Stratigraphic Surfaces of sequence stratigraphy

Stratigraphic Surfaces

1. GeoHikingClub-2020

2. 2. Stratigraphic Surfaces
Introduction
Types of Stratal Terminations
Truncation
Toplap
Onlap
Downlap
Offlap
Sequence Stratigraphic Surfaces
1.Subaerial unconformity
Type-1 Sequence boundary
Type-2 Sequence boundary
2.Correlative conformity
3.Basal surface of forced regression (sequence boundary type-2)
4.Regressive surface of marine erosion
5.Maximum regressive surface (transgressive surface)
6.Maximum flooding surface
Condensed section at the maximum flooding surface
7.Transgressive ravinement surfacesGeoHikingClub-2020

3. Introduction
Stratigraphic surfaces mark shifts through time in depositional
regimes (i.e.,
Changes in depositional environments,
Sediment loadand/or
Environmentalenergy flux),
These surfaces are created by the interplay of
Base-level changesand
Sedimentation.
These surfaces may or may not be associated with stratigraphic
hiatuses.
May or may not place contrasting faciesin contact across a
particular surface.
The correct identification of the various types of stratigraphic
surfaces is key to the success of the sequence stratigraphic
approach.
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4. Stratigraphic surfaces provide the fundamental
framework for the genetic interpretation of any
sedimentary succession, irrespective of how one may
choose to name the packages of strata between them.
Stratigraphic surfaces may be identified based on a number
of criteria, including;
The nature of contact(conformable or unconformable).
The nature of facieswhich are in contact across the surface.
Depositional trendsrecorded by the strata below and above the
contact (forced regressive, normal regressive, or transgressive),
ichnological characteristics of the surface or of the facies which
are in contact across the surface.
Stratal terminations associated with each particular surface.
Introduction
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5. Stratigraphic surfacesmay generally be classified in
environment-dependent surfaces, which have specific
environments of origin and hence a specific stratigraphic
context (e.g., surfaces of fluvial incision, transgressive wave
scouring, regressive wave scouring).
Geometric surfaces,defined by stacking patterns and stratal
terminations (e.g., onlap surface, downlap surface).
Conceptual surfaces,which are environment-dependent
and/or geometric surfaces that carry a specific significance (e.g.,
systems tract or sequence boundary) within the context of
sequence stratigraphic models (e.g., subaerial unconformities,
correlative conformities, maximum flooding or maximum
regressive surfaces) (Galloway, 2004).
Introduction
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6. Once this sequence stratigraphic framework is established,
additionalsurfacesmay be traced within the genetic units (i.e.,
systems tracts) bounded by sequence stratigraphic surfaces.
Such internal surfaces have been defined as within-trend facies
contacts (Embry and Catuneanu, 2001, 2002), and help to
illustrate the patterns of facies shiftswithin individual systems
tracts.
Introduction
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7. Types of Stratal Terminations
Stratal terminations are defined by the geometric relationship
between strata and the stratigraphic surface against which they
terminate, and are best observed at larger scales, particularly on
2-D seismic lines
Large-scale outcrops (Figs. 2.1, 2.2).
The main types of stratal terminations are described by
truncation,
Toplap,
Onlap,
Downlap, and
Offlap (fig. 2.3). GeoHikingClub-2020

8. Figure2.12Dseismictransectshowingtheoverallprogradationofadivergent
continentalmargin.Theshelfedgepositioncaneasilybemappedforconsecutivetime
slices,andhenceapreliminaryassessmentofthepaleodepositionalenvironmentscan
beperformedwithahighdegreeofconfidence.Theprogradingclinoformsdownlapthe
seafloor(yellowarrows),butduetotheriseofasaltdiapir(bluearrow)somedownlap
typeofstratalterminationsmaybeconfusedwithonlap(redarrows).
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13. Truncation
Termination of strata against an overlying erosional
surface.
