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J. E. HOFFMEISTER Institute of Marine Science, University of Miami, Miami, Florida K. W. STOCKMAN H. G. MULTER College of Wooster, Wooster, Ohio

Miami Limestone of Florida and

Its Recent Bahamian Counterpart

Abstract: The Miami Oolite, named by Sanford deposits that are being actively produced in a near- (1909) for the oolitic limestone of Pleistocene age by area. Immediately east of Miami on the western which covers a large part of the southern tip of edge of the Great Bahama Bank, strung in a north- Florida, has been found to consist of two separate south line, are the islands of Bimini, Cat Cay, Sandy units—an upper unit, herein designated the oolitic Cay, etc., the region described by Newell and others facies, and a lower unit, called here the bryozoan (1959). East of the Cays and parallel to them, a facies. In this paper the two units are combined as large underwater mound of unstable oolite is form- the Miami Limestone,1 a formational name which ing, and east of the mound in the shallow lagoon, now seems more appropriate than the Miami Oolite. massive, tubular bryozoans (Schizoporella flondana The bryozoan facies, the dominant constituents of Osburn) are growing. The oolite from the mound is which are massive compound colonies of the cheilo- slowly encroaching over the bryozoan beds. The stome bryozoan Schizoporellaflondana Osburn sur- bathymetric and ecologic conditions now extant in rounded by ooids and pellets, covers the greater this area are probably similar to those which existed part of Dade County and extends in places into ad- during the Pleistocene to form the units of the joining counties—a total area of about 2000 square Miami Limestone. miles. It averages 10 feet in thickness in southeastern The eastern slope of the unstable oolite mound of Florida and thins to 1 foot or so westward to the the Cat Cay and Sandy Cay area is cut by tidal Gulf of Mexico. It is the surface rock of the southern channels which run normal to the direction of the Everglades and is one of the most extensive bryo- mound itself. Narrow valleys, similar to these chan- zoan limestones in the country. In southeastern nels, can be found in the indurated rock of the Florida it is covered by an elongated mound of cross- oolitic facies of the Atlantic Coastal Ridge. The bedded oolitic limestone, the upper unit or oolitic valleys probably had their origin as channels pro- facies. This is the rock of the southern end of the duced by tidal currents at the time the oolitic Atlantic Coastal Ridge, with a maximum thickness mound of the Ridge was in an unstable condition. It of 35 feet under the Ridge summit thinning west- is also believed that the shape and orientation of the ward toward the low-lying Everglades as it en- Lower Keys of Florida originated in a similar fashion. croaches over the bryozoan facies. Interest in the origin of the two units has been 1 The Miami Limestone refers to the formation which heightened recently by the recognition of similar has been called the Miami Oolite hy previous writers.

CONTENTS Introduction 176 Main events in the origin of the Miami Lime- Acknowledgments 178 stone 187 The upper unit or oolitic facies 178 The Miami Limestone of the Lower Florida The lower unit or bryozoan facies 180 Keys 188 The Bryozoa 180 References cited 189 Other constituents of the bryozoan facies . 182 Areal extent of the bryozoan facies 182 Figure Geographic distribution of bryozoans according 1. Main physiographic features and geology of the to zoarial growth forms 183 southern tip of Florida 177 Resume 183 2. Generalized east-west cross section of Miami Interpretation 183 Limestone, Florida 179 Oolitic deposits of northwestern part of the 3. Map showing transverse valleys or "glades" in Great Bahama Bank 183 the Atlantic Coastal Ridge 181 Comparison of Great Bahama Bank deposits 4. Map of southeastern Florida and northwestern with the Miami Limestone 185 section of the Great Bahama Bank . . . 184

Geological Society of America Bulletin, v. 78, p. 175-190, 5 figs., 6 pis., February 1967 175

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5. Geologic map of the Lower Keys of Florida 3. Pleistocene and Recent specimens of Schizo- composed of the oolitic facies of the Miami porella floridana Limestone 188 4. Illustrations of abundance of bryozoan colonies in bryozoan facies of Miami Limestone . . 5. Comparison of a colony of Schizoporella florid- Plate Following ana from the Miami Limestone of Florida 184 1. Types of oolitic rock of Miami Limestone, with one from the shelf lagoon of the Great Florida Bahama Bank 2, Multilaminate bryozoan colony of Schizoporella 184 6. Nine-lens aerial photograph of unstable oolite floridana Osburn ridge, Great Bahama Bank

surface of indurated rock although it is veneered INTRODUCTION in places by Pleistocene sands as far south as The large area of oolitic limestone of Pleisto- Miami. North of Boca Raton, which is 34 miles cene age which occupies the southern tip of the north of Miami near the border of Palm Beach Florida peninsula was named the Miami Oolite and B reward counties, the bedrock is the sandy by Sanford (1909, p. 211-214). It is the most limestone of the Anastasia Formation. South of prominent stratigraphic unit of southeastern Boca Raton and extending to the point where it Florida. Upon it are located the main cities of disappears southwest of Homestead, its surface the area, including Fort Lauderdale, metropoli- is the Miami Oolite. tan Miami, and Homestead. In addition, it un- The highest point on the Atlantic Coastal derlies the extensive area of the southern Ever- Ridge in the Miami Oolite section is about 24 glades. Sanford's original description, although feet in the Coconut Grove area of Miami. From brief, covers the essential points which could be the ridge, the land slopes eastward to the nearby discerned at that time. Later workers have con- Atlantic and westward more gently to the Ever- siderably increased our knowledge of the for- glades. The low, broad expanse of the Ever- mation in dealing with the region as a whole, glades is about 10 feet above sea level in south- but no careful study of the unit per se has ever ern Broward County and drops imperceptibly been made. southward to a 5-foot level in Dade and Monroe This paper calls attention to several impor- counties. This large, flat area with its cover of tant features of the rock which hitherto have muck, organic soils, and calcareous muds is un- not been reported. The writers have deter- derlain by the Miami Oolite. mined that the formation possesses two distinct The geologic map of southern Florida (Parker units. The purpose of the paper is to describe and others, 1955, PL 4) outlines the territory these units and outline the conditions under covered by the Miami Oolite. Figure 1 is a which they were formed. One rather unique as- somewhat modified version of the map. The pect of the study was the realization that similar chief difference is the inclusion of an area along rocks are now being formed in an area in the the southwest coast between Cape Sable and nearby Bahamas and that the conditions now Lostmans River. existing there must be nearly identical to those There are numerous outcrops of the forma- which prevailed in southern Florida during the tion, and the most prominent natural exposures late Pleistocene. are along the Atlantic Coastal Ridge. Probably The Miami Oolite is located in the southern the most famous of these is at Silver Bluff (Fig. part of the topographic division originally de- 1, between Stations 205 and 206) in Coconut scribed by Cooke (1939, p. 14) as the Coastal Grove, bordering Biscayne Bay, where a wave- Lowlands. Several subdivisions of this area were cut bench about 8 feet above mean sea level has later created by Parker and Cooke (1944, PL been cut in a cliff of the cross-bedded oolite. 8), and in these the oolite occupies large areas of Numerous canals and road burrows have been the Atlantic Coastal Ridge, the Everglades, the cut in all directions across the Everglades, es- Sandy Flats, the Coastal Marshes and Man- pecially along the eastern side. Many reach the grove Swamps, and a smaller section of the Big sea through the Coastal Ridge. The high spoil Cypress Swamp. banks lining the canals afford excellent oppor- The highest, and therefore the most promi- tunities to examine the bedrock to depths of 15 nent, subdivision, the Atlantic Coastal Ridge feet or more below sea level. In addition, nu- (Fig. 1), borders the Atlantic shore as a narrow merous quarries, some as much as 30 or 40 feet ridge with a smooth to slightly undulating sur- in depth, are scattered over the terrain. Even in face. For most of its length this ridge has a the undisturbed sections of the Everglades Na-

