klein 1970 - depositional and dispersal dynamics of intertidal sand bars

8/2/2019 Klein 1970 - Depositional and Dispersal Dynamics of Intertidal Sand Bars

1/33

JOURNAL OP ~EDIMENTARY ~ETROLOGY, VO L. 40, No . 4, v. 109 5-11 27FIGS. 1 34 , DECE ~B~, 1970

D E P O S I T I O N A L A N D D I S P E R S A L D Y N A M I C S O F I N T E R T I D A L S A N D B A R S 1

G E O R G E n ~ V R I E S K L E I NDep a r tm e n t o f Geo lo gy , Un iv e r s i t y o f I l l in o i s , Ur b an a , I l l i n o i s , 6 1 80 1

A B S T R A C TT h e in t e r t i d a l san d b a r s o f t h e Min as B as in , No v a Sco t i a , a r e a sy m m et r i ca l i n c r o ss - sec t io n an d l i n ea r i np l an . T h ey a r e f o r m ed an d r ewo r k ed b y t i d a l cu r r en t s wh ich a r e ch a r ac t e r i zed b y an a sy m m et r i c t im e -v e lo c i ty p r of il e. A cau sa l co n n ec t io n b e tween t im e - v e lo c i ty a sy m m et r y o f t i d a l cu r r en t s an d b a r t o p o g r ap h yi s d em o n s t r a t ed . Av e r ag e b o t to m e bb cu r r en t v e lo c i t i e s ( 9 0 cm /sec ) we r e f o u n d to ex ceed av e r ag e b o t to mf lo o d cu r r en t v e lo c i t i e s ( 6 5 cm /sec ) o v e r g en t ly - s lo p in g ( 2 t o 3 d eg r ee ) b a r su r f ace s , wh e r ea s o v e r s t e ep -s lo p in g ( 8 d eg r ee ) b a r su r f ace s , av e r ag e b o t to m f l o o d cu r r e n t v e lo ci t i es ( 9 0 cm /sec ) we r e f o u n d to ex ceedav e r ag e b o t to m eb b cu r r en t v e lo c i ti e s ( 6 5 e r a / s ee ) .B o th b a r t o p o g r ap h y an d zo n es o f f lo o d- o r eb b - d o m in a t ed b o t to m t i d a l cu r r en t s co n t r o l t h e d i s t r i b u t io no f sed im en t t ex tu r e an d sed im en ta r y s t r u c tu r e s . On s t eep e r b a r s lo p es , t h e sed im en t i s f i n e - g r a in ed san d an di s ch a r ac t e r i zed b y a l r h o l e s , p l an a r l am in a t io n , an d su r f ace d u n es an d r i p p l e s . On th e g en t l e r b a r s lo p es , t h et ex tu r e o f t h e sed im en t i s m ed iu m - g r a in ed an d co a r se - g r a in ed san d wh ich h a s b een f a sh io n ed in to cu r r en tr i p p l e s , s im p le d u n es , co m p lex d u n es , s im p le san d wav es an d co m p lex san d wav es . T h e in t e r n a l o r g an iza t io no f so m e d u n es an d san d wav es i s ex t r em e ly co m p lex , i n a sm u ch a s t h i ck n ess o f i n t e r n a l se t s o f c r o ss - s t r a t i f i -cat ion is considerab ly le ss t h an d u n e an d san d wav e h e ig h t . A to t a l o f 1 4 sed im en ta r y b a r f ac i e s a r e d e f in edf r o m co m b in a t io n s o f t ex tu r e , i n t e r n a l e r o ss - s t r a t l f i c a t i o n an d su r f ace b ed f o r m s .B o th t o p o g r ap h y an d zo n es o f eb b - an d f l o o d - d o m in a t ed b o t to m t i d a l cu r r en t s co n t r o l t h e o r i en t a t i o n o fd i r ec t i o n a l cu r r en t s t r u c tu r e s . Ov e r s t eep f ace s o f b a r s , t h e s l i p f ace s o f san d wav es a r e o r i en t ed i n t h esam e d i r ec t i o n a s f l ow d i r ec t i o n s o f b o t to m f loo d t i d a l cu r r en t s , a l t h o u g h th ey d o sh o w ev id en ce o f r ewo r k in gb y eb b cu r r en t s . Ov e r g en t ly s lo p in g b a r su r f ace s , s l i p f ace s o f b o th d u n es an d san d wav es a r e o r i en t edp a r a l l e l t o t h e d i r ec t i o n o f f l o w o f b o t to m eb b cu r r en t sy s t em s . B ecau se d u n es an d san d wav es m ig r a t e o n lyd u r in g a s in g l e p h ase ( eb b o r f l o o d ) o f a t i d a l cy c le , t h e i r o r i en t a t i o n i s g en e r a l l y u n lm o d a l . C u r r en t r i p p l e sa r e f o r m ed in d ep th s o f wa te r l e s s t h an 0 . 6 m e te r s , d u r in g l a t e - s t ag e sh ee t - l i k e r u n o f f t h a t i s co n t r o l l ed b ylo ca l s l op e ch an g es o n th e b a r . I n d iv id u a l t r a c e r g r a in s a r e d i sp e r sed in a r ad i a l - e l l l p t ic a l p a t t e r n f o r m a p o in tsource.T h e s i ze o f d i r ec t i o n a l p r o p e r t i e s is h i e r a r ch i ca l ly sen s i t i v e t o d i sp e r sa l h i s to r y . T r ac e r g r a in s ( m o d e l in gm in e r a l i n d i ca to r g r a in s ) a r e d i sp e r sed in a r ad i a l - e l l i p t i c a l p a t t e r n f r o m a p o in t so u r ce . T r im o d a l , h ig h lyv a r i an t , cu r r en t r i p p l e s l i p f ace o r i en t a t i o n d ev e lo p s d u r in g l a t e s t ag e sh ee t r u n o f f a t l o w wa te r d ep th s ; t h i sf lo w i s co n t r o l l ed b y lo cal b a r s lo pe . Un im o d a l , l o w v a r i an t d u n e s l i p f ace s , san d wa v e s l i p f ace s an d a sso c i a t edm ax im u m d ip d i r ec t i o n o f c r o ss - s t r a t i f i c a t l o n a r e a l i g n ed p a r a l l e l t o t i d a l cu r r en t f l o w an d b as in a l t o p o g r ap h ict r en d . T h e san d b a r s a r e a l i g n ed p a r a l l e l t o b a s in a l t o p o g r ap h ic t r en d an d in t u r n seg r eg a t e zo n es o f f l o o d -an d eb b - d o m in a t ed b o t to m cu r r en t sy s t em s .T h e t l d a ] san d b a r s o f t h e Min as B as in a r e eq u i l i b r iu m f o r m s . Sa n d i s d i sp e rsed a l t e r n a t e ly a r o u n d th eb a r t h r o u g h zo n es o f eb b - an d f l o o d - d o m in a ted b o t to m t i d a l cu r r en t s . As a co n seq uen ce , t h e sed im en ta r yf ac i e s d is t r i b u t io n o n th e b a r s h a s r em a in ed e ssen t i a l l y u n ch an g ed s in ce 1 9 3 8 . C o m p ar i so n o f l o w - t id e a i r -photos taken in 1938, 1947 an d 1 9 6 3 in o n e o f t h e s tu d y a r ea s sh o w s a s l i g h t e r o s io n a l r eg im e . T h i s e r o s io n a lr eg im e co n t r o l s t h e ex t r em e r ewo r k in g o f sed im en t s , an d th e f o r m a t io n o f an e ro s iona l s a n d w a v e b e d f o r mby wa ve processes.Ph y s i ca l c r i t e r i a ch a r ac t e r i s t i c o f t i d e - d o m ln a t ed san d b o d ie s i n c lu d e : sh a r p e r o s io n a l co n tac t s b e tweense t s o f c r o ss - s t r a t i f i c a t i o n ; r o u n d ed u p p e r se t b o u n d a r i e s o f c r o ss - s t r a t i f i c a t l o n ; u n lm o d a l an d b lm o d a l d i s -t r i b u t io n s o f o r i en t a t i o n o f c r o ss - s t r a t i f i c a t i o n ; b im o d a l d i s t r i b u t io n s o f se t t h i ck n ess an d d ip an g le s o f c r o ss -s t r a t i f i c a t i o n ; o r i en t a t i o n o f d u n es , san d wav es an d c r o ss - s t r a t i f i c a t i o n in t h e d o m in an t d i r ec t i o n o f f l o o d o reb b t i d a l f l o w, b a s ln a l t o p o g r ap h ic t r en d an d san d b o d y ax i s ; t r im o d a l o r i en t a t i o n o f cu r r en t r i p p l e s ; o b l iq u eo r 9 0 su p e r p o s i t i o n o f sm a l l e r cu r r en t r i p p l e s o n l a r g e r cu r r en t r i p p l e s ; d o u b le - c r e s t ed cu r r en t r i p p l e s ;su p e r p o s i t i o n o f cu r r en t r i p p l e s a t 9 0 o r 1 8 0 o n s l i p f ace s an d c r e s t s o f d u n es an d san d w av es ; co m p lexo r g an iza t io n o f i n t e r n a l c r o ss - s t r a t i f i c a t i o n in san d wav es ; e t ch m a r k s o n s l i p f ace s o f d u n es an d san d wav es ;an d a I ig n m en l o f t h e l o n g ax i s o f san d b o d ie s p a r a l l e l t o t i d a l cu r r en t f l o w, b a s in a l t o p o g r ap h ic t r en d an dbasin ax is .

INTRODUCTIOND u r i n g t h e p a s t 2 0 y e a r s , s t u d i e s o f a n c i e n t

s e d i m e n t a r y r o c k s h a v e i n c l u d e d t h e m a p p i n g o fd i r e c t i o n a l p r o p e r t i e s t o d e l i n e a t e t r e n d s o f s e d -i m e n t d i s p e r s a l . C o m p l e m e n t a r y m i n e r a l o g i c a l ,

2 Man u sc r ip t r e ce iv ed Oc to b e r 2 7 , 1 9 6 9 ; r ev i sedMay 20 , 1970.

t e x t u r a l a n d i s o p a e h d a t a s u p p l e m e n t e d s u c h d i -r e c t i o n a l d a t a t o d e l i n e a t e m o d e l s o f b a s i n g e -o m e t r y , p a l e o c u r r e n t f l o w , d ep o s ~ t i o n al p a l e o -s l o p e a n d p r o b a b l e l o c a t i o n o f s o u r c e a r e a s f r o mw h i c h t h e s e d im e n t s w e r e d e r iv e d ( P o t t e r a n dP e t f i j o h n , 1 9 6 3 ) . A c a u s a l . c o n n e c t i o n b e t w e e no r i e n t a t i o n o f d i r e c t i o n a l p r o p e r t i e s a n d s a n d -b o d y t r e n d w a s al s o e s t a b l i s h e d ( P o t t e r , 1 9 6 2 ;P o t t e r a n d o t h e r s , 1 95 8 ; P o t t e r a n d M a s t ,


2/33

1096 GEORGE DEVR[ES KLEIN..... f i l L , o , .~ %~,,~, . . . . . .

Fro. 1.-Hap of Minas Basin, Nova Scotia, showinglocations of areas of investigation.1963). In fluvial sedimentary rocks and trubi-dites, directional current structures have beenused to delineate paleoslope inasmuch as suchsediments are deposited by slope-controlled pro-cesses. In modern marine environments and fos-sil equivalents, environmental distinctions in pa-leocurrent modal patterns emerge that are inde-pendent of slope (Tanner, 1959; Klein, 1967;Selley, 1968) and ill fact across-slope and up-slope flow systems are common (Hayes and oth-ers, 1969). Many of the earlier paleocu rrentmodels need reappraisal and testing, therefore,partienlarly by comparison to dispersal modelsfrom Recent sedimentary environments.Additional problems posed by paleocurrentanalyses include: (1) What are the relation-ships between flow direction of depositional cur-rent systems and the orientation of directionalcurrent structures in modern sedimentary envi-ronments? (2) To what extent do directionalcurrent structures in Holocene sediments indi-cate all possible flow directions to wh ich sedi-ment is subjected? (3) How does the directionof dispersal of individual sedimentary particlescompare with the larger-scale directional cur-rent structures that are used to map paleocur-rent systems? (4) Does the detailed organiza-tion of flow over a bedform control orientationmore than m ajo r flow systems, as suggested byAllen (1966) ?This paper aims to examine some of theseproblems in the intertidal environment. The in-tertidal environment was selected because logis-tically, it permits rapid comparison of sedimen-tary features to flow directions and other pa-rameters of depositional currents. At low tide, avariety of sedimentary properties can be map-ped by conventional means and compared to hy-dro-dynamic data obtained at buoys moored atcritical geological locations.The area selected for this study was the Mi-nas Basin of the Bay of Fun@, Nova Scotia.Its sediments were discussed in reconnaissanceby Klein (1963). Regional geological studies by

Belt (1964, 1965), Klein (1962) and Weeks(1948) in Carboniferous and Triassic rocks,and by Swift and Borns (1967) in Pleistocenesediments established a depositional frameworkwhich permits comparison of directional proper-ties of intertidal sediments to patterns of disper-sal from rocks of different sources.Two areas were selected for study on thenorth shore of the Minas Basin (fig. 1). Thesand bars at Five Islands and Economy Pointwere selected because they are exposed forlonger intervals at low tide than sand bars oc-curing on the south side of the Minas Basin(Swift and McMullen, 1968). Field observa-tions were confined to the summer months of1965, 1966, 1967 and 1968.D E P O S I T I O N A L PROCESSES

Depositional processes in the intertidal zoneat Five Islands and Economy Point include tidalcurrents, wind-generated waves, wave-gener-ated currents, low-tide open-channel flow, andice. Each agent transports and redistributes sed-iment and, as summarized in Table I, controlsthe gross textural characteristics.

