Sedimentology of a lacustrine barrier system at Wasaga Beach, Ontario, Canada

Sedimentary Geology, 14 (1975) 169--190 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

SEDIMENTOLOGY OF A LACUSTRINE BARRIER WASAGA BEACH, ONTARIO, CANADA

SYSTEM AT

I.P. MARTINI

Department of Land Resource Science, Unwerslty of Guelph, Guelph, Ont. (Canada) (Received November 4, 1974; revised and accepted May 7, 1975}

ABSTRACT Martini, I.P, 1975. Sedimentology of a lacustrine barrier system at Wasaga Beach, Ontarm, Canada. Sediment. Geol., 14. 169--190 In an area of 4 by 15 miles (6.5 x 24 km) at Wasaga Beach, Ontario, a Holocene system is exposed that can be considered sedimentologically to be a lacustrine "barrier island complex", although the initial features were formed as a spit--baymouth bar combination. The sedimentary facies of the system are comprised of lagoonal or bay deposits calcareous, fosslhferous clays and silts mterstratifmd with sandy layers, some showing regular alternation and which originated as storm layers; beaches of the barrier itself that range from older coarse shingle-beaches to more recent sandy and locally fossihferous ones. The beach sediments show several cycles of deposition. A type of macrocycllcity is related to coarsening-upward cycles m the pebble beaches, the coarser and higher layers indmatmg strong storm conditions. Smaller cycles within the sections have characteristic fining-upward sequences mdmatmg different storm or fair-weather conditions. Swash zones migrating during falling stages of storms are well defined by typical openwork granule layers. Cycles of the sandy beaches are characterized by erosional surfaces and alternation of plane beds and ripple-drift cross-lamination. The whole barrmr Is capped by foredunes, transverse and high parabolic dunes made up of very well sorted sands showing regular to slightly modified large-scale cross-bedding. Unhke marine systems, no intense bioturbation has occurred in these lacustrine units, the strandlmes are well defined because of lack of significant influences from tides, the various subenvironments can be readily recogmzed, the approximate energy condltmns existent at the time of growth of the barrier can be reconstructed, and sedimentologmal models can be built. A descriptive analogue model of the lacustrine barrier system is presented.

INTRODUCTION T h e o b j e c t i v e o f t h i s p a p e r is t o p r e s e n t a s c h e m a t i c s e d i m e n t o l o g i c a l m o d e l of a l a c u s t r i n e barrier system, t h a t was f o r m e d d u r i n g the H o l o c e n e a n d w h i c h is b e i n g m o d i f i e d a t t h e p r e s e n t t i m e , a t Wasaga B e a c h , O n t a r i o o n t h e c o a s t s o f L a k e H u r o n ( F i g . 1). T h i s s y s t e m is c o m p r i s e d o f preA l g o n q u i n tills, A l g o n q u i n b e a c h e s , a N i p i s s m g b a r r i e r c o m p l e x a n d r e c e n t spits, a n d s u b a q u e o u s b a r s i n a s a n d y , s h a l l o w a n d w i d e shelf. T h e s e c o m p o n e n t s are well d e f i n e d g e o m o r p h o l o g i c a l l y in p l a n e v i e w a n d t h e i r i n t e r n a l

170

LAKE

HURON

•

IAKE

ONTARIO )

TORONTO

..... O

~ 30 Mt

i F~SHALE& LIMESTONE PALEOZOI[C] DOLOSTONE ~ SHALE [~ PRKAMBRIAN

Flg~ 1 Generalized geologmal map of the bed-rock o! ~outhwestern Onta~q~,. ~'ap.ada, ~, Iocatmn of Wasaga Beach

features are well preserved and e x p o s e d m natural sections along the N o t t > wasaga River, which crosses the area and in sand and gravel pits ( Ft~. 2 t. A l t h o u g h m u c h is k n o w n a b o u t m a r i n e barriers and lagoons, few g e o [ o ~ cal m o d e l s have been p u b h s h e d c o n c e r n i n g snnilar c o m p l e x e s f o r m e d alon~ the shores o f large f r e s h w a t e r lakes (Warme, 1 9 7 1 ; King, 1972; D m k l n s o n ,,~ al., 1 9 7 2 ; Le Blanc, 1 9 7 2 , J e n n m g s and C o v e n t r y , 1 9 7 3 ) . F u r t h e r m o r e , fe~ papers have p r e s e n t e d m o d e l s o f sandy, gravelly beaches (Bluck, 1967; Cli~ t o n et al., 1 9 7 1 ) or have analysed m detail processes t h a t m o d i f y the charm ters o f pebbles along shores ( D o b k m s and Folk, 1970). Essentially, a classic m o d e l o f a m a r i n e " b a r r i e r island s y s t e m " ¢'onslst~ ~! a c o a r s e n i n g - u p w a r d sequence, f r o m o f f s h o r e m u d s at the base. ~flts at~ ~, clays, and finally t o sands of beaches and a e o h a n d u n e s (Davms et ai.~ 1 9 7 1 , Local d i s t m g m s h a b l e m t e r s t r a t i f m a t l o n s m a y be present, and t h e y relat,: ~,. tidal channels (Le Blanc, 1972), w a s h o v e r fans (Andrews, 1970~, or the.:, consist o f p e a t and o t h e r lagoonal m a t e r m l including shell beds. Plane-bed.~. ripple-beds and cross-beds are c o m m o n s e d E n e n t a r y structures. H o w e v e r , th, m a j o r i t y o f the p r E n a r y features o f m a r i n e barrier islands are r e w o r k e d and o b l i t e r a t e d b y bmgenic agents. T h e r e f o r e , structural states o f a n c m n t or full\ d e v e l o p e d barrier islands are c h a r a c t e r i z e d p r e d o m m a n t l y b y a b u n d a n t m(, t u r b a t e d , a p p a r e n t l y massive strata and s o m e residual bedding, primarily ~,~' a e o h a n d u n e s and s t o r m layers (Warme, 1971). U n h k e the m a r i n e examplt,.

