TIDAL DEPOSITS AND THEIR SEDIMENTARY STRUCTURES
(Seven examples from Western Europe)
J.F.M. DE RAAF t) and J.R. BOERSMA t)
ABSTRACT
Seven examples of tidal sedimentation ranging betweenmodern and Devonian age are illustrated and briefly dis-cussed. They cover known (modern intertidal and subtidal)and mostly undetermined ancient tidal subenvironments,and have been taken from:,1. The estuarine reach of a tidal river, subtidal, Holocene,
Barendrecht excavation, The Netherlands.2. An estuarine channel, subtidal, Holocene, Haringvliet
excavation, The Netherlands.3. A Lower. Pleistocene (Tiglian), possibly subtidal estuar-
ine succession, Hattem (Veluwe), The Netherlands.4. A dune-bearing estuarine sand-bank, intertidal, modern
Western Scheldt, The Netherlands.5. The Lower Cretaceous (Lower Greensand) Woburn sands
± 50 km NW of, London, England, being probablydeposited in an open marine tidal environment.The Oligocene (Tongrian) Kerkom- and Neerrepen sandsSE of Brussels, Belgium, representing areas yet uncertain'type of tidal subenvironment.
7. An Upper Devonian tidal succession belonging to thetransgressive, complex ' (Cork beds) overlying the Old
- _ Red,. W. of Cork, Eire.
The following features were considered to be diagnosticfor these (and other?)' tidal deposits (a) vectorial bimodali-ty of the cross-stratification, (b) common joint occurrence atdifferent proportions of largescale and smallscale structuredunits in super- of juxtaposition. (c) Usually poorly developedsequential regularity with occasional occurrence of fining-upward sequences. (d) Unidirectional cross-stratified setsdisplaying several' 'kinds of features resulting from theintermittent and bidirectional character of, the currents(discontinuity planes). (e) Fairly common occurrence of
t)Sedimentology Department, University of Utrecht; The
Netherlands.
(laser and/or lenticular bedding respectively 'consanguineousmud-sand interlaminations in smallscale-structured units. (f)Slight to intense bioturbation in several types of sandyand/or muddy units.
At the present state of knowledge a reliable determine-tion of the tidal sub-environment (e.g. inshore, offshore,intertidal, subtidal) seems to be virtually impossible forancient clastic deposits, except for a few cases. Establish=ment of detailed paleocurrent patterns may help in distin,guishing open-sea tidal deposits from inshore ones.
INTRODUCTION
General
The past few decades sedimentologists have con-tributed considerably to the knowledge of recenttidal deposits and they have tried with variable.success to demonstrate the tidal nature of a numberof ancient successions in Western Europe (v a nStraaten, 1954x; Hiilsem,ann, 1955; Gu,l -lentops, 1957; Nieboff, 1958; Allen andNarayan, 1964; Reading and Walker;1966; Wunderlicb, 1970; de Raaf, 1970;Kuijpers, 1970; de Vries Klein, 1970a;K ui j p e r s, 1971). During their own study ofpre-Holocene deposits the present authors becameconvinced that there are sufficient criteria pointingto tidal deposition in general but experienced that itis at the present state of knowledge in most casesimpossible to tell the type of tidal sub-environment.It is felt that this, is principally due to the fact thatin the studies of modern tidal environments atten-tion was mainly focussed on the intertidal zonebecause of its better accessibility.
GEOLOGIE EN MIJNBOUW VOLUME 50 (3), p.479-504 1971
6.
480
Ossenisse
Antwerpen0
Mechelen
Brussel
Leuven
10 0 km.
5 10 miles
General location map
Diest
locution of numbered item
quarry
Rotterdam
Bur drectl.lezcav
Antwerpen
0
FLEVOPOLDER
Linsabe
sevenHeads
Hattum
20 k m.J
Leighton Buzzard
Kinsale
Kinsale
O
Zwolle
Dunstable
n2 miles
IO miles
HOnngvli 1- -escav' O---
Oostersbhelde
f4) iest'-s--- f °he/pe 0
v _
S,
A 0
Rhine
Maos
-=
0
Harderwijk
00 0 10
0 5 10 miles
open Id
eventer
- _ -` - paso c
- -- - - - 00 Leighton
qu' Gorsidaqu ® quarry
Buzzard
London
E astsrnwoY
®0
Fatkeste
- CoP
un oysd Hill qua try edsIt
_- . - -__ - - < 50krtOi
-_ - = o Squ. PI-- -- - c9
_o
Da 9y
- - -- II I IIII-Zwolle'
II ,
Leiua7dBQy
gA
C oRotter-,. aE
pLonOOn °T Bi--- g.
France r s
- Cork
f r` , `r'
®Ti en - --
0 10 0 30 km Old hood of - -
r.
=- =. 0 5 IO miles_ -0 1bkm
Oqu.
---E -' -
In this respect reference can be made to thestudies of H a n t z s c h e l , 1936; van S t r a a -t e n, 1951, 1953, 1954b, 1964; H ii l s e ni a n n,1955; R e i n e c k and his' school (1958-1970, seebibliography); d e V r i e s K 1 e in, 1963, 1970b;Evans, 1965.
As to the studies in modern sub-tidal environ-ments, these are largely dealing with morphological,geophysical, hydrographical and textural-composi-tional features (v a n V e e n, 1936; S t r i d.e, 1963;Houbolt, 1968; James and Stanley, 1968;T e r w i n d t, 1970a, 1970b) and do not providemuch information about the sedimentary upbuild-ing. An exception' forms R e i n e c L's, (1963) in-vestigation of the southeastern bight of the NorthSea (Deutsche Bucht), which provides a wealth' ofinformation on composition, texture and sediment-ary structures, their association and distribution, notonly for the intertidal but also for the subtidalzone. As regards The ;valuable insight isgained into inshore subtidal deposits from studies ofthe Haringvliet (O o m k e n s and T e r w i n d t,1960; Terwindt; 1971) and Barendrechtexcavations (the present article).
Seven examples
In the course of their general research pro-gramme, concerning sediments from the continental,transitional and marine environments the authorshave come across, several examples of tidal deposits,from which seven are selected here for a rathercursory treatment. These seven examples range inage between modern and Devonian, and in consoli-dation between loose and, completely lithified. Theyare briefly introduced in separate sections numbered1-7 and dealt with in seven correspondingly num-bered figures with extensive captions. For locationsee map. The photographs' are slightly retouched inorder to enhance contrast.
1. BARENDI1ECHT EXCAVATION(fluvial subtidal)
In 1966, with the assistance of Messrs. van Beek.and Koster (Utrecht) a large (± 380 x 80 m), 1ough-1Y NW-SE trending excavation was studied on thenorthern embankment of the Oude , Maas- (OldMeuse); south of Rotterdam. The long
481
edge of the excavation ran parallel to the presentlocal river course at a few tens of metres distance.The vertical succession from a depth of 10 m belowNAP2) upward showed a distinct fining-upwardcharacter, which deviates, however, distinctly fromthe normal type found more landinward in thefluvial deposits of the Dutch deltaic plain. Indeed acomparison with present day hydrographically equi-valent sections of the nearby Lower Rhine (T e r -w i d t et al:, 1963) suggests that estuarine condi-tions (i.e. bidirectional water and sediment move-ment) may very well have existed in former days inthe Old Meuse near Barendrecht. To what extentthis tidal influence was active around 1200 A.D.,the most probable period of deposition as deter-mined by archeological finds, is unknown, but itseffect is clearly reflected in the directional bimodal-ity characterising the upper part of the Barendrechtsection.
2. HARINGVLIET EXCAVATION(estuarine subtidal)
During construction of the closing dam in theHaringvliet estuary (for position see location map) alarge excavation reaching to a depth of about 15 inbelow NAP permitted the study of an estuarinesuccession in great detail. O o in k e n s and, T e r -w i n d t (1960) described, several lithologically andstructurally different units and related them' toconditions of flow. Student reports on behalf of theSedimentological Department Utrecht Universitywere made by Verde nius (1963) and Lier(1967). T e r w i and t (1971) studied the estuarinedeposits in the SW Netherlands on a regional scale,using borings and, current data from the -Haringvlietand nearby tidal inlets so as to gain insight into therelationship between lithology, depth and, wherepossible, hydrographic characteristics. This authordistinguished three estuarine lithofacies characterizedby:1. Largescale cross-stratification of trough, tabular
or fill character.II.. Flaser bedding, smallscale cross-laminated and
some horizontally laminated sand.III. Lenticular bedding, sand-clay alternations.
