Clastic Coasts and Estuaries

Coasts

Erosional-Depositional systems with morphologies being very variable from cliffs of bedrock to gravelly or sandy beaches to lower energy lagoons or tidal flats.

Erosional coastlines

Also known as reflective coasts, have relatively steep gradients where much of energy wave is reflected back into the sea from the shoreline.

Depositional coastlines

Also known as dissipative coasts, have relatively gentle gradient and much of wave energy is dissipated in the shallow water and, with supply of sediment, can be sites of accumulation.

1. Rock types exposed along the shore

2. Supply of sediment

3. Intensity of waves

4. Tidal range

5. Nature of coastline currents

6. Climate

7. Sea level changes

8. Stability of sinking or rising coasts

Factors affecting Shoreline Features (8)

Erosional coastal landforms

Sea cliffs, wave-cut notches, caves, sea stacks, sea arches are ________ coastal landforms.

Depositional coastal landforms

Beaches, barrier, spit, lagoon, tombolo are _________ coastal landforms.

Beach

Coastal landforms where wave energy is strong, with sand or gravelly material may be reworked on the foreshore forming low-angle stratification of well-sorted and well-rounded sediments.

Berm

A ridge of sand that separates the foreshore from the beach.

Dune ridge

Coastal dunes that form lying parallel to the shoreline and may build up to form dune complexes.

Coastal plains

Low-lying areas adjacent to the sea.

Strand plains

Sandy coastlines where an extensive area of beach deposits lie directly adjacent to coastal plains.

Barrier

Sediments that separate the open sea from a lagoon that lies between the barrier and the coastal plain.B

Beach spit

Barriers composed of sand and/or gravel and largely built by wave action.

Welded barrier

Barriers partially attached to the land.

Barrier island

Barriers that are wholly attached to the land and completely encloses a lagoon.

1. Wave energy is high and tidal range is small.

2. Abundant supply of sand or gravel to match or exceed any losses from erosion.

Formation Conditions for Barrier Systems (2)

Lagoons

Coastal bodies of water that have very limited connection to the open ocean, only through a channel to the sea or via seepage through a barrier.

Washover deposits

Coarser sediments that may enter when storms wash sediments over the barrier.

1. runoff or rainfall

2. estuary

3. shallow

4. fine, clastic, suspended

5. Mangroves

6. open ocean

   • low, brackish

   • hypersaline

7. mudstone, wave-rippled sand

Characteristics of Lagoons

1. Freshwater lagoons are supplied by ______ or ______.

2. Part of an _______ system if fed by a river.

3. Typically, very _______ (in terms of depth)

4. _____-grained ______ sediments are supplied as ______ load in seawater entering the barrier or from adjacent coastal plains.

5. _________ colonize shallow fringes and act as sites for sediment accumulation.

6. Limited connection to the ________ with:

   • ____ salinity, _______ water in areas of high rainfall or runoff.

   • ________ water in arid settings which leads to precipitation of evaporate minerals.

7. Have successions typically ________, organic-rich and thin ________ beds.

1. marine

2. lagoonal, marine

Evidence Used to Distinguish Lagoons from Lakes:

1. Fossil assemblage of ______ influence.

2. Facies association with ______ deposits occur above or below beach/barrier island sediments and fully _______ shoreface deposits.

Estuaries

The marine-influence portion of the seaward portion drowned river valley that occurs due to sea level rise.

1. freshwater, seawater

2. river, marine

3. river, wave and tidal

4. mouth

5. drowned river valley

6. transgression

Characteristics of Estuaries

1. Region where _________ and _________ mix.

2. Sediments are supplied by both ______ and _______.

3. Transport and deposition of sediments are done by combinations of ____, _____, and ______ processes.

4. Common features at the ______ of rivers.

5. Different from deltas due to sedimentation occurring within the ___________.

6. Temporarily existing due to only occurring during ___________.

Wave-dominated Estuary

An estuary system dominated by wave processes and comprised of a bay-head delta, central lagoon, and beach barrier.

Bay-head delta

The zone where fluvial processes are dominant.

Central lagoon

The lowest energy part of the estuarine system where the river flow rapidly decreases and the wave energy is mainly concentrated at the barrier bar, therefore, a region of fine-grained deposition often rich in organic.

