An Introduction to the Geology of the Bocas Del Toro Archipelago, Panama

Home , Bastimentos Island, Geology of North America, Punta Laurel

An Introduction to the Geology of the Bocas del Toro Archipelago, Panama

A. G. COATES1,D.F.MCNEILL2, M-P. AUBRY3,W.A.BERGGREN4,L.S.COLLINS5

1Smithsonian Tropical Research Institute, Apartado 2072, Republic of Panama 2Division of Marine Geology and Geophysics, Rosensteil School of Marine and Atmospheric Science, University of Miami, Florida, 33149, USA 3Department of Geological Sciences, Rutgers University, Wright Labs, 610 Taylor Road, Piscataway, New Jersey, 08854-8066 4Woods Hole Oceanographic Institute, Department of Geology and Geophysics, Woods Hole, Massachusetts, 02543, USA and Department of Geological Sciences, Rutgers University, Wright Labs, 610 Taylor Road, Piscataway, New Jersey, 08854-8066, USA 5Department of Earth Sciences, Florida International University, Miami, Florida, 33199, USA Corresponding author: [email protected]

ABSTRACT.—We review the stratigraphy of the Neogene rocks of the Bocas del Toro archipelago, western Caribbean coast of Panama, and provide new geological maps and a preliminary description of new Neogene formations on the islands of Bastimentos and Colon. The Punta Alegre and Valiente formations range in age from 19 to 12 Ma. After a hiatus from 12 to 8 Ma, a transgressive/regressive sedimentary cycle is recorded by the Tobobe, Nancy Point, Shark Hole, Cayo Agua, and Escudo de Veraguas formations (=the Bocas del Toro Group), that range in age from 7.2-5.3 to 1.8 Ma. In contrast, in the northern region, the Old Bank, La Gruta, and Ground Creek units and the Swan Cay Formation only range in age from about 3.5 to 0.78 Ma. The hiatus represented by the unconformity is from 12 to 3.5 Ma. We integrate the geology of the Bocas del Toro archipelago into a brief history of the Neogene of the lower Central American isthmus.

KEYWORDS.—Neogene, Bocas del Toro, Central American Isthmus

INTRODUCTION framework for the evolutionary and eco- logical studies of the macrobiota. Background This overview paper provides an intro- Regional Geologic History duction to the geological foundation of the modern biological systems found today in The Central American isthmus forms the the Bocas del Toro region. The study of the western margin of the Caribbean Plate and geology of Bocas del Toro was undertaken lies at the center of a complex intersection as part of the Panama Paleontology Project of the Pacific Cocos and Nazca plates with (PPP; Collins and Coates 1999), a collabo- the Caribbean Plate and the small Panama rative research program to study sediments Microplate (Fig. 1). The dominantly oceanic deposited during the last 20 million years Caribbean Plate lies between the North and (involving the Miocene, Pliocene, and Pleis- South American plates. Its relative east- tocene Epochs, which are together known ward motion, with respect to the North and as the Neogene) along both sides of the South American plates is accommodated isthmus of Central America and of north- by strike-slip faults to the north and in part ern South America (Fig. 1). to the south (now confounded by compres- We systematically mapped the whole re- sion from the west-northwestward-moving gion, named the physical stratigraphic for- South American Plate). In the east, it is mations (Fig. 2) and located the rich and bounded by the Lesser Antilles subduction diverse macrofossil sites. After additional zone. The western margin of the Caribbean paleomagnetic studies and radiometric dat- Plate is more complex; in the northern part, ing, these studies provide a detailed geo- the Cocos Plate is in contact with the Car- logic history of the region and a temporal ibbean Plate. 374 GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 375

FIG. 1. Map of southern Central America (dark shading) and the Panama microplate (pale shading). Dashed lines with teeth mark zones of convergence; zippered line is Panama-Colombia suture. Very heavy dashed line marks location of Neogene volcanic arc. Fine arrows are Paleogene faults; thick arrows are late Neogene faults. Principal Neogene sedimentary basins located by striped ovals. Spotted pattern defines the Cocos Ridge. Arrows on the inset indicate directions of relative motions of the plates. PFZ = Panama Fracture Zone

