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7. Controls on basin stratigraphy
Driving mechanisms for basin stratigraphy
Tectonic mechanism: (a) flexure under
applied loads (rift basin and foreland
basin); (b) fault array evolution; (c) inplane stress
Steer’s-head
geometry
Elastic
Eustatic mechanism: (a) change in
volume of the ocean basin; (b) changes of
ice volume on polar regions
Climate change: Influence on sediment
discharge to basins
Viscoelastic
7.1 Tectonic mechanisms: flexure
under applied loads
7.1.1 Effects of flexure on stratigraphy
in basins due to stretching
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The mechanisms of subsidence in stretched basins comprise: (i) fault-controlled
initial subsidence caused by mechanical stretching of the upper brittle layer of the
lithosphere, (ii) a thermal subsidence caused by the cooling and contraction of the
upwelled asthenosphere, and (iii) sediment and water loading.
In rift basins:
•During the stage of rifting: fault-controlled Airy-type subsidence.
•During post-rift stage: flexural-controlled subsidence.
•The increase of Te with increasing plate thermal age leads to stratigraphic onlap
pattern for post-rift strata.
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• Initial strong onlap onto the basement at the transition from fault-controlled Airy-type
subsidence to flexural-controlled subsidence.
• Lateral heatflow causes thermal uplift on the coastal plain, abruptly terminating onlap.
• By about 16 Myr after rifting, flexural subsidence outstrips thermal uplift and the
sediments again progressively onlap basement.
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7.1.2 Role of flexure in generating
foreland basin stratigraphy
Transition from passive margin to foreland basins
1. Early stage: thermal age of passive
continental margin is an important control on
foreland basin development.
2. Later stage: the thickness of the
overthrust load is more important.
Fig. 4.31
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Wedge-shaped basin geometry and progressive stratigraphic onlap of a foreland basin
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7.1.3 The flexural forebulge unconformity
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Forebulge unconformity in eastern Switzerland
Calculated erosion
Bathymetry before orogenic loading
Inherited deeper
bathymetry:
no erosion
Observed erosion
Hiatus of the unconformity
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7.1.4 Foreland basin isopachs and pinch-outs
A
Progressive eastward shift of depocenters
during Sevier orogeny
A’
A
A’
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7.2 Tectonic mechanisms: fault array evolution
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Basin Analysis
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Basin Analysis
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7.3 Changes of in-plane stress
In-plane stresses acting on a
deflected plate may enhance
or reduce the curvature of the
deflection.
Compressive in-plane stress
causes basin margin to uplift and
basin center to subside.
Tensile in-plane stress caused
basin margin to subside and basin
center to uplift.
In-plane stress may have
buckled layered lithosphere
and produced long wavelength
lithospheric folds.
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7.4 Eustatic mechanisms
Eustasy, relative sea-level, water depth
Relative sea-level: the distance between
a local datum (e.g. top of the basement of
a basin) and sea-surface. Relative sealevel change is influenced by: (1) eustasy,
(2) basin uplift/subsidence.
Water depth: the distance between the
sea-bed and the sea-surface or water
level.
Eustatic sea-level (or eustasy): This is
global sea-level and is a measure of the
distance between a fixed datum, usually
taken as the centre of the Earth, and the
sea-surface.
Figure 3.6 Cartoon showing the relationship between relative sealevel, water depth, eustatic sea-level, tectonics (uplift and subsidence),
and accumulated sediment. Note that relative sea-level incorporates
subsidence and/or uplift by referring to the position of sea-level with
respect to the position of a datum at or near the sea-floor (e.g.
basement rocks, top of previous sediment package) as well as
eustasy. Eustasy (i.e. global sea-level) is the variation of sea-level
with reference to a fixed datum, for
example the centre of the Earth.
Coe et al. (2003)
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Five possible causes that may cause global sea-level changes
1. Continuing differentiation of lithospheric material as a
result of plate tectonic processes. (not important)
2. Changes in the volumetric capacity of the ocean
basins caused by sediment influx or removal. (not
important)
3. Changes in the volumetric capacity of the ocean
basins caused by volume changes in the mid-ocean
ridge system. (important for first-order eustasy)
4. Thermal expansion and contraction of the oceanic
water reservoirs. (not important, 1°K increases, 0.45 m rise in sea level)
5. Changes of available water by abstraction in and
melting of polar ice caps and glaciers (glacial eustatic).
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Considering isotasy in eustatic sea level changes
⎛ ρ − ρw ⎞
⎟⎟
Δ SL = S ⎜⎜ m
ρ
w
⎝
⎠
If ρ m = 3.3 g/cm3 ; ρ w = 1.0 g/cm3 The isostatic subsidence of the
ocean floor is approximately 0.4 of
the sea level change (Δ SL ). Or the
seal level change is 0.7 of the
increase in the water depth of the
ocean (h2-h1).
