J. E. HOFFMEISTER Institute of Marine Sciences, University of , H. G. MULTER College of Wooster, Wooster, Ohio

Geology and Origin of the

Abstract: The Florida Keys form a crescentic chain of small limestone islands which extend from near Miami to Key West, a distance of about 150 miles. They are made of two main formations of Pleistocene age—the Key Largo Limestone and the Miami Limestone. The former, named and described by Sanford, is an elevated coral reef rock, and the latter, also described by Sanford, is an oolitic limestone in this area. The Key Largo Limestone is the surface rock of the Upper Keys, and the Miami Limestone covers the Lower Keys. A contact found at Big Pine Key shows that the oolitic limestone overlaps the Key Largo, and core borings show that the Key Largo underlies the oolitic cover for the entire area of the Lower Keys. The Key Largo, therefore, extends for the total length of the Keys. A core placed at , 70 miles west of Key West, encountered it at 30 feet below sea level. The Key Largo has a maximum thickness of over 200 feet. The fact that the Keys are located about 5 miles from the seaward edge of the Florida coral reef platform creates an interesting problem. They may be (1) remnants of an ancient outer reef similar to that found today bordering the living coral reef tract, or (2) they may have become established as a line of patch reefs in the back reef zone of a pre-existing platform which extended seaward some distance, possibly as far as the present platform. It is believed that the answer to this problem can be found through an understanding of what was happening seaward and leeward of the old reef at the time its corals were flourishing. Consequently, the composition and structure of the reef platform seaward of the Keys and the geologic history of the rocks of the Florida mainland im- mediately behind the Keys were studied. Information thus obtained plus observations on the composition, especially the coral content, of the Keys themselves have led the authors to believe that the Keys were formed as a line of patch reefs in a back reef area which was bordered on its seaward edge by an outer reef which has since been lowered, chiefly by erosion, and covered by more recent material. CONTENTS Introduction 1487 References cited 1501 Acknowledgments 1489 The Key Largo Limestone 1489 Figures „•• i ..„„ 1. Main features and geology of the Florida Keys 1488 Significance of corafreef framework' '.'.'.'. 1490 2. Generalized block diagram showing conditions The Miami Limestone (oolitic fades) 1491 across Florida coral reef tract in Key Largo The Florida Keys—back reef or outer reef ? . . 1492 .. „ ,e ',;,' ,' ,'. - ' ' ,' '. - ' ' ,' •' ' Back-reef hypothesis 1492 3. Generalized block diagram showing conditions Outer-reef (M. annularis) hypothesis .... 1494 across Florida coral reef tract at present Depth of Key Largo water 1495 me The reef platform 1495 p] Interpretation 1497 Lowering of the original platform 1497 1. Top of outer reef about 5 miles southwest of Erosion 1497 Carysfort light, tract. See Structural tilting and faulting 1497 2. Important Floridian and West Indian corals Plate Elongate, crescentic pattern of the Keys . . 1500 3. Living and fossil colonies of multilobate Section Conclusions 1500 Montastrea annularis.

INTRODUCTION about 150 miles. Together they describe a graceful arc with the convex side bounded by The Florida Keys represent a narrow chain the Atlantic Ocean and the concave by the Bay of small islands which extend from the vicinity of Florida, with its adjoining bodies of inland of Miami on the north to, and including, Key water, and the Gulf of Mexico (Fig. 1). West on the south and west, a total distance of Work by the authors began in the area with

Geological Society of America Bulletin, v. 79, p. 1487-1502, 3 figs., 3 pis., November 1968 1487

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 MIAMI BEACH ^"VIRGINIA KEY O KEY BISCAYNE

\ F L 0 R I DA LEGEND w pa KEY LARGO LIMESTONE C3 MIAMI LIMESTONE a (OOLITIC FACIES) o CORE HOLES _ CARYSFORT ocH LIGHT MEXICO i) STATIONS

B ^ PLANTATION KEY / WINDLEY-v> o o o z o .r^^w o 2 o NEWFOUND HARBOR KEYS z B LOWER KEYS 73

-SCALE-

20 30 40 STATUTE MILES

Figure 1. Main features and geology of the Florida Keys.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 THE KEY LARGO LIMESTONE 1489

a study of the Key Largo Limestone, the more habitable conditions. The rocks thus ex- Pleistocene coral reef which is the main for- posed contribute a great deal to the knowledge mation of the Keys. It was soon apparent that of the terrain and reveal much which was not in order to understand the geologic history of available to earlier workers. Construction, the old reef it would be necessary to know what however, has also created a certain amount of was happening seaward and leeward of it at the confusion, in that rocks have been removed time its corals were flourishing. This brought from one place and deposited in another, fre- us to an examination of the reef platform upon quently miles away. which the living corals are growing and the Florida Mainland respectively. The authors ACKNOWLEDGMENTS have recently published an account of the main- land area (Hoffmeister and others, 1967), and The authors gratefully wish to acknowledge the reef platform will be described here. It their indebtedness to the National Science should be emphasized that only through a Foundation for making their studies on the knowledge of the whole area can the geologic Florida Reef Tract possible. They also wish to history of the Keys be derived. thank Dr. Robert Ginsburg of the Johns The greater area of the Keys is lowlying, Hopkins University who originally suggested covered by mangrove swamps or projecting the project; he has aided us by his interest, his only 2 or 3 feet above high tide. The highest stimulating discussions, and his many helpful point is on Windley Key where the Key Largo suggestions. Drs. Mahlon Ball and Cesare reaches an elevation of about 18 feet. It is esti- Emiliani of the Institute of Marine Sciences mated that mangrove swamps occupy at least have greatly improved the paper by their care- one half of the total area of the Keys. By far the ful review of the manuscript. Mr. E. A. Shinn commonest species is the red mangrove, of the Shell Development Company worked Rhizophora mangle, which possesses the "prop" with the authors in the field and gave them the roots, although both the black and white benefit of much of his considerable knowledge mangroves are also present. of the living coral reefs as well as the use of Sand beaches are remarkably few and of several illustrations. Dr. John Wells, of Cornell limited extent. Those which occur are found University, helped greatly in the identification chiefly on the Atlantic side and notably on of the fossil corals. Dr. Taro Takahashi of the parts of Key Largo, Plantation, the Mate- University of Rochester and Dr. John Goddard cumbes, Long, Key Vaca, and Sugar Loaf of the Lament Geological Observatory kindly Keys. Intertidal flats border both sides of the did the radio carbon dating of the corals. The islands. These are generally shallow water authors also wish to acknowledge the aid and areas, barely covered at low tide, which encouragement given them by the late Dr. gradually slope into the deeper water of the Friederich (Fritz) Koczy of the Institute of surrounding platform. In some places they are Marine Sciences. exposed at low tide and covered by soft THE KEY LARGO LIMESTONE laminated algal crusts. One of the best ex- amples of this is found on the ocean side of It has long been known that the Keys are Spanish Harbor Key. composed of two main types of limestone of The surfaces of most of the Keys are flat and Pleistocene Age. One of these is an elevated of about the same elevation throughout their coral reef rock, the Key Largo Limestone, and extent. Others, particularly the northern the other, the oolitic facies of the Miami Lime- Keys, are a few feet higher along their central stone. A comprehensive examination was made elongated axis and slope gradually to the ocean of the rocks at numerous surface outcrops of and bay sides. each of the Keys which are connected by U.S. Although bed rock extends only a few feet Highway No. 1. A few important Keys on both above the high-tide level, there are numerous sides of the main chain were also visited. In outcrops, the best of which have been created addition, the large piles of material dredged artificially. Small quarries, borrow pits, dug from the many workings scattered along the during the construction of roads and boat slips, shores afforded an excellent opportunity to expose the bedrock in many places both inland examine the rocks to a depth of as much as 40 and along the coasts. Offshore dredging opera- feet. Core borings provided information on tions are numerous in the making of new land thickness, composition, and the foundation and the conversion of mangrove areas into upon which the limestones rest.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 1490 HOFFMEISTER AND MULTER-GEOLOGY AND ORIGIN, FLORIDA KEYS