In the southern portion of the western and is associated with active seismicity and margin, a triple junction brings the Cocos volcanism. Northern Central America also and Nazca Plates in contact with the small has a broad zone of older continental crust, Panama Microplate (Fig. 1). The Panama and has a geologic history extending back Microplate appears to have formed by to the early Paleozoic (Donnelly et al. 1990). northward escape from compression of the In contrast the Nazca Plate has a relative South American and Cocos/Nazca plates easterly motion but is not actively subduct- (Burke and Sengor 1986; Coates et al. 2004). ing under Panama. The Panama Microplate Much of Central America lies either on the is formed of oceanic crust that is typical of trailing western edge of the Caribbean the widespread basalt plateau that under- Plate or on the Panama Microplate but a lies much of the rest of the Caribbean Plate portion also lies on the southwestern cor- (Case et al. 1990). ner of the North American Plate (Fig. 1). Three major movements have affected Since their formation in the Miocene, the the Neogene tectonic evolution of the Nazca and Cocos plates have impinged on southern Central American isthmus (CAI; Central America with different motions. Kolarsky et al. 1995; Coates and Obando The Cocos Plate (Fig. 1), with relative 1996). The first is convergent tectonics of northeasterly motion, is subducting vigor- the eastern Pacific subduction zone (Fig. 1), ously under northern Central America as the primary driving force that created the far south as the Costa Rica-Panama border Central American isthmus by forming a 376 A. COATES ET AL.