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However, sediment in the ocean is removed by tectonic accretion and subduction
at active margins and continued spreading creates new ocean floor. It is likely that
the balance between influx and removal of sediment, when averaged over long
periods of time, is insufficient to cause rates of sea-level change of more than ~ 1
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mm per 1000 yr.
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Volume of present world ridge system is about 10% of the volume of the ocean water.
Change in spreading rate and change in the length of ridge systems influence the ridge volume.
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First-order (225300 Myr) eustatic
curve of Vail: due
to ridge volume
fluctuation.
~ <100 to 150 m above present
Maximum sea level: latest Cretaceous (Maastrichtian)
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Melting of Present Ice Cap
Total melting of Antarctic land ice would result in an increase in water
depth, ranging from 60~75 m. Melting Greenland ice cap > 5 m rise,
Taking into account the isostatic effect, if all the land-locked ice melted, it
would cause a 50 m rise in sea level (ΔSL).
In geological term, rate of melting ice caps is a rapid process (~10 mmyr-1)
Melting of Pleistocene Ice Cap
May cause about 150 m sea level rise.
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For the last 120,000 yrs, 8 sea-level cycles.
Magnitudes: 20~180 m, periods: 100,000 yrs (primary),
40,000 yrs, and 20,000 yrs.
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現在溫度
地質
年代
百萬
年前
新生代
上新世
中新世
第三紀
漸新世
始新世
北半球開始發育冰川
大片冰帽覆蓋南極洲
南極洲冰帽開使成形
古新世
中生代
全球溫度隨地質時間的變化
第四紀
白堊紀
侏羅紀
南北極
沒有冰帽
三疊紀
古生代
二疊紀
二疊紀~石炭紀冰河期
石炭紀
泥盆紀
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志留紀
日照量改變:米蘭科維奇循環 (Milankovitch cycles)
(a) 地球公轉軌道的偏心率 (eccentricity)改變造成41萬年與10萬6千年的氣候循環
(b) 地球自轉軸傾角 (obliquity)的改變造成4萬1千年的氣候循環
(c) 地球自轉軸繞著垂直軸運轉一圈的週期(即歲差或進動, precession) ，
造成1萬9千年至2萬3千年的氣候循環
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氧同位素,冰帽與海水面變化
冰河期
海水中的O18/O16比值增加
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間冰期
海水中的O18/O16比值減小
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改變地球日照量與古代海水溫度測量
地球公轉與自轉的
軌道與參數變化
改變地球
日照量
造成氣候
改變
若地球表面平均溫度低，
南北兩極形成冰川；
平均溫度較高，
南北極沒有冰川
測量有孔蟲殼體
的氧同位素得知
以前海水的溫度
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7.5 A primer on process stratigraphy
Process stratigraphy (as defined in Allen and Allen (2005), p.268) is the
science of the recognition and interpretation of the genetic structures of
stratigraphy. The fundamental aim of process stratigraphy is to understand the
driving mechanisms for the range of stratigraphic architectures found in
sedimentary basins. The key concept of process stratigraphy is the
generation/destroy of accommodation space and the amount of sediments
supplied.
The stratigraphy in a sedimentary basin is the result of the interplay of the
generation of space or accommodation and the influx of sediments (sediment
supply).
Accommodation is the interplay of eustatic sea-level changes, basin
subsidence/uplift, local patterns of faulting.
Sediment supply is a function of climate (exerting controls on vegetation,
weathering, erosion, and far-field sediment transport to basins) and sediment
routing systems for siliciclastic deposits. For carbonate systems, carbonate
productivity determines how much carbonate sediments will be generated
and carbonate productivity depends on water depth (available of light), water
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turbidity and temperature, and type of biota.
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Major Controls on Sedimentary Fill of Basins
The sedimentary fill of basins is controlled by three major variables (Figure 1.8.1):
Subsidence:
"The thermal and mechanical properties of the lithosphere exert important controls on the
formation of sedimentary basins" (Steckler, 1990). Thermal subsidence rates and the magnitude
and distribution of subsidence due to loading vary in basins of different tectonic settings
(Steckler and Watts, 1978; Stephenson, 1990).
Eustasy (global sea level):
Eustasy refers to sea level relative to a fixed datum, such as the center of the earth. Global sea
level variations result from changes in either oceanic basin volume or water volume. Eustasy
combined with subsidence results in relative sea level variations, which control accommodation
for sediment deposition (Posamentier et al., 1988; Posamentier and Vail, 1988).
