QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

Sequence Stratigraphy T R Naish, Victoria University of Wellington, Wellington, New Zealand S T Abbott, Southern Cross University, Lismore, NSW, Australia R M Carter, James Cook University, Townsville, QLD, Australia ã 2013 Elsevier B.V. All rights reserved. This article is a revision of the previous edition article by S.T. Abbott and R.M. Carter, volume 4, pp. 2856–2869, ã 2007, Elsevier B.V.

Introduction Sedimentary cyclicity is an intrinsic feature of marine sedimentary basins, and is controlled by relative sea-level change resulting from the interplay of tectonics, sediment supply, and eustasy (Miall, 1997). Higher frequency cycles of glacioeustatic origin have periodicities of tens or hundreds of thousands of years. Lower frequency cycles are millions to hundreds of millions of years in length and are driven by sea-level changes tied ultimately to plate tectonic movements. Seismic reflection images of continental margins depict unconformity-bounded sedimentary cycles with an internal arrangement of reflectors that correspond to stratal surfaces (¼depositional surface of shelf margin) (Mitchum et al., 1977). In profile, the stratal architecture of sedimentary cyclicity is revealed on a basin-wide scale, and its development can be tracked across many successive cycles of relative sea-level change. Mitchum et al. (1977) termed individual cycles of this type ‘third-order seismic sequences,’ where a sequence is defined as “a stratigraphic unit composed of a relatively conformable succession of genetically related strata and bounded at its top and base by unconformities or their correlative conformities.” Historic studies of cyclic Quaternary sediments grouped repetitive faunal and lithological facies into units termed ‘cyclothems’ (Fleming, 1953; Vella, 1963), and stratal relationships within similarly cyclic sequences were later inferred using outcrop sedimentary facies analysis (Loutit et al., 1988; van Wagoner et al., 1990). Since the late 1980s, a modern sequence stratigraphic approach has been applied successfully to cyclic outcrop successions of Quaternary age (Abbott and Carter, 1994; Ito, 1992; Naish and Kamp, 2007), in which a much higher stratal resolution (down to centimeters) can be differentiated than is the case for conventional seismic analysis. Following the seismic work of Payton et al. (1977) and Vail et al. (1987), seismic sequences have become variously known as stratigraphic sequences, depositional sequences, or (as used herein) sequences. Clarity of thought is aided by drawing a clear distinction between a sequence stratigraphic model (SSM) – which summarizes the geometric stratal relationships of sediments deposited during a single major cycle of sea-level change – and a global sea-level model (GSM), which hypothesizes a sea-level curve for past times (Carter and Naish, 1998; Carter et al., 1991). A major aspect of classic sequence stratigraphy (Payton, 1977) was the development of techniques whereby a sea-level curve could be reconstructed from geometric analysis of sequences on seismic profiles, which led to the widely used sealevel curves of Vail et al. (1977) and Haq et al. (1987). Such studies contain an inescapable element of circular reasoning, and it is the single greatest strength of Quaternary sequence

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stratigraphic studies that they are made against the independent, and now well-tested, model of sea-level variation that is provided by oceanic oxygen isotope measurements (e.g., Shackleton et al., 1990; Lisiecki and Raymo, 2006).

Sequence Stratigraphic Models An SSM is a summary of the stratal architecture and facies composition that occur within a sequence (Carter et al., 1991). The stratal patterns and sedimentary environments that define the architecture of the classic SSM of Payton et al. (1977) and Vail et al. (1987) are depicted in Figure 1. Between bounding disconformities formed by subaerial exposure during lowered sea level, the model depicts an arrangement of stratal geometries (onlap, downlap, toplap, backlap) that track the development of the sequence as it built firstly landward and then seaward during a relative sea-level cycle (Figures 1(a) and 2). Stratal geometries allow sequences to be subdivided into component packages of strata called ‘systems tracts,’ each associated with a segment of the controlling sea-level curve. Lowstand, transgressive, highstand, and shelf-margin systems tracts are recognized. Systems tracts are defined as a linkage of contemporaneous depositional systems, where a depositional system is in turn defined as a three-dimensional assemblage of lithofacies (Brown and Fisher, 1977; Van Wagoner et al., 1988). Thus, the SSM predicts a systematic distribution of environmentally controlled lithofacies (Figure 1(b)). During the initial falling limb of the sea-level curve, the shoreline moves basinward toward and ultimately below the shelf edge. The former continental shelf is exposed to subaerial erosion, forming a lower bounding unconformity referred to as the sequence boundary (SB1). Subsequently, sediment is delivered to the slope where it onlaps the SB to form a basinfloor turbidite fan followed above by a wedge of terrestrial, shoreline, and shelf facies, the whole termed as a lowstand systems tract (LST). Subaerial exposure and consequent slow rates of lignite or soil formation at SBs are confirmed by their marked 10Be-isotope signature (Carter et al., 2002). With rising sea level, the shoreline moves landward and inundates the lowstand coastal plain. Commonly, a transgressive surface of erosion (TSE; ¼ ravinement surface, RS) is superimposed upon the former subaerial SB, accompanied by a shell lag containing reworked shoreface mollusks and remanie fossils. Any fluvial channels that crossed the shelf to the former lowstand shoreline are delimited by the SB below, but have their LST fill beveled above by the TSE. Sediment bodies within such fluvial channels are referred to as incised valley fill. Deposition of a transgressive systems tract (TST) follows, with shallow marine sediments onlapping the TSE/SB in a landward

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

261

Concordance Offlap Onlap (Subaerial)

Sigmoid clinoforms

Oblique clinoforms

HST TST

dls

Concordance

ts

iv

LST

Onlap (marine)

dls Downlap

(a)

sb2 HST

SMST

iss

TST

ts

iv Explanation Fluvial and coastal plain Shoreface and deltaic

Depth

sb1

HST

LST sf bff

Shelf and slope Submarine ‘fan’ (b)

Figure 1 The third-order sequence model. (a) Systems tracts and their internal stratal geometries (offlap, onlap, downlap, backlap, toplap). Reproduced from Miall AD (1997) The Geology of Stratigraphic Sequences, p. 433. Berlin and Heidelberg: Springer-Verlag. (b) Systems tracts, surfaces, and the distribution of lithofacies (Christie-Blick, 1991). LST, lowstand systems tract; TST, transgressive systems tract; HST, highstand systems tract; SMST, shelf-margin systems tract; sb, sequence boundary; ts, transgressive surface; dls, downlap surface; iv, incised valley; bff, basin-floor fan; sf, slope fan; iss, interval of sediment starvation.

direction. Above the TSE and any shell lag, the vertical succession of lithofacies deepens upward from inner to offshore shelf facies. The distal TST tapers to a feather edge as the decreasing rate of terrigenous sediment supply causes stratal surfaces to converge seaward. The sediment-starved offshore shelf seafloor that results is marked in outcrop by a local flooding surface (LFS). 10Beisotope studies show that the outcrop LFS corresponds with a significant hiatus (Graham et al., 1998), and the surface is often followed by a condensed, in situ shellbed with offshore fauna termed the mid-cycle shellbed (MCS) or “backlap” shellbed (Kidwell, 1991; Kondo et al., 1998). Such mid-cycle condensed successions are often associated with the presence of authigenic minerals such as glauconite and phosphate (Loutit et al., 1988). As the rate of sea-level rise slows toward highstand and subsequent fall, clinoform strata advance basinward by offlap and downlap to form the highstand systems tract (HST). An abrupt boundary termed the downlap surface (DLS) occurs between the base of the HST and the underlying MCS or, in its absence, the top of the TST. The vertical succession of highstand facies shallows upward from offshore sediments at the base through shoreline and then into nonmarine facies at the top. As for the distal TST, distal highstand deposition is characterized by stratal convergence associated with low rates of terrigenous sediment supply. At the approach of the next sea-level low, which ends each cycle, the shoreline and locus of deposition again shift basinward. Should the lowstand shoreline not fall below the shelf edge, Payton et al. (1977) distinguishes a SMST as forming at the start of the next new sequence, instead of a succeeding LST. As for the LST and HST, a SMST is characterized by an offlapping, shallowing-upward facies succession.

