(S8) Clastic Coasts and Estuaries Flashcards
1
Q
What three features determine whether a coastline is depositional or erosional?
A
Morphology, wave energy and sediment budget
2
Q
What is an erosional coastline and what is it’s main feature?
A
A coastline where material is reflected back into the sea - usually has a characteristic steep graident
3
Q
What is a depositional coastline and what is it’s main characteristic?
A
A coastline which is accumulating sediment - usually genetle gradient
4
Q
Why is a gentle gradient key for a depositonal coastline?
A
Wave energy is dissapated over the shallow water
5
Q
What four weathering processes takes place on a cliff exposure on an erosional coastline?
A
Oxidation, Hydration, Salt growth, Physical impact
6
Q
What is the name for the feature left behind when a cliff is eroded?
A
Wave-cut platform
7
Q
What type of sediment is accumulated along a depositional coastline? (2)
A
Terrigenous clastic detritus or bioclastic debris
8
Q
What are the three modes of transportation to a depositional coastline, not including fluvial/aeolian?
A
Tidal currents, windblown currents, geosptrophic currents
9
Q
What are the four controls on longshore drift?
A
Sediment supply, wave energy, tidal range, climate
10
Q
What is the main control on carbonate and evaporite deposition along depositional coastlines?
A
Climate
11
Q
What does barrier and lagoon formation depend upon?
A
Tidal range
12
Q
Why does the backwash wave have less energy on a gravel beach?
A
Water percolates into the porous gravel
13
Q
What is a storm ridge?
A
Formed on gravel beackhes when clasts wash up at the top of the foreshore
14
Q
What are the three sources of clasts found on a gravelly beach?
A
Terrigenous clastic, Volcaniclastic, Bioclastic
15
Q
What is the name for the ridge which divides the foreshore and backshore?
A
Berm
16
Q
Where would we expect to find sedimentary structures on a beach and under what formation conditions?
A
Behind the Berm, when waves wash over to the landward side during storm events
17
Q
What is the backshore and what are it’s two features?
A
Collonised by plants, loose sand reworked by aeolian processes
18
Q
Wave ripples may be preserved as __-___ ___ ___, or they may also be destroyed by ___.
A
Wave-ripple cross-lamination, Bioturbation
19
Q
What are the typical dimensions of beach dune ridges?
A
10’s m high, 100’s m inland
20
Q
What is the main limiting factor of beach dune ridges?
A
Suplly of sediment from the beach
21
Q
What two type of coasts do beach dune ridges usually form along?
A
Coasts with barrier systems + strand plain coasts
22
Q
What is the main difference in beach dune ridges and aeolian dunes in the geological record?
A
Beach dune ridges are less likely to show preservation of cross-bedding due to the later stabilization of vegetation
23
Q
What are the four processes likley to be found on a coastal plain?
A
Fluvial, Alluvial, Aeolian, Pedogenic
24
Q
What type of material is usually deposted on the coastal plain after a storm event? (2)
A
Bioclastic debris, Marine fauna
25
What is a strand plain?
Ajacent to the coastal plain as a sandy beach, where sediment is deposted on foreshore and backshore and backshore merges onto the coastal plane
26
What are the typical dimensions of a strand plain?
10's - 100's km long
27
What are two pieces of evidence which determine the subaerial conditions of a coastal plain?
Plant colonisation and aeolian dune formation
28
What is the main purpose of a barrier?
Seperates sea from a lagoon by sand/gravel buildup
29
What is a beach spit?
A partially attached barrier
30
What is a welded barrier?
A wholly attached barrier
31
What is a barrier island?
A unattached barrier
32
What is the range of lengths of a barrier?
100's m to 10's km
33
What is the maximum width a barrier could be?
100's m wide
34
Where are the largest barriers found?
Open coasts of large oceans where wave energy is high and tidal range is small
35
What does the seaward margin of a barrier look like?
Beaches and dune ridges where aeolian processes rework the sand and vegetation stabilizes dunes
36
What does the landward margin of a barrier look like?
Sand deposted during storms, pinches out to mud deposits at edge of lagoon margin
37
What would the deposit after a storm surge look like over a barrier?
Washover deposits form a low-angle cone of stratified sands
38
What are the three conditions of barrier formation?
Abundant sand/gravel supply, Tidal range small, Slow relative sea level rise
39
Why does a macrotidal range prevent barrier formation?
Restricted inlet is not big enough for high flow from rate of macrotidal
40
Why is slow relative sea level rise benificial in barrier formation?
Coastal plain behind the ridge may be lower than top of the ridge - becomes flooded and sediment is continually added
41
If a lagoon is fed by a river, what may the lagoon be considered?
Part of an estuary system
42
How deep is a typical lagoon?
Few m's
43
What is the fetch like in a lagoon and what does this mean for bedforms?
