergoing rapid uplift; associated with meandering fluvial valleys and playa lakes
GEOMETRY: wedge-shaped and limited in lateral extent from only a few tens of meters to kilometers
TYPICAL SEQUENCE/ SEDIMENTOLOGY: coarsening upward sequence; fining upward sequence during decay of the fan
FOSSILS: rare because of high oxidation, high-energy flood waters and coarse cgl
b. Fluvial/River systems
Braided fluvial system
TECTONIC SETTING: upper reaches of alluvial plains; assoc. with downdropping basins because they require an upland to provide the coarse material and high stream gradient
GEOMETRY: elongate, fairly straight, lenticular or sheetlike sand bodies grade laterally into finer deposits of an alluvial plain
TYPICAL SEQUENCE/SEDIMENTOLOGY: fining upward sequence; occasional cross-beds; gravel, sand, very little silt and mud
FOSSILS: root casts and burrows
Meandering fluvial system
TECTONIC SETTING: low parts of the craton; preserved in downdropping basins or in aggrading coastal sequences; grade downstream into the deltaic system and upstream into a braided system
GEOMETRY: long, ribbon-like bodies of sand (“shoestring sands”) within a thick sequence of shales
TYPICAL SEQUENCE/SEDIMENTOLOGY: fining upward sequence; cross-beds; more fine- grained components than braided rivers
FOSSILS: organic matter and fossil wood, land vertebrates and invertebrates, freshwater molluscs
c. Lacustrine (lakes)
A lake is