Though it was part of the initial formulation of the SSM based on third-order cyclicity (Payton et al., 1977), the SMST has found little subsequent use. Rather, later authors have preferred to recognize two other types of regressive sediment bodies as characteristic of the falling sea-level phase. Regressive packages of strata form when the supply of sediment is large enough to form an offlapping body of sediment that builds into the basin as sea-level falls and the shoreline moves seaward (Plint, 1988), as is characteristic of Quaternary sequences from activemargin basins where high sediment fluxes are derived from nearby orogens. When they are bounded below by a regressive surface of erosion (RSE), generated by wave-base scour of the seafloor during regression, such deposits are assigned to a forced regressive systems tract (FRST) (Hart and Long, 1996; Hunt and Tucker, 1992). However, in many cases, similar sand-dominated regressive packages are gradationally based, presumably reflecting subsidence rates high enough to prevent a sea-level lowered wave base impinging on the seafloor. Such gradationally based sediment packages are common in the Wanganui Basin and are termed regressive systems tracts (RST) (Naish and Kamp (1997a). Sea-level lowstand is associated with the formation of the upper sequence-bounding unconformity (SB1).

Five Fundamental Sequence-Bounding and Intrasequence Surfaces Following the theoretical analysis of Embry (1990), the study of Quaternary sequences has played a key role in developing our understanding of the outcrop characteristics of the

262

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

Basin margin

Inner shelf

Mid-shelf

l Slope

Outer shelf

FRST RST

HST

LST

TST

LST

(a)

FRST

HST

RST

LST2

TST

LST LST1

nm

I V F = LS T + T S T

40 ka or 100 ka cycle LST

(b) SB(CC)

SB RSE

(c)

B O

O

O

Facies Terrestrial Shoreline Offshore

Systems tracts

B

C

TSE

RSE DLS

Relative sea level

HST

High HST1

LST2 Low

SB(CC)

Surfaces

RST = Regressive systems tract

SB = Sequence boundary

FRST = Forced regressive systems tract

SB(CC) = Sequence boundary (correlative conformity) HST/RST boundary RSE = Regressive surface of erosion DLS = Downlap surface TSE = Transgressive surface of erosion

HST = Highstand systems tract TST = Transgressive systems tract LST = Lowstand systems tract

LST1

Shellbeds O Onlap B Backlap C Compound

Figure 2 Quaternary sequence model based on outcrop studies of active-margin basins. (a) Quaternary sequence model emphasizing systems tracts, stratal architecture, and generalized lithofacies distribution. (b) Quaternary sequence model emphasizing systems tracts, and the distribution of onlap and backlap shellbeds. (c) Indicative sequence motifs showing across-shelf variation in the vertical succession of facies, surfaces and systems tracts. Adapted from Naish TR and Kamp PJJ (1997) Sequence stratigraphy of sixth-order (41 ka) Pliocene-Pleistocene cyclothems, Wanganui Basin, New Zealand: A case for the regressive systems tract. Geological Society of America Bulletin 109(8): 978–999; Saul G, Naish T, Abbott ST, and Carter RM (1999) Sedimentary cyclicity in the marine Plio–Pleistocene: Sequence stratigraphic motifs characteristic of the last 2.5 my. Geological Society of America Bulletin 111: 524–537.

stratigraphic discontinuities that punctuate a typical stratigraphic sequence. However, note that a widely used term in older literature – the maximum flooding surface – is a conceptual horizon that has no necessary physical manifestation in outcrop (Carter et al., 1998). Recognition of the key physical surfaces, and the abrupt facies shifts that occur across them, are primary tools for sequence stratigraphic interpretation. The characteristics of sequence surfaces are summarized in Figure 2 and below.

Sequence Boundary A SB is a surface formed by subaerial exposure that occupies a sequence-bounding position between an underlying RST, or HST, in the case where erosion has remove the RST and an overlying TST. The SB may be marked by incised fluvial channels, by a paleosol, or by terrestrial facies such as lignite, all of which formed during the sea-level lowstand associated with the formation of the SB. An SB-correlative conformity (conceptual horizon projected from the SB into adjacent conformable strata) may occur inland if aggradation of coastal plain facies

continues uninterrupted across the contact between two sequences. Offshore, an SB-correlative conformity extends basinward from beneath the LST.

Ravinement Surface or Transgressive Surface of Erosion The RS and TSE are alternative, widely used synonyms for the surface that is wave-cut by the landward passage of a transgressing shoreface. The RS often erodes any underlying LST strata, its lower bounding SB and sometimes the upper part of the underlying sequence. The RS may be penetrated by marine crustacean burrows (Thalassinoides, Ophiomorpha) and pholad borings, and is often overlain by an onlapping shell lag or conglomerate.

Local Flooding Surface The LFS marks the development of a sediment-starved seabed seaward of the shore-connected prism of the TST, and results from water deepening associated with shoreline transgression. The LFS is usually marked by a burrowed diastemic surface

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

between the top of the TST and an overlying MCS containing an in situ offshore shelf fauna.

Downlap Surface The DLS is an abrupt but conformable boundary formed by downlap of the HST on to the underlying MCS or (in its absence) TST. The DLS may be burrowed and often coincides with a sharp lithological contrast between an underlying in situ shellbed and an overlying HST shelf siltstone.

Regressive Surface of Erosion The RSE is a surface cut by a lowering wave base during regression and sea-level fall (Plint, 1988), and, where present, comprises the boundary between the HST and FRST. As for the DLS, a sharp lithological contrast may occur across the RSE in shelf settings, where it separates HST mudstone from FRST sand. In rapidly subsiding basins, where a balance exists between the rates of subsidence and sea-level fall, the HST passes gradationally upward into the RST without an intervening RSE.

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Seven Empirical Orders of Sea-Level Cyclicity Among the voluminous literature on sequence stratigraphy, examples exist of sequence architecture, which is interpreted in terms of about seven different orders of sea-level cyclicity (Fulthorpe, 1991). The first and second orders are ultimately tied to plate tectonic processes (Carter et al., 1991). Third- and fourth-order cycles are variously attributed to regional tectonic change (Saul et al., 1998) or to eustasy of unknown origin (Payton et al., 1977). The fifth, sixth, and seventh orders of sea-level cyclicity correspond to glacio-eustasy at orbitally forced Milankovitch scales (Miall, 1997). The product of these various orders of sea-level variation can be integrated as a GSM (Haq et al., 1987), but such curves are bedeviled by their low resolution (sequences 1–10 My long) and uncertain accuracy. In reality, we only possess an acceptably accurate model of sea-level change for the last few million years, as underpinned by high resolution oxygen isotope timeseries and related studies (Lisiecki and Raymo, 2005). It is the accuracy of the oceanic oxygen isotope sea-level curve as a proxy against which to assess stratigraphic change that makes studies of Quaternary sequence stratigraphy so exceptionally powerful.

