Transcript Tectonics & Sedimentation

Tectonics &
Sedimentation
Sedimentary basins
Sedimentary basins are the subsiding areas where sediments
accumulate to form stratigraphic successions
The tectonic setting is the premier criterion to distinguish different
types of sedimentary basins
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Extensional basins occur within or between plates and are associated
with increased heat flow due to hot mantle plumes
Collisional basins occur where plates collide, either characterized by
subduction of an oceanic plate or continental collision
Transtensional basins occur where plates move in a strike-slip
fashion relative to each other
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I) Tectonics and Sedimentation
A. Can explain sedimentary
sequence with plate tectonic
models
B. Cratonic sedimentation
Wiley.com
1. craton = stable continental
interior, positive relief
2. thin sedimentary sequences,
unconformities
3. positive relief leads to
erosion & unconformities
4. sedimentary sequence = ~ 1
km of Paleozoic and Mesozoic
rks
i. l.s, s.s., sh = shallow
marine, fluvial-deltaic
5. local development of basins &
arches
i. origin of basins = failed rifts?=
Michigan basin
Alberta Geol Society
II) Geosynclines
Steven Dutch
A. Trough that parallels continental margin = geosyncline
1. subdivided in miogeosyncline & eugeosyncline
2. miogeosyncline
i. = shallow marine ls & ss adjacent to craton
ii passes to deep water lithologies
3. eugeosyncline
i. deep marine sediments, submarine volcanics, volcaniclastic sediments
ii. tectonically deformed
4. no explanation of how geosynclines formed
Steven Dutch
Steven Dutch
Sedimentary basins
Extension
Rift basins develop in continental crust and constitute the incipient
extensional basin type; if the process continues it will ultimately
lead to the development of an ocean basin flanked by passive
margins, alternatively an intracratonic basin will form
Rift basins consist of a graben or half-graben separated from
surrounding horsts by normal faults; they can be filled with both
continental and marine deposits
Intracratonic basins develop when rifting ceases, which leads to
lithospheric cooling due to reduced heat flow; they are commonly
large but not very deep
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III) Plate Tectonics &
Sedimentation
A. Explains geosynclines (now obsolete)
1. miogeosyncline = shelf;
eugeosyncline = slope & rise
B. Divergent margins
1. 2 plates separating
2. uplift = mantle plume
3. extension = rift valley development
1. normal faulting & down dropping
ii. eventually forms ocean basin
4. coarse immature sediments
deposited; alluvial, fluvial, lacustrine
5. aulacogens may develop & fill
i. fluvial & deltaic deposits fill basin
6. junction coalesce to form ocean
basin
i. evaporites, marine sediments
7. seafloor spreading develops &
pelagic oozes
Mississippi & Connecticut-Hudson
Valleys--Inactive
Rio Grande Rift--Active
Nicolle Rager, NSF
Properties of crust and upper mantle beneath the Rio Grande. Pure shear
model is probable explanation, with a "taffy-like" thinning of the lower crust and
the upper crust faulting in many places to produce the rift valley. This contrasts
to "simple shear" model wherein a single, large detachment fault controls
continental rifting.
Red Sea-Ocean Beginning
Deep axial trough, broad
shallow shelf
Miocene (5-25mya)
evaporites (over 4km thick)
below shelf
Evaporties probably overlie
thin, stretched continental
crust
Evaporite deposition end 5
mya- connection to Indian sea
established
Open ocean water led to
flourishing plankton
Biogenic seds give way
laterally to thin terrigenous
clays, sands, gravels from
eroding flanks
Stephen A. Nelson
III) Plate Tectonics &
Sedimentation
C. Convergent margins
1. cont-cont collision = uplift & coarse clastic debris,
fluvial deposits
2. oceanic-oceanic collision = island arc
i. submarine volcanism & turbidites, shales, pelagic oozes
3. ocean-continent collision = continental margin arc
i. felsic batholiths, silicic volcanics
ii. immature seds = alluvial & fluvial ss
ii. accretionary wedge, melange
Sedimentary basins
Collision
Forearc basins form between the accretionary prism and the volcanic
arc and subside entirely due to sediment loading; like trench basins,
their fill depends strongly on whether they are intra-oceanic or
proximal to a continent
Backarc basins are extensional basins that may form on the overriding
plate, behind the volcanic arc
Retroarc foreland basins form as a result of lithospheric loading behind
a mountainous arc under a compressional regime; they are
commonly filled with continental deposits
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ARC Morphology/Terminology
Forearcs
Trenches and Accretionary
Wedges
III) Plate Tectonics &
Sedimentation
D. Transform Margin
1. strike slip motion
2. irregularities produce local extension &
compression
3. typical of southern California
i. may develop sediment-starved basin
ii. eventually infilled
San Andreas Transform
Sedimentary basins
Transtension
Strike-slip basins form in transtensional regimes and are usually
relatively small but also deep; they are commonly filled with coarse
facies (e.g., alluvial fans) adjacent to lacustrine or marine deposits
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Woods Hole
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