Usually limited, ripples only form in very shallow water
44
What vegetation regeme would be expected in a tropical lagoon?
Aerial root systems - mangraves which aid progradation into the lagoon
45
What vegetation regeme would be expected in a temerate lagoon?
Saline tolerent grasses, trees and shrubs
46
What processes are likely to form a brackish lagoonal system?
High rainfall, local runoff, small streams
47
What processes are likely to form a hypersaline lagoonal system?
Evaporation, arid environment
48
What are the three characteristics of a lagoonal succession?
Mudstone, organic-rich, thin wave-rippled sand beds
49
What is the distinguishing feature between lake and lagoonal successions?
Presence of marine fossil assemblages in lagoons or brackish/hypersaline fauna
50
What is a typical feature of a microtidal coast?
Barrier system with widely speaced inlets
51
What would the barrier system on a mesotidal coast look like?
More inlets than microtidal, thus likley that barrier islands were present
52
What is a possible effect of mesotidal regeme on a lagoon?
Currents may be strong enough to redistribute sediment in a lagoon - higher energy environment
53
What is a flood tidal deposit/delta?
A deposit from sediment brought through the inlet by a mesotidal regeme and deposited suddenly due to drop in energy forming low angle, thin cone
54
What is an ebb tidal deposit/delta?
A deposit of sediment brought back through an inlet from the lagoon to create a low angle, thin cone on the sea-ward side of the barrier
55
What is the direction of paleocurrents on a flood tidal delta?
Landwards
56
What does the barrier system on a macrotidal coastline look like and why?
No barrier system - tidal currents are stronger control on sediment distribution than waves are
57
What is a common feature of a macrotidal coastline?
Intertidal mudflats and saltmarches
58
What is the name for dry-tolerent vegetation?
Xerophytes
59
What is a tidal creek?
A small channel of stronger flow which cuts into a tidal flat
60
What sedimentary structures may form on the lower parts of a tidal mudflat?
Flaser/lenticular bedding, ripple laminated sands interbedded with mud-drapes
61
What does a prograding barrier succession look like?
Barriers become wider, inner margins become stabilized by vegetation
62
What does a retrograding barrier succession look like?
Loss from erosion as supply is too low, reduces in width and height - more susceptable to washovers, lagoon becomes partially filled in, beach moves landwards
63
What would a coastal succession for slow relative sea level rise look like?
Landwards movement of beach and lagoonal fill
64
Breifly state what the succession of a barrier system would look like
Coastal plain deposits at base, lagoon facies, capped by beach deposits
65
Breifly state what the succession of a strand plain system would look like
Coastal plain deposits overlain by beach deposits
66
What is the definition of a estuary?
Marine influenced portion of river valley which becomes flooded with seawater
67
Where does sediment come from in an estuary?
Marine and Fluvial sources
68
Where does all of the sedimentation occur in an estuary?
Drowned valley
69
When do estuaries form?
During and immediately after a transgression - hence modern examples after the holocene
70
What are the two categories of estuary?
Wave dominated and tide dominated
71
What are the four main variables affecting the form of an estuary?
Sediment supply volume, relative importance of marine/fluvial, size of valley, depth of flooding
72
What is the range of dimensions for modern estuaries?
1-100km long, 0.1-10km wide
73
What is the equilibrium of a estuary system?
Drowned valley will eventually fill to sea level and the area will cease to have an estuarine character
74
After equilibrium has been reached in an estuary system, what is the next phase for a high sedimentary supply?
Deltaic system forms at the mouth
75
What will occur after a estuary ceases to exist in a marine, tidal dominated system?
Tidal flats will form at the mouth
76
What will occur after a estuary ceases to exist in a marine, wave dominated system?
Strand plain will form at the mouth
77
What are the three main features found in a wave dominated estuary?
Bay-head delta, Central lagoon, Beach barrier
78
How and why does a bay-head delta form?
Fluvial processes dominate and sudden deceleration into a lagoon forms a delta - barrier protected from wave energy
79
What is the process of formation and progradation of a central lagoon in a wave dominated estuary?
Fill with sediment, becomes salt water marsh which is crossed with channels
80
What determines the relatvie thickness of a wave-dominated estuary succession?
The balance between fluvial and marine supply
81
What would be the dominating factor in a fluvial dominated wave-estuary succession?
Bay head delta facies
82
What would be the dominating factor in a marine dominated wave-estuary succession?
Barrier deposits
83
What are the three main features found in a tide-dominated estuary?
Tidal channels, Tidal flats, Tidal bars
84
What are the characteristics of a typical tidal channel? (3)
Low gradient, Meandering, Point-bar formation
85
What is the main difference between tidally influenced meandering channels and normal meandering channels?
More than one grainsize on point bar deposits
86
What is the name for more than one grainsize on a point bar deposit?