Sequence Stratigraphy in Quaternary Sediments Parasequences In many depictions of the SSM, marine flooding surfaces correspond to the boundaries between high order, shallowingupward, sedimentary cycles referred to as parasequences. These are regarded as the fundamental building blocks of sequences and systems tracts by Van Wagoner et al. (1988), who defined them as “a relatively conformable succession of genetically related beds . . ., bounded by flooding surfaces and their correlative surfaces.” Depositional sequences are ultimately the product of the interplay between sedimentation, subsidence, and eustasy. Changes in the episodicity, magnitude, and rates of these fundamental parameters interact to vary the architecture and facies composition of depositional sequences according to the order of cyclicity and the particular basin setting. These considerations led Carter et al. (1991) to conclude that higher order sequences (e.g., parasequences) within lower order sequences are likely to be topologically distinct only at their particular level, rather than stacked as in a nested set of Russian dolls. These authors suggested that, rather than having a primary significance, parasequences are simply a convenient descriptive label, the scale of which varies according to sequence order. Table 1

Extending back to 2.6 Ma and beyond, orbitally forced glacioeustasy has operated throughout the Quaternary with dominant frequencies of 20 ka (precession), 41 ka (obliquity), and 100 ka (eccentricity), and magnitudes between 70–130 m (see review by Pillans et al., 1998). Eustatic variation at these Milankovitch frequencies has driven numerous transgressions and regressions of the shorelines across the world’s continental shelves, and imposed a distinct cyclicity on the Quaternary sedimentary successions that reside beneath modern continental shelves. A number of such basins located adjacent to active plate margins have been uplifted and exposed during the late Quaternary (Table 1), thereby allowing their detailed sequence stratigraphy to be described against the background of a known sea-level history. The discussion of Quaternary sequences below is based on the published literature on these active-margin successions.

Eustasy as the Dominant Control on Sediment Deposition Tuning (or calibration) of the isotopic proxy sea-level curve with astronomically based master curves (e.g., seasonal insolation)

Well documented outcropping Quaternary sequences from active-margin plate margins

Basin

Region and country

Key references

Wanganui Esmeraldas-Caraquez, Canoa Merced Group Kazusa Group, Omma Formation Peradriatic Corinth

North Island, New Zealand Central Ecuador San Francisco, USA Central Japan

Abbott and Carter (1994), Naish and Kamp (1997a), Saul et al. (1999) Cantalamessa and Di Celma (2004), Di Celma et al. (2005) Carter et al. (2002), Clifton et al. (1988) Ito (1992, 1998), Kitamura et al. (1994)

Italy Greece

Cantalamessa et al. (2005), Rio et al. (1996) McMurray and Gawthorpe (2000)

264

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

has established that between 2.6 and 0.8 Ma, sea level varied systematically at the 41 ka obliquity wavelength, but that since 0.8 Ma, the 100 ka eccentricity signal has dominated. Magnitudes of Quaternary glacioeustasy can be calibrated between the oxygen isotope record and the sea-level changes inferred from uplifted coral terraces younger than the last interglacial (Chappell, 1974). This calibration has been used to estimate eustatic magnitudes of  70 m for obliquity with cycles and up to 130 m for eccentricity cycles (Chappell et al., 1986). The oxygen isotope record from deep sea cores thus furnishes an independently established proxy eustatic curve against which to interpret Quaternary sequence stratigraphy. Generally, rates of Quaternary glacio-eustasy outpace both subsidence and sediment supply as the dominant control on the sedimentary architecture of continental margin basins. Exceptions include the supply-driven Mississippi delta complex (Boyd et al., 1988) and the Canterbury Plains of New Zealand (Leckie, 1994), where different segments of the same coast in each case display concurrent offlapping and onlapping behavior during the Holocene highstand. However, more generally, the sequence architecture of some basin successions with good chronological control can be correlated to the oxygen isotope proxy sea-level curve. Following the conventional SSM, sediments deposited across a Quaternary highstand shelf can be matched to interglacial sea-level highs, while their contained sequence boundaries correspond to the intervening glacial lowstands (Abbott and Carter, 1994; Ito, 1992; Pillans et al., 1994, 2005).

Sedimentary Facies Analysis The architecture and depositional history of sequences are rendered using standard sedimentary facies analysis. This approach uses sediment attributes such as grain size, physical sedimentary structures, biogenic sedimentary structures, and macrofossil content to interpret environments of deposition (Walker, 1984). Lithofacies analysis is enhanced by identification of the significant surfaces that punctuate sequence successions and by focused sedimentological and paleoecological analysis. The taxonomic composition of macrofossil assemblages is indicative of environmentally diagnostic paleocommunities (Abbott and Carter, 1997; Kidwell, 1991; Kondo et al., 1998). Thus, estuarine faunas are distinct from open shoreface faunas, and both are distinct from offshore subtidal communities. Taphonomic attributes of macrofossil material indicate sedimentary processes (Kidwell, 1991b). For example, broken and abraded assemblages indicate reworking in an energetic environment (death assemblages), whereas pristine assemblages characterized by the presence of paired valves (life assemblages) indicate deposition in low energy settings. Foraminiferal paleoecology is also a powerful tool with which to interpret facies and track bathymetric changes in Quaternary marine strata (Abbott, 1997; Haywick and Henderson, 1992; Naish and Kamp, 1997b). Overall, analysis of the sedimentology and paleoecology of Quaternary sedimentary successions is highly robust because close contemporary analogues often occur in adjacent modern sedimentary environments. The distribution of facies within a sequence is the basis from which stratal geometries and sequence architecture can

be inferred. For example, a deepening-upward facies succession that fines upward from physically stratified shoreline sand into pervasively bioturbated shelf mud, has inferred onlapping stratal geometry such as characterizes the TST. Conversely, a shallowing- and coarsening-upward succession represents offlapping geometry such as that found in the HST–RST. Thus a conformable succession of gradually changing facies may often correspond to a systems tract (Walker, 1990).

The Importance of Shellbeds Shell-rich facies are a hallmark of eustatically influenced Quaternary sequences and their interpretation is crucially important for resolving sequence architecture. Shell material becomes concentrated under conditions of low net terrigenous sediment accumulation created by either reworking and bypass in shallow energetic sandy environments (type A shellbeds; Abbott and Carter, 1994), nondeposition in nearshore deeper channel or offshore deeper water muddy environments (type B shellbeds, op. cit.), or by infaunal penetration of specialist boring taxa into a current-swept, hard substrate (type C shellbeds, op. cit.). All such shelly deposits represent stratigraphic condensation, and type A and B shellbeds both imply convergence of stratal surfaces toward sequence and systems tract bounding surfaces (Kidwell, 1991a; Kondo et al., 1998; Naish and Kamp, 1997a). Individual shellbeds can be assigned an inferred mode of origin with respect to sequence architecture (Figures 2 and 3), as follows. Basal onlap shellbeds represent transgressive reworking of contemporaneous shelly shoreline and estuarine sediments at TSE, with an admixture of underlying remanie fossils. Fossil content comprises mostly mixed, rounded, and transported assemblages dominated by sandy shoreface and estuarine mollusks. Inferred backlap shellbeds correspond to MCS, and are characterized by offshore shelf faunas, which include in situ articulated bivalves. Downlap shellbeds that mark the contact of MCS and HST are characterized by similar offshore shelf faunas but display a more dispersed biofabric than do the immediately underlying backlap shellbeds. Finally, inferred toplap shellbeds occur within the upper parts of RST or FRST, where stratal convergence results from sand bypass in high-energy shoreface environments. Skeletal material is preserved in the sediments in which the organisms lived, and though assemblages are reworked, disarticulated, and fragmented, they are neither significantly rounded nor display the other typical lag features that characterize basal onlap shellbeds. In some sequences, onlap and backlap shellbeds are superimposed to form a compound shellbed.