western South America (Coates et al. 2004; Silver et al. 1990; Mann and Kolarsky 1995). The relative northwestward movement of South America (Fig. 1) has increasingly compressed the southern Caribbean Plate margin in the late Neogene. This convergence has uplifted eastern Panama and the northern Andes of Colombia and Venezu- ela. The resulting shoaling of the CAI (de- tected paleoceanographically by a marked divergence between planktonic foraminiferal oxygen isotope records (a proxy for salinity changes) was to less than 100 m from 4.7-4.2 Ma (Keigwin 1982; Haug and Tiede- mann 1998; Gussone et al. 2004). This initiated the development of the modern Atlan- tic-Pacific contrast in sea surface salinities (SSS), with higher SSS in the Caribbean. Recent studies by Tiedemann, Steph, and Groenveld and others (Poster sessions, American Geophysical Union Meeting, 2004 and pers. comm. 2005) have suggested 2.8 as the time of final closure of the CAI. FIG. 2. Physical stratigraphic nomenclature of the Using Ca/Mg measurements of planktonic Northern and Southern regions of the Bocas del Toro foraminifera, they show that Caribbean and archipelago with ages in millions of years Pacific Sea Surface Temperature (SST) records are similar from 5-2.8 Ma. Then larger volcanic arc extending southwards from scale sea level fluctuations with 41 kyr. cy- North America. It forms part of an exten- clicity became dominant in response toam- sive zone of subduction that runs the plification of the Northern Hemisphere gla- length of the western margin of North, ciation. After 2.8 Ma, glacial stages, when Central, and South America (Astorga et al. sea level is lowest, show minimum Pacific 1991). SSTs, but maximum SSTs occur in the Car- The second tectonic effect was subduc- ibbean. This anomaly is explained by low tion of the Cocos Ridge (Kolarsky et al. sea stands preventing cooler less saline wa- 1995; Collins et al. 1995), a lighter and rela- ter from entering the Caribbean from the tively thick welt of Pacific oceanic crust, Pacific (the CAI is emergent), and the re- under the Central American volcanic arc in verse applies in interglacials when sea level Costa Rica (Fig. 1). This hard-to-subduct is high, breaching the CAI. ridge rapidly elevated the Central Ameri- The closure of the Isthmus of Panama can Isthmus from the Arenal volcano in triggered profound environmental changes Costa Rica to El Valle in Panama (de Boer et on land and in the sea. The formation of a al. 1988) culminating in the center where bridge between the North and South the Talamanca Range rises to about 4000 m. American continents gave rise to the Great The elevation of the Talamanca range prob- American Biotic Interchange on land ably substantially reduced the number of (Webb and Rancy 1996; Webb 1999). Less marine connections between the Pacific and well known are the timing and nature of Caribbean. the changes in the sea, consequent upon the The third tectonic influence on southern growth of the Central American volcanic Central America was the collision of the arc and its eventual collision with South Central American volcanic arc (the western America. This created a marine barrier that margin of the Caribbean plate) with north- increasingly affected ocean circulation dur- GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 377 ing Neogene time. In the process, a striking in these two areas (Fig. 2). We then attempt contrast evolved between the relatively to synthesize the geologic history of Bocas warm, more saline, nutrient-poor Carib- del Toro and compare it with adjacent re- bean and the more seasonal, less saline and gions in Costa Rica, Darien, Panama, and more pelagically productive eastern Pacific the Atrato Valley, Colombia. (Jackson and D’Croz 1999). These environmental changes apparently altered the 1) The northern region comprises Swan course of evolution, first of the deep-water Cay, Colon, Pastora, San Cristobal, Cari- planktonic organisms like radiolaria and nero, and Bastimentos islands, and the diatoms from about 15 Ma, and then suc- Zapatillo Cays. cessively shallower taxa until complete 2) The Southern region comprises the is- emergence at about 2.8 Ma. By this time, lands of Popa, Deer, Cayo Agua, and Es- the eastern Pacific had evolved rich pelagic cudo de Veraguas, and the Valiente Pen- biotas but poorly developed, low diversity, insula. coral reefs (Jackson and D’Croz 1999). In In general, the northern region exhibits a contrast, the Caribbean had become domi- late Pliocene-Pleistocene succession of shal- nated by coral reef-seagrass-mangrove low water sediments, especially coral reef coastal ecosystems (Collins et al. 1996) and deposits, that either unconformably overlie a profound taxonomic turnover had oc- middle Miocene volcanic arc basalt (Basti- curred in corals and mollusks (Budd and mentos Island) or rest on a thick (>2500 m) Johnson 1997, 1999; Jackson et al. 1993). siliciclastic shale (Colon Island) that is late Much of this history is documented in Pliocene at its top and of unknown age at the long geological section preserved its base. This suggests that there is a major around the Bocas del Toro Archipelago structural break in the volcanic arc base- whose deposits range in age from the early ment rocks between Bastimentos and Co- Miocene (about 20 Ma). The sequence can lon islands. The southern region reveals a be assigned to four phases in the rise of the more extensive volcanic arc suite of lower isthmus as follows: 1) Deposition of lower and middle Miocene rocks, including a se- bathyal, pre-isthmian, oceanic sediments in quence of deep-sea ooze, basalt, coarse vol- early Miocene time (21.5-18.5 Ma); 2) canic sediments and small scale patch reefs, Growth of a volcanic arc during middle that tracks the onset and rise of an active Miocene time (∼18 to ∼12 Ma) characterized volcanic arc in the Bocas del Toro region. by terrestrial and marine deposits includ- Subequently, an unconformably overlying, ing columnar basalt and flow breccia, non-reefal, upper Miocene and Pliocene, coarse volcanic sediments, and scattered marine, transgressive/regressive shelf se- small coral reefs; 3) Extinction of the arc quence was deposited. about 12 Ma and subsequent extensive emergence and erosion; and 4) Subsidence of the volcanic arc during the latest part of Stratigraphic definitions Miocene time (∼7.2-5.3 Ma), resulting in a marine transgression, followed by a marine Stratigraphy of sedimentary rocks in- regression, that culminated in the wide- volves the integration of four main kinds spread development of Plio—Pleistocene of units, each of which provides the basis reefs (McNeill et al. 2000; Coates et al. of a subdiscipline of stratigraphy. The 2003). first, lithostratigraphy, describes the physical stratigraphic units and their three- STRATIGRAPHY dimensional geometry across the region studied. Each mappable unit or Formation is For the purposes of this paper, we first distinguished by its rock type or lithology describe the stratigraphic units that occur and is named, usually from the place where in the south and north of the Bocas del Toro it most typically can be observed. A series Archipelago. These are discussed sepa- of formations deposited in vertical succes- rately because the sequences are different sion in a genetically related depositional 378 A. COATES ET AL. episode may be lumped together as a (i.e., Milankovich periodicity), usually in Group. conjunction with paleomagnetic stratigra- If the contact of two lithostratigraphic phy, to determine the ages of chronostrati- units shows evidence of a break in sedi- graphic and biostratigraphic boundaries. mentation this line is called an unconfor- i.e. the stratigraphic level common to two mity. Unconformities usually reflect major successive stages or biozones. Numerical geological events (like tectonic uplift or sea ages vary depending on the criteria se- level change) in the area where they occur. lected in the building of a gechronologic The significance of unconformities will framework or time scale. The ages given be- vary depending on how different the units low refer to the time scale of Berggren et al. are above and below, and how much time (1995). The boundaries between lithostrati- the break represents. From the nature of the graphic units may be of the same age re- different sediments and their associated gionally, but over larger regions they may sedimentary structures and fossils, the become younger or older in age as the physical environment and water depth in physical environments they represent mi- which the formation was deposited can be grated across the sedimentary basin reconstructed. Fig. 2 outlines the nomencla- through time. They are then said to be di- ture of the lithostratigraphy of the Neogene achronous. formations of the Bocas del Toro archipelago. The second subdiscipline is biostratigra- The southern region phy, which takes advantage of the fossil content of rocks, and is based on the range Each lithostratigraphic unit, starting with of species, i.e., the stratigraphic interval be- the lowest, will first be named and de- tween two specific stratigraphic horizons scribed, and then evidence for its age and corresponding to the lowest (LO) and the environment of deposition will be added. highest (HO) occurrence of a taxon. The ba- For a more detailed description of the sic unit of biostratigraphy is the biozone,a stratigraphy of these units see Coates et al. stratigraphic interval defined between LO (1992, 2003) and Coates (1999). and HO of taxa selected for their distinct Punta Alegre Formation.—This formation morphology and vast geographic distribu- is named for Punta Alegre, the nearest tion. Biozones allow stratigraphic correlation, small village to its solitary exposure. Punta the fundamental procedure of establishing Alegre is located on the western tip of the that two horizons have the same relative north coast of Bahia Azul (Bluefield Bay) in age. Chronostratigraphy, the third element the northern part of the Valiente Peninsula of stratigraphy, is a system of reference for (Fig. 3). The formation can be observed in a the relative dating of sediments. Its basic prominent small cliff about 1.3 km north- unit is the stage, defined by its base (= a west of the village, on the west-facing coast stratigraphic horizon) and a stratotype (a 1 km south of Valiente Point. It consists of stratigraphic interval). Correlation of rocks clay and silty ooze containing abundant in a given basin to a stage is established via calcareous nannofossils and benthic and biostratigraphy. Stages are grouped in a planktonic foraminifera (see Coates et al. nested hierarchy of Series, Systems, and Er- 2003, Tables 1, 2), many of the latter are eas- athems. Their temporal equivalents are ily seen by a hand lens and by the naked called Ages, Epochs, Periods, and Eras, respec- eye. The formation can be seen to lie un- tively. derneath weathered coarse volcanic flow The fourth subdivision, geochronology, breccia (the broken up bouldery rock that is is the science of numerical time. Whereas crated when lava flows and cools at the chronostratigraphy deals with relative time same time). From its abundant planktonic (younger/older), geochronology trans- foraminifera and calcareous nannofossils, forms specific stratigraphic horizons into the age of the Punta Alegre Formation is numerical markers. Geochronology uses 19-18.3 Ma. (Coates et al. 2003), and by its radioisotopic ages and/or astrocyclicity benthic foraminifera it is interpreted to GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 379