171

Fig. 2. Geomorphologmal subdivisions of part of the Barrier System (A), and sections in the mare bamer (B) and at the transition between the mare barrier and the lagoon (C) in a lacustrine barrier s y s t e m all p r i m a r y s e d i m e n t a r y s t r u c t u r e s and t e x t u r e s are preserved, and the r e c o n s t r u c t i o n and u n d e r s t a n d i n g o f physmal conditions o f the e n v i r o n m e n t o f d e p o s i t i o n is facilitated. T h e f o r m a t i o n o f the barrier o f Wasaga Beach is related t o the Pleistocene glamal and post-glacial h i s t o r y o f the L a k e H u r o n basin. During t h e glamatlons, erosion p r o d u c t s o f Palaeozoic r o c k s were m i x e d with m m o r a m o u n t s o f P r e c a m b r l a n material t r a n s p o r t e d f r o m the n o r t h e r n shield, and were r e d i s t r i b u t e d and d e p o s i t e d m till sheets. T h e tills and glacio-fluvial materials c o n s t i t u t e d the s o u r c e for s e d i m e n t s r e w o r k e d in the coastal lacustrine env i r o n m e n t s during post-glacial times. A p p r o x i m a t e l y 1 2 , 0 0 0 to 1 2 , 5 0 0 years ago, the glaciers r e t r e a t e d n o r t h w a r d f r o m their m a x i m u m advance, and the waters o f L a k e A l g o n q u i n i n u n d a t e d the Wasaga B e a c h - - L a k e Slmc o e L o w l a n d s and, at times, discharged eastward into the C h a m p l a i n Sea (Deane, 1 9 5 0 ; C h a p m a n and P u t n a m , 1 9 6 6 ; Lewis, 1 9 6 9 ; Prest 1970). In this r e e n t r a n c e , several till-islands persisted, and gravelly and sandy beaches

172

were formed around them. When the glacmrs retreated farther north, norLhern outlets were opened; the level of Lake Algonquin dropped to an all-ttme low and it was split in two, one portion (Lake Hough) m Georgian Bay, the, other (Lake Stanley) in the Huron Basin (Lewis, 1969) (Fig. 3). As the glacier retreated further to the north, strong differential isostatm rebound occurred and the level of water m the southern parts of the lakes started t~. rise toward the levels of Lake Nipissing (Fig. 3). Approxtmately 7000 years ago, m the last stages of transgressmn and m Early Nip~ssing times (Fig. 3) a gravel spit was built m the Wasaga Beach area and it enclosed a lagoon. During the p e n o d of nsmg lake levels, Lhe barn~ ~. grew by beach accretion and dune formation. The landward spreading of the windblown sand allowed the lagoon to keep pace with the rising lake levels. A progressive colonization of the sand by plants from the more sheltered lagoonal envtronment allowed the surface of the barner to grow upward above water level with the formation of backdunes and foredunes I McHar~, 1969). A Carbon-14 date from a peat layer found at the base of high parabolic dunes indicates that the predominantly subaqueous sedtmentatlon m the barrier termmated approximately 4600 years ago. After this time all southern outlets of Lake Nlplssing, except one that underwent conslderabh. erosion closed, and the lake level dropped relatively rapidly to the Algoma stage (F,g. 3). During this last event a large a m o u n t of sand was exposed tu wmd erosmn. This, combined with dry conditions that were present in thenorthern hemisphere around 2600 B.P, (Reeves, 1968) and perhaps locm natural and man-made forest ftres, led to modffmation and deflatmn ol existent or newly built transverse dunes and to the formation and the 1,~ goonward migration of the high parabohc dunes that cap the barner complex 12

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TABLE I Depositional model of the lacustrine barrmr system of Wasaga Beach (sed~mentc source material)

GEOMORPHOLOGIC

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LIGHT GRAY GRAY MINOR GRAY TO B R O W N I S H G R A Y D A R K G R A Y L E N S E S FINE TO MEDIUM SANO I F~E SANOTO COARSE I MEOIUM SAND TO COARSE SORTINGPEBBLES