Quaternary Sequences How Are They Special? It is a prime feature of Quaternary sediments from activemargin basins that they exhibit a much greater resolution of sequence architecture than that depicted by the generic thirdorder SSM. For example: 1. Figure 2 depicts an SSM for the Quaternary, based mainly on outcrop studies of uplifted basins adjacent to active plate margins; and

Symmetric cycle

Condensed deposit

Toplap Condensed toplap shellbed

Asymmetric cycle

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

Condensed downlap shellbed

265

Sequence boundary

HST

Downlap

TST

Sequence boundary

Onlap Condensed onlap shellbed

Backlap

Condensed onlap-backlap compound shellbed

HST: highstand systems tract TST: transgressive systems tract

Condensed backlap shellbed

(a) Inferred water depth

Columnar section

Inferred water depth

Columnar section

Condensed toplapshellbeds Transported or indigenous, low diversity, infaunal benthic assemblage

Condensed toplap. shellbed Transported or indigenous, relativity lowdiversity, infaunal benthic assemblage

Mostly in-situ, lowdiversity infaunal benthic associations Downlap surface

Condensed backlapshellbed or burrowed bed

Mostly in-situ, lowdiversity infaunal benthic association; rapid burial common; Downlap surface

Condensed onlapbacklap shellbed

Onlap-shellbed (transgr.Lag) SB/RS

Shallow Deep

m s

Symmetric cycle *(inner shelf) (b)

l

1

m s Shallow Deep

SB/RS

Asymmetric cycle *(outer shelf)

Figure 3 The association between shellbed type and sequence architecture in Plio–Pleistocene sequences. Reproduced from Kondo Y, et al. (1998) The relationship between shellbed type and sequence architecture: Examples from Japan and New Zealand. Sedimentary Geology 122: 109–127. (a) Distribution of shellbed types within an idealized sequence, showing their relationship to stratal convergence and systems tract-bounding surfaces. (b) Vertical facies succession within a sequence showing the stratigraphic context of shellbed types.

2. Figure 4 is an example of a measured section from the Canoa Basin, Ecuador, labeled to show the component facies, sequences, systems tracts, and surfaces. A second important feature of Quaternary sequences is that subaerial sequence boundaries are not usually preserved but are instead superposed by the TSE cut by the passage of a transgressing marine shoreface. A TSE may cause erosion of up to several tens of meters into the top of the underlying sequence, which removes all traces of original sequence boundaries almost basin wide (Abbott, 1992; Abbott and

Carter, 1994) and results in the preservation of top-truncated sequences (Castlecliff motif of Saul et al., 1998). Deep erosion during transgression also leads Quaternary sequences deposited in inner-shelf and basin margin settings to possess proportionally thick TSTs. A third difference between the Quaternary SSM and the generic third-order SSM is the common presence of strata deposited during the falling limb of the relative sea-level curve. Regressive packages of strata deposited during falling sea level form when the supply of sediment is large enough

Sequence stratigraphy Systems Sequence tract

Legend

Tb2 BSW

58

TST Wave-winnowed shell association

34 32 30

TST HST

Tb1

BSW

TST

Cupp6

20 18 16 14

8

Trachycardium association

FSW

Pegophysema association

6 4

HST

Shell bed type

Sequence stratigraphy Systems Sequence tract

HST ?

100

TST

Cupp5

96

92 90 88 86

Argopecten-Undulostrea association Wave-winnowed shell association

84 82

76

Wave-winnowed shell association Lag concentration Argopecten-Undulostrea association

74

70

TST

Wave-winnowed shell association

94

72 Corbula association

Tb6

98

80

2 0

Sand Gravel fmc

78

BSW

10

Grain size

102

26

12

BBW

104

28

22

TST

RS

106

Argopecten-Undulostrea association

24

OSB

Mudstone

108

Upper canoa formation

36

BSW

Wave-winnowed shell association Pinna association

FSW

38

HST

BSW

SB

42 40

FSW

Lithostratigraphy

44

DS LFS

Sandy mudstone

Lithosome

46

SB DSB BSB

Wave-winnowed shell association

FSW

48

BBW

50

Architectural elements

Sandstone

HST

BSW

52

Lithology

TST

BSW

54

Heavily bioturbated

Plane lamination

TST

FSW

56

Shell concentration

HST

BSW

60

Plant fragments

Convolute bedding Ophiomorpha burrow

Argopecten-Undulostrea association

Lithology

62

Thickness (m)

64

HST Tablazo formation

66

Internal molds

Estuarine muds

TST

Tb5

Tb4

Tablazo formation

FSW

68

Trough cross-bedding

Clay Silt

Shell bed type

Lithostratigraphy

Sand fmcGravel

Lithosome

Grain size Clay Silt

Lithology

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

Thickness (m)

266

Tb3

Figure 4 Vertical succession of facies (including shellbeds), sequences, and systems tracts within the Canoa formation, Canoa Basin, central Ecuador. Reproduced from Di Celma C, Ragaini L, Cantalamessa G, and Landini W (2005) Basin physiography and tectonic influence on sequence architecture and stacking pattern: Pleistocene succession of the Canoa Basin (central Ecuador). Geological Society of America Bulletin 117: 1226–1241.

to form an offlapping body of sediment that builds into the basin as the shoreline regresses. As described earlier, such sediment bodies are either bounded below by an RSE and termed FRST, or else grade up from underlying HST sediments to comprise a simple RST. Fourth, very high sedimentation rates and rapid shellbed formation accompanied active-margin basin-filling during Quaternary eustatic cycles. Individual 40 ka-long late Pliocene sequences attain 120 m or more in thickness, with HST–RST alone over 100 m thick (Haywick et al., 1992; Naish and Kamp, 1997a) (Figure 5). Therefore, average sedimentation rates at times reached 5 m ka1 or more, and MCS up to  1 m in thickness, despite being ‘condensed’ with respect to their enclosing TST–HST sediment, nonetheless took only a few thousand years to accumulate (Abbott and Carter, 1994). Finally, and fifth, it is only in Quaternary successions that the complete three-dimensional architecture of continental margin sequences can be studied within a known sea-level context. Outcrop studies can be accomplished not only on uplifted Plio-Pleistocene shelf (Abbott and Carter, 1994) and slope (Ito, 1992) successions, but also on the important shoreface-coastal cliff-coastal plain interface that is preserved in the treads of flights of uplifted marine terraces back to midPleistocene in age (Chappell, 1974; Pillans, 1983).

Sequence Motifs The vertical stratigraphic succession of facies, faunas, and surfaces within a sequence varies according to its location along a hypothetical shore-normal profile. Particular types of stratigraphic succession can be differentiated as sequence motifs. As discussed by Saul et al. (1999), sequence motifs are arbitrary end-members in a continuous spectrum of possible sequence architectures. Furthermore, the interplay of subsidence and sediment supply, and therefore shore-normal variation in sequence motifs, varies in detail both within and between basins. The generic motifs depicted in Figure 2(c) are drawn from earlier studies of geographically named motifs, generalized here in order to illustrate typical cross-basin variation in Quaternary sequence architecture and facies composition (Figure 6).