Extent Consequently, it appears that the formation is of variable thickness and that it rests upon an The Key Largo, which was named and well undulating irregular surface. described by Sanford (1909, p. 214-218), ex- tends on the surface from Soldier Key on the Significance of Coral Reef Frameworl^ north through the westernmost of the small The Key Largo Limestone of the Florida Newfound Harbor Keys where it terminates at Keys is a typical organic reef composed of in Newfound Harbor Channel, a distance of 110 situ, wave-resistant elements, the most im- miles. The small Keys on the north side of the portant of which are hermatypic corals. These channel are composed of Miami Limestone. form the framework of the structure and are The center of the channel thus marks the responsible for the trapping of large amounts of dividing line between the two types of rock. calcarenite in which they are now embedded. The Key Largo, however, extends over a Stanley (1966, p. 1927-1947), who made a much greater territory than its surface outcrops study of "that part of the Key Largo Lime- indicate. In the north, borings have revealed stone which stands above sea level," has very its presence under Miami Beach. There is little competently described the composition of the doubt that it continues southward beneath upper part of the formation. He concentrated Virginia Key and Key Biscayne, in a direct line on two localities where excellent exposures are to Soldier Key. Although no surface exposures available—one at a quarry on Windley Key of the Key Largo are visible west of Big Pine and the other at the Cross Key Canal (Station Key, dredging projects and a core boring at 62) where a channel has been cut across the Key Key West indicate that it underlies all of the dividing it into two entirely separate parts. Lower Keys. On the southern shore of Boca An examination of many exposures through- Chica, the coral reef rock lies under a cover of out the length and breadth of the Keys indi- oolitic Miami Limestone 6 to 8 feet in thick- cates that the principal frame-building corals ness. The core boring at Key West reaches it are Montastrea annularis, Diploria strigosa, D. beneath a 30-foot cover of oolitic Miami Lime- clivosa, D. labyrinthiformis, and several species stone. of Forties of which P. astreoides is the most com- An extension of the arc of the Keys in a mon. Stanley's observations agree with this, and western direction from Key West leads to the he concludes from his study of the Windley , Rebecca Shoal, and finally to Key quarry that they comprise "about 30 the Tortugas. A core boring recently placed at percent of the rock volume, of which Montastrea Dry Tortugas encountered the Key Largo annularis makes up half" (1966, p. 1930, Fig. 4). Limestone at a depth of 30 feet below sea level. Although we made no statistical studies, we Thus, this formation is known to exist at a believe that in general the relative proportion distance of 70 miles beyond Key West. by volume of the species he records holds for the entire area. Although of lesser importance, Thickness Acrouora cervicornis, Montastrea cavernosa, and The thickness of the Key Largo Limestone Siderastrea radians are commonly found. In has been determined by core borings at several other words, the ecologic conditions which widely spaced localities. Where penetrated, the existed during this time were similar through- Key Largo rests on a. quartzose calcareous sand. out the chain, and the result is a rather Near the northern tip of Key Largo it was homogeneous structure. Practically all the found to be 145 feet in thickness. About 10 coral species living today in the patch reefs of miles farther south on the same Key it had the Florida reef tract have been found in the thinned to 75 leet. A well drilled at Tavernier, Key Largo Limestone. near the southern tip of Key Largo, is reported There is no doubt that Montastrea annularis to have penetrated the formation to its base is by far the most important coral species. It at 100 feet. At Grassy Key its thickness had possesses several growth forms, the most increased to 170 feet. On Big Pine Key (Sta- significant of which are (1) smooth sub- tion 23), the core drill went through 20 feet of hemispherical colonies, (2) large multilobular followed by 180 feet of Key Largo with- heads, and (3) sheet-like masses which are out reaching its base. either large with undulating surfaces or smaller A well drilled at Key West penetrated 27 sheets which extend over each other in shingle feet of oolite followed by 171 feet of Key formation. The first two forms are common in Largo. Here again its base was not reached. the Key Largo Limestone, but the third ap-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 THE MIAMI LIMESTONE 1491

