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Geomorphological and sequence stratigraphic variabilityin wave-dominated, shoreface-shelf parasequences
GARY J. HAMPSON* and JOEP E. A. STORMS�*Department of Earth Science and Engineering, Imperial College London, South Kensington Campus,London SW7 2AZ, UK (E-mail: [email protected])�Department of Applied Earth Sciences, Delft University of Technology, Mijnbouwstraat 120,2628 RX, Delft, The Netherlands
ABSTRACT
Physical stratigraphy within shoreface-shelf parasequences contains a detailed,
but virtually unstudied, record of shallow-marine processes over a range of
historical and geological timescales. Using high-quality outcrop data sets, it is
possible to reconstruct ancient shoreface-shelf morphology from clinoform
surfaces, and to track the evolving morphology of the ancient shoreface-shelf.
Our results suggest that shoreface-shelf morphology varied considerably in
response to processes that operate over a range of timescales. (1) Individual
clinoform surfaces form as a result of enhanced wave scour and/or sediment
starvation, which may be driven by minor fluctuations in relative sea level,
sediment supply and/or wave climate over short timescales (101)103 years).
These external controls cannot be distinguished in vertical facies successions,
but may potentially be differentiated by the resulting clinoform geometries. (2)
Clinoform geometry and distribution changes systematically within a single
parasequence, reflecting the cycle in sea level and/or sediment supply that
produced the parasequence (102)105 years). These changes record steepening
of the shoreface-shelf profile during early progradation and maintenance of a
relatively uniform profile during late progradation. Modern shorefaces are not
representative of this stratigraphic variability. (3) Clinoform geometries
vary greatly between different parasequences as a result of variations in
parasequence stacking pattern and relict shelf morphology during shore-
face progradation (105)108 years). These controls determine the external
dimensions of the parasequence.
Keywords Clinoform, facies model, parasequence, shelf, shoreface, shorelinetrajectory.
INTRODUCTION
It is frequently difficult to reconcile modernshallow-marine processes with ancient stratigra-phy because of the vastly different timescalesconsidered and the incompleteness of the strati-graphic record, particularly with regard to shore-face-shelf morphology. In this paper, we addressthis issue of comparison using geomorphologicalobservations from high-quality outcrop data setsof ancient wave-dominated shoreface-shelf sys-tems. Our observations provide sufficient detail toreconstruct ancient shoreface-shelf morphologyand to track the evolving morphology of the
ancient shoreface-shelf within a detailed sequ-ence stratigraphic context. The aims of this workare: (1) to present a consistent conceptual frame-work that incorporates geomorphological andsequence stratigraphic variability in wave-dom-inated shoreface-shelf deposits and their moderncounterparts; and (2) to examine the implicationsof this framework for current facies models andsequence stratigraphic paradigms.
Shoreface-shelf systems in high wave andstorm energy settings are commonly representedin the stratigraphic record by upward-coarsen-ing sandstone tongues that contain a distinctivevertical facies succession (i.e. the parasequences
Sedimentology (2003) 50, 667–701 doi: 10.1046/j.1365-3091.2003.00570.x
� 2003 International Association of Sedimentologists 667
of Van Wagoner et al., 1990). Each sandstonetongue represents an episode of shorelineregression, and is capped by a thin transgressivesuccession that culminates in condensed marineshales (i.e. the flooding surfaces of Van Wagoneret al., 1990). Current facies models of theseshoreface-shelf sandstones emphasize their com-mon, generic features, but fail to address twokey geomorphological and stratigraphic issuesthat account for the variability between them.First, facies models focus on the relationshipbetween vertical facies successions and thedepth of fairweather and storm-wave base (e.g.Elliott, 1986; Walker & Plint, 1992), but do notdirectly relate these properties to ancient shore-face-shelf morphology. However, there is asignificant difference in scale between modernshorefaces, which are defined using nearshoremorphology, and their ancient counterparts,which are interpreted from vertical faciessuccessions using facies models (e.g. Clifton,2000; Fig. 1). Secondly, there is considerablevariability in the external dimensions (thicknessand width) of wave-dominated shoreface-shelfparasequences (Reynolds, 1999; Fig. 1). Thisvariability bears a strong relationship to the
sequence stratigraphic context of individualparasequences within larger progradational orretrogradational parasequence sets (Reynolds,1999; Fig. 1). Such stratigraphic variability can-not be accounted for by ‘static’ facies models(e.g. Elliott, 1986; Walker & Plint, 1992), butmay be explained instead by variations in theangle of shoreline migration (i.e. the shorelinetrajectory of Helland-Hansen & Martinsen, 1996)during different episodes of shoreline regression(e.g. Budding & Inglin, 1981). In this paper,these two aspects of parasequence variabilityare addressed via a consideration of nearshoremorphology and shoreline trajectory withindifferent shoreface-shelf parasequences. Twocase studies of parasequences with markedlydifferent dimensions (thickness and width) andsequence stratigraphic context are presented, inwhich the ancient shoreface-shelf profile andshoreline trajectory are reconstructed via analy-sis of detailed intraparasequence facies archi-tecture. These reconstructions are comparedwith similar data from modern and Holoceneshoreface-shelf sandbodies and with verticalfacies successions of the type emphasized incurrent facies models.
Highstand SystemsTract
ShelfMargin SystemsTract Transgressive Systems Tract
Lowstand Systems Tract
max
imum
wid
th(m
)
maximum thickness(m)
50 000
40
1:100
1:1000
30201000
40 000
30 000
20 000
10 000
'SC4'shoreface tongue
'K4'shoreface tongue
50
Holocene shoreface sands,TexasCoast, Gulf of Mexico
Fig. 1. Plot showing dimensions of ancient shoreface-shelf parasequences differentiated by their sequence strati-graphic context within different systems tracts (modified from Reynolds, 1999). The ‘SC4’ and ‘K4’ tongues describedin this paper are highlighted. Also shown is the range of Holocene shoreface sandbody dimensions along the TexasCoast, Gulf of Mexico (Rodriguez et al., 2001), where the height of the modern shoreface is defined using nearshoremorphology (after Clifton, 2000).
668 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
Morphology, processes and facies modelsof wave-dominated shorefaces and shelves
The main morphological elements of a modernshoreface-shelf system are illustrated in Fig. 2.The foreshore is sculpted by the swash andbackwash of breaking waves, which producedistinctive planar-parallel and wedging lamina-tions (Clifton, 1969), and it dips steeply seawardat 2–3� (Fig. 2; Elliott, 1986; Walker & Plint,1992). The shoreface is characterized by day-to-day sand transport by fairweather waves and dipsseaward at � 0Æ1–0Æ3� (Fig. 2; Elliott, 1986; Cant,1991; Walker & Plint, 1992). Modern shorefacestend towards a concave-upward equilibriumprofile that reflects a balance between sedimentcalibre, active depositional processes and energylevel (Tanner, 1982; Walker & Plint, 1992). Thebase of the shoreface is identified as a break inslope at the base of the equilibrium profile(Clifton, 2000). The dominant fairweather deposi-tional processes on the shoreface involve along-shore and cross-shore sediment transport drivenby shoaling waves (Davis & Hayes, 1984; Walker &Plint, 1992). These processes result in onshoremovement of sand, which maintains the steep(0Æ1–0Æ3�) equilibrium profile, and the develop-ment of a distinctive series of bedforms fromlower to upper shoreface: symmetrical ripples,asymmetrical ripples and asymmetrical dunes(Clifton, 1976). The offshore shelf, where fair-weather waves do not impinge, dips seaward at� 0Æ01–0Æ03� (Fig. 2; Elliott, 1986; Cant, 1991;Walker & Plint, 1992). Deposition on the shelf iscontrolled by episodic storm-wave processes,which result in graded, waning flow beds char-
acterized by hummocky cross-stratification (Dott& Bourgeois, 1982; Walker & Plint, 1992), andother active shelf processes (e.g. tides). However,shelf morphology may be strongly influenced byinactive, relict processes.
The most significant short-term changes inshoreface-shelf profile occur during stormevents when wave base is lowered. This resultsin severe scouring of the shoreface, flattening ofthe shoreface profile and remobilization ofsediment (Hobday & Reading, 1972; Reineck &Singh, 1972; Walker & Plint, 1992). The remo-bilized sediment is transported offshore beyondstorm-wave base (Walker & Plint, 1992),reworked at the shoreface or transported intobackshore environments such as barrier-islandwashovers (Penland et al., 1985). It may takeseveral years for the equilibrium profile of theshoreface to be restored by fairweather waveprocesses after a major storm (e.g. Larson &Kraus, 1994; Lee et al., 1998), and storm-waveproducts may have a high preservation potentialon the shoreface (e.g. Clifton et al., 1971;Greenwood & Sherman, 1986). The preservationof storm-generated deposits above fairweatherwave base presents a challenge when interpret-ing the base of the shoreface in vertical faciessuccessions. As a result, different workers haveinterpreted the base of the shoreface at differentplaces in the same, idealized facies succession(Fig. 3): at the base of hummocky cross-stratifiedsandstone beds (Van Wagoner et al., 1990;Kamola & Van Wagoner, 1995), at the baseof amalgamated swaley-cross-stratified beds(Elliott, 1986; Walker & Plint, 1992) and at apebble lag that underlies trough and tabular
foreshore/beach(dip = 2-3˚)
(lithology: sandstone)
shoreface(dip = 0.1-0.3˚)
(lithology: sandstone)(common burrows:
Skolithos, Arenicolites,Diplocraterion, Ophiomorpha,
Thalassinoides)
inner shelf(dip = 0.03-0.1˚)
(lithology: sandstone and mudstone)(common burrows:
Phycodes, Rhizocorallium,Teichichnus, Terebellina)
mid to outer shelf(dip = 0.01-0.03˚)
(lithology: mudstone)(common burrows:
Phycosiphon, Zoophycos)
L/2
L
5-15 m
1000-2000 m
fairweather wave base
storm wave base
longshore bars
wav
es b
egin
to b
uild
up
spilli
ng b
reak
ers
Fig. 2. Schematic shoreface-shelf profile showing its main morphological elements (modified from Walker & Plint,1992).
Variability in wave-dominated, shoreface-shelf parasequences 669
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
cross-beds (Clifton, 2000). In this paper, we usethe terminology of Van Wagoner et al. (1990)and Kamola & Van Wagoner (1995), summarized
in Table 1, to describe shoreface-shelf faciessuccessions, because it can be applied mosteasily to vertical sections.
670 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
DATA SETS AND METHODOLOGY
This paper presents data from two shoreface-shelfparasequences in the Campanian (Upper Creta-ceous) Blackhawk Formation, both of which arenearly continuously exposed in the Book Cliffs,Utah, USA (Figs 4 and 5). These parasequencesoccur within the Kenilworth Member (‘K4’ sho-reface tongue; Figs 5 and 6A) and the SpringCanyon Member (‘SC4’ shoreface tongue; Figs 5and 6B). The time represented by these parase-quences is poorly constrained. Sparse radiometricand palaeontological age data constrain depos-ition of the Blackhawk Formation to between 82Æ5and 79 Ma (Fouch et al., 1983), implying thateach member represents � 0Æ5–0Æ6 Myr, and thatindividual parasequences, including those des-cribed here, represent � 70–120 kyr. Shorelinesin the Blackhawk Formation have a depositionalstrike orientation varying between SSW–NNE(e.g. ‘SC4’ shoreface tongue; Fig. 4A and C) andSSE–NNW (e.g. ‘K4’ shoreface tongue; Fig. 4Aand B).