2) NAP = 'Dutch ordnance level = approximate presentmean sea level.
482
The division adopted by us is twofold: A large-scale-structured group (henceforth called LS-group)corresponding to Terwindt's facies I and a smallscale-structured, generally heterolithic, group (henceforthcalled SS-group) embracing both lithofacies Il and 111.
The sedimentary succession in the Haringvlietexcavation showed marked lateral changes of facies inthe wall running parallel to the long axis of the pit. Infact the LS-lithofacies group was much strongerdeveloped toward the northeastern and southwesternends of the pit than in its centre. This should beattributed to the influence exerted by nearby ebb andflood channels, which for many tens of years (Oom-kens and Terwindt) appeared to have been situatedjust north and south of a broad submerged shoal onwhich the excavation was located. Consequently thegreat development of heterolithic sediments found inthe centre of the pit is presumably related to therelatively more current-protected environment of thementioned shoal. Apart from the structures dealtwith in our example (fig. 2) other structures areencountered, which, however, have- no diagnosticalvalue (e.g. the presence of fill structures).
T e r w i n d t (1971) arrived at the importantconclusion that no sequential order on a larger scale(embracing tens of metres) exists in the tidal depositsof the inlets south of the Haringvliet. Regarding .theHaringvliet estuary, however, this author states thathis facies III shows a gradual increase and facies 11 adecrease with decreasing depth, the frequency offacies I remaining the same at all depths.
3. HATTEM MUNICIPAL SAND PIT(possibly estuarine subtidal)
In the Noord-Veluwe region (The Netherlands)bordered to the east by the valley of the river IJsselPleistocene deposits are exposed in several -large sandpits. The strata are dipping eastward, generally at30-500. The succession is, however, split up intoseveral tectonic imbrications, which are thrust to thewest and attain several tens to a hundred metres inthickness. The thrustplanes dip accordingly towardthe IJssel valley. Lateral push by an ice lobe, which-moved up the IJssel valley from the North (d eJ o n g, 1952; 1955; 1967) during the Riss glacia-tion, is presumably responsable for the structure inquestion. Similar, but east-thrusted imbricate sheetsare found to the east of the present IJssel valley but
have not yet been investigated sedimentologically..The deposits found in these imbricated units range
in age from Lower Pleistocene. to Middle Pleistocene(inclusive) according to the stratigraphical subdivi-sion of v a n d e r H e i d e and Z a g w ij n (1967).
In the quarry presently investigated the entiresuccession is outcropping and comprises the Tiglian-Harderwijk-Enschede and Urk (I and II) Formations.Except for the Tiglian Formation from which thepresent tidal example is, taken all Formations areclearly of fluviatile origin. The tidal Tiglian Forma-tion is characterized, by a recurrent alternation of LS-and SS-lithofacies groups. In both groups the tidalaction manifests itself by a vectorial bimodality, inwhich the landward direction (eastward) is thesubordinate one. The mud content in the successionis strikingly high, which is in sharp contrast with theoverlying fluviatile beds. The" outcrop in questionthrows a new light upon the position of the shorelinein Tiglian time. Sedimentological investigations of themunicipal quarry were carried out in 1969-1970 withthe assistance of Messrs. Beekman and van, der Bilt(Utrecht), Stratigraphic subdivisions were kindly pro-vided by Mr. J.G. Zandstra, Netherlands GeologicalSurvey, Haarlem. Investigations on a more regionalscale are still in progress (1971).
4. OSSENISSE SHOAL, WESTERN SCHELDT,
(estuarine intertidal)
In the summer of 1969 an investigation pro-gramme of one month duration, was carried out onthe shoals (sand banks) of Ossenisse (south ofHansweert) by the Department of Sedimentology,University of Utrecht, with the assistance of Rijks-waterstaat and the Royal Dutch Navy. The investiga-tions comprised the recording of changes in,surfacetopography (dune configuration, etc.), the study ofinternal structures sampled by lacker peels, the rateof sand "movement, etc. in relation to the neaptide-springtide cycle. These data were collected at ninedifferent places on the shoal. Simultaneously con-tinuous current measurements were made from twoplatforms during the inundation periods of the shoal.The results, are still being worked out and will bepublished by Terwindt and Boersma. A preliminarynote was issued by B o e r s in a (1969).
Dune morphology and behaviour was found to be
483
highly variable from place to place and often unpre-dictable from the external shape.
On completing the present article an importantcontribution by d e V,r i e s K 1 e i n. (1970b) dealingwith, in many respects, comparable sediments cameto hand. As regards the thirteen sedimentary featuresobserved by this author on sand bars (his table 8, p.1124) more than half cannot be considered in ouropinion as.criteria of intertidal sand bars, as they areequally characteristic of subtidal deposits. Amongstthe real intertidal criteria left (e.g. late-stage sheetrun-off and water-level reduction phenomena) fossilpreservation may occur, as W u n d e r 1 i c h (1966,1970) admirably ,demonstrated, but, as far as weknow is exceedingly rare.
5. LOWER CRETACEOUS WOBURN SANDS,LOWER GREENSAND
(Open-sea tidal)
The Lower Greensand, which contains first ranktidal deposits, is very.well exposed in two regions insouthern England; respectively south and north ofLondon (c.f. inset to location map). In the southernbelt of outcrops the Lower Greensand is amongstothers represented by the Folkestone Beds. In thenorthern belt beds of equivalent age occur in the
,neighbourhood of the town of Leighton Buzzard andare named "Woburn sands". Especially in the latterregion a dense network of quarries exists, whichseems to offer a good opportunity for a three--dimensional reconstruction of the environment, of
,deposition. As argued in the caption of Fig. 5 a partly_very LS- and a predominantly SS- (heterolithic) faciesassociation can be distinguished at Leighton Buzzard.
In the first-mentioned association giant foresetting(height up to 5 m) is of common occurrence. Upslopeand downslope transport of sediment took placealong these giant slopes as manifested amongst othersby largescale foresetting of moderate height, ascend-ing or descending the depositional slopes and byobserved downwards or upwards wedging out of giantforesee bundles. The investigations so far suggest thatone is dealing here with an. ancient tidal open-seaenvironment (with spiral flow effects, etc.) com-Parable to the present North Sea as found byloubolt(1968)andTerwindt(1970b).
One of the authors (Boersma) has started aninvestigation in these deposits at a more regional scale
to provide additional evidence in support of last-mentioned assumption.
As regards the Lower Greensand (Folkestone beds)of the southern belt as far as we know only A 11 e nand N a r a y a n (1964) reported on some structuralaspects.
6. OLIGOCENE AND LOWER PLIOCENE OFCENTRAL BELGIUM, LEUVEN-TIENEN AREA
(tidal of different types)
Here many quarries,. some of them very large butunfortunately rather at a distance from each other,enable us to study several types of shallow-marinesands. Of these,, the Kerkom, Neerrepen and Diestiansands were studied in some detail for their sediment-ary structural and sequential characteristics. Thisstudy was carried out in the summer of 1970 with theassistance of a number of students from, Utrecht.Necessarily the study had a limited scope. Compre-hensive investigations are known from G u 11 e n -t o p s (1963) and other Belgian scientists (e.g.G u 1 i n c k, 1963), who mainly studied granulo-metry, composition and to a lesser degree structures.
In the often very coarse (up to crs. sd'.) Kerkom,sands directional bimodality is ubiquitous in all
investigated quarries. This precludes a fluviatile gene-sis. Moreover, truer fluviatile fining-upward cycleswere not found. The balance between the opposingcurrents was variable and gave sometimes rise to astrong predominance of one direction. As far as the,as yet, incomplete current measurements permit astatement, it would appear that northerly and south-erly directions prevail, indicative of an inshore en-vironment.. However, also easterly directions occurthough at a, subordinate rate and only in a fewquarries. As to the implication of the latter data(longshore or strongly curving inlet configuration) itis hoped that future research will clarify the matter.
In the overwhelmingly horizontally laminated,fine-grained Neerrepen sands it came rather as asurprise that tidal currents, though weak, were alsolocally active, as is manifested by bimodality inpredominantly small-scaled structures.
As regards the Diestian sands (Lower Pliocene) anopen-sea tidal origin was already brought to the forebyGullentops(1957).
Further research work regarding the Tertiaryformations in Belgium is planned.