Toplap may develop into truncation, but truncation is
more extreme than toplap and implies either the
development of erosional relief or the development of an
angular unconformity.
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14. Seismic reflector termination –Erosional truncation
Erosional truncation between basinward dipping Miocene –Pliocene
strata and overlying horizontal Pleistocene beds. Northern North Sea,
west of Nordfjord, South Norway
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15. Seismic reflector termination –Erosional truncation
Erosional truncation between basinward dipping Miocene –Pliocene
strata and overlying horizontal Pleistocene beds. Northern North Sea,
west of Nordfjord, South Norway
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16. Toplap
Termination of inclined strata (clinoforms) against an overlying
lower anglesurface, mainly as a result of non-deposition
(sediment bypass).
Strata lap out in a landward direction at the top of the unit, but
the successive terminations lie progressively seaward.
The toplap surface represents the proximal depositional limit of
the sedimentary unit.
In seismic stratigraphy, the topset of a deltaic system (delta plain
deposits) may be too thin to be “seen” on the seismic profiles as a
separate unit (thickness below the seismic resolution).
In this case, the topset may be confused with toplap (i.e., apparent
toplap).
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17. Seismic Boundaries
Below Boundary -Truncation of surface
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18. Seismic Boundaries
Channeled
Surface
–Below
Boundary
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19. Seismic Boundaries
Below Boundary -Toplaptermination
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20. Onlap
Termination of low-angle strataagainst a steeper stratigraphic
surface.
Onlap type of stratal terminations may develop in marine, coastal,
and nonmarine settings:
Marine onlap:Develops on continental slopes during transgressions (slope
aprons, Galloway, 1989; healing-phase deposits, Posamentier and Allen,
1993), when deepwater transgressive strata onlap onto the maximum
regressive surface (transgressive surface).
Coastal onlap:Refers to transgressive coastal to shallow-water strata
onlapping onto the transgressive (tidal, wave) ravinement surfaces.
Fluvial onlap:Refers to the landward shift of the upstream end of the
aggradation area within a fluvial system during base-level rise (normal
regressions and transgression), when fluvial strata onlap onto the subaerial
unconformity.
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21. Seismic Boundaries
Over Boundary -Onlap onto surface
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22. Termination of inclined strata against a lower-angle surface.
Downlapmay also be referred to as baselap, and marks the base of
a sedimentary unit at its depositional limit.
Downlap is commonly seen at the base of prograding clinoforms,
either in shallow-marine or deep-marine environments.
Downlap therefore represents a change from marine (or
lacustrine) slope deposition to marine (or lacustrine)
condensationor nondeposition.
Downlap
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23. The progressiveoffshore shift of the updip terminations of the
sedimentary units within a conformable sequence of rocks in
which each successively younger unit leaves exposed a portion of
the older uniton which it lies.
Offlap is the product of base-level fall, so it is diagnostic for
forced regressions.
Offlap
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25. In some instances, the interpretation of stratal
terminations in terms of shoreline shifts is unequivocal,
as for example;
Coastal onlapindicates transgression.
Offlap is diagnostic for forced regressions.
Down-lap (MFS)may form in relation to either normal or forced
regressions.
Evidence of scouring, as indicated by an
Uneven erosional relief
Lag deposits
The presence of offlap at the top of the prograding package would
point towards forced regression.
And coastal aggradation would suggest base-level rise
and hence normal regression.
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26. Figure 2.4 Interpretation of stratal terminations in terms of syndepositional
shoreline shifts and base-level changes. Exceptions from these general trends
are, however, known to occur, as for example fluvial incision (truncation) may
also take place during base-level rise and transgression. Abbreviations: R––
regression; FR––forced regression; NR––normal regression; T––transgression.
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27. The correct interpretation of stratal terminationsis of paramount
importance for the success of the sequence stratigraphic method,
as it provides critical evidence for the reconstruction of
Syndepositional shoreline shifts.