Both parasequences were studied using meas-ured, logged sections combined with detailedphotomontages and field sketches covering theirentire outcrop extent (Figs 4 and 6). Cliff-facephotomontages allow minor, intraparasequencestratigraphic discontinuities identified in meas-ured vertical sections to be traced laterally, wherethey define clinoforms (Hampson, 2000). Thisapproach has allowed the extents and geometriesof these clinoform surfaces, and the intraparase-quence facies architecture that they define, to bemeasured to a first approximation (relative tophotogrammetric techniques such as those des-cribed by Dueholm & Olsen, 1993). The precisionof the data presented here is limited by twofactors. First, some discontinuity-bounded unitsare too thin (< 50 cm) to be resolved sharply inthe photomontages. Secondly, accurate measuredthicknesses for the studied successions wereobtained only at localities with logged sections. T
able
1.
Su
mm
ary
of
facie
sass
ocia
tion
sin
the
stu
die
dp
ara
sequ
en
ces
(mod
ified
from
Van
Wagon
er
et
al.
,1990;K
am
ola
&V
an
Wagon
er,
1995;P
att
ison
,1995;
Taylo
r&
Lovell
,1995).
Lit
hofa
cie
sass
ocia
tion
Lit
holo
gy
an
dse
dim
en
tary
stru
ctu
res
Bio
turb
ati
on
Fore
shore
(FS
)U
pp
er
fin
e-g
rain
ed
san
dst
on
e.
Pla
nar-
para
llel
lam
inati
on
.A
bse
nt
Up
per
shore
face
(US
F)
Up
per
fin
e-
tolo
wer
med
ium
-gra
ined
san
dst
on
e.
Tro
ugh
an
dta
bu
lar
cro
ss-b
ed
s,m
inor
pla
nar
lam
inati
on
an
dsw
ale
ycro
ss-s
trati
ficati
on
Sp
ars
eto
mod
era
te(O
ph
iom
orp
ha,
Skoli
thos,
Cyli
nd
rich
nu
s,A
ren
icoli
tes)
Pro
xim
al
low
er
shore
face
(pL
SF
)A
malg
am
ate
dbed
sof
up
per
fin
e-g
rain
ed
san
dst
on
e.
Sw
ale
yan
dh
um
mocky
cro
ss-s
trati
ficati
on
,m
inor
wavy
lam
inati
on
an
dw
ave
rip
ple
cro
ss-l
am
inati
on
.
Mod
era
teto
inte
nse
(Op
hio
morp
ha,
Pala
eop
hycu
s,A
ren
icoli
tes,
Teic
hic
hn
us,
Th
ala
ssin
oid
es)
Dis
tal
low
er
shore
face
an
din
ner
shelf
/ram
p(d
LS
F)
Non
-am
alg
am
ate
dbed
sof
up
per
fin
e-g
rain
ed
san
dst
on
ew
ith
mu
dst
on
ean
dsi
ltst
on
ein
terb
ed
s.H
um
mocky
cro
ss-s
trati
ficati
on
,m
inor
wavy
lam
inati
on
an
dw
ave
rip
ple
cro
ss-l
am
inati
on
.
Mod
era
teto
inte
nse
(Op
hio
morp
ha,
Pla
noli
tes,
Pala
eop
hycu
s,T
ere
bell
ina,
Are
nic
oli
tes,
Teic
hic
hn
us,
Th
ala
ssin
oid
es)
Off
shore
shelf
/ra
mp
(OS
)M
ud
ston
ean
dsi
ltst
on
ew
ith
bed
sof
very
fin
e-
tou
pp
er
fin
e-g
rain
ed
san
dst
on
e.
Para
llel
lam
inati
on
,w
ave
an
dcu
rren
tri
pp
lecro
ss-l
am
inati
on
.
Inte
nse
(Pla
noli
tes,
Pala
eop
hycu
s,T
ere
bell
ina,
Teic
hic
hn
us,
Ch
on
dri
tes,
Helm
inth
op
sis)
Wave-i
nfl
uen
ced
delt
afr
on
t(D
F)
Up
per
fin
e-g
rain
ed
san
dst
on
ebed
sw
ith
mu
dst
on
ean
dsi
ltst
on
ein
terb
ed
s.B
ed
sth
icken
an
dam
alg
am
ate
up
ward
sth
rou
gh
the
success
ion
.P
lan
ar-
para
llel
lam
inati
on
,cli
mbin
gcu
rren
tri
pp
lecro
ss-l
am
inati
on
,w
ave
an
dcu
rren
tri
pp
lecro
ss-l
am
inati
on
.
Mod
era
te(O
ph
iom
orp
ha,
Cyli
nd
rich
nu
s,P
lan
oli
tes,
Pala
eop
hycu
s,R
oss
eli
a,
Con
ich
nu
s,T
eic
hic
hn
us,
Dip
locra
teri
on
,R
hiz
ocora
lliu
m,
Th
ala
ssin
oid
es)
Fig. 3. Idealized vertical facies succession through awave-dominated shoreface-shelf parasequence, high-lighting different interpretations of the morphologicalelements shown in Fig. 2 (after Elliott, 1986; VanWagoner et al., 1990; Walker & Plint, 1992; Kamola &Van Wagoner, 1995; Clifton, 2000). This paper uses thefacies association terminology of Van Wagoner et al.(1990) and Kamola & Van Wagoner (1995): offshoreshelf/ramp (OS), distal lower shoreface and inner shelf/ramp (dLSF), proximal lower shoreface (pLSF), uppershoreface (USF), foreshore (FS).
Variability in wave-dominated, shoreface-shelf parasequences 671
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
Elsewhere, the successions are exposed in inac-cessible, sheer cliff faces.
The two studied parasequences differ mark-edly in their thickness, their internal sedimen-
tological character and their sequence strati-graphic setting. The ‘SC4’ shoreface tongue hasa maximum thickness of 20 m, a dip extent of22 km (from landward to seaward pinch-outs of
A
B
C
672 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
marine sandstone) and is documented to record‘normal regression’ within the early part of ahighstand systems tract (Fig. 1; Van Wagoneret al., 1990; Kamola & Van Wagoner, 1995). Thisparasequence is also interpreted to record atransition in shoreline type from wave-domi-nated shoreface to wave-influenced delta duringprogradation (Kamola & Van Wagoner, 1995).The ‘K4’ shoreface tongue has a maximumthickness of 45 m and a dip extent of 15 km(Fig. 1; Pattison, 1995; Taylor & Lovell, 1995;Hampson, 2000). This parasequence is documen-ted to record ‘forced regression’ of a wave-dominated shoreface (Pattison, 1995; Hampson,2000) and has been placed within the late part ofa highstand systems tract (Taylor & Lovell, 1995)and, alternatively, the late part of a highstandsystems tract to a lowstand systems tract (Patti-son, 1995; Hampson, 2000).
In order to reconstruct true spatial relation-ships in the study data sets, the clinoformgeometries and clinoform-defined facies architec-tures measured along cliff-face panels have beenprojected into the plane of regional depositionaldip (as defined by Kamola & Van Wagoner, 1995in the ‘SC4’ shoreface tongue and by Hampson,2000 in the ‘K4’ shoreface tongue; Fig. 4B and C).This procedure is relatively straightforward inthe ‘K4’ shoreface tongue and the palaeoland-ward portion of the ‘SC4’ shoreface tongue,which are characterized by linear, wave-domin-ated shorelines (Kamola & Van Wagoner, 1995;Taylor & Lovell, 1995; Hampson, 2000). Deposi-tional dip trends are more difficult to reconstructfor the wave-influenced deltaic shorelines of thepalaeoseaward portion of the ‘SC4’ shorefacetongue.
FACIES ASSOCIATIONS ANDCLINOFORM SURFACES
Intraparasequence facies architecture is definedby the facies associations present within theparasequence and by the dipping clinoform sur-faces to which intraparasequence facies distribu-tions are conditioned (e.g. Budding & Inglin,1981). These two components are describedbriefly below.
Facies associations: wave-dominatedshoreface-shelf and wave-influenced deltafront
The facies associations present within thetwo studied parasequences have been describedand interpreted in detail by previous workers(Howard & Frey, 1984; Van Wagoner et al.,1990; Kamola & Van Wagoner, 1995; Pattison,1995; Taylor & Lovell, 1995) and are sum-marized below. Five facies associations areinterpreted to represent wave-dominated shore-face-shelf deposits (e.g. Van Wagoner et al.,1990; Table 1): (1) interbedded rippled sand-stones and bioturbated mudstones, interpretedas offshore marine shelf/ramp (OS) deposits; (2)non-amalgamated hummocky cross-stratifiedsandstones, interpreted as distal lower shorefaceand inner shelf/ramp (dLSF) deposits; (3) amal-gamated hummocky and swaley cross-stratifiedsandstones, interpreted as proximal lower shore-face (pLSF) deposits; (4) cross-bedded sand-stones, interpreted as upper shoreface deposits(USF); and (5) planar-parallel-laminated sand-stones, interpreted as foreshore (FS) deposits.These five facies associations are arranged in adistinctive vertical succession of facies that isinterpreted to record an overall shallowing fromoffshore shelf/ramp deposits via distal andproximal lower shoreface deposits to uppershoreface and foreshore deposits (Figs 6, 7A–Dand 8).
An additional facies association in the ‘SC4’shoreface tongue is interpreted to represent wave-influenced delta front deposits (Kamola & VanWagoner, 1995; Table 1). This facies associationcomprises an upward-coarsening succession ofnon-amalgamated to amalgamated sandstonebeds, in which individual beds are characterizedby a distinctive vertical succession of structuresthat records deposition from waning, unidirec-tional currents: planar-parallel lamination over-lain by climbing or non-climbing current ripplecross-lamination (Figs 6B, 7E and 9). Bed tops are
Fig. 4. (A) Map of the Book Cliffs in east-central Utahshowing the location and extent of the two study areas.(B) Detailed maps of the first study area, which con-tains the ‘K4’ shoreface tongue, Kenilworth Member(Fig. 5). (C) Detailed maps of the second study area,which contains the ‘SC4’ shoreface tongue, SpringCanyon Member. The detailed maps of both areas showthe location of measured outcrop sections (includingthe logged sections illustrated in Figs 7, 8A and 9A),correlation panels (Fig. 6), photomontage-based cliff-face panels (Figs 12 and 13) and depositional strike anddip. Closed circles denote measured, logged sections.Open circles denote the location of prominent topo-graphic features that allow the mapped cliff line to betied directly to continuous photomontages of the cliffface (e.g. Fig. 10).
Variability in wave-dominated, shoreface-shelf parasequences 673
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
Fig
.5.
Su
mm
ary
stra
tigra
ph
iccro
ss-s
ecti
on
thro
ugh
the
Bla
ckh
aw
kF
orm
ati
on
(aft
er
Bals
ley,
1980;
Ham
pso
net
al.
,2001
an
dre
fere
nces
there
in).
Datu
mh
ori
zon
sare
regio
nall
yexte
nsi
ve
lith
ost
rati
gra
ph
icm
ark
ers
.D
ocu
men
ted
sequ
en
ce
bou
nd
ari
es
are
labell
ed
as
foll
ow
s:A
SB
,A
berd
een
sequ
en
ce
bou
nd
ary
;K
SB
,K
en
ilw
ort
hse
qu
en
ce
bou
nd
ary
;S
SB
,S
un
nysi
de
sequ
en
ce
bou
nd
ary
;G
SB
1–3,
Gra
ssy
sequ
en
ce
bou
nd
ari
es
1–3;
DS
B,
Dese
rtse
qu
en
ce
bou
nd
ary
;C
SB
,C
ast
legate
sequ
en
ce
bou
nd
ary
.S
hore
face
ton
gu
es
are
nu
mbere
dw
ith
inth
eS
pri
ng
Can
yon
(SC
1–7),
Aberd
een
(A1–4),
Ken
ilw
ort
h(K
1–5),
Su
nn
ysi
de
(S1–3)
an
dG
rass
yM
em
bers
(G1–4).