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177

(Martim, 1974). After that time, the climate became more humid; the dunes became fully stabilized by vegetation; and, although some m o v e m e n t of sand has occurred, the geomorphological subdivisions of the system, and the several beach ridges formed in the northwestern part have been retained {Fig. 2). In the last 50 years, a higher rate of remobilization of sand has modified parts of the high dunes, because of indiscriminate logging and an increase m recreational activities that tend to destroy the protective vegetation cover (Martini, 1974). SEDIMENTOLOGICAL MODEL

A descriptive-analogue model (Buttner, 1972) of the barrmr system has been built (Table I, Fig. 4), and some aspects of three most important subenvironments, lagoon, beach, and dune, are analysed in some detail.

Lagoon The lagoon or bay environment of this system can be recogmzed either where it is geomorphologically defined by a plane surrounded by highlands, or where it is defined by typical sediments exposed in outcrops along the Nottawasaga R]ver. The plane, that is exposed in the southeastern part of the system, is b o u n d e d on one side by the high dunes of the barrier and on the other by sandy and gravelly beaches of the older Algonquin Lake and by till (Fig. 2). A typical surficial sequence of this plane consists of coarse, mmarich sand with lenses of peat, overlain by silty, sandy and calcareous clays, in

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178 turn overlain by black organic soil (Fig. 5A). The clay layer is referred to as " m a r l " because it consists of calcareous, whitish to light-gray clay. It is highly fossiliferous, predominantly with mollusks and disseminated plant fragments. The lagoonal fill changes m facies in different parts of the plane. In areas close to the high dunes, the marl is overlam by fine, well-sorted windblown sand. Near the Nottawasaga River the ancient sediments have been eroded and a sandy flood plane is now bemg formed. In the northeastern area, a small swampy lake (Marl Lake) represents a vestige of the old lagoonal environment (Figs. 2, 5C). There, plant matter and calcareous ooze are being actively deposited. To the southeast, shoreline sands were deposited over till. This lateral variation in sedimentary facms is duplicated, and is perhaps, better illustrated in vertmal sections where several lagoonal sequences are interstratlfmd with beach, spillover delta and dune sediments (Fig. 4A). In the southwestern sections, a lower lagoonal sequence overlies sand and/or gravel beaches. In several Instances, the lowermost lagoonal unit is a lensitic dense peat layer that contains logs and transported wood fragments (Fig. 5B). Occasionally these logs are found m channel-like fills. A few shells and fragments of beetles are also found. Marl layers overlie, with sharp contacts, the peats or the sandy gravelly beaches. The lower few centimeters of the marls often assume a reddish tinge due to deposition of Iron oxide which is introduced through capillary action from the underlying peats or more porous, water-saturated beach layers. Above this lower horizon, the main body of the marl shows regular laminae (not always well defined) and rich faunal assemblages (Fig. 5D). Farrand and Miller (1968) reported that the mollusk-fauna consists of 22 specms, representing 14 genera. Except for a few allochthonous specunens, the species represent a relatively silt-free, permanent, quiet-water, lacustrine environment, where, locally, soft calcareous ooze was deposited. The sheltered character of the Nipissing lagoon at Wasaga Beach is further demonstrated by the finding of the total species population of the lagoon (except for Sphaerlum lacustre and Pzs~d~um ferrugmeum) m Georgian Bay at the present time. The two missing specms can be found in small lakes surrounding Georgian Bay. Frequently, a gradatlonal lithological change occurs toward the top of the marls. The layers become less calcareous and become slltier and sandier. The gradation continues upward with lnterstratifmations of mica-rich sands and clays that are fossiliferous in the lower horizons and progressively less fossiliferous upwards. Sometimes these interstratifications are highly irregular and contam thin, calcareous, clay drapes on wavy sand surfaces. The interstratifications achieve regular alternations in several instances (Fig. 5E), and although this rhythmic deposition resembles proximal varves and/or shallow-water turbidites, it is believed that the coarser layers of these couplets have been deposited during storms, breaks of the barrier and formation of spillover deltas. The finer clayish layers represent the regular deposltmn of the lagoon, where clays were transported m by ancestral rivers and mLxed

179

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180 with allochemmal material generated in the lagoon itself. These typical sequences are interstratified and capped m the southwest by sandy beaches and dunes. In these sands occasional small amounts of organic matter are found that could have been deposited in dune lakes or in swales of beach ridges (B~rd, 1969). In some southeastern areas, a basal marl layer has been capped by a cyclic sandy sequence that has been ascribed to materials derived from washover fans. These small cycles are characterized by ripple-bedded and cross-bedded sands and silts that can be subdivided into two alternating components. One is characterized by a brownish, medium-grained quartzose sand that is relatively rich in heavy mmerals and it has an average thickness withm each cycle of 5 cm. The second is constituted of a gray, medmm- to fine-grained silty sand that reaches an average thickness of 1 cm (Fig. 5F).