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tional Park many patches of bedrock appear a ans from the Florida coasts for comparative few inches above the soil. Only in the mangrove purposes. Among the many persons with whom swamp sections of the south and southwestern the writers held fruitful discussions and who, in shores are outcrops difficult to locate, but even some cases, reviewed the paper critically were here bedrock can be discovered at depths of 3 Drs. Helen Duncan, Harry S. Ladd, Cesare feet or so below low tide in some of the many Emiliani, James I. Jones, F. W. Meyer, R. J. small creeks which drain the glades. Dunham, Harbans Puri, William S. Hoffmeis- Examination of the Miami Oolite of the ter, and John Milliman. Coastal Ridge in the Miami area shows that it is made of two rather distinct units. An upper THE UPPER UNIT OR part includes the typical, locally well-known OOLITIC FACIES cross-bedded oolitic rock such as that exposed at This part of the formation is confined largely Silver Bluff. Here it has a maximum thickness to the Coastal Ridge although it extends as a of 34 feet, and its base reaches to about 10 feet thin sheet several miles westward into the below sea level. Beneath it lies a unit, about 10 Everglades (Figs. 1 and 2). It is evident that it feet thick, which contains large numbers of has been greatly modified by solution. In many massive tubular bryozoans in an oolitic and pel- places, it is indented by small circular sink holes letoidal matrix. Although both units are oolitic, which lead to numerous channel-ways of ir- they are sufficiently different to be considered regular shape and varying size. as separate facies of one formation. Accordingly Where it is exposed along canal cuts and in the upper unit has been designated the oolitic quarries in the Coastal Ridge the oolitic facies facies and the lower unit the bryozoan facies. exhibits an intricately cross-bedded structure Together they are here referred to as the Miami (PI. 1, fig. 1). The beds may dip as much as 30 Limestone, a name which now seems more ap- degrees and strike in all directions. Groups of propriate than the Miami Oolite of Sanford. dipping beds are commonly separated from each other by thin, nearly horizontal layers about 1 ACKNOWLEDGMENTS inch thick characterized by small mollusk The writers gratefully acknowledge their in- shells, Halimeda, and a few bryozoans. The debtedness to the National Science Foundation mollusks which seem to be the most numerous for making possible their studies on the Florida are Transennella stimpsoni Dall, Chione cancel- Coral Reef Tract. In addition, they have re- lata (Linne), Columbella mercatoria (Linne), ceived aid from many specialists. They particu- and Thericium sp. The bryozoan is Schizoporella larly wish to thank Dr. Alan Cheetham of Loui- floridana Osburn. All are shallow-water types. siana State University who spent some time Soon after exposure the rock becomes surface- with them in the field and who studied speci- hardened, and directly below the hardened mens of bryozoans from a large area. Drs. B. F. layer the material is softer, more friable, and the Howell of Princeton University and Olga Hart- ooids and other particles can be separated by man of the University of Southern California the fingers. Except for the surface the rock is and Mr. Kenneth Ebbs, Jr., of the Institute of poorly cemented down to the water table. It is Marine Science were especially helpful in ex- so highly permeable that there is practically no amination of fossil worm tubes. Dr. Axel runoff and no standing water even immediately Olsson aided greatly in examination of the bry- after heavy rains. ozoan facies and in identifying fossil mollusks. The chief constituent particles of the oolitic Drs. Norman Newell and John Imbrie of the facies are ooids, pellets, and skeletal sand. In American Museum of Natural History and Dr. this paper, the term "pellet" follows the usage E. G. Purdy of the Esso Production Research of Newell and others (1959, p. 220): it refers to Laboratory were generous in their aid and en- grains which are ellipsoidal in shape and carries couragement in the comparison of the Bahama no implication of origin. A rough examination area with its Florida counterpart. The writers indicates that ooids (concentrically laminated are most grateful to Dr. Robert Ginsburg of spherical to subspherical grains) are by far the The Johns Hopkins University for his many dominant constituent of the Atlantic Coastal suggestions which improved the paper. Messrs. Ridge. West and northwest of the Ridge sum- Terry Thomas, John A. Jones, Durbin Tabb, mit, on the sides which slope toward the Ever- Robert Work, Wayne Bock, and Dr. Donald glades, and extending to the border of the fa- Moore of the Institute of Marine Science were cies, ooids decrease to approximately 10 per tireless in their efforts to collect living bryozo- cent of the rock and varying amounts of pellets

