Stratigraphy-SEQUENCES

1. Stratigraphy:
A Modern Synthesis
Andrew D. Miall

2. The Importance of Stratigraphy
[Stratigraphy supplies unique and essential information regarding:]
(1) Rates of tectonic processes;
(2) Rates of sedimentation and accurate basin history;
(3) Correlation of geophysical and geological events;
(4) Correlation of tectonic and eustatic events;
(5) Are epeirogenic movements worldwide [?]...
(6) Have there been simultaneous extinctions of unrelated animal and plantgroups [?];
(7) What happened at era boundaries [?];
(8) Have there been catastrophes in earth history which have left a simultaneous record over a wide region or worldwide [?]
(9) Are there different kinds of boundaries in the geologic succession [?] (That is, "natural "boundaries marked by a world-
wide simultaneous event versus“ quiet "boundaries, man-made by definition).[question marks added]
Eustasy (yo͞ostəsē)
a change of sea level throughout the world, caused typically by
movements of parts of the earth's crust or melting of glaciers.

3. Plate 276 –
The main parameters controlling depositional
systems are indicated in this sketch.
They are
(i) Eustasy,
(ii) Subsidence,
(iii) Sedimentary Influx and
(iv) Climate.
Landward of the Shelf Break (Depositional Coastal
breaks are not depicted),
the combination of Eustasy and Subsidence can
increase, or Decrease the Space Available for
Shelfal Accommodation Can be Positive or Negative. In
the first case, there is Sedimentation, in the second,
there is erosion.
Assuming that between each chronostratigraphic line
(1 to 29) there is 100 ky, in this sketch Three Sequence
Stratigraphic Cycles are Represented.
However, only the cycle Composed by time lines 6-21 is
complete.
Notice the Unconformities, the Downlap surfaces, as
well as, the time line Terminations.
Controlling Parameters of Sequential Stratigraphy

4. Theoretically, sequential stratigraphy must solve the problems that classical stratigraphic approaches, such as
Lithostratigraphy, Biostratigraphy, Chronostratigraphy, Magnetostratigraphy, etc., can not explain.
It also explains what was already explained by classical approaches, particularly by Transgressive-Regressive Facies Cycles, which is one of the
principal geological concepts resulting from classical stratigraphic studies.
Trangressive/regressive cycles represent an assembled picture of lithofacies in relationship to the shoreline location and its position throughout geological time.
Suess (1888) believed that transgression-regression displacements of the shorelines were caused by Sea Level Changes.
He used the term Eustasy to coin Sea Level Changes, which he believed were global.
However, with time, the eustatic concept became unpopular as studies on different continents showed that transgression/regression facies cycles did not correlate
globally and were mainly due to local uplift and subsidence.
Concerning sea level changes recorded by geologists there is always the question of what actually changed, that is to say, is it the elevation of the continent or the
absolute level of the sea?
After all, wrote MacDougal (1966),
Sediments only record relative changes, and we know that the continents undergo vertical movements.
Rocks high in the Alps and the Rockies contain fossils deposited in the ocean, for example, and we know that
oceans were never that deep”
Geologists have mapped the occurrence of various sediment types almost everywhere on earth in considerable detail. Through synthesis of such data there is now a
fairly good understanding of the magnitude and timing of global sea level changes. If the rock record indicates there have been large changes in sea level, the
obvious question is: Why?
As far as we know there are Really Only Two Possibilities:
A) There must have been Changes in Either the Volume of Water in the Oceans Itself.
B) In the Volume of Other things that Displace the Water, such as Continents, Islands or Ocean Ridges.

5. We know that Glacial Periods are Characterized by Sea Level Lowering.
Large amounts of the earth‘s surface water are tied up in ice sheets on the continents.
It is estimated that at the height of the last glacial advance, roughly 20000 years ago, Sea Level Was Well Over 100 meters Lower Than it is Today.
Although much of that ice is gone, there is still a considerable amount of water frozen in the ice caps.
If all of it were to Melt, Sea Level Would Rise by About Another 65 Meters.
That may not sound like much, but a large fraction of the earth’s population lives close to sea level, Mexico City would be spared, but much of Los Angeles, New
York, Tokyo, and Berlin (to cite just a few examples) would be inundated.
Glacial episodes have a major effect on sea level.
Most fluctuations that are recorded in Phanerozoic rocks don‘t occur at times in which there is independent evidence for global ice ages.
Most likely they were caused by variations in the volume of the oceanic ridges.
In order to achieve global or regional correlations, sequential stratigraphy uses physical criteria to define chronostratigraphic intervals and biostratigraphy to
determine their age.
These intervals are considered genetic, in the sense that the rocks inside them are related by facies and bounded by physical surfaces that are, in part,
discontinuities.
In addition, they are believed to be regional.
Some of them can even be global.
They can be generally mapped within a basin, and sometimes in any basin around the world with a marine base level.
Complex interactions between:
(i) Eustasy, (ii) Tectonic, (iii) Sediment supply and (iv) Climate,
which control the sequential stratigraphic patterns, are recognized in the rock record.
Tectonic and Eustatic Effects cause relative changes of sea level, which control the space available for sediments (accommodation).
Sediment supply controls how much of the accommodation space, created by relative changes of the sea level, is filled.
Tectonics and Climate control the amount and type of sediments.
Each of these parameters has a stratigraphic signature and a certain rate of change, which can be recognized in rock records. P. Vail (1977) assumed that:

6. Eustatic changes have a higher rate of change than the other parameters and control the stratal patterns”
A large majority of geologists agree that long-term eustatic changes are driven by changes in ocean-basin volume and that these changes are induced by
mechanisms of basement movement that act over time periods of tens to hundreds of millions of years and are continental in scope. However, the causes of short-
term sea level changes are still very controversial.
Three Major Factors Determine Eustatic Ocean Level Changes:
(i) Climate changing the ocean water volume.
(ii) Earth movements changing the ocean basin volume.
(iii) Gravitational changes of the ocean level distribution.
Ocean Basin Volume Changes, Controlled by Earth Movements and Ocean Water Volume Changes Mainly Induced by Glacio-Eustasy (Climate), Determine the Ocean Level:
A) The ocean level is not equally distributed but rough and uneven, due to gravity. It forms the equipotential surface of the geoid or the geodetic sea level.
B) The vertical ocean level changes may be caused both by real ocean changes, i.e. true eustasy and by geodetic sea level changes (geoidal eustasy).
‫البحر‬ ‫سطح‬ ‫مستوى‬ ‫بانخفاض‬ ‫تتميز‬ ‫الجليدية‬ ‫الفترات‬ ‫أن‬ ‫نعلم‬ ‫نحن‬
.
‫القارات‬ ‫في‬ ‫جليدية‬ ‫صفائح‬ ‫في‬ ‫مقيدة‬ ‫لألرض‬ ‫السطحية‬ ‫المياه‬ ‫من‬ ‫كبيرة‬ ‫كميات‬
.
‫من‬ ‫يقرب‬ ‫ما‬ ‫منذ‬ ، ‫األخير‬ ‫الجليدي‬ ‫التقدم‬ ‫ذروة‬ ‫في‬ ‫أنه‬ ‫إلى‬ ‫التقديرات‬ ‫تشير‬
20000
‫كان‬ ، ‫عام‬
‫عن‬ ‫يزيد‬ ‫بما‬ ‫اليوم‬ ‫عليه‬ ‫هو‬ ‫مما‬ ‫بكثير‬ ‫أقل‬ ‫البحر‬ ‫سطح‬ ‫مستوى‬
100
‫متر‬
.
‫في‬ ‫المجمدة‬ ‫المياه‬ ‫من‬ ‫كبيرة‬ ‫كمية‬ ‫هناك‬ ‫تزال‬ ‫ال‬ ، ‫الجليد‬ ‫هذا‬ ‫من‬ ‫الكثير‬ ‫اختفاء‬ ‫من‬ ‫الرغم‬ ‫على‬
‫الجليدية‬ ‫القمم‬
.
‫بحوالي‬ ‫البحر‬ ‫سطح‬ ‫مستوى‬ ‫سيرتفع‬ ، ‫ذلك‬ ‫كل‬ ‫ذاب‬ ‫إذا‬
65
‫أخرى‬ ً‫ا‬‫متر‬
.

7. Plate 278-
The Three Ocean Variables are:
(i) The Ocean Basin Volume, which
is a function of vertical and horizontal
earth movements (silting up plays a
minor role),
(ii) The Ocean Water Volume,
mainly determined by climate and
the glacial volume (juvenile water,
water in sediments, water in clouds
and lake volumes play a minor role),
(iii) The Ocean Level, that is to say, the
geological eustatic level, assumed to be
parallel to the Earth‘s ellipsoid, changed
to rough and uneven geodetic sea level,
or equipotential surface of the geoid, due
to gravity irregularities.

8. A) Eustasy or Eustatism
A.1- Eustasy Metaphor
Eustasy can be illustrated by the variations of the level of wine in a cup.
The size of the cup simulates the ocean basin volume (Plate 278), which can be changed by compressing and expanding the cup (earth movements simulation)
causing the rise and fall.
The rise and fall of the wine‘s surface simulates tectono-eustasy.
The wine volume in the cup can be changed by drinking and refilling (climate); giving rise to corresponding rises and falls in the wine level (glacial-eustasy).
Dilatation depending on temperature (which is sometimes advocated) plays no significant role.
Earth‘s movements and climate determine the level of the water in the oceans, that is to say, the eustatic sea level. In the cup, the wine table is not flat but a rough
and uneven one (geodetic sea level), in other words, any change in the gravity gives rise to redistribution in irregularities in the water surface. This metaphor will be
better understood after reviewing the concepts of geoid and eustasy.
PLate 288 - The ocean basin can be considered as a rubber cup of wine: (i)
when you refill it, the wine-level rises, (ii) when you drink it, the wine-
level falls, (iii) when you stretch the cup (shortening), the wine-level rises,
(iv) if you extend the cup (lengthening), the wine-level falls. In addition, if
you take a close look at the surface of the wine, you will see that it is not
flat, but undulated with highs and lows.

9. A.2- Geoid
The geoid is the equipotential surface of the Earth‘s gravity field, which is determined by attraction and rotation potentials.
The ocean geoid is often termed geodetic sea level.
The sea level profiles of the Smithsonian Standard Earth III geoid map are illustrated in Plate 289.
With respect to the Earth’s center, one can note that there is a 180 meter sea level difference between the geoid hump at New Guinea and the geoid depression at
Maldives Islands. In addition, the present geoid configuration is, of course, not stable. It must have changed with changes in gravity and the factors controlling it.
In other words, through geological time, the location of humps and depressions of sea level have changed continuously.
This feature must be taken into account when proposing global stratigraphic correlations.
In fact, the geoid map clearly emphasizes that two areas, not too far apart, can have, at same time, different geological conditions (highstand and lowstand).
A.3- Geoid Changes
As said previously, the best definition of eustasy is simply ocean level changes instead of crustal tectonic and isostatic movements.
However, eustasy was also defined as “worldwide simultaneous changes in sea level”, as distinguished from local sea level changes.
According to Mörner (1976)
The Geoid Changes must be Included Under the General term Eustasy for the Following Reasons:
1) They have a direct effect on Ocean Level Changes and most sea level records are faced with the problem of Separating the
Ocean Eustatic Factor from the Crustal Factor.
2) They affect the Ocean Level Globally (though by different signs) and distinguish from local effects.
3) It will be very hard, almost impossible, to Distinguish them from Glacial-Eustatic and Tectonic Eustatic Changes and
will therefore, at any rate, and in the majority of papers, be included in term Eustatic Changes.

