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The Evolution of the Caribbean Seaway: Jurassic to Present Manuel A. Iturralde-Vinent Museo Nacional de Historia Natural Obispo No. 61, Plaza de Armas La Habana Vieja 10100, Cuba www.medioambiente.cu/museo Abstract This paper presents a summary of the history of the Caribbean Seaway, from its Lower to Middle Jurassic Pangaean epicontinental sea precursor (rift valleys), its debut as an oceanic seaway in the Oxfordian, and its subsequent evolution until the Present. Since Oxfordian, marine connectivity between the Tethys/Atlantic and the Pacific oceans along the Caribbean Seaway have been shaped by the occurrence of different topographic barriers, sometimes as isolated islands and submarine highs, sometimes as continuous land barriers. This scenario can be used to evaluate possible biotic interchange, either by land between the American continents or by water between the Pacific and Tethys/Atlantic oceans. It is demonstrated that during the Eocene-Oligocene transition (35-33 Ma) there was a land barrier in the Caribbean (Gaarlandia), that precluded free ocean water circulation between the Pacific and the Atlantic/Caribbean, probably contributing to the climatic change that took place at this time interval. This barrier was progresively drowned during the Oligocene, restoring the Circumtropical current that warmed up temperature within the Caribbean Sea and the Tropical Pacific. 1 Introduction It is well known that, due to changing Earth paleogeography, global ocean water circulation has changed, controlled by the configuration of the continents, islands, oceans, seas and shallow submarine areas, as well as atmospheric and water composition and dynamic factors (Barrow and Peterson, 1989). As a consequence, present-day patterns of marine circulation cannot be extrapolated to evaluate paleobiogeographic scenarios (Berggren and Hollister, 1974; Frakes et al., 1992; Parrish, 1992). For these reasons, in this paper I briefly explore the origin and evolution of the Caribbean area, using the database compiled by Iturralde-Vinent and MacPhee (1999), as well as the paleogeographic reconstructions published recently (Iturralde-Vinent and MacPhee, 1999; Kerr et al., 1999; Iturralde-Vinent, 1998, Lawver et al., 1999). This is a necessary step toward the understanding of the history of marine biotic exchange between the Pacific and Tethyan/Atlantic oceans. In order to summarize the evolution of the Caribbean Seaway, figure 1 is presented to illustrate the history of topographic barriers between North and South America, and their bearing on the history of marine flow across the area. This history can be subdivided into the following major steps: 1. The Western Pangaean epicontinental seaway, 2. The early opening of the Caribbean Seaway, 3. The Mesozoic evolution of the Caribbean Seaway, 4. The early Cenozoic evolution, and 5. The latest Eocene to Recent evolution of the Seaway. Acknowledgement. This is a contribution to UNESCO/IUGS IGCP Project 433 Caribbean Plate Tectonics. The author wish to thanks his colleague Ross MacPhee (American Museum of Natural History), and an anonymous reviewer, for important suggestions to the original typescript and drawings. Attending the GSA Penrose Conference on The Marine EoceneOligocene Transition (Seattle, 1999) was possible thanks to a grant from the Cuba Group of SSRC. Field work in the Greater Antilles for this paper was partially supported by a NGS Grant to the author. Laboratory work at the Institute for Geophysics of the University of Texas at Austin (UTIG) was possible thanks to grants from the Institute for Latin American Studies (UTEXAS) and UTIG. The Western Pangaean epicontinental Seaway Similarities among several groups of marine animals (pelecipods, ammonites, marine reptiles) that occur both in the western Tethys and the East Pacific suggest that since the 2 Pliensbachian-Hettangian (nearly 190±5 m.y. ago) an aquatic connection existed between these regions (Smith, 1983; Damborenea and Maceñido, 1979; Ricardii, 1991; Gasparini, 1992, 1996). Although the connection, theoretically, may have taken place eastward across the eastern Tethys into the Pacific