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TRANSISI DAN SHALLOW

MARINE

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Barrier Island and Near Shore Environments

Barrier Island: long, narrow sand bodies

Barrier Island: formed by wave processes

Marine part of Barrier and beach environment can be split intoseveral zones based on main process:

1.Backshore: Above mean high tide, low angle land dippinglaminae; eolian dune at top.

2. Foreshore: Between High and low tide. Swash zone, wedgeshape sets of low angle seaward dipping laminae. Minor ripple,dune lamination. Heavy mineral concentration.

3. Shoreface: Between low water mark and fair weather wavebase. Low angle seaward dipping lamination and/or dune crossbedding. Ripple lamination more common towards base ofsequence. Abundant bioturbation.

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Upper offshore: below fair weather base, above

stormweather base. Interbedded thin sandstones

and claystones, hummocky and swaley crossstratification. Intense bioturbation.

Barrier islands formed in areas with high tidalranges. Cut by tidal inlets. Fining upward channel-

fill sequences with dune trough and planar cross

bedding, herringbone cross-stratification.

Tidal inlets are associated with ebb and flood tidaldeltas.

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Deltaic Environments

Delta are distinct extension from the shore line where rivers

enter marine or fresh-water depositional basins and supplysediments faster than the basin process can redistributethem.

The primary character of delta usually results from thestruggle between fluvial and basinal processes.

ALLUVIAL sediments and the Sediment basin Types of sediments supplied to marine basins have large

influence on the sediments that accumulated.

- Amaunt of sediment supplied vs reworking ability of basin.

- grains sizes of supplied sediments

- fluctutions in alluvialdischarge -timing of fluctuations in fluvial discharge vs fluctuations in

basinal energy regimes.

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DELTA MODELS

1. High constructive delta dominated by fluvial process:

A. Lobate

B. Birdsfoot

2. Highly destructive deltas dominated by basinalprocess:

A. Wave Dominated

B. Tide dominated

Fluvial Dominated Deltas:

Unidirectional flow.

Highly sinous patern.

Deltas with sporadic discharge and high bedload candevelop braided patern.

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Facies and sequences resembles alluvial deposits,

erosive basal and basal lag. Multy strory sequences.

Overal fining upward of the channel sequences. The inter distributary area are enclosed, shallow

water quiet or stagnate waters. Dominated

sequence and facies are flood generated events:

1. overbank flooding

2.Crevase splay

3. minor mouth bar/ crevase channel couplets:

permanent crevase channel and small scale mouthbar.

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TIDE dominateed Deltas:

Region with medium to high tidal ranges

Distributary channel , low sinousities and funnel shape

with high width to depth ratios. Interdistributary composed of lagoons, tidal creek,

intertidal flats.

WAVE dominated Deltas

Wave processes redistribute sediment supplied to deltafront.

Regular beach shore line.

Distributary mouth bars can not develop.

Bioturbated, fossiliferous muds pass upward in toalternating mud, silt, and sand beds, scouring, grading,cross lamination.

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Recognition af ancient delta Types

Vertical facies sequences are important in

recognizing regime defined deltas Lateral, regional facies relationships allow

reconstruction of proximal/ distal and axial/lateral

changes.

Isopach maps can identify the concentrations of

sands and hopefully provide insight to delta channel

locations.

Abandonment markr horizons can reflect sanddistributions and indirectly indicate the delta type

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Growth faults in alluvially dominated deltas

Growth faults: Result of compaction disequilibrium

Found in deltas with prolific net sediment accumu-lation and high shale/ sand rartios.

Overpressured clays are abnormally high in porosityand therefore relatively plastic, compared to adjacent

sediments. Generation of mud diapir, which servw as weakspots

that allow sediments failure,instigating spoon-shapedgrowth faults with maximum throws in the center.

Rollover anticlines form along the contact with

upthrown sides of this faults resulting in structurally-high contour closers.