10. Plate 289-
Sea level profiles show strong irregularities.
Sea level is not flat.
Large humps and depressions, related to gravity irregularities and the factors that control them, are quite evident.
Between the highest area, near New Guinea, and the lowest, near Maldives,there is a difference of around 180 m.
So, eustatic sea level changes must take into account local sea level variation induced by gravity anomalies.
On the Earth’s Morphology, Illustrated on the Right,
the amplitude of the undulations is exaggerated by a factor 100000 to the Earth ‘s radius.
B) Eustatic Cycles
Five Orders of Eustatic cycles have been identified in the geological
record (Plate 290).
They have been designated as 1st to 5th order cycles.
The 1st order eustatic cycle corresponds to continental flooding cycles
defined on the basis of major times of encroachment (landward extension) and
restriction of sediments onto the cratons (Plate 291).
They are associated with the break-up of supercontinents (Plate 293).
They are recognized on all continents and are believed to be global.
Their Time Duration is Greater than 50 My, which P. Vail takes as the
minimum duration for a 1st order cycle.
 Since the Phanerozoic Two Eustatic Cycles of 1st Order have
been Recognized in the Rock Record (Plate 290).
 P. Vail (1977) Considered that the Youngest Phanerozoic
1st Order Eustatic Cycle started at the Base of the Triassic and
Extended to Present (more than 200 My).
 The Older Cycle Started in the Uppermost Proterozoic and
Extended to the End of Permian (more than 300 My).
Eustatic Cycles of 2nd to 4th order are believed to be caused by
Smaller Magnitude, but Higher Frequency, and More Rapid
Rates of Eustatic Change.
They cause high frequency variations on the relative change of sea level curve
(Eustasy + Tectonics).
In spite of the fact that time duration of these cycles has changed since the birth of sequential
stratigraphy,
The Majority of Geologists Assume the Following Time Durations:
1) > 50 My for 1st order eustatic cycles,
2) 3-5 to 50 My for 2nd order eustatic cycles,
3) 0.5 to 3-5 My for 3rd order eustatic cycles
4) 0.1 to 0.5 My for 4th and 5th order eustatic cycles
.

11. Plate 290 –
Five orders of eustatic cycles can be recognized on Exxon’s eustatic curve.
Since the Phanerozoic, there are two 1st order eustatic cycles.
The first one defines the Paleozoic and the second one the Ceno-Mesozoic.
The time duration of these cycles is as follows:
1st order > 50 My, 2nd order between 3-5 and 50 My, 3rd order, between 0.5 and 3-5 My, 4th and 5th
order between 0.1 and 0.5 My.
The classification of eustatic cycles in five orders clearly illustrated that P. Vail and co-authors
considered Eustasy as a multi-leveled complex geological structure, in which each eustatic cycle
forms a whole with respect to its parts, while, at same time, it is a part of a larger whole.
Systems thinking paradigm recognizes the existence of levels of complexity in eustasy with
different kinds of laws operating at each level.
At each level of complexity, that is to say at each eustatic cycle, the associated observed
phenomena exhibit properties that do not exist at the lower levels.
In other words, the stratigraphic cycle deposited in association with each eustatic cycle has specific
properties.
Thus, during 3rd order eustatic cycles, stratigraphic cycles dubbed sequence-cycles are deposited.
They are often considered as the fundamental building blocks of the stratigraphy.
The term building blocks suggests a Cartesian approach, which I do not think, was the Exxon‘s
approach.
Indeed, stratigraphy, as a whole, is more than the mere sum of its parts or building blocks.
The 1st order eustatic curve, illustrated on Plate 290, is bimodal:
- It shows high sea level during two geological intervals:
(i) Cambro-Ordovician
(ii) Late Cretaceous.
- These periods have long been recognized as Thallassocratic (craton of an oceanic block).
- They contrast with the widespread Epeirocratic (craton of a continental block) emergences in
the latest Precambrian, Permo-Triassic, and Oligocene-Neogene times.
- Each order of eustatic cycles seems to have a particular cause. The most likely cause of 1st
order eustatic cycles is the Tectono-Eustasy, that is to say, change in ocean basin volume
(believed to be related with the length of spreading ridges).
Indeed, oceanic ridges are thermal bulges that displace seawater.
The landward migration of a ridge increases the volume of the ocean basin and so induces a drop
in sea level.
This argument is readily expanded.
The number of lithospheric plates varies in time, and the total length of the ridges increases with
the number of plates.
It seems likely that the number of plates and the length of the ridge system are maximal during
times of continental dispersal and minimal during times of aggregation.
As illustrated on Plate 291, rapid spreading rates cause broad and high mid-ocean ridges.
Contrariwise, slow rates cause narrow and lower mid-ocean ridges.

12. Plate 291 –
Assuming, since Earth’s formation, the total water volume is constant, a
fast oceanic expansion induces a large volume of oceanic ridges, and so,
sea level rises with the sea encroaching the continents.
Contrariwise, a slow spreading induces a regression of the sea, that is to
say, shorelines are displaced seaward.
During the Phanerozoic, the amplitude of sea level changes seems to be
roughly 300 meters and the rate of oceanic expansion around 1 cm per
1000 years, roughly speaking, the rate of nails’ growth.
Fig. 292-
This sketch illustrates the profiles of fast and slow spreading mid-
ocean ridges, through 70 My of spreading.
In A, a ridge that had been spreading at 6 cm/y, after 70 My, has
one-third of its original volume.
In B, a ridge that had been spreading at 2 cm/y and changes to 6
cm/y increases the volume of the ridge
During times of rapid sea floor spreading the ocean basins are relatively shallow and sea level rises onto continents (transgression).
During times of slow sea floor spreading the ocean basins are deeper.
The seas retreat from the continents, and are restricted to the ocean basins and areas of rapid tectonic subsidence (regression)

13. Pitman (1978) calculated the profiles of a fast and a slow spreading mid-ocean ridge, through 70 My of spreading emphasizing
the changes in the rate of sea floor spreading on eustasy (Plate 292):
- In A, a ridge that had been spreading at 6 cm/y, after 70 My, it has one-third of its original volume.
Epeiric seas return to the ocean basins (regression).
- In B, a ridge that had been spreading at 2 cm/y changes to 6 cm/y.
Such a change increases the volume of the ridge, which displaces water that causes a sea level rise (transgression).
Geologists have assumed spreading rates could change sufficiently to move sea level by few hundreds of meters.
Cretaceous spreading rates are still imprecisely known, and those of the earlier times are probably lost beyond recall.
Relative roles might be played by changes in the ridge length versus changes in spreading rate.
It seems clear that plate activity must have a strong influence on long-term eustasy.
Plate 293 –
The majority of the margins limiting a supercontinent are Pacific-type (convergent margins). The break-
up of a supercontinent induces the creation of new ocean and continental divergent margins (Atlantic-
type).
After the maximum dispersion of the continents, i.e., when oceans reach their maximal size, they
become, progressively, smaller and smaller to finally close.
Divergent margins collide against oceanic crust (subduction B-type) or other margins (subduction A-
type), closing the oceans and forming a new supercontinent.
Such a tectonic evolution creates changes in the volume of the oceanic basins which controls 1st order
eustatic cycles and so the lowest hierarchic stratigraphic cycles, as illustrated on Plate 294 and 295.

14. Plate 294 –
As depicted, the Phanerozoic 1st order eustatic cycles are clearly related with the plate tectonic activity.
Indeed, the Paleozoic eustatic high, with a sea level probably 200-250 meters higher than today, took place
around 500 Ma, when the dispersion of Paleozoic continents was maximal.
Similarly, around 91.5 Ma, the Meso-Cenozoic eustatic high corresponds to the maximal dispersion of the
post-Pangea continents.
Contrariwise, sea level was low during the Pangea and Proto-Pangea supercontinents.
Admittedly, such sea level variations were induced by volume variations of the oceanic basins created by
the volume changes of the oceanic ridges.
As shown by Pitman, volume effects are too gradual to be the
principal cause of eustatic changes of 2nd or 3rd order.
They are adequate only to explain the 1st order eustatic cycles,
particularly if the role of continental thickness changes, which can be
regarded as an indirect response to plate activity, is the driving
factor.
Other factors contributing to changes in ocean basin volume are:
(i) Continental collisions.
(ii) Subduction trenches.
(iii) Submarine volcanism.
(iv) Sediment fill.
The combination of all these variables is estimated to cause a
maximum rate of tectono-eustasy around 1.2 to 1.5 cm/ky3.
The 2nd to 5th order eustatic cycles are believed to be caused by
smaller magnitude, but higher frequency, and more rapid rates of
eustatic change.
Such eustatic variations would cause high frequency variations on
the relative sea level curve.
Second order eustatic cycles consist of sets of 3rd order cycles.
According to Vail, a set of 5-7 third order cycles form a 2nd order
cycle with a time duration averaging 5-10 My.
As we will see later, the boundaries of 2nd order eustatic cycles are
characterized by particularly large eustatic falls.

15. Generalized graphic sedimentary logs that summarize deposits produced by different types
of submarine flow (cf. Fig. 5).

16. Figure 1.
Sedimentary logs showing different types of hybrid beds.
(A) Bed 5 in the Agadir Basin off-shore NW Africa.
(B) Clast-poor debrites in the Marnosoarenacea Formation in the Italian Apennines.
(C) Distal lobe of the Mississippi fan in the Gulf of Mexico .
(D) Clast-rich debrites in the Marnosoarenacea Formation.
(E) Jurassic and Paleocene subsurface reservoir units in the North Sea., (vf—very fi ne; f—fi
ne; m—medium; c—coarse; vc—very coarse).
(F) Permian Karoo Group in South Africa.
(G) Dysodilic Shale in the Carpathians in Romania .
(H) Banded slurry beds in the Britannia Formation, North Sea.
(I) Megabed in the Hecho Group, Spanish Pyrenees.
(J) Debrites with low mud content from the Boso Penin sula, Japan.