7. UPPER DEVONIAN CORK BEDS OFSOUTHERN IRELAND(tidal of different types)
Along the south coast of Ireland, W. of Cork, anUpper Devonian transgressive series overlying the OldRed forms extensive outcrops. In this series transi-tional in facies between continental and marine,investigations are being carried out (1969-1971) theresults of which will be laid down in PhD theses byvan Gelder, Kuijpers, and Leflef (see d e R a a f,1970). In the investigations the emphasis is laid, onsedimentary structural and sequential characteristicsin vertical and lateral, distribution. These studies leanheavily upon the work by N a y 1 or (1964, 1969,N a y 1o r et al., 1969),' who unraveled, the majortectonic, stratigraphic. and gross facies features of thearea.
The example of tidal sedimentation given in thepresent publication has been taken from the topmostpart of the exposed Devonian rocks just north of theSeven Heads. Bay syncline, east coast of Seven. Headspeninsula. K u i j p e r s (1971) described the succes-sion exposed to the south of this syncline.
The tidal deposits, discussed in fig. 7 are made upby a LS, and a heterolithic SS-facies organized in amore or less distinct fining-upward sequence: By farthe major part (some ten metres) of the sequencehere comprises LS-facies. The,SS-facies embraces not
morethan a few metres thickness.
Further down in the succession the LS-facies andthe SS-facies are getting more in balance with eachother and concomitantly the fining upward characteris clearer developed, This part of the successionamounts to a thickness of about 50.m. Still furtherdown in the stratigraphical column (northward alongthe coast) the SS-facies becomes predominant, andthe fining-upward tendency gradually, makes place foran irregular., alternation of LS- and SS=facies. The,whole succession described above probably belongs toNaylor's Hole-open Formation as` distinguished byhim on the Old Head of Kinsale-peninsula to the eastof the Seven Heads. 'Very recently d e ,V ri e sK I e i n (1970) described Precambrian- tide-dominated deposits, which resemble extraordinarilythose of the Devonian section with largescale herring-bone structures described in this article. His facies Iseems to correspond fairly well to our gro.sso-modoLS-facies association and his, facies II to our, SS-faciesbut for the ubiquitous mudcracks he mentioned,which seem to be absent at Seven Heads Bay. We didnot find clear evidence for late-stage sheet-runoffneither for a.high tidal=flat nature of our SS-intervalsand are, in. doubt whether the organization into afining-upward- sequence.. has a bathymetric signifi-cance and points to a regression in the Irish example.The vertical changing 'over, from a LS-interval into aSS one corresponding to a decrease of energy mayalso develop, under subtidal conditions.
4x
484
iii lorgescale
smollscole cross-strotificotion'
smollscole climbing sets
wave ripple (cross-etratlf ication )
bioturbation
wdirectionol bimodality
- current and wave ripple(cross-strotificotion)on top of-- ,g subhorizontal lam. set
485
DESCRIPTIONAL PART
LEGEND TO THE LOGS
I
thin l
bedded(massive)
I 1
medium
thick
horizontal lom.
subhoriz. lom.
I IC $ mojor structurolintervols,focies groups
f
'.
floser-bearing ss!
floser bedding
linsen bedding
BARENDRECHT
Fig.
1A
-DE
xam
ples
of
tran
sitio
nal (
inne
r es
tuar
ine
- fl
uvia
ltida
l) d
epos
its. B
aren
drec
ht e
xcav
atio
n. T
he s
ucce
ssio
n is
fin
ing-
upw
ard
(see
log)
, thr
ee in
terv
als
(1-I
II)
can
be d
elin
eate
d on
the
basi
s of
gro
ss g
rain
size
and
sca
le, t
ype
and
dire
ctio
nal c
hara
cter
istic
s of
the
sedi
men
tary
str
uctu
res.
The
low
er in
terv
al, I
(se
e fi
g. A
), c
onsi
sts
of lo
ng, p
lana
r se
ts (
up th
e 20
in s
et le
ngth
) sh
owin
g la
rges
cale
uni
mod
al s
eaw
ard
(W)
- di
rect
edcr
oss-
stra
tific
atio
n. A
thic
k bo
ttom
set l
ayer
und
erlie
s th
e fo
rese
t lay
er o
f ea
ch s
et. C
lose
exa
min
atio
n sh
ows
that
the
botto
mse
t lay
ers
larg
ely
cons
ist
of s
mal
lsca
le b
ackf
low
-rip
ple
type
. Her
e an
d th
ere
thes
e co
unte
rcur
rent
'ripp
le s
truc
ture
s ap
pear
to c
limb
high
tip
on th
e fo
rese
ts (
see
low
erm
ost
larg
esca
le s
et f
ig. A
and
fig
. D).
Cla
y pe
bble
s m
ay r
epla
ce th
e m
ediu
m-c
oars
e sa
nd o
f th
e m
ega-
fore
sets
. The
fill
ing-
up o
f er
osio
nal h
oles
res
ults
inlo
cal d
evia
tions
fro
m th
e un
idir
ectio
nal p
atte
rn a
nd c
once
ntra
tion
of c
lay
frag
men
ts.
The
mid
dle
inte
rval
, II
(fig
. D a
nd u
pper
par
t of
A),
is c
hara
cter
ized
by
an a
ssoc
iatio
n of
larg
e- a
nd s
mal
lsca
le s
ets
with
loca
l but
non
cons
eque
ntdi
rect
iona
l bim
odal
ity. H
erri
ngbo
ne s
truc
ture
s, w
here
fou
nd, a
re d
ue to
sup
erpo
sitio
n of
opp
osite
ly-d
irec
ted
sets
of
a si
mila
r or
dif
fere
nt s
cale
.A
vera
ge g
rain
size
her
e is
fin
er th
an in
inte
rval
I a
nd to
a h
ighe
r ex
tent
-cou
pled
with
mud
adm
ixtu
re, e
spec
ially
in th
e sm
alls
cale
cro
ss-s
trat
ifie
d un
its.
Not
ewor
thy
is th
e di
scon
tinuo
us n
atur
e of
for
eset
ting
in th
e lo
wer
mos
t lan
dwar
d -d
irec
ted
larg
esca
le s
et (
see
fig.
A);
sta
rtin
g fr
om "
reac
tivat
ion
plan
es (
C o
11
i n s
o n
, 1-9
70)
only
sm
all b
undl
es o
f fo
rese
ts a
re f
orm
ed s
ucce
ssiv
ely.
Sm
alls
cale
set
s fo
und
in th
is in
terv
al a
reof
the
plan
ar ty
pe w
ithm
oder
ate
to lo
ng s
etle
ngth
s (u
p to
40
cm).
The
upp
er S
S-in
terv
al, I
II (
fig.
B a
nd C
), m
ainl
y co
nsis
ts o
f al
tern
atin
g un
its o
f fl
aser
and
lins
en ty
pes
(nom
encl
atur
e R
e i
n e
ck
and
W u
n d
e r
1 i c
h, 1
968)
. How
ever
, a .p
redo
min
ance
of
flas
er s
truc
ture
(ir
regu
lar
mud
dra
pes
inte
rspe
rsed
in s
mal
lsca
le c
ross
-str
atif
ied
sand
s) w
as,
obse
rved
in th
e lo
wer
por
tion,
whi
ch p
asse
s up
war
d in
to li
nsen
str
uctu
re (
sand
lent
icle
s in
,mud
).
The
sed
imen
tary
str
uctu
ral u
pbui
ldin
g of
the
low
er in
terv
al b
ears
str
ong
rese
mbl
ance
to th
at o
f up
per-
poin
tbar
dep
osits
fro
m p
urel
y fl
uvia
l rea
ches
-(cf
-B
o e
r s
in a
, 196
8). A
ppar
ently
the
tidal
flo
od c
urre
nt if
act
ive
at a
ll in
Bar
endr
echt
at t
he ti
me
of u
pbui
ldin
g:w
ere
of in
suff
icie
nt s
tren
gth
and
dura
tion
to p
rodu
ce s
truc
tura
l fea
ture
s im
port
ant e
noug
h to
y es
cape
sub
sequ
ent e
bb e
rosi
on. T
he s
ituat
ion
was
qui
te d
iffe
rent
in th
e m
iddl
e,tr
ansi
tiona
l int
erva
l. H
ere,
at-
aver
age
low
er in
tens
ities
of
flow
(no
te s
ize
of s
truc
ture
s, s
mal
ler
grai
nsiz
es),
the
effe
cts
of f
lood
cur
rent
s ar
e cl
earl
ydi
scer
nabl
e an
d al
mos
t as
impo
rtan
t as
thos
e of
the
seaw
ards
run
ning
cur
rent
s.T
heup
per
SS, i
nter
val w
as a
ppar
ently
dep
osite
d un
der
still
low
er in
tens
ities
of
flow
, bec
omin
g m
inim
al to
war
ds th
e to
p as
is w
itnes
sed
by th
eup
war
d-in
crea
sing
mud
con
tent
. Alth
ough
dir
ectio
nal c
hara
cter
istic
s w
ere
here
rat
her
diff
icul
t to
quan
tify,
the
obse
rvat
ions
sug
gest
ed th
at a
rig
orou
sdi
rect
iona
l bim
odal
ity g
over
ns th
is p
art o
f th
e se
ctio
n.T
he m
etre
sca
le a
long
side
the
log
refe
rs to
dep
th b
elow
NA
P. T
he m
easu
ring
tape
in ,f
ig. B
is d
ivid
ed in
tens
of
cent
imet
res;
the
key
in f
ig. D
bea
rsa
1 -c
m r
efer
ence
mar
k.