Ocean, similarities between the western Tethyan and the East Pacific taxa suggest that the connection passed trough the central part of the Pangaean supercontinent (Gasparini, 1978; Smith, 1983; Riccardi, 1991; Gasparini, 1978, 1992, 1996; Gasparini and Fernández 1996; Damborenea, 2000, Aberham, 2001). This connection first yielded a limited exchange of shallow marine taxa (Smith, 1983; Damborenea, 2000, Aberham, 2001), but with time the waterway widened (Pindell, 1994; Lawver et al., 1999) allowing an increasing exchange of marine animals, including both open and shallow marine taxa, limited during the Bathonian-Oxfordian, and extensive since the Oxfordian (Westermann, 1981; Westermann, 1992; Hilldebrandt, 1981; Hilldebrandt et al., 1992: Imlay, 1984; Sandoval and Westermann, 1986; Bartok et al., 1985; Riccardi, 1991; Gasparini, 1978, 1992, 1996; Gasparini and Fernández, 1996; Iturralde-Vinent and Norell, 1996; Damborenea, 2000). According to recent paleogeographic reconstructions, this passway was established before the break-up of Pangaea, probably across a dominantly shallow siliciclastic interior sea located within western Pangaea (Fig. 1; Salvador, 1987; Pindell, 1994; Pindell and Tabbutt, 1995). The fact that large ocean dwelling saurians are recorded from the Middle Jurassic of the southeastern Pacific (Gasparini, 1992; Gasparini and Fernández, 1996) suggest that the western Pangaean epicontinental seaway may have been transected by some deep water channels, probably along grabens and semigrabens produced by crustal extension (rift valleys). This hypothesis is supported by the existence of "continental margin and marine facies" in the preOxfordian probably Bathonian-Bajocian siliciclastic rocks of western Cuba (San Cayetano Formation), with sedimentary features suggesting the occurrence of paleoslopes from fluvio-marine facies into marine environments (Haczewski, 1976; Pszczolkowski, 1978); and by the occurrence of Jurassic rift grabens and semigrabens in the eastern and southern continental margin of North America (Salvador, 1987; Pindell, 1994; Marton and Buffler, 1994, Bullard et al., 1965; Klitgord et al., 1988; Gradstein et al., 1990; Jones et al., 1995, Pindell and Talbut, 1995; Milani and Tomas Filho, 2000). The Pangaean Epicontinental Sea should not be thought of as the ProtoCaribbean basin itself, but as a precursor situated within western Pangaea (Iturralde-Vinent and MacPhee, 1999). For this reason, I propose to avoid the confusing terms "Hispanic Corridor" or "Caribbean Corridor" to designate this seaway and refer to it instead by a more descriptive term, the Western Pangaean Epicontinental Seaway and rift valley system (Fig. 1). 3 The early opening of the Caribbean Seaway As the break-up of Western Pangaea completely separates Laurasia and Gondwana, a new paleogeographic feature formed: the Caribbean Seaway. This Seaway is here understood as a truly oceanic basin located between the North and South American continental landmasses. This seaway represents a linkage between the Pacific and the Atlantic/Tethyan Oceans. In order to explore the origin of this basin, two sources of information are needed: Earliest Mesozoic occurrence of ocean crustal indicators and the first occurrence of true marine environments. The earliest occurrence of Mesozoic oceanic crustal indicators within the Mesoamerican realm comprise the pillow basalts and associated marine sediments reported from the Andean terranes of northern South America (Bajocian/Bathonian Siquisique basalts: Bartok et al. 1985) and from the Guaniguanico terrane of western Cuba (Oxfordian El Sábalo basalts: Pszczolkowski, 1994; Kerr et al., 1999). The original position of the Siquisique basalts is not yet well understood, but probably they belong to the Pacific margin of Pangaea, as do the Andean terranes (Pindell, 1994; Pindell and Tabbutt, 1995, Aleman, A. and V.A. Ramos, 2000). If this is true, they predate the formation of the early Caribbean oceanic crust (Iturralde-Vinent, 1998). This is not the case for the El Sábalo basalts, which probably formed on the Mayan (Yucatan) block margin facing the Caribbean (IturraldeVinent, 1994; Hutson et al., 1999), so they can be thought of