17. Figure 6.
(A) Simplified summary of the cross-
sectional and planform shape of
hybrid beds containing clast-rich
and clast-poor cohesive debrites
in the Marnoso-arenacea
Formation.
(B) (B) Potential models for the
origin of clast-poor debrites,
which are absent in the proxi-
mal part of the hybrid bed, noting
aspects of the fi eld evidence in
favor (√) or against (X) each of
the models

19. Turbidities and Turbidity Currents from Alpine ‘flysch’ to the Exploration of Continental Margins
In many outcrops of the Alps and Apennines, turbidity sandstone layers of the flysch type are disrupted, intricately folded and occur together with boulders and
blocks of ‘exotic’ lithologies in a matrix of highly deformed clays or shales, often displaying a characteristic block-in-matrix fabric and, on a mesoscopic to
microscopic scale, a scaly fabric (Fig. 2).
These chaotic rock associations contrast strongly with the usually well-bedded classical turbidities successions of Macigno-type or Alberese-type flysch and because
of their ‘‘undisciplined nature of bedding’’ (Hsu¨ , 1974) were called wild flysch by F.J. Kaufmann (in Studer, 1872; Kaufmann, 1886).
Other, more shaly or clayey examples include the Argille scagliose (Bianconi, 1840), Argille varicolori, Argille brecciate and the various so-called ‘chaotic
complexes’ of the Apennines and Sicily and the highly deformed complexes de base underlying the far-travelled helminthoid flysch successions
of the Western Alps and Apennines (Pini, 1999; Camerlenghi and Pini (2009) and references therein).
Two features fed the controversy about the wildflysch from the beginning: the occurrence of exotic, extraformational blocks and the problem of their emplacement,
and the intense deformation of the host sediments, be they sandstone or shale.
In particular, the supporters of the young nappe theory in the Alps, Schardt (1898), Lugeon (1916) and later Tercier (1947), interpreted the wildflysch
as the result of submarine sliding, leading to the mixing of sediments and blocks derived from the front of the advancing thrust nappes, in modern terms as
‘precursory debris flows’ or ‘olistostromes’ (cf. Flores, 1955, 1959; Tru¨mpy, 1960; Elter & Trevisan, 1973).
Other authors (e.g. Beck, 1911; Adrian, 1915; Beck in Lugeon, 1916; Ha¨fner, 1924) stressed the tectonic overprint, already observed by Schardt (1898) and pointed
out that the wildflysch included blocks and slabs of underlying and overlying formations suggesting tectonic reworking and/or tectonic imbrication
(Ha¨fner, 1924; Badoux, 1967).
This tectonic overprint certainly applies in the case of the Kaufmann (1886) type area (see Bayer, 1982).
In the Apennines, where a similar controversy developed, the Argille scagliose were interpreted commonly as being connected to the submarine,
gravitational emplacement of allochthonous complexes (‘orogenic landslides’; e.g. Migliorini, 1948; Merla, 1951) or thrust sheets and only in recent years has the
tectonic imprint been emphasized (see Bettelli & Panini, 1987; Pini, 1999; Bettelli & Vannucchi, 2003; Vannucchi et al., 2003).

20. However, observations in modern oceans suggested that sand was also transported from continents to the deep sea.
Well sorted sands were discovered at abyssal depth by the Gazelle Expedition and the now classical turbidity deposits of the Alpine and Carpathian flysch sequences, that defied an easy interpretation from
the beginning, were interpreted as deep-sea deposits by several late 19th Century authors.
Because of the close association of the flysch deposits of the Apennines with the chaotic complexes of the Argille scagliose, Fuchs (1877a,b) interpreted the flysch deposits in general as
the Eruptive Products of Mud Volcanoes but Admitted that the Sands and Muds Emplaced on the Sea Floor by them could be Redeposited by Currents.
Later, in a fundamental review of ‘modern’ deep-sea sediments, Fuchs (1883) argued for a deep-water origin of the flysch, without, however, mentioning the earlier mud-volcano hypothesis.
Fuchs based this new interpretation on:
• the Generally Fine-grained Nature of the Sediments and the absence of (large-scale) Cross-Bedding (that was named ‘false bedding’);
• the Absence of traces of Birds, Mammals or Reptiles and Mud Cracks;
• the Exclusively Pelagic (ammonites) or Deepsea Organisms (fishes);
• the Occurrence of Sponge Spicules and Radiolarians;
• the Ubiquitous Trace Fossils, Particularly Fucoids (Chondrites) that, in contrast to most authors of the time, were interpreted by Fuchs as burrows;
• Wrinkles on Bed Surfaces (load casts on lower bed surfaces).
The excellent preservation of all these Biogenic or Inorganic Structures Indicated to Fuchs (1883) the absence of Erosion and, therefore, Deep and Quiet Waters.
The mechanisms of Transport, however, Remained unexplained.

22. Fig. 1.
(A) Outcrop of the sandy Schlierenflysch(Paleocene–Eocene) in a landslide scar near Sorenberg, central Switzerland.
This outcrop corresponds, in terms of stratigraphy and facies, to part of the flyschof the Simmental area(Studer, 1827) and was proposed by Hsu ̈(1970) as the
type section of Alpineflysch.
In modern terminology, the exposure shows the alternation of metre-thick turbidities sandstone lobes (thick-bedded sandstone packages) and moreshaly
intervals.
The outcrop is about 120 m wide and the younging direction is from right to left .
(B) Classic example of Northern Apennines calcareous flysch(Alberese-type) characterized by impressively tabular (sheet-like) deposits made up of an
alternation of sandstone (dark), shale (grey) and calcareous(whitish) units (upper Cretaceous Monte Cassio Flysch, Baganza valley, Northern Apennines, Italy).
Farmhouse in the foreground for scale. See text for more details (photograph by E. Mutti)
A B

23. Fig. 2.
(A) The ‘Type Locality’ of the Wild Flysch of Kaufmann, the Lombach creek near Habkern, Bernese Oberland.
Exotic blocks and phacoids of pink hemipelagic marlstones (Couches rouges) are set in a sheared matrix of dark grey
and black shales. Hammer, about 60 cm long, for scale.
(B): Example of Chaotic Rocks
(tectonic mélange) from the Eocene Canetolo thrust sheet (tectonic window of Bobbio, Northern Apennines).
Note folding, disruption and boudinage of turbidity limestone beds enclosed in a predominant and intensely sheared
matrix of dark grey shales . Person (circled) for scale is approximately 1.8 m tall.

24. Fig. 3.
Typical examples of Tertiary sandy flysch of the Northern Apennines, Italy;
(A) Upper Oligocene Macigno
Formation near Mount Marmagna (photograph courtesy of G. Zanzucchi).
The stratigraphic succession, in the background, is about 220 m thick.
(B) Langhian to Tortonian Marnoso-arenacea
Formation near Firenzuola, Santerno valley (photograph by E. Mutti).

25. Fig. 5.
Current Bedding and Graded Bedding (from Bailey, 1936).
New light on sedimentation and tectonics’’ came from Bailey
(1930). Bailey distinguished between
‘Current Bedding’ and ‘Graded Bedding’
(a term introduced by Bailey), this term roughly coincides with the one in
general use today(Fig. 5).
Bailey (1930) thought that the two types of bedding did not occur ‘in
conjunction’ and observed ‘‘that no sandstone I have seen shows both
Graded and Current Bedding’’.
Bailey (1930,1936) interpreted Current Bedding – obviously
meaning Medium-Scale to Large-Scale Cross-Bedding, not ripple
cross-lamination – as typical for Subaerial or Shallow-water Deposition
and the Graded Sandstones which were observed in the
Palaeozoic greywacke formations of Britain as typical of rather Deep water
‘‘to which Sandy material has Penetrated’’, its transport being triggered by
seaquakes.
Graded beds, bounded by a Sharp Lower Contact, were also
observed by Bramlette & Bradley (1940) in North Atlantic
Deep-Sea Cores and Interpreted as ‘‘Material thrown into
Suspension by a Submarine Slump, Carried Beyond the Slide
itself, and Deposited Rapidly’’.
Before Bailey (1930, 1936),
Sedimentary Structures Observed in Turbidities' were
used to recognize the polarity of beds and to
Distinguish Between Lower and Upper bed surfaces
however,
the Mechanics of Their Formation Remained Largely
Unexplained and Their Bathymetric Significance Unrecognized.

26. A
B C
Fig. 7.
(A) Turbidity current in tilted
aquarium’, from Kuenen &
Migliorini (1950, Plate 1A, no
scale given by Kuenen and
Migliorini).
(B) Artificial turbidite ‘beds
showing excellent vertical
grading’, from Kuenen &
Migliorini (1950, Plate 3B).
Centimeter scale on the left.
(C) Bed showing normal grading.
The bed depicts a very distinct
bipartition between a basal, coarse-
grained division and an upper finer-
grained sandy division.
Upper Oligocene to Lower Miocene
Rapalino system, Tertiary Piedmont
Basin, Italy ,Plate 31B; hammer,
about 33 cm , long, for scale).

27. Fig. 8. The Bouma sequence and its ‘depositional cone’ (from Bouma, 1962).
The Bouma Sequence
The Bouma Sequence (Bouma, 1962; Fig. 8),
the summary of the observations of Bouma in the Tertiary turbidities' of the Annot
Sandstone and, to a lesser extent, the sandy flysch formations of the Northern
Apennines, became synonymous with Turbidities and the Standard Model.
approaches were developed to define ‘Proximal’ versus ‘Distal’ turbidity deposits,
i.e. a Means of Recognizing the Products of a Turbidity Current Implicitly Viewed as
an Unsteady and Non-Uniform flow Decelerating with Time and Distance.
By the mid-1960s, the Turbidity Concept had become relatively well-established and
accepted in most of the scientific community, though with some exceptions.
Among them, was Mangin (1962), a brilliant French geologist,
who Argued that the Association of Flute Casts and Bird
Tracks Observed at the Base of Some Graded Beds Near
Liedena in the Tertiary of the Pyrenees would Cast
Serious Doubt on the Deepwater Nature of Turbidities'
(it is now known that those beds were deposited in ephemeral lakes of a
delta plain where Fluvial Floods can form Graded Beds with Sole Marks).
The state of the art of the knowledge of turbidity sedimentation until 1964 was reviewed
extensively in the volume entitled ‘Turbidities'’ edited by Bouma & Brouwer (1964).

28. Fig. 9.
(A) Fluidized flowing grain layer.
(B) Velocity profile of a turbidity current consisting of a basal, fastermoving,flowing grain layer overlain by a
turbulent flow (from Sanders, 1965).
The commonly, and unfortunately, overlooked paper by Sanders (1965) first raised the problem in its real terms and inevitably forced
geologists to reconsider turbidities' within a more complex process–response framework (Fig. 9).
Some of the conclusions of Sanders were probably also inspired by his close co-operation with the great Polish sedimentologist,
a masterpiece on sole marks and some aspects of turbidity deposition).
in ‘hand-specimen’ geology should look at this atlas that shows the deep passion of this great Polish geologist for the sedimentary structures
of turbidity beds.
Sanders argued that only the current-laminated divisions of the Bouma sequence are the deposit of a turbidity current, i.e. a traction-plus-
fallout deposit from an overlying and waning turbulent flow, whereas the Coarser-Grained, Graded and Massive division (division a)
would be the deposit of a faster moving, Flowing Grain Layer, or Inertia Flow, impelled by the Shear Stress Imparted from the
Overlying Suspension (Fig. 9).
Laboratory experiments on turbidity currents, pioneered by Kuenen (1937, 1950),
have been regarded as fundamental to an understanding of the transport and the deposits of these currents which are
inherently difficult to observe in the Recent, mainly because of their episodic and catastrophic nature and the water depth
which they fully develop.
Classic papers by Middleton (1966a,b, 1967, 1970) and Middleton & Hampton (1973) described the way in which these currents propagate as
surges in laboratory experiments and clearly showed how these currents consist of a head, a body and a tail.
Results from flume experiments carried out in the early 1960s and substantiated by observations in modern rivers (see ‘Summary’ in the
seminal publication edited by Middleton, 1965) showed the origin of sedimentary structures formed in sand under conditions of bed load
transport produced by an overlying unidirectional flow at different flow velocity and depth.
Basic concepts such as upper flow and lower-flow regimes and critical and subcritical flows appeared in sedimentology for the first time.
Walker (1967) was the first to attempt to relate the Bouma sequence and its internal divisions to the flow regime concept, though it may be
argued that flume experiments had been devised primarily to study bedload
transport whereas turbidities, if intended in the sense of their original definition, instead had to be considered as the result of traction-plus-
fallout processes from a waning turbulent flow.