Basin margin motif The edges of active-margin basins often record a history of progressive Quaternary uplift. Wave-cut terraces are formed at interglacial highstands, and flights of terraces formed at successive highstands extend from the modern highstand shoreline into the uplifting hinterland (Pillans, 1983). Terrace treads comprise sediments that represent the landward margins

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

MIS 89/88 MIS 91/90 MIS 92 MIS 93

267

7

6 5

80 m

4

Rangitikei River seection stratigraphic log Sequences (in photo above)

d18O(‰) ODP site 607 North Atlantic 4.5

Earth’s orbital variations obliquity(⬚)

Ma

3.5 22 23 24 25 26

2.5

2.1 11 Orangipongo sandstone 10 Ohingaiti Tephra 9 8 7 Ohingaiti sandstone

1500 1550 1600

Sandstone Siltstone Shellbed Carbonaceous sandstone Carbonaceous siltstone

1650

6

1700

5 4

82 84

2.2

86 88 90

2.3

92

1750

Tuha shellbed 3 Tuha sandstone

1800

Hautawa shellbed 2

M

S G

94

2.4

96 98 100

2.5

102

Figure 5 Photo of outcrop exposure of Early Quaternary (2.5–2.0 Ma), 40-ka-duration, shallow-marine sequences exposed in cliffs of the Rangitikei Valley, Wanganui Basin. Sequence boundaries (TSEs) are marked by red dashed line. Individual 40-ka sequences are up to 45 m thick. The stratigraphic column shows these sequences correlated with deep sea oxygen isotope record. Modified from Naish TR and Kamp PJJ (1997) Sequence stratigraphy of sixth-order (41 ka) Pliocene–Pleistocene cyclothems, Wanganui Basin, New Zealand: A case for the regressive systems tract. Geological Society of America Bulletin 109(8): 978–999.

of depositional sequences, and sequences formed in this paleogeographic setting are intimately related to the geomorphic expression of the terraces (see Morphostratigraphy/ Allostratigraphy). For most of the sea-level cycle, the basin margin is subaerially exposed. Sedimentation in this setting consists of nonmarine facies, including substantial paleosol development, together with shallow marine facies deposited at and near each interglacial sea-level peak. The sediments can be partitioned into

transgressive and HSTs. In this setting, sequence-bounding RS may terminate at paleocliffs that represent the position of the highstand paleoshoreline.

Inner-shelf sequence motif The inner-shelf setting is inundated from mid- to late-rise through to highstand. In contrast to the basin margin motif, paleodepths in this setting may reach several tens of meters, so a proportion of sequences in this paleogeographic setting

268

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

Maxwell motif (shoreface–paralic–coastal plain) Seafield motif TST (marine, thick volcaniclastic TST) RSOS

Birdgrove motif

LSTnm SB

Tewkesbury motif

Shakespeare motif

HST/RS

(innershelf–shoreface)

(marine, sharp-based RST)

(coastal plain)

Nukumaru motif

SB

(shoreface–foreshore)

HST

(Nonmarine cycle motif. Systems tracts designation estimated. TST comprises supratidal heterolithic facies)

DLS OS

TST OS RS/SB

RSE HST

Z

HST

DLS DS BS TSTOS

HST

OS SB/RS

OS TST RS/SB

TST

TST OS RS/SB

RS SB

RST

RST

OS

DLS FS BS

TST

SB/RS

SB/RS

HST

HST

LST

HST DLS TST BS RS/SB OS

Z

sZ S zS G

sZ S zS G

Z

DS DLS BS TST OS RS/SB

OS SB/RS

sZ S zS G

Z

sZ S zS G

Z

sZ S zS G

S

sZ Z

zS

G

IVF

SB3

6

Sequence 2

HST SB2

5

2

RST

TST

HST

Sequence 1

4

7

1 RST

3

8

LST

LST

SB1 SB2 SB1

SB3

Turakina motif

Oroua motif

(marine, thick TST, RST) Rangitikei motif (marine, thin TST, HST, no RST) (marine, thin TST, RST)

Pakihikura motif

(incised-valley-paralic) Castlecliff motif

(coastal plain–paralic) SB

SB/RS

SB

SB/RS

SB/RS

RST

HST

RST HST

DLS

HST TST OS RS

HST DLS

LSTnm

HST

DS DLS BS TST OS RS/SB

BS

TST OS RS

sZ Z

DLS

S zS

G

LST/IVF

DS BS

HST

OS

SB

OS

DLS

SB

TST

sZ S Z zS G

sZ S Z zS G

SB/RS

OS

RS/SB

DS BS OS

sZ

(a)

Z

Z

S

sZ zS

S zS

G

G

Relative sea level High

Low

8

LST

7

8 RS/TS

Fluvial incision

SB2 RST

6

HST

4 2

3

1

RST HST

SB3 Sequence 2

6 5

DLS

TST LST

7

Regress

Subaerial erosion

RSE

5

sion

ne ero ive mari

Marine ravin

RS/TS SB1

ement

Subaerial erosion

FDS DLS

Stratigraphic condensation

4 3

2

SB2 Sequence 1 (incomplete)

1

Outcrop example 100-ka Pleistocene shallow-marine sequence

High

Relative sea level Low

8

LST

RS/TS

78

SB3

7 HST

4

5 2 1

3

TST LST RST HST

RSE DLS RS/TS SB2 FDS DLS

RST (Shakespeare Cliff Sand) RSE

6 20 m Innerself

HST (Shakespeare Cliff Siltstone)

10

0

1

Sequence 1 – TST shoreline

2

Sequence 1 – HST shoreline

3

Sequence 1 – RST shoreline

4

Sequence 2 – LST shoreline

5

Sequence 2 – TST shoreline

6

Sequence 2 – HST shoreline

RS/SB3 Shoreface

RST

6

Shoreline migration

Cyclothem 40, Castlecliff. NZ

Outer/mid-self

5 3 4 Inner/mid-self

DLS TST (Tainui Shellbed) RS/SB2

7

Sequence 2 – RST shoreline

8

Sequence 2 – LST shoreline

Key surfaces Subaerial exposure surface (sequence boundary; SB) Sequence boundary correlative conformity (SB) Ravinement surface (RS), transgressive surface of erosion (TSE) Transgressive surface (TS) Downlap surface (DLS) Forced-regressive downlap surface (FDS) Regressive surface of erosion (RSE)

Lithofacies Coastal plain facies

Shoreline facies

Shelf-slope facies

(b)

Figure 6 (a) Conceptual sequence stratigraphic and (b) chronostratigraphic models for orbital scale Quaternary sequences based on Wanganui Basin. The stratigraphic architecture timing of development of systems tracts and key surfaces are shown with respect to a relative cycle of sea level. Outcrop motifs of Wanganui sequences are illustrated in the context of a 2D coastal plain and outer shelf progradational setting. Reproduced from Naish T, Field B, Zhu H, et al. (2005) Integrated outcrop, drill core, borehole and seismic stratigraphic architecture of a cyclothemic, shallow-marine depositional system, Wanganui Basin, New Zealand, Journal of the Royal Society of New Zealand 35: 91–122.

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

consists of facies deposited at shelf depths. Thick TSTs begin with an onlap shellbed that deepens upward. Because this motif is proximal to the basin margin, transgressive sedimentation switches rapidly to highstand deposition as relative sea level approaches its peak. Therefore, backlap shellbeds may not be well developed at the transgressive-HST boundary. Highstand deposits are mud-rich, but may become sand-rich toward the top. During the ensuing sea-level fall, there is an accompanying abrupt basinward shift in deposition and wave base is lowered to the point where it scours the shelf. This basinward passage of wave base may generate a RSE, over which lies a body of shoreface sand assigned to the forced RST. As for the basin margin, the inner-shelf paleogeographic position may also be affected by tectonic uplift. Thus, inner-shelf sequences from the Peradriatic basin (Cantalamessa and Di Celma, 2004) are stacked in a basinward stepwise manner, describing a loworder tectonically forced regression.