Th
etw
osh
ore
face
ton
gu
es
desc
ribed
ind
eta
ilin
this
pap
er
(‘S
C4’
an
d‘K
4’)
are
hig
hli
gh
ted
.
674 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
A B
Fig
.6.
Corr
ela
tion
pan
els
thro
ugh
the
stu
die
dp
ara
sequ
en
ces:
(A)
the
‘K4’
ton
gu
ean
d(B
)th
e‘S
C4’
ton
gu
e,
show
ing
logged
secti
on
san
dgro
ssfa
cie
sd
istr
i-bu
tion
s.B
oth
pan
els
are
pro
jecte
din
toth
ep
lan
eof
regio
nal
dep
osi
tion
al
dip
for
each
para
sequ
en
ce
(Fig
.4).
Logged
secti
on
ssh
ow
nin
more
deta
ilin
Fig
.7
are
hig
hli
gh
ted
.T
he
corr
ela
tion
pan
els
do
not
rep
rese
nt
cli
nofo
rm-d
efi
ned
facie
sarc
hit
ectu
re,w
hic
his
show
nin
stead
inth
ep
hoto
mon
tage-b
ase
dli
ne
dra
win
gs
inF
igs
12
an
d13.
Th
ed
ep
osi
tion
al
dip
exte
nt
of
these
ph
oto
mon
tages
ish
igh
ligh
ted
.
Variability in wave-dominated, shoreface-shelf parasequences 675
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
A
Fig. 7.
676 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
reworked by wave ripples and bioturbation.These beds are interpreted to record episodicdeposition from unidirectional flows, most prob-
ably fed by river floods at the mouth of the deltadistributary. The upward thickening and upwardamalgamation of beds within the succession are
Fig. 7. Detailed sedimentary logs through the studied parasequences showing sedimentology, facies and sequencestratigraphic interpretations: (A) the ‘K4’ tongue at Middle Mountain measured section 1 (Figs 4B, 6A and 12A); (B)the ‘K4’ tongue at Middle Mountain measured section 3 (Figs 4B, 6A and 12A); (C) the ‘SC4’ tongue at Peerless Mine(Figs 4C, 6B and 8A); (D) the ‘SC4’ tongue in the northern face of Spring Canyon (Figs 4C, 6B and 12C); and (E) the‘SC4’ tongue in the eastern ‘Kenilworth Face’, at Kenilworth measured section 1 (Figs 4C, 6B, 9A, 11B and 13C).Minor stratigraphic discontinuities are highlighted here and discussed further in the text. Key as for Fig. 3.
Variability in wave-dominated, shoreface-shelf parasequences 677
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
interpreted to represent increasing proximity tothe distributary mouth, which was the source ofthe episodic unidirectional flows, during anoverall shallowing. Waning-flow beds character-
ized by climbing current ripple cross-laminationare also observed in the storm-dominated, prox-imal lower shoreface deposits of the ‘SC4’ tongue(Fig. 9C). Their occurrence implies that episodic
C
E
Fig. 7. Continued.
678 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
D
Fig
.7.
Con
tin
ued
.
Variability in wave-dominated, shoreface-shelf parasequences 679
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
storm- and river-mouth-derived currents wereboth active during deposition of the ‘SC4’ tongue,and the latter may have played a more significantrole in intratongue facies architecture than hasbeen interpreted previously (Van Wagoner et al.,1990; Kamola & Van Wagoner, 1995).
The vertical successions described aboverepresent the progradation of depositional sys-tems in which all the facies components arelinked genetically (i.e. the parasequences of VanWagoner et al., 1990). These successions can besubdivided internally into smaller genetic faciessuccessions bounded by minor stratigraphic dis-continuities (i.e. the bedsets of Van Wagoneret al., 1990).
Clinoform surfaces defined by minor,intraparasequence stratigraphicdiscontinuities
Minor stratigraphic discontinuities are recog-nized in both the parasequences described in
this paper (e.g. Figs 7 and 10) and in similaroutcrop and subsurface data sets (Valasek, 1990;O’Byrne & Flint, 1995; Jennette & Riley, 1996).The discontinuities have greater genetic signifi-cance than simple bedding surfaces and corre-spond closely to the bedset boundaries of VanWagoner et al. (1990). These surfaces defineclinoforms that dip gently palaeoseaward(Fig. 11) and are interpreted as preserved rem-nants of the ancient shoreface-shelf profile (e.g.McCubbin, 1982; Hampson, 2000). The utility ofthe surfaces is twofold. First, the physical char-acter and geometry of the discontinuity surfacesrecords the response of the ancient shoreface-shelf profile to short-term processes that arecomparable to those observed and measured inmodern settings (estimated at 101)103 years;Table 2). Secondly, the spatial distribution ofthe discontinuities within a parasequenceprovides a record of the shoreline trajectoryduring intermediate-term regression (estimatedat 102)105 years).
A B
C
Fig. 8. Photographs of wave-dominated shoreface-shelf successions in the ‘SC4’ tongue. (A) The vertical successionat Peerless Mine (Figs 4C, 6B and 7C) contains several non-depositional discontinuities. (B) The upper two non-depositional discontinuities in this succession are marked by rooted surfaces within anomalously thick foreshore(FS) deposits (at 21Æ3 m and 22Æ0 m in Fig. 7C), and they record minor transgressions. (C) Non-depositional dis-continuities in proximal lower shoreface facies (pLSF) are typically marked by intense bioturbation (e.g. at 13Æ5 m inthe eastern measured section in the northern face of Spring Canyon, Fig. 7D).
680 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
Non-depositional discontinuitiesNon-depositional discontinuities are observedin both wave-dominated shoreface successionsand wave-influenced delta front successions(Table 2). In the former, they are marked by anabrupt decrease in the thickness and amalgama-tion of storm-generated event beds within prox-imal and distal lower shoreface and offshoreshelf/ramp facies (Fig. 7A–D). In the latter, theyare marked by a similarly abrupt decrease in thethickness and amalgamation of river flood-gen-erated event beds within delta front facies(Figs 7E and 9A). In both types of succession,the discontinuities are also marked by anincrease in the intensity of bioturbation. Asthe surfaces are traced palaeolandward intomore proximal strata, where mudstones areabsent, they may be characterized only bymoderate to intense bioturbation (Fig. 8C, alsocompare the palaeoseaward section shown inFig. 7B with the palaeolandward section shownin Fig. 7A). Further palaeolandward, the surfa-ces become more cryptic in expression and maybe represented by bedding surfaces with nodistinctive characteristics in vertical section[e.g. the surface between Pattison’s (1995) bed-sets 8a and 8b cannot be identified clearly
palaeolandward of the section shown in Fig. 7A].In these proximal settings, however, some discon-tinuities are marked by an anomalous incursion ofmore distal facies; for example, an incursion ofamalgamated storm-generated event beds, repre-senting proximal lower shoreface facies, intoupper shoreface facies [e.g. the surface betweenPattison’s (1995) bedsets 8b and 8c in Fig. 7A]. Inthe ‘SC4’ tongue, several of these discontinuitiescan be traced to their palaeolandward limit, wherethey occur within anomalously thick (> 2 m)successions of foreshore deposits (Fig. 7C andD). Individual discontinuity surfaces may bemarked by rooted surfaces in these foreshoresuccessions (Figs 7C and 8A and B).
The physical characteristics of these surfacessuggest that they record episodes of reducedsedimentation, which produced more intensebioturbation, synchronous with a decrease insand supply and/or river flood frequency or stormwave energy, which suppressed bed amalgama-tion (Hampson, 2000). Thus, these surfaces mayhave formed by three mechanisms: (1) decreasesin storm or river flood event frequency; (2)changes to a less energetic wave/storm climate;and (3) minor rises in relative sea level (e.g. Dott &Bourgeois, 1982; Hampson, 2000; Storms, 2003).
A B
C
Fig. 9. Photographs of wave-influenced delta front successions in the ‘SC4’ tongue. (A) The vertical succession atKenilworth measured section 1 (Figs 4C, 6B and 7E) contains several non-depositional discontinuities that can betraced out to define clinoform surfaces (Fig. 11B). The transgressive surface at the top of this succession (B) is markedby a coarse-grained lag deposit (at 13Æ7 m in Fig. 7E). (C) Continuous successions of climbing asymmetrical ripplesoccurring within proximal lower shoreface facies (pLSF) of wave-dominated shoreface successions, such as that atGilson Gulch (Figs 4C and 6B), record deposition from sustained unidirectional currents. These successions mayindicate episodic deposition by river floods in an environment that is otherwise dominated by storm-wave processes.
Variability in wave-dominated, shoreface-shelf parasequences 681
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
A B C
Fig
.10.
Exam
ple
of
the
meth
od
olo
gy
use
dto
recon
stru
ct
deta
iled
,cli
nofo
rm-d
efi
ned
facie
sarc
hit
ectu
rein
the
stu
die
dp
ara
sequ
en
ces.
(A)
Ph
oto
mon
tage
of
the
‘SC
4’
ton
gu
ealo
ng
part
of
the
nort
hfa
ce
of
Sp
rin
gC
an
yon
(Fig
.4C
),an
nota
ted
tosh
ow
the
tran
sgre
ssiv
esu
rfaces
that
bou
nd
the
para
sequ
en
ce
an
dse
lecte
dd
iscon
tin
uit
ysu
rfaces
wit
hin
the
para
sequ
en
ce.
Th
ep
hoto
mon
tage
isori
en
ted
ap
pro
xim
ate
lyalo
ng
dep
osi
tion
al
stri
ke.
(B)
Lin
ed
raw
ing
of
the
ph
oto
mon
tage
hig
hli
gh
tin
gth
esa
me
surf
aces
an
dfa
cie
sd
istr
ibu
tion
s.(C
)S
imp
lifi
ed
an
dvert
icall
yexaggera
ted
lin
ed
raw
ing
from
the
ph
oto
mon
tage,in
the
form
at
of
the
cli
ff-
face
pan
els
show
nin
Fig
s12
an
d13.
682 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
A B
Fig
.11.
Un
inte
rpre
ted
an
din
terp
rete
dp
hoto
mon
tages
show
ing
cli
nofo
rmsu
rfaces
inth
est
ud
ied
para
sequ
en
ces.
(A)
Non
-dep
osi
tion
al
an
dero
sion
al
dis
-con
tin
uit
ies
(labell
ed
‘nd
’an
d‘e
’re
specti
vely
)d
efi
nin
geast
ward
-dip
pin
gcli
nofo
rms
inw
ave-d
om
inate
dsh
ore
face
dep
osi
tsof
the
‘K4’
ton
gu
e,
alo
ng
the
sou
thern
face
of
Blu
eC
ast
leB
utt
e(F
ig.
4B
).(B
)N
on
-dep
osi
tion
al
dis
con
tin
uit
ies
(labell
ed
‘nd
’)d
efi
nin
gso
uth
ward
-dip
pin
gcli
nofo
rms
inw
ave-i
nfl
uen
ced
delt
afr
on
td
ep
osi
tsof
the
dis
tal
‘SC
4’
ton
gu
e,
at
Ken
ilw
ort
hm
easu
red
secti
on
1(F
igs
4C
,7E
an
d9A
).B
oth
ph
oto
mon
tages
are
ali
gn
ed
ap
pro
xim
ate
lyalo
ng
dep
osi
tion
al
dip
.