Beach In the Wasaga Beach area, there are several raised beaches that were formed along the coasts of Lake Algonquin, Lake Nipissing and more recent lakes. The beaches appear to record three stages of evolution of a beach system. The earliest stage is characterized by poorly sorted, sandy-gravelly beaches that have traits intermediate between fluviatile and nearshore sediments. The middle stage consists of sand and gravel beaches, fairly well sorted, with interlayers of well-sorted sand and shmgles. The last t y p e is a well-sorted sand deposit with few pebbles and occasional fossiliferous layers. The frequency of occurrence of these deposits is related to the energy levels of the environments, to the availability of sedimentary types and to the distance from primary till or glacio-fluvial sources. Accordingly, a trend exists from older and more poorly sorted Algonquin beaches in the southeast (Fig. 2) to Niplssing sorted sand and gravel beaches in the main body of the barrier system, to well-sorted Algoma and more recent sand beaches.

Poorly sorted beaches. The poorly sorted sandy, gravelly beaches of Lake Algonquin consitute a northern and eastern boundary of the Nipissing lagoon of the Wasaga Beach System. They were formed along the coasts of a shallow reentrance where normal periods of low energy alternated with occasional storms. Tills and glacio-fluvial sediments making up the coasts were the source of the beach material. The peculiar characters of these deposits resulted from the combination of a nearby source for the sediments, inability of the lacustrine environment to rework sediments effectively, and the relatively short time during which the level of the lake water remained at one elevation. Resultant characteristics were accretionary beds that dip 25--30 ° lakeward (Fig. 6B) and generally poor sorting, with only the clay and silt fraction having been removed. Most of the pebbles are composed of limestone. They are rounded, and very often subspherical in shape, i.e. they have not been flattened by prolonged beach processes.

1S1 Lateral and vertical facies changes occur. The major change relates to the fact that the higher beaches, f o r m e d at higher water stages of the lake, tend to be coarser than the topographically lower and y o u n g e r beaches that were f o r m e d at lower water levels. This t r e nd m c o m m o n m m a n y regressive beach sequences of Quaternary lakes in Ontario and relates to two major causes. The first one is that m m a n y cases the materials f o r m m g the y o u n g e r and topographically lower beaches derive p r e d o m i n a n t l y from rew orkm g of older beaches and dunes, rather than directly from tills and glaclo-fluvlal sedlments. The second reason, partmularly for beaches form ed m bays or along large spillways, is t hat the older and higher beaches were f o r m e d when the water m the restricted basins was deeper; thus, during storms the waves could exert higher energy u p o n the shore, rather than being dissipated by frictmn along shallow, extenmve and sheltered b o t t o m s of lower lakes. Supemmposed on the overall regressive trend are ot her features t hat consmt o f macrocycles of deposition related to storms, and smaller cycles related to sorting processes acting during fmr-weather conditions. Although these variatmns are n o t as well defined m the p o o r l y sorted beaches as in the better sorted sandy gravelly beaches, the storm macrocycles are characterlzed by coarse gravel lenses, occasionally with o p e n w o r k t ext ures that grade downwards and laterally along a c c r e t m n a r y beds to sandy gravel and to gravelly sand (Fig. 6B). Of the minor cycles, the best developed ones appear m the gravelly sands and consmt of sets of small- to intermediate-scale crossbeds piled on top of each other and subdivided by erosional surfaces and/ or plane-bedded layers (Fig. 6A). The thmkness of the smaller cycles varies widely, with modal values of 5--16 cm. As a possible genetic m t e r p r e t a h o n , it is suggested that these cross-bedded layers were deposited very rapidly under an tuner rough zone of the beach (Clifton et al.. 1971). The plane beds or erosmnal surfaces m a y record shifting to the tuner or outer planar facms (Chfton et al., 1971).

Well-sorted sand and pebble beaches. Along the coasts of Lake H uron and Georgian Bay, several Algonquin and Nlpissmg beaches which were f o r m e d on spits facing major lakes, show fair to good sorting. The carbonate pebbles have fiat shingle shapes, partly due to the original flat bedding of the Paleozolc carbonates from which t hey demve, and partly due to actwe abrasion m the shore environment. The lower and older part of the barrier system of Wasaga Beach contains several well-developed deposits of this t ype t hat were f o r m e d during Early Nlpissmg times. Many different sed~menta~ faczes are f o u n d in these deposits. A wellsorted sand facms is usually f ound in lensitm remnants (Figs. 6C,F). The sand is c on s titu ted of subangular quartz and feldspar with heavy minerals concentrated m laminae. In a few layers, retained as erosional lenses among coarse gravels, the sand is m a de up of 95% h e m a t i t e and ot her heavy minerals. Regular alternation m a y occur with a thin, quartz-inch, free-grained, light-gray layer sandwiched be t w een two dark, heavy-mineral-rich beds (Fig. 6C). The