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and skeletal material compose the remainder. By far the most comprehensive description of the rock is that by R. N. Ginsburg (1953, Ph.D. thesis, University of Chicago). He has shown that many aragonitic ooids and pellets have been entirely or partially replaced by calcite and that with depth these have become in- creasingly embedded in a matrix of crystalline calcite. In addition, in the lower levels, especial- OJ -C ly below the water table, the ooids and pellets have been completely dissolved away, leaving only spherical and ellipsoidal cavities in the calcitic cement which bound them together (PL 1, fig. 2). In other words, the rock has assumed an oomoldic condition. Ginsburg has demonstrated that the calcitic matrix is a postdepositional precipitation filling the empty interstices. The Coastal Ridge shows some interesting aspects concerning its structure and topography. There is a decided difference in the amount and intricacy of the cross-bedding in different 2 6 parts of the Ridge. Beneath the Ridge summit, which in general occupies the eastern side of the mound, the cross-bedding is distinct and decid- edly complicated. This can be seen in many places where the rock is exposed in small cliffs along the eastern or seaward slope, such as the Silver Bluff area of Coconut Grove (Fig. 1). It can also be seen along the sides of several canals which have been cut through the Ridge, especially the Coral Gables Canal at the southern end of Lejeune Road (Fig. 1, Station 205). Far- ther south along old Cutler Road, which follows the Ridge summit on its eastern side, there are many outcrops of cross-bedded oolite. There is a gradual change in the rock structure along the western side of the Ridge. Under- lying the gentle slope in this direction the cross- bedding at existing outcrops becomes less noticeable. The thin layers extend for long dis- I 5 tances without change in the direction of dip. Where observed, the low dip is in a western direction toward the Everglades. The low relief on the Ridge makes it difficult to observe topographic features or patterns. However, topographic maps bring out some interesting details. Figure 3, part of which is re- produced from map NG178 of the U. S. Geo- logical Survey, shows a number of narrow, flat- bottomed valleys which extend northwest- southeast and normal to the trend of the Ridge. These are no more than 4 or 5 feet lower than the bedrock divides which separate them. The valleys are filled to a depth of 4 or 5 feet with unconsolidated organic soil, marl, and quartz sand. Consequently, the depth of the valleys in

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the bedrock may be as much as 8 to 10 feet. The to observe the size and growth forms of the spe- U. S. Geological Survey quadrangle maps bring cies as well as the relative abundance of the out the details more clearly. specimens (PI. 4, fig. 1). These valleys are significant in the interpreta- It should be emphasized that this is not a tion of the origin of the Ridge. The origin of facies which contains bryozoans sufficiently nu- the valleys poses an interesting question. It is merous merely to make them the outstanding or doubtful that they were made by streams, as no dominant organism. This is a rock which is naturally running water occurs in the region, made largely of bryozoan zoaria. It has been for all the rain water immediately seeps under- estimated that bryozoans occupy at least 70 per ground into the porous oolite. The cause of this cent of the rock by volume in many places, and topographic pattern will be considered in more they are so numerous that some of the unfin- detail later in the paper. ished roads near canal banks are paved largely Westward from the Coastal Ridge the rock of with their fragments. Along some of the canals the upper unit thins as it extends into the low- of the eastern Everglades, where the rock is lying Everglades (see Fig. 2). Over most of the close to the surface, spoil banks 4 and 5 feet eastern half of the Everglades National Park it high, made chiefly of bryozoans, can be traced is only 1 foot or more in thickness; farther west for 2 or more miles. The relative abundance of it disappears entirely. bryozoans in the facies can best be seen from large boulders dredged from canals. Some of THE LOWER UNIT OR these, which measure 3 by 4 feet, are estimated BRYOZOAN FACIES to contain from 60 to 80 per cent of bryozoans by volume (PI. 4, fig. 2). The Bryozoa The colonies vary tremendously in shape but Beneath the upper unit of the Coastal Ridge seem to fall into two main growth forms. Speci- there is a rather unique rock layer which is mens of the more important group, from the about 10 feet thick. It consists of large numbers point of numbers and zoarial size, are rough, ir- of massive tubular cheilostome bryozoan com- regular masses with knobby projections. The pound colonies (PI. 2, fig. 1; PI. 5, fig. 1), many latter are subcylindrical and vary greatly in of which are 1 foot or more in diameter. These length (to a maximum of 2-3 inches) and thick- are mixed with ooids, pellets, and skeletal sand. ness (to as much as 2 inches). The ends are Most of the ooids and pellets have been dis- commonly flattened domes and many are bulb- solved away but the hard calcitic matrix which ous. Where the knobs are broken they reveal a enveloped them now forms a cellular or vesicu- central hollow tubelike interior which varies in lar structure. The material which surrounds the diameter from knob to knob and which tapers bryozoans is sufficiently fragile so that the in each knob from its base toward its end. The zoaria can commonly be easily separated from thickness of the knob depends on the number it and from each other. However, surfaces of the of laminae it possesses. In one specimen (PL 3, zoaria in most places are plastered by a layer of fig. 1), as many as 46 laminae could be seen in cellular calcite which adheres strongly to the cross section; this super-multilaminate type has colonies and therefore covers the minute struc- a diameter of \}/% inches. ture of the bryozoans. In many other places, the The zoaria of the second growth form are zoaria are free of this material and the anatomi- smaller than the first, commonly no more than cal structure is beautifully revealed (PI. 2, fig. 4-5 inches in their largest dimension. They also 2). are irregular in shape, with crooked branches The entire facies is below the ground-water emanating from a massive, bumpy surfaced level here, and is not exposed to view. Exami- base. The tubes have a tendency to flange out nation can be made only by core drilling and by near the top and thus produce wide, gaping study of rock material dredged from the many tube openings with irregular edges. In other canals which empty into Biscayne Bay. Be- words, instead of tapering with length to make cause the rock is relatively easily broken, coring a closed top, as in the first group, they grow out- produces only fragments of the original large ward near the top to increase the size of the in- bryozoan zoaria and recovery is far from satis- terior opening. There is also a smaller number of factory, dredging has broken the zoaria into laminar layers, commonly five or six as a maxi- smaller pieces. Spoil banks along the sides of the mum, so this is a more delicate form than the canals, however, afford an excellent opportunity first type mentioned. There has not been much

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Figure 3. Map showing transverse valleys or "glades" in the Atlantic Coastal Ridge. The valleys are comparable to the tidal channels of the unstable oolite ridge of the Bahama area (see PL 6).

mixing between the two types; each seems to be conditions remain intact but in most cases they more common in certain localities although not would have disintegrated. Even if they were no necessarily limited to these localities. longer present, the shape of the encrusting The shape of the zoaria generally depends zoaria would reveal their former presence. on the character of the encrusted organisms of The most plausible explanation for the shapes the substrate. Bryozoans of the Cheilostome and hollow tubes of the zoaria is that the bry- type encrust a wide variety of animals and ozoans formerly encrusted clumps of some type plants. Some common living examples in this of marine vegetation. In the shallow waters region are colonies of the green alga Halimeda, around the shores of the Keys and in places in gorgonian fronds, and various types of grasses, Florida Bay, excellent examples of bryozoan- especially Thalassia. Each of these produce encrusted Thalassia may be found. Figure 2 of zoaria which are rather distinct from each other Plate 3 shows a recent specimen of the same and which roughly simulate the form of the species as that found in the bryozoan fades en- encrusted material. crusting a Thalassia clump. It is believed that In practically all specimens of the fossil zo- most of the fossil zoaria were formed in a similar aria, the knobs and more elongated branches manner. The zoecia form layer after layer have hollow centers. The encrusted material around the grass blades or rhizomes. They do must have disappeared by decomposition. Ha- not, however, always extend only the length of limeda or any other calcareous organism would the branch, but may grow beyond it so that the still be preserved and could easily be identified. bryozoan knob is longer than the encrusted The hard axes of gorgonians might under some branch. In such cases the central hollow in the