Tidal CurrentsTidal currents dominate the summer sedimenttransport regime. The tidal range in the MinasBasin is the highest recorded in the world,reaching 18 meters at Burntcoat Head, HantsCounty (Canadian Hydrographic Service, 1968;Klein, 1963; Swift, 1966). Swift (1966, p. 118)summarized the origin of the high tidal range,indicating that the dimensions of the Bay ofFundy produce a natural period of oscillationthat is identical to the semidiurnal component ofthe tides. Consequently, resonant amplificationof these periods of oscillation gives rise to a

high volume inflow of water which produces tilehigh vertical range.Within the two study areas, tidal currentsreach maximum surface velocities of 280 cm/see. Bottom current velocities reach maxima of110 cm/sec. Bottom flood current velocitiesaverage 65 cm/sec, whereas bottom ebb currentvelocities average 90 em/sec. Tidal current ve-locity and directional data reported in this paperwere obtained by a calibrated Pritchard-BnrtCurrent Meter (Pritchard and Burr, 1951).The tidal currents are thoroughly mixed fromthe bottom to the surface as indicated by thevertical distribution of water temperature (fig.2) and vertical profiles of current velocity andcurrent directions (fig. 3). The flood and ebbtidal currents are dynamically similar to open-channel flow or sheet flood (cf. Leopold andothers, 1964, p. 153-156).


3/33

D Y . V N 3 1 1 C S ( ) .F 1 X T E I f T I D A L , S ' . . I , V I ~ L - I N X 1 0 9 7TABLE 1 . - -Process-response re la t ions between sed iment lex lure and sed imentary processes,In tert ida l Zone, M ina s Bas in , Ba y o f Fundy , Nova 5"co tia (a fter Laub , 19 68: Kle in , 1968)

Sed in l en t Occu r r en ce So u r ce E r o s io n a l Dep o s i t i o n a lT y p e Pr o cesse s P r o cesse sMar g in a l Gr av e l A lo n g sh o r e a t h ig h - Seael if fs o f b ed r o ck W av e ac t io n L o n g sh o r e d r i f twa te r l l n e an d g l ac i a ls e d i m e n t sSan d y Gr av e l B a r s o r i en t ed Seacl if fs o f b ed r o ck L o w- t id e , o p en - L o w- t id e , o p en -p a r a l l e l an d an d g l ac i a l ch an n e l f lo w, ch an n e l f lo w,n o r m a l t o s e d i m e n t s w a v e a c t i o n , e b b w a v e a c t i o n ,s h o r e t i d a l c u r r e n t s t i d a l c u r r e n t sSan d L in ea r san d b a r s Seacl if fs o f b ed r o c k T id a l cu r r en t s T id a l cu r r en t sin l o w t i d a l an d g l ac i a lf l a t s sed im en t sMu d Hig h t i d a l f l a ts , Seac l if fs o f b ed r o c k W a v e ac t io n Su sp en s io n sed i -e s t u a r i e s a n d g l a c ia l m e n t a t i o n d u r i n gs e d i m e n t s s l a c k p e r io d s a th ig h t i d e

T h e f l o w d i r e c t i o n s o f b o t t o m t i d a l c u r r e n t sa t F i v e I s la n d s a n d E c o n o m y P o i n t a r e s u m m a -r i z e d i n F i g u r e s 4 a n d 5 . F l o o d b o t t o m c u r r e n t sf l o w e a s t to e a s t - n o r t h e a s t i n b o t h a r e a s ,w h e r e a s e b b c u r r e n t s f l o w w e s t t o w e s t - s o u t h -w e s t .L o c a l l y , c o u n t e r e d d y f lo w s y s t e m s d e v e l o p i nr e s p o n s e t o fl o w s e p a r a t i o n o f t i d a l c u r r e n t sa r o u n d c o a s t a l i r r e g u l a r i t i e s . A t F i v e I s l a n d s( F i g . 4 ) , a c o u n t e r e d d y f o r m s d u r i n g t h e f lo o dp h a s e o f t h e t i d a l c y c l e o n t h e n o r t h e a s t s i d e o fP i n n a c l e I s l a n d , w h e r e a s t w o c o u n t e r e d d i e sf o r m o n th e n o r t h w e s t s id e o f L o n g a n d P i n n a -c l e I s l a n d d u r i n g t h e e b b p h a s e o f t h e t i d a l c y -c le . B o t h L o n g a n d P i n n a c l e I s l a n d s o b s t r u c tt h e f lo w o f ti d a l c u r r e n t s a n d t h u s p r o d u c e af l o w s e p a r a t i o n a n d a s s o c i a t e d c o u n t e r e d d i e s o nt h e d o w n - c u r r e n t e n d . S i m i l a r c o u n t e r e d d i e so c c u r o n th e s o u t h w e s t s i de o f E c o n o m y P o i n t

STATI 0 NTom p" C

0 5 I05 J ' [ - - '1 0 1 0 2 0 h o u r s

1.E

STATION # 2 -6 /14/67J= T e m D - C0. 0 5 I0 15o10 632 h o u r s

# -00 - - 6 /6167TS m p'C

15 0 5 I0

10 1910 h o u r s

STATION ~5 - 6/191 67T s m p - "C0 5 I0 15

1047 hoursF iG . 2 . - - B a t h y t h e r m o g r a m s a t S t a t i o n s # 0 0 , # 7 - 2

a n d # 7 - 5 , E c o n o m y P o i n t . A l l s h o w t h a t w a t e r i st h o r o u g h ly m ix ed f r o m b o t to m to su r f ace , an d th a tsu r f ace t em p e r a tu r e s a r e i n eq u i l i b r iu m wi th a i rt em p e r a tu r e s .

d u r i n g t h e e b b p h a s e o f t h e t i d a l c y c l e ( f i g. 5 )w h e r e E c o n o m y P o i n t j u t s i n t o t h e m a i n s y s t e mo f e b b fl o w a n d i n d u c e s a s m a l l c o u n t e r e d d y .A l l t h e s e e d d i e s d e c r e a s e i n s i z e d u r i n g t h e l o w -e r i n g o f w a t e r l e v e l a s s o c i a t e d w i t h e b b ti d e .

W i n d - g e n e r a t e d W a v e sW i n d - g e n e r a t e d w a v e s a r e t h e s e c o n d - m o s ti m p o r t a n t a g e n t o f s e d i m e n t a t i o n i n t h e i n t e r t i -d a l z o n e d u r i n g t h e s p r i n g a n d s u m m e r m o n t h s .

T h e p r e v a i l i n g s u m m e r w i n d s a r e d i r e c t e d p re -d o m i n a n t l y f r o m s o u t h w e s t t o n o r t h e a s t ( A n -n u a l M e t e r e o l o g i c a l S u r v e y , 1 9 6 6 ; f i g . 6 ) , p a r -a l l el to t h e a x i s o f b o t h t h e B a y o f F u n d y a n d~ i n a s B a s i n . B e c a u s e o f t h i s pa r a l le l a l ig n m e n t ,1 5 t o 3 0 k n o t w i n d s g e n e r a t e w a v e s r a n g i n gf r o m 6 0 c m t o 3 m i n h e i g h t a t F i v e I s l a n d s a n dE c o n o m y P o i nt .W a v e a c t i o n d i r e c t e d a g a i n s t s e a c l i f f s u n d e r -m i n e a n d e r o d e b e d r o c k a n d d r i f t , r e d i s t r ib u t e i ta n d l e a v e a l a g g r a v e l a t t h e h i g h w a t e r l i n e .U n c o n s o l i d a t e d s a n d a n d c l a y a r e r e m o v e d b y

%

" L _ . _ _ i "F I G . 3 . - - V e r t i c a l p r o fi l e s o f c u r r e n t v e l o c i t y a n df l o w d i r ec t i o n a t S t a t i o n s # 3 . - 1 , # . 3 - 3 , # 3 - - 5 an d

# 3 . . - 6 , P in n ac l e F l a t s , F iv e I s l an d s , d u r in g f l o o d an deb b p h ase . Un i f o r m f lo w d i r ec t i o n an d v e lo c i ty p r o -f i l e i n d i ca t e t i d a l cu r r en t s a r e u n id i r ec t i o n a l f l o wsy s t em s .


4/33

1 0 9 g GEORGE DEVRIES KLEINFLOOD

k . _ _ I- 4 o I

a l ' ' 1F I G . 4 . - -F l o w d i rec t i o n s o f bot tom flood (A) andb o t to m ebb (B ) cu r ren t s F i v e I s l an ds (A b b rev i a t i o n :L - - L o n g I s l a n d ) .

t i d a l a c t i o n a f t e r t h e i n i t i a l u n d e r m i n i n g(K l e i n , 1 9 6 8 ; Lau b , 1 9 6 8 ; R . S . Smi t h , 1 9 6 9 ) .Wave-generated Currents

C u r r e n t s g e n e r a t e d 'b y w a v e m o t i o n a r e c o n -f in e d t o th e u p p e r s u r f a c e z o n e ( m a x i m u m o :[t h r e e m e t e r s b e lo w s u r f a c e ) w h e n w i n d v e l o c i -t i e s e x c e e d e d 1 5 k n o t s . C u r r e n t v e l o c i t y m e a -s u r e m e n t s d u r i n g s l a c k t i d e s h o w e d t h a t w a v e -g e n e r a t e d c u r r e n t s r e a c h a m a x i m u m v e l o c i t yo f 2 0 c m / s e c , a v e r a g i n g 1 0 c m / s e c .

E B B C U R R E N T S , E C O N O M Y P T.( 0 vz i ,~

t " : tF L O O D C U I t R E N T B , E C O N O M Y P T .

0 , ~ , I,t, ll

% "2;-,~ ~ ......... , " o r ~ _ ~

Fro . &--Flow di rect ion of bot tom flood and bot tomebb currents , Economy Poin t .

Low-tide Opcn-Cha~mel FlowI n t h e l a t e s t a g e s o f e b b - c u r r e n t r u n o f f , a n da f t e r e m e r g e n c e , o p e n - c h a n n e l f l o w tr a n s p o r t ss e d i m e n t i n t h e i n t e r t i d a l z o n e . T h i s o p e n - c h a n -n e l f l o w o c c u r s e i t h e r i n l a r g e , h i g h l y o r d e r e d ,s e m i - p e r m a n e n t c h a n n e l s o n t h e s a n d b a rs a n dm u d f l at s , o r i n t r o u g h t s o f p r o g r e s s i v e l y e m e r -

g e n t d u n e s a n d sa n d w a v e s ( K l e i n , 1 9 6 3 ; I m -b r i e a n d B u c h a n a n , 1 9 6 5) . S e m i - p e r m a n e n t ,m e a n d e r i n g a n d s t r a i g h t c h a n n e l s a r e d e v e l o p e do n m u d f l a t s o n t h e n o r t h e r n s i d e o f t h e F i v e I s -l a n d s a r e a . O n t h e s a n d b a r s , s m a l l s e m i - p e r m a -n e n t c h a n n e l s y s t e m s o c c u r i n a r e a s o f l o w e s te l e v a t i o n o r b e t w e e n s a n d b a r s .A s t i d a l c u r r e n t s e b b a n d p r o g r e s s i v e l y e x -p o s e t h e b a r s , p r e d o m i n a n t l y w e s t e r l y e b b c u r -r e n t f l o w c e a s e s . T h e t i d a l c u r r e n t s a r e t h e n d e -f l e e t e d a r o u n d t h e e x p o s e d b a r s a n d a l s o d r a i no f f t h e b a r a s a s h e e t f l o o d in t h e d i r e c t i o n o fl o c a l b a r s l o p e ( K l e i n , 1 9 6 3 ) . A s w a t e r l e v e lc o n t i n u e s t o f a l l , s l o p e - c o n t r o l l e d f l o w i s c o n -f i n e d t o t h e s e m i - p e r m a n e n t c h a n n e l s y s t e m s .S h e e t r u n o f f b e c o m e s s u b d i v i d e d i n t o a s e r i e s o fp a r a l l e l , d o w n s l o p e - f l o w i n g c h a n n e l s w i t h i n t h et r o u g h s o f d u n e s a n d s a n d w a v e s a s t h e s e b e d -f o r m s e m e r g e . A s t h e b a r b e c o m e s c o m p l e t e l yd r a i n e d , t h i s s y s t e m o f c h a n n e l f l o w m a i n t a i n si t s e lf b y d e w a t e r i n g o f t h e b a r s e d im e n t .