182

C

183 dark layers are characterized by plane lamination; the light layer by smalland medmm-scale cross-beds. The indication of lower flow regime conditions, finer average size but similar grain-size distribution suggest that both the dark and light layers are beach deposits and the cyclicity is due to a shift of the environment from the swash and backwash zone for the heavy-mmeral-rmh layers to an inner rough zone for the lighter layer (Clifton et al., 1971). A similar indication of this t y p e of shift of the environment of deposition is present in other, compositionally uniform sand layers where ripple laminae alternate with plane-beds. A gravelly sandy facies is characterized by fairly well-sorted, coarse to medium sand with few disseminated pebbles. Irregular alternation of sand and sandy gravels exists as well (Fig. 6D). The pebbles tend to be rod-shaped or subspherical, while a few, usually those that are intermediate in sLze, achmve a flat disc shape. Inclined lamination constitutes the predominant sed~nentary structure. Locally, a few ripples, and a few scour and fills are recogmzable. The exposed thickness of this type of layer ranges up to 70 cm. This facies may be considered to record a sandy zone that has trapped larger pebbles in a foreshore environment. A third facms is characterized by a pebble framework with an infiltrated matrix of sand and small pebbles. This facies can be subdivided into three sub-facms on the basis of pebble size. One sub-facies has the principal modal class in the free gravel range. Few large pebbles are present and they are well oriented parallel to the depositional surfaces. Sand is the mfiltrated m a m x of these layers. A second sub-facies is similar to the previous one, but the principal modal class has shifted to medium-sized pebbles and granules (free pebbles) from the matrLx. A final sub-facies, whmh is very distractive, is comprised of a coarse pebble framework with infiltrated sand and small gravel (Fig. 6E). These layers can be formed in the lower part of a gravelly beach, just below the water line ( " o u t e r frame zone", Bluck, 1967; "tuner rough", Clifton et al., 1971), or in the lower portion of the upper storm beach whmh contains large discs and where the sand and free gravel constitute a "sieve deposit" (Bluck, 1967). A last facms which ~s present in these types of beach is made up of openwork gravel layers and lenses that can be further classified on the bas~s of size and sorting of pebbles. Thin lensitlc layers of well-sorted, round, subsphermal pebbles to granules constitute the first sub-facies (Figs. 7D,E). In modern analogues of sandy gravel beaches, it has been observed forming m the swash zone m small ridges or thin lensltm beds during fair-weather conditions and during falling stages of storms. At tm~es, a similar sub-facms is made up of small discs that show well-developed imbrication (Fig. 6G). A second sub-facies is characterized by lenses of fairly well sorted, free to medium gravel, which are usually associated with and surrounded by coarser gravels that may or may n o t have a sand matrix. This t y p e of openwork gravel lens probably is formed in low-pressure areas behind obstructions, during the building up or reworkmg of the storm beaches, or it may repre-

184 sent material rafted up from the f o o t of the beach by ice as it is observed happening along the recent coasts of Lake Huron. The coarser sub-facms o f the o p e n w o r k gravels is f o r m e d durmg storms and is characterized by medram to coarse pebbles that, when t h e y are dmcoldal m shape, show welldeveloped imbrication (Fig. 6H). Several types o f faczes-sequences charactemze the sorted beaches. The storm cycles are well developed and t he y are similar to those dmcussed for the poorly sorted Algonquin beaches. However, some different processes resulting m different facies and vertmal and lateral variations, have been acnve m the sorted beaches. The coarsening-upward storm cycles have been formed both by the piling up of shingles, as well as through the staving effect that these have on freer materials (Fig. 7A). That m, sand that may have been transported up during storms, is flowing through the large pores among the shingles and is deposited m lower layers of tile beach (Bluck, 1967). Consequently, the modal or average SLZe of the beach sequence tends to increase upwards, although the coarsest pebbles are not necessarily at the top. In rare, particularly favourable outcrops, that cut the old beaches transversely, it is possible to observe that the coarse sand and gravel facies {"refill z o n e " , Bluck, 1967) grades upward into gravelly sands ("sand r u n " ) and thin grades upward into progressively coarser layers 0 m b n c a t e d and/ or large disc zone) (Bluck, 1967) (Fig. 7C). Thin double-ended textural trend, when preserved, is difficult to recogmze and normally the interpretation is made of r h y t h m i c deposition due to different storms that toward the upper part of the beach may create a well-defined alternation of coarse and free layers (F~g. 7B). Typmal of these sorted beaches are num erous examples of small-scale cycles that have been f or m ed as a response to changing energy conditions m the envLronment and they have been superimposed within the larger facms sequences of the beaches. Coarsening-upward minor cycles are c o m m o n (Fig. 7D). Small-scale inverse grading m beach laminae has been observed by Sanders (1965) and studmd m detail by Clifton (1969). Essentially, the reverse sorting is achmved during the backwash period of waves. The thin heavy-mineral rich layers are deposited first and the coarser sand grams are deposited last from a c o n c e n t r a t e d partmle--flmd m i xt ure {Chfton, 1969). These features are c o m m o n l y f or m e d m sandy beaches and are preserved m fossil sedkrnents, however, they are not easily recogmzable. Other types of coarsening-upward cycles, with occasmnal coarse--fine--coarse cychc~ty, relate more to the size--shape sorting that occurs during deposition under faroweather conditions, during storm c o n d m o n s (Bluck, 19671 or during falhng storm stages when the storm beach undergoes reworkmg. In these types of layer, the flatter a nd/ or coarser pebbles remain ent rapped at the top of the swash zone because of the asymmetrical energ2¢ dmtnbut~on of the swash and backwash of waves and the lntergranular flow that, at time, may constitute a large c o m p o n e n t of the backwash. Fining-upward cycles are also found; d e p e n d m g u p o n the t y p e of sedl-