Mid-shelf sequence motif As for the proximal motifs, sequences in the mid-shelf paleogeographic position also commence with a relatively thick TST with a basal onlap shellbed. In contrast to the inner-shelf motif, the uppermost TST in the mid-shelf position is more likely to be isolated from terrigenous sediment, and the time until downlap by the highstand is likely to be greater. Thus, here and also in the more distal motifs, shell material accumulates in situ to form well-developed backlap shellbeds. Highstand deposition on the mid-shelf is heralded by downlapping shelf mud that ‘quenches’ shell accumulation, resulting in an abrupt yet conformable DLS between shellrich and relatively shell-poor facies. Shelly clumps and bands at the base of some highstand successions represent downlap shellbeds, but these are not as well developed as the underlying backlap shellbeds. As for the inner-shelf motif, highstand shelf mud passes into shoreline sand deposited during falling sea level. However, on the mid-shelf, the rate of subsidence is higher, so wave base is not lowered to the extent where it cuts a RSE. Instead, the transition is conformable and the overlying sands are attributed to the RST rather than the forced RST.

Outer-shelf sequence motif This sequence motif results from deposition on the outer shelf, between early relative sea-level rise through to the late part of sea-level fall. The outer-shelf motif is highly asymmetrical in the sense that sand-rich transgressive facies are not well developed compared to the thick, sand-rich RST. The poor development of the TST may result from rapid transgression over a low gradient coastal plain, which then becomes isolated from the supply of terrigenous sediment. The resulting TSTs are thin and particularly rich in skeletal material. The basal onlap shellbed may be directly overlain by a backlap shellbed to form a compound shellbed. As for the mid-shelf motif, the DLS forming the boundary between the transgressive and HSTs is an abrupt shell-rich to relatively shell-poor boundary. The upper part of the motif is a gradationally based RST of shoreline sand.

Slope sequence motif Quaternary sequences of this motif are less well known from outcrop, so this motif is based on the Plio-Pleistocene of the Hawke’s Bay basin described by Haywick et al. (1992). This setting lies basinward of the lowstand shoreline, so is

269

inundated through the entire relative sea-level cycle. Erosional sequence-bounding surfaces associated with subaerial exposure or marine ravinement are often not present. Instead, sequences in this paleogeographic position are bounded by correlative conformities. Another feature of this motif is that it comprises exclusively offshore facies because the slope paleogeographic setting is submerged to depths of over 100 m during most of the relative sea-level cycle. Only the basinwardtapering edges of the transgressive and HSTs are represented and, because of the pronounced convergence of stratal surfaces in the distal TST, backlap shellbeds may be well developed. Facies successions shallow upward as the regressing shoreline reaches lowstand. In the case of the Hawke’s Bay basin, this coincided with a reorganization of terrigenous sediment transport paths, such that LSTs comprise coquina limestone.

Case Study 1: Characterizing, 5th- and 6th-Order Quaternary Shallow-Marine Sequences from Outcrop, Borehole, Drillcore, And Seismic Data from Wanganui Basin, New Zealand Continental margins are relatively rare that afford an opportunity to study the stratigraphic architecture of shallow-marine depositional systems on spatial scales ranging from core and borehole (millimetres/centimetres) to outcrop and seismic (tens of meters), during periods of known sea-level oscillations. Wanganui Basin, New Zealand is one of a small number of Pliocene-Pleistocene basins worldwide (Browne & Naish 2003; Kitamura et al., 2000) in which sedimentation evidently kept pace with subsidence through much of the basin history, resulting in a 5-km-thick record of predominantly shelf and shallow-water sediment. Gentle upwarping of the eastern margin of the basin has produced spectacular exposures, along coastal cliffs and inland (Figure 5) within the heavily dissected and uplifted landscape, through as many as 44 depositional sequences deposited during the last 2.5 Ma (Carter & Naish, 1998; Naish et al., 1998; Saul et al., 1999). The Wanganui stratigraphic succession comprises a range of siliciclastic and carbonate sediments deposited in shelf, shoreline, and coastal plain depositional environments during orbitally controlled sea-level fluctuations of 41 ka- and 100 kaduration. Over the last 10 years, this margin has gained a reputation as one of the world’s outstanding outcrop examples of a Pliocene-Pleistocene shallow-marine, clastic depositional system (e.g., summary papers: Abbott and Carter 1994, Abbott 1997; Naish & Kamp 1997a; Naish et al., 1998; Saul et al., 1999). Outcrop analogues of this quality are rare, as most Quaternary shelf margins underlie flooded continental shelves (e.g., Gulf of Mexico). Late Pliocene to mid-Pleistocene (ca. 2.1–0.4 Ma) strata exposed in the coastal cliff sections northwest of Wanganui City, North Island New Zealand, comprise 25, 6th(41 ka)and 5th(100 ka)-order, shallow-marine to marginal marine stratigraphic sequences, deposited during global glacio-eustatic sea-level cycles corresponding to Marine Isotope Stages (MIS) 78–10. Naish et al. (2005) characterized the sequences using: (1) a series of drill cores sited above and behind the coastal outcrops, which recovered a composite record of ca. 450 m, (2) a new high-resolution multichannel seismic reflection profile acquired along the beach adjacent to the coastal cliffs, and (3) downhole digital logs from the boreholes (Figures 7 and 8). They integrated the outcrop and subsurface data sets to

Sequence

Core log

stratigraphy

1.75G/C32.6 C

20

Z

S

G

Depositional setting Paleobathymetry 0

100 m

13.00 Downlap Backlap Onlap

HST TST RST

Karaka Siltstone 41 Mid-shelf SB/RSE MIS 11 Upper Castlecliff Shellbed Inner-shelf foreshore 21.39 Shakespeare Cliff Sandst. mid-upper shoreface RSE innermost shelf DLS

Shakespeare Cliff Siltstone

HST

40

Formation

NZ stages

0.6 V/V0.05 30 GAPI120 RH08

Sequence and MIS

EHGR

FMI static

NPHI

Synthetic

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

Meters

270

DLS

Downlap Backlap

MIS 13–12

TST Onlap

Mid-shelf

Tainui Shellbed SB/CC 49.15

RST Downlap Backlap

HST

Inner-shelf

40

Pinnacle Sand Lower Castlecliff Siltstone

DLS LFS

Lower Castlecliff Shellbed

60

Innermost shelf Inner-shelf mid-shelf inner-shelf

Shoreface

39 MIS 15–14

TST

Inner-shelf

Seafield Sand Intertidal (behind barrier)

Onlap

SB/TSE 76.93

Tom’s Conglomerate

80 Inner-shelf HST

Upper Kai-iwi Siltstone 38

100

Backlap TST Onlap

Mid-shelf Upper Kai-iwi Shellbed

Inner-shelf

Kupe Formation

Intertidal mud-sand flat and channels

Kupe tephra

SB/TSE

Castlecliffian

MIS DLS 17–16

110.60 Inner-shelf HST

120

Upper Westmere Siltstone 37

Mid-shelf

MIS DLS 19–18 Backlap TST

Upper Westmere Shellbed

Inner-shelf

Kaikokopu Formation

Intertidal

SB/TSE

Onlap

135.36

Inner/midshelf

140 HST

36

Lower Westmere Siltstone Inner-shelf

MIS 21–20 DLS

160

TST RST

Lower Westmere Shellbed equivalent

SB/CC FDS

162.50

HST

Omapu Shellbed

Lower Kai-iwi Siltstone

Innermost shelf Shoreface

Inner-shelf

35 DLS

MIS LFS 25–22

Backlap

180

Lower Kai-iwi Shellbed

Innermost shelf

Kai-iwi Shellbed equivalent

TST

Kaukatea tephra SB/TSE 187.90

RST

200 RSE HST

34

TD castlecliff-1: 192.46 m Kaimatira Pumice Sand Potaka Tephra (reworked)