HA1tINGVLIET.
Fig. 2A, B.Photographs of lacker peels examplifying the
estuarine sediments exposed in the Haringvliet exca-vation. Peels made at a depth of 12-15 in below NAP.Two lithofacies groups are distinguished:
The LS-lithofacies group is dominated by largescalecross-stratified sets of the planar but more usually ofthe trough type. Diagnostic (tidal) features of these'sets are:a. Directional, bimodality between individual sets or
co-sets.b. Prevalence of short setlengths either due to
erosional truncation or to "dying", out of foreset.ting by gradual decrease of the foreset-angle.
c. Traces or stretches betraying discontinuities, whichinterrupt but do not destroy the unidirectionalforesetting in one set (see B at 1).
d. High mud content either, in the form of muddrapes or pebbles and flakes (see A at 1, B at2).,High concentrations (also pockets) of shell frag-ments.Smallscale oppositely-directed ripple structuresmay be interspersed between and climb high upthe slope, of largescale foresets, but are of adifferent (non -interfingering) character than thoseencountered in fluvial deposits (see 'A at 2, B at 3).
The SS-lithofacies group is characterized by aninterlamination of mud and sand at a variable rate
-,giving rise to its heterolithic nature. Between thehardly'mud-flasered sand and the hardly sand-lineatedm`uds being the two' end members of the series, manytransitional types occur (see classification of flaserand linsen bedding of Reineck and Wunder-1 i c h, 1968). The interlaminations may have. a moreor less straight, streaky .character, but lenticularityand wavy bedding strongly prevails. Directional bi-modality in this' lithofacies group is a common
feature especially between, differently-structured,(minor) intervals. Within one interval, however, aunimodality may exist (see B4); in case of bimodalityits degree may be quite variable and changinglaterally. As such,' unimodal, and bimodal intervalsmay be encountered in any order of superposition.The type of modality of a heterolithic unit may beidentical to or contrasting with that, of the adjacentlarge scale -structured unit.
Wave-generated cross-stratification was not ob-served in the present' examples of subtidal deposition.However its recognition is often very difficult, sincethe reversing tidal, currents responsible for the ripplestructures in some heterolithic, intervals are of soshort aperiodical character as to simulate (wave-)orbital -oscillations. Smallscale sets with pseudo-wavefeatures found in A- at 3, are 'enlarged in fig. C.Burrows may occur.
Presence or absence of sequential, order
At a scale covering only a few metres of thicknessor, less a fining-upward tendency was observed inseveral instances.
This fining-upward shows up in the followingways:a. A decrease. in number and thickness of the
individual ,sets participating in the successive LS-units. ,
b. A decrease of clay (pebble) admixture and shell_ fragments in the LS-cross-stratified units,
c. An' upward increase in the clay, content in theheterolithic units.Often the fining-upward takes place in 'a more (B)
or less (A) distinct stepwise (manner. The changingover from a heterolithic unit to its overlying large-scale cross-stratified unit, or from a clay-rich type ofheterolithicum to a clay-poor one is generally abrupt(see A at 4) as is demonstrated by an erosive, straightor scouring, lower boundary. The jump in grainsizemay be conspicuous, but more often is not.
489
e.
490
1 -orlem.n.. or .,posse -115 (in plan)
N ' ..
,
w ikeSedlon
.
Z lyVtal'47 ..
I
r.-11 .
.H 'M- - ' "c- le t cried fd
F
n
,v - 6ii
P*tee, , !f ,.
'
,kx
m
0
o,
rain
491
Fig. 3A-C.General view (A) and detailed pictures (B, C) of
lower Pleistocene ("Tiglian") tidal deposits lying atthe base of an essentially fluviatile Pleistocene succes-sion (see log). The latter's pure white sands areorganised in tabular, largescale sets of cross-stratifica-tion. These sets are inclined with respect to theconglomeratic boundary between the tidal and fluvia-tile formations. Note the exposed walls changeorientation with respect to tectonic as well as
sedimentary directions; turnings x and y (see inset ofA). The tidal deposits (thickness ± 8.50 in) arecomposed of the same two types of lithofacies groupsas distinguished in the I-laringvliet (item 2) and LowerGreensand (item 5): a LS-group and a heterolithicSS-group. The parts in the succession taken up bythese groups are delineated in photograph A. Thegroup seems to occur in couples (bipartite cycles)each starting off with the erosively-based largescalegroup.
The LS-groups are dominated by trough andsemi-tabular cross-stratified sets mostly of shortlength at least in part generated by dune migration.Clay is a major constituent of the sets and occurseither as clay-flakes and -pebbles or as drapes on theforesets. In addition, minor beds showing SS- sand-Clay interlaminations (heterolithicum) may separatethe large sets.
in the lowermost (± 17.20-18 m) and the uppermost(± 23.30-25 m) intervals where semitabular largescalesets of cross-stratification are intercalated (see photo-graphs B and C taken from the lowermost interval).
Directional bimodality is manifest throughout thepresent Tiglian tidal succession. Westward directionsprevail over eastward directions particularly in theLS-intervals. This westward direction tallies well withthe general direction found in the overlying fluviatileformations of the area and probably represents theseaward direction. This defective bimodality stronglypoints to a fluviatile influence in the tidal environ-ment. In several aspects there is a strong resemblanceto estuarine deposits. found in the northern, channel-fill, part of the Haringvliet excavation (no general viewpresented here). For instance in both cases we see invertical sections a recurrence of laterally extensivechannelling levels with festoon-like lower boundary.It seems therefore likely that the Tiglian deposits arelaid down in an inlet of the sea through which therewas also considerable seaward outflow. Whether thisoutflow was due to a strong fluviatile influence or toebb-channel character in an estuary or to both couldnot be ascertained at this stage of investigation. TheHattem deposits have characteristics in common withboth the Haringvliet and the Barendreclit sedimentsbut seem to be more tide-dominated and seawarddeposited than the latter.
Scale: Ruler in A measures 1 metre; in fig. C forscale see lighter.
HATTEM
r
E 1u0P
0
Nco
I.
o.M
8
Fig.
4A
, BE
xam
ples
of
the
inte
rnal
str
uctu
re o
f tid
al d
unes
fou
nd o
n to
p of
an
estu
arin
e in
ter-
chan
nel b
ar la
rgel
y em
erge
nt d
urin
g eb
b (O
ssen
isse
sho
als,
Wes
tern
Sch
eldt
, The
Net
herl
ands
):U
pper
bou
ndar
ies
of d
emon
stra
ted
lack
er p
eels
coi
ncid
e w
ith lo
cal r
elie
f, b
ound
arie
s ar
e ar
bitr
arily
set
by
limita
tions
of
the
peel
ing
tech
niqu
e.Fi
g. A
sho
ws
a m
ore
or le
ss s
ymm
etri
cal d
une
cont
aini
ng tw
o st
ruct
ural
inte
rval
s: A
low
er, e
ssen
tially
LS-
cros
s-st
ratif
ied
inte
rval
and
an
uppe
r SS
one.
The
latte
r co
vers
the
dune
.E
xcep
t for
a f
ew s
mal
lsca
le c
ross
-str
atif
ied
sets
inte
rcal
ated
bet
wee
n tw
o la
rges
cale
. set
s in
the
mid
dle
left
of
the
figu
re th
e lo
wer
str
uctu
ral i
nter
val
is d
irec
tiona
lly, u
nim
odal
(fl
ood)
whe
reas
the
uppe
r in
terv
al is
str
ongl
y bi
mod
al. A
mos
t rem
arka
ble
feat
ure
of th
e L
S-cr
oss-
stra
tifie
d in
terv
al is
that
the
sets
hav
e in
clin
ed b
ound
arie
s ei
ther
dow
ndip
ping
(le
ftha
nd s
ide
of f
igur
e) o
r up
dipp
ing
(rig
htha
nd s
ide)
in th
e di
rect
ion
of c
ross
-str
atif
icat
ion.