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knob of a fossil specimen ends where the branch eastern end in the vicinity of Fort Lauderdale is ended. Beyond this, the laminae become closed hard to map because of the abundance of loose and encircle a center as growth continues. sand which tends to cover the rock. It is safe to say, however, that it extends as far north as Fort Other Constituents of the Bryozoan Fades Lauderdale. West of Fort Lauderdale, in the In addition to the bryozoans, calcareous Everglades, the north-central boundary of the worm tubes are numerous and in places com- formation is obscure. It has been traced to a prise as much as 10-20 per cent of the rock by point about 2 miles east of the intersection of volume. The tubes average about !}/£ mm in Dade, Broward, and Collier counties. How far diameter and are for the most part only slightly north it extrends into Broward County is not tortuous. They commonly lie parallel to each known, but this is probably near its northern other in tightly packed groups and may be as limit. Along its western side, it can be traced much as 3 cm long. Most have been broken into for over 10 miles west of the 40-mile bend of the smaller fragments 1 cm or less in length. Some, Tamiami Trail and thence to the southwest especially those isolated from the mass, are tor- where it reaches the Gulf of Mexico at a point tuous in form. The tubes possess sides which are about 10 miles south of Lostmans River. roughened by irregularly arranged minute pits The swampy, mangrove character of the Gulf of various shapes. Coast makes it very difficult to locate bedrock, Identification of the species is difficult be- but sufficient information has been obtained to cause of the absence of the living organisms. Dr. make it possible to approximate the boundary Olga Hartman (personal communication) has of the formation. It is not known whether it likened them to the filograne serpulid genus underlies all of Cape Sable, but Flamingo is one Salmacina but states that ". . . without pre- of the most prolific bryozoan localities. Here served specimens it is not possible to determine the surface layer is a hard, almost flinty tex- either the genus or species." Dr. B. F. Howell tured oolitic limestone which contains a few (personal communication) has recognized two bryozoans. This overlies the main bryozoan species of Serpula and one of Dodecaceria in layer which has been dredged from the shallow rock specimens from a different locality in the bank immediately off shore and piled in large bed, but has been unable to designate specific mounds preparatory for road building. By far names. the most important organism in these mounds There is no doubt that the worm tubes in the is the large knobby type bryozoan. bryozoan facies have been made by many spe- Eastward from Flamingo the mangrove shore cies. At the present time, it is safe to say only line of Florida Bay again makes mapping diffi- that most of them were produced by polychaetes cult. However, an east-west strip bordering and that serpulids seem to have been dominant. Florida Bay, about 5 miles wide, is probably Other recognizable lime-secretmg organisms composed of oolite and skeletal sand with very are few and far between. However, several few bryozoans present (Fig. 1). This type of poorly preserved specimens of a species of sediment is clearly exposed along canal banks Strombushave been observed (Pi. 4, fig. 2). which extend from the Aerojet site (Station As mentioned earlier, the grains of the facies 173) southeastward to the coast just east of are composed of ooids, pellets, and skeletal sand. Jewfish Creek. This is also true of the canal ex- Of these, pellets are the most important con- posure along U. S. 1 in the same direction. In stituent. A rough estimate indicates that be- addition, a core from a drill site at Jewfish neath the Atlantic Ridge the facies contains no Creek (no. 9) shows a paucity of bryozoans. more than about 15 per cent of ooids and larger This strip apparently does not seem to be under- amounts of pellets and skeletal material. South- lain by the typical bryozoan facies. It should east and south of the Ridge the ooids are very also be noted that a fair number of corals, es- scarce, the pellets comprise about 15 per cent of pecially branching Porites, are found in this the grains, and the skeletal material about 80 area. North of the 5-mile strip, bryozoans ap- per cent. West and north of the Ridge and be- pear in greater numbers. yond the cover of the oolitic facies the ooids are The entire eastern coast is underlain by the scarce and the pellet content varies from 25 to bryozoan facies upon which lies a cover of vary- 75 per cent of the indurated sand. ing thickness of the oolitic facies limestone, as determined by several core borings (Fig. 1, nos. Areal Extent of the Bryozoan Facies 6, 7, 10, 11, 12, and 13) and material from nu- Figures 1 and 2 show the approximate area merous canal dumps. It is believed that the underlain by the bryozoan facies. The north- area which lies within the borders just outlined

