7. Controls on Basin Stratigraphy

7. Controls on basin stratigraphy

Driving mechanisms for basin stratigraphy Tectonic mechanism: (a) flexure under Steer’s-head applied loads (rift basin and foreland geometry basin); (b) fault array evolution; (c) in- Elastic plane stress 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

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin • 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin Wedge-shaped basin geometry and progressive stratigraphic onlap of a foreland basin

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 6

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 7.1.3 The flexural forebulge unconformity

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin Forebulge unconformity in eastern Switzerland

Calculated erosion Inherited deeper bathymetry: Bathymetry before orogenic loading no erosion

Observed erosion

Hiatus of the unconformity

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 7.1.4 Foreland basin isopachs and pinch-outs

A A’

Progressive eastward shift of depocenters during Sevier orogeny A A’

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 10

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 11

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 7.2 Tectonic mechanisms: fault array evolution

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 13

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 14

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 15

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 16

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 17

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 sea- level 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 sea- level, 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)

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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).

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin Considering isotasy in eustatic sea level changes

⎛ ρ − ρ ⎞ ⎜ m w ⎟ If ρ = 3.3 g/cm3; ρ = 1.0 g/cm3 ΔSL = S⎜ ⎟ m w The isostatic subsidence of the ⎝ ρw ⎠ 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).

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 mm per 1000 yr. 22

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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. 23

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin First-order (225- 300 Myr) eustatic curve of Vail: due to ridge volume fluctuation.

~ <100 to 150 m above present Maximum sea level: latest Cretaceous (Maastrichtian)

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 現在溫度地質百萬年代年前

全球溫度隨地質時間的變化第四紀

上新世新生代北半球開始發育冰川中新世大片冰帽覆蓋南極洲第三紀漸新世南極洲冰帽開使成形始新世古新世

中生代白堊紀南北極沒有冰帽侏羅紀

三疊紀

古生代二疊紀二疊紀~石炭紀冰河期石炭紀泥盆紀 27 志留紀 Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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) ， 28 造成1萬9千年至2萬3千年的氣候循環 Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 氧同位素,冰帽與海水面變化

冰河期間冰期

海水中的O18/O16比值增加海水中的O18/O16比值減小 29

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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若地球表面平均溫度低，改變南北兩極形成冰川；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

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 turbidity and temperature, and type of biota. 31 Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Vail (1987) Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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. 33

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 Sinusoidal eustatic fluctuation: ⎛ ⎞ h = h0 sin⎜ ⎟ λ: wavelength ⎝ λ ⎠ Adding the tectonic subsidence rate: h0: amplitude a: rate of tectonic subsidence ⎛ 2πt ⎞ (linear) hrel = h0 sin⎜ ⎟ + at t: geological time ⎝ λ ⎠ 34

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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): aλ Ψ = 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin Variations in relative sea level through a cycle of 100 kyr is the dominant signal for the Pleistocene glacio-eustatic fluctuations. eustatic change with wavelength λ and (critical rate of basin subsidence (100 m variations in height) amplitude h0 in a basin for no relative with a linear tectonic sea-level fall) subsidence rate a.

In this diagram, the relative sea- level 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. 36

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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:

-1 • 3.14 mm yr : h0=50 m, λ= 100 kyr -1 • 0.3 mm yr : h0=20 m, λ= 400 kyr -1 • 0.06 mm yr : h0=10 m, λ= 1 Myr 37

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin Considering the effects of sediment supply

Water depth Sediment supply eustasy ⎛ 2πt ⎞ 1 λ ⎧2πt ⎛ 2πt ⎞ ⎫ w(t) = h0 sin⎜ ⎟ + at − s0 ⎨ − cos⎜ ⎟ +1⎬ ⎝ λ ⎠ 2 2π ⎩ 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin Water depth and potential sediment accumulation during a cycle of relative sea-level change with variable tectonic subsidence rate and sediment supply, using the glacio- eustatic function. C B A

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 -1 with a constant maximum sedimentation parameter s0=2 mmyr . 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 water- filled until 40 kyr, after which erosion and sediment bypass take place until the beginning of the next glacio-eustatic cycle. 39

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 -1 -1 illustrations at s0=2 and πmmyr ), whereas at low supply rates (s0=0.1 mmyr ), 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. 40

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 -1 velocity s0, from 0.1 to 5 mmyr . Cycle thickness and water depth trends vary strongly from the thin, sediment starved, -1 deep water case (s0=0.1 mmyr ) with a nonerosional flooding surface as an upper boundary, to the thicker, top-

truncated 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 43

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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. 44

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 47 Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin Geometric Model

Basin Analysis Eberli, et al, 1994 Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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 shallowing- upward 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.

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).

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 (透光帶) organisms dominate.

(無光帶) 52

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin 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.

Basin Analysis Dept. Earth Sci., Nat. Central U. Prepared by Dr. Andrew T. Lin