Sediment Supply:
"The role of sediment supply in transgressions and regressions is a fundamental one..."
(Schlager, 1994). When the rate of sediment supply is greater than the rate of relative sea level
rise, accommodation space will be filled.
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Vail (1987)
Process Stratigraphy History
•
1960s – The recognitions of unconformity-bounded sequences of
inter-regional extent (Sloss, 1950, 1963) and the shape of sedimentary
bodies is controlled by quantity of sediment supplied (Q), rate of basin
subsidence (R), sediment dispersal (D), and composition and texture
of the sediment supply (M).
• 1970s – Use of seismic stratigraphy (Payton, 1977, AAPG Memoir 26).
The recognitions of seismic reflection horizon representing time lines
and sequences bounded by unconformities and their correlative
conformities (Exxon group, Payton (eds.), 1977, AAPG Mem. 26)
• 1987 – “Global” sea-level chart (Haq et al., 1987)
• 1988 – Concept of “accommodation” was introduced in Wilgus et al.
(1988)
• Late 1980s and early 1990s – Criticism on eustasy as the
overwhelming controls on sequence development and on presumed
global synchroneity of key stratigraphic surfaces.
• Since 1978 – Numerical simulations on stratigraphy to explain &
predict stratal geometries within sequences.
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7.5.1 Forward modeling of stratigraphic cycles from first principles
Stratigraphy is packaged into large and small genetic units, from
megasequences (or supersequences) to depositional sequences and then
parasequences (or higher order genetic units, they may be driven by orbital
mechanism - Milankovitch band, or unforced - autocyclic).
Stratigraphic cycles can be modeled using expressions for accommodation and
sediment supply. A fundamental parameter is the magnitude of the eustatic
change compared to the subsidence rate.
Considering the stratigraphic cycles generated under a sinusoidal eustatic
variation in a basin with a background tectonic subsidence rate and with a
sediment supply coupled to the relative sea-level variation.
⎛ 2πt ⎞
h = h0 sin ⎜
⎟ λ: wavelength
⎝ λ ⎠ h0: amplitude
Adding the tectonic subsidence rate:
Sinusoidal eustatic fluctuation:
⎛ 2πt ⎞
hrel = h0 sin ⎜
⎟ + at
⎝ λ ⎠
a: rate of tectonic subsidence
(linear)
t: geological time
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A number of different relative sea-level scenarios due to the interplay between
eustasy and basin subsidence can be expressed in terms of the dimensionless
parameter (relative sea-level parameter):
Ψ=
aλ
h0
z When aλ << h0: Ψ is small, the relative sea-level changes is similar
to that of eustasy;
z As aλ increases, Ψ becomes larger the relative sea-level becomes
more asymmetrical and the peak of relative sea level becomes delayed
in the eustatic cycle.
z At a critical tectonic subsidence rate (Ψis large and greater than 2π),
there is no relative sea-level fall, but instead an inflexion point in relative
sea level significantly following the eustatic peak.
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Variations in relative sea
level through a cycle of
eustatic change with
wavelength λ and
amplitude h0 in a basin
with a linear tectonic
subsidence rate a.
100 kyr is the dominant signal for the Pleistocene glacio-eustatic fluctuations.
(100 m variations in height)
(critical rate of
basin subsidence
for no relative
sea-level fall)
In this diagram, the relative sealevel is equivalent ot
accommodation since the curves
begin at zero water depth rather
than at some point on a graded
profile.
(comparison: Taiwan foreland
sequences: basin subsidence
ranges from 0.95 ~1.9 mmyr-1
during the deposition of
Liuchungchi to Erchungchi
Formations (Chen et al., 2001))
Fig. 8.2 The dimensionless parameter Ψ varies from 0.2 to 2π, corresponding to tectonic subsidence rates
from 0.1 to π mmyr-1 (grey area). Increasing values of Ψcause the relative sea-level maximum (open circle) to
be delayed in the cycle. For the “glacial” eustatic parameters used, tectonic subsidence must be > πmmyr-1 in
order for the relative sea-level fall to disappear.
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¾ Key stratigraphic surfaces (e.g., basal surface of forced regression,
sequence boundary, transgressive surface of marine erosion, maximum
flooding surfaces) are commonly diachronous, with a phase shift of up to ¼
of a eustatic period (λ). Because (1) the variations of tectonic subsidence
rate in co-existing basins, (2) the different response times of sediment
routing systems to base level change produces different sediment inputs in
coeval basins.
¾ Typical glacio-eustatic cycles have a high enough frequency and
amplitude to generate unconformities, even at high tectonic subsidence
rates.