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is underlain by the bryozoan facies. Surface out- This ridge swings to the southwest and west at crops, canal and quarry dumps, and cores scat- its southern end and disappears about 22 miles tered over the territory confirm this. It is safe west of Homestead. to conclude that the facies covers an area of at (2) The eastern side of the Ridge is some- least 2000 square miles and that it is one of the what steeper than the western side which grades most extensive bryozoan limestones in the almost imperceptibly into the low level of the country. Everglades. (3) The gentle western slope is cut by a Geographic Distribution ofBryozoans number of narrow valleys which run normal to According to Zoarial Growth Forms the direction of the Ridge itself (Fig. 3). The There seems to be a definite relationship be- relief is very slight (average 4 feet) but they tween the major growth forms and their geo- can be clearly recognized on the contour quad- graphic location. The large knobby, super-mul- rangle maps of the area. tilaminar specimens are confined chiefly to the (4) West of the Ridge and occupying the eastern part of the facies. They border the east- entire remainder of the southern tip of the pen- ern coast line and underlie the oolitic facies of insula is the low, flat country of the Everglades the Coastal Ridge. They also extend west and bordered by the coastal swamps of the Gulf and northwest of the Ridge for at least 10-15 miles the Bay of Florida. into the Everglades, and are also found in the (5) The rocks of the Coastal Ridge are com- Flamingo section of Cape Sable. From these posed of oolite. They are intricately cross- areas the colonies become smaller and are gradu- bedded on the crest and eastern side. On the ally replaced by the type with short, thin walls western side the oolitic layers are less cross- and wide-open funnel-shaped ends. This is the bedded, with beds dipping gently away from main growth form of the greater part of the the Ridge crest in the direction of the Ever- Everglades. glades. A thin-walled variety which has long, twist- (6) The maximum thickness of the oolite ing, anastomosing branches is found in a few (oolitic facies) beneath the Ridge crest is about places around the periphery of the areas with 34 feet, the lower 10 of which are beneath sea thick, knobby forms. Examples are found along level. the south border (Station 173) and the north (7) Beneath the oolitic facies of the Coastal border (Station 172). Also, in various places Ridge lies a limestone which is made predomi- along the western bank of the Coastal Ridge, nantly of zoaria of the bryozoan Schizoporella where there is a noticeable amount of quartz floridana (bryozoan facies). Mixed with these sand mixed with the oolite, the tubes are thin- are ooids, pellets, and skeletal grains of which ner and inclined to be scraggly in shape. pellets are the most numerous, as well as tubes Along the eastern coast line and underlying of polychaete worms. A few specimens of the the Atlantic Coastal Ridge the bryozoan facies gastropod Strombus have also been observed. has a rather consistent thickness of about 10 (8) The bryozoan layer extends in all direc- feet. Farther west and north of the Ridge, un- tions so that it covers the major part of ths derlying its western slope, the facies increases southern tip of Florida. It is overlain by the somewhat in thickness and reaches a maximum oolitic facies in the east and is the surface rock of 15 feet at core site 11. of the western part of the Everglades. Where the facies is thickest, the large multilaminar, knobby type is most prevalent. Where INTERPRETATION it is thin, as in the western part of the Ever- glades and along the Gulf Coast, the thin type Oolitic Deposits of Northwestern Part of tube is common. Apparently the eastern sec- of the Great Bahama tion of the area was optimal for bryozoan The next step in the study of the region is to growth. try to understand the conditions which gave rise to the features just outlined. Knowing that RESUME the present is a great help in understanding the In summary, the chief topographic and geo- past, it was natural to look for a place where logic features of the southern tip of Florida are conditions similar to those which existed in the following: southern Florida during the Pleistocene are (1) The eastern coast is bordered by a gentle now producing corresponding rock formations. ridge (the Atlantic Coastal Ridge, Fig. 1), with Such a place is relatively close at hand. a maximum height of 24 feet above sea level. Directly east of Miami on the opposite side of

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the Florida straits lies the Great Bahama Bank steeper on this side. Eastward from the crest a (Fig. 4). On its western edge are the islands of relatively gentle slope leads to the level of the Bimini, Cat Cay, Sandy Cay, Brown's Cay, and shelf lagoon. The eastern slope is characterized others extending in a north-south line. This is by numerous channels which run normal to the the area so well described by Newell and his co- direction of the ridge and which, in some cases, workers (1959). On the northwestern part of cut through the ridge crest (PI. 6). The bank-

FLORIDA FORT -100 fathoms MAINLAND LAUDERDALE

. ^ELLIOTT HOMESTEAD / KEY UNSTABLE V% / OOLITE

KEY LARGO

STATUTE

0 MILES .10 .ORANGE / CAY

Figure 4. Map of southeastern Florida and the northwestern section of the Great Bahama Bank showing the chief topographic and stratigraphic features of southern Florida and the mirror image relationship to their Recent Bahamian counterparts

the bank is a conspicuous underwater physio- ward ends of many of the channels are termi- graphic feature immediately east of the line of nated by small deltas (Newell and Rigby, 1957, Cays. This is a ridge (or bore) of unstable PI. XI; Newell and others, 1959, PI. 60). The oolite approximately 20 miles in length and % channels have been formed by tidal currents mile wide, lying parallel to the edge of the bank. flowing bankward and depositing deltas upon It begins at the southern end of North Cat Cay reaching the deeper water of the Bank. and extends southward to the vicinity of South According to Newell and others (1959), the Riding Rock (Fig. 4; PI. 6). optimum conditions for oolite growth occur In places the ridge rises to near the low-tide along this ridge. At the ridge crest where the level. The ridge crest for the most part is closer water is shallowest, the sand is constantly mov- to the western side of the ridge, and the slope to ing and consequently lacks a protective vegeta- the Outer Platform of the Bank is generally tive cover. In general (Newell and others, 1960,

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/78/2/175/3417168/i0016-7606-78-2-175.pdf by guest on 26 September 2021 Figure 1. Cross-bedded oolite of oolitic facies at Silver Bluff (between stations 205 and 206, Fig. 1), Coconut Grove, Miami

Figure 2. Oomoldic structure, commonly found in bryozoan facies. Ooids and pellets dissolved away and calcitic matrix remains. (X 3) TYPES OF OOLITIC ROCK OF MIAMI LIMESTONE, FLORIDA

HOFFMEISTER AND OTHERS, PLATE 1 Geological Society of America Bulletin, volume 78

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/78/2/175/3417168/i0016-7606-78-2-175.pdf by guest on 26 September 2021 Figure 1. Typical knobby specimen from bryozoan facies of Miami Limestone. Knobs and tubes commonly hollow

Figure 2. Well-preserved cellular structure as seen along portion of surface at a. (X 9) MULTILAMINATE BRYOZOAN COLONY OF SCHIZOPORELLA FLORIDANA OSBURN

HOFFMEISTER AND OTHERS, PLATE 2 Geological Society of America Bulletin, volume 78

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/78/2/175/3417168/i0016-7606-78-2-175.pdf by guest on 26 September 2021 Figure 1. Enlarged view of transverse section of knob (b in PL 2, fig. 1). Central hollow tube filled with calcareous debris and surrounded by 46 laminae

Figure 2. Recent specimen from Florida Bay, Florida. Arrow points to rhizome of Thalassia around which colony encrusted. Natural size PLEISTOCENE AND RECENT SPECIMENS OF SCHIZOPORELLA FLORIDANA

HOFFMEISTER AND OTHERS, PLATE 3 Geological Society of America Bulletin, volume 78

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/78/2/175/3417168/i0016-7606-78-2-175.pdf by guest on 26 September 2021 Figure 1. Spoil bank along canal near Dade County-Broward County line. At least 70 per cent of the rock specimens are fragments of bryozoan colonies.