Sequence stratigraphic surfaces.
Identification of systems tracts.
Shoreline trajectories, as inferred from stratal terminations and
stacking patterns, are also important for understanding sediment
distribution and dispersal systems within a sedimentary basin.
This, in turn, has important ramifications for the effort of locating
facieswith specific economic significance, such as
Petroleum reservoirs.
Coal-bearing successions.
Mineral placers.
Advantage of interpretation of stratal terminations
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28. Reflection Terminations
Lap-out
Truncation
Fault Truncation
Mobile Salt Truncation
Top Lap
Base Lap
On-lap Down-lap
Marine On-lap
Coastal On-lap
Tariq Mahmood (2013_OGDCL)
Fluvial On-lap
Stratal Terminations Structural Terminations
Regression/Progradation/Still stand,
angular unconformity/S.B
Transgression/Retrogradation/
Still stand, T.S/MFS/SB
Transgression/Retrogradation/
Still stand/Regression, T.S/MFS/SB
Transgression, TS
Transgression, SB/TS
Transgression, Subaerial unconformity
Salt Diapirism
Modified after Emery and Myers, 1996; Catuneanu, 2006
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29. Sequence Stratigraphic Surfaces
Surfaces that can serve, at least in part, as systems tract or
sequence boundaries, are surfaces of sequence stratigraphic
significance.
Sequence stratigraphic surfaces are defined relative to two
curves;
One describing the base-level changes at the shoreline.
Other describing the associated shoreline shifts (Fig.
2.5).
Base-level changes in Fig. 2.5 is idealized, being defined by
symmetrical sine curves.
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30. Figure 2.5 Base-level and transgressive–regressive (T–R) curves. Sequence stratigraphic surfaces, and
systems tracts, are all defined relative to these curves. The T–R curve, describing the shoreline shifts,
is the result of the interplay between sedimentation and base-level changes at the shoreline.
Sedimentation rates during a cycle of base-level change are considered constant, for simplicity.
Similarly, the reference baselevel curveis shown as a symmetrical sine curve for simplicity, but no
inference is made that this should be the case in the geological record. In fact, asymmetrical shapes
are more likely, as a function of particular circumstances in each case study (e.g., glacio–eustatic
cycles are strongly asymmetrical, as ice melts more rapidly than it builds up), but this does not
change the fundamental principles illustrated in this diagram. Abbreviations: FR––forced regression;
NR––normal regression
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31. Four main events associated with changes in depositional trends
are recorded during a complete cycle of base-level shifts (Fig. 2.5):
Onset of forced regression(onset of base-level fall at the
shoreline): this is accompanied by a change from
sedimentation to erosion/bypass in the fluvial to shallow-
marine environments;
End of forced regression(end of base-level fall at the
shoreline): this marks a change from degradation to
aggradation in the fluvial to shallow-marine environments;
End of regression(during base-level rise at the shoreline):
this marks the turnaround point from shoreline regression to
subsequent transgression;
End of transgression(during base-level rise at the shoreline):
this marks a change in the direction of shoreline shift from
transgression to subsequent regression.
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32. Figure 2.7 Generalized trend of
peat accumulation during the
various stages of a base-level
cycle, in response to changes in
accommodation. See text for
discussion. No temporal scale is
implied for the relative duration
of systems tracts. Abbreviations:
TST—transgressive systems
tract; RST—regressive systems
tract; HST—highstand systems
tract; FSST—falling-stage
systems tract (early lowstand
system); LST—lowstand systems
tract; MFS—maximum flooding
surface; BSFR—basal surface of
forced regression; CC—
correlative conformity (sensu
Hunt and Tucker, 1992); MRS—
maximum regressive surface.
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33. Figure 2.6 Types of stratigraphic surfaces. The seven surfaces are
proper sequence stratigraphic surfaces that may be used, at least in
part, as systems tract or sequence boundaries.