Inclined heterolithic straitifcation
87
What is a typical characteristic of a tidal flat?
Seawater covers at high tide and exposed at low tide, saltmash
88
What determines tidal bars from fluvial bars? (3)
Mud-drapes, reactivation surfaces, herringbone cross stratification
89
What is the orientation of a dune bedform on a tidal bar?
Elongate to flood-tide direction
90
What could cause herringbone cross-stratification in a tidal bar? (2)
Overlap of banks of beds with different directions, Current changes position
91
What would the sedimentary structure for the strongest of tidal currents be?
Upper flow regime plane beds - horizontally laminated sands
92
What do the proportions of tidal channel, tidal flat and tidal bar deposits depend on in succession?
Strength of the tidal currents, Amount of mud/sand/gravel
93
What would a typical succession of a tide dominated estuary look like?
Base of channel, scouring and lag - fining up, cross-bedded sands, mudrapes, Inclined heterolithic stratifcation
94
What is the main difference between a delta and estuary in succession?
Delta is progradational, estuary is aggradational
95
What is the benefit of having a sea level change on hydrocarbon formation?
Beach sands a very good reservoir potential, change in sea level could result in trapping of sands under mud
96
What are the typical lithologies associated with beach/barrier system deposits?
Sand and conglomerate
97
What would be expected of the mineralogies of beach/barrier system deposits?
Mature quartz sand and shelly sands
98
What would be expected of the texture of beach/barrier system deposits?
Well sorted, well rounded clasts
99
What would be expected of the bed geometry of beach/barrier system deposits?
Elongate lenses
100
What sedimentary structures would be expected in beach/barrier system deposits?
Low-angle strata + wave reworking
101
What paleoflow would be expected in beach/barrier system deposits?
Mainly wave-formed structures
102
What fossils would be expected in beach/barrier system deposits?
Robust shelly debris
103
What would be expected of the sedimentary colouring of beach/barrier system deposits?
Not diagnostic
104
What are the facies associations of beach/barrier system deposits?
Coastal plain, lagoonal, shallow marine
105
What are the typical lithologies associated with lagoonal system deposits?
Mainly mud, some sand
106
What would be expected of the mineralogies of lagoonal system deposits?
Variable
107
What would be expected of the texture of lagoonal system deposits?
Fine-grained to moderately to poorly sorted
108
What would be expected of the bed geometry of lagoonal system deposits?
Thinly bedded mud with thin sheets and lenses of sand
109
What sedimentary structures would be expected in lagoonal system deposits?
May be laminated wave ripples
110
What paleoflow would be expected in lagoonal system deposits?
Rare, not diagnostic
111
What fossils would be expected in lagoonal system deposits?
Often monospecific assemlages of hypersaline or brackish tolerent organisms
112
What would be expected of the sedimentary colouring of lagoonal system deposits?
May be dark due to anerobic conditions
113
What are the facies associations of lagoonal system deposits?
Coastal plains, beach barrier deposits
114
What are the typical lithologies associated with tidal-channel system deposits?
Mud, sand and less commonly conglomerate
115
What would be expected of the mineralogies of tidal-channel system deposits?
Variable
116
What would be expected of the texture of tidal-channel system deposits?
May well be sorted in high energy settings
117
What would be expected of the bed geometry of tidal-channel system deposits?
Lenses with erosional bases
118
What sedimentary structures would be expected in tidal-channel system deposits?
Cross bedding and cross laminations and inclined heterolithic stratification
119
What paleoflow would be expected in tidal-channel system deposits?
Bimodal in tidal estuaries
120
What fossils would be expected in tidal-channel system deposits?
Shallow marine
121
What would be expected of the sedimentary colouring of tidal-channel system deposits?
Not diagnostic
122
What are the facies associations of tidal-channel system deposits?
May be overlain by fluvial, shallow marine, continental or delta facies
123
What are the typical lithologies associated with tidal-mudflat deposits?
Mud and sand
124
What would be expected of the mineralogies of tidal-mudflat deposits?
Clay and shelly sand
125
What would be expected of the texture of tidal-mudflat deposits?
Fine-grained, not diagnostic
126
What would be expected of the bed geometry of tidal-mudflat deposits?
Tabular muds with thin sheets and lenses of sand
127
What sedimentary structures would be expected in tidal-mudflat deposits?
Ripple cross-lamination and flaser/lenticular bedding
128
What paleoflow would be expected in tidal-mudflat deposits?
Bi-modal in tidal estuaries
129
What fossils would be expected in tidal-mudflat deposits?
Shallow marine fauna and salt marsh vegetation
130
What would be expected of the sedimentary colouring of tidal-mudflat deposits?
Often dark due to anaerobic conditions
131
What are the facies associations of tidal-mudflat deposits?
Shallow marine or continental