as representing a magmatic event related to the initiation of ocean spreading within the Caribbean (Iturralde-Vinent, 1998; Iturralde-Vinent and MacPhee, 1999; Kerr et al., 1999). This inference is corroborated by the occurrence of an important assemblage of Oxfordian marine animals (pelecipods, ammonites, ganoid fish and marine reptiles) in the Guaniguanico terrane of western Cuba (Iturralde-Vinent and Norell, 1996) that are clearly related to both the western Tethys and the eastern Pacific faunas (Ricardii, 1991; Gasparini, 1992; Gasparini and Fernández, 1996; Fernández and Iturralde-Vinent, 2000). The opening of the Caribbean Seaway represents an important paleoceanographic golden spike, --the initiation of Mesozoic deep circumequatorial ocean water circulation that linked the Tethys, the Central Atlantic and the Pacific oceans. The Mesozoic evolution of the Caribbean Seaway 4 It is generally understood that active seafloor spreading between North and South America lasted from Late Jurassic through late Albian, widening the gap between the continents (Pindell, 1994). Subsidence of the crust produced abyssal water depth sections within the area, as early as the Tithonian (Pszczolkowski, 1978; 1982; Iturralde-Vinent, 1998; Iturralde-Vinent and MacPhee, 1999). These processes generally improved the chances for inter-oceanic marine communication across the Caribbean Seaway. This paleoceanographic scenario allowed extensive biotic exchange between the Tethys, the Caribbean and the Pacific, as recorded by the distribution of several mollusks taxa (Shol and Kollmann, 1985; Ricardii, 1991; Rojas et al., 1996; Boitrón-Sánchez and López-Tinajero, 1996). Some numerical models of Cretaceous ocean circulation across the Tethys suggest that the main circulation was directed eastward (Barron and Peterson, 1989). This hypothesis is contradicted by the pattern of ammonite (cephalopod), acteonelid (gastropod) and rudist (pelecipod) dispersion from east to west (Shol and Kollmann, 1985; Ricardii, 1991; Rojas et al., 1996; Boitrón-Sánchez and López-Tinajero, 1996). Marine connectivity along the Caribbean Seaway was eventually moderated by local and regional uplift within the Caribbean (Fig. 1). Iturralde-Vinent and MacPhee (1999) have compiled abundant information concerning the occurrence of locals and regional unconformities and hiatuses, as well as the presence of shallow-water banks, indicating both subaereal exposure and/or submarine topographic highs during the time interval under consideration. These positive topographies must have ultimately interrupted deep ocean circulation, and forced circulation along deep trenches and channels. However, the present state of our knowledge precludes accurate reconstruction of the specific paleoceanographic scenarios. An important permanent barrier that occurs within the Caribbean Seaway is the Bahamas. By Late Jurassic-Early Cretaceous, this shallow water structure included presentday Florida and Bahamas, but since Aptian this megaplatform has been subdivided into smaller platforms separated by a network of abyssal channels (Buffler and Hurts, 1985; Iturralde-Vinent, 1994; 1998). This general barrier allowed restricted deep marine circulation through the channels, but had the special effect of concentrating the main circulation across the Strait of Florida and the Central Atlantic Ocean. Some other barriers probably occurred as islands chains (erosional surfaces and hiatuses within the volcanic sections) and shallows (interbedded shallow marine limestones) along the active volcanic arcs of the Caribbean realm (Iturralde-Vinent and MacPhee, 1999), but these topographic features, during the Cretaceous, were mostly located on the western periphery of the 5 Caribbean (Pindell, 1994; Iturralde-Vinent, 1998). Within these volcanic terranes major uplift events are recorded during the Neocomian, Aptian-Albian, and Coniancian-Santonian; but these barriers were surely non-permanent, because subsidence and deposition of marine rocks are also recorded in them after each uplift (Iturralde-Vinent and MacPhee, 1999). The documented interchange of large terrestrial tetrapods between North and South America, late in the Cretaceous, strongly