185

Fig. 7 Sedimentary features of gravel beaches. A. Various types of coarsening-upward sequences. B. Various types of rhythmic deposition in gravel beaches. C. Coarsemngupward and possibly coarse-fine-coarse cycle in beach. D. Coarsening-upward, openwork granule to fine pebble layer. E. Fining-upward, openwork granule to medmm-slzed pebble layer F. Burred berm showing backslope beds, free-grained, lensltm backfill layers and coarser boulders at the top of the berm. G. Close-up mew of lakeside part of buried berm showing regular, lakeward (to the right) dipping accretlonary beds and backslope beds dipping toward lagoon to the left.

186 ment and energy available m the beach, it is found that finer and more pivotable pebbles tend to accumulate at the top of the swash zone, forming lensitic layers of openwork granules (Fig. 7E). Seldom occurring, but important for the interpretation of ancient environments, are structures such as buried berms, that are preserved as isolated mounds showing internal medium scale cross-beds dipping both lakeward (foreslope beds) and landward (backslope beds) (Fig. 7F,G; Jennmgs and Coventry, 1973). In rare Instances, the filling of the trough behind the berm is preserved, and a continuous lateral varmtlon is present from the low-energy free silt and clay layers of the backfilling, changing to the high-energy coarse gravel at the top of the berm, changing to a fmmg-downward sequence along the lakewards-dlppmg beds (Fig. 7F,G). In other beaches, m m o r bars or gravelly sandy cross-beds are mterstratified with normal accretionary beds (Fig. 8A). Occasmnally, channels filled with coarse gravel and infiltrated sand are preserved (Figs. 8B, 4B). Sand beaches. The sedimentary charactenstms of sand beaches are well known (McKee, 1957; Andrews and Van der Lingen, 1969). Essentially, they consist of well-sorted sand with local concentrations of heavy minerals and micas m thin laminae, occasional shell layers, lensitm, mchned bedding, plane lamination, ripple marks and occasional medium-scale cross-bedding. When sandy beaches grade into the gravelly beaches, some disseminated pebbles can be found m them. This character is often useful for dlstmgmshmg m the field between beaches and foredune deposits. All recent and ancmnt sandy beaches of the barrmr system of Wasaga Beach contain most of these charactensUcs, but, a distinction can be made between two types of sequences which vary m their frequency of occurrence through time and geographic location. Older beaches located m the southeastern region are characterized by well-defined patterns of sedimentation with well-developed ripple-drift cross-lammaUon alternating with plane beds. This pattern IS considered to indicate a continuous and rapid supply of sand to a changing environment of deposition (Fig. 8C, right) (Walker, 1963; Sanders, 1965; MacKee, 1965; Coleman and Gaghano, 1965}. In the younger beaches, the ripple-bedded c o m p o n e n t of the cycle decreases markedly, and m time, it disappears (Fig. 8C, left). A second characterlstm that distinguishes between older and younger beaches is that, m the younger ones, a few shell beds and occasionally small amounts of organic, peaty material are preserved (Fig. 8C, left). Dunes

The Quaternary beaches at Wasaga are capped or are mterstratlfmd with sand dunes (Fig. 4, Table I). The transition between the two sedtments is gradatlonal, but they can be differentiated by the freer texture and better sorting of the wind-blown sand (Table I), by the large-scale cross-beds of the dunes, with steep dips and variable azimuths, and the occasional pebbles

187

Pi

Fig. 8. Sedimentary features of beaches and dunes. A. Cross-beds dipping lakeward (to the left) m the same direction of inclined accretionary beds. B. Small channel cut into a beach and filled with gravel and infiltrated sand. C. Sandy beaches: left photo shows plane-laminated, accretionary beds with frequent erosional surfaces and one lenmtic shelllayer, right one shows rhythmic alternation of thin plane beds and thicker ripple-bedded layers. D. Areal view of part of the barrier system with storm sandy beaches capped by parallel dunes to the right; transition to high transverse dunes with deflation basins, to high parabolic dunes, and to flat lagoonal plane to the left. E. Large-scale cross-stratification in high parabolic dunes. F. Variable direction of inclinations of cross-strata of transverse dunes. G. Minor slumps outlines by concentrations of dark minerals, m forests of parabolic dunes.