MIS 27–26

TD castlecliff-1A: 220.15 m

Kaimatira Pumice Sand (mud facies)

Intertidal channel -bar complex

Tidal delta front

Figure 7 Summary composite log of the Castlecliff-1/1A drillcore, Wanganui Basin, and borehole shows neutron porosity (NPHI), density (RH08), and natural gamma (EHGR) borehole electric logs, synthetic seismic well-tie, lithologic log, sequence stratigraphic interpretation, oxygen isotope stages, lithostratigraphy, and environmental and paleobathymetric interpretations. Reproduced from Naish T, Field B, Zhu H, et al. (2005) Integrated outcrop, drill core, borehole and seismic stratigraphic architecture of a cyclothemic, shallow-marine depositional system, Wanganui Basin, New Zealand, Journal of the Royal Society of New Zealand 35: 91–122.

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

271

Figure 8 Pleistocene, shallow marine sequences exposed in the coastal Castlecliff section, Wanganui Basin, New Zealand are correlated with drill core logs from ‘behind-outcrop’ boreholes and high-resolution seismic data from along the beach at the base of the coastal cliffs (after Naish et al. (2005); reproduced from Graham (2008)).

produce a high-resolution model of the stratigraphic signatures and 2-D architecture of a cyclical, shallow-marine depositional system.

Case Study 2: Outcrop Examples of Orbitally Influenced Pleistocene Shelf Sequences Preserving Forced Regressive Deposits, Crotone Basin, Southern Italy On a global scale, the Crotone Basin preserves one of the bestdeveloped and most complete Pleistocene marine records available in outcrop, as important as those in California, New Zealand, and Japan. The preservation of high-resolution Quaternary sequences occurred through the interaction between high-amplitude global sea-level fluctuations within an extension rift basin. The 550 m-thick composite succession contains 13 orbital-scale sedimentary cycles correlated with Marine Isotope Stages 33 to 7 during a long-term shallowing from upper slope-outer shelf to marginal marine-coastal plan environments between  1.2–025 Ma (Massari et al., 2002). An unconformity of tectonic origin, which is marked by an abrupt shallowing and the first evidence of fluvial incision, punctuates the succession at the base of Sequence 9 removing the record corresponding to MIS 16–12 (0.65–0.45 Ma) (Figure 9). Correlation of the sedimentary cycles with the deep-sea oxygen isotope record is constrained by an integrated, tephro-, bio-, magneto stratigraphy (Rio et al., 1996; Massari et al., 2002). The cyclothemic nature of the record is characterized by a stack of simple or composite, seaward-prograding, sand-dominated tongues deposited during regressions and intervening aggradational mud-dominated deposits related to transgressivedeepening and highstand episodes. High rates of basinal subsidence and high rates of sediment supply have allowed exceptional outcrop examples of forced regressive systems tracts to be preserved in some sequences (Massari et al., 1999) (Figure 10).

Astronomical Calibration Calibration of orbitally forced oxygen isotope records from the deep sea with astronomical solutions for orbital precession, obliquity, and eccentricity have led to the development of an oxygen isotope numerical timescale extending back to the late Miocene (Lourens et al., 1996; Shackleton et al., 1990). Peaks and troughs in oxygen isotope records are consecutively numbered as isotope stages. For Quaternary shelf successions, the preserved sequences generally correspond to interglacial (oddnumbered) stages, while sequence-bounding unconformities correspond to glacial (even-numbered) stages. Extended Quaternary successions in the Boso Peninsula, Japan, and the Wanganui Basin, New Zealand, have been correlated in detail with the sea-level history contained in the oceanic oxygen isotope scale. For example, Naish et al. (1999) and Pillans et al. (2005) used geomagnetic reversals and numerous dated tephra horizons to calibrate 43 Wanganui sequences with oxygen isotope stages 1–100 (Figure 11), and Pickering et al. (1999) correlated Boso sequences with isotope stages 15–35. Apart from their intrinsic interest, such calibrations enable absolute dates to be estimated for the boundaries of local Stages, for biostratigraphic events such as first and last appearances, and for many otherwise undated stratigraphic units (cf. Carter 2005).

Summary 1. Glacioeustasy driven by orbital precession (20 ka), obliquity (41 ka), and eccentricity (100 ka) has imposed sedimentary cyclicity on the fill of Quaternary continental margin basins. Such cycles are represented as fifth- to seventh-order sequences by sediments within recently uplifted active-margin basins, each sequence being attributable to deposition during one cycle of sea-level change.

272

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

Mud Biozone

(Ma)

Polarity

Age

Muddy silt Silty mud

Shelf to slope

d18O (benthos)

Sandy silt Prograding sand/gravel wedge

Age (Ma)

2.0

−2.0

0.0

0.2

E. huxleyi acme zone

0.1

E. huxleyi +

Lagoonal mud Fluvial gravel Transgressive sheet 5.1 5.3

S. Mauro succession

6.3 6.5 7.1

0.3 9.3

?

?

12

10.3 11.1

San Mauro 3

11.23

Up to 20 m

0.5

8.3 8.5 9.1

Upper part of San Mauro sandstone

G. oceanica zone

0.4

0.2

7.3 7.5

? 13

0.3

0.1 5.5

11.3

0.4

?

11

13.11 13.13 13.3

0.5

15.1 15.3 15.5

0.6

Parmenide ash 9

M

.3

1.1

S.Mauro2

7 Pitagora ash

17.3 17.5 18.3

B

6

19.1 19.3

M

FO

5

sp

0.8

0.9

23 25 27

1.0

4

28

3

J 31

2

1.1

33

1 a LO

ps

35

a oc

r

1.2

0.7

21.1 21.3 21.5

ca

Small Gephyrocapsa zone

J

a ps

Up to 40 m

Gephyro

1.0

Up to 30 m Up to 26 m

0.9

17.1

S.Mauro1

0.8

16.3

? ?

Cutro 2

B

Lower part of

0.7

San Mauro sandstone

P. lacunosa zone

0.6

Polarity

10

y Large Gep h

1.2

1.4

Cutro 1

More than 260 m

1.3

Large Gephyrocapsa zone

37 39

1.3

41 43 Cyclothem boundary

1.4

45

Major unconformity Biostratigraphic

47

correlation

49

Climatic–eustatic correlation

5.0

4.0

3.0

Figure 9 Correlation of the Pleistocene San Mauro shallow-marine cyclothemic succession, Crotone Basin, with the marine oxygen isotope stratigraphy. Reproduced from Massari F, Rio D, Sagvetti M, et al. (2002) Interplay between tectonics and glacio-eustasy: Pleistocene succession of the Crotone basin, Clabria (southern Italy). GSA Bulletin 114: 1183–1209.