[coA l t h o u g h f i el d o b s e r v a t i o n s w e r e c o n f i n e d tot h e l a te s p r i n g a n d s u m m e r m o n t h s , i c e tr a n s -p o r t a p p e a r s t o b e o f s o m e s i g n i f i c a n c e . D u r i n ge x t r e m e l y c o l d w i nt e r s , t h e M i n a s B a s i n i s

k n o w n t o b e c o m p l e t e l y f r o z e n . L o c a l p o l y g o n a lp a t c h e s o f i c e - r a f t e d g r a v e l o c c u r o n a l l t h es a n d b a r s . T h e g r a v e l i s r e d i s t r i b u t e d b y p o l y g o -WIND D I R E C T I O N

6 / 1 2 / 6 8 - - 8 / 1 7 / 6 8

S \F I G . &-- W i n d d i rec t io n s , M i n as Bas i n n o r t h sh o re ;data co l lected a t Parrsboro , Nova Scot ia , by author,June 12-August 17, 1968.


5/33

D Y N A ; I I C S ( )F I N T E R T I D A L S A N D I Lq R S 1099hal ice floes duri ng the sprin g ice break-up (cf.Bancroft, 1902; Di(mne, 1968). Between 1965and 1968, isolated boulder and pieces of tidalmarsh have appeared and then were removed byice rafting.

SEDIMENTOLOGY OF THE SAND BARSGeology (figs. 7 and 8)The intertidal-zone geology at Five Islandsand Economy Point (figs. 7 and 8) show a coar-sening-seaward textural distribution similar tothat reported from intertidal sediments else-where (Van Straaten and Kuenen, 1957, 1958).Clayey and silty muds occur on both the high_and part of the low tidal flat environment. Theseaward tow-tide zone is dominated by sandbars comparable to Van Straaten's (1952, I954)low tidal flat environment.The muddy tidal flats are drained by mean-dering tidal creeks. Th ese migra te lateral ly re-suiting in alternating cutting and back-filling(cf. Van Straaten, 1952). The tidal channelsare floored with a mixture of coarse shelly de-

bris and gravel derived from outcrops on shore(Klein, 1963).Within the estuaries of larger streams enter-ing the intertidal zone, mud sedimentation hasproceeded at a sufficiently rapid rate so thatmud flats are built high enough to be submergedonly during spring tides. Tidal marshes have de-veloped on these flats.Because the Minas Basin shoreline is flankedby seacliffs of Carboniferous and Triassic bed-rock and Pleistocene glacial drift, wave actionon shore has formed a marginal gravel at ap-proximately high water. These marginal gravelsare produced by a comNnation of wave action,longshore drift and tidal current redistribution(Laub, 1968; Klein, 1968; R. S. Smith, 1969).Durin g slack water at high tide, mud suspensionsettlement occurs within this marginal gravelzone, leaving both a mixture of gravel with amuddy matrix, and a thin veneer of mud on thegravel surface.Sand bars and sandy deposits occur in thelowest areas of the low tidal flat environment.

D IA M O N D I S . 0P IN N A C L E I S .E X P L A N A T / O N |

E ~ ] G R A V E L ~ S A N D , w i th S E C O N D & T H IR DO R D E R R I P P L E S .M U D ~ S A N D ,w i th F I R S T O R D E R R IP P L E S .

. .RSH I I BE0.OCK BELO* .H *

I 2 K M

I N D E X ~

FIG. 7.--Sediment distribution in intertidal zone, Five Islands, Nova Scotia. BB (Big Bar) .PF (Pinnacle Flats).


6/33

1 1 0 0 G E O R G E D E ~.;J IE S K L E I N

IN D E M AP I

FIG. 8 .--S edim ent d is t r ibu t ion in in tert ida l zone , Econ omy Poin t , N ov a Scotia .A t F i v e I s la n d s , t w o m a j o r s a n d b a r s o c c u r .T h e b a r i n t h e c e n t e r o f t h e a r e a i s r e f e r r e d t oh e r e a f t e r a s " B i g B a r . " T h e s e c o n d o c c u r s a s al i n e a r s a n d b e l t c o n n e c t i n g L o n g a n i l P i n n a c l eI s l a n d a n d i s r e f e r r e d t o h e r e a f t e r a s " P i n n a c l eF l a t s " ( F i g . 7 ) . T h r e e l a r g e s a n d b o d ie s o c c u ri m m e d i a te l y so u t h a n d w e s t o f E c o n o m y P o i n ta r e a r e r e f e r r e d t o f r o m w e s t t o e a s t a s " W e s tB a r , " " C e n t e r B a r " an d " E a s t B a r " ( F i g . 8 ) .

Topograpl~Y (tiP. 9)T h e t o p o g r a p h y o f B i g B a r , P i n n a c l e F l a t sa n d W e s t B a r i s l i n e a r i n p l a n a n d a s y m m e t r i ci n c r o s s - s e c t io n . C e n t e r B a r i s t r a p e z o i d a l i np l a n a n d a s y m m e t r i c i n s e c t i o n a n d E a s t B a r i sl i n e a r a n d n e a r l y s y m m e t r i c a l ( f i g . 9 ) . T h e b a rc r e s t s a r e d i s p l a c e d t o w a r d t h e s o u t h s i d e o f a l l

t h e b a rs e x c e p t W e s t B a r w h e r e t h e c r e s t i s d i s -p l a c e d t o w a r d t h e n o r t h s i d e . T h e s t e e p s l o p e sr e s u l t in g f r o m t h e b a r a s y m m e t r y a v e r a g e 8 i ns l o p e a n g l e , w h e r e a s t h e g e n t l e r s l o p e s a v e r a g e2 .C o n t i n u o u s 1 3 - h o u r o b s e r v a t i o n s o f b o t t o mc u r r e n t v e l o c it i e s, f lo w d i r e c t i o n a n d w a t e rd e p t h s f r o m h i g h t i d e t o s u c c e e d i n g h i g h t i d e( f i g . 1 0 ; T a b l e 2 ; T a b l e 9 2 ) s h o w s t h a t t h et i m e - v e l o c i t y p r o f i l e f o r b o t t o m t i d a l c u r r e n t s i sa s y m m e t r i c . O v e r t h e s t e e p f a c e s a t W e s t B a r ,E i g B a r a n d P i n n a c l e F l a t s , f lo o d b o t t o m c u r -r e n t v e l o c i t ie s a r e d o m i n a n t, w h e r e a s o v e r t h e

F o r T a b l e 9 o r d e r D o c u m e n t N u m b e r N A P S0 10 62 , f r o m A S I S - - N a t i o n a l A u x i l i a r y P u b l ic a ti o n sServ ice , e/o C C M - - I n f o r m a t i o n C o r p o r a t i o n , 9 0 9T h i r d A v e n u e , N e w Y o r k , N e w Y o r k 1 0 0 2 2 ; r e m i t-t ing $2 .0 0 for each microfiche , o r $5 .00 for eachphotocopy . Advance payment i s requ i red .

g e n t l y - s l o p i n g b a r s u r f a c e s, b o t t o m e b b c u r r e n tv e l o c i t ie s a r e d o m i n a n t .T h e d i s t r ib u t i o n o f t h e t i m e - v e l o c i t y a s y m m e -

A

P I 6

CFIG. 9 . - - T o p o g r a p h i c m a p s o f ( A ) B i g B a r , ( B )P i n n a c l e F i a t s , a n d (C ) Ec o n o m y Po i n t . C o n t o u ri n t e rv a l i s 2 me t e r s . Da t u m i s me a n l o w wa t e r o n(A ) Au g u s t 1 , 1 9 6 5 , (B ) Ju l y 1 7 , 1 9 6 5 , a n d (C )August 19 , 1966 .


7/33

D Y NAMICS O F INT ERT I D AL SANI ) BARS 1101

, ' ~ . . ' K ' ~ , , . ' ~ , . . ~ - ,

~ 5o

~ o

~ ~, ~

tH O U R S B E F O R E A N D A F T E R L O W T I D E

FI G. 1 0 .- - R eco r d o f 1 3 - h o u r co n t in u o u s o b se r v a -t i o n s o f b o t to m cu r r en t v e lo c i ty , wa te r d ep th an df lo w d i re c t io n s a t S t a t i o n ~ 2 ( S t e e p f a c e ) , W e s tB a r , S t a t i o n # P - 9 ( g e n t l e f a c e ) , W e s t B a r , a n dS t a t i on # 1 0 ( g e n t l e f a c e ) , E a s t B a r . S t a t i o n lo c a li -t i e s sh o wn in F ig . 1 2 . Ve r t i c a l l i n e sh o ws t im e o fs u b m e r g e n ce o f W e s t B a r .

t r y o f b o t t o m ti d a l c u r r e n t s w a s m a p p e d o v e rt h e b a r s ( f i g . 1 1 ) b o t h f r o m b o t t o m c u r r e n t v e -l o c i ty d a t a ( s p o t c h e c k s ) a n d f r o m 1 3 - h o u r c o n -t i n u o u s o b s e r v a t i o n s ( T a b l e 2 , 9 ) . T h e d i s t r i b u -t i o n o f z o n e s o f f l o o d - a n d e b b - d o m i n a t e d b o t -t o m t k l a l c u r r e n t s c o i n c i d e s w i t h b a r t o p o g r a -p h y ( c f . f ig s . 9 a n d 1 1 ) . A t P i n n a c l e F l a t s , al o c a l a r e a o f f l o o d - d o m i n a t e d b o t t o m c u r r e n t v e -l o c i t i e s o c c u r s n o r t h w e s t o f L o n g I s l a n d w h e r ee b b c u r r e n t s y s t e m s c o n v e r g e a f t e r s t r e a m l i n i n ga r o u n d L o n g I s l a n d i n a w e s t e r l y d i r e c t i o n . T h ec o n v e r g e n c e o f t h e s e e b b c u r r e n t s g e n e r a t e s as h o c k w a v e w h i c h r e d u c e s t h e e f f e c t i v e b o t t o mc u r r e n t v e l o c i t i e s d u r i n g e b b t i d e . T h i s c o n v e r -g e n c e z o n e i s f l o o d - d o m i n a t e d , t h e r e f o r e , e v e nt h o u g h t h e m a x i m u m v e l o c i t i e s o f t h e f l o o d b o t -t o m c u r r e n t s i n it ( s t a t i o n N o . 1 1 ) a r e l e s s t h a n

B

0 5 0 0 M .

I l F O O O, D E oo* , . . . .E B B T I DE O O M I N A N r

FI G. l l . - - Di s t r i b u t io n o f f l o o d - an d eb b - d o m in a t edb o t to m cu r r en t v e lo c i ty zo n es a t ( A ) F iv e I s l an d s ,a n d ( B ) E c o n o m y P o i n t .

o v e r t h e s te e p f a ce ( S t a t i o n N o . 7 ) a t P i n n a c l eF i a t s ( T a b l e 2 ) .T h e s t e e p - s l o p i n g , fl o o d - t id e d o m i n a t e d s e d -m e n t s o f B i g B a r , P i n n a c l e F l a t s , W e s t B a r a n dC e n t e r B a r a c t t o r e d u c e t h e e f f e c t i v e f l o o d - t i d e ,b o t t o m c u r r e n t s c o u r o n t h e g e n t l y - s l o p i n g p o r -t i o n s o f t h e b a r s ( s e e f i g . 1 0 , S t a t i o n N o . p . - 9 ) .I n t h i s w a y , t h e b a r c r e s t s a n d t h e f l o o d - d o m i -n a t e d s t e e p s l o p e s s h i e l d t h e g e n t l y - s l o p i n g , e b b -d o m i n a t e d p a r t o f t h e b a r . S u c h s h i e l d i n g a re a sa r e r e f e r r e d t o as F l o o d S h i e l d s a s d e f i n e d b yH a y e s a n d o t h e r s ( 1 9 6 9 , p . 2 9 6 ) a n d D a b o l l( 1 9 6 9 , p . 3 4 I ) . T h e s h i e l d i n g a r e a s r e d u c e t h el e n g t h o f t i m e d u r i n g w h i c h F l o o d t i d e b o t t o ms c o u r c a n r e w o r k t h e g e n t l y - s lo p i n g p o r ti o n s o ft h e s a n d b a r s .

T a m . t ; 2 . - - S u m m a r y of ma xim um bot tom current velocit ies (an d associa led water depths) an d d i fference i n m axim umvelocity of flood an d ebb bottohl currents, a t station s where 13-hour con tinuo us observations of velocity and wa terdepth were obta ined. B ar facies a t s ta t ion a lso ind ica ted (Abbreviat ions as per Table 3) .Lo ca t io n a b brevia tion s : B B - B ig B a r ; P F - P in n a c le F la t s ; E P - E co n o m y P o in t .