Figure 2. Surface view of large boulder made chiefly of bryozoan fragments surrounding Strombus shell (at point of hammer) ILLUSTRATIONS OF ABUNDANCE OF BRYOZOAN COLONIES IN BRYOZOAN FACIES OF MIAMI LIMESTONE

HOFFMEISTER AND OTHERS, PLATE 4 Geological Society of America Bulletin, volume 78

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/78/2/175/3417168/i0016-7606-78-2-175.pdf by guest on 26 September 2021 Figure 1. Typical tubular fossil growth form from the bryozoan facies of the Miami Limestone

Figure 2. Similar tubular growth form of recent specimen from Great Bahama Bank COMPARISON OF A COLONY OF SCHIZOPORELLA FLORIDANA FROM THE MIAMI LIMESTONE OF FLORIDA WITH ONE FROM THE SHELF LAGOON OF THE GREAT BAHAMA BANK

HOFFMEISTER AND OTHERS, PLATE 5 Geological Society of America Bulletin, volume 78

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/78/2/175/3417168/i0016-7606-78-2-175.pdf by guest on 26 September 2021 NINE-LENS AERIAL PHOTOGRAPH OF UNSTABLE OOLITE RIDGE, GREAT BAHAMA BANK Northern part of ridge from South Cat Cay at top of photograph to Sandy Cay in south — distance about 9 miles. Transverse tidal channels with deltaic ends show clearly. Bryozoans grow in somewhat deeper water (darker area) east of ridge. U.S.C. and G. Survey, Aerial photograph 48386

HOFFMEISTER AND OTHERS, PLATE 6 Geological Society of America Bulletin, volume 78

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p. 487), ". . . the shoaler the water the greater derms and mollusks living in a moderately heavy the percentage of oolitically coated grains in the plant cover of grass and algae." In addition, they sediment." Thus it is their belief that the point out that a conspicuous element of the oolite grains are growing more rapidly over the community is a branching cheilostome bryozoan upper surface of the ridge in waters which are (Schizoporella pungens) which encrusts a species rarely more than 6 feet deep at low tide. There of Halimeda. Dr. Alan Cheetham, who identi- is no doubt that intricate cross-bedding is pro- fied the bryozoan as S. pungens, now considers duced by wave and current action in the upper it a synonym of S. floridana. According to part of the mound. According to Newell and Purdy (personal communication), "... the others (1960, p. 485), Prof. E. Seibold obtained colonies are rather widespread in occurrence on core samples from the sloping borders of the the Bank but are particularly numerous and ridge and found that they were characterized large (approximately one foot in height) on the by small-scale cross-bedding. It would seem east side of South Cat Cay-Sandy Cay oolite doubtful that the border slopes which are con- shoal." A moderate degree of substrate mobility sidered analogous to foreslopes of tidal deltas is suggested by the rippled sand bottom. It is would be underlain by sands as intricately cross- his belief that an environment such as this is bedded as are those in the shoaler more turbu- optimal for Schizoporella because the oolite lent areas higher up. shoal provides a shelter from large waves from Newell and others (1959) have described and the Florida Straits and also because tidal cur- mapped the main habitat communities of the rents are strong enough to provide a good food shelf lagoon which lies to the east of the western supply. Newell (personal communication) has rim of the Bank. Immediately east of the oolitic told the writers that, in view of the large num- ridge in water 12-15 feet deep is a bottom ber of bryozoans in this community, if he had it type mapped as pellet sand. Although this type to do over again, he would call it the bryozoan of sediment is dominant here it is mixed with community instead of the Strombus costatus. lesser amounts of skeletal grains, oolite, and The writers have examined the shelf lagoon grapestones. The bottom is sheltered from from Bimini to Brown's Cay, south of Sandy storm waves by the oolite ridge and subjected Cay, and agree with Purdy that an environment to vigorous tidal flow and waves and currents of this type seems to afford excellent conditions caused by average winds. Its surface is protected for bryozoan growth. Tidal currents are unusu- by marine grasses which exert a stabilizing in- ally strong and the oolitic mound provides pro- fluence on the bottom. Newell and others (1959, tection from storm waves from the Straits. In p. 220) point out that "... this situation may all probability, however, occasional hurricanes reflect combined advantages of shelter and have created their usual amount of damage. availability of fresh supplies of sea water rich in Patches of living bryozoans seem to be sparsely nutrients as compared with the depleted Bank distributed over the bottom. In many places waters of the interior." It has also been observed well-developed, partially buried dead colonies that rippling of the surface is not so common protrude above the pellet sand and are evidence here as in the more exposed seaward zones. of the widespread occurrence of the organisms The pellet sands are differentiated from others during the present and very recent past. on the Bank by the presence of ellipsoidal grains in excess of 25 per cent and with a maximum Comparison of Great Bahama Ean\ Deposits content of 80 per cent. Although these have with the Miami Limestone been considered fecal pellets, the term as used A paper entitled, "Bryozoan Limestone of by Newell and others (1959, p. 220) refers only Southeast Florida" (Hoffmeister and Multer, to their ellipsoidal shape and does not take into 1965), was presented at the Miami meeting of account their origin. The Geological Society of America in 1964. It has long been recognized that in the Baha- During the ensuing discussion John Imbrie mas and elsewhere there is a close connection commented on the similarity between the re- between habitat and organism communities, cent Bahamian occurrence of Schizoporella and that the substrate exerts an important in- floridana and the Pleistocene occurrence in fluence on the latter. Newell and others (1959, Florida. This led the writers to examine the two p. 220) have identified the pellet-sand bottom situations in more detail. type with a biotic community which they des- It was soon evident that the two areas were ignate the Strombus costatus community. This alike not only in respect to bryozoans but in is "... characterized especially by many echino- many other features as well. In fact, it might be