The
se in
clin
ed b
ound
arie
s m
ost l
ikel
y re
pres
ent d
une
stos
s-si
de ty
pe e
rosi
on p
lane
s ge
nera
ted
by th
e eb
b (l
efth
and
side
) an
d th
e fl
ood
(rig
htha
ndsi
de)
curr
ents
. Thu
s du
ring
ebb
the
fron
t of
the
left
war
d po
intin
g fl
ood
ripp
le is
ero
sive
ly a
ttack
ed a
nd m
odif
ied
into
a m
ore
gent
ly in
clin
ed s
urfa
ce,
over
whi
ch d
urin
g th
e su
cces
sive
flo
od ti
de th
e' d
une
build
s pu
t aga
inby
mea
ns o
f la
rges
cale
cro
ss-s
trat
ific
atio
n. E
bb e
rosi
ve p
ower
may
be
so h
igh
asto
red
uce
the
thic
knes
s of
the
-lar
gesc
ale
cros
s-st
ratif
ied
(flo
od)
sets
to th
ose,
nor
mal
for
str
uctu
res
from
the
smal
lsca
le d
omai
n (c
f. a
l). I
n ot
her
inst
ance
s, h
owev
er, t
he e
bb a
ppar
ently
fai
ls to
pro
duce
any
oth
er e
ffec
t tha
n a
kind
of
brea
k, in
the
othe
rwis
e co
ntin
uous
larg
esca
le f
ores
ettin
g. T
his
feat
ure
show
s up
by
a ve
ry s
light
trac
e of
ero
sion
al u
ncon
form
ity a
nd/o
r a
chan
ge in
the
fore
set a
ngle
(cf
. 'a2
). S
omet
imes
at t
he tr
ace
ofun
conf
orm
ity a
sin
gle
set o
f re
vers
ely-
dire
cted
sm
alls
cale
cro
ss-s
trat
ific
atio
n is
fou
nd (
cf. a
3).
The
str
uctu
ral b
i-pa
rtite
upb
uild
ing
of th
e du
ne s
ugge
sts
that
the
latte
r un
derw
ent t
wo
stag
es o
f de
posi
tion,
dif
fere
nt in
man
y re
spec
ts. T
he u
pper
inte
rval
was
laid
dow
n by
alte
rnat
ing
ebb
and
floo
d cu
rren
ts o
f ab
out e
qual
, tho
ugh
rela
tivel
y sm
all s
tren
gth.
By
coun
ting
the
supe
rim
pose
d"g
ener
atio
ns"
of A
ppos
itely
dir
ecte
d se
ts o
ne m
ay c
oncl
ude
that
a m
inim
um o
f fo
ur e
bb-f
lood
sem
idiu
rnal
cyc
les
wer
e re
spon
sibl
e fo
r th
e fo
rmat
ion
of th
is in
terv
al.
Dur
ing
depo
sitio
n of
the
unde
rlyi
ng L
S-in
terv
al th
e du
ne w
as a
ppar
ently
sub
ject
to m
uch
high
er e
nerg
y co
nditi
ons
whe
reby
the
floo
d cu
rren
tsou
twei
ghed
thos
e of
ebb
in d
epos
ition
al e
ffec
t. It
was
obv
ious
ly d
urin
g fl
ood
that
the
dune
was
,sub
ject
to m
ovem
ent.
The
sub
sequ
ent e
bb a
t mos
tsc
alpe
d th
e fl
ood
dune
's to
p, p
ossi
bly
lead
ing
to s
ome
mod
ific
atio
n (r
ever
sal?
) of
its
exte
rnal
asy
mm
etry
.T
he a
bove
inte
rpre
tatio
ns a
re in
goo
d ac
cord
ance
with
the
visu
al r
ecor
ding
of
even
ts, w
hich
took
pla
ce a
t the
pre
sent
loca
lity
duri
ng th
e pe
riod
prec
edin
g an
d fo
llow
ing
the
sam
plin
g. I
t was
lear
nt th
en th
at th
e du
nes
wer
e "a
ctiv
e" o
nly
duri
ng a
few
day
s ar
ound
spr
ing-
tide,
whi
le th
ey w
ere
virt
ually
imm
obile
but
for
thei
r co
veri
ng s
mal
lsca
le r
ippl
es, f
or th
e la
rger
per
iod
in th
e m
iddl
e of
whi
ch li
es th
e ne
ap-t
ide.
In
fact
the
lack
er p
eel
was
proc
esse
d so
me
thre
e, d
ays
afte
r op
timal
spr
ing-
tide
(ran
ge n
r. 7
; Aug
ust 2
, 196
9). B
y co
mpa
ring
this
laps
e of
tim
e w
ith th
e m
inim
um "
age"
of
four
times
twel
ve h
ours
(tw
o da
ys)
dedu
ced
for
the
uppe
r. s
truc
tura
l. in
terv
al o
ne m
ay c
oncl
ude
that
the
dune
s ha
lted
with
in o
ne d
ay a
fter
the
give
nsp
ring
-tid
e..
'
Figu
res
131-
3 re
pres
ent v
ertic
al s
ectio
ns th
roug
h on
e an
d th
e' s
ame
dune
fro
nt a
t a f
ew m
etre
s fr
om e
ach
othe
r m
ade
just
aft
er th
e ne
ap-t
ide
peri
od(J
uly
27; s
prin
g-tid
e, J
uly
30; l
ocat
ion,
obs
erva
tion
plat
form
Nor
th).
Fro
m v
isua
l rec
ordi
ng it
is k
now
n th
at th
e du
nes
had
been
pra
ctic
ally
imm
obile
for
seve
ral p
rece
ding
day
s an
d ju
st, s
tart
ed to
mov
e fo
rwar
d at
ver
y lo
w s
peed
s, w
hich
wer
e sl
ight
ly d
iffe
rent
for
adj
oini
ng s
tret
ches
of
the
fron
t.H
esita
ting
lee-
side
acc
retio
n du
ring
the
neap
-tid
e st
age
of th
e du
ne is
rep
rese
nted
in th
e la
cker
pee
ls b
y a
bund
le o
f w
aver
ing
fore
sets
(cf
. NT
).N
ewly
set
-in
mov
emen
t mak
es it
self
vis
ible
in th
e fo
rm o
f a
mor
e ri
gidl
y cr
oss-
stra
tifie
d st
retc
h oc
curr
ing
at th
e ex
trem
e le
ftha
nd e
nd o
f th
e pe
els.
An
extr
apol
atio
n of
thes
e ob
serv
atio
ns m
akes
it p
laus
ible
that
the
long
, reg
ular
ly c
ross
-str
atif
ied
stre
tche
s (c
f. S
T)
of th
e se
ts f
urth
er to
the
righ
t wer
ege
nera
ted
in p
rece
ding
spr
ing-
tide
peri
ods.
OSS
EN
ISSE
494
A
LEIGHTON BUZZARD - WOBURN, AREA
Fig. 5A-C.Two examples are given of tidal-sea deposits
belonging to the Lower Greensand (Woburn beds) ofsouthern Engeland. The illustrations (A-C)' only con-cern parts of two of the many quarries of the area.The Woburn beds display here two lithofacies groups:1. LS-lithofacies group.II. Predominantly heterolithic, SS-lithofacies group.
Within each group several subfacies can be dis-tinguished. The examples dealt with below representbut a random selection, from a hostof,tidal pheno-mena.