have been deposited in water depths of flows and coral reef lenses. The latter con- 100—2000 m (Coates et al. 2003). sist of several species of Montastraea (in- The Valiente Formation.—This unit over- cluding M. imperatoris and M. canalis), mas- lies the Punta Alegre Formation and crops sive Porites waylandi and thin branching out extensively on the Valiente Peninsula Stylophora (possibly S. granulate; Ann Budd (Fig. 3) and nearby Deer and Popa islands pers. comm. 2005). These facies intercalate (Fig. 4). The Valiente Formation is of com- and replace each other over very short dis- plex and highly variable lithology because tances, both laterally and vertically (for de- it represents the suite of facies, marine and tailed descriptions of the facies, see Coates terrestrial, igneous and sedimentary, that is et al. 2003). Fig. 3 shows that the basalt lava associated with an active emergent volca- and flow breccia facies form a core around nic island arc. It includes columnar basalt, which the other facies are distributed pe- basalt flow breccia, pyroclastic tuff (air- ripherally as terrestrial, coastal or marine borne volcanic ash deposits), fluviatile/ slope deposits. Planktonic microbiotas and estuarine conglomerate, marine debris radiometrically dated basalt in the se-

FIG. 3. Geological map and cross section (a –á) of the Valiente Peninsula, Bocas del Toro, western Panama, showing the distribution of the Punta Alegre and Valiente formations and the Bocas del Toro Group. The five lithofacies of the Valiente Formation are indicated by separate colors and numbers on the key (upper right) as follows; v1) basalt lava and flow breccia facies; v2) coarse volcaniclastic facies; v3) pyroclastic facies; v4) coral reef facies; v5) marine debris flow and turbidite facies.