Variability in wave-dominated, shoreface-shelf parasequences 683
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
Each of these mechanisms is highly probablealong wave-dominated and wave-influencedshorelines, but distinguishing their products inthe stratigraphic record is not easy. Those dis-continuity surfaces in the palaeolandward, wave-dominated part of the ‘SC4’ tongue that can betraced into upper shoreface and foreshore depos-its (Figs 7D, 8A and B and 12B and C) and aremarked by rooted surfaces in the latter (Figs 7Cand 8B) are demonstrably associated with minortransgressions (mechanism 3 above). However,discontinuity surfaces that can only be identifiedand traced within lower shoreface and delta frontdeposits, where sandstone deposition occursexclusively via episodic storm and/or river floodevents, are equally attributable to each of thethree mechanisms. Each mechanism impliessubtle, geometrical changes in the shorefaceprofile and resulting clinoforms: (1) a decreasein sedimentation event frequency will result in nosignificant change in shoreface profile; (2) adecrease in wave energy, and resulting shallow-ing of fairweather wave base, will result in adecrease in the gradient of the shoreface profile,as a result of reduced onshore sand advection(Inman & Bagnold, 1963; Carey et al., 1999;Storms, 2003); and (3) a minor rise in relativesea level will not cause a change in shoreface-shelf profile geometry, although some transgres-sive reworking of upper shoreface and foreshoredeposits may occur if sediment supply rates arelow. These changes in clinoform geometry are notapparent in one-dimensional, vertical logged sec-tions and are discussed below in relation toobservations in the ‘SC4’ and ‘K4’ tongues.
Erosional discontinuitiesErosional discontinuities are observed in wave-dominated shoreface successions only (Table 2).They are marked in vertical sections throughproximal and distal lower shoreface and offshoreshelf/ramp facies by erosion, a discontinuous lagof wood fragments and plant debris and abruptincreases in storm-generated event bed amalga-mation, grain size and sand content (Fig. 7A). Thediscontinuities occur at the base of amalgamatedhummocky cross-stratified beds in units 30 cm to7 m thick that pass upward into non-amalgama-ted beds (Hampson, 2000). The surfaces may alsobe associated with steep-walled gutter casts and aGlossifungites ichnofacies. The discontinuitiesare traced palaeolandward into amalgamated,erosionally based sandstone beds in proximallower shoreface facies, where they become diffi-cult to identify.T
able
2.
Su
mm
ary
of
min
or
stra
tigra
ph
icd
iscon
tin
uit
ysu
rfaces
inth
est
ud
ied
para
sequ
en
ces.
Su
rface
Recogn
itio
ncri
teri
aG
eom
etr
y,
exte
nt
Gen
esi
s
Non
-dep
osi
tion
al
dis
con
tin
uit
y(1
)A
bru
pt
decre
ase
ineven
tbed
thic
kn
ess
an
dam
alg
am
ati
on
(OS
,d
LS
F,
pL
SF
,D
Ffa
cie
s);
(2)
Incre
ase
inbio
turb
ati
on
inte
nsi
ty(O
S,
dL
SF
,p
LS
F,
DF
facie
s);
(3)
An
om
alo
us
facie
sin
terfi
ngeri
ng
(pL
SF
,U
SF
,F
Sfa
cie
s)
Gen
tly
dip
pin
g,
con
cave-u
pw
ard
cli
nofo
rms
(Fig
.12A
,B
an
dD
)H
iatu
sin
sed
imen
tati
on
:(1
)d
ecre
ase
inst
orm
or
river
flood
even
tfr
equ
en
cy;
(2)
ch
an
ges
toa
less
en
erg
eti
cw
ave/s
torm
cli
mate
;(3
)m
inor
rise
inre
lati
ve
sea
level
Ero
sion
al
dis
con
tin
uit
y(1
)A
bru
pt
incre
ase
sin
storm
-gen
era
ted
even
tbed
am
alg
am
ati
on
,gra
insi
ze
an
dsa
nd
con
ten
t(d
LS
F,
pL
SF
facie
s);
(2)
Dis
con
tin
uou
sla
gof
wood
fragm
en
tsan
dp
lan
td
ebri
s;(3
)S
teep
-wall
ed
gu
tter
cast
san
dG
loss
ifu
ngit
es
ich
nofa
cie
s.
Gen
tly
dip
pin
g,
con
cave-u
pw
ard
cli
nofo
rms
(Fig
.12C
)E
nh
an
ced
storm
-wave
scou
r:(1
)ch
an
ge
toa
more
en
erg
eti
cw
ave/s
torm
cli
mate
;(2
)m
inor
fall
inre
lati
ve
sea
level
684 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
Fig
.12.
An
nota
ted
cli
ff-f
ace
pan
els
thro
ugh
wave-d
om
inate
dsh
ore
face
dep
osi
tsin
the
stu
die
dp
ara
sequ
en
ces,
base
don
measu
red
secti
on
s(e
.g.F
igs
6an
d7A
–D
)an
dp
hoto
mon
tages
(e.g
.F
igs
10
an
d11A
).T
he
pan
els
are
pro
jecte
din
toth
ep
lan
eof
regio
nal
dep
osi
tion
al
dip
for
each
para
sequ
en
ce
(Fig
.4).
Tra
nsg
ress
ive
surf
aces
an
dse
lecte
dm
inor,
intr
ap
ara
sequ
en
ce
stra
tigra
ph
icd
iscon
tin
uit
ies,
wh
ich
defi
ne
cli
nofo
rms,
are
labell
ed
.T
he
min
or
stra
tigra
ph
icd
iscon
tin
uit
ies
are
dip
pin
g,
thro
ugh
goin
gsu
rfaces
that
can
be
traced
up
-dip
an
dd
ow
n-d
ipbetw
een
facie
sass
ocia
tion
s,alt
hou
gh
they
coin
cid
elo
call
yw
ith
facie
sass
ocia
tion
bou
nd
ari
es
over
part
of
their
len
gth
.P
an
els
are
from
the
foll
ow
ing
para
sequ
en
ces
(Fig
s4
an
d6):
(A)
the
‘K4’to
ngu
ealo
ng
the
sou
thern
face
of
Mid
dle
Mou
nta
inan
dG
un
nis
on
Bu
tte;
(B)
the
‘SC
4’
ton
gu
ealo
ng
the
nort
hern
face
of
Wil
dcat
Can
yon
;an
d(C
)th
e‘S
C4’
ton
gu
ealo
ng
the
nort
hern
face
of
Sp
rin
gC
an
yon
.N
ote
that
(A)
issh
ow
nat
half
the
hori
zon
tal
an
dvert
ical
scale
of
(B)
an
d(C
).K
ey
as
for
Fig
.10.
Variability in wave-dominated, shoreface-shelf parasequences 685
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
Fig
.13.
An
nota
ted
cli
ff-f
ace
pan
els
thro
ugh
wave-i
nfl
uen
ced
delt
afr
on
td
ep
osi
tsin
the
‘SC
4’
ton
gu
e,
base
don
measu
red
secti
on
s(e
.g.
Fig
.7E
)an
dp
hoto
-m
on
tages
(e.g
.F
igs
10
an
d11B
).T
he
pan
els
are
pro
jecte
din
toth
ep
lan
es
of
regio
nal
dep
osi
tion
al
dip
an
dst
rike
(Fig
.4).
Tra
nsg
ress
ive
surf
aces
an
dse
lecte
dm
inor,
non
-dep
osi
tion
al
dis
con
tin
uit
ies,
wh
ich
defi
ne
cli
nofo
rms,
are
labell
ed
.D
ipp
an
els
are
locate
das
foll
ow
s(F
igs
4C
an
d6B
):(A
)alo
ng
the
nort
hern
face
of
Pan
ther
Can
yon
;(B
)alo
ng
the
‘Mart
inF
ace’;
an
d(C
)alo
ng
the
‘Help
er
Face’
an
d‘K
en
ilw
ort
hF
ace’.
Str
ike
pan
els
are
locate
das
foll
ow
s(F
ig.
4):
(D)
alo
ng
the
east
ern
face
of
Help
er
Can
yon
;(E
)alo
ng
the
west
ern
‘Ken
ilw
ort
hF
ace’;
an
d(F
an
dG
),east
of
Ken
ilw
ort
h.
Key
as
for
Fig
.10.
686 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
These discontinuities are characterized byerosion, a discrete increase in sand supply andan increase in storm wave energy, whichenhanced bed amalgamation. In combination,these features suggest a lowering of storm wavebase. Gutter casts and Glossifungites ichnofaciesassociated with some of the discontinuitiesrecord scouring and burrowing into a partlylithified substrate (MacEachern et al., 1992) thatmay have been exhumed by erosion at thediscontinuity surface. These surfaces, recordinga lowering of storm wave base, may have formedby two mechanisms: (1) changes to a moreenergetic wave/storm climate; and (2) minorfalls in relative sea level (e.g. Dott & Bourgeois,1982; Storms, 2003). Distinguishing the productsof these two mechanisms in the stratigraphicrecord is difficult, particularly where the dis-continuity surfaces can only be traced withinlower shoreface and inner shelf deposits (e.g. inthe ‘K4’ tongue, Figs 7A and 12A). The formermechanism implies no relative change in waterdepth, but would be associated with a steepen-ing of the shoreface profile, as a result of anincrease in advective, onshore sand transport(Inman & Bagnold, 1963; Carey et al., 1999;Storms, 2003). The geometry of the shorefaceprofile produced via the latter mechanism isdependent on the shoreline trajectory and theshelf geometry. Where the forced-regressiveshoreline trajectory is steeper than the localshelf dip, the shoreface profile would steepen,because of increased wave stress on the sea-bedand a resulting increase in advective, onshoresand transport (Carey et al., 1999). Where theforced-regressive shoreline trajectory is equal to,or less than, the local shelf dip, the shorefaceprofile would maintain its previous equilibriumgeometry (Inman & Bagnold, 1963). Thesechanges in shoreface profile are discussed laterin relation to clinoform geometry in the ‘SC4’and ‘K4’ tongues.
CLINOFORM GEOMETRY ANDSHOREFACE-SHELF PROFILE
When traced laterally, the discontinuity surfacesdescribed above are observed to define clinoformsthat are interpreted as preserved remnants of theancient shoreface-shelf profile (Figs 7D and 11–13). Thus, the ancient shoreface-shelf profile canbe reconstructed directly from clinoform dips,subject to constraints imposed by data quality anddata distribution.
Assumptions
Clinoform geometry and intraparasequence faciesarchitecture in both ‘SC4’ and ‘K4’ tongues arereconstructed using three assumptions: (1) localclinoform dip is parallel to regional depositionaldip; (2) coal seams and transgressive surfaces atthe base and top of the shoreface-shelf parase-quences are used as local stratigraphic data; and(3) clinoform geometry is not significantly alteredby post-depositional compaction.
Depositional dipThe assumption that local clinoform dip is par-allel to regional depositional dip appears to bejustified in wave-dominated shoreface deposits,which are characterized by long, linear shorelines(e.g. McCubbin, 1982; Elliott, 1986; Walker &Plint, 1992). For example, in the ‘K4’ tongue,Hampson’s (2000) study of intraparasequencefacies architecture interprets a local palaeoshore-line orientation that is entirely consistent withTaylor & Lovell’s (1995) regional reconstructionof palaeoshoreline trends. This assumption is notjustified in wave-influenced delta deposits,which are characterized by more complex, lobateshoreline trends (e.g. Bhattacharya & Walker,1992). Near the seaward pinch-out of the ‘SC4’tongue, clinoform surfaces define lobes with amean dip to the south-south-west (Fig. 13E–G),implying a local palaeoshoreline orientation thatis perpendicular to the regional palaeoshorelinetrend (Fig. 4C).