pears to be absent. The multilobular forms are the calcarenite itself at all levels contains an spectacular when seen in growth position (PI. appreciable amount of coral material indicates 2, fig. 2, PL 3, fig. 1). The pillarlike lobes rise that corals were flourishing during the entire from a common massive base and in places time represented by the limestone. The general reach a height of 7 or 8 feet. During formation, impression is that patches of corals were form- the surface of the base becomes irregular with ing in different places throughout the period grooves which intersect to form a checkerboard and that calcarenitic material was accumulating pattern. The areas between the grooves grow between the patches as well as in the interstices upward and become the pillars. The mature of the framework. colony can be likened to a huge pincushion from which protrude numerous closely set THE MIAMI LIMESTONE club-shaped pins. The strength of the indi- (OOLITIC FACIES) vidual lobes and their nearness to each other The southern or Lower Keys, beginning with makes them efficient baffles for the collection Big Pine Key and extending through Key of loose particles which are washed against West, are covered by an oolitic limestone which them. Their large number in the Key Largo Sanford (1909, p. 218-221) called the Key makes them the chief element in the framework West Oolite. Although he recognized its great which produced the reef (PL 3, fig. 2). similarity to what he called the Miami Oolite As previously noted, the above account is of the southern tip of the mainland of Florida, concerned entirely with that part of the Key he gave it a different name because he believed Largo which stands above sea level. What can that locally it contained less quartz sand. be said about the great thickness of reef Cooke and Mossom (1929, p. 204) later com- material which lies beneath it? For the purpose bined them into one, the Miami Oolite. The of this paper it is believed sufficient to make the authors (1967, p. 175-189), after a study of the following observations. Miami Oolite of the mainland, recognized the (1) The deepest point at which coral reef existence of two units, a lower unit which they rock was found is 200 feet beneath sea level in called the bryozoan facies and an upper one, the Key West boring. the oolitic facies. They combined the two (2) Coral framework is more prolific in the facies as the Miami Limestone. The surface upper 100 feet than below that level. rock of the Lower Keys is the oolitic facies of (3) Calcarenite becomes somewhat more the Miami Limestone. The bryozoan facies important in the deeper levels, as indicated by seems to be absent in this area. the cores. It has been shown that the oolite rests upon (4) The same species of corals which are the Key Largo. The best place to see the found in the exposed part of the formation are stratigraphic relation between the two forma- found in the cores. tions is at a contact at the southeastern point (5) Montastrea annularis is by far the most of Big Pine Key (Station 23). Here the oolite important species, followed by species of overlaps the old coral reef at a low angle in a Diploria and Porites. southern direction. The contact appears to be (6) The cores indicate that in general the of a transitional character (Ginsburg, 1964, p. same relative proportion by volume of the coral 60). The oolite covers all the Lower Keys and species found in the exposed part of the for- is thinnest over their southern borders, in- mation is maintained beneath the surface. creasing in thickness to the north. It reaches its It must be stressed that the above points are greatest known thickness of about 35 feet on based on only 5 cores, each 21/4 inches in the northern part of Stock Island. diameter and scattered over a distance of 125 There is not much question that the rock miles along the emergent Keys (Ginsburg, originally began as an underwater east-west 1964, p. 58, Fig. 34). Other borings placed at mound or bore of unstable oolite lying north of, somewhat different geographic points might and parallel to, the Key Largo coral reef. As it tell a different story. For example, they might grew higher the mound gradually became show coral structure at the levels where the broader to the south as well as north and present cores record calcarenite, and vice versa. eventually covered the corals. As explained in Thus, there is no conclusive proof that the greater length in a previous paper (Hoffmeister basal parts of the formation are more cal- and others, 1967, p. 188-189) tidal currents carenitic and that hermatypic corals became cut channels in the unstable oolite normal to more important at a later time. The fact that the direction of the mound. It is believed that

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 1492 HOFFMEISTER AND MULTER—GEOLOGY AND ORIGIN, FLORIDA KEYS

the present shape and northwest-southeast present platform. If the latter were the case, the orientation of the Lower Keys originated as platform presumably would have been edged underwater topography created by the tidal on its seaward side by an outer reef. Each of currents. these two hypotheses will be considered There has been a good deal of speculation separately. Before doing this, several general concerning the possibility that the oolitic facies statements should be made. of the Miami Limestone at one time extended (1) It should be stressed that the corals and under and joined the same rock other constituent organisms of the old reef of the Atlantic Coastal Ridge of the mainland. are the same throughout its mass, from top to A core placed in Florida Bay failed to en- bottom, a vertical distance of at least 180 feet. counter the oolite. This indicates that the oolite There is not much question that the general mound of the Lower Keys was, in all prob- ecologic conditions under which they grew ability, formed as an isolated underwater ridge were similar throughout its history. The ex- totally separated from that of the mainland. posed part of the formation, therefore, cannot THE FLORIDA KEYS—BACK be separated from the underlying part. REEF OR OUTER REEF? (2) Certainly the most important clues of origin should come from the composition of the The Florida reef tract which borders the old reef itself. If it was an outer reef, it should Atlantic side of the Keys for their entire reveal the characteristics found on the present- length has an average width of about 5 miles. day outer reef. If it was formed in what was a Ginsburg (1956, p. 2404) recognized three di- back-reef environment, it should possess fea- visions of the tract—fore reef, outer reef, and tures similar to those found in the numerous back reef. The outer reef which edges the patch reefs of the present back reef region. Atlantic side of the platform is composed of ' 'a (3) On the basis of its coral species content series of elongate living reefs and rocky shoals and its lithology, it must have been formed separated by areas of deeper water which are under the conditions of relatively low level in most places floored by ripple-marked wave energy. Any hypothesis for its origin calcareous sediments." The fore-reef division must take this into account. edges the seaward side of the outer-reef be- ginning at a depth of + 150 feet and sloping Bac^-Reef Hypothesis into deeper water. The back-reef division in- The coral species of the Key Largo Limestone cludes roughly the section from the base of of the Keys are commonly found in the living the inner side of the outer reef to the Keys. The patch reefs of the back-reef area of the Florida back reef, therefore, covers the largest part of coral-reef tract. The main species in the old reef the reef tract. Its surface is rough with un- are also the most common on the back-reef area dulating, submerged ridges of various lengths today. All flourish best in a somewhat re- separated by elongated channel ways, both of stricted environment with only limited wave which normally run parallel with the platform energy. edge. On many of the ridges are numerous It should now also be noted that there are knolls and reef patches which may reach within certain species which are found in typical outer a foot or so of sea level. reefs of the Florida and West Indian regions For the sake of simplicity the authors are which are conspicuous by their absence or recognizing in this paper only two main divi- paucity in the Key Largo Limestone. sions: (1) the outer or bank-reef division which Acropora palmata. It is well known that the includes the seaward slope to a depth of about dominant species of the outer reef of Florida is 50 feet, and (2) the back-reef division with its Acropora palmata, the moose-horn coral (PI. 1 patch reefs. and PL 2, fig. 1). Ginsburg (1956, p. 1407) ob- The fact that the Keys are located several served that this large branching coral is the miles from the seaward edge of the platform primary structural element of the outer-reef poses an interesting problem. They could be mass and that "it provides both a framework (a) remnants of an ancient outer reef similar to around and in which detrital material can what is found today bordering the living coral accumulate." It is significant that this species reef tract or (b) they may have become es- has never appeared in the Key Largo Limestone tablished as a line of patch reefs in the back-reef of the Keys either in the numerous exposures zone of a pre-existing platform which extended at the surface, in the cores, or from the many seaward some distance, possibly as far as the dredgings which have been carried out on both