suggests that there was a landbridge between these continents (Gingerich, 1985; Gayet et al., 1992). Iturralde-Vinent and MacPhee (1999) suggested that this landbridge probably coincided in time with the regional uplift that took place by late Campanian-early Maastrichtian along the Antillean Cretaceous volcanic arc (Fig. 1). This event would have closed the Caribbean Seaway for a period of 1-3 Ma., producing a major change in ocean water circulation and global climate, as the one recorded after the formation of the Panamanian bridge in the Pliocene. The pre late Campanian topographic barriers within the Cretaceous volcanic arcs where ephemeral and probably not continuous landmasses and shallows separated by local deep-water channels (IturraldeVinent and MacPhee, 1999), so their effect on the marine flow across the Caribbean Seaway was not so drastic (Fig. 1). The early Cenozoic evolution of the Caribbean Seaway The end of the Cretaceous in the Caribbean realm was accompanied by strong modifications in the tectonic regime of the area. Rock deformation and collisional tectonics associated with important vertical movements played an outstanding role since latest Campanian and the formation and destruction of topographic barriers was a common phenomenon during the Cenozoic (Khudoley and Meyerhoff, 1971; Pszczolkowski and Flores, 1986; Droxler, et al., 1998; Iturralde-Vinent and MacPhee, 1999). This dynamic of the crustal movements within the Caribbean also produced a more complicated landscape, as several volcanic chains and ridges were present, with a clear tendency toward the reduction of the size of the marine basins (Iturralde-Vinent and MacPhee, 1999: Figs. 6-8). Nevertheless, those barriers did not prevent marine currents from flowing across the Caribbean Seaway (Fig. 1), as Paleogene and Neogene biotas from the Pacific and Atlantic/Tethys intermingled in the Caribbean and/or migrated between these oceans (Papers in this volume; Duque Caro, 1990; Collins, 1996; Iturralde-Vinent, et al., 1997). This biotic interchange was particularly marked during the periods of high stand, recorded by the frequent occurrence of deep water environments within Caribbean early Cenozoic stratigraphic sections (Iturralde-Vinent and MacPhee, 1999). 6 Consequently, during the Paleocene and Eocene, the so-called Circumglobal equatorial current (Droxler, et al., 1998) flowed between the Tethys/Atlantic and the Caribbean/Pacific across the Caribbean Seaway. Figure 2 (60-35 Ma) illustrates, in a very general manner, the Caribbean paleogeography during this time interval. The latest Eocene to Recent evolution of the Caribbean Seaway The transition between the end of the Eocene and the beginning of the Oligocene (zones P16 to P18 of Berggren et al., 1995) coincides with the Pyrenean phase of tectogenesis (Leonov and Khain, 1987), the effects of which are well represented in the Caribbean Region (MacPhee and Iturralde-Vinent, 1995; Iturralde-Vinent and MacPhee, 1999). During this phase, regional tectonic uplift coincided with a major eustatic sea level drop at ca. 35 Ma (Miller et al., 1996). As a result, subaerial exposure within the Caribbean Region was probably more extensive then than at any other time in the Cenozoic, including the late Quaternary. The map (Fig. 2: 35-33 Ma) reflects this fact. However, it is important to compare this map with other “Oligocene” reconstructions which represent this period as one of overall minimum land exposure (e.g., González de Juana et al., 1980; Galloway et al., 1995; Macellari, 1995). The explanation for the difference in treatment lies in the fact that most Oligocene reconstructions depict the paleogeography of the mid- to later Oligocene, by which time the Pyrenean orogenic phase had terminated (Iturralde-Vinent and MacPhee, 1999). Evidence for Pyrenean uplift can be seen in stratigraphic sections as well as submarine dredge samples, drill cores, and seismic lines recovered from many parts of the Caribbean and surrounding continental borderlands (Table1). Many stratigraphic sections consistently lack marine sediments of latest Eocene-Early Oligocene age, presenting instead hiatuses, red beds, and other kinds of terrestrial