Datum surfacesIn this study, the base of the Sowbelly CoalSeam is used as a datum in the landwardportion of the ‘SC4’ tongue (Fig. 12B and C),and a transgressive surface at the top of thetongue is used as a datum in its seaward portion(Fig. 13). Similarly, transgressive surfaces at thebase and top of the ‘K4’ tongue are used as localstratigraphic data (Fig. 12A). However, none ofthese data represent a smooth, palaeohorizontalsurface. For example, the base of the SowbellyCoal Seam is a composite, time-transgressivesurface that can be traced down-dip into rootedsurfaces within foreshore sandstones (e.g. thenon-depositional discontinuity surfaces at21Æ4 m and 22Æ0 m in Fig. 7C). Although thebase of the coal seam most probably approxi-mates palaeohorizontal over short distances(< 1 km), such that clinoform geometry relat-ive to this surface may be reconstructedwith reasonable confidence, a more complex
Variability in wave-dominated, shoreface-shelf parasequences 687
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
treatment of the coal seam is needed over largerdistances (> 1 km) in order to reconstructintraparasequence facies architecture. Similarproblems are encountered for the transgressivesurfaces used as local stratigraphic data. Thereis some degree of erosion associated with eachof these transgressive surfaces (e.g. the ravine-ment surfaces marked by lag deposits at 45Æ3 min Fig. 7A and 13Æ7 m in Figs 7E and 8A and B),and the transgressive surface at the top of the‘K4’ tongue is onlapped in its palaeoseawardpart by hummocky cross-stratified sandstonebeds. In combination, these observations suggestthat the transgressive surfaces had a very gentle(<< 1�) palaeoseaward dip, comparable to amodern shelf, with minor erosional topographyproduced by wave ravinement. Consequently,clinoform dips reconstructed relative to thesetransgressive-surface data are apparent dips thatslightly and systematically underestimate truedip relative to an (imaginary) horizontal datum.
Post-depositional compactionThe studied parasequences are uniform in thick-ness, have a quartz-rich mineralogy and uniformlithological composition over most of their extent,implying that they have undergone little differen-tial compaction internally and, hence, clinoformgeometries have not been significantly modified.Differential compaction may play an importantrole in modifying clinoform dips near the pinch-out of the parasequences, where there is an abruptlateral transition from sandstone-dominatedfacies to mudstone-dominated facies. Becausepeat compacts by a factor of approximately sevenduring the transition to coal (Ryer & Langer, 1980),there may be significant differential compactionassociated with abrupt lateral thickness variationsin the Sowbelly Coal Seam, above the ‘SC4’tongue. The most abrupt thickness changes inthe Sowbelly Coal Seam occur near its down-dippinch-out (Kamola & Van Wagoner, 1995).
Reconstruction of shoreface-shelf profile
In the ‘SC4’ tongue, clinoform dips have beencollated for well-preserved, non-depositionaldiscontinuities in wave-dominated shorefacedeposits (i.e. in the landward portion of thetongue; Figs 12B and C and 14A) and in wave-influenced delta front deposits (i.e. near theseaward pinch-out of the tongue; Figs 13 and14B). Similar collations of data are presented fornon-depositional discontinuities and erosionaldiscontinuities in wave-dominated shoreface
deposits in the ‘K4 tongue’ (Fig. 14C and D;Hampson, 2000).
Although each clinoform has a unique geom-etry, all display a concave-upward geometry inwhich the shoreface-shelf or delta front dipdecreases progressively offshore (Fig. 14). Abruptbreaks in slope and convex-upward geometriesalong sections of some clinoform surfaces areartifacts of data collection and geometrical recon-struction. The former are the result of using one-dimensional, vertical sections at photomontagetie-points to reconstruct two-dimensional clino-form geometries (Fig. 10). The latter are inter-preted to reflect protuberances from the cliff line,which impose minor along-strike variability onclinoform geometries reconstructed from panelsaligned along local depositional dip (Figs 12 and13D–G).
Using the collated data (Fig. 14), mean shore-face-shelf and delta front profiles have beenconstructed for clinoforms defined by non-depo-sitional discontinuities in the ‘SC4’ tongue(Fig. 15A and B). The delta front profile (Fig. 15B)is constructed from panels that are orientedperpendicular to the regional depositional dip(Fig. 13E–G). There is significant variance aboutboth these mean profiles (Fig. 14). Hampson(2000) used the same method to construct meanprofiles for non-depositional discontinuities anderosional discontinuities in wave-dominated sho-reface deposits in the ‘K4’ tongue (Fig. 15C andD). These mean shoreface-shelf profiles wereinterpreted as equilibrium profiles, because thepopulations of non-depositional and erosionaldiscontinuities in the ‘K4’ tongue possess dis-tinctive clinoform geometries (Hampson, 2000).The validity of this interpretation and its impli-cations are discussed later. The approach of usingmean profiles is appropriate given the inaccur-acies associated with data set collection, but itdoes not allow the geometries of individualclinoforms to be evaluated in detail. For example,we cannot distinguish discrete populations ofnon-depositional discontinuities with shallowerdips, which may have formed as a result ofchanges to a less energetic wave/storm climate,from those with steeper dips, which may haveformed by decreases in sedimentation eventfrequency or rises in sea level (Inman & Bagnold,1963; Carey et al., 1999; Storms, 2003).
Variability in shoreface-shelf profile
Each of the four mean clinoform profiles recon-structed for the ‘SC4’ and ‘K4’ tongues has a
688 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
pLS
FU
SF
dLS
FF
S
nond
epos
ition
al d
isco
ntin
uitie
s (w
ave-
dom
inat
ed s
hore
face
, 'S
C4'
tong
ue)
gradient = 0.037 ± 0.013clinoform dip = 1.4-2.9˚ (n = 12)
gradient = 0.024 ± 0.010clinoform dip = 0.8-1.9˚(n = 13)
gradient = 0.015 ± 0.007clinoform dip = 0.5-1.3˚(n = 12)
gradient = 0.010 ± 0.006clinoform dip = 0.2-0.9˚ (n = 5)
A
0 m
510
vert
ical
exa
gger
atio
n x5
0
nond
epos
ition
al d
isco
ntin
uitie
s (w
ave-
influ
ence
d de
lta fr
ont,
'SC
4' to
ngue
)D
F
grad
ient
= 0
.016
± 0
.011
clin
ofor
m d
ip =
0.3
-1.5
˚ (n
= 5
2)
B
gradient = 0.0082 ± 0.0043clinoform dip angle = 0.22-0.72(n = 33)
gradient = 0.0139 ± 0.0027clinoform dip angle = 0.64-0.95˚(n = 3)
gradient = 0.0145clinoform dip angle = 0.83˚(n = 1)
pLS
FU
SF
dLS
F
eros
iona
l dis
cont
inui
ties
(wav
e-do
min
ated
sho
refa
ce, '
K4'
tong
ue)
grad
ient
= 0
.005
6 ±
0.0
045
clin
ofor
m d
ip a
ngle
= 0
.06-
0.58
˚(n
= 4
)
grad
ient
= 0
.002
9 ±
0.0
025
clin
ofor
m d
ip a
ngle
= 0
.02-
0.31
(n =
4)
dLS
F
nond
epos
ition
al d
isco
ntin
uitie
s(w
ave-
dom
inat
ed s
hore
face
, 'K
4' to
ngue
)pL
SF
C
D
Fig
.14.
Coll
ate
dcli
nofo
rmd
ips
inth
e‘S
C4’
an
d‘K
4’
shore
face
ton
gu
es.
Data
are
deri
ved
from
(A)
non
-dep
osi
tion
al
dis
con
tin
uit
ies
inw
ave-d
om
inate
dsh
ore
face
dep
osi
tsin
the
lan
dw
ard
port
ion
of
the
‘SC
4’to
ngu
e(F
ig.
12C
);(B
)n
on
-dep
osi
tion
al
dis
con
tin
uit
ies
inw
ave-i
nfl
uen
ced
delt
afr
on
td
ep
osi
tsn
ear
the
seaw
ard
pin
ch
-ou
tof
the
‘SC
4’
ton
gu
e(F
ig.
13D
–G
);(C
)ero
sion
al
dis
con
tin
uit
ies
inw
ave-d
om
inate
dsh
ore
face
dep
osi
tsin
the
cen
tral
port
ion
of
the
‘K4’
ton
gu
e(e
.g.
Fig
.12A
;‘z
on
es
IVan
dV
I’of
Ham
pso
n(2
000);
an
d(D
)n
on
-dep
osi
tion
al
dis
con
tin
uit
ies
inw
ave-d
om
inate
dsh
ore
face
dep
osi
tsn
ear
the
seaw
ard
pin
ch
-ou
tof
the
‘K4’
ton
gu
e(F
ig.
12A
;‘z
on
eV
III’
of
Ham
pso
n(2
000).
Bold
lin
es
show
obse
rved
dis
con
tin
uit
ies,
an
dth
inli
nes
show
pro
jecti
on
sof
obse
rved
dis
con
tin
uit
ies
tocorr
esp
on
din
gfa
cie
sch
an
ges
inu
pp
er
shore
face
(US
F)
or
dis
tal
low
er
shore
face
(dL
SF
)d
ep
osi
ts.
Abru
pt
bre
aks
incli
nofo
rmsl
op
ean
dcon
vex-u
pw
ard
geom
etr
ies
are
art
ifacts
of
data
coll
ecti
on
an
dgeom
etr
ical
recon
stru
cti
on
.M
ean
cli
nofo
rmgra
die
nts
an
dst
an
dard
devia
tion
sfr
om
these
valu
es
are
show
n,an
dth
era
nge
of
cli
nofo
rmd
ipan
gle
sis
for
on
est
an
dard
devia
tion
from
the
mean
gra
die
nts
.It
shou
ldbe
note
dth
at
man
yof
the
coll
ate
dd
ata
sets
are
too
small
toass
ess
rigoro
usl
yby
stati
stic
al
mean
s.
Variability in wave-dominated, shoreface-shelf parasequences 689
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
0 m
510
0 m
1000
500
vert
ical
exa
gger
atio
n x5
0
coas
tal p
lain
= 0
.02˚
sea
leve
l
pLSF =
0.1
-0.6
˚
dLSF =
0.0
2-0.
3˚
shor
efac
e an
d in
ner
shel
f/ram
pof
fsho
re s
helf/
ram
p =
0.0
1-0.
3˚
FS = 2
-3˚
DN
on
dep
osi
tio
nal
dis
con
tin
uit
y in
wav
e-d
om
inat
ed s
ho
refa
ce-s
hel
f ('K
4' t
on
gu
e)
coas
tal p
lain
= 0
.02˚
offs
hore
she
lf/ra
mp
= 0
.01-
0.3˚
shor
efac
e an
din
ner
shel
f/ram
p
sea
leve
l
FS = 1
.4-2
.9˚
AN
on
dep
osi
tio
nal
dis
con
tin
uit
y in
wav
e-d
om
inat
edsh
ore
face
-sh
elf
('SC
4' t
on
gu
e)
BN
on
dep
osi
tio
nal
dis
con
tin
uit
y in
wav
e-in
flu
ence
dd
elta
fro
nt
('SC
4' t
on
gu
e)
coas
tal p
lain
= 0
.02
˚
offs
hore
she
lf/ra
mp
= 0
.01-
0.3˚
delta
fron
t
sea
leve
l
shor
efac
e an
d in
ner
shel
f/ram
p
coas
tal p
lain
= 0
.02˚
offs
hore
she
lf/ra
mp
= 0
.01-
0.3˚
FS = 2
-3˚
sea
leve
l
USF = 0
.8˚
pLSF =
0.2
-0.7
˚
dLSF =
0.6
-1.0
˚
CE
rosi
on
al d
isco
nti
nu
ity
in w
ave-
do
min
ated
sh
ore
face
-sh
elf
('K4'
to
ng
ue)
USF = 0
.8-1
.9˚
pLSF =
0.5
-1.3
˚
dLSF =
0.2
-0.9
˚
DF = 0
.3-1
.5˚
USF = 0
.5-0
.9˚
Fig
.15.