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 THE FLORIDA KKYS 1493

sides of the Keys, some reaching depths of 40 tions in the back reef. Such attempts have, so to 50 feet. The absence of A. palmata would far, been unsuccessful—the colonies die within seem to indicate that the rock of the Keys did a few months. The cause for these failures is not not form as an outer reef. definitely known. It is believed, however, that It could be argued, however, that during a plausible explanation is their inability to cope emergence of the reef the stands of A. palmata, with the greater amount of silt and sand which presumably occupied its surface zone, present in this environment. In any event, it were eroded away. Even if this had happened, seems that A. palmata is a species that grows fragments of the colonies should be present in only in a very selective environment. the sediments immediately bordering the Keys In summary, it can be said that although the and even be incorporated in the body of the absence of A. palmata in the Key Largo Lime- Key Largo Limestone. Such fragments have stone of the Keys is not definite proof of a back- never been located in this area. reef origin for the old reef, it is certainly a It could also be argued that A. palmata did significant indication of such an environment. not exist in Florida during the Pleistocene. Millepora and coralline algae. Other char- Certainly to the best of our knowledge it has acteristic species of the outer reef are the hy- never been found in the Pleistocene deposits of droids Millepora alcicornis and M. complanata. the Keys, the only coral limestone of this age The latter is so prolific that Shinn (1963, p. exposed in the state. This, of course, does not 295) has designated a zone, on the seaward slope disprove its presence as it may have flourished of the outer reef, the Millepora zone. Ginsburg in sections of the reef tract more suitable to its (1956, p. 2407) describes the outer reef with its growth. framework of A. palmata and detrital body as The possibility that Florida was too cold for being "stabilized by a covering of the hy- the species during interglacial times was con- drozoan M. alcico nis and encrusting algae." sidered. That it lived in this period in ad- Although such action is small as compared with joining areas is known, since it has been re- the binding operation of similar organisms of ported to occur widely in the Pleistocene reefs the lithothamnium ridge of Pacific reefs, of eastern Central America and the West nevertheless, it is appreciable. Indies. Vaughan (1919, p. 225) reported it from Millepora and calcareous algae are relatively Monkey Point, Costa Rica, and said it came scarce in the patch reefs of the back reef area. from an elevated seaward-facing reef. Mesolella Voss and Voss (1955, p. 217) describe Millepora (1967, p. 638-640) reported it from Barbados. alcicornis as commonly found in the Alcyonarian Emiliani (1965, oral commun.), who has made zone surrounding Soldier Key. They state that a study of the temperatures of Key Largo time, the colonies have a lacy appearance due to the has informed us that it is his belief that the substrate and that the more typical plate-like climatic conditions of that period were about form is found only in the outer reefs of the similar to those of today and that A. palmata tract. The coralline algae form a thin coating on could have lived here, provided other ecological dead corals and on the basal parts of some living conditions were favorable. corals, but those familiar with the area agree A. palmata is one of the best known and most that they play a minor part in the life of the widely dispersed species of corals living in the back reef zone. For example, Ginsburg (1956, Atlantic today. It thrives chiefly where the p. 2413) reports that the constituent composi- surf is strong. In spite of its branching char- tion of sediments reveals a substantial decrease acter, the strength of its branches and oriented of coralline algae from the outer- and fore-reef growth are sufficient to enable it to withstand zones toward the back-reef zone. waves of tremendous force. One of the best Examination of the Key Largo reef reveals descriptions of it in its natural habitat has been a paucity of both Millepora and coralline given by Shinn (1963, p. 297-298). On the algae. Fragments of Millepora occur in some Florida reef tract it is found almost exclusively places, but there is no evidence of the strong on the outer reef. In a few places where there plate-like forms that are common on the outer is a break in the outer reef, it may occur a short reef today. Encrusting calcareous algae are far distance landward from the margin of the from conspicuous. In places they form thin platform. It is never found on the patch reefs coatings on the basal parts of some coral heads, on the back-reef area. but they appear to compose only an in- The authors have attempted to transplant significant part of the old reef. living A. palmata from the outer reef to sec- Evidence from these two types of carbonate-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 1494 HOFFMEISTER AND MULTER—GEOLOGY AND ORIGIN, FLORIDA KEYS