29. Further Developments of the Turbidite Concept
Sediment gravity flows and more complex facies schemes
Middleton & Hampton (1973, 1976) first recognized the complexity of facies and depositional
processes of deep-water sediment associated with classical turbidities (those conforming to the Bouma sequence) and
attempted to develop the broader concept of ‘sediment gravity flows’ (commonly abbreviated to ‘gravity flows’).
Four Basic Types of Flow (and, in a more cursory way, their related types of deposit) were identified
According to the Different mode in which Particles can be sustained within each type of flow:
(i) Debris flow (flow strength);
(ii)Grain flow (grain-to-grain collisions);
(iii)Fluidized flow (upward water escapement);
(iv)Turbidity current (turbulence) (Fig. 10A).
At this point, it was recognized clearly by many Researchers that
Turbidities' could no longer be described merely in terms of the Bouma Sequence
and its Derivatives but they also had to include other types of Deposits that were
Observed commonly in the fill of Ancient Turbidity Basins.
Mutti & Ricci Lucchi (1972) set forth a twofold facies Classification Scheme mainly based on
the Tertiary Turbidite Successions of the Northern Apennines and South-central Pyrenees:
The First Classification was purely descriptive and based on Grain-Size, Bed Thickness and Sand-to-Mud ratio;
The Second Classification, which was more interpretative, also included Primary Depositional Divisions and their possible
hydrodynamic interpretation (see also Mutti & Ricci Lucchi, 1975; for an updated interpretation).
The authors first assigned to the turbidity facies spectrum a variety of Sediments Ranging from
Conglomerates to Mudstones and considered Chaotic Deposits (slumps, olistostromes, etc.) and
Thin Hemipelagic Interbeds as Closely Associated with Turbidity Sedimentation
(their ‘associated facies’).
Derivatives of these schemes were provided later by Walker & Mutti (1973) and Walker (1978) who emphasized the
Contrast Between ‘Classical Turbidities’ and Other Types of Re Sediment Facies,
most commonly Coarser-Grained, Showing Departures from the Bouma Sequence (Fig. 10B).

30. Attempts to frame turbidity deposits within process-oriented schemes were those of Mutti (1979) and Lowe (1982) shown in Figs 11 and 12, respectively.
The latter author, in particular, developed a very popular model whereby cohesive debris flows would pass into gravelly highdensity turbidity currents which would,
in turn, transform into more dilute types of flow.
Unfortunately, no detailed data from field studies and stratigraphic correlations were used to support these interpretations.
Most of the above concepts were amply reviewed and discussed by Pickering et al. (1989) in their book on deep-water sedimentation, a sort of summa of what was
known at that time.
Of course, these authors also provided their own scheme of turbidity facies classification (Pickering et al., 1986).
An attempt to provide a turbidity facies classification based on strictly descriptive criteria came from Ghibaudo (1992)
in view of the ‘‘increasing need for computer storage, rapid numerical analysis and comparison of large data sets’’ (Ghibaudo, 1992).

33. Normark (1970)
attempted to develop a depositional
model for modern fans essentially based
on the detailed analysis of relatively
small deep-sea fans from continental
borderland basins and from deep-water
settings offshore of California and Baja
California, Mexico (Fig. 15A).
Independently,
Mutti & Ricci Lucchi (1972)
elaborated a fan model on the basis of
outcrop studies in the Northern
Apennines and the South-central
Pyrenees (Fig. 15B).
Both models of
Normark and Mutti & Ricci Lucchi
became very popular:
the first model was based mostly on
physiography and limited data from
surface sediments, the second model
was based on facies and facies
associations thought to represent slope,
fan and basin-plain sedimentation.
The fan was subdivided
further into inner, middle and outer
fan facies associations.
Normark (1970)
used the term ‘depositional
lobe’ or ‘supra fan’ to define the
lobate deposits formed at the
terminus of the fan valley.
Mutti &Ricci Lucchi (1972)
used the term ‘sandstone lobe’ to
denote meter-thick sandstone
packages thought to have formed
in outer-fan settings away from
feeder channels and contrasted
thinning upward and fining-upward
facies sequences of
channel deposits with thickening-
upward and coarsening-upward
facies sequences of sandstone
lobes, the latter interpreted as the
product of basin ward
progradations (see also
Mutti & Ghibaudo, 1972).
These models, and their somewhat
unnatural combination
suggested by Walker (1978),
formed the basis of subsequent
research for many years and still
are in some use.

35. The concept of flow efficiency was also introduced to discriminate between small and sand-rich systems and large and mud-rich systems.
Efficiency is essentially ‘‘the ability of a flow to carry its sediment load basin ward and to effectively segregate its grain size populations into
distinct facies types with distance’’ (Mutti et al., 1999).
All other things being equal, efficiency seems to depend largely on the amount of fines originally carried by the flow or eroded and re
suspended through bed erosion at the head of the flow.
Fan models and their derivatives became widely accepted in both the scientific community and industry.
Because of their assumed predictive potential, it might be said that these models inspired or were the standard reference for much
hydrocarbon exploration in many basins worldwide, both onshore and offshore, for at least two decades.
Main turbidity elements
Figure 18 shows the main turbidite elements as discussed by Mutti &
Normark (1987, 1991), Normark et al. (1993), and Mutti et al. (1999).
These elements include:
(i) Major erosional features (other than channels);
(ii) Channels;
(iii) Overbank deposits;
(iv) Channel-lobe transition deposits;
(v) Lobes;
(vi) Basin-plain deposits; and in some systems, both recent and
Ancient:
(vii) Mega turbidites; and
(viii)Chaotic deposits may be volumetrically significant.
Many of the above elements have been

37. The origin of turbidity currents: sediment failure and rivers in flood
Turbidity currents can be triggered by many causes, including sediment failure, earthquakes, high rates of sedimentation, tectonic over steepening,
cyclic wave loading and rivers in flood
Herein, the focus is on sediment failures and rivers in flood, apparently the two most common and important triggering mechanisms of submarine landslides
and turbidity currents.
As shown in the scheme of Fig. 19, turbidity currents probably form a broad spectrum of flows ranging from surge-type flows, produced by the
sliding and disintegration of a finite volume of sediment, to sustained flows, i.e. flows with a relatively constant discharge of suspended load
for long periods (Kneller, 1995), probably produced by rivers in flood and/or large and closely following retrogressive slides.
Although the issue of turbidity-current initiation is crucial to an understanding of turbidity facies and facies distribution patterns in turbidity systems, both
recent and ancient, understanding unfortunately remains in its infancy, mainly due to the lack of detailed outcrop studies integrating data from
basin-margin deltas and deeper-water turbidity systems.
Sediment failure
Sediment failure is common all along modern continental margins and contributes large amounts of terrigenous material to adjacent basin floors.
Several examples of this transformation have been reported, particularly from large sediment failures mostly triggered by seismic activity, gas hydrate release
associated with periods of sea-level low stand, or a combination thereof.
o The best-known example of a Turbidity Current generated by an Earthquake is certainly that of the Grand Bank that dates to 1929 .
This current and its deposit have been described in great detail in a number of papers that show the complex process of multiple slope failures following a major
earthquake, initiation of the flow, its phases of erosion, bulking and by pass, and the final deposition in the Sohm abyssal plain with a runout distance in excess of
1500 km and a final volume of some 200 km3.
Similarly huge Late Quaternary turbidity current deposits are, for instance, the Black Shell turbidity in the Hatteras abyssal plain (Elmore et al., 1979), with an
estimated volume of 100 km3 and a run-out distance of at least 500 km, and those of the Balearic and Herodotus Abyssal Plains of the Mediterranean Sea .
The latter, in particular, are very impressive, each involving volumes up to 300 to 600 km3 of re sediment fine-grained sediment.
In reality, the presence of gigantic turbidity current deposits in deep-sea basins related to catastrophic collapses of basin margins is not surprising at all to
stratigraphy's and sedimentologists who are familiar with orogenic-belt geology.
Spectacular examples of one-event mega beds interpreted to be the deposits of catastrophic collapses of basin margins probably triggered by tectonic activity have
been reported, for instance, from the Palaeogene of North-eastern Italy (Gnaccolini, 1968; Catani & Tunis, 2001), the Miocene Marnoso-arenacea Formation,
Northern

38. Sequence-stratigraphic framework of
turbidite deposition
Sequence-stratigraphic concepts – a natural evolution of earlier
seismic–stratigraphic concepts (see above) and the way in which
turbidity systems would fit these new schemes – were
introduced in the extremely influential Society of Economic
Mineralogists and Paleontologists (SEPM) Special Publication No. 42
edited by Wilgus et al. (1988) and in numerous subsequent
volumes .
Most of this work was devoted largely to assessing the exploration
potential and the seismic expression of turbidity systems around the
world.
Sequence-stratigraphic concepts for an interpretation of turbidity
systems are shown in Fig. 21, describing basin-floor and slope-fan
depositional systems as low stand system tracts during the
development of a cycle of relative sea level variation.
The basin-floor fan is thought to be coeval with the basal
unconformity of the depositional sequence to which it belongs (and
therefore the early low stand basin-floor fan has no stratigraphic
equivalent on the shelf) and the slope fan would form immediately
after, during the rapid progradations of a low stand delta under
conditions of much reduced accommodation space.
In general, the basin-floor fan is a sand rich feature, commonly with a
mounded geometry (e.g. Mitchum, 1985), whereas the slope fan is
mud-prone, locally containing ‘shingled’ sandy turbidity's deposited in
a mudstone-dominated delta-slope environment.
Although it does not discuss the sedimentological characteristics, nor
the inferred processes of the deposits, the model certainly offers a
very useful tool to place turbidity systems within coherent
stratigraphic
Fig. 21. Sequence-stratigraphic model for low stand deep-water siliciclastic
systems (from Van Wagoner et al., 1988).
Note the basal sand-rich basin-floor fan with a pronounced mounded external
geometry overlain and down lapped by the mud-rich slope fan.