Fi 3 li 4/C 380 A. COATES ET AL.

pelago above the Valiente Formation, sig- nifying extensive emergence and erosion of the volcanic arc from ∼11.5-∼7.2 Ma (Fig. 2, 3). This unconformity can be clearly observed in the inner islands of the Plantain Cays and along the coast immediately to the west. The underlying columnar basalt of the Valiente Formation can be seen on the north side of the Cays and the fossilif- erous conglomerate and sandstone of the Tobobe Sandstone on the south side. The Bocas del Toro Group signifies a new depositional cycle as a marine transgression submerged the older eroded volcanic arc rocks. The oldest sediments thus represent the first shallow-water, beach, and near-shore sand deposits. As the transgression developed, subsequent overlying marine units reflect deeper water deposition until the reverse occurred and the sea re- gressed to shallow water again. Thus, the

FIG. 4. Geological map of Popa Island. Section (b-b’) units of the Bocas del Toro Group are ge- shows the Valiente Formation on Popa Island, where netically related and document a single ma- it is unconformably overlain by the Pliocene Cayo rine transgressive/regressive event. The Agua Formation (ca). Numbers and symbols as for most continuous section lies along the east Figure 3. On Popa Island, only the v1 basalt flow facies and west coasts of the Valiente Peninsula and the v2 coarse volcaniclastic facies (not associated (Fig. 3) where it ranges in age from late with reef lenses) are present, with thin layers of low Miocene (Messinian, 7.2-5.3 Ma) to late rank coal, an example of which is exposed along the ∼ coast immediately north of Punta Laurel. A prominent Pliocene ( 3.5 Ma). basalt dike is exposed at the tip of the Punta Laurel Tobobe Sandstone.—This lowest unit is a (here shown in red as v1 facies) where it cuts the Va- pebble conglomerate that passes up into liente Formation. clean, hard quartz sandstone containing sand dollars, spatangoid echinoids, mollusks, including the large, thin-shelled bi- quence indicate that the Valiente Formation valve Amusium, vermetids and serpulids, ranges in age from 16.5-11.5 million years as well as an array of infaunal burrow old and includes marine deposits from structures. It is best observed on the small near-shore to as deep as 1000 m, as well as Plantain Cay and an adjacent smaller un- several types of terrestrial deposits (Coates named island to the west (Fig. 3). The de- et al. 2003). posit represents a beach and near-shore Bocas del Toro Group.—Columnar basalt sand body and documents the earliest stage and pyroclastic and fluviatile rocks of the of the marine transgression. Planktonic Valiente Formation required extensive foraminifera from laterally equivalent de- emergence of parts of the growing volcanic posits on Toro Cay (Fig. 3) indicate that the arc (columnar basalt is formed by the cool- age of the unit is Messinian (7.2-5.3 Ma). ing of lava ponded lakes). About 12 Ma, the Here the deposit contains a variety of mol- arc had become inactive and recent studies lusks including turritellids and pectens, in Darien, Panama (Coates et al. 2004), sug- erect bryozoa, and echinoids. Classic ex- gest that the collision of the southern tip of amples of complex thalassinoid burrow the Central American volcanic arc with systems constructed by callianasid crusta- South America was initiated at the same ceans are also present. time. These events may explain the major Nancy Point Formation.—It was named unconformity in the Bocas del Toro Archi- for the promontory called Nancy Point