producing organisms seems to favor a back-reef This has also been shown by Goreau (1959, origin for the Key Largo Limestone. p. 72) in his description of the Jamaican reefs. Hahmeda. Halimeda is one of the most im- At Ocho Rios the reef crest of turbulent wave portant organisms found in the reef tract today. action contains his "palmata zone" with a It is abundant in all three of Ginsburg's divi- depth range of 0.5 to 6 m. Below this on the sions. However, Ginsburg (1956, p. 2413) has seaward slope lies "the annularis" zone with an noted a gradual increase of sediment fractions average depth of 15 m and consequently less of the genus from the outer- and fore-reef wave energy. divisions toward the back-reef area. It is a most The lower or Montastrea annularis zone is also important constituent of the Key Largo Lime- characterized by species such as Diploria stone. It is found in the cores in significant strigosa, D. labyrinthiformis, Parties astreoides, P. numbers at all depths. Also in the numerous ex- furcata, and Siderastrea siderea. All of these are posures along canal banks, large sections com- commonly found in the Key Largo Limestone posed exclusively of Halimeda may be found. as well. Here, then, is another environment Although we are dealing with a ubiquitous which, on the basis of coral content and re- organism, its presence in such large numbers stricted wave energy, fulfills the Key Largo argues for a back-reef environment. growth requirements. In summary, it can be said that the fact that Stanley (1966) believes that the Key Largo the species found as fossil in the old reef are can best be compared to the deeper water identical with those of the living patch reefs, "Montastrea annularis' zone of typical West the absence of a common species found only on Indian bank or outer reefs. He states (1966, p. the living outer reef and the favorable propor- 1939) that tion of other species which are common in all zones indicate that the Key Largo reef was ... it seems most reasonable at present to adopt the hypothesis that the exposed Key Largo Limestone formed in a back-reef environment. is a crescentic reef that grew in open water at a Outer-Reef (M. annulans} Hypothesis depth equivalent to the 'Montastrea' zones of the living reefs, rather than a series of coalescing patch The outer or bank reefs of Floridian and reefs that grew in the protection of a hypothetical West Indian reefs are composed of two main seaward barrier. sections—an upper or reef crest section which rises to or near the surface of the sea and a sea- He believes that "the chief problem with the ward slope which occupies levels roughly be- back reef hypothesis is that it requires a sea- tween 20 to 50 feet in depth. In most localities ward bank-reef arc for which there is at present coral zonation is distinct. Each zone is char- no concrete evidence." He argues that since acterized by certain dominant corals. Acropora the greatest elevation of the exposed Key Largo falmata is the dominant species of the turbul- Limestone is 18 feet above sea level and that ent, high-energy level of the reef crest. Farther "the living Florida bank reefs, which occupy downslope other species take over and Acropora the approximate position that the postulated palmata disappears, although Storr (1964, p. 59) older reefs would have had to occupy, stand on states that it is abundant in his Montastrea-deep- a rocky floor that is about 25 feet below sea water zone (20 to 50 feet) at Abaco Island, level," that "a wedge-shape prism of reef and Bahamas. At the 20-foot level Montastrea back-reef deposits, about 5 miles wide and at annulans begins to predominate and continues least 40 to 45 feet thick at its seaward margin, to do so to at least the 50-foot level. would have had to be removed by erosion if the References showing sequences similar to the exposed Key Largo reef grew in the protection above are numerous in the literature. For ex- of bank reefs growing in the vicinity of the ample, Newell (1958, p. 125) maintains that recent ones." He cannot conceive that erosion of this magnitude could have occurred in the . . . the best developed reefs in the West Indian time available since the beginning of the Wis- province usually show 3 principal biotic zones con- consin sea-level lowering. Also he finds it trolled by the conditions of turbulence and light difficult to understand why, if such erosion had at different depths. These are: (1) an outer belt of massive corals, especially Montastrea annularis, lying occurred, "an arcuate ridge of Keys oriented at substrate depths between 60 and 30 feet; (2) an parallel with the continental margin was left intermediate belt of elkhorn corals, Acropora standing above the seaward shelf and Florida palmata, in turbulent waters between 30 and 6 Bay." These questions will be dealt with later feet; and (3) an inner rocky shoal. . . . in the paper.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 THE FLORIDA KEYS 1495

Depth of the Key Largo Water Ridge of the oolitic facies of the Miami Lime- stone. The crest of the cross-bedded unstable It has been shown that a study of the Key ridge rises into the surf zone and is near the Largo Limestone from both surface exposures low-tide level. By analogy, it is believed that and subsurface cores reveals a certain common the crest of the cross-bedded oolitic Pleistocene assemblage of coral species and that this as- ridge of Florida was also at or close to sea level. semblage is characterized by a somewhat re- Since the highest part of the old ridge is about stricted and low-energy wave environment. 25 feet above present sea level, it is believed Both hypotheses as outlined above fulfill these that the sea stood at this level or a few feet two requirements. The difference between them higher at the time the upper part of the mound lies in the position where such a grouping of was being formed. corals occurred on the reef at the time it was Since the upper part of the Key Largo living. The back-reef hypothesis maintains a Limestone was contemporaneous with the shallow-water origin and the other, a deeper- Miami Limestone, the sea level must have been water environment. In one case the absence of about 25 feet above present level at the time the Acropora palmata, a species which normally coral reef was living. The highest part of the favors turbulent water, is explained by a re- Key Largo (Windley Key) stands 18 feet above stricted, protected back-reef location, and in the the present sea level. This is only 7 feet below other by its position in the low-energy, deeper- the surface of water of that day. If this were an water zone of the outer reef. The depth of the outer reef it would be difficult to explain the water therefore is of crucial significance. absence of Acropora palmata in water of such If the organic composition of the old reef shallow depth. It would appear that the corals does not reveal its depth of origin then evidence of the Key Largo grew under shallow water from other sources must be found. Probably the conditions very similar to those of the patch most important information comes from rocks reefs of the back-reef zone of the present Florida of the same age on the Florida mainland. reef tract. Hoffmeister and others (1967, Fig. 1, p. 177) recently published a paper on the Miami The Reef Platform Limestone1 of southern Florida in which they If we are correct that the exposed Key Largo described two facies of this formation—a lower Limestone of the Keys represents a series of or bryozoan facies and an upper or oolitic coalescing patch reefs in the rear of the back facies. The bryozoan facies covers a large part reef environment, then it is logical to assume of the southern tip of Florida and is the surface that it is all that is left of what was a broad reef rock of the . It is overlain on its flat, similar in structure and ecologic_features to eastern side by a north-south mound of cross- the present Florida reef tract. We should also bedded oolite (the oolitic facies) which forms expect that, like the present one, it was the Atlantic Coastal Ridge upon which the bordered on its seaward edge by an outer or main cities of southeastern Florida, such as bank reef with its characteristic zonation. More Fort Lauderdale, Miami, and Homestead are specifically, we should expect that the bank situated. The highest point of the ridge is in reef should have been crowned even in those the Coconut Grove area of Miami where it early days by colonies of Acropora palmata. reaches an elevation of about 25 feet above sea If, on the other hand, it is assumed that the level. That the upper part of the Key Largo Key Largo of the Florida Keys had a deeper Limestone is of the same age as the Miami water origin (average 45 feet), similar to the Limestone is shown by the fact that the coral M. annularis zone of the West Indian bank reef limestone interfingers with the Miami reefs, several questions immediately arise. (1) (Hoffmeister and others, 1967, Fig. 2, p. 179 How far did it extend seaward? Or in other and 187). The same publication describes a words, how wide was it? (2) What was the recent counterpart to the geologic features of depth of the water beyond its outer edge? southern Florida on the western edge of the Stanley is not specific about these problems. Great Bahama Bank, immediately east of He states merely that the horizontal scale of his Miami. One of the outstanding features here is diagrammatic cross section (1966, Fig. 9, p. a large underwater ridge of unstable oolite 1936) is "somewhat reduced." which is the equivalent of the Atlantic Coastal As regards the first question, he refers to it in places as a broad reef. For example, Stanley 1 Previously known as the Miami Oolite. (1966, p. 1939) says it was "a broad, low

