Stratigraphic Surfaces of sequence stratigraphy
- 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 surfaces GeoHikingClub-2020
- 3. Introduction Stratigraphic surfaces mark shifts through time in depositional regimes (i.e., Changes in depositional environments, Sediment load and/or Environmental energy flux), These surfaces are created by the interplay of Base-level changes and Sedimentation. These surfaces may or may not be associated with stratigraphic hiatuses. May or may not place contrasting facies in 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. GeoHikingClub-2020
- 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 facies which are in contact across the surface. Depositional trends recorded 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 GeoHikingClub-2020
- 5. Stratigraphic surfaces may 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 GeoHikingClub-2020
- 6. Once this sequence stratigraphic framework is established, additional surfaces may 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 shifts within individual systems tracts. Introduction GeoHikingClub-2020
- 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. Figure 2.1 2D seismic transect showing the overall progradation of a divergent continental margin. The shelf edge position can easily be mapped for consecutive time slices, and hence a preliminary assessment of the paleodepositional environments can be performed with a high degree of confidence. The prograding clinoforms downlap the seafloor (yellow arrows), but due to the rise of a salt diapir (blue arrow) some downlap type of stratal terminations may be confused with onlap (red arrows). GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 16. Toplap Termination of inclined strata (clinoforms) against an overlying lower angle surface, 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). GeoHikingClub-2020
- 17. Seismic Boundaries Below Boundary - Truncation of surface GeoHikingClub-2020
- 19. Seismic Boundaries Below Boundary - Toplap termination GeoHikingClub-2020
- 20. Onlap Termination of low-angle strata against 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. GeoHikingClub-2020
- 21. Seismic Boundaries Over Boundary - Onlap onto surface GeoHikingClub-2020
- 22. Termination of inclined strata against a lower-angle surface. Downlap may 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) condensation or nondeposition. Downlap GeoHikingClub-2020
- 23. The progressive offshore 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 unit on which it lies. Offlap is the product of base-level fall, so it is diagnostic for forced regressions. Offlap GeoHikingClub-2020
- 25. In some instances, the interpretation of stratal terminations in terms of shoreline shifts is unequivocal, as for example; Coastal onlap indicates 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. GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 27. The correct interpretation of stratal terminations is 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 facies with specific economic significance, such as Petroleum reservoirs. Coal-bearing successions. Mineral placers. Advantage of interpretation of stratal terminations GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 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 curve is 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 GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 34. 1. Sub-aerial unconformity The subaerial unconformity is a surface of erosion or non-deposition created generally during base-level fall by sub-aerial processes such as Fluvial incision, Sediment bypass. The subaerial unconformity has a marine correlative conformity whose timing corresponds to the end of base-level fall at the shoreline (sensu Hunt and Tucker, 1992). A small base-level fall at 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 fall at 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) GeoHikingClub-2020
- 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 boundary forms 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 GeoHikingClub-2020
- 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 boundary forms 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 GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 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). GeoHikingClub-2020
- 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 preserved as a conformable surface in the rock record. 2. Correlative conformity GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 43. 4. Regressive surface of marine erosion (time transgressive surface) This ravinement surface is a scour cut by waves in the lower shoreface during base-level fall at 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). GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 45. LUMSHIWAL FORMATION LUMSHIWAL FORMATION Time Transgressive Surface Northern Limb of Khanpur Dam Area The sandstone is generally medium grained glauconitic, has been related to regressive episodes. GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 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 regression to subsequent transgression. Therefore, this surface separates prograding strata below from retrograding strata above (Fig. 2.15). The change from progradational to 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). GeoHikingClub-2020
- 49. Characteristics of Transgressive Surface (TS) from seismic Defined by onlapping reflectors over and onto a surface (SB ) GeoHikingClub-2020
- 50. Characteristics of Transgressive Surface [TS) - well logs, core & outcrop Inferred from presence of Glossifungites in this surface) GeoHikingClub-2020
- 51. Where the transgressive marine facies are 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 firmground or even hardground, depending on the amounts of erosion and/or synsedimentary lithification. There are cases where this transgressive wave scouring may remove not only the transgressive coastal to fluvial deposits, but also all underlying coastal to fluvial lowstand normal regressive deposits as well. In such cases, the transgressive wave scour, the maximum regressive surface and the subaerial unconformity are all amalgamated in one unconformable contact (Embry, 1995). GeoHikingClub-2020
- 52. In deep-marine deposits, the maximum regressive surface is most difficult to identify within the facies succession 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 terrigenous sediment that is delivered to the deep-water environment. On continental slopes, the maximum regressive surface is the youngest prograding clinoform which is onlapped by 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). Depending on 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 lithological contrast. (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). GeoHikingClub-2020
- 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 retrograding strata 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). GeoHikingClub-2020
- 55. The maximum flooding surface is generally conformable, excepting for the outer shelf and upper slope regions 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) GeoHikingClub-2020
- 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. GeoHikingClub-2020
- 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 sections which 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 zones on seismic lines, due to their lithological homogeneity. 6. Maximum flooding surface (MFS)/Downlap Surface (DLS) GeoHikingClub-2020
- 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) GeoHikingClub-2020
- 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 marker for basin-wide correlations. 6. Maximum flooding surface (MFS)/Downlap Surface (DLS) GeoHikingClub-2020
- 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 surface is 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) GeoHikingClub-2020
- 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). GeoHikingClub-2020
- 62. Condensed section at the maximum flooding surface The transgressive and highstand systems 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 (Loutit et 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 biostratigraphic hiatus may form with associated concentrations of authingenic minerals such as Phosphate, Glauconite, Siderite, Pyrite, Dolomite, As well as airborne particles such as volcanic ash and iridium. GeoHikingClub-2020
- 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 below a transgressive ravinement surface are variable, from fluvial to coastal or shallow-marine, whereas the facies above are always shallow-marine. GeoHikingClub-2020
- 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) GeoHikingClub-2020
- 65. Characteristics of Sequence Boundary (SB) from seismic Defined by erosion or truncation of underlying reflectors or the correlative conformity Can be inferred from onlapping reflectors 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. GeoHikingClub-2020
- 66. Characteristics of Sequence Boundary (SB) from seismic GeoHikingClub-2020
- 67. Classical Cross bedding in the Pab Sandstone, Sulaman Fold Belt, Middle Indus Basin, Pakistan. (S.B at the top) GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 71. Cross bedding Cross bedding Flate pebble Coarsening upward sequence GeoHikingClub-2020
- 73. Often expressed as a downlap surface. Characteristics of Maximum Flooding Surface [mfs) from seismic GeoHikingClub-2020
- 74. Defined as lying immediately below the downlapping reflectors prograding reflectors of the HST Characteristics of Maximum Flooding Surface [mfs) from seismic GeoHikingClub-2020
- 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 GeoHikingClub-2020
- 76. Maximum Flooding Surface [mfs) well logs, core & outcrop MFS After Hanford GeoHikingClub-2020
- 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) 5 Correlative Conformity2 (CC2) 6 Regressive Surface of Marine Erosion (RSME) 7 Transgressive Ravinement Surfaces (TRS) SU RSME TRS GeoHikingClub-2020
- 78. Identification of systems tracts on seismic GeoHikingClub-2020