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EaES 455-6 1
Contents
• Introduction• Sedimentology – concepts• Fluvial environments• Deltaic environments• Coastal environments• Offshore marine environments
• Sea-level change• Sequence stratigraphy –
concepts• Marine sequence stratigraphy• Nonmarine sequence
stratigraphy• Basin and reservoir modeling• Reflection
Sedimentary Rocks and Stratigraphy:
• The three most abundant kinds of sediment:
• Quartz Sand,
• Shale,
• Limestone
Simple Ideal Model for the Evolution of Sedimentary Rocks:
“Rocks reflect the conditions at which they formed.” --Fichter & Poche
High ENERGY Low
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Offshore marine environments
• Shallow marine environments :– pericontinental seas that occur along continental margins
and have a shoreline-shelf-slope profile; and – epicontinental seas that cover continental interiors and
exhibit a ramp morphology
• Under idealized conditions the offshore-transition and offshore exhibit a systematic decrease in (wave) energy and grain size; however, such an ‘equilibrium shelf’ is commonly not encountered• Tides and ocean currents can strongly complicate shelf
hydrodynamics• Rapid sea-level changes (e.g., during the Quaternary) result
in relict shelf sediments that are genetically unrelated to the present conditions
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Offshore marine environments
• IDEAL: offshore-transition and offshore – decrease in (wave) energy and grain size; – however, such an ‘equilibrium shelf’ not common!
• Tides and ocean currents can complicate shelf hydrodynamics
• Rapid sea-level changes (e.g., during the Quaternary) leave relict shelf sediments that are genetically unrelated to the present conditions
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Offshore marine environments
• Wave/storm-dominated shelves, ideal: – lower shoreface: sands – below fairweather wave base: alternating sands and
muds, – below storm wave base: muddy facies
• Storms leave a strong imprint (i.e., storm deposits have a high preservation potential), since they wipe out fairweather deposits
• Tempestites form during storm events and exhibit a characteristic facies succession from an erosional basal surface with sole marks, to a sandy unit with hummocky cross stratification overlain by wave-rippled sand, finally giving way to muds
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FUS
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Offshore marine environments
• Tempestites form during storm events – Their facies succession:
1. erosional basal surface with sole marks, 2. sandy unit with hummocky cross stratification
topped by wave-rippled sand, 3. muds
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Blank Slide
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Offshore marine environments
• Tides lead to circulation around amphidromic points, ranging from circular to almost rectilinear depending on the shape of the water body
• Tide-dominated shelves exhibit a distinct suite of bedforms in relation to current velocity and sediment (sand) supply
• Erosional features, sand ribbons, and sand waves go along with decreasing flow velocities, commonly associated with mud-draped subaqueous dunes; tidal sand ridges (tens of m high, many km across) are characteristic of shelves with a high supply of sand
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Offshore marine environments
• Tides lead to circulation around amphidromic points, ranging from circular to almost rectilinear depending on the shape of the water body
• Tide-dominated shelves, bedforms: – Erosional features, – sand ribbons, and – sand waves go along with decreasing flow velocities, commonly
associated with mud-draped subaqueous dunes; – tidal sand ridges (tens of m high, many km across) are
characteristic of shelves with a high supply of sand
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Offshore marine environments
• Ocean current-dominated shelves are relatively rare; geostrophic ocean currents can lead to the formation of bedforms that are somewhat comparable to those of tide-dominated shelves
• Mud-dominated shelves – usually associated with large, tropical rivers with a high
suspended load (e.g., Amazon and Yellow Rivers) that can be transported along the shelf if currents are favorable
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Offshore marine environments
• Deep marine environments include the continental slope and the deep sea
• Subaqueous mass movements (mostly sediment gravity flows) involve a range of transport mechanisms, including plastic flows and fluidal flows• Debris flows are commonly laminar and typically do not
produce sedimentary structures• Turbidity currents are primarily turbulent and more
diluted; they commonly evolve from debris flows• Debris-flow deposits are poorly sorted, related to the
‘freezing’ that occurs once shear stresses can not overcome the internal shear strength
• A key mechanism in turbidity currents is ‘autosuspension’ (turbulence --> suspended load --> excess density --> flow --> turbulence)
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Animation