1. Fig. A (Garside"s quarry, Heath and Reach) showsan upper complex consisting of bimodal planar,largescale cross-stratified sets. It rests by means ofan horizontal boundary plane on a complex, whichas a whole shows cross-bedding 'at an ev:nlarger scale. Nearer inspection revealed that the'latter complex is of a very intricate structure, inwhich two types of major structural units can bedistinguished:'1. Wedge-shaped bodies (see fig. A extreme right
and, left of drawing) entirely consisting oflargescale tabular sets of , cross'-stratification,which show directional bimodality, -
2. A large body characterized by a superpositionof metre-scale foresetbundles (see central partof figure in between the bodies (1)). Thestructural differentiation occurring within eachforeset bundle belonging to (2) is remarkable,because close examination shows a subdivisionof the bundle in three discrete intervals-, a, b,and c (see fig. 3) marked by: '
a. Very largescale foresetting in coarse, pebblysand resting on an inclined base (= local
depositional "slope). This interval has often adark rusty colour apparently due to theprecipitation of ferrous material.
b. Largescale foresetting ascending the slope in"planar sets (b 1) and generally merging up-dip'into. slope-parallel waver-type lamination(b2) '
c. Slope-parallel lamination of the "giant" fore-setting type showing grain-size differentia-tion and an even' stratification. Downslope,the 'present interval, concordantly buries the
mega-ripple top of the (b)-intervalby bending over .the latter's relief in themiddle left of fig. B (at cl).
11. Fig. C (Munday's Hill Quarry, Heath and Reach)represents a predominantly heterolithic SS-faciesassociation, characterized" by beds showing small-scale cross-stratified sand-mud interlaminations(flaser and linsen) with random intercalations oflargescale cross-stratified sets.Directional bimodality is conspicuous and is cha-racteristic not only for the smallscale but also forthe largerscale structures, as well as for combina-tions of both types of structures.
The facies rich in heterolithic SS-beds shown infig..C is attributed to a, rather low-energy tidalenvironment without appreciable relief.
The facies association represented in fig. A on theother hand, indicates a prevalence of high-energy'conditions: The lower complex would have been,deposited in an environment with a pronouncedsubmarine relief in contrast with the upper complex,which is assumed to. represent an environment prac-tically devoid of relief. The horizontal discontinuityplane separating both complexes points to a radicalchange in submarine morphology.
495
496
9i. r duv -
5
i
30z
a/
F ,g p Iw X20
poorly i ie,poee -= t - 3
OLIGOCENE BELGIUM
Fig. 6A, B.Examples from, tide-governed Lower Oligocene
(Tongrian) succession, east of Leuven (Belgium).
Three lithofacies groups can be distinguished (seelog):
-1. A lower group, fine sandy and silty, greenishcoloured (glauconite); mainly characterized 'bysmallscale cross- and horizontal lamination. Thecross-laminated sets are often of the climbing type(see photograph A). The present"' lithofacies isknown as the "Neerrepen Sands" and-is marked bydirectional bimodality in the Academic Hospitalquarry. In other outcrops of the present lithofacies
-(e.g. Kesselberg) horizontal to subhorizontal lami-nation prevails strongly over cross-lamination, al-though isolated wave-ripple, and. current-ripplehorizons occur. In both cases largescale cross-stratified structures are an exceptional feature.Contorted bedding is a prominent feature in thepresent quarry and of two types. The first, thediapiric-convolution type, is probably the effect ofwater escape from, oversaturated sandy layers (atal). The second type is presumably mainly due toorganisms escaping from burial (e.g. at a2). On thewhole several kinds of structures produced byorganisms known from tidal and 'other shallow-marine environments (Crustacea, Annelidae, Mol-luscs) are abundant not only in the lower but also,in the middle lithofacies group.
2. A middle group, known as the "Kerkom ,Sands",with grain sizes varying largely between coarse andmedium grades.. Largescale cross-stratification is the
dominant feature (see photograph B). Smallscalecross-laminated (often of the climbing type) andhorizontally laminated intervals are common inter-calations' further to the east (Vissenaken, Ker-kom). In the present quarry this lithofacies groupstarts off with a conglomeratic bed containing claygalls and traces of scour-and-fill structures.Directional bimodality is ubiquitous in the middlegroup in LS- as well as SS-strata (see log).
,
3. An upper, group, comprising two metres of remark-ably evenbedded, horizontally laminated mediumsand. A few, scattered, shallow-depression fills, aswell as thin and short cross-laminated sets areoccasionally encountered here. This lithofaciesseems to be of local occurrence.
The above provides' convincing evidence of strongtidal action in 'the Oligocene during the "Kerkomian"along the SouthQrn, border of the predecessor of theNorth Sea., Nowhere have purely fluviatile KerkomSands been found in the visited quarries. As regardsthe lower lithofacies group comprising the Neerrepensands tidal currents also seem to have played a partthough to a less extent. The sequential characteristicsof these sands point moreover to intermittent in-fluxes of material separated by periods of slow orhon-deposition as suggested by the occurrence ofwave-ripple horizons covered by fine suspensionmaterial and of zones of maximum bioturbationalternating with less burrowed ones.
As yet the authors feel unable to decide on theexact tidal subenvironments of deposition for thepresent succession.
Photographs of lacker peels taken in the AcademicHospital Quarry, ± 4 km east of Leuven.
497
a-s
-iy
498
0
UO
--
eb.croo(of eaa)or ia.a. ecae
tor.seiliny in interval II
af,o
.inq
loca
lly e
sfic
le n
t (flo
odeo
min
ata)
eim
odam
v
-2
and
daya
in
499
UPPER DEVONIAN, SOUTHERN IRELAND
Fig. 7A-C.Examples taken from tidal deposits belonging to
the marine Upper Devonian of Seven Heads Bay(Cork beds, SW Ireland).
The photographs concern the upper part of the
succession, which can be divided into structural
cycles of the type shown in the log. Each cycleideally, consists of three major intervals (1-111) gradinginto each other from bottom to top.1. The lower interval characterized by subhorizon-
tally laminated sandstones exhibiting slight bed-dingplane divergencies and organised in beds ofupward decreasing thickness (from metre-scale todm-scale). Again and again it was observed thatcertain surfaces of individual beds bear ripple-marks or that horizontal lamination at the top ofindividual beds is erosively covered by a small-scale cross-laminated layer only one or a fewcm-ers thick. The latter may have a clearlywave-generated or current-generated structure,but fairly often both types of structure appear tooccur in direct superposition, in which cases thewave structures always form the very top. Cur-rent (parting) - lineation is absent in the presentinterval.
II. The middle interval is characterized by largescalecross-stratified sets often of the planar type,interbedded with (sub)horizontally laminatedsets and with some co-sets showing smallscale(current) cross-lamination. Again wave ripplesare found to occur here and there at the partings,which separate the sets. Current direction isbimodal, which is quite notable in the largescalecross-stratified units, but also, though lessstriking, to the field observer in their smallscalecounterparts as is perfectly shown by radiographs(see Q. The set thicknesses of the sandstone bedsof interval 11 vary from one or more centimetres'
to a maximum of 35 cm.111. The upper, heterolithic, SS-interval made up pri-
marily of flaser and linsen beds and some siltbeds, interspersed by a few thin .(± 5 cm),horizontally laminated or, smallscale cross-laminated sandstones.
Photograph A provides a general view from the2 m-level (see log, interval I) upwards. Subhorizontal-ly laminated beds in foreground display upwarddecreasing bed thickness and an increasing rate ofbedding-plane divergency, which seems to announcethe cross-stratification prevailing in interval II. Thefirst genuine largescale cross-stratified set occursabove the 40 cm long hammer shaft. The cross-strati-fied interval is distinctly more evenbedded, as is welldemonstrated in photograph B. Further salient fea-tures of the latter figure are:1. The occurrence of horizontally laminated beds and
smallscale cross-stratified cosets (at la and lbrespectively).
2. Largescale foresets merging into long and some-times thick bottom sets, which are asymptotic tothe lower set boundary (at 2).
3. The fanning up and down character of thelargescale foresets (at 3a and 3b).
4. The often low angle inclined or "hesitating"character of the foresetting (at 4).
Curiously enough part or whole of the cross-strati-fied interval (II) may over a distance of a few tens ofmetres laterally merge into thin-bedded, (sub-)horizontally-laminated complexes without alterationof thickness. In the latter smallscale wave and currentstructures are intercalated. This structural change iseffected by the gradual fading out of the megafore-sets through a fanning-up of the laminae to horizontalposition. On the other hand, megasets may start offwith horizontal lamination, which gradually inclinesmore and more downstream. This mode of birth anddisappearance of mega-foresetting seems to indicatethat mega-foresetting preferentially developed whereflow expansion was made possible by pre-existingshallow depressions. Greater difficulties arise when itis endeavoured to explain the generating conditionsof the lower, subhorizontal interval. A few pre-liminary considerations are given here: The absenceof current lineation on bedding planes of sub-horizontally laminated beds seems to indicate thatgrain traction and helical (current parallel) eddies(A 11 e n, 1968) could not develop or hardly so.