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34. 1. Sub-aerial unconformity
The subaerial unconformity is a surface of erosion or non-deposition created
generally during base-level fallby sub-aerial processes such as
Fluvial incision,
Sediment bypass.
The subaerial unconformity has a marine correlative conformitywhose
timing corresponds to the end of base-level fall at the shoreline (sensu Hunt
and Tucker, 1992).
A small base-levelfallat the shoreline may be accommodated by changes
in channel sinuosity, roughness and width, with only minor incision
(Schumm, 1993; Ethridge et al., 2001).
The subaerial unconformity generated by such unincised fluvial systems is
mainly related to the process of sediment bypass (Posamentier, 2001).
A larger baselevel fallat the shoreline, such as the lowering of the base
level below a major topographic break (e.g., the shelf edge) results in fluvial
down cutting and the formation of incised valleys (Schumm, 1993; Ethridge
et al., 2001; Posamentier, 2001; Fig. 2.8). (Forming Type-1 Sequence
Boundary)
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35. Sequence Boundary
The definition of types 1 and 2 sequence boundaries was first
provided by Vail et al. (1984), for the tectonic setting of a
divergent continental margin. According to these authors,
A type-1 sequence boundaryforms during a stage of rapid
eustatic sea-level fall, when the rates of fall are greater than the
rate of subsidence at the shelf edge.
By implication, as the rates of subsidence decrease in a landward
direction across a continental shelf, the rates of sea-level fall
exceed even more the rates of subsidence at the shoreline, leading
to a fast retreat (forced regression) of the shoreline and
significant erosion of the exposed shelf.
Sea-level fall Subsidence
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36. Type-1 sequence boundary includes a ‘major’ subaerial
unconformity that is characterized by significant erosion and areal
extent across the continental shelf,
A type-2 sequence boundaryforms during stages of slow
eustatic sea-level fall, when the rates of fall are less than the rate of
subsidence at the shelf edge (Vail et al., 1984).
As the rates of subsidence decrease in a landward direction, such
type 2 unconformities are inferred to be associated with very slow
rates of relative sea-level fall at the shoreline (slow eustatic fall
slower subsidence), and as a result with only minor subaerial
exposure and erosion of the continental shelf (Vail et al., 1984).
Sea-level fall Subsidence
Sequence Boundary
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37. Type-2 sequence boundary includes a ‘minor’ subaerial
unconformity associated with minimal erosion and a limited areal
extent.
The lowstand fan systems tract consists of autochthonous(shelf
perched deposits, offlapping slope wedges) and allochthonous
gravity-flow (slope and basin-floor fans) facies, whereas the
lowstand wedge systems tract includes part of the aggradational
fill of incised valleys, and a progradational wedge which may
downlap onto the basin-floor fan (Posamentier and Vail, 1988).
Sequence Boundary
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38. 2. Correlative conformity
The correlative conformity forms within the marine
environment at the end of base-level fall at the shoreline
(sensu Hunt and Tucker, 1992).
This surface approximates the paleo-seafloor at the end of
forced regression, which is the youngest clinoform
associated with offlap, and it correlates with the seaward
termination of the subaerial unconformity (Fig. 2.10).
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39. The correlative conformity separates
Lowstand normal regressive deposits (Younger)
Forced regressive deposits (Older)
In turn, the end-of-fall paleo-seafloor is down lapped by
the overlying prograding clinoforms, but no termination
is recorded by the strata below against this conformable
surface.
This ‘correlative conformity’ has therefore less
potential to be preservedas a conformable surface in
the rock record.
2. Correlative conformity
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40. The main problem relates to the difficulty of recognizing
it in most outcrop sections, core, or wireline logs,
although at the larger scale of seismic data one can infer
its approximate position as the clinoform that correlates
with the basin ward termination of the subaerial
unconformity (Fig. 2.10).