39. Sediment Waves
1 KM
Fig. 22.
(A) Spectacular Example of a Large Submarine Meandering
Channel in the Joshua channel– leve´e complex, North-eastern Gulf
of Mexico (from Posamentier, 2003).
Note the Similarity with Sub-Aerial Meandering Rivers.
(B) WSW–ENE
schematic cross-section across the Mississippi Fan, showing the
geometry of a typical channel–leve´e complex formed in front of a large and
mature river system (from Weimer, 1989).

40. Meandering Channels, Channel–leve´e Complexes, Ponded Slope Basins, Mass Transport Complexes & Bottom-Current Deposits
From a sedimentological standpoint, deep-water sedimentation of divergent continental margins,as recently depicted by 3D
seismic-reflection studies and marine geological investigations, appears to include depositional and erosional elements most of
which are basically unknown, and certainly under-represented, in collisional basins (and particularly flysch basins).
These elements include:
(i) Spectacular Meandering Channels Extending for Tens and Hundreds of kilometres;
(ii) Huge Channel–leve´e Complexes;
(iii) Ponded Slope Basins Associated with Salt and/or Shale Mobility;
(iv) Thick and Laterally Extensive Chaotic units (mass transport deposits);
(v) Erosional and Depositional Features Produced by Bottom Currents.
Meandering channels and channel–leve´e complexes
Meandering channels are among the best imaged features (Fig. 22A) of modern sea floor channel– leve´e complexes.
The origin and significance of these channels dissecting the sea floor of many modern and buried continental-margin basins are
beyond the objectives of this discussion.
Mutti et al. (2003b, with references there in) have argued that these features may essentially be produced by long-lived, high-
discharge hyper pycnal flows loaded with fine-grained sediment exiting the mouths of large rivers; at a much larger scale, such
features would be reminiscent of the ‘ravins sous-lacustres’ of Forel (1885; see above); in other words, deep-water meandering
channels may have a deep-water ‘fluvial’ component in their origin and would record the motion, erosion and deposition of
submarine sediment gravity flows generated by rivers in flood.
Similar large volume flows, derived from glacial outwash in the Var River and mainly loaded with fine-grained sediment, have been
described from the Late Pleistocene of the Var deep-sea fan by Piper & Savoye (1993).

41. Fig. 23.
Example of a Mudstone-dominated pro Deltaic slope wedge from the Lower
Eocene Castissent Group, South-central Pyrenees.
(A) General View Showing the Alternation of Thin-Bedded to very thin-
bedded mudstones and sandstones characterized by the common
occurrence of slump deposits (white arrow) ,Dog (circled) for scale.
(B) Close-up Showing Closely Spaced Millimetre-Thick
Sandstone/Mudstone Couplets.
Sandstone
is very fine-grained and either horizontally or ripple-laminated.
These couplets are thought to be the deposit of buoyant plumes and
dilute hyperpycnal flows .
These Mudstone
-dominated delta-slope deposits represent the distal depositional zone of
flood dominated river systems and should not be mistaken for overbank
turbidities. Coin, diameter about 1 cm, for scale.
A
B

42. Fig. 24. Scheme showing the main elements of a foreland basin and the relationships between a growing orogenic wedge and the outer flexed board .
The entire flexural basin, which links the growing orogenic wedge and the outer board, is referred to commonly as ‘foreland basin’.
The basin can be further subdivided into wedge-top basins formed on the growing wedge and a fore deep.
The axial zone of the fore deep is the depositional zone of the classic sandy flysches from which the concept of turbidities was developed.
The inner fore deep, which lies unconformable on the frontal thrust zone of the orogenic wedge, is the typical site of formation of the wildflysch (compare with Fig. 27)
Note that the slope region, connecting the inner fore deep to the axial fore deep, has a typical above-grade profile with accommodation controlled by thrust
propagation (see text for more details).
Note also that the ‘mixed systems’ of wedge-top basins show a close stratigraphic association of turbidite and deltaic deposits.

44. Fig. 26.
Spectacular exposure of the Proterozoic Zerrissene turbidite complex in the Namib desert.
Beds are vertical and the younging direction is from left to right.
The exposed section, some 1000 m thick, consists of at least three turbidity systems (in the sense of Mutti & Normark, 1987),
each of which includes a lower sandy member overlain by a predominant shaly member.
Lower sandy members are made up of turbidity sandstone lobes each characterized by an impressive tabular geometry over a
distance in excess of 100 km.
Individual metre-thick sandstone lobes are separated by more shaly packages of similar thickness.
The weathering profile of the exposed succession depicts a spectacular sedimentary cyclicity at different physical (and
temporal) scales.
Low-frequency cyclicity controls the stacking of the depositional system and is here interpreted as related to tectonic cycle of
uplift, relaxation and denudation in the source area.
High-frequency cyclicity, which is evident within each sandy member, is expressed by the alternation of sand-rich and muddier
packages and is interpreted herein as related to climatic and eustatic cycles in the Milankowich range (for a discussion see
Mutti et al., 1996, 1999, 2003b) (photograph by E. Mutti).

45. This kind of turbiditic body is quite distinctive of Alpine–Apenninic settings and its features can be summarized as follows:
1- Layers made of limestone-shale or limestone– marl couplets.
2- Fine-grained calcareous detritus, mostly intra basinal in character (coccoliths mainly).
3- Distal signature in terms of Bouma sequence (base-missing, laminated beds), with the exception of 4 below.
4- Individual layers thicker than typical (megabeds), tabular and laterally continuous (as far as continuity can be checked, within limits of tectonic fragmentation)
which show a mixed composition (Mutti et al., 1984; Fontana et al., 1994; Zuffa et al., 2002).
The layers start with a terrigenous fraction at the base and grade upwards into fine-grained carbonate.
5- Occurrence, in minor amounts, of siliciclastic beds whose petrographical composition indicates thrust units or uplifted basement rocks as sources.
6- Alternation of turbiditic layers with hemipelagic shales or mudstones, lacking indigenous fauna or containing only arenaceous foraminifera (Rhabdammina fauna).
7- Association with ophiolites included both as displaced blocks in ‘basal complexes’ and intra formational olistostromes and as clastic particles (Abbate et al., 1970).

46. Fig. 27.
(A) Model for the origin of a Melange Complex in a foreland basin as suggested by Vollmer
& Bosworth (1984).
Turbidity Currents and Slumping (single arrows) deliver sediments to the foreland basin.
Coarse Material (Pebbly and Boulder Mudstones-Stipple Pattern) is deposited near active
Fault Scarps, where it is progressively incorporated into an evolving Melange Zone.
Shearing across the Melange Zones (paired arrows) results in progressive boudinage
and eventual disruption of the bedded flysch sequence, producing the bulk of the melange blocks
and clasts.
Slaty and phacoidal cleavage is interpreted to form coevally, in differing deformational
environments.
(B) Model Derived from the Northern Apennines, showing how, in a Continent–Continent
collision zone, Submarine mass flows are Deposited in front of the advancing thrust sheets and
are Subsequently Incorporated into Evolving, tectonically controlled melange zones
characterized by a Stack of Thrust Sheets.
The Advancing Thrust Sheet is the Eocene Canetolo Group (Subligurian Unit) entering the Late
Oligocene Macigno basin.
Note that the so-called ‘precursory’ Olistostromes (see text) are interpreted by Elter &
Trevisan (1973) as submarine slides detached from the frontal part of the thrust sheet along low-
angle rupture surfaces.
Macigno
Olistostromi
Macigno
Macigno
Macigno
Macigno
Macigno
Turbidity Currents and Slumping
Melange
Zones

47. Fig. 13. (A) Framework for a predictive classification scheme of turbidite facies (slightly modified from Mutti, 1992; for a more updated
version, see Mutti et al., 2003b). (B) Main erosional and depositional processes associated with the downslope evolution of a turbidity current
(from Mutti et al., 2003b).
The facies observed within the same bed (or within the same bedset in the sense of
Campbell, 1967), i.e. along an ideally synchronous depositional profile reconstructed
through detailed stratigraphic correlations and palaeocurrent directions, has been referred
to as a ‘facies tract’ (Mutti, 1992) and is thought to represent the deposit of the same flow
or similar flows undergoing transformations along its (their) downslope direction of motion
(Fig. 13).
The importance of this approach was first perceived by Aalto (1976) in a sedimentological
analysis of the Franciscan me´lange of Northern California and was used extensively for the
first time over long distances (tens of kilometres) in the Chloridorme (Enos, 1969) and
Marnoso-arenacea Formations (Ricci Lucchi &
Valmori, 1980). The approach is time-consuming because it requires extensive and careful
fieldwork.
Fig. 14.
(A) Example of a bipartite turbidity current reproduced in laboratory experiments
(inspired from Mohrig & Marr, 2003);
(B) graded bed deposited by a bipartite turbidity current exemplified by the classic Bouma
sequence.
It should be noted that in (A) all the sediment grains of the dense flow are fine enough
to be incorporated within the overlying turbulent suspension (turbidity current s.s.);
most commonly, however, part of the grain-size population of the dense flow is too coarse
to be transported in suspension, thus forming a residual deposit bypassed by the flow (see
Mutti et al., 1999, 2003b, for a detailed discussion).
A B

48.  In this tentative interpretation, the
sedimentary packages correspond
to stratigraphic cycles,
i.e., sedimentary intervals deposited during
eustatic cycles.
o In the upper part, where the rate of
deposition was quite high, stratigraphic
sequence-cycles (associated with 3th order
eustatic cycles) can be recognized.
On the contrary,
o in the lower part, and particularly
during Mesozoic time, the seismic intervals
are too condensed.
As a result, only continental encroachment sub
cycles, associated with 2nd order eustatic
cycles, can be interpreted.
Actually, as we will see later, the large majority
of the seismic line cannot be interpreted in
terms of sequence-cycles.
So, in these notes,
 the title Seismic-Sequential Stratigraphy
seems preferable rather than Seismic-
Sequence Stratigraphy.
The proposed fault planes correspond to
seismic surfaces.
On a seismic line rarely a fault plane is shown
by a reflector but when it is injected by salt,
volcanic, or when it correspond to an interface
between sediments and a basement.

49. This Interpretation of a Seismic Line of the Onshore
USA was Performed at a high Hierarchic level
(sequence-cycles).
The post-salt interval was interpreted in stratigraphic
sequence-cycles, which are deposited during 3rd
eustatic cycles.
Each of these cycles is bounded by unconformities.
The time-interval between the lower and upper
unconformities ranges between 0.5 and 3-5 My.
Such a time-interval should not be confounded with
the total time-deposition of the sediments composing a
sequence-cycle (the completeness of the different
systems tracts making up a sequence-cycle is rarely 1).
From Bottom to Top, each Sequence-Cycle, when
Complete, is Composed by :-
(i) Low Stand systems tract (LST), in purple on the
interpretation,
(ii) Transgressive systems tract (TST), in green,
(iii) High stand systems tract (HST), in orange.
 Three Members can be often
Subdivided into Lowstand Systems
Tract (LST):
1- Basin floor fan (BFF) at the bottom,
2- Slope fan (SF) in the middle and
3-Lowstand prograding wedge (LPW) at the top.
A systems tract is a lateral linkage of contemporaneous
and genetically related depositional systems.
Do not forget that, by conventional My (millions years)
means an internal of time, while Ma, as for instance SB.
30 Ma, is an age, in this particular case the age of a
stratigraphic cycle boundary.