500
Possibly, successive, rapidly slackening currentscausing sudden high rates of fall-out from suspension,which is known to suppress vortical activity, might beresponsible for the formation of the "horizontal"beds of interval I. The recurrent appearance of waveand current ripples on top of these beds mightindicate that:1. These sand influxes were of a spasmodic nature,
short periods of rapid deposition alternating withpossibly longer periods during which tranquil butstill agitated water conditions existed.
2. Deposition must have taken place at shallowdepth, above wave base.
As to the tidal subenvironment(s) where this kindof deposition took place the authors as yet feelincapable of making a definite statement.
CONCLUDING REMARKS
Studies of sediments from the Transitional Zonemade by the authors indicate that there is a numberof characteristics that point to tidal action in modernand ancient environments. These diagnostic features,which seem to hold good with regard to intertidal aswell as subtidal deposits, can be listed in descendingorder of importance:
1. Directional bimodality in smallscale, largescale ormixed (small-large scale) cross-laminated set ups. Onedirection prevailing strongly over the other results ina deficient bimodality.
2. SS-units and grosso modo LS-units being common-ly coupled (in super- or juxtaposition) at differentproportions. The cross-lamination prevailing in bothunits is often accompanied by horizontal laminationof varying and' often speculative genesis, The unitsform generally discrete lithofacies associations ofvariable thickness but may also occur intimatelyintertwined. Their co-existence points to hydrodynamic conditions, which are highly variable inspace and time, connected with subaqueous (changesin) morphology. The SS-units, which are, oftenheterolithic (variable sand/mud ratio), were formedunder relatively low-energy conditions, The LS-unitsrepresent sedimentation patterns with prevalent high-energy conditions. Especially where the latter. unitsare thickly developed, they may contain subordinate
smallscale cross-laminated, often muddy, horizons,caused by ephemeral interruptions of the high-energyregime.
In open-marine tidal sedimentation, the largescalestructures tend to prevail and giant foresetting isknown to occur here.
`3. 'The intricate character of the sequential order.Composite fining-upward complexes, characterizedby a- basal, often channelling, LS-unit transitionallyfollowed by a SS-, usually muddy, unit were en-countered in certain tidal environments. In theHaringvliet the fining-upward complexes range inthickness from a few dm to a few metres and remaina feature of rather secondary importance. In Baren-drecht such a, sequence comprises, however, a numberof metres.
In ancient tidal sediments of bipartite upbuilding(LS- and SS-units) sequential regularity is. not ofcommon coccurrence. Only occasionally a fining-upward comes to the fore. Mostly the picture isblurred by sequential reversibility.
Thus, tidal deposits differ sequentially from flu-viatile (fining-upward) as well as from deltaic sedi-ments (coarsening-upward).
4. Secondary phenomena related to the bi-directionaland intermittent character of tidal currents.a. The frequent occurrence of discontinuity planes
(in grossly unidirectional megasets), which trun-cate or do not truncate previously depositedbundles. of foresets. These planes bear subsequentbundles, mostly characterized by a different angleof foresetting. This feature points to repeatedlyinterrupted progradation of the megaripple fol-lowed by reactivated sedimentation.
b. The discontinuity in question is often stressed bythe occurrence of one or a few sets of oppositelydirected smallscale ripples ascending the mega-foreset, slope or the truncation surface withoutshowing backflow-ripple character (no interfinger-ing between largescale and smallscale laminae).
c. Deposition of some silt or clay on the discontinui-ty plane or on the abovementioned ascending,,ripples.
d. The local fanning up and down of the mega-fore-sets.
c. The very frequent occurrence of megasets of ashort length or if they are long, containingdiscontinuity planes (see a).
f. The megasets mentioned under. e often have
Soi
scooping lower set boundaries.
5. The widespread and quantitatively important de-velopment of beds of (laser- and lenticular (linsen)character and of straighter types of'sand-mud inter-lamination in the SS-units. This feature, however,should be` handled with the utmost caution; as it mayalso occur in sediments from a greet number ofmodern non-tidal environments 3) (see e.g. R e i n. -e.ck,1960;CoIemanand Gagliano,1965andK a n e s, 1970). In the tidal flaser and linsen bedsstudied by the authors the following nodes ofcross-lamination were observed:
1: Bimodal current-ripplecross-lamination isometimes with wave-
2. Unimodal current-ripple reworked topcross-lamination
3. Wave-generated cross-lamination (Sevenheads bay,Ireland, in the succession underlying the describedexample).
The first type of cross-lamination points un-doubtedly to tidal deposition but is difficult torecognize in the field when lenticles are small-sized. AMaser and linsen complex. of unimodal directionalcharacter can only be considered as indicative of tidalaction if the observed foresetting is diametricallyopposite to that of certain intervals belonging toenframing non-heterolithic strata.
6. Slight to intensive bioturbatioh in several types ofsandy and/or muddy units, frequently suddenly,disappearing without being related to a,change incharacter of the sediments. This is a curious butfrequently occuring feature in ancient tidal deposits.Its diagnostic value so far remains uncertain.
The listed cross-sectional features shared bysubtidal and intertidal deposits as a rule overshadowentirely those upon which a distinction between both
3) A random selection: (Coastal) lake sediments (Rhonedeltaic plain);, proximal fluviomarine sediments (Rhone pro-delta); lagoonal sediments (W i g g e r s, 1955, fig. 33, 89:Almere formation Zuiderzee,'The Netherlands); marsh sedi-ments (Kanes, Colorado river delta, Texas); interdistributarybay sediments (Coleman et al. Mississippi delta); some Dutchinterfluvial and fluvial sediments (the authors' experience).Rhone delta core material obtained through courtesy of Kon.Shell EP Lab. Rijswijk, The Netherlands.
types of deposits could be made. This is presumablydue to the rare preservation of the original morpholo-gical surfaces and microreliefs observable during'emersion and last but not least to, the apparentscarcity of sequential features typical for the inter-tidal domain. In case marginal (salt-) marsh sedimentsare preserved the latter situation becomes less pro-blematic: One is therefore generally seriously handi-capped when endeavouring to discern subtidal sedi-ments from intertidal ones in a succession of beds.
As regards, the distinction between on the one sideoffshore to open sea and on the other inshore tidaldeposits structural and sequential evidence should,where possible, be supplemented, by data about theprevailing paleocurrent patterns so as to get informa-tion concerning- shore-line position, presence or ab-sence of bimodal longshore currents, etc. Theauthors' studies in Ireland and Belgium show that thisis not a simple affair. It is believed that painstakingfuture research may contribute considerably to theunderstanding of the manyfold aspects of tidalsedimentation and it is a "consolation" that up to thepresent but a very small fraction of the total amountof tidal deposits formed during the Geological Pasthas been discovered and studied, which leaves ampleopportunity to the elucidation of a number offeatures, which are still enigmatic at present.
REFERENCES.
Allen, J.R.L. and J. Narayan (1964) - Cross-stratified units,some with siltbands in the Folkestone Beds (LowerGreensand) of SE England. Geol. en Mijnbouw, 43, p.451-461.
Allen, J.R.L. (1968) - Current ripples. Their relation topatterns of water and sedimentation. North HollandPublishing Comp., Amsterdam.
Boersma, J.R.; E.A. van de Meene and R.C. Tjalsma (1968) -Intricated. cross-stratification due to interaction of amegaripple with its leeside system of backflow ripples(Upper-pointbar deposits, Lower Rhine). Sedimentol-ogy, 11., p. 147-162.
Boersma, J.R. (1969) - Internal structure of some tidalmega-ripples on a shoal in the Westerschelde estuary,The Netherlands. Geol. en Mijnb., 48, p. 409-414.
Coleman, J.M. and S.M. Gagliano (1965) - Sedimentarystructures: Mississippi river deltaic plain. In: SEPMSpecial Publication 12, p. 133-148.
Collinson, J.D. (1970) , Bedforms of the Tana river, NorwayGeogr. Annaler, 52, p.31-55.
Dorjes, J., S. Gadow, G. Hertweck, H.E_ Reineck and F.Wunderlich (1970) T Das Watt. Ablagerungs- and
Lebensraum. Senckenberg - Buch 50. Verlag Walde-mar Kramer, Frankfurt am Main,
Evans, G. (1965) - Intertidal flat sediments and theirenvironments of deposition in the Wash. Quart. Journ.Geol. Soc., 121 (2), p. 209-246.
Gdlinck, M. (1963) - Excursion guide, M-N; Part 1-3. 6eCongres International de Sedimentologie, Belgique et
.Pays-Bas.Gullentops, F. (1957) - L'origine des collines duHa$eland.