The shallow-marine portion of the correlative
conformity develops within a conformable prograding
package (coarsening-upward trends below and above),
lacking lithofacies and grading contrasts.
2. Correlative conformity
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41. In the deep-marine environment, the correlative conformity is
proposed to be mapped at the top of the prograding and
coarsening-upward submarine fan complex(the ‘basin floor
component’ of Hunt and Tucker, 1992).
At the same time, the correlative conformity is also defined in
relation to general stacking patterns, at ‘a change from rapidly
prograding parasequences to aggradational parasequences’ (Haq,
1991) or at the top of submarine fan deposits (Hunt and Tucker,
1992).
The latter definitions imply a diachronous correlative conformity,
younger basinward, with a rate that matches the rate of offshore
sediment transport (Catuneanu et al., 1998b; Catuneanu, 2002).
2. Correlative conformity
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42. 3. Basal surface of forced regression (Type-1 S.B)
The term ‘basal surface of forced regression’ was introduced by
Hunt and Tucker(1992) to define the base of all deposits that
accumulate in the marine environment during the forced
regression of the shoreline.
The basal surface of forced regression occurs within a fully
marine succession, separating highstand normal regressive
strata below from forced regressive strata above (Fig. 3.3).
Forced regressive strata (Younger)
Highstand normal regressive strata (Older)
On the shelf, both underlying and overlying deposits record
progradational trends, and, within this overall coarsening-
upward succession, the onset-of-fall surface is a clinoform that
downlaps the pre-existing strata.
In turn, the basal surface of forced regression is down-lapped
by the younger forced regressive prograding clinoforms.
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43. 4. Regressive surface of marine erosion (time
transgressive surface)
This ravinement surface is a scour cut by waves in the lower
shorefaceduring base-level fallat the shoreline, as the
shoreface attempts to preserve its concave-up profile that is in
equilibrium with the wave energy (Bruun, 1962; Plint, 1988;
Dominguez and Wanless, 1991; Fig. 2.11).
The amount of erosion that affects the seafloor of shallow-
marine wave-dominated settings during forced regression is
highest in the lower shoreface environment, close to the fair-
weather wave base, and is commonly in a range of meters (Plint,
1991).
Seaward of the toe of the shoreface, erosion is replaced by
sediment bypass and eventually by uninterrupted deposition in
the deeper shelf environment (Plint, 1991).
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44. Figure 2.11 Stratigraphic surfaces
that form in response to forced
regression in a wave-dominated
coastal to shallow-marine
setting(modified from Bruun,
1962; Plint, 1988; Dominguez and
Wanless, 1991). The shoreface
profile that is in equilibrium with
the wave energy is preserved during
forced regression by a combination
of coeval sedimentation and
erosion processes in the upper
and lower shoreface,respectively.
The onset-of-fall paleo-seafloor
(basal surface of forced regression)
is preserved at the base of the
earliest forced regressive shoreface
lobe, but it is reworked by the
regressive surface of marine
erosion seaward relative to a lever
point of balance between
sedimentation and erosion. As a
result, the earliest falling-stage
(early lowstand system)
shoreface deposits are
gradationally based, whereas the
rest of the offlapping lobes are
sharp-based.
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45. LUMSHIWAL FORMATION
LUMSHIWAL FORMATION
Time TransgressiveSurface
Northern Limb of KhanpurDam Area
The sandstone is generally medium grained glauconitic, has been related to
regressive episodes.
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46. Figure 2.14 Well-log expression of the regressive surface of marine erosion(arrows;
modified from Catuneanu, 2002, 2003). Note that the sharp-based shoreface deposits are
thicker basinward relative to the seaward termination of the subaerial unconformity, as
they include forced regressive and lowstand normal regressive strata. Abbreviations: GR––
gamma ray log; LST––lowstand systems tract; FSST––falling-stage systems tract (early
lowstand system); HST––highstand systems tract.