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 1496 IIOFFMEISTER AND MULTER—GEOLOGY AND ORIGIN, FLORIDA KEYS

homogeneous reef," different from "the typical countered to a depth of 50 feet. At 45 feet, a zoned structure of modern West Indian bank clearly identifiable specimen of Acropora reefs." He also says that "the exposed part of palmata occurred. Dating indicated an age of the Key Largo forms a broad, central ridge," about 1300 years. At 50 feet the hard bedrock and that it may have had the shape of a broad, of the Key Largo was reached and continued low-lying coral plantation. In other places he to the bottom of the hole. Corals typical of the implies that it was a relatively narrow band not formation were found. The chief species were much wider than the exposed Key Largo of Montastrea annularis, Acropora cervicornis, and today. For example, he refers to it as a ' 'cres- Porites sp. Drilling had to be discontinued at a centic reef" and states it "represents the domi- depth of 82 feet because of mechanical diffi- nant part of an ancient reef arc." culties. It was probably wider than the M. annularis Core No. 2 was located at the Basin Hill zone of the outer reef of typical modern West Shoals, a patch reef about halfway between the Indian reefs, but the question is, where was its Carysfort Lighthouse and Key Largo. Loose, outer, seaward edge located? shelly coralline sand followed by light to dark- If it extended seaward much more than the gray lime mud were found lying on encrusted exposed Key Largo, then it must have grown Key Largo bedrock which occurs at 34 feet on a wide flattish platform, and it is difficult to below sea level. Shelly, vuggy calcarenite pre- explain its present relatively narrow "cres- dominated to a zone of Montastrea annularis centic"- and "arc"-shaped condition without a coral at the 71-foot depth. Coarse-grained great amount of subsequent erosion on its sea- calcarenite alternating with coral (Montastrea, ward side. This is exactly what Stanley objects Acropora cervicornis, Porites} continued to a to in the back-reef hypothesis. If, on the other depth of 126 feet at the bottom of the hole. hand, its width was never much more than that Core No. 3 was located at Looe Key at the of the exposed Key Largo, then the water must seaward edge of the platform and about 5 miles have been too deep for hermatypic corals a from Newfound Harbor Key. Loose, shelly short distance seaward of the Keys. sand and coral fragments were found to a depth It is understandable that Stanley had of 52 feet. At 18 feet, an 8-inch core of Acropora difficulty in explaining the outer limit of his M, palmata appeared. Dating indicated an age of annularis zone of an incipient bank reef. The 1300 years. At 52 feet the hard Key Largo answer to the question obviously lies in a study Limestone was reached and continued to the of the composition of the present reef platform. greatest depth of the hole, 162 feet. The chief Without this knowledge much of the argument corals encountered were Montastrea annularis, for either hypothesis is not conclusive. The Acropora cervicornis, Porites Porites, and P. facts can be obtained only by an understanding astreoides. At the 92-foot level, a specimen of of what lies beneath the surface of the living Acropora which has doubtfully been referred to coral-reef tract. For this reason, the authors A. palmata was found. The fragment, however, core-drilled in several places. Three holes (Fig. is too small for a definite identification. 1) were placed in the bank- or outer-reef area Core No. 4 was located about 2500 feet north at the seaward edge of the platform and one in of No. 3. This places it a short distance back the back-reef zone. from the edge of the platform. The top 52 feet Since the back-reef hypothesis would or- of the core is composed of loose sand and shelly dinarily call for a broad platform covered in material with coral fragments. At the 52-foot places with patch reefs and edged by a bank level the Key Largo Limestone was encountered reef, the sites for the cores were selected with and it continued to the 72-foot level where the these factors in mind. Two bank-reef sites drilling had to be discontinued. Montastrea separated by 90 miles were chosen in order to annularis and Acropora cervicornis appeared in determine the possible existence of an under- places. The most important find, however, was lying bank reef of Key Largo. One patch reef a specimen of A. palmata at the 58-foot level of the back reef was picked in order to see what and another at 65 feet. This is the first time that the foundation was like in the middle of the this species has been reported in the Key Largo tract. Limestone. Core No. 1 was located at the Carysfort In summary, the chief findings uncovered by Lighthouse at the edge of the platform and the drilling program seem to be the following. about 51/2 miles east of Key Largo. Loose, (1) The Key Largo Limestone extends seaward shelly sand and coral fragments were en- from the Keys to the Florida Straits and is the