Fac ie s

2 ( E P )P- 9 ( EP)1 0 ( EP)1 6 ( B B )21 ( B B )11 (PF)7 ( P F )

( c m / s e c )M S S DC S S DC S C S W( C S S D )M S S DM F SF S S S WM S C R

F l o o d T i d eMax . Ve l . Assoc . De p th

1 0 07545

(m)5 . 2 56 . 03 . 7 52 . 04 . 06 . 05 . 0

E b b T i d eMax . Ve l . Asso c . De p th( c m / s e c ) (m)

6 . 06 . 55 . 05 . 04 . 7 55 . 08 . 3

60655375

S t a t i o nN o .779 59 5755347.3 0

Ve lo c i ty Di f f e r en ce ,M a x . F l o o d a n dM a x . E b b( C m / s e c )232 05 01512645


8/33

1102 GEO RGE DEI/R1E,S" KLIE IN

A 0 3 0 0 M ~ 1I ~ J

B

N

|

E2LE.LJLU.~LT.LO.bLBAR FACIES:TEXTURE, BEDFORM, eINTERNAL STRUCTURE.~ . ~ G r anu le G rav e l, S im p le Dune F ac ies

Coa r s e S an d , Com p lex S and W av e F ac iesCoarse Sand, S imple Dune Fac iesM ed ium S and , S im p le S an d W av e F ac iesM ed ium S and Com p lex Dune Fac iesM e d i u m S a n d S im p le D u n e F a ci esM e d i u m S a n d , C u r r e n t R i p p l e FaciesF ine Sand, S imple Sand W av e Fac ies ,

BAR FAC IES: TEXTURE 8" B EDFOR M- ~ S andy G r av e l , Ha r r ow M a r k F ac iesBAR FACIES: TEXTURE .m Cob ble-Bo ulder Gravel Fac ies

M e d i u m - F i n e S e n d F a c i e sT r a n s i t i o n F a ci es 7 - B u o y S t oCrest Facies

~ 1 M u d F e c , es ~ I n t e rt i d e tBed ockF r o . 1 2 . - -D i s t r ib u t io n o f s ed imen ta r y b a r f ac i e s a t ( A ) B ig B ar , ( B ) P in n ac le F la t s , an d ( C ) Eco n o m y P o in t .N u m b er s r e f e r t o s t a t io n s d es c r ibed in f ig u r es 1 0 an d 3 4 .


9/33

l ) } . \ : . .1 .1/ l ( . 'A" c)F I ,VTERTID. . I[ . .9 . . I? , /1; ~ . . IRS 1 1 0 3Sedimenta~3, Facies (fly. 12)

O n a l l t h e s a n d b a r s a t F i v e I s l a n d s a n dE c o n o m y P o i n t , s a n d b a r f a c i e s c a n b e d i s c r i m i -n a t e d a c c o r d i n g t o s e d i m e n t t e x t u r e , a c o m b i n a -t i o n o f t e x t u r e a n d e x t e r n a l b e d f o r m , o r a c o m -b i n a ti o n o f t e x t u r e , b e d f o r m m o r p h o l o g y a n di n t e r n a l o r g a n i z a t i o n o f c r o s s - s t r a t a i n t o s i m p l co r c o m p l e x s e t s . T h e d i s t r i b u t i o n o f t h e s e f a c i e s( f i g . 1 2 ) s h o w s g o o d a g r e e m e n t w i t h t o p o g r a -p h y ( f i g . 9 ) a n d t h e d i s t r i b u t i o n o f f l o o d - a n de b t ) - d o m i n a n t b o t to m c u r r e n t v e l o c i t y z o n e s( f i g . 1 1 ) .T h e f a c i e s d i s tr i b u t i o n c a n b e s u m m a r i z e d i nt h e f o l l o w i n g w a y . O v e r s t e e p f a c e s o f s a n db a r s a n d i n c h a n n e l s s e p a r a t i n g s a n d b a r s , t h et e x t n r e i s d o m i n a n t l y f i n e - t o m e d i n m - s a n d . A s -s o c i a t e d h e d f o r m s a r e d o m i n a n t l y c n r r e n t r i p -1 )l es a n d d u n e s . O n l y o n e s a n d w a v e f a c i e s o c -c u r s o n a s t e e p s l o p e . O v e r g e n t l y - s l o p i n g b a rs u r f a c e s , h o w e v e r , t h e s e d i m e n t t e x t u r e i s d o m i -n a n t l y m e d i u m o r c o a r s e - s a n d , w i t h a c c e s s o r yp e b b l e g r a v e l . A s s o c i a t e d b e d f o r m s a r e s i m p l ea n d c o m p l e x d un e s a n d s a n d w a v e s . G e n t l y -s l o p i n g a r e a s a r e f l a n k e d by g r a v e l d e p o s i t s a tt h e l o w w a t e r l i ne .T ex t ure . - - T ex t ura l d i s t i n c t i o n s f o r f a c i e s i d e n -t i f i c a t i o n a r e b a s e d o n m e g a s c o p i c a n d s i e v e - s i z ea n a l y s i s , T h e d i a g n o s t i c t e x t u r a l n a m e i s e i t h e rt h e m e d i a n d i a m e t e r , t h e m o d a l c l a s s o r a s i g -n i f i c a n t s e c o n d a r y m o d e . T h e s a n d s o f a l l f a c i e sa r e d o m i n a n t l y m e d i u m s a n d , t r o t i m p o r t a n tf i e ld d i s t i n c t i o n s o f h e d f o r m t y p e a n d i n t e r n a ls t r u c t u r e c o i n c i d e w i t h t h e p r e s e n c e o f a s i g n if i -c a n t s e c o n d a r y m o d e , r a th e r t h a n a p r i m a r y m o -d a l c l a s s . H e n c e t h e u s e o f s e c o n d a r y m o d a lc l a s s es t o d i s t i n g u i s h s e d i m e n t a r y f a c i e s .Bed/ot to morphology.- -Surface b e d f o r m s w e r ef o m l d t o b e o f t w o d o m i n a n t t y p e s : h a r r o wm a r k s ( K a r c z , 1 9 6 7 ) o r r i p p l e d b e d f o r m so f v a r y i n g l e n g t h . T h e f r e q u e n c y d i s t r i b u ti o n o fb c d f o r m w a v e l e n g t h s ( f i g . 1 3a , c ) i s g r o u p e di n to t h r e e m a j o r o r d e r s o f i n c r e a s i n g w a v el e n g t h ;i t P i n n a c l e F l a t s a n d E c o n o m y P o i n t ,a n d t w o o r d e r s a t B i g B a r ( f i g . 1 3 b ) . T h eh o n n d a r y l i m i t s b e t w e e n f ir s t o r d e r ( C n r r e n tr i p p l e s ), s e c o nd o r d e r ( d u n e s ) a n d t h ir d o r d e r( s a n d w a v e s ) b e d f o r m s a r e s h o w n i n F i g u r e 1 3.S o m e o v e r l a p e x i s ts b e t w e e n o r d e r s w h e n c o m -p a r i n g t h e th r e e a r e a s f r o m w h i c h m e a s u r e -m e n t s w e r e o b t a i n e d .T h e e x t e r n a l m o r p h o l o g y o f t h e r i p p l e s i sh i g h l y v a r i a b l e . L i n g u o i d , l u n a t e a n d s t r a i g h t -c r e s te d c u r r e n t r i p p l e s ( f i r s t o r d e r ) a r e c o m -m o n . S i n u o u s d u n e s a n d s a n d w a v e s a l s o o c c u r .T h e s i n u o si t y i s p r o d u c e d b o t h b y m e a n d e r i n g

Z

a .

> -

Z 0D0tJU

. h ~ s r s ~ c o m e Tw,mo" ' , " " . . . . ~ r ~ o m , i R

IO

0 ~ / ~ , i:i:i:i:i:i:i:!:i!~i~3:~;ii!I':~10 1O0 ~ l R s r O n O E ~ ~ S E C O N D ~Rotn

++ I o ~ B .

0 I 1 10 100

~iAsr S~CON~ o R o t m TH I RD

1 0 C .

:!!!)1 saw

O1 1 10 1OO 1OOOBE DF O RM W AVE L ENG TH ( M et e rs )F ro . ] 3 . - -F reque nc y d i s t r i bu t i on o f bed f o rm w av elengths a t ( A ) P i n n ac le F l a ts , ( B ) B i g B a r , an d(C) Eco n o my Po in t .

o p e n - c h a n n e l f lo w d u r i n g e m e r g e n c e , a n d b yd i f f e r e n t i a l r a t e s o f b e d f o r m m i g r a t i o n .T h e p r o f i l e o f m o s t o f t h e r i p p l e d b e d f o r m s ,r e g a r d l e s s o f o r d e r , i s a s y m m e t r i c , w i t h s l i pf a c e s o r i e n t e d i n t h e d o w n - c u r r e n t d i r e c t i o n .S l o p e a n g l e s o f s l i p f a c e s a v e r a g e 2 6 d e g r e e s .H o w e v e r , i n f l o o d - d o m i n a t e d a r e a s , s l o p e a n g l eo f s l i p f a c e s o f f l o o d - o r i e n t e d s a n d w a v e s a v e r -a g e 1 8 d e g r e e s b e c a u s e t h e b e d f o r m i s r e w o r k e db y e b b c u r r e n t s . N e a r l y a l l d u n e s a n d s a n dw a v e s a r e c a p p e d b y s u m p e r i m p o s e d l o w e r o r -d e r r ip p l e s a n d a r e t h e r e f o r e m e t a r ip p l e s ( I m -b r i e a n d B u c h a n a n , 1 9 6 5 ) .D u r i n g e m e r g e n c e o f s o m e o f t h e sa n d w a v e sa n d d u n e s , t h e c h a r a c t e r o f t h e .f lo w w a s o b -s e r v e d t o s h o w a p r o g r e s s i v e c h a n g e f r o m t r a n -q u i l t o r a p i d , p a r t i c u l a r l y d u r i n g t h e l a s t 1 0m i n u t e s p r i o r t o e m e r g e n c e . I n d u n e s a n d s a n dw a v e s o f c o a r s e - g r a i n e d s a n d, s e d i m e n t m i -g r a t e s a s g r a i n f l o w c h a r a c t e r i s t i c o f t h e p l a n eb e d p ha s e ( S i m o n s a n d o t h e r s , 1 9 6 5) . S o m e o ft h i s san d i s d ep o s i t ed o n t h e s l i p face o f t h e d u n ei n a m a n n e r s i m i l a r t o d e l t a b u i l d i n g r e p o r t e db y J o p l i n g ( 1 9 6 5 ) . S u c h o u t f lo w p r o d u c e s ap I a n e d r i p p l e ( e l . B o o t h r o y d , 1 9 6 9 , p . 427) o f -


10/33

1 1 0 4 G E O R G E r m U R I E S K L E I Nt e n s u p e r i m p o s e d o n a s a n d w a v e . T h e s e p l a n e dr i p p l e s a r e m e r e l y a m o d i f i c a t i o n o f e x i s t i n gb e d f o r m s b y la s t m i n u t e f l ow w h e n F r o u d en u m b e r s w o u l d b e e x p e c t e d t o in c r e a s e . B e c a u s eo f t h e h i g h t u r b u l e n c e , s c o u r p i t s f o r m o n t h ed o w n c u r r e n t f a c e o f t h e b e d f or m . T h e p l a n i n gp r o c e ss i s n o t a f u n c t io n o f n o r m a l b e d f o r m m i -g r a t i o n , w h e n F r o u d e n u m b e r s a r e l o w ( T a b l e9 ) .A t h i r d b e d f o r m , n o t m a p p e d i n f a c i e s d i s t r i -b u t i o n s, i s fl u t e m a r k s ( f i g . 1 4 d) . T h e y o c c u ro n a s e m i - p e r m a n e n t c h a n n e l , 7 c m d e e p , a t t h en o r t h e a s t m a r g i n o f th e m e d i u m s a n d, s i m p l ed u n e f a c i e s o n B i g B a r . T h e c h a n n e l f l o w i st r a n s i t i o n a l b e t w e e e n tr a n q u i l a n d r a p i d t u r b u -l e n t. T u r b u l e n c e i s h i g h a n d r a p i d s c o u r i n g a n df i l li n g i s c o m m o n o v e r t h e i r r e g u l a r c h a n n e lf l o o r. T u r b u l e n t s c o u r i n g p r o d u c e s a d e l t o id ,s c a l l o p e d s u r f a c e ( f i g . 1 4 d ) . T h e s e " s c a l l o p s "r e s e m b l e f l u te m a r k s b e c a u s e t h e n a r r o w , u p c u r -r e n t p a r t o f t h e s t r u c t u r e i s s t e e p l y - w a l l e d ,w h e r e a s t h e d o w n c u r r e n t e n d o f th e s t r u c t u r es l o p e s g e n t l y i n t o t h e c h a n n e l f l o o r .Internal organizc~tion.--Further s u b d i v i s i o n o fs e d i m e n t a r y f a c i e s i s b a s e d o n t h e i n t e r n a l o r -g a n i z a t i o n o f s e c o n d a n d t h i r d o r d e r r i p p l e b e d -f o r m s . T w o c l a s s e s o f i n t e r n a l o r g a n i z a t i o n a r er e c o g n i z e d : s i m p l e a n d c o m p l e x . S i m p l e d u n e sa n d s a n d w a v e s a r e c h a r a c t e r i z e d b y i n t e r n a lc r o s s - s t r a t i f i c a t i o n w h o s e t h i c k n e s s i s n e a r l y t h es a m e a s t h e v e r t i c a l h e i g h t o f t h e d u n e o r s a n dw a v e ( f i g . 1 5 b ) . C o m p l e x d u n e s o r c o m p l e xs a n d w a v e s a r e c h a r a c t e r i z e d b y i n t e r n a l c r o s s -s t r a t i f i c a t i o n w h o s e s e t t h i c k n e s s i s considerablyless t h a n t h e h e i g h t o f t h e d u n e o r s a n d w a v e i nw h i c h i t o c c u r s . S u c h b e d f o r m s a r e c h a r a c t e r -i z e d b y a c o m p o s i t e i n t e r n a l o r g a n i z a t i o n ( F i g s .3 2b , 3 3 c ) . S u c h c o m p l e x i n t e r n a l o r g a n i z a t i o no f c r o s s - s t r a t i f i c a t i o n h a s b e e n r e p o r t e d p r e v i -o u s l y f r o m s a n d w a v e s b y R e i n e c k ( 1 9 6 3 ) a n dCo l e ma n ( 1 9 69 , p . 2 08 - -2 1 4 ) .Facies characterisl ics.--A t o t a l o f 1 4 s e d i m e n -t a r y f a c i e s a r e r e c o g n i z e d o n t h e s a n d b a r s a tF i v e I s l a nd s a n d E c o n o m y P o i n t. D i a g n o s t i cm e g a s c o p i c f e a t u r e s o f t h e s e f a c i e s a r e s u m m a -r i z e d i n T a b l e 3 , w h e r e a s t h e a v e r a g e q u a n t i t a -t i v e p a r a m e t e r s o f t h e s a n d y a n d g r a v e l l y f a c ie sa r e g i v e n i n T a b l e 4 . T h e o r i g i n o f s o m e o f t h es t r u c t u r e s i n t h e s e f a c i e s i s d i s c u s s e d i n a l a t e rsec t i o n (p . 1 1 1 5 -1 1 2 3 ) .