51. a) The cyclicity of the data.
b) The downward shifts of coastal onlaps.
c) The sequence-cycle boundaries (associated with 3rd order eustatic cycles).
d) The lowstand and highstand deposits.
e) The regression/transgression cycles (Genetical Stratigraphy);
f) The maximum flooding surfaces.
g) The most likely location of the potential source-rocks.
h) The most likely location of the potential sandstone reservoir-rocks.
i) The most likely location of the potential seal-rocks.
j) The most likely potential of the potential stratigraphic traps, etc.

52. 2- Thrusting Model (Plate 24)
In a thrust or reverse fault,
the sediments of the up thrown block
(hanging wall) are shortened and uplifted,
whereas those of the downthrown block
(footwall) are relatively undeformed.
• In such conditions, as illustrated on Plate 24,
• the Hanging wall Sediments are Denser
than those of the Downthrown Block.
In addition, as the hanging wall sediments are
shortened, by folding, the structures’ heart is
denser.
The gravimeter response of such a geological
structure is shown on Plate 24,
where a strong positive anomaly correlates
with the up thrown block
Plate 24- Geological model and gravity response for a thrust fault (or reverse fault), in
which the density difference between the Hanging wall and the Footwall is d = 0.13 g/cm3.

53. 3- Normal Faulting (Plate 25)
During an extensional tectonic regime (a vertical 1), the sediments are
lengthened:
(i) lengthening is made by normal faults,
(ii) normal faults strike parallel to 2, i.e.the intermediate effective stress,
(iii) hangingwall sediments are buried deeper than those of the upthrown
block, hence density will be higher due to a stronger compaction.
In a Pre-Compaction Normal Faulting:
(i) Density and velocity of sediments of the downthrown blocks
are higher than those of the up thrown blocks,
(ii) When the amplitude of the vertical throw is big enough, the
associated lateral changes in density and velocity will create
relatively important gravimetric anomalies.
Fig. 25- In normal faulting, the hanging wall sediments are denser than the sediments of the up thrown block.
Hence, as illustrated in the gravimetry profile, the associated gravimetric anomaly can be relatively sharp.

54. 4- High Density Beds (Plate 26)
In a geological model with high-density beds, the dips of
the sedimentary beds can range from 10° to 60°.
Assuming that sedimentary tilting is pre-compaction, there
are lateral changes in density and velocity.
Higher are the dips of the beds, the bigger
are the lateral changes in density and
velocity.
Lateral contrasts are big enough to create sharp gravity
anomalies, as illustrated below.
Plate 26-
On this geological model, the dips of the strata increase in depth.
Hence, due to compaction, one can say that average density and
acoustical impedance increase too.
So, gravity anomalies can be associated with such a tectonic behavior.
In Conclusion:
- Gravity maps are seldom used for detailed interpretation.
- Seismic surveys are generally more useful for detailed
studies in Small Areas.
- Like Magnetic, gravity maps are useful to show the broad
architecture of sedimentary basins.
- In Gravimetric, Low-Density Depo centers appear as
Negative Anomalies (Salt Domes, Rim Synclines).
- Buried hills of Dense Basement rock, in gravimetric, show
up as Positive Anomalies.

55. Plate 51-
This line corresponds just to an enlargement
of the line illustrated on Plate 50.
It shows a transgressive back stepping-
interval (in green) thinning seaward.
Such a thinning corresponds to a lateral
change in facies and so, in velocity.
The different time-thickness of this
transgressive calcareous interval,
drilled in ASH-2 and ASH-21, readily explains
why the highest time-structural point of the
potential reservoir (lower green marker)
does not match with the highest depth-
structural point:
the seismic waves do not travel at the same
velocity in limestones and slope shales.
The markers below the slope shales are
pulled-down.

56. Plate 61-
This old unmigrated line from offshore Angola,
where a Cretaceous evaporitic salt layer was
deposited near the bottom of the Atlantic-type
divergent margin, strongly increases the
complexity of the data.
Halokinesis, associated with an extensional
tectonic regime, developed a sharp tectonic
disharmony at the base of the evaporates.
The sediments overlying the evaporates are quite
deformed, while the infra-salt strata are almost
un deformed.
This tectonic disharmony does not correspond to
a major stratigraphic boundary.
In other words, the segmentation of the Atlantic
margin sediments into supra and infra-salt strata
is a tectonic division.
It does correspond to any major stratigraphic
feature.
The salt induced tectonic disharmony is much
more evident in migrated data as illustrated on
Plate 62.
Notice that the lower part of the major listric
fault zone is filled by salt, which is enhanced by a
non chronostratigraphic seismic reflector.

57. Plate 62-
The migrated version of the previous line,
illustrated above, in which the majority of the
diffractions have disappeared, depicts much
better the seismic surfaces (surfaces defined
by the reflection terminations) than the
un migrated version Plate 61).
The tectonic disharmony, at the bottom of the
evaporitic interval, is quite evident.
Similarly, the geometric relationships and the
internal configuration in the extensional anti
form, developed in the hanging wall of the
listric growth-fault, are readily recognized.
Also, it is easy to notice that, at the present
time, the evaporitic interval is not continuous.
A salt roller (in the lower part of the listric
fault) separates two quite evident salt welds.
As theoretically expected, the sediments
underlying the tectonic disharmony are almost
un deformed, which contrasts with the post-
salt sediments.

58. Plate 63-
This depth-migration version of the previous
seismic line is at natural scale (1:1).
Theoretically, the dips of the reflectors correspond
to the real dips of the bedding planes.
Similarly, the dip of the listric fault plane is real.
However, as you already probably noticed, this
depth conversion is not perfect.
The salt-induced tectonic disharmony should be
more or less flat (dipping slightly seaward) and not
undulated, as illustrated above.
Actually, when this depth-migration conversion
was performed, explorationists, due to raft-
tectonics, did not properly control the velocity
intervals in offshore Angola.
Due to halokinesis, in which tectonic inversions are
frequent, the majority of the geometrical
relationships (reflection terminations) are
apparent.
Indeed, as we will see later, the reflection
terminations on the tectonic disharmony are not
down laps but tilted on laps.
In other words, the reflection terminations are not
pristine, but deformed by salt flowage.

59. Plate 64-
The previous depth migrated line is here
illustrated with a vertical exaggeration
of 2.5 times.
Explorationists and particularly those
using workstations or PCs for
interpretation of seismic data should
never forget that Geology is scale
dependent.
Indeed, a progradations, for instance,
can be interpreted as a continental
slope or as deltaic slope (pro delta);
it depends on vertical and horizontal
scales.
On the other hand, geological laws, as
Goguel’s law, Anderson’s fault law, can
only be applied at natural scale data.

60. Plate 74-
This unmigrated seismic section shows a great number of
diffraction patterns pointing to the existence of a
discontinuity between two fault blocks.
On the left block, it should be noticed that diffraction
amplitudes are greater that reflection amplitudes.
On the lower left corner, the right leg of a diffraction is
probably originated from a point located off the plane of the
section.

61. Plate 75 –
On this unmigrated seismic line
from Labrador Sea (Atlantic-
type margin overlying rift-type
basins) parasites (in yellow),
induced by an iceberg, are quite
evident.
Indeed, at the time of shooting,
an iceberg was located no more
than 1000 meters from the
seismic vessel.
Diffractions associated with the
top of the basement
(Precambrian supracrustal
rocks) are also quite visible.
Notice that, on the migrated
version of this line, the
downward hyperbolic geometry
of the parasites chances into an
upward hyperbolic geometry.
Parasite diffractions can be
associated with:
(i) Airwaves,
(ii) Surface waves,
(iii) Ambient noise (sea, wind, boats,
icebergs, etc.).

62. Plate 76-
This table gives some of the criteria useful to
interpret hyperbolic patterns on an unmigrated
section.
The elements considered here are the polarity (as
it changes from one leg of the conic to the other)
and the curvature as compared to the NMO
(normal move-out) hyperbola at the same depth.

63. Plate 77-
The presence of superposed hyperbolas on a seismic line
may assist in correctly interpreting a fault or a flexure.
In the case of a fault (on the left), hyperbolae line up
vertically over the intersection of the fault plane with the
plane of the section.
In the case of a flexure, two sets of displaced hyperbolas
pinpoint the top and the base on the flexure.
o Interpreters should not forget that vertical normal
Faults do not Exist in Geology.
Only very locally, the geometry of a normal fault plane is
vertical.
Indeed, the aim of a Normal Fault is to Lengthen the Sediments.
 Hence by definition, the Dip of a Normal Fault Must Increase
with depth, that is to say its hade (angle with the
vertical measured perpendicular to strike) must
increase, in order to length the sediments.
In addition, as the compressional wave velocity of the
sediments increase with depth, and seismic lines are
time-profiles, in a seismic line all fault planes must flatten
in depth.

64. Canyons
Submarine canyons, when not filled-up by sediments, induce important lateral velocity changes due to different properties of water and sediments.
Plate 112 shows the pull-down anomaly of the reflections underlying the bottom of the submarine canyon.
The geological depth interpretation is illustrated in the lower part of the figure and the more likely seismic response (unmigrated line) on the right part.
Plate 112- Canyons (submarine valleys) when unfilled by
deep water sediments, induce obvious seismic artifacts.
In fact, they create sharp lateral changes in the
compressional wave velocities (water versus sediments). On
a seismic line, when the markers directly below a submarine
valley show a synform geometry, the most likely hypothesis is
that such a geometry is induced by the lateral velocity
change between the water and sediments.
Note, the term canyon is often misleading.
In Geology, a channel is a linear current mark, larger than a
groove, produced on a sedimentary surface parallel to the
current, and is often preserved as a channel cast.
However, very often, petroleum geologists use the term
channel to express its sedimentary filling.
Indeed, and particularly, in deep offshore Angola, the filling
of turbidity submarine valleys are the most likely prolific
reservoir-rocks, explorationists have a tendency to name
turbidity channels the on lap filling of the submarine valleys.
In fact, the infilling of a submarine valley does not follow the
basic principles of the infilling of distributary valleys.
The filling of submarine valleys largely postdate the erosional
events.
On the other hand, the filling corresponds to the stacking of
instantaneous but quite time-spaced geological events, i.e.
gravity currents.

65. The velocity model and the seismic response of a geological model, in which a submarine canyon erodes the
surrounding sediments is illustrated below.
The seismic response is also illustrated below (Plate 113).
It was determined using the wave equations software.
Plate 113-
In the velocity model, illustrated above (left part of the figure),
there is no lateral changes in the Compressional Wave Velocity.
Only the concave geometry of the submarine valley induces local
velocity changes, which on the seismic response are represented
by the slight pull-down of the seismic reflector underlying the
submarine channel.
However, as depicted on the seismic line illustrated on
Plate 114, the seismic is not so obvious as above, since real
undulating seismic reflectors can be pictured, on a time-profile
(unmigrated or migrated) as horizontal.