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 INTKRPRETAT1ON 1497

chief constituent of the foundation upon which period of time. Farther inland less wave action the present Florida coral-reef tract is based. (2) occurred and solution was probably the chief It is covered by loose calcareous sand, shelly erosive agent in the rear areas. The result was material, and coral fragments upon which the an irregularly eroded surface gradually sloping living bank and patch reefs have developed. seaward. (3) The Key Largo surface seems to be ir- The character of the material of the platform regular, higher in the back-reef zone and be- is an important factor in considering the coming lower toward the seaward edge. (4) magnitude of the eroded deposit. An under- Its thickness beneath the platform is at least 110 standing of this may be obtained from a study feet as determined by the No. 3 core drill. (5) of the material which underlies the surface of The Key Largo Limestone has been found to the present platform. The core borings show possess A. palmata at its seaward edge. that the upper 30 to 50 feet down to the hard Key Largo is a loose, unconsolidated sediment INTERPRETATION interspersed with coral patches. If the sea level The discovery of Acropora palmata in the today were lowered and the material of the Key Largo Limestone at the seaward edge of present platform were subjected to wave the platform and at a depth of 58 feet below erosion, it is not too difficult to perceive that it the present sea level is strong evidence for the would be reduced relatively quickly, especially existence of an outer or bank reef at this posi- on its seaward edge. There is no reason to be- tion. It is logical to assume that, at that time, lieve that the material which underlay the patch reefs grew in the back-reef area behind original high surface was any different from this bank reef and that these extended at this this. In other words, we are not dealing with a level at least as far as the Key Largo of the hard consolidated rock similar to the presently Keys. Bank reef and back reef grew upward exposed Key Largo Limestone. Hardening oc- keeping pace with the rising sea level until the curred only after withdrawal of the sea and ex- maximum height of 25 feet above the present posure to the atmosphere. sea level was reached. Another factor to be considered is the At this time, the patch reefs represented by topography of the original reef platform before the Keys flourished. Broecker and Thurber erosion began. An examination of the topo- (1965, p. 58-60) dated the Key Largo corals graphic features of the present platform shows from the Windley Key as about 95,000 years a remarkably uneven surface. Bank reefs and old. Seaward of them there extended a shelf 5 patch reefs rise to the surface of the water but miles wide, with features similar to the present between them are large areas, 25 to as much as coral-reef tract and bordered by a bank reef 40 feet in depth. The surface to be eroded was with its characteristic zonation (Fig. 2). in all probability similar to this. This means that With the coming of the Wisconsin the sea a great deal of the original surface was already level was lowered, and a long period of marine as much as 25 feet or more below the maximum and subaerial erosion followed. When the sea height of the reefs at the time erosion began. returned, new reef growth began on the old That the amount of erosion was significant lowered platform and has continued to the can be seen when one considers the evidence present, eventually producing the coral-reef from the Keys themselves. The Windley Key tract as it stands today (Fig. 3). exposure of the Key Largo Limestone is the The above interpretation requires: (1) the only one which has an elevation of as much as lowering of the original platform to the extent 18 feet. Certainly the old reef must have of about 75 feet in places at its outer edge, 50 reached this level and more in many places at feet near the middle, and progressively less the time it was living. However, the general further inland; and (2) an explanation of the elevation of by far the greater part of the Keys elongated crescentic shape of the Keys today. today is only 2 to 4 feet above high tide. If this These will be considered in turn. amount of erosion has taken place at a distance as great as 5 miles from the seaward edge of the Lowering of the Original Platform platform, it is not difficult to understand that Erosion. When the sea level fell, maximum considerably more could have been removed in erosion occurred at the seaward edge of the ex- the bank reef zone. posed platform and progressively less inland Structural Tilting and Faulting. Although from it. The outer part of the shelf was exposed it is believed that erosion was the chief cause to the full force of the waves for an extended of platform lowering, there is the strong pos-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 1498 HOFFMEISTER AND MULTER-GEOLOGY AND ORIGIN, FLORIDA KEYS

.H u 2

32 Co

c ,0 •3c o

UJ -s

O

M E

«e=g (S o

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 INTERPRETATION 1499

G .0 '-3 a <_oj coo

a aM .3 -a

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 1500 HOFFMEISTER AND MULTER—GEOLOGY AND ORIGIN, FLORIDA KEYS

sibility that this was aided by a certain amount oarallel to the seaward edge of the shelf, and in of structural down tilting or faulting, or both. that way they receive the greatest amount of Down tilting is indicated by the changes in nutriment. In places they have their start on elevation of the Key Largo Limestone itself. the summits of elongated, subsurface ridges There is no doubt that the highest parts of the of calcarenitic material. A glance at the living formation occur in the northern Keys and that Florida reef tract (Coast and Geodetic Survey there is a gradual lowering in the direction of Chart 1249) shows clearly that the patch reefs the Lower Keys. Elevations of the limestone of are strung out parallel to the platform edge and 9 and 10 feet above high tide are common on also to the Keys. In all probability, at the time Key Largo itself. On Plantation Key it main- the corals of the Keys were living, one and pos- tains this height and on the adjoining Windley sibly two other similar elongated series of Key it rises to the maximum elevation of 18 parallel reef patches occupied the space be- feet. There is a marked reduction through the tween them and the bank reef (Fig. 2). They Matecumbees to Key Vaca where it averages were probably separated from each other by a about 2 or 3 feet above high tide. The Keys to mile or so of lower sea bottom. The crescentic the southwest are slightly lower, and at Big pattern of the Keys is not due to a peculiar Pine the Key Largo Limestone slips below sea accident of erosion. They were born that way. level under a cover of the Miami Limestone, This is one of the supporting reasons for be- except along its southern border and the lief in the back-reef origin of the Keys. If they Newfound Harbor Keys, where it stands a foot had originated as a "broad . . . plantation" or so above sea level. It disappears at this point (Stanley, 1966, p. 1940) of M. annularis zone and is not exposed again in the Lower Keys. corals, it would have been difficult to account Along the southern coast of Boca Chica Key, it for their crescentic shape today. The fact is that has been dredged at a depth of 6 to 8 feet be- the Key Largo band of the Keys is a relatively neath sea level and also from the same depth in narrow one. The present breadth and size of the a canal south of Stock Island. A hole drilled in islands themselves is due to the extensive addi- the middle of Key West at appoint about .5 mile tions created by mangroves on both the sea and north of the submerged axis of the formation Gulf sides. encountered it at a death of 30 feet beneath sea level. In summary, there is a drop of at least CONCLUSIONS 25 feet between the highest ooint in the Upper During the last interglacial period, about Keys and that at the end of the chain. This may 95,000 years ago (Broecker and Thurber, 1965, well be due to structural tilting and thus indi- p. 58-60), the coral reefs which today make up cates the possibility of such activity in the area. the Key Largo Limestone of the Florida Keys Downfaulting has been described along the were flourishing as a line of patch reefs in the edge of the Pourtales Terrace parallel to the back-reef area of a broad-reef platform similar Keys by Jordan and Stewart (1961) and Jordan to the Florida reef tract of today. Seaward of and others (1964). Similar type faults may have them the platform was occupied by parallel occurred in the outer reef area of the Florida lines of other patch reefs and edged by an outer reef tract and such may be partially resoonsible reef (Fig. 2). for the lowering of this area as observed today. Subsequent marine and subaerial erosion This can be determined only by further in- following the withdrawal of the sea during the vestigation. Wisconsin, possibly accompanied by a struc- tural downward tilting or faulting of the area, Elongate, Crescent ic Pattern of the Keys or both, resulted in the lowering of the plat- The question has arisen as to why, if the Keys form to a depth of about 75 feet at its seaward represent the last remnants of an eroded plat- edge and progressively less farther inland. With form of patch reefs, "an arcuate ridge of Keys the return of the sea, new reef growth began oriented parallel with the continental margin on the eroded platform and continued to the was left standing above the seaward shelf and present (Fig. 3). Florida Bay" (Stanley, 1966, p. 1939). The Some of the main observations upon which answer is not difficult. It lies in an understand- it is concluded that the Key Largo Limestone ing of how patch reefs grow on a broad, shallow of the Keys originated as a line of patch reef in platform. They do not dot the surface in a a back reef environment are the following. (1) haphazard, random manner. Rather, they The species of corals and other organisms found orient themselves in an elongated fashion fossil in the old reef are identical with those of