¾ Lower frequency/amplitude “non-glacial” cycles are easily overwhelmed
by tectonic subsidence to produce monotonically rising relative sea levels.
Some critical subsidence rates for a monotonic rise in relative sea-level:
• 3.14 mm yr-1: h0=50 m, λ= 100 kyr
• 0.3 mm yr-1: h0=20 m, λ= 400 kyr
• 0.06 mm yr-1: h0=10 m, λ= 1 Myr
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Considering the effects of sediment supply
Water depth
Sediment supply
eustasy
1 λ ⎧ 2πt
⎛ 2πt ⎞ ⎫
⎛ 2πt ⎞
w(t ) = h0 sin⎜
− cos⎜
⎟ + 1⎬
⎟ + at − s0
⎨
2 2π ⎩ λ
⎝ λ ⎠ ⎭
⎝ λ ⎠
Tectonic subsidence
Rate of sediment supply (s0):
Sediment supply is coupled to the rate of relative sea-level changes, with
sediment supply rate peaks at the maximum rate of relative sea-level fall,
and is zero at the maximum rate of relative sea-level rise.
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Water depth and potential
sediment accumulation during
a cycle of relative sea-level
change with variable tectonic
subsidence rate and sediment
supply, using the glacioeustatic function.
A
B
C
A: onset of bypass for Ψ=0.2
B: onset of bypass for Ψ=1
C: onset of bypass for Ψ=2
Fig. 8.3: (a) Variation in water depth as a function of the dimensionless relative sea-level parameter Ψ
with a constant maximum sedimentation parameter s0=2 mmyr-1. When accommodation is filled, sediment
starts to bypass the depositional site (illustrated for the case of Ψ=2). The onset of bypass occurs
progressively later as tectonic subsidence increases (Ψ increases). At Ψ=2. the basin remains waterfilled until 40 kyr, after which erosion and sediment bypass take place until the beginning of the next
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glacio-eustatic cycle.
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s0
Fig. 8.3: (b) Variation in water depth and potential accumulated sediment as a function of the sedimentation
velocity s0, with a constant dimensionless relative sea-level parameter Ψ of 2, corresponding to a tectonic
subsidence rate a of 1 mmyr-1. High sediment supply rates cause the available accommodation to be filled
early during the cycle of relative sea-level change, after which sediment is bypassed and eroded (two
illustrations at s0=2 and πmmyr-1), whereas at low supply rates (s0=0.1 mmyr-1), the accommodation
remains unfilled. The evolution of water depth during a cycle of relative sea level, sedimentary facies, and
the occurrence of erosional bypass surfaces are all critically dependent on the sediment supply.
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Cycle thickness
Fig. 8.4 Stratigraphic cycles generated using the
algorithms in the text for a glacio-eustatic cycle (Ψ=2)
using different values of the maximum sedimentation
velocity s0, from 0.1 to 5 mmyr-1. Cycle thickness and water
depth trends vary strongly from the thin, sediment starved,
deep water case (s0=0.1 mmyr-1) with a nonerosional
flooding surface as an upper boundary, to the thicker, toptruncated shallow-water cycles at higher values of s0.
• Accommodation-limited: cycles are facies
are determined by accommodation; sediment
supply is always adequate.
• Sediment supply-limited: depositional
space is always great enough to
accommodate the sediment supply.
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Fig. 8.5 Sensitivity of retrogradational versus
progradational cycles resulting from variations
in tectonic subsidence rate a, with a constant
maximum sedimentation velocity so= 2 mmyr-1.
(a) Aggradational cycles (parasequences)
containing offshore, shoreface (0~25 m) and
potentially thin coastal plain deposits are
produced at Ψ=2 (a=1 mmyr-1), using an intial
water depth of 50 m. Relative sea level and
sediment supply are in balance. (b)
Progradational cycles produced by a small
decrease in Ψ to 1.8 (a=0.9 mmyr-1), with and
initial water depth of 100 m, showing that
younger cycles contain progressively lesser
amounts of offshore deposits and more
shoreface deposits. (c) Retrogradational cycles
produced by a small increase in Ψ to 2.2
(a=1.1 mmyr-1), with an initial water depth of
zero, showing that coastal plain-shoreface
cycles are progressively replaced by
shoreface-offshore cycles with time. Small
variations in tectonic subsidence rate (relative
to the sediment supply) therefore cause major
variations in the stacking patterns of cycles.