Sch
em
ati
cequ
ilib
riu
msh
ore
face-s
helf
pro
file
sfo
rth
e‘S
C4’an
d‘K
4’sh
ore
face
ton
gu
es,
wit
hsl
op
es
deri
ved
from
data
show
nin
Fig
s12–14.P
rofi
les
are
for
cli
nofo
rms
defi
ned
by
(A)
non
-dep
osi
tion
al
dis
con
tin
uit
ies
inw
ave-d
om
inate
dsh
ore
face
dep
osi
tsin
the
lan
dw
ard
port
ion
of
the
‘SC
4’
ton
gu
e;
(B)
non
-d
ep
osi
tion
al
dis
con
tin
uit
ies
inw
ave-i
nfl
uen
ced
delt
afr
on
td
ep
osi
tsn
ear
the
seaw
ard
pin
ch
-ou
tof
the
‘SC
4’
ton
gu
e;
(C)
ero
sion
al
dis
con
tin
uit
ies
inw
ave-
dom
inate
dsh
ore
face
dep
osi
tsin
the
cen
tral
port
ion
of
the
‘K4’to
ngu
e;an
d(D
)n
on
-dep
osi
tion
al
dis
con
tin
uit
ies
inw
ave-d
om
inate
dsh
ore
face
dep
osi
tsn
ear
the
seaw
ard
pin
ch
-ou
tof
the
‘K4’to
ngu
e.R
econ
stru
cti
on
sof
equ
ilib
riu
mp
rofi
lein
the
‘K4’to
ngu
econ
tain
dip
valu
es
for
fore
shore
an
doff
shore
shelf
/ram
pd
eri
ved
from
the
lite
ratu
re(E
llio
tt,
1986;
Can
t,1991;
Walk
er
&P
lin
t,1992).
690 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
concave-upward geometry that contains no majorbreak(s) in slope (Fig. 15). There is some variab-ility between them.
Shoreface-shelf gradientThere is little difference in gradient betweenshoreface-shelf profiles (Fig. 15A) and wave-influenced delta front profiles (Fig. 15B) recon-structed from non-depositional discontinuity sur-faces in the ‘SC4’ tongue. The uniform, butrelatively steep, gradient of the ‘SC4’ shoreface-shelf and delta front profiles (Fig. 15A and B) isattributed to the importance of river-flood proces-ses, rather than storm processes, in supplyingsand to the distal part of both profiles (e.g.Fig. 9C). In the ‘K4’ tongue, where storm-waveprocesses controlled sand transport to the distalpart of the profile and where the shelf depth wasgreater, the lower shoreface had a consistentlyshallower gradient (Fig. 15C and D). Non-deposi-tional discontinuities in the ‘K4’ tongue(Fig. 15D) are also consistently shallower andmore gently dipping than corresponding ero-sional discontinuities (Fig. 15C). There is nochange in sediment calibre associated with thetwo discontinuity types. Instead, the shallower,more gently dipping geometries of the non-depo-sitional discontinuities are likely to reflect shore-face advance into shallower water, a decrease instorm-wave energy and/or a decrease in the rate ofsediment supply (e.g. Inman & Bagnold, 1963;Storms, 2003).
Shoreface-shelf depthShoreface-shelf profiles reconstructed from the‘SC4’ tongue are consistently less deep than thosereconstructed from the ‘K4’ tongue (Fig. 15). Therelative depths of these profiles indicate that the‘SC4’ shoreface was developed on a considerablyshallower shelf than the ‘K4’ shoreface. Indeed,the entire ‘SC4’ shoreface profile (Fig. 15A) isdirectly comparable in thickness, and gradient, tothe upper shoreface component of the ‘K4’ sho-reface-shelf profile (Fig. 15C and D). This differ-ence in palaeoshelf depth may account for theoccurrence of a thin (< 7 m) upper shorefacecomponent of the shoreface-shelf profile in the‘SC4’ tongue (Fig. 15A), because some fairwea-ther wave energy may have been absorbed asthese waves travelled across the shallower shelfto the ‘SC4’ shoreface. The greater shelf depthsassociated with the ‘K4’ tongue may have resultedin less attenuation of fairweather wave energyand a thicker (15–20 m) upper shoreface compo-nent of the shoreface-shelf profile (Fig. 15C and
D). Alternatively, the two tongues may have beendeposited when different wave-climate condi-tions prevailed in the Utah Bight of the WesternInterior Seaway, reflecting subtle changes inclimate or palaeogeography.
CLINOFORM DISTRIBUTION ANDSHORELINE TRAJECTORY
Minor stratigraphic discontinuities marked byclinoforms are not distributed with uniform spa-cing in the studied parasequences, and the phys-ical character and geometry of the clinoformsurfaces also varies within each parasequence(Figs 12 and 13). In order to analyse these varia-tions in an appropriate context, it is necessary toreconstruct the detailed, intraparasequence shore-line trajectory (sensu Helland-Hansen & Martin-sen, 1996).
Assumptions
In addition to the assumptions used to recon-struct shoreface-shelf profiles from clinoformsurfaces, two further assumptions have beenused to reconstruct shoreline trajectories in the‘SC4’ and ‘K4’ tongues: (1) local stratigraphicdata are assumed to have had an appropriatedepositional dip; and (2) each type of clinoformsurface identified in the two parasequences isassumed to possess the mean geometry shown inFig. 15.
Depositional dip of datum surfacesVarious transgressive surfaces and the base of theSowbelly Coal Seam are used as local stratigraph-ic data for the reconstruction of clinoform geom-etries (Fig. 16A and C). The transgressive surfacesare generally flat but characterized by minorerosion and onlap, implying that they are waveravinement surfaces across the palaeoshelf, withan inferred depositional dip of 0Æ02� in a seawarddirection (Fig. 16B, D and E; after Elliott, 1986;Cant, 1991; Walker & Plint, 1992). Two recon-structions are presented for the Sowbelly CoalSeam, assuming that either the base (Fig. 16D) orthe top (Fig. 16E) of the seam had a palaeosea-ward dip of 0Æ02� during deposition (Fig. 16D),typical for a coastal plain (Elliott, 1986; Cant,1991; Walker & Plint, 1992). The latter recon-struction is more consistent with our observationthat the base of the seam is a composite, time-transgressive surface that can be traced down-dipinto rooted surfaces within foreshore sandstones
Variability in wave-dominated, shoreface-shelf parasequences 691
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
(e.g. the non-depositional discontinuity surfacesat 21Æ4 m and 22Æ0 m in Fig. 7C). Both recon-structions include decompaction of the coal seamby a factor of seven (Ryer & Langer, 1980).
Mean clinoform geometriesIn order to simplify our reconstructions of shore-line trajectory and to extrapolate them into areasof poor exposure (Fig. 16), we have used the
A
B
C
D
E
692 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
mean shoreface-shelf and delta front profilesshown in Fig. 15 as a proxy for the uniqueshoreface-shelf profiles represented by eachclinoform surface. This simplification assumesthat the mean profiles possess an equilibriumgeometry about which the individual clinoformsrepresent temporary variations. The validity ofthis interpretation and its implications are dis-cussed later.
Reconstruction of shoreline trajectory
Using these assumptions, shoreline trajectory isreconstructed for both ‘SC4’ and ‘K4’ tongues insimple, two-dimensional transects along deposi-tional dip (Fig. 16). Within the ‘K4’ tongue, thedistribution of clinoform surfaces is interpreted toreflect subtle changes in progradation and aggra-dation rates of the shoreface-shelf profile, andthus shoreline trajectory (Fig. 16A and B). Inparticular, forced regressive shoreline trajectoriesare marked by the amalgamation of erosionaldiscontinuity clinoform surfaces into regressivesurfaces of marine erosion (Hampson, 2000;Hampson et al., 2001). Variations in shorelinetrajectory can be mapped in three dimensions inthe ‘K4’ tongue to define linear zones parallel tothe palaeoshoreline trend in which there is eithera forced regressive trajectory or a normal regres-sive trajectory (Fig. 17A; Hampson, 2000).
Similarly detailed variations in shoreline tra-jectory are not evident in the ‘SC4’ tongue,although they may be obscured by the effects ofdecompacting the Sowbelly Coal Seam (Fig. 16C–E). Instead, major changes in intraparasequencefacies architecture are related to increased flu-vio-deltaic influence near the seaward pinch-out
of the tongue (Kamola & Van Wagoner, 1995),as reflected in plan-view changes in the palae-oshoreline trend (Fig. 17B). Using the base of theSowbelly Coal Seam as a palaeo-coastal plaindatum surface (Fig. 16D) produces a near-hori-zontal geometry to the transgressive surfaces atthe base of the tongue, and thus presents a morelikely reconstruction of shoreline trajectory dur-ing progradation in the ‘SC4’ tongue. However,the top of the Sowbelly Coal Seam is interpretedto have been near-horizontal during transgressionat the end of ‘SC4’ tongue deposition (as por-trayed in Fig. 16E), because it is overlain by awidespread, shallow lagoon (Van Wagoner et al.,1990; Kamola & Van Wagoner, 1995). It is there-fore inferred that significant early decompactionof the Sowbelly Coal Seam occurred duringprogradation and/or early transgression of the‘SC4’ shoreline.
Shoreline trajectory and variability inshoreface-shelf profile
In the ‘SC4’ and ‘K4’ tongues, several key obser-vations outlined below suggest that the dip of theshoreface-shelf profile was gentle during trans-gression, steepened during the first 1–2 km ofprogradation and remained steep during subse-quent progradation (Fig. 16). The dip of theshoreface-shelf profile decreased at the turn-around from progradation to transgression. Thus,significant variations in shoreface-shelf profileappear to be caused by changes between regres-sion and transgression, rather than variations inshoreline trajectory during progradation.
Landward pinch-out of shoreface tonguesAt the landward pinch-out of a shoreface-shelftongue, its basal transgressive surface records theshoreface-shelf profile immediately before shore-face progradation (Nummedal & Swift, 1987;Olsen et al., 1999). The landward pinch-out ofthe ‘K4’ tongue is obscured by erosion at anoverlying sequence boundary (Pattison, 1995;Taylor & Lovell, 1995), whereas the landwardpinch-out of the ‘SC4’ tongue is only exposed ininaccessible vertical cliff faces in Wildcat Canyon(Fig. 4C). Our reconstructions of the latter fromphotomontages suggest that the basal transgres-sive surface of the ‘SC4’ tongue is significantlymore gently dipping than the mean clinoformgeometry within either tongue (Fig. 16B, D andE). This discrepancy suggests that the shoreface-shelf profile must have steepened significantlyduring the first 1–2 km of progradation. Olsen
Fig. 16. Reconstructions of shoreline trajectory insimple, two-dimensional transects along deposition-al dip for the ‘SC4’ and ‘K4’ shoreface tongues. (A)Observed facies architecture in the ‘K4’ tongue is usedto reconstruct progradational shoreline trajectory (B)via imposing a depositional dip on local transgressivesurface data and via the use of mean shoreface-shelfprofiles as a proxy for observed clinoform surfaces(Fig. 15C and D). (C) Observed facies architecture inthe ‘SC4’ tongue is used to reconstruct progradationalshoreline trajectory (D) via imposing a depositional dipon local base-coal and transgressive surface data andvia the use of mean shoreface-shelf profiles as a proxyfor observed clinoform surfaces (Fig. 15A and B). (E)An alternative reconstruction for the ‘SC4’ tongue usesthe top of the Sowbelly Coal as a datum and is appro-priate for reconstructing transgressive shoreline tra-jectory and geomorphology at the end of deposition ofthe ‘SC4’ tongue. Key for (A) and (C) as for Fig. 12.