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47. 5. Maximum regressive surface
(Transgressive surface)
The maximum regressive surface (Catuneanu, 1996; Helland-
Hansen and Martinsen, 1996) is defined relative to the
transgressive-regressive curve, marking the change from
shoreline regressionto subsequent transgression.
Therefore, this surface separates prograding strata below from
retrograding strata above (Fig. 2.15).
The change from progradationalto retrogradational
stacking patterns takes place during the base-level rise at the
shoreline, when the increasing rates of base-level rise start
outpacing the sedimentation rates (Fig. 2.5).
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48. Transgressive Surface (TS)
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49. Characteristics of Transgressive Surface
(TS) from seismic
Defined by onlapping reflectors over and onto a
surface (SB )
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50. Characteristics of Transgressive Surface [TS) -
well logs, core & outcrop
Inferred from presence of Glossifungites in this surface)
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51. Where the transgressivemarine faciesare missing, the marine
portion of the maximum regressive surface is replaced by the
maximum flooding surface, and this composite unconformity may
be preserved as a firmgroundor even hardground, depending on
the amounts of erosion and/or synsedimentarylithification.
There are cases where this transgressivewave scouring may
remove not only the transgressivecoastal to fluvial deposits, but
also all underlying coastal to fluvial lowstandnormal regressive
deposits as well. In such cases,
the transgressivewave scour,
the maximum regressive surfaceand
the subaerialunconformity are all
amalgamated
in one unconformable contact (Embry, 1995).
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52. In deep-marine deposits, the maximum regressive surface is most
difficult to identify within the faciessuccession of the submarine
fan complex on the basin floor, because the end-of-regression
event occurs during a stage of waning down in the amount of
terrigenoussedimentthat is delivered to the deep-water
environment.
On continental slopes, the maximum regressive surface is the
youngest progradingclinoformwhich is onlappedby the overlying
transgressive‘healing phase’ deposits (Fig. 2.17).
In shallow-marine systems, the maximum regressive surface is
relatively easy to recognize at the top of coarsening-upward
(prograding) deposits (Figs. 2.16).
Dependingon the rates of subsequent transgression, as well as on
the location within the basin, the maximum regressive surface
may or may not be associated with a
Shale (younger) Low acoustic impedance
Sand (older) High acoustic impedance
lithologicalcontrast. (Good Seismic Reflector).GeoHikingClub-2020

53. Figure 2.16 Outcrop examples of maximum regressive surfaces in proximal shallow-water settings. maximum
regressive surface (white arrow) in a conformable marine succession, at the top of coarsening-upward prograding
shoreface sands. Note that in this case the transition to the overlying transgressive facies is more subtle, and the
facies contact between sand and shale(flooding surface, grey arrow) is above the maximum regressive surface
(top of the Ryegrass Member, Bearpaw Formation, Late Campanian, Alberta, Western Canada Sedimentary Basin).
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54. 6. Maximum flooding surface (MFS)/Downlap
Surface (DLS)
The maximum flooding surface (Frazier, 1974; Posamentier et
al., 1988; Galloway, 1989) is also defined relative to the
transgressive–regressive curve, marking the end of shoreline
transgression(Fig. 2.5).
Hence, this surface separates retrogradingstrata below from
prograding(highstand normal regressive) strata above (Fig.
2.18).
Prograding strata
Retrograding strata
The presence of prograding strata above identifies the
maximum flooding surface as a downlap surface on seismic
data.
The change from retrogradational to overlying progradational
stacking patterns takes place during base-level rise at the
shoreline, when sedimentation rates start to outpace the rates
of base-level rise (Fig. 2.5).
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55. The maximum flooding surface is generally
conformable, excepting for the outer shelfand upper
sloperegions where the lack of sediment supply coupled
with instability caused by rapid increase in water depth
may leave the seafloor exposed to erosional processes
(Galloway, 1989; Fig. 2.19).