Bull. de la Soc. Beige de Geol., LXVI, p. 81-85.(1963) - Etude de divers, facies quaternaires et ter-tiaires dins le Nord et 1'Est de la Belgique. ExcursionO-P. 6e Congres international de Sedimentologie Bel-gique et Pays-Bas.
Hantzschel, W. (1936) - Die Schichtungsformen rezenterFlachmeer Ablagerungen im Jade-Gebiet. Senck. loth.18, p. 316-356.
Heide, S. van der and W.H. Zagwijn (1967) - Stratigraphicalnomenclature of the Quaternary deposits in TheNetherlands. Meded. Geol. Stichting,,N.S. 18, p. 23.29.
Houbolt, J.J.H.C. (1968) - Recent sediments in the southernbight of the North Sea. Geol. en Mijnb., 47, p.245-273.
Hiilsemann, J. (1955) - Grossrippeln and Schragschich-tungs-gefuge im Nordsee-Watt and in der Molasse.Senck. loth., 36, p. 359-388.
James, N.P. and D.J. Stanley (1968) - Sable Island Bank offNova Scotia: Sediment dispersal and recent history.Am. Ass. Petrol. Geol. Bull., 52, p. 2208-2230.
Jong, J.D. de (1952) -- On the structure of the pre-glacialPleistocene of the Archemerberg (Prov. of OverijselNetherlands). Geol. en Mijnb., 14, p. 86-90.(1955) - Geologisch'e onderzoekingen in de stuwwal-len van oostelijk Nederland I: Archemerberg en Nijver-dal. Meded. Geol. Sticht. N.S., 8, p. 33-58.(1967) The Quaternary of The Netherlands. In: TheQuaternary, 2, (K. Rankama editor), p. 301-426.Intersc. Publ. (John Wiley).
Kanes, W.H. (1970) - Facies and development of theColorado river delta in Texas. In:, J.P. Morgan (editor)Deltaic sedimentation, modern and ancient. SEPMSpec. Publ., 15, p. 78-106.
Klein, G. de Vries (1970a) - Tidal origin of a Precambrianquartzite. The lower fine-grained quartzite (MiddleDalradian) of Islay, Scotland. Journ. of Sed. Petr., 40,p. 973-985.(1970b) Depositional_ and dispersal dynamics ofintertidal sand bars. Journ. of Sed. Petr.,, 40, p,.
1095-1 127.(1963) Bay of Fundy intertidal zone sediments.Journ. of Sed. Petr., 33, p. 844-854.
Kuijpers, E.P.- (1970) - Preliminary note on the .BreamrockFormation (Upper Devonian) Co. Cork, Ireland Anancient tidal deposit. Sediment. Geol., 5, p. 83-89.(1971) - Transition from fluviatile to tidal marinesediments in the Upper Devonian of SevenhcadsPeninsula, South County Cork, Ireland. Geol. enMijnb., 50, p. 443.
Naylor, D. (1964) - The Upper Devonian and LowerCarboniferous stratigraphy of South County Cork,
Ireland. Thesis, Trinity College,, Dublin, 308 p. (un-published).
Naylor,, D., P.C. Jones and M.J. Clarke (1969) - Thestratigraphy of the Cork beds (Upper Devonian andCarboniferous) in Southwest Ireland. Sci. Proc. Roy.Dublin Soc., Ser. A, 3, p. -171-191: .
Naylor, D. (1969) - Facies change in Upper Devonian andLower Carboniferous rocks of Southern Ireland. Geol.J., 6, p. 307-328.
Niehoff, W. (1958) - Die primar gerichtete Sedimentstruk-turen, insbesondere die Schragschichtung im KoblenzQuartzit am Mittelrhein. Geol. Rdsch., 47, p. 252-321.
Oomkens, E. and J.H.J. Terwindt (1960) - Inshore estuarinesediments in the Haringvliet. Geol. en Mijnb., 39, p.701-710.
Raaf, J.F.M. de (1970) - Environmental studies concerningUpper Devonian (and Lower Carboniferous) coastalsections of South County Cork. Geol. en Mijnb., 49, p.247-248.
Reading, H.G. and R.G. Walker (1966) Sedimentation ofEocambrian tillites and associated sediments in Finn-mark, Northern Norway. Paleogeogr., Paleoclimatol.,Paleoecol.,.2, p. 177-212.
Reineck, H.-E. (1960) - Ueber die Entstehung, von Linseri-und Flaserschichten. Abliandl. Deutsche Akad. Wiss.Berlin, K I. 3, p. 369-374.(1963) - Sedimentgefiige im Bereich der sudlichenNordsee. Abh. Senck. Naturforsch. Ges., 505, p. 1-138.(1967) - Layered sediments of tidal flats, beaches andshelf bottoms of the North Sea. In: Estuaries F.H.Lauff, editor),. Am. Adv. of Sci: Washington D.C., p.191-206.
Reineck, H.-E. and F. Wunderlich (1968) - Classification andorigin of flaser and lenticular bedding. Sedimentology,11, p. 99-104.(1969) - Die Entstehungvon Schichten and Schieht-oanken im Watt. Senck. maritima, [1], 50, p. 85-106.
Straaten, L.M.J.U. van (1950) - Giant ripples in tidalchannels. Tijdschr. Kon. Ned. Aard.rijkskundig Genoot-schap: LXVII, p. 336-341.(1951) - Texture and genesis of Dutch Wadden Seasediments.'Proc. 3rd Int. Congr. Gro-ningen - Wageningen, The Netherlands, p. 225-249.(1953) - Rhythmic patterns on Dutch North Seabeaches.. Geol. en Mijnb. (Nw. Ser.), p. 31-43.(1954a) - Sedimentology of recent tidal flat depositsand the psammites du Condroz (Devonian). Geol. enMijnb., 16, p. 25-47.(1954b) - Composition and structure of recent marinesediments in The Netherlands. Leidse Geol, Meded.,19, p. 1-110.
-(1964) - De bodem der Waddenzee. In: Wadden-boek. Ned. Geol. Ver., Thieme, Zutphen, p. 75-151.
Stride, A.-H., (1963) - Current-swept sea floors near thesouthern half of Great Britain. Q.J. Geol. Soc. London,119, p. 175-199. '
Terwindt, J.H.J., J,D. de Jong and E_ van der Wilk (1963) -Sediment movement and sediment properties in thetidal area of the Lower Rhine. Verli. Kon. Ned'. Geol.Mijnb. Gen., Geol. Serie, 21-2, p. 243-258.
502
- -
-
-
-
Terwindt, J.H.J. (1970a) - Observation on submergedsandripples with heights ranging from 30 to 200 cmoccurring in tidal channels of SW Netherlands. Geol. enMijnb., 49, p. 489-501.(1970b) - Sand waves in the southern bight of the
North Sea. Marine Geol., 10, p., 51=67.-, (1971) - Litho-facies of inshore estuarine and tidal
inlet deposits. Geol. en Mijnb., 50, p.5 IS.,Veen, van (1936) - Onderzoekingen in de Hoofden,'
s-Gravenha6:Wiggers, A.J. (1955) - De wording van hot Noordoostpolder-
gebied. Een onderzoek naar de physisch-geografischeontwikkeling van een sedimentair,gebied.,Tjeepk Wil-
Zwolle, 214 p:link,Wunderlich, F. (1966) - Genese and Umwelt der Nellen-'
kopfchenschichten (oberes Unterems, Rhein. Devon)am locus typicus; im Vergleich mit der Kiistenfaciesder Deutschen Bucht. Frankfurt am Main, thesis (notpublished).
-- (1967) - Feinblattrige Wechselschichtung and Ge--eitenschichtung. Senck. leth., 48, p. 337-343.,(1970.) - Genesis and. environment of the "Nellen-kopfchenschichten" (Lower Emsian,.Rheinian Devon)at locus typicus in comparison with modern coastalenvironment of the German Bay. Journ. of Sed. Pet.,40, p. 10-2-130.
503
-
J. -
on-
o.
zi:V O
r In. een hugs waar alleen de woonkamerverwarmd was. Maar de studeerkamer
niet of nauwelijks.Die tijd is nu vborbij. Met aardgas
kunt u uw huis kamer-voor-kamer verwarmen. Waardoor het ook's winters volledig bewoonbaar is. Kunt u weer blokken.
60
SIN
GASUNIEE
Hoe geledenheeft u
,.06 I.