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Fig. 8.6 Large scale architecture of
depositional units in relation to
accommodation and sediment
supply (after Galloway, 1989). (a) A
rise in relative sea level causes an
increase in topset accommodation
volume ΔVta, equal to the product
of the relative sea-level rise and
the topset area; (b) Stratigraphic
patterns change from transgressive
to retrogradational, aggradational,
and progradational as the sediment
supply increases relative to the
topset accommodation. White
cicles approximate position of
beach (or offlap break).
Shoreline movements
Transgression:海進(海岸線往內陸移動)
Regression:海退(海岸線往海側移動)
Sediment accumulation resulting from shoreline
movement
Transgressive deposits: 海進堆積物(特指薄層海進殘
留物transgressive lags)
Retrogradation:進積
Aggradation:垂直加積
Progradation:外伸
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7.6 Numerical Simulation of Stratigraphy
Quantitative modeling of the filling of sedimentary basins was begun in 1960s.
The goal of modeling is to generate insight.
http://sedpak.geol.sc.edu/doc/help/
Chap1.html
Reading: Paoloa, C. (2000) Quantitative models of sedimentary basin filling.
Sedimentology, 47 (Suppl. 1), 121-178.
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Traditional Use of Sedimentary
Simulations
Sedimentary process models from outcrops, well
log & seismic cross sections used to:
• Understand complexities of clastic or
carbonate stratigraphy
• Identify & model sedimentary systems.
• Quantify models that explain & predict
stratal geometries within sequences.
• Used by specialized experts who design
& build the simulations.
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Some sedimentary models
• Short-term local events
• SEDSIM (Tetzlaff and Harbaugh, 1989)
• SEDFLUX (Syvitski et al., 1998a; Syvitski et al., 1998b)
Long-term regional events
• PHIL (Bowman et al 1999)
• SEDPAK (Eberli, et al, 1994)
• FUZZIM (Nordlund1999a&b)
• CSM (Syvitski et al., 2002)
• Robinson and Slingerland, 1998
• Steckler et al., 1993.
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Approaches to modeling
Geometric models
• Fixed depositional geometries are
assumed
• Conservation of mass
• Simple computations through general
nonlinear dynamic models
• Variations in depositional geometries
• Variations in surface slope vs
discharge
• More complex computationally
Paola (2000
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Geometric Model
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Eberli, et al, 1994
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Numerical models
9 For carbonates: rely on a carbonate productivity versus
depth function combined with rules for surface transport of
sediments.
9 For siliciclastics: require a linkage between catchment
processes, fluvial transport, and sediment distribution in the
basin.
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Fig. 8.32 Model for the generation of
unforced high resolution cyclicity in
peritidal carbonates, after Burgess et
al. (2001). (a) Illustration of different
processes involved in generating
prograding inter- and supratidal
islands and autocyclic shallowingupward cycles; (b) Depth-dependent
carbonate productivity relationship
and sediment transport rate; (c)
Different stages in the evolution of
prograding islands. Time 1: landward
transport of sediment causes
accretion of inter- and supratidal flat.
Time 2: Continued accretion drives
inter- and supratidal flate
progradation, which causes a
sediment starved leeward side to
develop. Time 3: Sediment starved
lee subsides and prograding island
forms, allowing a new subtidal
carbonate factory to develop. Time 4:
A second island system develops as
the entire process is repeated.
50
Basin Analysis
Dept. Earth Sci., Nat. Central U.
Prepared by Dr. Andrew T. Lin
Fig. 8.33 Carbonate productivity versus depth
from various authors (a), normalized by the
maximum production rate in (b), after Paola
(2000).
51
Basin Analysis
Dept. Earth Sci., Nat. Central U.
Prepared by Dr. Andrew T. Lin
(透光帶)
(無光帶)
Basin Analysis
Dept. Earth Sci., Nat. Central U.
Prepared by Dr. Andrew T. Lin
Fig. 8.34 Carbonate
depositional geometries,
modified after Pomar
(2001). (a) Range of
morphologies from ramps
to rimmed platforms; (b)
Carbonate productivity in
relation to the type of biota.
Variations in the dominant
biota control the water
depth range of maximum
productivity. Ramps may
be distally steepened
where oligophotic
organisms dominate.
52
Fig. 8.35 Examples of a
geometrical 2-D model for
stratigraphy at a passive margin
(after Burgess and Allen, 1996),
showing how depositional
sequences and bounding
unconformities can be simulated.
(a) Movement of the fluvial and
marine profile during relative
sea-level rise and fall; (b)
Computer-generated
stratigraphy with a Type 1
sequence boundary and its
distal marine conformity and a
transgressive ravinement
surface generated during
relative sea-level rise. Small
numbers are chrons.
53
Basin Analysis
Dept. Earth Sci., Nat. Central U.
Prepared by Dr. Andrew T. Lin