66. Plate 114-
On this seismic line, from the deep offshore Angola, a typical seismic artifact, induced
by the lateral change in water depth created by the Congo Canyon (in blue), is
illustrated by the horizontal geometry of the yellow marker.
Actually, the horizontal geometry of this marker is apparent.
Theoretically, the change in water-depth, induced by the Congo Canyon, delays, locally,
the seismic waves, hence, all seismic markers below it are pulled-down.
However, as the yellow marker is horizontal, that means, in reality, as in a depth-
converted line, it is concave upward, since the delay of the seismic waves is correct.
In fact, the yellow marker corresponds to the top of an inverted rift-type basin.
Subsequently, a potential structural trap, at the level of the rift-type basin, exists under
the canyon.

67. Plate 117- On this figure a geological model of a synform and its seismic response on an unmigrated seismic line is
illustrated. Notice the geometry of the synform (assuming the synform corresponds to an arc of circle) suggests a circle of
centre above the ground.
Plate 118- In the mathematical model of the previous geological model (circle centre of synform above the ground) the seismic
velocity of the upper interval was assumed to be 2000 m/s. On the seismic answer (unmigrated) the synform marker almost
does not have any “moustache”.
Plate 120- In relation to the previous mathematical model only the curvature of
the synform was changed. In this particular instance the curvature center is
under the Earth’s surface. The seismic response of the synform interface, on an
unmigrated line, strongly suggest a significant “moustache”.

68. Plate 125 –
As illustrated on this photograph, physical strata patterns strongly suggest that
depositional systems are cyclic.
Actually, since the advent of Geology, as a natural science, geologists advanced
several hypotheses to explain such cyclicity.
Eustacy has always been considered as the most likely cause of the cyclicity of
depositional systems (de Maillet, Lavoisier, Lemoine, Burrolet and, recently,
Exxon’s geologists).
Such hypothesis has been tested many times, but, so far, it has resisted quite well
to the refutation tests.
Admittedly, eustacy, that is to say, the global sea level changes can apply just to
sediments deposited under marine influence.
Nonmarine sediments, particularly those laid down landward of the bayline are
out of the scope of eustacy.

69. Plate 126-
The cyclist of the depositional systems recognized on the ground
(Plate 125) is, naturally, depicted on stratigraphic cross-sections.
The section illustrated on this plate comes from an Upper
Ordovician glacial interval, that is to say, from an environment in
which eustacy is meaningful.
In spite of that, four stratigraphic cycles are pictured.
They are bounded by erosional surfaces, which truncate the
underlying strata putting in vertical abnormal superposition
sediments with facies (lithology) and environments quite
different.
In addition, within each cycle, it is possible to identify a lower
thinning and fining upward package, which is overlain by a
coarsening and thickening upward package.
Eustacy, in this particular example (glacial deposit), cannot be
directly invoked as the main cause of the cyclist.
The landward and seaward movement of the glacier is probably
the more likely cause of the observed cyclicity, with glacial
erosion bounding the cycles.
As we will see later, eustacy explains quite well the cyclist
observed in marine sediments.
However, in turbidity depositional systems, deposition takes
place when the space available for sedimentation
(accommodation) increases (relative sea level rise).

70. Plate 127 –
Admittedly, the cyclist and striatal
patterns of marine sediments are readily
recognized on all electric logs.
Similarly, in glacial deposition, as
illustrated here, the correlation between
field stratigraphy and electric logs
patterns are difficult to refute.
Four cycles,
o glacial erosions,
o fining and thinning upward
(transgressive)
o coarsening and thickening upward
(regressive) intervals,
o identified on the stratigraphic section
(Plate 126), are easily recognized on
the electric logs.
o Despite such convincing regional
correlations, it is not astonishing that
some geologists still hypothesize that
eustasy was also active.

71. Plate 128 –
This seismic line illustrates the time stratigraphy
(seismic reflectors are chronostratigraphic lines)
and the cyclicity (eustasy) of the depositional
systems of onshore Algeria.
Time stratigraphy and cyclicity can also be
recognized on the electric logs of the wells
drilled in the area.
The glacial deposits (Upper Ordovician, glacial 1
& 2) depict quite different stratal patterns of
the marine deposits (Cambro-Ordovician,
Silurian and post-Silurian).
Glacial erosional surfaces bounding glacial
cycles look like angular unconformities, while
the limits between marine geological packages
look like eustatic unconformities.
The internal configuration of glacial intervals is
reflection free, while marine intervals have,
roughly, a parallel internal configuration.

72. Plate 130 –
The results of exploratory wells, or the knowledge of the
stratigraphic signature of the area, allow explorationists,
and mainly seismic interpreters, to calibrate seismic
profiles in time stratigraphy.
On this example, taken from deep offshore Angola, the
major unconformities bounding the different seismic
intervals, and down lap surfaces, are calibrated the
according to the stratigraphic signature of the South
Atlantic Margins.
Notice, on the western part of the line, the pull-up of the
bottom of the evaporitic layer induced by the high
velocity (17500 feet/second) of the seismic waves in a
salt layer.

73. Plate 131 –
Here again, it is easy to notice that seismic
reflectors follow chronostratigraphic lines.
Therefore, time-stratigraphy can be performed
using seismic data.
On this seismic profile, coming from offshore
Nigeria, different seismic packages can be
recognized above a granite-gneiss basement.
Rift-type basin sediments deposited during
the lengthening of the lithosphere, that is to
say, laid down before the break-up of Pangea
supercontinent, are separated from the
margin sediments by an angular unconformity
(BUU, Breakup unconformity).
On the margin, different sedimentary
packages can be recognized.
In the upper part, an erosional surface,
probably induced by Upper Tertiary glaciation
(Oligocene ?), eroded the sedimentary time
surfaces creating typically truncated reflection
terminations (see later).
The lower margin sediments look
transgressive, while the upper look regressive.
A major non-depositional hiatus is likely
between lower and upper parts of the margin.

74. Plate 132 –
When seismic data are of good quality, and with
appropriate resolution, as in modern lines of
offshore Mahakam (East Borneo, Kalimantan,
Indonesia),
(i) the strata patterns,
(ii) the geometrical relationships (between
seismic markers)
(iii) the seismic surfaces (hypothetical surfaces
associated with reflection terminations)
allow seismic interpreters to perform quite
detailed time stratigraphy and depositional
analysis.
On this line, for instance, it is utterly easy to see
the theoretical disconformity surfaces separating
the different seismic packages.
Similarly, it is quite evident that certain
depositional packages (seismic intervals) were
laid down not in aggradation, that is to say,
above the previous ones, but much lower on the
seaward side.
Such geometrical relationships, that we are
going to describe and interpret later, correspond
to significant relative sea level falls, which
displace the depositional coastal systems basin
ward and downward.

75. Plate 133 –
Theoretically, seismic markers should
underline significant contrast in acoustical
impedance.
In the 60's seismic interpreters, particularly
Esso’s geologists expected to recognize, on
the seismic lines of Portuguese Guinea, the
progradational delta front reservoirs, since
their acoustical impedance is much higher
than the landward costal silts and seaward
prodelta shales.
However, the well’s results strongly
indicated that the recognized seismic
reflectors, follow time lines (depositional
surfaces), and not facies lines (lithological
changes).
Indeed, as it will be shown later, lithological
predictions using seismic data require a
complete and exhaustive sequential
stratigraphic interpretation.
Seismic interpreter must pick and map
higher hierarchic intervals (systems tract) in
order to approach depositional systems,
which are characterized by a lithology
(facies) and an associated faunal
assemblage.

76. Plate 134 –
This environmental interpretation of the
seismic line illustrated on Plate 133, based on
strata patterns (seismic patterns) and
calibrated by the well results, corroborates the
hypothesis that seismic markers follow
chronostratigraphic rather than facies lines.
On this line, it is quite easy to follow the
successive positions of the depositional
coastal break that, in this particular instance
(basin without continental shelf), coincide
with the shelf break.
So, one can say that near depositional coastal
breaks, delta front sandstones and limestones
were likely deposited, while landward, on the
coastal plain, silts, sands and shales are
predominant.
Seaward of the depositional coastal break, on
the continental and deltaic slope, slope shales
are paramount.
Taking into account the facies (lithology), the
acoustical impedance contrast should
theoretically follow the bleu interval, but as
everyone can notice there is not an associated
seismic marker (see plate 133).
Therefore, lithological predictions, and mainly
reservoir-rocks predictions, cannot be made
by just looking at the seismic line.
They require, as we see later, a sophisticated
method that certain explorations call the
sequential-stratigraphic approach

77. Plate 135 –
When non marine depositional systems are
suspected, or recognized on seismic lines, as
illustrated above, lithological predictions, using
seismic data, still are possible.
This is particularly true when the non marine
depositional systems are under the influence of
relative sea level variations, that is to say, where
eustasy is active.
These types of non marine sediments are
deposited landward of the depositional coastal
break, but seaward of the bay line.
However, in order to make reasonable predictions,
a full understanding of the depositional systems is
required.
On this line, assuming that the erosional surface
was induced by the rupture of the equilibrium
profile of a river, the strata patterns of the filling
intervals are easily interpreted, in lithological
terms, by applying the meander belt and point bar
geological models.
Briefly speaking, seismic interpreters attempting in
advanced lithological prediction must imperatively
know, a priori, the sedimentological models:
Theory precedes Observation.

78. Depositional Model
The sand-shale depositional model used in these notes is the one proposed by P. Vail and coauthors (1977), in which it is assumed that:
1) Eustasy is the main factor driving the cyclicty of the sedimentary deposits.
2) Sedimentary Intervals have high completeness.
3) Eustasy, Subsidence, Accommodation, Terrigenous Influx and Climate are the major geological parameters affecting stratal patterns.
4) Rates of Subsidence and Terrigenous Influx are smaller than the rate sea level changes, i.e., Eustasy.
5) Terrigenous Influx is constant in time and space.
6) Subsidence increases gradually and linearly basin ward.
7) The time interval between each chronostratigraphic line is 100 k years, i.e., depositional events are instantaneous and catastrophic in geologic time.

79. Plate 136 –
On a seismic line, as we will see
later, a sequence-cycle is a
succession of genetically related
reflections bounded by
unconformities or their correlative
conformities associated with the
strata deposited during a 3rd order
cycle of sea level change between
two consecutive relative falls of
sea level (Mitchum et al., 1977).

80. Plate 137 –
Seismic lines, like this one, have confused a
lot of seismic interpreters, who used mega
and super sequences (see Vail et al., 1977)
to advance lithological predictions. They
erroneously considered mega and super
sequences as big sequence-cycles. They
assumed the presence of mega and super-
turbidite intervals, as is the case in a
sequence-cycle.
The basic Exxon depositional model, i.e., the
building blocks of sequential stratigraphy
are the stratigraphic cycles (sequence-
cycles) deposited in association with a 3rd
order eustatic cycle.
Such stratigraphic cycles are composed by
depositional systems tracts, which allow
lithological prediction, since each
depositional system is characterized by a
lithology and an associated typical fauna.
Lithological predictions can be only
advanced when seismic interpretation is
performed at this high hierarchical level.
Stratigraphic cycles associated with 2nd and
1st order eustatic cycles, as illustrated
above, are composed by Aggradational
(global sea level rising) and Progradational
intervals (global sea level falling), in which
several higher hierarchical stratigraphic
intervals can be recognized.