The maximum flooding surface is also known as the
maximum transgressive surface (Helland-Hansen and
Martinsen, 1996) or final transgressive surface
(Nummedal et al., 1993).
6. Maximum flooding surface (MFS)/Downlap
Surface (DLS)
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56. Figure 2.19 Stratigraphic expression of transgressive
strata. Note that the transgressive systems tract may
consist of two distinct wedges, one on the continental
shelf and one in the deep-water environment, separated
by an area of sediment bypass or erosion around the
shelf edge.
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57. Maximum flooding surfaces are arguably the easiest stratigraphic
markers to use for the subdivision of stratigraphic successions,
especially in marine to coastal plain settings, because they lie at
the heart of areally extensive condensed sectionswhich form
when the shoreline reaches maximum landward positions
(Galloway, 1989; Posamentier and Allen, 1999).
Such condensed sections are relatively easy to identify and
correlate on any type of data, as they consist dominantly of fine-
grained, hemipelagic to pelagic deposits accumulated during
times when minimal terrigenous sediment is delivered to the shelf
and deeper-water environments.
Condensed sections are typically marked by relatively transparent
zoneson seismic lines, due to their lithological homogeneity.
6. Maximum flooding surface (MFS)/Downlap
Surface (DLS)
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58. Condensed sections are typically marked by relatively transparent
zones on seismic lines, due to their lithological homogeneity.
They also tend to exhibit a high gamma-ray response caused by
their common association with increased concentrations of
organic matter and radioactive elements.
Condensed sections associated with stages of maximum flooding
may contain glauconite and/or siderite, or other carbonates or
biochemical precipitates (Fig. 2.20) which may exhibit a wide
range of log motifs (Posamentier and Allen, 1999).
6. Maximum flooding surface (MFS)/Downlap
Surface (DLS)
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59. Maximum flooding surfaces have a high preservation potential,
being overlain by aggrading and prograding highstand normal
regressive deposits.
It can be identified in all depositional environments of a
sedimentary basin, seaward and landward from the shoreline, on
the basis of stratal stacking patterns.
The broad areal extent, as well as its consistent association with
fine-grained, low energy systems across the basin, makes the
‘maximum flooding’ a surface that is, in many instances, easier to
identify than the subaerial unconformity, and potentially more
useful as a stratigraphic markerfor basin-wide correlations.
6. Maximum flooding surface (MFS)/Downlap
Surface (DLS)
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60. The basin-wide extent of the transgressive tract may, however, be
hampered by the absence of transgressive deposits in the area
around the shelf edge.
For this reason, the transgressive systems tract usually comprises
two distinct wedges;
One on the continental shelf consisting of fluvial to shallow-
marine facies.
And one in the deepwater environment (Fig. 2.19).
Where the transgressive deposits are missing, the maximum
flooding surfaceis scoured and replaces the maximum regressive
surface.
In this case, the maximum flooding surface is associated with a
lithological contrast and separates two coarsening-upward
successions (Fig. 2.21).
6. Maximum flooding surface (MFS)/Downlap
Surface (DLS)
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61. Figure 2.21 Outcrop examples of maximum flooding surfaces (scoured) that
rework the underlying maximum regressive surfaces. The transgressive facies are
missing. A––Young Creek Member (Bearpaw Formation, Early Maastrichtian),
Castor area, Alberta, Western Canada Sedimentary Basin; B––firmground
formed as a result of prolonged sediment starvation (Mississippian Shunda
Formation, Talbot Lake area, Jasper National Park).
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62. Condensed section at the maximum flooding surface
The transgressiveand highstandsystems tracts are bounded by
the maximum flooding surface. This surface commonly occurs
within the top of or at the base of a condensed section caused by
very low sedimentation rates (Loutitet al. 1988).
Condensed sections usually coincide with zones of maximum
diversity and abundance of fossils.