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stated that one is almost the mirror image of the oolite spread over the bottom of the shelf la- other. A mirror placed in the middle of the goon and cover its sediments and organic com- Straits of Florida, between Miami and Bimini, munities with a thin oolitic layer. Along its would reveal similar features in reverse order western side, the oolitic facies of the Miami (see Pig. 4). Limestone encroaches on the bryozoan facies Starting from the coast line and progressing and spreads a thin veneer over the latter. eastward, the outstanding features in the Ba- The rocks of the Everglades area also have hama area are: (1) The Cays; (2) The under- much in common with the sand deposits and water mound of unstable oolite; and (3) The organisms of the shelf lagoon in the region under shelf lagoon. On the Florida side from east to discussion. The dominant organisms in both are west are: (1) The Keys; (2) The Atlantic Coast- the numerous and well-developed bryozoan al Ridge; and (3) The low-lying Everglades. colonies of the species Schizoporella floridana A brief comparison will be made of the fea- Osburn (PI. 5). Bryozoan facies of the Miami tures which correspond to each other on the Limestone, however, contains a greater abun- two sides of the Florida Straits. dance of these organisms than does its Bahami- The Cays of the Bahama platform are made an counterpart. Also, in the Bahamian area the of indurated Pleistocene oolites. The Keys on colonies encrust branches oiHalimeda as well as the Florida side in the Miami area are made of other marine vegetation, such as Thalassia. several rock types, the most important of which Newell and others (1959, p. 220) have desig- is also of Pleistocene age. Miami Beach, Vir- nated this the Strombus costatus community. ginia Key, and Key Biscayne are topped by re- Several specimens of this genus have been found cent deposits much of which have been dredged in the bryozoan facies of the Miami Limestone. from Biscayne Bay. Beneath this lies a thin The sediments associated with the community layer of oolite which covers the lelatively thick have been listed by Newell and others as the Key Largo Limestone. Farther to the south, the pellet-sand type. Pellets also represent the dom- Keys, beginning with Soldier Key, are made en- inant constituent of the sands of the bryozoan tirely of Key Largo Limestone. Besides the dif- facies, especially in the area west of the Atlantic ferences in the composition of the rock, there is Coastal Ridge. a difference in distance between the Keys or Purdv (1963, p. 334-355; 472-497) has made Cays and the second main physiographic fea- a careful statistical study of the constituent parture. In the Bahamas, the Cays are close to or ticles on the Great Bahama Bank and has de- adjoin the mound of unstable oolite. In Florida, nned several main calcium carbonate facies. His the Keys are separated from the Coastal Ridge classification is somewhat different from the by Biscayne Bay, a distance of only about 4 bottom types originally described by Newell miles in the Miami area which increases to 10 and others (1959). Consequently, his map (Fig. miles farther south around Soldier Key (Figs. 1, p. 473), showing the distribution of facies, is 3 and 4). different from the reconnaissance map of bot- The Atlantic Coastal Ridge of southern Flor- tom types of Newell and others. For the pur- ida and the unstable oolite ridge of the Bahamas pose of this paper the designations of the latter are remarkably similar. They are alike in height report are sufficiently accurate. and shape, and both are made of oolite which In summary, the reefs of the Florida Keys seems to be more intricately cross-bedded on and the Cays of the Bimini region represent the the seaward side than bankward. In both cases, forward bastions behind which the oolitic sedi- the seaward side is somewhat steeper than the ments were formed. This does not mean that bankward side. The unstable oolite ridge is cut they were essential to the accumulation of the on the gently sloping eastern side by numerous oolites. Their presence, however, probably con- channels which run normal to the direction of tributed to the geographic position and shape of the mound and which in some cases cut through the ridges in the two localities. The Atlantic its crest. Commonly, the channels terminate in Coastal Ridge or oolitic facies is the Pleistocene deltaic mounds made of oolitic sand deposited counterpart of the unstable oolite Ridge of the by tidal currents. The Atlantic Coastal Ridge is Bahamas. The bryozoan facies of the Miami also cut by many narrow valleys (Parker and Limestone is the ancient equivalent of the sedi- Cooke, 1944, p. 54, 55) which run normal to the ments and organic community now forming on direction of the ridge and which in many cases the western part of the shelf lagoon. In conclu- terminate in deltaic mounds of oolitic sand sion it can be said that the two areas are so simi- (Fig. 3). The eastern borders of the unstable lar that the ecological conditions and events

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which gave rise to the Miami Limestone were conditions were reversed and the corals retreat- probably nearly identical with those which are ed eastward while the bryozoans took their taking place now on the northwestern section place. This sequence occurred once again, as of the Great Bahama Bank. shown in Figure 2, so that two sheets of the Key Largo Limestone intrude the bryozoan facies. Main Events in the Origin of Thus the upper part of the Key Largo Lime- the Miami Limestone stone seems contemporaneous with rocks of the During the last interglacial period, the coral bryozoan facies. reefs which today make up the Key Largo After the sediments of the bryozoan facies Limestone of the Florida Keys were flourishing. had attained a thickness in the eastern section Broecker and Thurber (1965, p. 58-60) dated of about 10 feet, oolites began to form in larger the Key Largo corals from the quarry at Wind- amounts in the area which is now the Atlantic ley Key as about 95,000 years old. The corals Coastal Ridge and pellets became relatively less which underlie Miami Beach, Virginia Key, important. As time went on, the oolitic sedi- and Key Biscayne farther north are believed to ments gradually accumulated until a northeast- be of similar age. West of these Pleistocene reefs, southwest mound was built up to the level of on what is presently the mainland of Florida, a the sea. The shoaler the mound became, the broad shallow-water platform extended across more abundant was the production of ooids. what is today the entire southern tip of the Cross-bedding was more prevalent at the state to the Gulf of Mexico. On this platform summit and on the eastern side of the mound the multilaminate bryozoan Schizoporella flon- than along its western slope. On the western dana grew in great profusion. Other important slope tidal currents running down the slope invertebrates of the community were species of created channels in the unstable oolite and de- polychaete worms. Some mollusks, including posited deltas at their western terminals over the gastropod genus Strombus, were present. the bryozoan communities of the lagoonlike Pellets and some ooids accumulated on the bot- shelf. tom and filled in the spaces around the organic While the mound was being formed, bryo- constituents. zoans continued to grow over the wide shelf to The ecologic conditions which prevailed over the west. Conditions were optimal for bryozoan the bank may be surmised by the organisms growth in the area immediately west of the found in the limestone and a comparison with oolitic mound due to the protective character conditions now extant on the Great Bahama of the mound from storm waves and the Bank. Dr. Alan Cheetham (personal communi- strength of the tidal currents which produced cation) who has studied the bryozoans from an abundance of food. The result was that here both localities believes that the form and abun- the large, knobby, super-multilaminar zoaria dance of the zoaria of S.floridana in the lime- lived in great numbers and formed a relatively stone indicate a shoal-water substrate covered thick deposit. Farther to the west, conditions by marine grasses and protected from turbu- were not so favorable and bryozoans having the lence seaward and from turbidity landward. He thin-layered growth form with open-ended also believes that the absence of other bryozo- branches grew. They were also fewer in number ans and paucity of other fossils indicates a de- and consequently produced here a thinner bry- parture from normal marine salinity. His study ozoan deposit. of the occurrence and distribution of the species With the lowering of sea level, due to the ice in other areas leads him to believe that the most age which followed, these deposits were sub- plausible conclusion is ". . . that the Miami aerially exposed. During this time rain water Limestone accumulations of S. floridana were flowing through the interstices of the rock even- produced in water of salinity analogous to that tually precipitated calcite around the grains and of the Great Bahama Bank, i.e., about 37 to 39 formed the indurated rock which is now pres- %c throughout the year." ent. It is believed that the eastern side of the There were times when a change in the salin- oolitic mound was subjected to considerable ity of the water and other ecologic conditions wave erosion and that much material from this along the eastern border of the bank made it side thus has been removed. possible for corals to encroach over the bryozoan The tidal channels, originally formed while community and extend westward to the area the oolite was in its unstable condition, have which today is overlain by the eastern part of been maintained in the indurated rock of the the Atlantic Coastal Ridge. Somewhat later, present day.