81. Stratigraphic Concepts (P. Vail, 1989)
a) Clastic Sediments are deposited in layers, called Strata or Beds.
This layering results from the tendency of water or wind spreading similar sediment types in a relatively thin sheet over a broad are a during a period of Similar Environmental Conditions.
 When Environmental Conditions Change at the Site of Deposition,
 Several Things may Happen:
 - Different sediment types may be Deposited on Top of the Previous Layer.
 - There may be a period where No Sediments are Deposited.
 - The original layer may be Eroded.
In any event, because of their common Depositional Environment, sediment types tend to be much More Similar Within Layers than Between Layers.
b) Although Sediments tend to be More Similar within a Layer than Across Layers, this Lateral Continuity has Finite Limits.
A particular layer may be (Thin and Pinch Out) laterally, leaving No Particular Record of the Time of Deposition in the pinch out region.
The Sediment Types Characterizing the Layer may Gradually Grade Laterally into other Sediment Types within the Same Layer,
suggesting that Depositional Environments also Change Really in a Gradual Fashion.
C) Certain Combinations of Depositional Environments Foster Abrupt Discontinuity of Layers of Similar Sediment Types.
For instance, River Laid Sands and Shales are Commonly Discontinuous because of repeated channeling and overbank flooding.
Other Environments Lead to More Continuous Layers: Pelagic Shales in Deep Marine Basins are a Good Example.
d) We are Left Then With Layers of Similar Sediments which are of variable lateral extent,
but almost universally have greater lateral extent than vertical, i.e., cross-layer, continuity.
These relationships have useful applications.
e) At the Practical Scale of Well Logs and of Seismic Interpretation
these layers can be correlated to define units of sediments deposited
within a common span of time. Such correlations are called Chronostratigraphic, or more simply time-stratigraphicto distinguish them from
Rock-Stratigraphic Correlations which Define physical units of Common Rock Type Deposited Under a Common range
of Depositional Environments Independent of Layering.
Fig. 138- In stratigraphy, bedded means formed, arranged, or
deposited in layers or beds, or made up of or occurring in the
form of beds. On this photograph, beds are grouped in
formations, which have similar rock-types.

82. Seismic-Sequential Stratigraphy
Geometric Relationships
Plate 141 –
In the next pages, we will review the geometrical relationships (reflection terminations) associated with
stratigraphic cycles and particularly with sequence-cycles, i.e., stratigraphic cycles associated with 3rd order
eustatic cycles also the building block of sequential stratigraphy.
Each geometrical relationship will be defined and illustrated on a regional seismic line.
We will try to explain its meaning in geological terms.
1) Onlap
A base-discordant relation in which initially (deposition time) horizontal strata terminate
progressively against an initially inclined surface, or in which initially inclined strata terminate
progressively updip against a surface of greater initial inclination.
Varieties of onlap are:
(i) Proximal onlap
(ii) Distal onlap
(iii) Coastal onlap
(iv) Marine onlap
(v) Apparent onlap
(vi) Nonmarine onlap
(vii) True onlap
(viii) Tilted onlap (Apparent downlap)

83. Plate 142 –
The Annot sandstones are deep-water
turbidity lobes, which onlap over a
major unconformity.
As illustrated, one can say, the
unconformity (in this case a marine
erosional surface) is fossilized by the
onlapping of turbidity depositional
systems.
As we will see later, in this particular
instance (turbidity deposition), the
onlap relations do not correspond to a
relative sea level rise, but to the stacking
of successive turbidities lobes induced
by gravity currents, which generally
developed during lowstand geological
situations.

84. Plate 143 –
The North Sea is composed of three different
sedimentary basins that are stacked together.
From bottom to top geologists generally have
no major difficulties recognizing a Paleozoic
fold belt (not illustrated on this line), often
considered as a petroleum basement, a
Mesozoic rift-type basin and a Cenozoic
cratonic basin.
On this seismic line, it is easy to recognize
that cratonic Cenozoic sediments onlap
Mesozoic rift-type basin sediments.
Geologists, and particularly seismic
interpreters, using the reflection terminations
of the Cenozoic sediments, consider that an
onlap seismic surface (not emphasized by
seismic reflectors) exists between the
Mesozoic and Cenozoic intervals.
Generally, onlap represents a marine
(or lacustrine) transgression over old
sediments, i.e., a relative sea level rise.
Different types of onlap can be recognized
either on the ground or on the seismic lines

85. Plate 144-
The pristine geometrical
relationships (deposition time) are
often deformed by later tectonic
regimes, as illustrated on this
seismic line from a SE Asia back-
arc basin.
Indeed, it is quite easy to infer
that a compressional tectonic
regime took place after the rifting
phase of the back arc basin.
In fact, the old normal faults of
the rift-type basin were
reactivated as reverse faults tilting
the original geometrical
relationships between the seismic
markers.
When the tilting is strong enough,
onlapping can apparently become
another geometrical relationship,
as it is the case in the orange
seismic interval.

86. f) Well log correlation of chronostratigraphic layers is very dependent on the continuity of sediment types within strata. Seismic correlation, fortunately, gives a
much better view of large scale chronostratigraphic layering in discontinuous sediments than do well logs, but seismic resolution of individual layers is
limited when compared to well logs. Thus the two media should be used as mutually helpful tools for chronostratigraphic correlation. Detailed ties of
individual thin layers from logs to seismic sections is a critical step in the use of the two media.
g) Stratal surfaces typically represent relatively small time-gaps. If the time-gap is large, the surface is called an unconformity. Such a time-gap often receives the
name of hiatus, indicating that it might have represented the time-gap.
h) All unconformities somewhere have a minimum time-gap, often at the slope portion of the basin. It is this minimum gap-time which is the
appropriated age designation for the unconformity. An understanding of the chronostratigraphic correlation sections (see later) are essential to understand
the relationships of physical stratigraphy in a framework of geologic time.
Stratal surfaces implications can be summarized as follows:
a) Stratal surfaces typically represent a relatively small time-gap.
b) If the time-gap (hiatus) is large, the surface is called an unconformity.
c) Stratal surfaces may represent different amounts of time from place to place.
d) Stratal surfaces represent at least some small unit of time common to the surface over its entire extent.
e) The concept of stratal surfaces is completely dependent of the time scale and rock under consideration.

87. Stratigraphic Boundaries (P. Vail, 1989)
 Stratigraphic Boundaries Separate Rocks of Significantly Different Environments or Lithology.
A) Stratigraphic Surface - Continuous Physical Boundary
(i) Stratal Surface
(ii) Discontinuity surface
(iii) Diachronous surface
B) Stratigraphic Boundaries
(iv) Synchronous: Parallel to Stratal surfaces
(v) Diachronous: Step across strata surfaces
 Stratigraphic Boundaries Separate Different Lithologies Resulting from Different Depositional Environments.
They are of two types of continuous physical boundaries:
A) Physical stratigraphic surfaces
B) Litho facies or bio zone boundaries

88. Stratigraphic Boundaries Separate Different Lithologies resulting from Different Depositional Environments.
They are of two types of continuous physical boundaries:
A) Physical Stratigraphic Surfaces
B) Lithofacies or Biozone Boundaries
A) Physical stratigraphic surfaces are of three types:
(A.i) Stratal surfaces
(A.ii) Stratal discontinuities
(A.iii) Diachronous surfaces
(A.i) Stratal Surfaces are Physical Depositional Surfaces Separating Sedimentary Rock Layers.
- They bound laminae, bed and large stratal units and represent periods of non deposition or abrupt shifts in depositional environment.
- They are easily recognized where they separate distinctly different rock types or environments, but the same stratal surfaces may be difficult to recognize
where they bound layers of the same rock type.
- They are the physical Boundaries of Sedimentary Strata and form Practical Geologic Time-Horizons, consequently these are Synchronous Surfaces that
represent (within the limitations of practical subsurface technology) the same instant in geologic time over large areas.
(A.ii) Stratal Discontinuities are physical surfaces caused by Erosion or by Non Deposition.
They include (1) unconformities, (2) disconformities (3) depositional hiatuses.
Unconformity Time-Gaps may Simply Represent
prolonged periods of subaerial exposure with minimal erosion, possibly with local valley or channel down-cutting, or
They may represent periods of uplift and major subaerial erosion of strata, or
They may represent submarine erosion by turbidites, slump or
submarine currents.
Classical Subaerial Unconformities are of Two Major Types:
a) Angular unconformities (Plate 140), with the Discontinuity Surface Created by Truncated Strata Beneath the Boundary.
b) Disconformities (Plate 139) with Beds Parallel Above and Below the Boundary.

89. Disconformities do not show discontinuity patterns, consequently they are recognized either by paleontological evidence of a time-gap or by
tracing regional discontinuity surfaces into the disconformity.
These classic unconformity types remain significant, but we also find discontinuity patterns of
On lap (marine, or lacustrine, transgression of the old sub aerially exposed and gently tilted surface) and
Top lap (rapid progradations of deltaic or bank-edge sediments into the basin from a common depositional surface) commonly associated with
subaerial unconformities.
Submarine unconformities have many of the same discontinuity patterns.
Truncation is created by turbidity and gravity-slump erosion of submarine valleys and canyons.
High energy submarine currents may also produce truncation patterns, although this is usually local and rarely removes
consolidated sediments.
Subaqueous nondepositional discontinuities are time-gaps caused by non depositional or very slow deposition.
(A.iii) Diachronous surfaces are continuous physical boundaries that cross and are essentially independent of stratal boundaries.
These are generally not stratigraphic surfaces and are mentioned here because they are sometimes confused with stratal surfaces.
Litho Facies and Biozone Boundaries may be Synchronous, i.e., the particular Litho facies or bio zone assembly is laterally
continuous within synchronous stratigraphic surfaces.
They may also be diachronous, i.e., they may Step Across Stratal Surfaces in a Transgressive or Regressive Pattern.

90. Plate 139 –
 Time-gap surfaces can be
Bedding Planes, when the time-gap is Small,
and
 Unconformities or Disconformities when the
Time-gap is Significant.
As you will see later,
 unconformities Can be Tectonically
enhanced (angular unconformities) or not.
When they are
 Not Tectonically enhanced,
unconformities are sometimes named
Disconformities as illustrated above.
On these notes,
the term Unconformity will be used for all
Erosional Surfaces induced by Significant
Relative Sea Level Falls.

91. Plate 140 –
The stratal relationships
(Reflection Termination on Seismic Lines),
between
the Marine Diamictites and the
Tannezuft Shales characterize an
erosional surface,
which created a large time-gap or hiatus,
i.e., an unconformity between the
sedimentary intervals.
In addition,
as we will see in next chapter
(geometrical relationships) the stratal
relationships are those associated with
an angular unconformity.