However, in deeper marine areas the fossil tests may be destroyed
or dissolved (below CCD), and a submarine biostratigraphichiatus
may form with associated concentrations of authingenicminerals
such as
Phosphate,
Glauconite,
Siderite,
Pyrite,
Dolomite,
As well as airborne particles such as volcanic ash and iridium.
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63. 7. Transgressive ravinement surfaces
Transgressive ravinement surfaces are scours cut by tides
and/or waves during the landward shift of the shoreline.
In the majority of cases, the two types of transgressive
ravinement surfaces (i.e., tide-and wave-generated) are
superimposed and onlapped by the transgressive shoreface
(i.e., coastal onlap) (Fig. 2.22).
For this reason, the facies that may be found belowa
transgressive ravinement surface are variable, from fluvialto
coastalor shallow-marine, whereas the facies aboveare always
shallow-marine.
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64. Figure 2.22 The transgressive ravinement surface (arrow) separates an iron-rich paleosol horizon
(ferricrete) from the overlying glauconitic marine deposits. The formation of ferricrete is attributed
to the in situ alteration of marine glauconite under subaerial conditions (i.e., a paleo-seafloor
subaerially exposed by a fall in base level; El-Sharkawi and Al-Awadi, 1981; Catuneanu et al., in press).
Note that, in this case, the amount of erosion associated with the subsequent transgressive scouring
is minimal, due to the indurated nature of the ferricrete. However, even though the preserved
ferricrete formed originally as a subaerial unconformity, the presence of marine deposits on top of
this contact qualifies it as a transgressive ravinement surface (where two or more sequence
stratigraphic surfaces are superimposed, we always use the name of the younger surface; see text for
details)
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65. Characteristics of Sequence
Boundary (SB) from seismic
Defined by erosion or truncation of
underlyingreflectors or the correlative
conformity
Can be inferred from onlappingreflectors
overlying a surface
Should the upper surface of a falling stage
system tract be eroded when a shoreline is
forced seaward (a forced regression!) by a
drop in sea level (or base level) the
interpretation of a sequence boundary is
ambiguous.
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66. Characteristics of Sequence
Boundary (SB) from seismic
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67. Classical Cross bedding in the Pab Sandstone, Sulaman Fold
Belt, Middle Indus Basin, Pakistan.
(S.B at the top)
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68. Characteristics of Sequence Boundary (SB) from
well logs, core & outcrop
Defined by erosion or incision of underlying flooding surfaces (mfs and
TS)
Inferred from interruption in the lateral continuity of these surfaces
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69. SAMANA SUK FORMATION
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70. Cross
bedding in
the
Samanasuk
Foamation
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71. Cross bedding
Cross bedding
Flate pebbleCoarsening upward
sequence
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72. Maximum Flooding Surface
(mfs)
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73. Often expressed as a downlap surface.
Characteristics of Maximum Flooding
Surface [mfs) from seismic
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74. Defined as lying immediately below the downlapping
reflectors prograding reflectors of the HST
Characteristics of Maximum Flooding
Surface [mfs) from seismic
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75. Defined by organic often radioactive (big kicks on gamma
ray logs) black shales
Not infrequently overlain by coarser sediments (often sand
sized)
Inferred from presence of condensed faunal association
Inferred from presence of finest grain size
Characteristics of Maximum Flooding
Surface [mfs) from well logs, cores, &
outcrop
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76. Maximum
Flooding
Surface
[mfs)
well logs,
core & outcrop
MFS
After Hanford
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77. High
Low
Time
MRS
MRS
MFS
MFS
CC 1
CC 2
CC 1
Seven Surfaces
1 Sequence boundary (SB-SU)
2 Maximum flooding surface (MFS)
3 Maximum regressive surface (MRS)
4 Correlative Conformity1 (CC1)
5Correlative Conformity2 (CC2)
6Regressive Surface of Marine Erosion (RSME)
7Transgressive Ravinement Surfaces (TRS)
SU
RSME
TRS
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78. Identification of systems tracts on seismic
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