Variability in wave-dominated, shoreface-shelf parasequences 693
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
0m
iles
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osit
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e-in
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n-di
p te
rmin
atio
nof
upp
er s
hore
face
dep
osit
s
A
n=1
n=2
N.R
.
F.R
.
long
shor
e sa
nd tr
ansp
ort
N.R
.
N.R
.
F.R
.
F.R
.
F.R
.
n=1
wav
e-rip
ple
cres
ts, d
LSF
and
DF
fac
ies
(n =
num
ber
of r
eadi
ngs)
n=1
trou
gh a
nd ta
bula
r cr
oss-
beds
, US
F fa
cies
(n =
num
ber
of r
eadi
ngs)
Pal
aeoc
urre
nt k
ey
'nor
mal
' reg
ress
ive
shor
elin
e tr
ajec
tory
(ris
ing
rela
tive
sea-
leve
l)N
.R.
appr
oxim
ate
shor
elin
e or
ient
atio
n
Pal
aeog
eogr
aphy
key
'forc
ed' r
egre
ssiv
e sh
orel
ine
traj
ecto
ry(f
allin
g re
lativ
e se
a-le
vel)
F.R
.
up-d
ip te
rmin
atio
nof
mar
ine
depo
sits
N.R
.
3
Fig
.17.
Pala
eogeogra
ph
icre
con
stru
cti
on
sof
vari
able
shore
lin
etr
aje
cto
ryin
the
‘SC
4’
an
d‘K
4’
shore
face
ton
gu
es.
(A)
Th
e‘K
4’to
ngu
econ
tain
sli
near
zon
es
of
alt
ern
ati
ng
forc
ed
regre
ssiv
ean
dn
orm
al
regre
ssiv
esh
ore
lin
etr
aje
cto
ry(s
how
nin
cro
ss-s
ecti
on
inF
ig.
16B
)th
at
are
para
llel
toth
elo
cal
pala
eosh
ore
lin
etr
en
d.
Th
ela
tera
lcon
tin
uit
yof
these
zon
es
iscon
sist
en
tw
ith
asi
mp
le,li
near
wave-d
om
inate
dsh
ore
lin
ew
ith
litt
lealo
ng-s
trik
evari
ati
on
inse
dim
en
tsu
pp
ly.(B
)T
he
‘SC
4’
ton
gu
eis
inte
rpre
ted
tocon
tain
an
orm
al
regre
ssiv
esh
ore
lin
etr
aje
cto
ryth
rou
gh
ou
t(F
ig.
16D
),bu
tit
sse
aw
ard
part
isd
om
inate
dby
alo
bate
,d
elt
aic
pala
eosh
ore
lin
etr
en
d.L
on
gsh
ore
cu
rren
tsd
om
inate
pala
eocu
rren
tori
en
tati
on
sin
wave-d
om
inate
du
pp
er
shore
face
(US
F)
dep
osi
tsan
dap
pear
tocon
trol
wave-
infl
uen
ced
delt
alo
be
geom
etr
y.
694 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
et al. (1999) documented similar steepening ofthe shoreface-shelf profile during early prograda-tion near the landward pinch-out of two shorefacetongues in the Cretaceous Cliff House Sandstone,Colorado.
Main body of shoreface tonguesThe clinoform geometry within both ton-gues remains relatively constant between theirlandward and seaward pinch-outs (portrayedschematically in Fig. 16B, D and E). The wave-dominated shoreface component of the ‘SC4’tongue contains only non-depositional disconti-nuities that exhibit a limited variance in clino-form geometry (Figs 12B and C, 14 and 15A).Except for its seaward pinch-out, the ‘K4’ tonguecontains only erosional discontinuities with alimited variance in clinoform geometry (Figs 12Aand 15C).
Seaward pinch-out of shoreface tonguesAt the seaward pinch-out of the ‘K4’ tongue, theshoreface-shelf profile became shallower and hada gentler dip (Fig. 16B), coincident with a changein the physical character of clinoform surfacesfrom erosional discontinuities (Figs 12A and 15C)to non-depositional discontinuities (Figs 12A and15D). The seaward pinch-out of the ‘SC4’ tongueis more difficult to interpret, because it is associ-ated with complex palaeogeographies (Fig. 17B).However, the basal transgressive surface of the‘SC5’ tongue (Fig. 16D and E) may be reconstruc-ted as a proxy for the shoreface-shelf profileduring transgression at the end of ‘SC4’ tonguedeposition. The geometry of this surface is wellconstrained by preservation of flood-tidal deltadeposits at the landward pinch-out of the ‘SC5’tongue (Van Wagoner et al., 1990; Kamola & VanWagoner, 1995). The foreshore (FS) and uppershoreface (USF) components of the shoreface-shelf profile recorded by the transgressive surfaceare comparable in height to those interpreted inthe ‘SC4’ tongue (Fig. 15A), although the dip ofthis part of the profile is not constrained by ourobservations. The lower shoreface component ofthe shoreface-shelf profile recorded by the trans-gressive surface is much thinner than thoseinterpreted for the ‘SC4’ tongue (Fig. 15A), andis interpreted to have a more gentle dip, corres-ponding to the top of the decompacted SowbellyCoal Seam (Fig. 16D and E). Thus, it appears that,in both ‘SC4’ and ‘K4’ tongues, the shoreface-shelf profile became shallower and more gentlydipping at the tongues’ seaward pinch-out and/orduring subsequent transgression.
DISCUSSION: DYNAMIC CHANGESIN SHOREFACE-SHELF PROFILE
The observations and interpretations presentedabove suggest that the stratigraphic record con-tains considerable evidence for variability in theshoreface-shelf profile. Spatial variability reflectsalong-strike changes in depositional process andpalaeogeography that are inherent in any shore-line (e.g. Rodriguez et al., 2001). For example, thedistribution of wave-influenced delta front depos-its in the ‘SC4’ tongue (Fig. 17B) most probablyrecords switching of distributary channel loca-tion. The origin of temporal variability and itsimplications for current models of shorefacebehaviour are discussed below (Fig. 18).
Equilibrium profile
Modern shorefaces tend towards an equilibriumprofile (sensu Tanner, 1982; Walker & Plint, 1992)that forms in response to fairweather waveprocesses of low magnitude and high frequency.However, most shoreface-shelf deposits recordstorm-wave processes of high magnitude and lowfrequency, which are preferentially preserved inthe stratigraphic record (Dott, 1982; Dott &Bourgeois, 1982; Niedoroda et al., 1989; Stormset al., 2002; Storms, 2003). Thus, the portion of theshoreface-shelf profile above fairweather wavebase may maintain an equilibrium profile, whereasthat below fairweather wave base is widely inter-preted to respond over longer timescales to epi-sodic storm waves (e.g. De Vroeg et al., 1988; Stive& De Vriend, 1995; Fig. 18). Therefore, the conceptof equilibrium profile is most applicable to theupper parts of the shoreface-shelf profile (abovefairweather wave base) where the timescale ofintrinsic, dynamic response is fast relative tochanges in extrinsic controls such as sea level,sediment supply and wave climate (Stive & DeVriend, 1995; Fig. 20). Supporting evidence forthis view may occur at the seaward pinch-out ofthe ‘K4’ tongue, where clinoform surfaces changefrom steeply dipping erosional discontinuities togently dipping non-depositional discontinuities(Figs 12A and 16B). The associated change inshoreface-shelf profile geometry is most pro-nounced in the lower part of the profile (corres-ponding to pLSF and dLSF facies in Fig. 15C andD), which may have been unable to re-equilibrateto storm-wave climate as shoreline trajectory and/or sediment supply changed.
Temporal changes in external controls such asrelative sea level, wave climate and sediment
Variability in wave-dominated, shoreface-shelf parasequences 695
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
calibre will alter the geometry of the equilibriumprofile (e.g. Storms et al., 2002; Storms, 2003).Such variability is likely to occur over geologicaltimescales, for example in response to minor,climatically driven cycles in sediment supply andwave climate (102)104 years; Fig. 18), and mayproduce clinoform surfaces characterized by ero-sional or non-depositional discontinuities.
The ‘Bruun rule’
The ‘Bruun rule’ (Bruun, 1962), which hasbeen used widely in coastal engineering studies,implies that the shoreface-shelf profile maintainsa constant, equilibrium geometry during trans-gression. The rule has since been applied ingeometric models of stratigraphic architecturethat include both regressive and transgressiveshorelines (e.g. Cant, 1991; Nummedal et al.,1993). Our interpretation that the shoreface-shelfprofile varies markedly between episodes oftransgression and regression questions the appli-cability of the ‘Bruun rule’ in such modellingstudies.
Landward pinch-out of shoreface tonguesSteepening of the shoreface-shelf profile duringearly progradation is interpreted in several geo-logical data sets (Van der Valk, 1992; Olsen et al.,1999; ‘SC4’ and ‘K4’ tongues described in thispaper) and is reproduced in numerical massbalance models (Stive & De Vriend, 1995) andprocess response models (Storms et al., 2002).Steepening is interpreted to result from progra-dation of the shoreface-shelf profile into deeper
water as a result of coeval aggradation of theprofile and/or seaward-dipping shelf geometry.As the shoreface-shelf profile advanced intodeeper water, where wave energy was less attenu-ated, an increasing amount of wave energyreached the shoreface, which steepened in re-sponse (Olsen et al., 1999).
Main body of shoreface tonguesThe shoreface-shelf profile is interpreted to havevaried little during the main progradation historyof the ‘SC4’ and ‘K4’ tongues. A similar pattern isnoted in Holocene progradational shoreface-shelfsuccessions (Fig. 19). In all cases, shelf depthremained relatively uniform, implying that therewas little change in the attenuation of waveenergy as the shoreface advanced. Observedvariability in the shoreface-shelf profile may beattributed to minor changes in wave climate andsediment calibre supplied by longshore drift.
Seaward pinch-out of shoreface tonguesThe shoreface-shelf profile in the ‘SC4’ tongue isinterpreted to have been shallower and moregently dipping during transgression (Fig. 16D andE). This is attributed to a reduction in water depthas the shoreface-shelf profile retreated acrossthe underlying progradational deposits, whichattenuated wave energy and caused a decrease inthe profile dip. Attenuation would have beenmore pronounced for the larger storms thatsculpted the lower part of the shoreface-shelfprofile. Also, low sediment supply and/or rapidshoreline retreat may have produced a flattened,disequilibrium shoreface-shelf profile, partic-
100
101
102
103
104
105
106
107
108
10-1
10-2
time
scal
e (y
ears
)
10-3
indi
vidu
al s
torm
eve
nt
ret
urn
perio
d of
sto
rm e
vent
s(v
arie
s w
ith s
torm
mag
nitu
de)
min
or c
ycle
s in
wav
e cl
imat
e
min
or c
ycle
s in
rel
ativ
e s
ea-le
vel (
6th
orde
r?)
depositionalprocesses
analytical techniquesand models
depositionalproducts
cyc
les
in r
elat
ive
sea
-leve
l (5t
h or
der?