188 found m beaches. Essentially, two malor types of dunes can be recogmzed m this area, locally separated by deflation basms: transverse and parabolic dunes. They can be distinguished by thetr geomorphological expression and/or by the larger scale of the structures of the parabolic dunes (Fig. 8D,E,F). Parallel dunes (small transverse dunes) are exposed m the northwest side of the barner system, where they cap raised beaches and form regular geomorphological trends parallel to the coast (Figs. 2, 8D). Internal structures of these dunes tend to be obhterated by roots and other soil-forming processes. Where preserved, they are comprised of medmm-scale cross-beds defined by weak concentrations of heavy minerals m some laminae. To the southeast, the parallel dune zone grades into mtermedmte-helght transversal dunes and high parabohc dunes (Figs. 2, 8D). In these higher dunes, numerous old or new small-scale blowouts modify the surface of the land. The internal structures of these dunes consist essentially of 13rge co very large scale, mchned, accretlonary beds that record the downwind advance of the preclpitatmn ridges (Figs. 8E,F). Minor deformatmnal structures from avalanching can occasionally be recogmzed (Fig. 8G). CONCLUSION Carbon-14 dates of orgamc layers mterstratihed with sands of the lagoon, beach and dunes, have established that the lacustrme barner of Wasaga Beach was already in existence approximately 6800 years ago, and it g~rew by beach, lagoon, washover fan, and dune accretion until approximately 4600 years B.P. The bulk of high parabohc dunes was formed between 3700 to 2000 years B.P. and the raised beaches--parallel dune zone continued its formation from that time when the water level started to drop from t~he Algoma levels to the recent strandline of Lake Huron. The analysis of the lateral and vertmal successions of textures and sedimentary structures at Wasaga Beach have resulted m a sedtrnentelogmal model of a lacustrine sandy and gravelly barrier complex that is suffmlently mmilar m its Holocene history to other systems and it has been presented m a sufficmntly general way to constitute an alternative to well-known marine sandy type models (Fig. 4, Table I). Coarse material is present at Wasaga Beach where the growth of the barrier started with a gravelly spit and ended with sand dunes giving an overall fining-upward sequence (Fig. 4). Internally, coarsening-upward cycles, finmg-upward cycles and coarse--free--coarse cycles have been found superimposed and/or juxtaposed on eoch other m ancient storm and farr-weather, well-sorted, gravelly and sandy beaches. Cycles characterized by alternatmns of cross-beds and plane beds and/or erosional surfaces characterme both the oldest, poorly sorted, gravelly sand beaches of the area as well as the youngest beaches formed exclumvely of sand. These cycles are related to shifting strandlines and/or energy levels of the beach area, combined w~th a readily available, but varmble source of

189

sediments. In younger beaches or in areas where the rate of sedimentation was lower and the depth of reworkmg of sediments was deeper, the sand layers tend to lose the ripple features and become more uniformly laminated. ACKNOWLEDGMENT