deposits (Iturralde-Vinent and MacPhee, 1999). In many sedimentary basins located near former topographic highs, latest EoceneEarly Oligocene sediments carry abundant land-derived debris, chiefly very coarse conglomerates (matrix or clast-supported) and sandstones. This type of sedimentary unit is so common in the Caribbean realm that Iturralde-Vinent and MacPhee (1999) dubbed it the "Eocene-Oligocene transition conglomerate event". In places far removed from terrestrial sediment sources, such as the Colombian, Venezuelan and Yucatan basins, deep-marine deposition was condensed (Edgar et al., 1973; Sigurdsson et al., 1997). The Aves Ridge is considered to have constituted the southeastern continuation of the Greater Antilles ridge in latest Eocene-Early Oligocene time. Iturralde-Vinent and 7 MacPhee (1999) argue that exposure of the ridgecrest created, for a short time ca. 33-35 Ma, a series of large, closely-spaced islands or possibly a continuous peninsula (as part of Gaarlandia) stretching from northern South America to the Puerto Rico-Virgin Islands to Central Cuba. Noteworthy, during the Eocene-Oligocene transition is the fact that western Cuba was uplifted, but separated by the Havana-Matanzas deep-water channel from central Cuba (actually from Garrlandia), and by the Strait of Yucatan from the Yucatan Peninsula (Fig. 2; Iturralde-Vinent et al., 1996). Some positive topographic features characteristic of the present Caribbean sea floor did not exist in Eocene-Oligocene times (and are therefore not depicted in Fig. 2). These are the Cayman Trench, Mona Channel, Anegada Trough, etc. (see discussion by MacPhee and Iturralde-Vinent, 1994, 1995). About Latest Eocene, after the colision of the Antillean arc with the Bahamas, general uplift started all along the axis of the present day Greater Antilles, about 37 Ma ago (Iturralde-Vinent and MacPhee, 1999). Short after, during the Eocene-Oligocene transition (c.a. 35-33 Ma) a pronounced topographic barrier (Gaarlandia) reduced to a minimum water exchange between the Atlantic and the Caribbean/Pacific, and a special pattern of ocean water circulation similar to present day was established for a short time (Fig. 2), probably contributing to the climatic change recorded at the Eocene-Oligocene transition (Prothero, 1994). Since the Lower Oligocene, Gaarlandia progressively drowned. Inundation of terrestrial environments began as early as zone P19 (Berggren et al., 1995) and continued into zone P22, as it is indicated by the widespread occurrence of transgresive Oligocene marine sediments in the Caribbean Region (Iturralde-Vinent and MacPhee, 1999, its table 3 and appendix 1). Marine communication between the Atlantic and Pacific reestablished, and the Circumtropical current warmed up the water temperature within the Caribbean Seaway and the equatorial Pacific (Droxler, et al., 1998). This scenario lasted until the Middle Miocene (Fig. 2: 33-9 Ma), and by Late Miocene water circulation across the Caribbean Seaway was restricted again by regional uplift during the Late Miocene (Fig. 2: 9-7 Ma; Coates and Obando, 1996; Iturralde-Vinent and MacPhee, 1999), as is suggested by a foraminiferal faunal turnover in the Panamanian area, by the abundance of high latitude Californian elements in the Panamanian fauna, and the occurrence of South American land mammals in the Late Miocene-Pliocene of North America (Gingerich, 1985; Duque-Caro, 1990; Collins, 1996). The Panamanian barrier was drowned at the end of the Miocene (Fig. 2: 7-3.7 Ma), and soon erected again, first as a shallow submarine ridge, later as a landbridge between North and South American continents (Fig. 2 3.7-0 Ma; Duque-Caro, 1990; Collins, 1996; Coates and Obando, 1996). 