Meandering streams.ppt

Meandering streams

1. SEDIMENTARY ENVIRONMENTS
•A sedimentary environment is an area of the earth's surface
where sediment is deposited. It can be distinguished from
other areas on the basis of its physical, chemical, and
biological characteristics.

2. TYPES OF SEDIMENTARY ENVIRONMENTS
•There are three main types of sedimentary environments:
1.Continental
2.Marine
3.Transitional

3. CONTINENTAL ENVIRONMENTS
•Continental environments are those environments which
are present on the continents and include:
1.Fluvial (Rivers)
2.Lacustrine (Lakes)
3.Paludal (Swamps)
4.Glacial
5.Desert

4. 1. Meandering streams
•Have a single channel with a sinuous pattern and a broad
floodplain.
•The most common pattern on floodplains.
•Meandering channels form where streams are flowing over a
relatively flat landscape.
•Associated facies are point bar, oxbow lakes, levees, crevasse
splay and floodplain.
Meandering river

5. Fluvial (Rivers)
•The river channel includes two main types:
•Meandering stream.
•Braided stream.
Meandering stream
Braided stream

6. Point bar
•It develops where stream flow is locally reduced because
of friction and reduced water depth.
•The eroded materials from the cut banks at the outside
bend; will be deposited as point bars that lie at inside
bend.
•Point bar composed of cross-bedded sand.

7. Oxbow lake
•As the channel migrates, parts of it may become abandoned and
left behind as oxbow lakes which made up of fine-grained sand to
silt (lake sediments).
Point bar
deposits
Cut bank
erosion
Meander
loop

8. Levees
•They are ridges found
along the sides of the
stream channel and
composed of silt and fine
sand.

9. Crevasse splay
•The crevasse splay will be formed when an overloaded
stream breaks a natural or artificial levee and deposits
sediments on a flood plain. It made up of sands, fining
upwards to a mud.
Crevasse splay
Crevasse splay

10. Floodplain
•Itis a plain that subjected to periodic floodingand
composed of fine-grained materials which are very fertile
soil.
Flood plain

11. Meandering river fining upward sequence

12. Sand dunes
•They are the most common aeolian landforms; their
geometry and resulting sedimentary structures depend
primarily on sediment supply and prevailing wind
direction.
•Eolian sand sheetsdevelop when sediment supply is
limited and are characterized by planar stratification.
•Vegetation can contribute to dune formation under such
circumstances.

13. The Continental Shelf (Continental Platform)
–The continental shelves are commonly covered by terrigenous sediments, in
addition to non-clastic sediments such as carbonates, phosphates.
–Terrigenous sediments usually become increasingly fine with distance from the
shoreline whereas, sand is limited to shallow, wave-agitated waters, while silt
and clays are deposited in quieter, deep water far offshore.
–The carbonates of the continental shelf (carbonate factory) are rich in algae,
larger foraminfera etc..
–These shelf sediments accumulate at an average rate of 30cm/1000 years, this
rate is much faster than that for deep-sea pelagic sediments.

14. The continental slope and continental rise
–They are located seaward of the continental shelf and may reach a depth of
4000 m.
–The continental slope is the steep (5-25
o
) part at the edge of the continent.
–The continental slope passes seaward into the continental rise, which has a
more gradual slope.
–The continental rise is the site of deposition of thick accumulations of
sediment, much of which is in submarine fans, deposited by turbidity currents.
–Submarine fans are essentially turbidites dumps most typically at the mouths of
the submarine canyons that feed them.

15. The abyssal plain
–It is flat or very gently sloping areas of the deep ocean basin floor.
–It covered by very fine-grained sediment, consisting primarily of clays and the
shells of microscopic organisms (such as small foraminifera, radiolarians, and
diatoms).

16. The abyssal plain
–The carbonate rocks of the deep marine water (above the CCD) are formed
mainly by the accumulation of tests such as planktonic foraminifera.
–The Carbonate Compensation Depth (CCD) is the depth below which no
carbonate sediments can accumulate.
–Below CCD, the deep marine environments are cold, with high PCo
2, due to
the decay of the few organisms that may be buried there.
–Therefore, this environment is not suitable for the direct precipitation of
carbonates from seawater. As a matter of fact, below the depth of about 5000
m, no carbonate sediments can accumulate.

17. TRANSITIONAL ENVIRONMENTS
–Transitional environments are those environments at or near the transition
between the land and sea.
–These environments include delta, tidal flats, beach, barrier islands and lagoons
Delta
Tidal Flat
Lagoon
Barrier Island
Beach

18. Delta
–A delta forms where a river transporting significant quantities of sediment
enters a receiving basin such as ocean or other body of water.
–Name from the Greek letter ‘∆’, from the shape of the Nile Delta.

19. Delta
–Delta is subdivided into the delta plain, delta front and prodelta:
1.The delta plain
comprises a flat area dominated by alluvial deposition. The resulting
vertical deposits include alluvial channel fills, overbank muds and the
fine-grained sediment infill of lakes.
2.The delta front
is located at the distal edge of the delta plain; sediments are deposited in
mouth bars as the rivers emerge into the sea.
3.The prodelta
is most distal part of the delta whereas the finest grained sediments are
deposited.

20. Delta
–Controls on delta environments and facies.