I wish to thank R.I. Yurlck, B. Carlisle and B. Day for having introduced me to Wasaga Beach and its many problems, and J. Sanders for critical comments. Carbon-14 age determinations were made at the laboratory of Brock University, St. Catharines, Ontario. Financial support was provided by the National Research Council of Canada, Grant No. A-7371, and by the Ontario Ministry of Natural Resources. REFERENCES A n d r e w s , P.B., 1 9 7 0 . Facms a n d Genesis o f a H u r r m a n e Washover F a n , St. J o s e p h Island, Central Texas Coast. B u r e a u of E c o n o m i c Geology, T h e U n i v e r s i t y of Texas, A u s t i n , Texas, R e p o r t o f I n v e s t i g a t i o n s No. 67 147 pp. A n d r e w s , P.B. a n d V a n der L m g e n , G.J., 1 9 6 9 E n v i r o n m e n t a l l y s i g m f i c a n t c h a r a c t e r l s t m s of b e a c h sands. N . Z . J . Geol. G e o p h y s . , 12 1 1 9 - - 1 3 7 Bird, E.C.F., 1 9 6 9 . Coasts. M.I.T. Press, C a m b r i d g e , Mass., 2 4 6 pp. Bluck, B.J., 1 9 6 7 . S e d i m e n t a t i o n of b e a c h gravels e x a m p l e s f r o m s o u t h Wales J Sedim e n t Petrol., 37 1 2 8 - - 1 5 6 B u t t n e r , P J., 1 9 7 2 . S y s t e m s analysis a n d m o d e l b u d d i n g . In P F e n n e r ( E d i t o r ) , Quantitative G e o l o g y Geol Soc Am., Spec Pap , 146. p. 69 C h a p m a n , L J. a n d P u t n a m , D.F , 1966. T h e P h y s i o g r a p h y of S o u t h e r n O n t a r i o . University of T o r o n t o Press, T o r o n t o , O n t , 3 8 6 pp C h f t o n , H.G., 1 9 6 9 . B e a c h l a m i n a t i o n n a t u r e a n d origin Mar. Geol., 7. 5 5 3 - - 5 5 9 . C h f t o n , H.G., H u n t e r , R.E. a n d Phllhpps, R.L., 1971. D e p o s i t i o n s t r u c t u r e s a n d processes in the n o n - b a r r e d h i g h - e n e r g y n e a r s h o r e . J. S e d i m e n t . P e t r o l , 41 6 5 1 - - 6 7 0 . C o l e m a n , J.M. a n d G a g h a n o , S.M , 1 9 6 5 . S e d i m e n t a r y s t r u c t u r e s - - Mississippi River Deltam Plato In G.V. M l d d l e t o n ( E d i t o r ) , P r i m a r y S e d i m e n t a r y S t r u c t u r e s a n d t h e i r H y d r o d y n a m i c I n t e r p r e t a t i o n . Soc. Econ. P a l e o n t o l Mineral. Spec. P u b l , 12 p. 133 Davies, D . K , E t h r l d g e , F.G. a n d Berg, R R., 1 9 7 1 . R e c o g m t l o n of b a r r i e r e n v i r o n m e n t s Am. Assoc Pet. Geol. Bull., 55 5 5 0 - - 5 6 5 Deane, R.E , 1950. P l e i s t o c e n e geology o f the Lake S l m c o e District, O n t a r i o Geol Surv Can , M e m o 256 D i c k i n s o n , K A., Berryhill, H L. a n d Holmes, C W , 1 9 7 2 Criteria for r e c o g m z m g a n c i e n t barrier coastlines. In J . K R l g b y a n d W.H. H a m b h n (Editors), R e c o g n i t i o n of A n c i e n t S e d i m e n t a r y E n v i r o n m e n t s Soc E c o n P a l e o n t o l Mineral Spec P u b l , 16 p 192 D o b k l n s , J E. a n d Folk, R L., 1 9 7 0 S h a p e d e v e l o p m e n t o n T a h i t l - N m J S e d i m e n t Petrol,40 1167--1203 F a r r a n d , W.R. a n d Miller, B . B , 1 9 6 8 R a d i o c a r b o n dates a n d d e p o s l t l o n a l e n v i r o n m e n t o f the Wasaga Beach ( O n t a r i o ) marl d e p o s i t Ohio J Scl , ,68 2 3 5 - - 2 3 9 J e n n l n g s , J N. a n d C o v e n t r y , R J., 1 9 7 3 . S t r u c t u r e a n d t e x t u r e of a gravelly b a r r i e r Island in the F i t z r o y estuary, W e s t e r n Australia, a n d t h e role of m a n g r o v e s in t h e s h o r e d y n a m i c s . Mar Geol., 15 1 4 5 - - 1 6 7 . King, C.A.M , 1972. Beaches a n d Coasts. E. A r n o l d , L o n d o n , 570 p p Le Blanc, R J , 1972. G e o m e t r y of s a n d s t o n e reservoir bodies. A m . Assoc Pet. Geol M e r e . , 1 8 p 133

190 Lewis, C.F.M., 1969 Late Quaternary history oi lake levels in the Huron and Erie basins In Proc. 12th Conf. of Great Lakes Resources. Great Lakes Res Dlv , University of Michigan, Ann Arbor, Mich., pp 250--270. Lewis, C.F.M, 1970. Recent uphft of Manitouhn Island, Ontario Can d Earth Sc~., 7 655--675 Mackee, E . D , 1965. Experiments on ripple lamination In G V Mlddleton (Editor), Primary Sedimentary Structures and Their Hydrodynamic Interpretation Soc Econ Paleontol Mineral Spec. Publ., 12 p 66 Martin1, LP., 1974. Wasaga Beach a Quaternary classic landscape, its geological h~tory and blologmal carrying capacity of the sand dunes In Quaternary Environments Geographmal Monograph 5, York University Serms, University of Toronto Press, Toronto, Ont., p 61 McHarg, I L., 1969. Design with Nature. American Museum of Natural History, The Natural History Press, New York, N . Y , 197 pp Mckee, E.D., 1957 Primary structures m some Recent sediments. Am P~ssoe Pet Geol Bull., 41 1704--1747 Prest, V.K , 1970. Quaternary geology of Canada In R.J.W. Douglas (E(htor), Geology and Economm Minerals of Canada. Can Geol Surv Eeon Geol. R e p , 1 p 677 Reeves, C.C., 1968. Introduction to Paleohmnology Elsewer, New York, N Y , 228 pp Sanders, J.E., 1965 Primary sedimentary structures formed by turbidity currents and related resedlmentatmn mechamsms In. G V Mlddleton (Editor), Primary Sedimentary Structures and their Hydrodynamm Interpretation Soc Econ Paleontol Mineral Spec Publ.,12: p 192. Stanley, G M , 1936 Lower Algonquin beaches of Penetangulshene Peninsula Geol Soc Am , 47. 1933--1959 Walker, R.G., 1963 Distinctive types of ripple-drift cross-lamination Sed~mentology, 2 173--188. Warme, J.E., 1971 Paleoecologlcal Aspects of a Modern Coastal Lagoon University of Cahforma Press, Los Angeles, C a h f , 110 pp.