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 EaES 455-6
Sedimentary Rocks and Stratigraphy: The three most abundant kinds of sediment: Quartz Sand, Shale, Limestone
Simple Ideal Model for the Evolution of Sedimentary Rocks: High ENERGY Low “Rocks reflect the conditions at which they formed.” --Fichter & Poche
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 EaES 455-6
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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 EaES 455-6
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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 EaES 455-6
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Offshore marine environments Tempestites form during storm events Their facies succession: erosional basal surface with sole marks, sandy unit with hummocky cross stratification topped by wave-rippled sand, muds EaES 455-6
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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 EaES 455-6
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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 EaES 455-6
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 EaES 455-6
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
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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
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
Animation 1 Animation 2 http://www.physics.utoronto.ca/~nonlin/turbidity/turbidity.html http://faculty.gg.uwyo.edu/heller/SedMovs/middletonturb.htm EaES 455-6
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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 EaES 455-6
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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 EaES 455-6
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 EaES 455-6
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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 EaES 455-6
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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 EaES 455-6