)
sho
refa
ce to
ngue
(sho
refa
ce-s
helf
para
sequ
ence
)
indi
vidu
al s
torm
-eve
nt b
ed
clin
ofor
m/d
isco
ntin
uity
-bou
nded
unit
("be
dset
", "
clin
othe
m")
clin
ofor
m s
urfa
ce(d
isco
ntin
uity
sur
face
)
"Bru
un R
ule
"(c
oast
al e
ngin
eerin
g) sequ
ence
stra
tigra
phy
seas
onal
cha
nges
inst
orm
inte
nsity
phys
ical
and
num
eric
al m
odel
s(in
divi
dual
sto
rm e
vent
)
num
eric
al m
odel
s(in
tra-
tong
ue fa
cies
arc
hite
ctur
e)
min
or c
ycle
s in
sedi
men
t sup
ply
Fig. 18. Schematic illustration ofthe timescales represented by (1)key depositional processes in wave-dominated shorefaces and shelves;(2) depositional products preservedwithin facies successions; and (3)analytical techniques and modelsused to study and predict shallow-marine stratigraphy. Note that thetimescales represented by the de-positional products within a singleshoreface-shelf parasequence spaneight orders of magnitude(10)3)105 years).
696 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
AB
D
C
E
F
Fig
.19.
Com
pari
son
sof
shore
face-s
helf
pro
file
an
dsh
ore
lin
etr
aje
cto
ryin
an
um
ber
of
wave-d
om
inate
d,H
olo
cen
esh
ore
lin
ed
ep
osi
ts:(A
)cen
tral
Holl
an
dcoast
(aft
er
Van
der
Valk
,1992;S
tive
&D
eV
rien
d,1995);
(B)
Galv
est
on
Isla
nd
,T
exas
coast
,U
SA
(aft
er
Bern
ard
et
al.
,1970;M
cC
ubbin
,1982);
(C)
Wil
lap
aB
ay
barr
ier
isla
nd
,W
ash
ingto
n,U
SA
(aft
er
Sm
ith
et
al.
,1999);
an
d(D
)N
ayari
tst
ran
dp
lain
,M
exic
o(a
fter
Cu
rray
et
al.
,1969).
Th
ecen
tral
Holl
an
dcoast
was
pro
gra
dati
on
al
betw
een
ap
pro
xim
ate
ly5000
an
d2000
years
BP
an
dis
now
un
derg
oin
gtr
an
sgre
ssio
n(V
an
der
Valk
,1992).
Cli
nofo
rmsu
rfaces
inth
eW
illa
pa
Bay
barr
ier
isla
nd
are
mark
ed
by
heavy
min
era
lcon
cen
trati
on
s(S
mit
het
al.
,1999).
Cli
nofo
rmsu
rfaces
inth
eN
ayari
tst
ran
dp
lain
dep
osi
tsare
tran
sgre
ssiv
era
vin
em
en
tsu
rfaces
that
pu
nctu
ate
overa
llst
ran
dp
lain
pro
gra
dati
on
(Cu
rray
et
al.
,1969).
Th
etw
op
ara
sequ
en
ces
dis
cu
ssed
inth
isp
ap
er
are
als
osh
ow
nfo
rcom
pari
son
:(E
)th
e‘S
C4’
ton
gu
e,
Sp
rin
gC
an
yon
Mem
ber
(Fig
.16D
);an
d(F
)th
e‘K
4’
ton
gu
e,
Ken
ilw
ort
hM
em
ber
(Fig
.16B
).K
ey
as
for
Fig
.16.
Variability in wave-dominated, shoreface-shelf parasequences 697
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
ularly in the lower, storm-generated part (e.g.Inman & Bagnold, 1963).
Our interpretations suggest that the ‘Bruun rule’is applicable only when an equilibrium profile ismaintained during periods of uniform shorelinetrajectory across portions of the shelf with littleantecedent topography. These conditions may bemet over the short timescales considered in coastalengineering studies (100)103 years; Fig. 18), butthey are unlikely to prevail over the timescalesconsidered in numerical models of sequence-scalestratigraphy (105)108 years; Figs 18 and 19).Thus, numerical models that assume the geome-tries implied by the ‘Bruun rule’ are unlikely toreproduce accurately the detailed morphology oftransgressive surfaces or the parasequence-scalestratigraphy that they define (Olsen et al., 1999).In particular, they may overestimate the depth oftransgressive ravinement.
Variability between modern shorefaces andancient shoreface-shelf parasequences
The interpretation that shoreface-shelf profilevaries with shoreline trajectory and shelf mor-phology, in addition to sediment calibre andwave energy, provides a mechanism to explainthe discrepancy in scale between modern shore-faces and ancient shoreface-shelf parasequences(Fig. 1). Most well-studied modern shorefacesare developed on the inner shelf in relativelyshallow water (e.g. Holocene shoreface depositsof the Central Holland Coast, Galveston Island,Willapa Bay and Nayarit shoreface in Fig. 19;Curray et al., 1969; Bernard et al., 1970; McCub-bin, 1982; Van der Valk, 1992; Stive & DeVriend, 1995; Smith et al., 1999) and conse-quently are relatively thin compared with an-cient shoreface-shelf parasequences (Fig. 1).These modern shorefaces are in the early stagesof progradation, and we infer that they willbecome higher and steeper as they advance intodeeper water on the middle to outer shelf. Inaddition, progradational shoreface-shelf profilesin the two studied parasequences do not containprominent breaks in slope at either fairweatheror storm-wave base, but grade seawards to thedip of the inner shelf. Their smooth geometryimplies that the profiles were developed oversufficiently long timescales to enable near-equi-librium geometries to form in response to storm-wave climate. Modern shoreface-shelf profiles,which developed during transgression and earlyprogradation, exhibit a break in slope at, or nearto, fairweather wave base (e.g. Clifton, 2000).
The lower part of these profiles is interpreted tobe in disequilibrium with storm-wave climateand/or sediment supply.
Differences between ancient shoreface-shelfparasequences can also be explained by variationsin shoreline trajectory and shelf morphology. Forexample, the ‘K4’ tongue is interpreted to havebeen deposited in relatively deep water, seawardof the antecedent shelf topography generated byunderlying shoreface-shelf parasequences (‘K1’–‘K3’ tongues in Fig. 5). Consequently, this para-sequence attains an anomalously large thickness(Figs 1 and 19), despite evidence for a forcedregressive shoreline trajectory during its depos-ition (Fig. 16B; Pattison, 1995; Hampson, 2000).Other unusually thick parasequences in the BookCliffs succession overlie major flooding surfacesassociated with the generation of large amounts ofaccommodation across the entire shelf (e.g. the‘A1’ and ‘K1’ tongues in Fig. 5; fig. 12A inReynolds, 1999). In contrast, the wave-dominatedportion of the ‘SC4’ tongue was deposited directlyabove the antecedent shelf topography generatedby underlying shoreface-shelf parasequences(‘SC2’–‘SC3’ tongues in Fig. 5), and it is signifi-cantly thinner than the ‘K4’ tongue (Figs 1 and19). Differences in parasequence thickness relatedto stacking patterns within larger parasequencesets are predictable, because they reflect system-atic variations in the generation of shelfal accom-modation (Reynolds, 1999). Antecedent shelftopography is likely to cause anomalous thicken-ing of parasequences that extend a significantdistance palaeoseaward of their precursors (e.g.the ‘K4’ tongue; Fig. 5).
IMPLICATIONS FOR FACIES ANDSEQUENCE STRATIGRAPHIC MODELS
Shoreface-shelf stratigraphy at intraparasequencescale is considerably more complex than repre-sented in current facies and sequence stratigraph-ic models (Fig. 20).
• Although modern shoreface systems are idealnatural laboratories for the study of wave andstorm processes, they are not fully representativeof ancient shoreface-shelf parasequences. Modernshorefaces are invariably developed on the innershelf and record only the early stages of progra-dation. Ancient shoreface-shelf parasequencesrecord the dynamic response of the shorefaceprofile to prolonged progradation and subsequenttransgression.
698 G. J. Hampson & J. E. A. Storms
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
• The geometry and physical character of theshoreface-shelf profile varies over several time-scales. (1) Over short geological timescales(102)104 years), erosional and non-depositionaldiscontinuities are produced along the profile as aresult of minor cycles in relative sea level, waveclimate and/or sediment supply. (2) Over inter-mediate geological timescales (103)105 years), thegeometry of the shoreface-shelf profile varies withshoreline trajectory in a single parasequence, suchthat it steepens during early progradation,remains steep and relatively constant during lateprogradation, and becomes shallower and moregently dipping during transgression. These chan-ges in shoreline trajectory are controlled by sho-reface advance into deeper water and shorefaceretreat into shallower water, and are modulated byrelative sea level and/or sediment supply. (3) Overlong geological timescales (105)108 years), be-tween-parasequence variations in shoreface-shelfprofile most likely reflect changes in long-termrelative sea level, shelf morphology, sedimentcalibre and wave energy in the basin.
• Vertical facies successions lack geometricaldata on the shoreface-shelf profile and shorelinetrajectory. Consequently, such successions do notallow the construction of geometrically robust
facies models, and neither do they allow adetailed sea-level history to be reconstructed. Keygeometrical attributes within parasequences maybe measured at well-exposed outcrops, allowingshoreface-shelf profile and shoreline trajectory tobe carefully reconstructed. In the absence of veryhigh-resolution seismic data, accurate recon-struction of geometrical attributes in the subsur-face is likely to prove extremely difficult, even infields with high well density. As a result, con-fident prediction of parasequence dimensions(e.g. location of their landward and seawardpinch-outs) and detailed internal heterogeneity(e.g. clinoform dip angle) is limited. Genericpredictive models at this level of detail may beachieved via the comparative study of well-exposed parasequences at outcrop, combinedwith process-response numerical models, usingthe former to calibrate the latter.
ACKNOWLEDGEMENTS
G.J.H. would like to thank Diane Kamola for anintroduction to the Spring Canyon Member,Andalex Resources for access to Panther Canyon,and John Howell for insightful discussions. The
100 101 102 103 104 105 106 107 10810-110-2
time scale (years)
10-3
minor cycles inwave climate
minor cycles in relative sea-level (6th order?)
minor cycles insediment supply clinoform surface
(discontinuity surface)
disequilibriumshoreface-shelf profile?
equilibriumshoreface-shelf profile?
minor cycles in relative sea-level (6th order?)
minor cycles insediment supply
intra-parasequenceshoreline trajectory
(clinoform distribution,"bedsets", clinothems")
cycles in relative sea-level (5th order?)
maintenance of equilibriumprofile ("Bruun Rule")
breakdown ofequilibrium profile
parasequence
cycles in relative sea-level (5th order?)
sediment supply
cycles in relativesea-level (4th order ?)
shelf morphology
sediment supply parasequence stacking
stra
tigra
phic
hie
rarc
hy
Fig. 20. Hierarchy of stratigraphicunits at intraparasequence andparasequence scales. The timescalesof formation and driving processesfor these units are suggested, andthe inferred applicability of theequilibrium profile concept (for theentire shoreface-shelf) and the‘Bruun rule’ are shown.
Variability in wave-dominated, shoreface-shelf parasequences 699
� 2003 International Association of Sedimentologists, Sedimentology, 50, 667–701
‘K4’ tongue study was funded by Shell UK Expro.The authors are grateful to Tina Olsen for herconstructive review, and to Chris Fielding andPeter Haughton for editorial comments.
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