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

273

Major unconformity

8 100 m S.Mauro3

Ferrara E

7 S.Mauro1 S.Mauro2

Km 162 Scandale fault

S. Mauro E 5 6

Key Fluvial gravel Valle di Manche S

cm T.S.Margherita S

Prograding units (silliciclastic to variably bioclastic sand/gravel wedges fraying downdip into thinly interbedded sand and silt)

Valle di Manche N

1000 m

Offshore mud Cyclothem boundary

S. Mauro S

Minor unconformity

(a)

Pitagora ash 7

Number of cyclothem

TST + HST (sigmoid clinoforms) Rayin surface

FRST (oblique clinoforms)

A

C DWS

30 m 20

fau lt

HST (sigmoid clinoforms)

B TST

Slump scar

Sc an da le

FRST (oblique clinoforms)

C

10

B

0

Slump scar

A

(b)

Figure 10 (a) Schematic, dip-oriented cross-section linking cyclothemic sections within the Crotone Basin shows the 2-D sequence stratigraphic architecture of orbitally influenced Pleistocene shallow-marine sequences. Note the preservation of thick, seaward prograding, shore-connected sediment wedges interpreted as forced regressive deposits. (B) A more detailed example of the sequence architecture of Crotone Basin sequences showing the downward shift of facies during forced regression, marked by an RSE or DWS (downward shift surface) beneath the FRST.

2. Analysis of sedimentary sequences is undertaken using standard sedimentary facies analysis, supported by paleoecological and taphonomic analysis of fossil faunas. Stratal architecture within sequences is inferred from the succession of facies (grouped as systems tracts) and stratigraphic surfaces that occur within a sequence in the following invariant order: lower SB, LST, TSE, TST, LFS, MCS, DLS, HST, regressive or forced RST, and upper SB. 3. The vertical representation of facies and systems tracts within a Quaternary sequence varies along a hypothetical cross-shelf profile. Five sequence motifs are recognized, which characterize the spectrum of sedimentary variation that exists between the inner basin margin and the offshore basin slope. 4. Calibration of lengthy Quaternary sequence successions from Japan (Boso Peninsula) and New Zealand (Wanganui Basin) with the orbitally tuned oxygen isotope timescale has been achieved using geomagnetic reversals and dated tephra. Sequences deposited in shelf settings correspond to odd-numbered (interglacial) stages on the oxygen isotope timescale, while the even-numbered (glacial) stages are represented by sequence-bounding unconformities. Such

calibration allows numerical ages to be assigned to otherwise undated stratigraphic entities such as local lithostratigraphic units, relative time scales, and fossil first and last appearances. 5. Studies of Quaternary sequence stratigraphy have demonstrated: (i) a much greater resolution of sequence architecture than is depicted by generic sequence stratigraphic models; (ii) that subaerial sequence boundaries are rarely preserved intact, but instead are superposed by a TSE cut by shoreline passage during the rising sea-level stage of the next eustatic cycle; (iii) the common preservation of thick, sandy RST strata during the falling stage of a eustatic cycle; (iv) the occurrence of highstand and RST sedimentation rates as high as 5 m/ka, and the formation of shellbeds in as little as a few ka, in sequences from uplifted active-margin basins; and (v) the availability for study of the three-dimensional architecture of complete continental margin sequences in the light of the independent proxy sea-level history that is represented by the oceanic oxygen isotope record.

274

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

18

d O (‰) ODP site 607 North Atlantic 4.5

2.5

Earth’s orbital variations obliquity(⬚) 3.5

22 23

24

Climate transitions

Polarity Chron

Timescale (Ma)

25 26

0

Lower Onepuhi Shellbed Tom’s Shellbed Tom’s Conglomerate 39 Kupe tephra (0.63 ± 0.08 Ma), FAD Pecten kupei Waiomio Shellbed 38 FAD Pecten 37 Matuyama/Brunhes Kaukatea Tephra (0.86 +0.08 Ma) 36

150 200 250

300

100-ka

8

10

12

14

16

400

35 Top Jaramillo Potaka Tephra (0.99 ± 0.11 Ma) 34

450

33 Base Jaramillo ?

20

500

32

22

350

31 Rewa Tephra (1.2 ± 0.14 Ma) Cobb Mountain 30

550

18

Middle

100

0.12 Late

0.5

0.78

24

Pleistocene

50

4

6

Brunhes

Halcombe Conglomerate 43 Fordell, Griffins Road, Kakariki tephras 42 Rangitawa Tephra Rangitawa Shell bed LAD Pecten Marwicki Ruamahanga Conglomerate 41 Upper Onepuhi Shellbed 40 Onepuhi Tephra

0

2

Mid-Pleistocene transition

Rangitikei River composite section

26

600

Unnamed Tephra (AT-360) FAD Maorimactra n. sp. (Castlecliffian)

30

650

29 Unnamed Tephra (AT-362) 28

34

28

Jaramillo 32

1.0

41-ka

27 26 25 Unnamed Tephra (BP-590) Mangapipi24Upper Tephra (1.51 ± 0.16 Ma) Mangapipi Lower Tephra Ridge Ash 23 Mangapipi Unnamed Tephra (AT-292) Unnamed Tephra (AT-290) Unnamed Tephra (AT-291) Pakihikura Tephra (1.58 ± 0.08 Ma) Birdgrove Tephra Unnamed Tephra (BP-607) 22 Mangahou Tephra Maranoa Tephra Ototoka and Table Flat Tephra

750 800

850

900

36 38

Cobb Mountain

40 42 44 46 48

Early

700

50

Table Flat Tephra (reworked) Table Flat Tephra 21 LAD Patro undatus

1000

54 56 58

1050

60

20

1.5

Matuyama

52

950

1100 62 64

Top Olduvai 18

68

74 76

15

78

1350

80

14 82

Reunion 84

12

86

11 Orangipongo Sandstone 10 Tephra 9

1500

88 90

Ohingaiti

1550

92

8 7

1600

Ohingaiti Sandstone

94 96

5

1700

4

1750

Tuha Shellbed 3 Tuha Sandstone

1800

Hautawa Shellbed 2

First major 41-ka-duration N.H. glacial cycles

98

6

1650

100 102

106 108 110 112 114

Mangarere Sandstone 1

1950

116 118 120

2000

122 Gauss-Matuyama Boundary

M

2.5 2.59

104

1850 1900

2.0

Gelasian

13 Mangamako Shellbed

1450

S G

Piacenzian

1400

Quaternary

72

Pliocene

1300

Olduvai

70

Plio - Pleistocene Boundary Waipuru Shellbed 17 Waipuru Tephra (1.79 ± 0.15 Ma) 16

1250

Gauss

1200

1.81

66

Ice growth on NH continents

Vinegar Hill Tephra (1.75 ± 0.25 Ma) 19

1150

3.0

0.05 0.04 0.03

0.02 0.01

0

Eccentricity

Figure 11 Composite stratigraphic section from Rangitikei River valley, Wanganui Basin showing ‘one-to-one’ correlation of Quaternary sequences with global ice volume/sea-level cycles on the deep ocean isotope curve. This astronomical calibration of the Wanganui sequences is constrained independently by an integrated bio-, tephro-, magnetostratigraphic age model. Modified from Pillans BJ, Alloway BV, Naish TR, Abbott SA, Westgate JA, and Palmer A (2005) The distal archive of North Island silicic volcanism recorded in Pleistocene shallow marine sediments of Wanganui Basin, New Zealand. Journal of the Royal Society of New Zealand 35: 43–90.

QUATERNARY STRATIGRAPHY | Sequence Stratigraphy

See also: Glaciation, Causes: Astronomical Theory of Paleoclimates. Quaternary Stratigraphy: Lithostratigraphy.

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