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 REFERENCES CITED 1501

the living patch reefs. (2) There is an absence of Largo Limestone, underlying the more recent Acropora falmata, a coral species found com- material of the outer reef, demonstrates its monly in the turbulent waters of living outer presence at the time the Keys were being reefs. (3) There is a favorable proportion of formed and indicates that its absence in the other species common in all zones. (4) Since rocks of the Keys is due to the unfavorable en- the community of coral species found in the vironment of a back reef. Its presence also Key Largo requires an environment of low- indicates the existence of an outer reef at the level energy and since it was determined that edge of the platform during Key Largo time, the water in which the corals grew was shallow, (6) The elongated crescentic shape of the Keys, it becomes clear that they must have developed running approximately parallel to the outer in the protected area of a back reef zone. (5) edge of the platform, is similar to the align- The discovery of Acropora palmata in the Key ment of present day patch reefs.

REFERENCES CITED Broecker, W. S., and Thurber, D. L., 1965, Uranium-series dating of corals and from Bahaman and Florida Key limestones: Science, v. 149, p. 58-60. Cooke, C. W., and Mossom, S., 1929, Geology of Florida: Florida Geol. Survey Ann. Rept. 20, p. 29-227. Ginsburg, R.N., 1956, Grain size of Florida carbonate sediments: Am. Assoc. Petroleum Geologists Bull., v. 40, p. 2384-2427. 1964, South Florida carbonate sediments: Guidebook No. 1 for Geol. Soc. America Miami Meeting, 1964, 72 p. Goreau, T. F., 1959, The ecology of Jamaican Coral Reefs: Ecology, v. 40, p. 67-90. Hoffmeister, J. E., Stockman, K. W., and Multer, H. G., 1967, Miami limestone of Florida and its recent Bahamian counterpart: Geol. Soc. of America Bull., v. 78, p. 175-190. Jordan, G. F., and Stewart, H. B., Jr., 1961, Submarine topography of the Western Straits of Florida: Geol. Soc. America Bull., v. 72, p. 1051-1058. Jordan, G. F., Malloy, R. J., and Kofoed, J. W., 1964, Bathymetry and geology of Pourtales Terrace, Florida: Marine Geology, 1, p. 259-287. Mesolella, K. J., 1967, Zonation of uplifted Pleistocene coral reefs on Barbados, West Indies: Science, v. 156, p. 638-640. Newell, N. D., 1958, American coral seas: New York Acad. Sci. Trans., ser. II, v. 21, p. 125-127. Sanford, S., 1909, Topography and geology of southern Florida: Florida Geol. Survey Ann. Rept. 2, p. 175-231. Shinn, E. A., 1963, Spur and groove formation on the Florida Reef Tract: Jour. Sed. Petrology, v. 33, no. 2, p. 291-303. Stanley, S. M., 1966, Paleoecology and diagenesis of Key Largo limestone, Florida: Am. Assoc. Petroleum Geologists Bull., v. 50, No. 9, p. 1927-1947. Storr, J. F., 1964, Ecology and oceanography of the coral-reef tract, Abaco Island, Bahamas: Geol. Soc. America Spec. Paper'79, p. 1-98. Vaughan, T. W., 1919, Fossil corals from Central America, Cuba, and Porto Rico, with an account of the American Tertiary, Pleistocene, and Recent coral reefs: U. S. Natl. Mus. Bull., no. 103, p. 189-524. Voss, G. L., and Voss, N. A., 1955, An ecological survey of Soldier Key, , Florida: Bull. Marine Sci. of the Gulf and Caribbean, p. 203-229.

MANUSCRIPT RECEIVED BY THE SOCIETY, NOVEMBER 28, 1967 REVISED MANUSCRIPT RECEIVED MAY 22, 1968 CONTRIBUTION No. 960 FROM THE INSTITUTE OF MARINE SCIENCES, UNIVERSITY OF MIAMI, MIAMI, FLORIDA

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 <"~\ "T^ ~

i" "

Large branching fronds of the moose-head coral, Acropora palmata, surrounded by a thicket of Acropora cervicornis. Depth of water about 3 feet.

TOP OF OUTER REEF ABOUT 5 MILES SOUTHWEST OF CARYSFORT LIGHT, FLORIDA REEF TRACT

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 Figure 1. Colony of Acropora palmata showing the flat palmate branches. Outer reef at Carvsfort light, Florida reef tract.

Figure 2. Lobate colonies of Montastrea annularis, Exuma Bank, Bahamas. Depth of water 12 feet.

IMPORTANT FLORIDIAN AND WEST INDIAN CORALS

HOFFMEISTER AND MULTER, PLATE 2 Geological Society of America Bulletin, v. 79, no. 11

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021 ------tract. Depth of water about 6 feet.

------colony of Montastrea annularis in growth position.

LIVING AND FOSSIL COLONIES OF MULTILOBATE MONTASTREA ANNULARIS

HOFFMEISTER AND MULTER, PLATE 3 Geological Society of America Bulletin, v. 79, no. 11

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/11/1487/3432457/i0016-7606-79-11-1487.pdf by guest on 02 October 2021