Directional Properties (figs. 16, 17, 18)T h e o r i e n t a t i o n o f s e d i m e n t a r y b e d f o r m s a n di n t e r n a l c r o s s - s t r a t i f i c a t i o n i s s u m m a r i z e d i nF i g u r e s 1 6 a n d 1 7 . G o o d a g r e e m e n t e x i s t s b e -t w e e n o r i e n t a t i o n o f s e d i m e n t a r y b e d f o r m s , s e d -

i m e n t a r y f a c i e s a n d b a r t o p o g r a p h y . O n s t e e pf a c e s o f W e s t B a r a n d t h e e b b - c o n v e r g e n c ez o n e a t P i n n a c l e F l a t s , s a n d w a v e s a r e o r i e n t e de a s t e r l y , i n a g r e e m e n t w i t h f l o w d i r e c t i o n s o ff l o o d - d o m i n a t e d b o t t o m t i d a l c u r r e n t s . O n t h eg e n t l y - s lo p i n g s a nd b a r s u r f a c e s a t B i g B a r ,P i n n a c l e F i a t s , W e s t B a r a n d M i d d l e B a r , b o t hd u n e s a n d s a n d w a v e s l i p f a c e s a r e o r i e n t e d t ot h e w e s t , i n a g r e e m e n t w i t h e b b - d o m i n a t e d t i d a lc u r r e n t f lo w . A t E a s t B a r , s l i p / a c e s o f b o t h d e-p o s i t i o n a l s a n d w a v e s ( i n t h e f l o o d - d o m i n a t e dw e s t e r n p a r t ) a n d e r o s i o n a l s an d w a v e s ( p . 1 1 2 0-1 1 2 2 ) a r e o r i e n t e d t o t h e e a s t , w h e r e a s s l i pf a c e s o f d u n e s a r e o r i e n t e d t o t h e w e s t , i na g r e e m e n t w i t h e b b - d o m i n a t e d t i d a l c u r r e n t s .G e n e r a l a g r e e m e n t o c c u r s b e t w e e n f lo o d - o re b b - d o m i n a t e d f l o w a n d t h e o r i e n t a t i o n o f i n t e r -n a l c r o s s - s t r a t i f i c a t i o n ( f i g . 1 7 ) . T h e a g r e e -m e n t b e t w e e n o r i e n t a t i o n o f b e d f o r m s , a n df l o o d- a n d e b b - d o m i n a t e d a r e a s , c o m p a r e s : f a-v o r a b l y w i t h s i m i l a r o b s e r v a t i o n s b y V a n S t r a a -t en (1 9 5 0 , p . 78-79) f r o m s u b t i d a I c h a n n e l s a n da d j o i n i n g s u b t i d a l f l a t s i n t h e B a s i n d ' A r c a c h o no f F r a n c e .S l i p f a c e s o f c u r r e n t r i p p l e s a r e o r i e n t e d p a r -a l l e l t o t h e d i r e c t i o n o f e b b c u r r e n t f l o w , o r a tr i g h t a n g l e s o r o p p o s i t e t o e bb c u r r e n t f l o w(f i g s . 1 4 b , f , 1 6 , 2 7 b , c, f , g ) . Cu r re n t r i p p l e sa r e o r i e n t e d a t r i g h t a n g l e s t o d u n e s o n l y i nt r o u g h s ( f i g . 1 4 f ) a n d a r e f o r m e d b y l a t e - s t a g eo p e n - c h a n n e l f l o w i n t h e t r o u g h s a s d u n e c r e s t se m e r g e . I n t h e n o r t h e a s t p a r t o f B i g B a r , l a t e -s t a g e s h e e t r u n o f f f l o w s to t h e e a s t ( i n r e s p o n s et o a n e a s t e r l y b a r s lo p e ) a n d t h e r e f o r e , o r i e n t a -t i o n o f cu r r en t r i p p l e s i s a l so ea s t ( f i g . 1 4 b ) .T h e d i r e c t io n a l d a t a a r e s u m m a r i z e d i n t or o s e d i a g r a m s ( f i g . 18 ) a n d th e v a r i a n c e w a sd e t e r m i n e d b y g r a p h i c a l m e t h o d s o u t l i n e d b yD e n n i s o n ( 1 9 6 2 ) . T h e s e d a t a s h o w th a t c u r r e n tr i pp l e s a r e c h a r a c t e r i z e d b y a h i g h v a r i a n c e a n da r e t r i m o d a l i n t h e i r d i s t r i b u t i o n , i n r e s p o n s e t ot h e i r f o r m a t i o n d u r i n g s l o p e - c o n t r o l l e d , l a t es t a g e s h e e t r u n o f f . L o w v a r i a n t a n d u n i m o d a l o rb i m o d a l - b i p o l a r ( o p p o s i t e l y o r i e n t e d ) d i s t r i b u -t i o n s c h a r a c t e r i z e t h e o r i e n t a t i o n o f d u n e s , s a n dw a v e s a n d c r o s s - s t r a t i f i c a t io n , a n d s h o w g o o da g r e e m e n t w i t h e b b , o r b o t h e b b a n d f l o o d b o t -t o m c u r r e n t f l ow d i r e ct i o n s .T h e v e c t o r m e a n a n d v a r i a n c e a r e t a b u l a t e di n F i g u r e 1 8 . T h e v e c t o r m e a n s h o w s a g r e e m e n to n l y w i t h m o d a l c l a s s i n u n i m o d a l d i s t r i b u t i o n s .I n b i m o d a l d i s t r i b u t i o n s , t h e v e c t o r m e a n i s o fn o v a l u e i n d e l i n e a t i n g d e p o s i t i o n a l c u r r e n tt r e n d s . T h e s e f i n d i n g s r e - e m p h a s i z e t h e i m p o r -t a n c e o f u s i n g m o d a l p a t te r n s , r a t h e r t h a n v e c -t o r m e a n s , i n d e t e r m i n i n g d e p o s i t i o n a l c u r r e n tt r e n d s i n m a r i n e s e d i m e n t s ( T a n n e r , 1 95 5,1 9 5 9 ) .


11/33

D Y : \ , A M I C S O F I N T " E R T I D A [ , ,S '.,,IN Z) B /I R. S" 1 1 0 5

FIG. 1 4 . - - B e d f o r m s a t B i g B a r , F i v e I s l a n d s . ( A ) R h o m b i c r ip p l e s, g r a d i n g l a te r a l l y in t o l o n g it u d in a lr i p pl e s , C r e s t F a c i e s , B i g B a r . V i e w t o n o r t h . ( B ) D u n e w i t h s u p e r i m p o s e d o p p o si t e ly o r ie n t e d , d o u b l e-c r e s t e d c u r r e n t r i p p le s , c o a r s e s a n d s im p l e d u n e f a c i e s , B i g B a r . V i e w t o n o r t h . E b b c u r r e n t f l o w t o w e s t( l e f t ) . ( C ) S i m p l e d u n e w i th s u p e r i m p o s e d c u r r e n t r i p pl e s , c o a r s e s a n d s i m p I e d u n e f a c i e s , w i t h s c o u r p i t.S c a l e i n d e ci m e t e r s . V i e w t o so u t h . E b b c u r r e n t f l o w t o w e s t ( r i g h t ) . ( D ) F l u t e - m a r k e d s u r f a c e i n t i da lc r e e k, a t n o r t h e r n m a r g i n o f n m d i u m s a n d , s i m p l e d u n e f a c i e s , B i g B a r ( S c a l e i n c m a n d d e c i m e t e r s ) . V i e wt o n o r t h . ( E ) L a t e r a l c h a n g e f r o m t r a n s i t i o n a l fa c i e s w i t h s t r a i g h t - c r e s t e d c u r r e n t r i p p l e s ( f o r e g r o u n d ) t os t r a i g h t a n d l i n g u o id c u r r e n t r i p pl e s in c o a r s e s a n d s i m p l e d u n e f a c ie s ( b a c k g r o u n d ) , B i g B a r . S c a l e i n c ma n d d e c im e t e r s . V i e w t o s o u th . E b b c u r r e n t f l o w to w e s t ( r i g h t ) . ( F ) S i m p l e d u n e w i th s t r a i g h t - c r e s t e dc u r r e n t r i p p l e s s u p e r i m p o s e d a t r i g h t a n g l e s o n s i i pe f a c e ; a n d l i n g u o id c u r r e n t r i p p l e s in t r o u g h , m e d i u ms a n d s im p l e d u n e f a c ie s , B i g B a r . S c a l e i n c m a n d d e c i m e t e r s . V i e w t o n o r t h . E b b c u r r e n t f l ow t o w e s t( l e f t ) .


12/33

i

m


13/33

I ) I N . 1 .1 11 C5 ' ( ) l ; I X T E t f T I D A L 5,'. I N / ) l L l 1 5 1107"I'AI{LI'; 3. - l ) i tt g n o s l i c m e ~ a s ~ o p i c fe a t u r e s o fs e d i m e n t a r y fa c i e s , H & B a r , P i n n a c l e F A t/ s,lVesl B a r , M i d d l e B a r a n d E a s l B a r

F a c i e s ( a n d f a c i e sa b b r e v i a t i o n s f o r D i a g n o s t i c F e a t u r e sTab les 2 , 4 , 6 , 7 )( A ) F a c i e s c l a s s i f le d a c c o r d i n g t o t e x t u r e , b e d f o r m a n di n t e r n a l s t r u c t u r eG r a n u l e G r a v e l ,S i m p l e D a n e( G G S D )

"I'AI~I.E 3. ( c o n t i n u e d )F a c i e s ( a n d f a c i e sa b b r e v i a t i o n s f o r I ) i a g n o s t ic F e a t u r e sT a b l e s 2, 4, 6, 7)

M e d i u m S a n d ,S i m p l e D u n e( M S S D )