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All the Lower Keys, with their surface de- The Miami Limestone of the Lower posits of the oolitic facies of the Miami Lime- Florida Keys stone, are probably underlain by the Key Largo The Lower Keys, from Big Pine Key to Key Limestone. The stratigraphic relationship be- West, differ in several aspects from those to the tween the two formations can be seen at a con- northeast. Instead of being strung out in a long, tact at the southeastern point of Big Pine Key thin line they form an irregular, roughly tri- (Hoffmeister and Multer, 1962, p. 199-200;

(VACA KEY

" NEWFOUND HARBOR o,tftf<* KEYS "COHrtOtt* £^_r^t-~-/BOCA CHICA KEY KEY WEST .--60 •LEGEND- -* KEY LARGO FM. •^ MIAMI LIMESTONE FM., OOLITIC FACIES

Figure 5. Geologic map of the Lower Keys of Florida composed of the oolitic facies of the Miami Limestone. The shape and orientation of these Keys owe their origin to tidal currents which cut transverse channels in the unstable oolitic ridge which formerly occupied the area.

angular grouping with Key West at the apex Ginsburg and others, 1964, p. 60). Here the and Big Pine at the base (Fig. 5). Most of the oolite gently overlaps the old coral reef to the Keys are elongated in a northwest direction and south. The oolite cover of these Keys is rela- lie parallel to each other, becoming progressive- tively thin, particularly along their southern ly shorter from east to west. borders, and thickens in a northern direction as Another major difference is that they are it extends into the Gulf of Mexico. For exam- composed of oolite instead of Key Largo coral ple, at the southern shore line of Boca Chica reef limestone. Sanford (1909, p. 218-221) Key it is only about 6 feet thick and at about named this rock the Key West Oolite. He rec- 1^2 miles to the north it reaches a thickness of ognized its great similarity to the Miami Oolite 35 feet. It is not known what happens to it be- but gave it a different name because locally the neath the waters of the Gulf. latter contained more quartz sand. Cooke and In general, the Lower Keys are elongated in a Mossom (1929, p. 204) later considered this dif- northwestern direction and are separated from ference unimportant and combined them into each other by shallow well-defined channels. one, the Miami Oolite. The reason for the orientation of the Keys in

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this direction, so different from those to the reefs there was a tendency for the oolite to en- east and north, has been a subject of interesting croach over them and eventually to cover them speculation. It has long been known that the entirely. As in the case of the Bahamas, tidal Upper Keys are composed of the coral-reef Key currents cut channels in the unstable oolite nor- Largo Limestone and their orientation, roughly mal to the direction of the mound and probably parallel to the edge of the reef platform, can be deposited deltas in the slightly deeper waters to easily understood. It is only natural to assume the north. When the land was exposed during that the Lower Keys, made of a different rock, the following glacial period, the rock became the Miami Limestone (oolitic facies), should indurated as in the case of the Atlantic Coastal have a different shape and orientation. But why Ridge. Subsequent rise in sea level exposed the this particular orientation and relationship to mound to erosion by waves and currents. These each other? concentrated on the tidal channels originally An understanding of the conditions now ex- formed while the mound was composed of loose isting in the Cat Cay—Sandy Cay area of the ooids, and have eventually formed the narrow Bahamas throws considerable light on the prob- channels which today separate the Lower Keys lem. Oolites probably formed on the platform from each other. This process continues at the behind, or north of, the coral reefs which now present time. In summary, it is believed that lie beneath the oolite cover of the Lower Keys. the present shape and orientation of the Lower An east-west mound of unstable oolite with a Keys had their start in the underwater topogra- thickness of at least 35 feet and extending the phy created by tidal currents on an unstable entire length of the Lower Keys was eventually oolitic mound, built up. As the mound became higher than the

REFERENCES CITED Broecker, W. S., and Thurber, D. L., 1965, Uranium-series dating of corals and oolites from Bahaman and Florida Key limestones: Science, v. 149, p. 58-60 Cooke, C. W., 1939, Scenery of Florida: Fla. Geol. Survey Bull. 17, p. 11-118 Cooke, C. W., and Mossom, S., 1929, Geology of Florida: Fla. Geol. Survey Ann. Rept. 20, p. 29-227 Ginsburg, R. N., and others, 1964, South Florida carbonate sediments: Guidebook No. 1 for Geol. Soc. America Mtg. in Miami, 1964, 72 p. Hoffmeister, J. E., and Multer, H. G., 1962, The Key Largo Limestone of Florida, p. 199-200 in The Geological Society of America, Abstracts for 1961: Geol. Soc. America Special Paper 68, 322 p. 1965, Bryozoan limestone of southeast Florida, p. 93 in The Geological Society of America, Abstracts for 1964:'Geol. Soc. America Special Paper 82, 400 p. Newell, N.D., and Rigby, J.K., 1957, Geological studies of the Great Bahama Bank: Soc. Econ. Paleon- tologists and Mineralogists Special Pub. no. 5, p. 15-72 Newell,N. D., Purdy, E. G., and Imbrie, J., 1960, Bahamian oolitic sand: Jour. Geology, v. 68, p. 481-497 Newell, N. D., Imbrie, J., Purdy, E. G., and Thurber, D. L., 1959, Organism communities and bottom facies, Great Bahama Bank: Am. Mus. Nat. History Bull., v. 117, art. 4, p. 183-228 Parker, G. G., and Cooke, C. W., 1944, Late Cenozoic geology of southern Florida, with a discussion of the ground water: Fla. Geol. Survey Bull. 27, p. 1-119 Parker, G. G., Ferguson, G. E., Love, S. K., and others, 1955, Water resources of southeastern Florida with special reference to the geology and ground water of the Miami area: U. S. Geol. Survey Water- Supply Paper 1255, 903 p. Purdy, E. G., 1963, Recent calcium carbonate facies of the Great Bahama Bank: Jour. Geology, v. 71, p. 334-355; 472-497 Sanford, Samuel, 1909, Topography and geology of southern Florida: Fla. Geol. Survey, 2d Ann. Rept., p. 175-231

MANUSCRIPT RECEIVED BY THE SOCIETY JULY 29, 1966 CONTRIBUTION NUMBER 766 FROM THE INSTITUTE OF MARINE SCIENCE, UNIVERSITY OF MIAMI, FLORIDA

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