8 Conclusions The history of the Caribbean Seaway is very complicated, but can be generally explored with the available data. Figure 1 is a summary of the history of marine connections and topographic barriers within the Caribbean area. This scenario can be used to evaluate possible biotic interchange, either by land between the American continents or by water between the Pacific and Tehys/Atlantic oceans. Figure 2 illustrates the Paleocene to Recent evolution of the seaway, which is the main interest of the present volume. In general, the evolution of the Caribbean Seaway must have had a strong bearing on the global patterns of ocean circulation and climate change in the past, but this is an issue that remains to be studied in more details. References Aberhan, M., 2001, Bivalve paleogeography and the Hispanic corridor: time of opening and effectiveness of a proto-Atlantic seaway, Paleogeography, Paleoclimatology and Paleoecology, v. 165 p. 375-394. Aleman, A. and V.A. Ramos, 2000, Northern Andes, In U.C. Cordani, E.J. Milani, A. Thomaz Filho and D.A. 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Jurassic and Cretaceous marine connections between the southeast Pacific and Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 87:155-189. Rojas, R., M. Iturralde-Vinent and P. Skelton 1995. Stratigraphy, composition and age of Cuban rudist-bearing deposits. Revista Mexicana de Ciencias Geológicas, 12 (2) 272-291 Salvador, A., 1987. Late Triassic-Jurassic paleogeography and origin of the Gulf of Mexico basin: AAPG Bull. 71(4):419-451. Shol, N.F. and Kollmann, H.A., 1985. Cretaceous actaeonellid gastropods from the western hemisphere. U. S. Geological Survey, Prof. Pap. 1304:1-104. Smith, P.L., 1983. The Pliensbachian ammonite Dayiceras dayiceroides and Early Jurassic paleogeography. Can. J. Earth Sci., (20):86-91. 14 FIGURES Figure 1. Major events in the evolution of the Caribbean Seaway from Jurassic to Recent. Data from Iturralde and MacPhee (1999:Fig. 12 and tables 1 - 4). On the left part of the graphic, the dotted vertical strips are the permanent continental masses of North and South America (NA and SA), the central patternless zone represent the Caribbean marine area, and the bubble rows indicate topographic barriers within the Caribbean. The right part of the graphic bring information about the topographic barriers and the marine seaway. The thin vertical strip within the textual area is intended to show in black major shutdowns of the flow along the Caribbean Seaway, and with 15 horizontal pattern the time lapses when water exchange was possible between the Pacific and Atlantic/Tethyan oceans. Chronology not to scale. Figure 2. Main scenarios of Late Eocene to Recent marine surface circulation across the Caribbean Seaway. After data from Prothero (1994), Coates and Obando (1996), Droxell et al. (1998), Iturralde-Vinent and MacPhee (1999: Fig. 10). Since the Late Eocene the course of westward-flowing currents in the mid-Atlantic/Tethys across the Caribbean Seaway has been greatly affected by the appearence and disappearence of various topographic barriers. Thus, the Circumtropical current, which originally passed into the western Pacific (Late Eocene) was temporarily disrupted during the Eocene-Oligocene transition by the emergence of Gaarlandia, during the Late Miocene by the partial emergence of Central America, and was permanently disrupted by the uplift of Central America in the Late Pliocene. 16 Table 1. Stratigraphic indicators for land, shallow marine, and deep marine environments during the latest Eocene-early Oligocene (35-33 Ma, Zones P16-18) interval within the Caribbean realm and its surroundings. Some present-day geographic areas are not listed because they do not existed at this time interval (Cayman Trench, Windward Passage, Mona Passage, Anegada Trough, etc.). Compiled from Iturralde-Vinent and MacPhee, 1999, table 2 and appendix 1. Location Land indicators Shallow marine and Deep marine (hiatuses, red beds, costal indicators indicators alluvia, paleosls, (lagoonal sediments, (Globigerine ooze, terrestrial plant and carbonate shelf, etc.) etc.) animal fossils, nearshore conglomerates) Florida Peninsula X X - Bahamas Platform X X X Southern Mexico X X X Yucatan Peninsula X X X Northern Central X - - - X X X X X X X - Nicaragua Rise X X - Cayman Ridge X X - Beata Ridge - X - Aves Ridge X X - Cuba X X X Jamaica X X X Hipaniola X X X Puerto Rico-Virgin X X - Lesser Antilles X X ? Yucatan Basin and - ? X America Southern Central America Northeastern South America Northeastern South America shelf and islands Islands 17 Cayman Rise Colombia and - - X - X X Venezuela Basins Grenada Basin 18