G r a n u l e g r a v e l , w i t h s e c o n d a r ym o d e o f v e r y c o a r s e s a u d .P l a n e d d u n e s . T h i n , p l a n a rc r o s s - s t r a t i l i c a t i o n w i t h s h a r pc o n t a c t s ; t r o u g h - l i k e t o e s e t s .C o a r s e S a n d , C o a r s e s a n d , w i t h s e c o n d a r y n m d eC o m p l e x o f m e d i m n s a n d . S a n d w a v eS a n d W a v e c r e s t s s p h t y i n t o t i e r o f d u n e s( C S C S W ) a r r a n g e d i n s t e p s . T h i n s e t s o fp l a n a r c r o s s - s t r a t if i c a t i o n w i t hs h a r p c o n t a c t s b e t w e e n s e t s .T r n u g h - l i k e t o e s e t s . T h i c k n e s so f c r o s s - s t r a t i l i c a t i o n i s l e s s t h a ns a n d w a v e h e i g h t . I ( ~ ) u n d e du p p e r s e I s . ( F i g s . I S e ; 2 7 d ; 3 3 a ,I); 34b, c).C o a r s e S a n d , M e d i m n g r a i n s a n d w i t h s e c o n d a r yS i m p l e I ) u n e m o d e o f c o a r s e s a n d . S i m p l e( C S S I ) ) d u n e s . T r o u g h a n d p l a n a r c r o s s -s t r a t i li e a t i o u w i t h s h a r p s e t c o n -t a c t s . S u p e r i m p o s e d c u r r e n t r i p -p l e s . T r o u g h s l i n e d w i t h p e b b l e sa n d s h e l l s o f M v a a * ~ n a r ea ,Cre p i du l a f orn i c a t ~ , a n d p l a n ts t e m s . R o u n d e d u p p e r s e t s o fc r o s s - s t r a t i i i c a t i o n . M e t a r i p p l e s .(Figs. 14b, c; 15b, c, f; 27c, g).M e d i u m S a n d , M e d i u m s a n d w i t h n e a r ly e q u a l C o b b l e - B o u n d e rS i m p l e S a n d p r o p o r t i o n o f f in e s a n d . S i m p l e G r a v e lW a v e s a n d w a v e s . P l a n a r e r o s s - s t r a ti - ( C B G )( M S S S W ) f i c a ti o n , w i t h s h a r p s e t b o u n d - M e d l u m - F i n ea r i e s. R o u n d e d u p p e r s e t b o n n d - S a n da r i es . S u p e r i m p o s e d c u r r e n t r i p - ( M F S )p i e s o r i e ii t e d o p p o s i t e t o s a n d T r a n s i t i o nw a v e s . ( T )M e d i u m S a n d , F i n e s a n d w i t h m a j o r s e c o n d a r yC o m p l e x l ) n u c m o d e o f m e d i m n s a n d . C o m p l e x( M S C I ) ) d u n e s . I . o w - a n g l e c r o s s - s t r a t i-f i c a t i o n ; c o n s i s t i n g o f i n l c r o -c r o s s - l a m i a u t e d l a y e r s . S h a r ps e t b o n n d a r i e s b e t w e e n c r o s s -s t r a t i f i e d s e t s . S u p e r i m p o s e dc u r r e n t r i p p l e s .F i n e s a n d w i t h m a j o r s e c o n d a r ym o d e o f m e d i u m s a n d . S i m p l ed u n e s . P l a n a r c r o s s - s t ra t l f i c a tl o n

w i t h s h a r p c o n t a c t s . C u r r e n tr i p p l e s s u p e r i m p o s e d o n c r e s ta n d s l i p f a c e a t 9 0 1 8 0 o rp a r a l l e l t o d u n e o r i e n t a t i o n .M e t a r l p p l e s . ( F i g s . 1 4 f ; 2 7 a, b ) .M e d i u m S a n d , M e d i u m s a n d w i t h si g n i fi c a n tC u r r e n t R i p p l e m o d e o f f in e s a n d . S t ra i g h t ,( M S C R ) l i ng u o l d a n d l u n a t e c u r r e n t r i p - l e s . P a r a l l e l l a m i n a e b e l o w s u r -m e s e t s o f n f i c r o - c r o s s - l a m i n a ei n c h a n n e l b o r d e r s . F l u t e m a r k so n s u r f a c e o f c h a n n e l w a l l a n df loo r .

F i n e S a n d , M e d i u m s a n d w i t h s i g n i f i c a n tS i m p l e S a n d s e c o n d a r y m o d e o f f in e s a n d .W a v e S i m p l e s a n d w a v e s w i t h s u p e r -( F 'S S S W ) i m p o s e d c u r r e n t r i p p l e s p a r a ll e l ,a t r i g h t a n g l e s o r o p p o s i t e t os a n d w a v e o r i e n t a t io n , l . o wa n g l e , p l a n a r c r o s s - s t r a t i f i c a t i o nw i t h s h a r p s e t b o u n d a r i e s . ( F i g s .15d ; 27 f ) .( B ) F a c i e s cl a ss i fi e d a c c o r d i n g t o t e x t u r e a n d b e d f o r m .S a n d y G r a v e l , P e b b l e a n d c o b b l e g r a v e l w i t hH a r r o w M a r k m a j o r s e c o n d a r y m o d e o f m e -( S G H M ) d i u m s a n d . H a r r o w m a r k s .

C u r r e n t c r e s c e n t s . L o c a l a r e a so f s t r a i g h t - c r e s t e d , p l a n e d c u r -r e n t r i p p l e s . G r a n u l e g r a v e lm i x e d w i t h s a n d i n h a r r o w s .( C ) F a c i e s c l a s s i l i e d a c c o r d i n g t o t e x t u r e o n l y .P e b b l e g r a v e l w i t h m a j o r s e c o n -d a r y m o d e s o f c o b b l e s a n db o n l d e r s .F i n e s a n d w i t h s e c o n d a r y m o d e o fm e d i u m s a n d . A i r h o l e s . P l a n a rl a m i n a t i o n ( F i g . 1 5 a ) .F i n e s a n d w i t h s e c o n d a r y m o d e o fg r a v e l . S t r a i g h t - c r e s t e d c u r r e n tr i p p l e s w i t h g r a n u l e s a n d p e b -b l e s in t r o u g h s ( c f. H o o k e ,1 9 6 8 ) . H a r r o w m a r k s . C u r r e n tc r e s c e n t s .F i n e S a n d . S t r a i g h t a n d f i n gu o l dr i p p l e s . L o n g i t u d i n a l r i p p l e s .R h o m b i c r i p p l e s . ( F ig . 1 4 a ).S i l t y c l a y . P a r a l l e l l a m i n a t e d . B u r -r o w e d b y M y a a r e n a r e a , A r e n i -c o la m a r i n a , N e r e i s v i r e n s , H e t e r -o m a s t u s f i l i f o r m i s .

C r e s t(c )M u d

F u ; . 1 5 . - - E p o x y p e e l s f r o m F i v e I s l a n d s a n d E c o n o m y P o i n t. ( A ) M e d i u m - f i n e s a M f a c i es , B i g B a r ,s h o w i n g p a r a l le l l a m i n a t io n a n d ai r h o l e s ( P e e l # 5 - A ) . ( B ) C o a r s e s a n d si m p l e d u n e f a c ie s , B i g B a r , s h o w -l u g p l a n a r c r o s s -s t r a t if i c a t i o n ( P e e l # 5 - D C ) . ( C ) C o a r s e s a n d s i m p l e d u n e f ac i e s, C e n t e r B a r, s h o w i n gs l ig h t r o u n d i n g a n d t r u n c a ti m l o f c r o s s - s t r a ti f i c a t io n a t b e d f o r m s u r f a c e ( P e e l # 7 - 3 7 B ) . ( D ) F i n e s a n ds i m p le s a n d w a v e f a c ie s . P i n n a c l e F l a t s, s h o w i n g t r o u g h c r o s s - s t r a ti f i c a t io n i n s u r f a c e s e t a n d t r u n c a t e dc r o s s - s t r a ti f i c a t io n i n Io , a cr s e t ( P e e l # 4 - B u - g A ) . ( E ) C o a r s e s a n d c o m p l e x s a n d w a v e f a c i e s, P in n a c l eF l a ts , s h o w i n g t h i n s e t s o f t r o u g h c r o s s - s t r a t if i c a t i o n ( P e e l # 3 - 1 A ) . ( F ) C o a r s e s a n d s i m p l e d u n e f a c i e s ,l ' i n n a c l e F l a ts , s h o w i n g a t a r r o w a r o u n d e d u p p e r s e t : b o u n d a r y ( r e a c t i v a t i o n s u r f a c e ) a n d p l a n a r c r o s s -s t r a t i f i c a t i o n w i t h t r o u g h - l l k e t o e s e t s ( P e e l #3 - 103A ) .


14/33

1 1 0 S G E O R G E D a U R I E S K L E I N"I'Am.E 4.---Average Quantitalive Parameters of sandy and g ravelly Sedimenlary Facies.

( T e x t u r a l p a r a me t e r s a f t e r F o l k a n d \ V a r d , 1 9 5 7 1

Facies

P a r am ete r

~u

Z g ~ "- o

CM F SM S S DM S C DCS S DS G H MT

C B GM S C RC S C S WCSSDF S S S W

GGS I )M S C RMS S DMS S S W( 'S S DC S C S W,~GHM

2,752 .752 .252 .251 . 5 0- - 0 .25

- - 1 .75

2 .241.751 . 2 5(I.751 . 7 5

- - 1 .752 .252 .251 . 7 31 . 7 51 . 7 5

-- I .7 5

2 .132 .351.551.550 . 9 6- - 0 .130 . 5 2

0 .471 . 2 30.910 . 7 01 . 3 1 )

- - 0 . 8 91 . 6 01 . 8 91 . 2 41 . 3 50.81- - 0 .27

4 150 76 912 2314 2816 218 15

7 1721 3334 4332 4516 53

82 J.544 362921 3624 3818 17

B i g B a r6 0 2 . 2 6 0 . 6 2 - 0 . 2 281 2 .35 0 ,31 - 0 .0167 1 .61 0 ,79 - - 0 .0950 1 .67 0 .86 - - 0 .222O ] 1.20 1.19 - -0.2 9

9 [ - 0 .23 1 .45 0 .0827 ~ 2 .21 2 .09 0 .17Pi n n a c l e F l a t s

12 --1.119 1.6 0 0. 4922 1 .29 0 .69 - - 0 .1513 0 .98 0 .68 - - 0 .1610 0 .85 0 .75 - -0 .1126 1 ,33 0 .64 - - 0 .10

Economy PointI - - 1 .08 1 .11 0 .2657 1 ,69 0 .58 - - 0 .2560 1.90 ( I .41 - -0.3 5311 1.16 0.5 8 0.0122 1.50 ( I .67 - -0.2713 / 1 .00 0 .77 - - 0 .2411 ] 0.6 3 1. 36 0.10

006 .023.252 . 7 02 .21

1.110:1.00

.1 3o

16.110.23. 2

m

7.557 ,655 ,84

0 . 2 013 .2

2.4416 .84

5 .012 ,45 . 5 44 7 . 3 63 .5850 .7

0 .18 30 0 .19 29 0 .16 30

0 , 0 30 .77 20 0 .17 31 0.17 14

0 .53 1800 .008 28 ~0 .27 28 0 .69 18 0.21 27 ~1.17 30~

N12,512.0 23

5.2 16 12,0 27

8.1 21 9 .8 29 n14.3 23

12.9 32 8.23 32 7.9 24 9 .5 29 7,9 27

S a n d D i s p e r s a l S y s t e m sA s e r i e s o f g r a i n d i s p e r sa l e x p e r i m e n t s w e r ec o m p l e t e d a t B i g B a r i n c o o p e r a t i o n w i t h C . L .S a n d u s k y ( 1 9 6 8 ) , u s i n g s a n d s t a i n e d w i t h a na c r y l i c l a c q u e r ( S e e Y a s s o , 1 9 6 6 , f o r a d i s c u s -s i o n o f s u c h t e c h n i q u e s ) . A t o t a l o f e i g h t s t a -t i o n s w e r e o c c u p i e d .T h e d i s p e r s a l p a t t e r n o f g r a i n s f r o m a p o i n ts o u r c e w a s f o u n d t o b e r a d i a l l y - e l l i p t i c a l ( f i g .1 9 ) . T h e d i r e c t i o n o f m a x i m u m d i s t a n c e o fg r a i n t r a n s p o r t f r o m a p o i n t s o u r c e s h o w s e x -c e l l e n t a g r e e m e n t w i t h t h e f l o w d i r e c t i o n o ff l o o d - d o m i n a n t b o t t o m t i d a l c u r r e n t s o n t h es t e e p e r b a r s lo p e s ( f i g . l l a ) a n d w i t h f l o w d i -r e c t io n o f e b b - d o m i n a n t h o t t o m t i d a l c u r r e n t so n t h e g e n t l e r b a r s l o p e s ( F i g . 2 0 a ) .T h e s e d a t a s u g g e s t a g e n e r a l i z e d t r a n s p o r tm o d e l ( f ig . 2 0 b ) w h i c h i s e l li p t i c a l i n ac o u n t e r - c l o c k - w i s e m a n n e r a r o u n d B i g B ar .T h i s e l l i p t i c a l t r a n s p o r t p a t t e r n i s a r e s p o n s e b ys e d i m e n t to a l t e r n a t e t r a n s p o r t t h r o u g h f lo o d -a n d e b b - d o m i n a t e d p o r t i o n s o f B i g B ar . A s i m i -

l a r p a t t e r n o f s a n d t r a n s p o r t w a s d o c u m e n t e dl ly P h i l i p p o n n e a u ( 1 9 5 5 ; c i t e d i n V e r g e r , 1 9 68 ,p . 18 4 - 1 8 81 f r o m s a n d b a r s i n t h e B a l e d e M o n tS a i n t M i c h e l i n F r a n c e , a n d a p p e a r s a l s o t o

~ DUNES~ SAND WAVES

CURRENT RIPPLESFIG. 16.--Orientatlon of sedim entary bedforms at(A ) Big Bar , (B) Pinnacle Flats , and (C) EconomyPoint.


