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

EaES 455-6 4

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 5

EaES 455-6 6

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 7

EaES 455-6 8

EaES 455-6 9

EaES 455-6 10

EaES 455-6 11

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 12

FUS

EaES 455-6 13

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

EaES 455-6 14

EaES 455-6 15

EaES 455-6 16

EaES 455-6 17

EaES 455-6 18

Blank Slide

EaES 455-6 19

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 20

EaES 455-6 21

EaES 455-6 22

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 23

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 24

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 25

EaES 455-6 26

Animation

EaES 455-6 27

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)

EaES 455-6 29

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 30

EaES 455-6 31

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 32

EaES 455-6 33

EaES 455-6 34

EaES 455-6 35

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 36

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 37

EaES 455-6 38

Animation

EaES 455-6 39

EaES 455-6 40

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 41

EaES 455-6 42

EaES 455-6 43

EaES 455-6 44

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