STRATIGRAPHY AND SEDIMENTATION (DELTA) Flashcards
DISCRETE SHORELINE PROTUBERANCE (EXTENSION BEYOND) formed at a point where RIVER ENTERS OCEAN or OTHER BODY OF WATER. Formed from sediments brought down by river builds out as a body into the lake or sea. (Needs visible building of sediments)
Delta
A RIVER MOUTH where there is a mixture of FRESH WATER and SEAWATER with the accumulation of the sediment WITHIN THE CONFINES of the ESTUARY but WITHOUT ANY BUILD UP INTO THE SEA
Estuary
Generally what kind of deposits is tranported by a delta to coastal zones
Siliciclastics
How are deltas formed?
1) When there’s A LARGE DRAINAGE SYSTEMS with HEAVY SEDIMENT LOAD
2) Common in PASSIVE CONTINENTAL AREAS
3) related to SEA LEVEL RISE
A process which aid in DELTA FORMATION by which tiny particles in suspension like silt and clay COAGULATE w/ the salt in water by CHEMICAL REACTION and becomes heavy enough to sink and be deposited. (Nangyyari kasi nga nag mimix ang heavy sediment loaded fresh water with sea water)
Flocculation
How does depostion happen in a delta?
River quickly loses velocity when it meets a standing water thus, coarse particles Drop out then susunod na ung fine suspened load na medyo matataboy pa sa malayo before it settles thru Flocculation
When the river becomes chocked with sediments due the rising of topset beds, triver branches into distributaries which will form the fan shaped deltas
The transitional deltaic subenvironment between the Fluvial/Alluvial Environment and the shallow marine environments where coarse sediments are usually deposited
Delta Top or Plain
Sheltered areas along the edges of Delta Top of shallow water that may be protected from strong waves and currents
Interdistributary Bays
Other features in the Delta Top
1)Subaerial Overbank Areas
2) Crevasse Splay
The Subenvironment directly forward of the channel and is the site of deposition of bedload material
Delta Front
IN the Delta front, the bedload material is deposited first in SHALLOW WATER
Subaqueous Mouth Bar
The area that is steeply dipping or inclined awat from the delta top with slope variying from 1 to 2 deg or 30deg in coarse grained seds
Delta Slope
The part of the delta where deposition of finest suspension sediments are deposited
Prodelta
deposition results in the sediment body building out into the lake or sea (Pag nagdeposit tapos may naform na sed body or landform)
PROgradation
Parts of delta from Top to Bottom
Delta Top
Subaq Mouth Bar
Delta Front
ProDelta
A SHALLOWING UP pattern of a delta implies that
Strata that is deposted in the shallower water is younger than the ones it overly
General Pattern of Deltaic Deposit which is distinctive
COARSENING UP PATTERN, SHALLOWING UP
What could be more diagnostic of a delta deposit
If the TOPSET have river channel, signs of plant growth and soil formation and other exclusively subaerial processes
what can be the closest deposit type to delta which also shows coarsening up deposits
COASTLINE (Marine supplied sediments). Deciding factor will be an evidence of river or alluvial fan supplying sediments from land
Differentiate a finegrained delta from coarse grained delta
Fine graine would have smaller mouthbar and extensive delta front anf prodelta
Coarse grained “FAN DELTA” would havemore extensive mouthbar and small muddy prodelta
Differentiate Shallow Water Delta and Deep Water Deltas
Shallow water deltas have more extensive mouth bar and shallow widespread delta front due to shallow water redistribution
Deep water deltas have much restricted mouth bar and a slope deposits and turbidites in deeper water
Arc or Fan shaped
Arcuate
Example of Fan Shaped Delta
Nile Delta in Egypt
Resembling Spread Claws of a Bird’s Foot
also known as Bird’s foort delta
Digitate
Example of Bird’s Foot Delta
Mississippi
Delta where river drops sediments onto straight shorelines with strong waves that hit head-on
Cuspate
Example of straight deltas
Tiber and Ebro Delta Spain
the discharge of river water and sediment into a lake or ocean
Jet
Delta forms because sed input exceed capability of waes, tidal curent, and long shore currents to redistribute the sediments
Fluvial Capability > Redistribution of Wave, Tides an Current
River Dominated Delta
Delta in which wave erosion primarily controls where and how much sediments remain in the delta after being dropped by the river
Wave Action>Fluvial Action
Wave Dominated Delta
Tidal currents are stronger than river outflows the currents redistribute sediments forming SAND FILLED, FUNNEL SHAPED, DISTRIBUTARIES
Tide Dominated Delta
Formed when rivers deposits LARGE COARSE SEDIMENTS AND are usually confined to rivers emptying into FRESHWATER LAKES in mountainous rivers
Gilbert Type Data
Part of Gilbert type delta which are thin horizontal laters of differing sizes, COARSER SAND AND GRAVEL as well as finer material from the suspende load tht are deposited on the surface of the delta and are said to be BRAIDED RIVERS and WAVE DEPOSIT
Topset
Closer to the mouth yet still underwater and are beds of sand and ravel that slope steeply down 5-30 degrees and make up the main body of the delta
Foreset
Nearly horizontal or flat layers of fine clay and silt that form underwater farthest from the mouth of the river and active delta front
Bottomset
World’s Largest Lacustrine Delta
St.Clair Delta
formed when a river does not empty into the ocean but instead forms an estuary and the load is deposited along the sides of the estuary
Estuary Delta
Delta wherein Stream deposition, Tidal forces and Wave action are about equal and an arcuate delta fors
Hybrid Delta
Delta by which sediments are not exclusively terrigenous clastic but of volcaniclastic material
Non-Alluvial delta
Usual lithology in Deltas
Conglo, Sandstones and Mudstones
IN a delta what part can be compositionally mature?
Delta Front
In terms of textural maturity which part is most mature?
Delta Front
IN terms of fossil association how can one distinguish a deltaic deposit?
Felta Top terrestrial plants and animarls , Marine fauna delta front
Facies associated with deltaic deoposit
Overlain by Fluvial Facies
Underlain by Shallow Marine
Overall Progradational Pattern