15/33

D }'N..IMIC3" OF IN TE RT ID AL .S'AND IL4tCS 1109characterize other sand bars as seen by compar-ing aerial photographs and tidal current flowmaps shown by Verger (1968, p. 67-68, 104-105, 205-207) from the Basin d'Arcachon, LesPertuis d'Oleron and the Baie de Somme alongthe French coast (See also Van Straaten, 1950,p. 78-79). Newton and Wern er (1968) docu-mented a similar dispersal system of sand trans-port on intertidal sand bars near Cnxhaven,West Germany, and Reineck (1963) proposed asimilar dispersal system of sand transport for asnbtidal sand bar in the deeper channels of theJade. A comparison of Newton and Werner's(1968) observations with airphotos of intertidalsand bodies elsewhere on the North Sea Coastof We st Germany (Gierlofff-Emden, 1961, p.35-36, 43-45, 49, 53, 55, 58-59) suggests a his -tory of sand transport identical to that at BigBar.In sub-tidal, tide-dominated regimes, a similarsystem of sand transport also is known. Houbolt(1968) inferred such a dispersal system fromdune orientation on the Well Bank of theNorth Sea (p. 257), whereas James and Stanley(1968) documented a similar transport patternby heavy mineral studies from the Scotian Shelfnear Sable Island. J. D. Smith (1969) reporteda similar circulation pattern of tidal flow over

\"~, ,."q~- . ,d l , -" ~, , , , ~ -2 ~ )

o 4 o o M /

~ r o 2 0 0 M TB ' '

I cFro. 17.--Orientation o f.maximum dip direction ofcross-stratification at (A) Big Bar, (B) PinnacleFlats, and (C) Economy Point. (Abbreviations:P--Pinnacle Flats; L--Long Island).

B IG B A R .C R 11521

N

5 io 25 50 2"J i . )D[ 8 81

NCS {26)

p IN N A C L E F L A T SN

C R(192N

I ~ i ~ L 5 I 02 5 5 0 ,: '0 1142)

NS W 1 7 6 1

NI ~ l l l l l ~ C S 2 4

E C O N O M , P TC R 461

D (139)

SW(15

~ p C S 1 8 6 )

CR D SW CS/ 1 9 1 2 3 5 - 2 5 ~} S I , , ~ - -~ 2 6 4 0 0 2 2 5 - 6 2 fi~i 2 ~ 2 5 ~ 1 2 g 233

(~2 2025 225 90( 289012 2 ~ a , ~ 1 3 ~ 2 8 (E P L -1 ~ 2 e ~2 5 0 0 2 2 5 4 0 ( .I

m

Fro. 18.--Summary rose diagram of orientationdata for current ripple (CR), sand wave (SW),dune (D), and cross-stratification (CS) at PinnacleFlats, Big Bar and Economy Point. Table summarizesvector mean (X) and variance (~=) for each propertyat each study area (BB--B ig Bar, PF PinnacleFlats, EP--Economy Point).tide-dominated sand bars off the coast of Mas-sachusetts, as did Verger (1968, p. 165) fromsubtidal sand bars off the Loire River Delta,France. The conclusion is therefore inescapablethat this elliptical pattern of sand transportthrough both flood- and ebb-dominated portionsof tidal sand bars is a characteristic transportpattern for intertidal and subtidal sand bodies.Examination of low-tide airphotos taken in1947 (Canadian Air Photo Library Photo No.Al1790-66) and in 1963 (Canadian A ir PhotoLibr ary No. A18061-21) at Big Bar shows thatboth the sedimentary facies and morphologythere has remained unchanged since 1947. Theelliptical sand transport system must be an equi-librium system, and consequently, Big Bar is anequilibrium intertidal sand bar. The equilibriumexists between tidal current sand transport, tidalcurrent time-velocity asymmetry, bar topogra-phy, distribution of sedimentary facies, and ori-


16/33

( ) .1110 ( i l : JAgi: r~nI'A'IES KI.EIN

S to . 3 - 1 0 2 ( W 1 ~ P in na c le F I0 t l )

tSla. 3"1 03 [W. Pinnacle Flats)

$t~ 7-L.I...(Eollorny Pt)CO A RS E SAND.

S ta 3-1 01A (E P innac le F lo t l )

.o........,n .. , , ,.Fr o. 1 9 . - - Di r ec t io n o f d i sp e r sa l o f san d s t a in edwi th an ac r y l i c l a cq u e r . D i s t an ces f r o m p o in t so u r cem easu r ed a f t e r two t i d a l d ay s ( f o u r t i d a l cy c l e s ) .

e n t a t i o n o f d i r e c t i o n a l c u r r e n t s t r u c t u r e s .A t l ' i n n a c l e F l a t s , t h e s a m e 1 9 6 3 l o w - t i d e a i r

p h o t o s h o w s t h a t t h e t o p o g r a p h y a n d d i s t r i h u t i o no f s e d i m m ~ t a r y f a c i e s o b s e r v e d b e t w e e n 1 96 5 a n d1 9 6 8 h a s e x i s t e d a s f a r b a c k a s 1 9 6 3. O n l y t h r e es t a t i o n s w e r e o c c u p i e d f o r g r a i n d i s p e r s a I e x -p e r i m e n t s , a l i i n d i c a t i n g m a j o r d i s p e r s a l p a r a l l e lt o e b b - d o m i n a t e d b o t t o m t i d a l f l o w . A t o n e s t a -t i o n ( S t a t i o n N o . 3-103) o r a n g e s a n d , o r i g i n a l l yp l a c e d i n 1 9 6 6 , w a s o b s e r v e d t h e r e a g a i n i n 1 9 6 7 ,1 9 68 a n d 1 9 7 0 w h e n t h i s s t a t i o n w a s r e - o c c u p i e d .P i n n a c l e E l a t s m u s t b e a n e q u i l i b r i u m s a n d b a ra l so .A i r p h o t o a n a l y s i s a t E c o n o m y P o i n t i n d i c a te st h a t t h e f a c i e s d i s t r i b u t i o n m a p p e d b y t h e a u -t h o r i n 1 9 66 , 19 6 7 a n d 1 9 68 ( F i g . 1 2 ) i s i d e n t i -c a l to t h a t s h o w n o n a n a i r p h o t o t a k e n i n 1 9 63( f ig . 2 1 ) . A s o m e w h a t s i m i l a r f a c ie s d i s t r i b u -t i o n w a s p r e s e n t ; i s f a r b a c k a s 1 9 4 7 ( f i g . 2 2 )a n d 1 9 3 8 ( fi g . 2 3 L T h e s a n d b a r s a t E c o n o m yP o i n t w e r e d e f i n i t e l y s u b j e c t e d t o a n e r o s i o n a lr e g i m e b e t w e e n 1 9 3 8 a n d 1 9 6 3 (f i g s . 2 1 , 2 2 ,2 3 ) , h o w e v e r . I n t h e a x i a l p o r t i o n o f E a s t B a r ,a p r o m i n a n t " V " - s h a p e d d e p r e s s i o n o c c u r s i n1 9 6 3 ( f i g . 2 I ) b u t w a s a b s e n t i n 1 9 3 8 ( f i g . 2 3 )a n d s m a l l i n 1 9 4 7 ( f i g . 2 2 ) . A n e s t i m a t e d 5 , 0 0 0c u b i c m e t e r s o f s a n d w a s e r o d e d f r o m t h i s p a r to f E a s t B a r s i n c e 1 9 3 8 .C e n t e r B a r a n d \ V e s t B a r w e r e o n e c o n t i n u -o u s s i n u s o i d a l b a r i n 1 9 3 8 a n d 1 0 4 7 ( f i g s . 2 2 ,2 3 ) . t ~ e t w e e n 1 9 4 7 a n d 1 9 6 3 , t h e t w o b a r s b e -

c a m e s e p a r a t e d h y t he d e v e l o p m e n t o f a m a j o rc h a n n e l s o u t h o f a b e d r o c k l e d g e j u s t n o r t h w e s to f w h a t i s n o w C e n t e r B a r . A n e s t i m a t e d1 6 0, 00 0 c u b i c m e t e r s o f s a n d w a s r e m o v e d b e -t w e e n 1 9 47 a n d 1 96 3 b y t h i s c h a n n e l .F i g u r e s 2 1 , 2 2 a n d 2 3 s h o w t h a t t h e p r e s e n tc r e s t a l e l e v a t io n o f C e n t e r B a r i s h i g h e r t h a n i n1 9 3 8 a n d 1947. I n 1 9 3 8 , a s m a l l c r e e k ( " s " o nf ig . 2 3 ) d r a i n e d C e n t e r B a r , f l o w i n g e a s t . T h i sc r e e k r e v e r s e d i t s f l o w d i r e c t i o n b y 1 9 47 ( f i g .2 2 ) a n d d r a i n e d i n t o a c h a n n e l s o u t h o t h e b e d -r o c k l e d g e o n th e n o r t h w e s t s i d e o f C e n t e r B a r .T h e c r e e k c o n t r i b u te d a n i n c r e a s e d d i s c h a r g ei n t o t h e l a r g e r c h a n n e l a n d p r o b a b l y c a u s e d i t tob r e a c h t h e c o n n e c t i o n b e t w e e n w h a t i s n o wC e n t e r a n d ' W e s t B a r . T h e i n c r e a s e i n c r e s t a le l e v a t i o n o f C e n t e r B a r b e t w e e n 1 9 38 a n d 1 9 63w a s c a u s e d b y s a n d s u p p ly f r o m E a s t B a r a n de r o s i o n o f t h e c h a n n e l s e p a r a t i n g W e s t a n dC e n t e r B a r . T h e c h a n n e l b e t w e e n W e s t a n dC e n t e r B a r d i s p e r s e s s a n d s o u t h o f t h e b a r sw h e r e f l o o d -d o m i n a t e d c n r r e n t s ( f l o w i n g on t h es o u t h s id e o f C e n t e r B a r ) r e d i s p e r s e s o m e o ft h i s e r o de d s a n d b a c k o n t o C e n t e r B a r b y n o r t h -e a s t e r l y t r a n s p o r t . A n e s t i m a t e d 1 0 0, 00 0 c u h i cm e t e r s o f s a n d w a s r e s t o r e d o n t o C e n t e r B a r b yf lo o d ti d a l c u r r e n t t r a n s p o r t . T h e r e m a i n i n g6 5 ,0 0 0 c u b i c m e t e r s o f s a n d r e p r e s e n t s t h e t o t a lv o l u m e o f s a n d l o ss f r o m t h e b a r s a t E c o n o m yP o i n t b e t w e e n 1 9 38 a n d 1 9 68 .

T h i s a i r p h o t o a n a l y s i s s h o w s t h a t a l t h o u g he a c h o f t he s a n d b a r s a t E c o n o m y P o i n t p r o b a -b l y a r e c h a r a c t e r i z e d b y a n e l l i p ti c a l d i s p e r s a lm o d e l s i m i l a r t o B i g B a r , a s l i g h t e r o s i o n a l r e -g i m e e x i s t s o n s o m e o f t h e s a n d b a r s . T h e e r a -

. . . . o o o M

o . . . . s p o .

F tG . 2 0 . - - ( A ) . D i r e c ti o n s o f m a x i m u m d i s p er s a lo f san d f r o m a p o in t so u r ce a f t e r o n e t i d a l d ay( d a t a i n p a r t f r o m San d u sk y , 1 9 6 8 ), B ig B a r . ( B ) .Gen e r a lk ed c i r cu l a t i o n m o d e l o f san d t r an sp o r tt r an sp o r t t h r o u g h zo n es o f f l o o d - an d eb b - d o m in a t edt id a l cu r r en t s . Dash ed l i n e sh o ws p o s i t i o n o f b a rc r e s t a t B i g B a r .


17/33

D F . V A .1 1 I C .q " 0 ] ; I A T E R T I D . I L ' .. I .V I ) ], '..I k.~ ;" 1 1 1 1

F m 2 1 . - - Ai r l J h o to # A - I S lE d - 1 6 t ak e n a t lo w t id e in 1 9 6 3 , i n t e r t id a l s an d h a r s a t Eco n o my P o in t ( Ab -b r ev ia t io n s : E - es k e r , V- - ' v ' - s h ap ed d ep r es s io n ; S I s t r e am ) . Nu m b er s r e f e r to t r en ch mtmb er 's . ( R ep r in t e ( lb y p e r mis s io n o f th e Na t io n a l : \ i rl~ h o to I . i b r a r y , S u r v ey s an d Map p in g 1 3 r an ch, C an ad ian Dep a r tmen t o fEn e r g y , Min es an d R es o u r ces ) .

F i e . 2 2 . - - A i r p b o t o # A - 1 1 7 8 7 - 4 2 t a ke n a t l o w t i d e , s u m m e r 1 9 4 7 , i n t e r t id a l s a n d b a rs , E c o n o m y P o i n t ., ~ hh r e vi a ti o n s a s i n F i g ' . 2 1 . ( R e p r i n t e d b y p e r m i s s i o n o f t h e N a t i o n a l A i r p h o t o L i b r a r y , S u r v e y s a n d M a l J -l ) m g B r a nc h , C a n a d ia n D e p t . o f E n e r g y , M i n e s a n d R e s o u r c e s ) .