Salt-water marsh

A central lagoon that becomes filled with sediment crossed by channels where wave-ripples form and draped with mud.

Barrier

Formed in the outer zone of the estuary where the wave action reworks marine sediments.

Tide-dominated Estuary

An estuary system where tidal processes may dominate in mesotidal and macrotidal coastal regime, which forms a funnel-shaped estuary which tends to increase the flood tidal current strength, and low gradient tidal channels adopting a meandering form in the inner part of the estuary.

heterolithic, bioclastic, lag

In a tide-dominated estuary, deposits in the point bar are ________, with _______ debris being common among the gravelly detritus deposited as _______ deposits on the channel floor.

• Estuary - waterbody

• Delta - landform

Estuary vs. Delta (Classification)

• Estuary - mixing of freshwater and saltwater

• Delta - deposition of sediment carried rivers along its mouth

Estuary vs. Delta (Mode of formation)

• Estuary - brackish water

• Delta - freshwater or saltwater

Estuary vs. Delta (Water salinity)

• Estuary - fewer sediment deposits

• Delta - larger sediment deposits

Estuary vs. Delta (Sediment input)

• Estuary - narrower & elongated

• Delta - wider & fan-shaped

Estuary vs. Delta (Geomorphology)

Wave-dominated estuary deposits

Estuary with facies deposits (top to bottom):

1. Beach

2. Estuary mouth

3. Central lagoon

4. Bay-head delta

Tidal-dominated estuary deposits

Estuary with facies deposits (top to bottom):

1. Upper tidal flat

2. Tidal creek

3. Lower tidal flat

4. Tidal-channel

5. Scoured base of channel

Sand & Conglomerate

Lithology of Beach/Barrier

Mainly mud with some sand

Lithology of Lagoon

Mud, sand, and less commonly, conglomerate

Lithology of Tidal Channel

Mud and sand

Lithology of Tidal Mudflats

Mature quartz sands and shelly sands.

Mineralogy of Beach/Barrier

Variable.

Mineralogy of Lagoon

Variable

Mineralogy of Tidal Channel

Clay and shelly sand.

Mineralogy of Tidal Mudflats

Well-sorted, well-rounded clasts

Texture of Beach/Barrier

Fine-grained, moderately to poorly sorted

Texture of Lagoon

May be well-sorted in high energy settings

Texture of Tidal Channel

Fine-grained, not diagnostic

Texture of Tidal Mudflats

Elongate lenses

Bed geometry of Beach/Barrier

Thinly bedded mud with thin sheets and lenses of sand.

Bed geometry of Lagoon

Lenses with erosional bases

Bed geometry of Tidal Channel

Tabular muds, with thin sheets and lenses of sand

Bed geometry of Tidal Mudflats

Low-angle stratification and wave reworking

Sedimentary structures of Beach/Barrier

May be laminated and wave rippled

Sedimentary structures of Lagoon

Cross-bedding, cross lamination and inclined heterolithic stratification

Sedimentary structures of Tidal Channel

Ripple cross-lamination and flaser/lenticular bedding

Sedimentary structures of Tidal Mudflats

Mainly wave-formed structures.

Paleocurrents of Beach/Barrier

Rare, not diagnostic

Paleocurrents of Lagoon

Bimodal in tidal estuaries

Paleocurrents of Tidal Channel

Bimodal in tidal estuaries

Paleocurrents of Tidal Mudflats

Robust shelly debris

Fossils of Beach/Barrier

Often monospecific assemblages of hypersaline or brackish tolerant organisms.

Fossils of Lagoon

Shallow marine

Fossils of Tidal Channel

Shallow marine fauna and salt marsh vegetation

Fossils of Tidal Channel

Not diagnostic.

Color of Beach/Barrier

May be dark due to anaerobic conditions.

Color of Lagoon

Not diagnostic

Color of Tidal Channel

Often dark due to anaerobic conditions

Color of Tidal Mudflats

May be associated with coastal plain, lagoonal or shallow-marine facies.

Facies Associations of Beach/Barrier

May be associated with coastal or beach barrier deposits.

Facies Associations of Lagoon

May be overlain by fluvial, shallow marine, continental or delta facies.

Facies Associations of Tidal Channel

May be overlain by shallow marine or continental facies.

Facies Associations of Tidal Mudflats