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Offshore marine environments
• Deep marine environments include the continental slope and the deep sea
• Subaqueous mass movements (mostly sediment gravity flows) involve a range of transport mechanisms, including plastic flows and fluidal flows• Debris flows are commonly laminar and typically do not
produce sedimentary structures• Turbidity currents are primarily turbulent and more
diluted; they commonly evolve from debris flows• Debris-flow deposits are poorly sorted, related to the
‘freezing’ that occurs once shear stresses can not overcome the internal shear strength
• A key mechanism in turbidity currents is ‘autosuspension’ (turbulence --> suspended load --> excess density --> flow --> turbulence)
EaES 455-6 28
Offshore marine environments
• Deep marine environments include the continental slope and the deep sea
• Subaqueous mass movements (mostly sediment gravity flows) involve a range of transport mechanisms, including plastic flows and fluidal flows• Debris flows are commonly laminar and typically do not
produce sedimentary structures• Turbidity currents are primarily turbulent and more
diluted; they commonly evolve from debris flows• Debris-flow deposits are poorly sorted, related to the
‘freezing’ that occurs once shear stresses can not overcome the internal shear strength
• A key mechanism in turbidity currents is ‘autosuspension’ (turbulence --> suspended load --> excess density --> flow --> turbulence)
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Animation 1
Animation 2
http://www.physics.utoronto.ca/~nonlin/turbidity/turbidity.html
http://faculty.gg.uwyo.edu/heller/SedMovs/middletonturb.htm
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Offshore marine environments
• Contrary to debris flows, turbidites exhibit a distinct proximal to distal fining
• The idealized Bouma sequence, is most useful for medium-grained, sand-mud turbidites, but it must be applied with care– divisions A-E (bottom to top):
• A: Rapidly deposited, massive sand• B: Planar stratified (upper-stage plane bed) sand• C: Small-scale (climbing ripple) cross-stratified fine sand• D: Laminated silt• E: Homogeneous mud
• High-density and low-density turbidity currents give rise to incomplete, coarse-grained (A) and fine-grained (D-E) turbidites respectively
• Contourites are formed by ocean currents and commonly represent reworked turbidites
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Offshore marine environments
• Contrary to debris flows, turbidites exhibit a distinct proximal to distal fining
• The idealized Bouma sequence, consisting of divisions A-E, is most useful for medium-grained, sand-mud turbidites, but it must be applied with care• A: Rapidly deposited, massive sand• B: Planar stratified (upper-stage plane bed) sand• C: Small-scale (climbing ripple) cross-stratified fine sand• D: Laminated silt• E: Homogeneous mud
• High-density and low-density turbidity currents give rise to incomplete, coarse-grained (A) and fine-grained (D-E) turbidites respectively
• Contourites are formed by ocean currents and commonly represent reworked turbidites
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Offshore marine environments
• Submarine canyons at the shelf edge (commonly near river deltas) are connected to submarine fans on the ocean floor
• Size of submarine fans is inversely related to dominant grain size – mud-dominated submarine fans are 104–106 km2, – sand or gravel-dominated submarine fans are 101–102 km2
• Submarine fans share several characteristics with deltas; they consist of a feeder channel that divides into numerous distributary channels bordered by natural levees (‘channel-levee systems’) and are subject to avulsions• Proximal fan (trunk channel)• Medial fan (lobes)• Distal fan
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Animation
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Offshore marine environments
• Submarine canyons at the shelf edge (commonly related to deltas) are connected to submarine fans on the ocean floor
• The size of submarine fans is inversely related to dominant grain size (i.e., mud-dominated submarine fans are 104–106 km2, sand or gravel-dominated submarine fans are 101–102 km2)
• Submarine fans share several characteristics with deltas: – feeder channel that divides into numerous distributary channels
bordered by natural levees (‘channel-levee systems’) and are subject to avulsions
• Proximal fan (trunk channel)• Medial fan (lobes)• Distal fan
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Offshore marine environments
• Hemipelagic sediments: – at least 25% of fine-grained (muddy) terrigenous material – deposited from suspension, commonly after transport by
hemipelagic advection• Distal, muddy turbidites merge gradationally into hemipelagic
deposits• Eolian dust is an important component (~50%) of hemipelagic
(and pelagic) facies• Black shales have a 1–15% organic-matter content and form in
anoxic bottom waters, sometimes in shallow seas (e.g., Western Interior Seaway)
• Pelagic sediments are widespread in the open ocean and primarily have a biogenic origin