18/33

1 1 1 2 GEORGE DeI'RIES KLEIN

FIG. 23 .--Airph otos #A-592 3-86, 88 , 90 taken a t low t ide , summer, 1938. Photom osaic of in tert idal sandhars a t Economy Poin t . Abbrevia t ions as in Figure 21 . (Reprin ted by permission of the Nat ional AirphotoLibrary , Surv eys and Mapping Branch, Canadian Dept . of Energy , Mines and Resource s).s i o na l r e g i m e a c co u n t s f o r e x t r e m e r e w o r k i n go f t h e b a r s ( D i n k e l m a n , 1 96 8) a n d a p p e a r s t oh e r e m o v i n g s a n d f r o m e b b - d o m i n a t e d s e g m e n t so f E a s t a n d C e n t e r B a r s . T i d a l c u r r e n t t r a n s -p o r t i n f l o o d - d o m i n a t e d z o n e s is r e t u r n i n g s o m eo f t h i s e r o d e d s a n d o n t o t h e b a r s , s u c h a s C e n -t e r B a r . T h e 6 5, 00 0 c u b i c m e t e r s o f s a n d e r o d e db y th i s r e g i m e a p p e a r s t o h a v e b e e n d i s p e r s e d i na w e s t e r l y d i r e c t i o n .

Provenance of the SedimentsT h e s e d i m e n t s o n t h e i n t e r t i d a l s a n d b a r s a r ed e r i v e d f r o m t w o m a j o r s o u r c e s , T r i a s s i c s e d i-m e n t a r y r o c k s o c c u r i n g b o t h a s i n t e r t i d a ll e d g e s , a n d s e a c li f f s ( K l e i n , 1 9 6 2 ) , a n d P l e i s t o -c e n e f l u v i o - g l a c i a l s e d i m e n t s o f t h e F i v e I s l a n d sF o r m a t i o n ( S w i f t a n d B o r n s, 1 9 67 ) w h i c h o c -c u r b o t h o n s h o r e i n s e a c l i f fs a n d i n t h e i n t e r i -d a l z o n e . S w i f t a n d M c M n l l e n ( 1 9 6 8) d e m o n -s t r a t e d t h a t m o s t o f t h e s e a b e d o f t h e M i n a sB a s i n i s u n d e r l a i n b y n e a r l y e q u a l p r o p o r t i o n so f T r i a s s i c s e d i m e n t a r y r o c k s a n d P l e i s t o c e n es e d i m e n t s w h i c h a r e a v a i l a b l e f o r r e w o r k i n ga n d r e d i s t r i b u t i o n b y t i d a l c u r r e n t s .

Pleistocene sources.-~he P l e i s t o c e n e f l u v i o -g l a c i a l d e p o s i t s o f t h e F i v e I s l a n d s F o r m a t i o na r e e x p o s e d o n s h o r e . T h e y c o n s i s t m o s t l y o fg r a v e l l y s an d s ( f i g . 2 4 ) . T h e i r t e x t u r e i s b i m o -d a l , w i t h t h e t w o m o d a l c l a s s e s f a l l i n g a t + 2P h i a n d - - 2 P h i . T h e y a r e m e d i u m r e d d i shb r o w n a n d c o n s i s t o f s u b a r k o s i c a n d q u a r t z o s es a n d m i x e d w i t h p e b b l e s a n d c o b b l e s o f g r a n i t e ,r h y o l i t e , m e t a q u a r t z i t e a n d r e c o g n i z a b l e P e n n -s y l v a n i a n s e d i m e n t a r y r o c k s k n o w n t o o c c u r i nt h e C o b e q n i d H i g h l a n d s t o t h e n o r t h . T h e s a n d

f r a c t i o n i s s i m i l a r i n c o m p o s i t i o n t o t h e T r i a s s i c( K l e i n , 1 9 6 2) a n d i n t hi s c a s e i s s n b a r k o s e a n do r t h o q u a r t z i t e ( F o l k , 1 95 4, c l a s s i f i c a t i o n ) . T h es a n d f r a c t i o n i s s t a i n e d w i t h h e m a t i t e , d e r i v e df r o m t h e T r i a s s ic .M u c h o f t h e P l e i s t o c e n e s a n d y g r a v e l i s r e c -o g n i z e d in r e w o r k e d f o r m b y m e g a s c o p i c co m -p a r i s o n b e t w e e n i n t e r t i d a l s e d i m e n t s a n d t h eF i v e I s l a nd s F o r m a t i o n . T h e c o a r s e s an d , s i m -p l e d u n e f a c i e s , t h e c o a r s e s a n d , c o m p l e x s a n dw a v e f a c i e s , t h e s a n d y - c o b b l e g r a v e l f a c i e s , a n dt h e s a n d y g r a v e l , h a r r o w m a r k f a c i e s a r e s i m i -l a r i n c o l o r a n d c o m p o s i t i o n t o t h e F i v e I s l a n d sF o r m a t i o n .

#

E O | C O t ,i P O S iT P L E I S T O E k I IE 8 ~ T R I A S S I C

NZE I~l ~ - O . SSZE(~)

? , p - e - I ,R E C E N T S A M O .T~.L~ANOiRS l Z E ( . ~ ) ~

S I Z E [ n )FIG. 24.--S ize-freq uency d is t ribut ions of Ple is to-cene t tuvio-g lacia l sand , Five Is lands Form at ion (up-p e r l e f t ) , T r i a s s i c W o l fv i l l e Fo rm a t i o n ( l o w er l e f t ) .composi te of equal propert ions of Triassic and Ple is-tocene sand (upp er r ight ) , and Holocene sand fromi n t er t i da l san d b a r a t S t a t i on # 7 - P- 8 , W es t Ba r ,Econ omy Poin t . Size analyses taken f rom rep resenta-tive samples.


19/33

[)t'.\ '.t .1/[C.f OF [N TE RT ID .J L .f:tND B,-tRX 1 1 1 3T h e e a s t e r n t h i rd o f E a s t B a r a t E c o n o m yP o i n t i s a n e s k e r o f P l e i s t o c e n e a g e c r o p p i n go u t in th e i n t e r t i d a l z o n e ( " E " i n fi g . 2 1 ) a n di s b e i n g r e w o r k e d b y t i d a l c u r r e n t s . T h e e s k e rc o n s i s t s o f a p e b b l y - c o b b l y s a n d y g r a v e l ; m o s to f t h e s a n d is m e d i u m - a n d f i n e - g r a i n e d . T h es u r f i c i a l p a r t o f t h e e s k e r i s c o v e r e d b y a s a n d -

f r e e g r a v e l l a g - c o n c e n t r a t e w h i c h g r a d e s l a t e r -a l l y i n t o a f in e - a n d m e d i u m - s a n d . T h i s s a n dr e s t s a s a s u r f a c e v e n e e r o n t h e p e b b l y - c o b b lys a n d y g r a v e l o f t h e e s k e r ( f i g . 2 5 a , c ) .T h e e s k e r i s b e i n g r e w o r k e d b y ti d a l c u r r e n t sa n d m o d i f i e d b y i c e - r a f t i n g . I n A u g u s t , 1 9 6 6 , at h i n s t r i p o f s a n d o c c u r r e d o n t h e c r e s t o f t h ee s k e r a n d w a s o b s e r v e d t o g r a d e l a t e r a l l y i n t o ag rav e l l ag ( f i g . 2 5 a ) . By Ju n e , 1 9 6 7 , t h e su r f i -e i a l s a n d w a s r e m o v e d b y ti d a l c u r r e n t s a n d t h ec s k e r w a s c o m p l e t e l y a r m o r e d w i t h g r a v e l ( f i g .2 5 b ) . I n J u n e , 1 9 6 8 , c o n d i t i o n s w e r e s i m i l a r t o1 9 6 6 ( F i g . 2 5 c ) . D u r i n g t h e w i n t e r o f 1 9 6 7 - 6 8 ,t h e M i n a s B a s i n w a s f r o z e n a n d t h e 1 9 6 7 g r a v e ll a g d e p o s i t w a s r e m o v e d b y i c e - r a f t i n g i n t h es p r i n g o f 1 9 6 8 . T h e p e b b l y - c o b b l y - s a n d y g r a v e lo f t h e i n t e r i o r o f t h e e s k e r w a s e x p o s e d a g a i na n d t h e n r e w o r k e d b y ti d a l c u r r e n t s . B y J u n e ,1 96 8 ( F i g . 2 5 e ) , s a n d w a s w i n n o w e d i n t o a l i n -e a r s t r i p o n t h e c r e s t o f t h e e s k e r .T h e s e o b s e r v a t i o n s r e c o n f i r m t h a t t h e t i d a lc u r r e n t s o f t h e M i n a s B a s i n t r a n s p o r t , r e d i s -t r i b u t e a n d l o c a l i z e s a n d o n s a n d b a r s a n d l e a v eg r a v e l b e h i n d a s a l a g c o n c e n t r a t e .Triassic sources.--~riassic s a n d s t o n e l e d g e s a r ec o m m o n i n t h e i n t e r t i d a l z o n e o f t h e t w o s t u d ya r e a s . A t E c o n o m y P o i n t , t h e y o c c u r a s a s u b -s t r a t e f o r t h e s a n d b a rs , w h e r e a s a t F i v e I s -l a n d s , T r i a s s i c b e d r o c k u n d e r l i e s t h e s o u t h s i d eo f P i n n a c l e F l a t s a n d c r o p s o u t o n a l l t h e i s -l a n d s ( K l e i n , 1 9 6 0 , 1 9 6 2 ) .

T h e T r i a s s i c b e d r o c k i s b o t h s c o u r e d , s t r i a t e d ,a n d p o l i s h e d . N o o r g a n i c g r o w t h , s u c h a s a l g a eo r b a r n a c l e s , o c c u r o n t h e p o l i s h e d l e d g e s . S o m eo f t h e p o l i s h e d b e d r o c k l e d g e s a r e s i m i l a r t ob e d r o c k s u r f a c e s s c o u r e d b y s a n d f l o w i n s u b -m a r i n e c a n y o n s ( D i l l , 1 9 6 4 ) .T h e s u r f a c e s o f T r i a s s i c b e d r o c k a r e a l s os t r a i t e d b y ti d a l c u r r e n t s c o u r a n d s a n d b l a s t i n g( f i g . 2 5 d , e , f ) . T h e s t r i a e a r e o r i e n t e d p a r a l l e lt o p r e s e n t e b b a n d f l o o d c u r r e n t f l o w d i r e c t i o n sa n d t h e o r i e n t a t i o n o f s l i p f a c e s o f c u r r e n t r i p -p l es a n d d u n e s ( f i g . 2 5 f ) . T h e s t r i a e a l so c u tH o l o c e n e c l a m s h e l l s w h i c h b o r e d i n t o T r i a s s i cs a n d s t o n e ( f i g . 2 5 e ) .S o m e w o r k e r s ( S w i f t a n d L y a l l, 1 9 68 ) p r o -p o s e d a P l e i s t o c e n e g l a c i a l o r i g i n f o r t h e e a s t -w e s t o r ie n t e d s tr i a e. H i c k o x ( 1 9 6 2) d e m o n -s t r a t e d f r o m p e t r o l o g i c s t u d y o f t i l l b o u l d e r st h a t W i s c o n s i n g l a c i a l t r a n s p o r t w a s d i r e c t e d

f r o m n o r t h t o s o u t h a c r o s s t h e M i n a s B a s i n ,h o w e v e r . T h e s t r i a e o r i e n t a t i o n d o n o t a g r e ew i t h k n o w n d i r e c t i o n s o f g l a c i a l t r a n s p o r t .A g r e e m e n t b e t w e e n s t r i a e o r i e n t a t i o n , t i d a l c u r -r e n t f l o w d ir e c t i o n s , a n d o r i e n t a t i o n o f b e d -f o r m s i n d i c a t e s a n o r i g n b y t i d a l c u r r e n t s c o u r .C u t t i n g o f H o l e c e n e c l a m s b y s t r i a e c o n f i r m st h e i r H o l o e e n e a g e .Provenance summary.--Recognition o f b o t hT r i a s s i c a n d P l e i s t o c e n e s e d i m e n t s a s s o u r c e sf o r t h e i n t e r t i d a l s a n d b a r s p l a c e s k n o w n l i m i t so n t h e p a r t i c l e s i z e s a v a i l a b l e f o r t i d a l c u r r e n tt r a n s p o r t . F i g u r e 2 4 s h o w s t h e t e x t u r a l d i s t r i b u -t i o n s f o r r e p r e s e n t a t i v e s a m p l e s o f P l e i s t o c e n es a n d c o l l e c te d f r o m t h e F i v e I s la n d s F o r m a t i o na n d o f T r i a s s i c s a n d s to n e c o l le c t e d f r o m E c o n -o m y P o i

klein 1970 - depositional and dispersal dynamics of intertidal sand bars

Documents