Fi 4 li 4/C GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 381 which lies 2.5 km southwest of the village only along the southern coast of the Va- of Tobobe (Fig. 3). The formation is almost liente Peninsula, east of Secretario. The continuously exposed southward along the Shark Hole Formation consists of mica- coast as far as Chong Point (= Nispero ceous, clayey siltstone that is pervasively Point). The Nancy Point Formation is con- bioturbated and rich in large scaphopods. formable with the Tobobe Formation below The uppermost part of the formation also and the Shark Hole Point Formation above contains abundant, thin, shelly beds and in- (Fig. 2 and 3). It consists of shelly, muddy traformational slumps with pillow folds and silty sandstone, and muddy siltstone and rip-up clasts. Benthic foraminifera in- with occasional coarse volcaniclastic and dicate that the paleobathymetry of this unit bioclastic sandstone beds. It contains scat- ranges from 100-200 m (Collins 1993). This tered mollusks and occasional leaves and represents the first stage of the regressive plant fragments with diverse moderately phase of the Bocas del Toro Group trans- abundant molluscan assemblages through- gressive/regressive cycle. Calcareous nan- out the section and several, rich, low- nofossils and planktonic foraminifera are diversity, thick-shelled mollusk beds at the abundant in several horizons and suggest base. the age of the formation is early Pliocene The transition from Tobobe Sandstone to (5.3-3.6 Ma). Nancy Point Formation is best seen on Toro Escudo de Veraguas Formation.—The Cay (Fig. 3) where dark blue-gray, silty stratigraphic order of the formations de- sandstone, typical of the Nancy Point For- scribed above has been determined by mation, contains occasional, clearly defined physical superposition. The three remain- infaunal burrow systems and extremely ing formations of the Bocas del Toro group abundant and diverse mollusks. It overlies are known only on islands and their posi- coarse, channeled Tobobe Sandstone with tion relative to the other units has been de- only a 10-m exposure gap. Nancy Point termined through stratigraphic correlation. Formation benthic foraminifera indicate The Escudo de Veraguas Formation is that deposition of the Nancy Point Forma- known only from the island of the same tion was in 200-500 m. water depth (Collins name that lies 27 km east of Nancy Point 1993) demonstrating that relatively rapid (Fig. 5) . Its stratotype, for the lower part of deepening took place from near-shore (To- the formation, is along the coast on the east bobe Sandstone) to upper slope (Nancy side of the V-shaped embayment situated Point Formation). This represents the maxi- in the central part of the north coast, about mum depth of the transgressive/regressive 1 km east of Long Bay Point (Fig. 5). The cycle. Planktonic foraminifera and calcare- stratotype for the upper part of the forma- ous nannofossils date the Nancy Point For- tion lies along the west coast for about one mation as Messinian (7.2-5.3 Ma), the same km south of Long Bay Point. time range as for the Tobobe Sandstone. Lithologically, the Escudo Formation Within that time frame the Nancy Point consists of, in the upper part (1.8 Ma), per- Formation is younger because it overlies vasively bioturbated clayey siltstone and the Tobobe Sandstone. silty claystone, with frequent concretions, Shark Hole Point Formation.—It is named and scattered shelly hash, often with scat- for the promontory of the same name that tered whole and diverse mollusks, small, lies 3 km east of Chong Point (Fig. 3) and cornute, ahermatypic corals. The lower part the stratotype lies along the coast between of the formation (3.5 Ma) is more indurated Chong Point and Bruno Bluff, south of Old with very common and densely packed ce- Bess Point. The Shark Hole Point Forma- mented burrow concretions and thalassi- tion conformably overlies the Nancy Point noid galleries at the base, scattered aher- Formation (Fig. 2 and 3) and is overlain by matypic corals through the middle part, an unnamed conglomeratic, cross-bedded, as well as variably abundant mollusks, and coarser grained sequence of volcaniclastics at the top a coral biostrome dominated by containing large pieces of wood and plant Stylophora and sand dollars. The top and fragments. This unnamed unit is exposed botton units suggest deposition in inner 382 A. COATES ET AL.

mon in the middle of the formation. Com- pared to the Shark Hole and Escudo de Veraguas formations, the Cayo Agua For- mation is consistently coarser-grained, with common basalt grains and granules, phosphatic pebbles, and wood fragments. A distinctive marker bed of corals occurs near the top of the formation and is well exposed at Tiburon Point and the unnamed point to the south. The corals appear to be mostly free living, hermatypic, grass flat corals, such as Placocyathus and Manicina (= Teleiophyllia), as well as ahermatypic species, and they suggest deposition in water depths of 30-50 m (Ann Budd, pers. comm. FIG. 5. Geological map of Escudo de Veraguas island. Ages in millions of years in brackets for lower 2005). Evidence from benthic foraminifera and upper parts of the Escudo de Veraguas Forma- (Collins 1993) indicates paleobathymetry of tion. 20-80 m, overlapping the inference from lithology and coral fauna that the Cayo Agua Formation represents a shallow-water fa- neritic water depths, but the middle part of cies. this lower succession has abundant benthic The age of the Cayo Agua Formation is foraminifera indicating deposition in outer dated at the base ∼5.0-3.5 Ma and at the top neritic to upper bathyal water depths (Col- 3.7-3.4 Ma, which suggests it is a contem- lins 1993). porary, shallow water equivalent of the Cayo Agua Formation.—This formation Shark Hole Point Formation and the lower- was named for the island that lies about 6 most part of the Escudo de Veraguas For- km to the west of Toro Point, Valiente Pen- mation. insula. The formation is well exposed along the east coast (Fig. 6) and consists lithologi- The northern region cally of pervasively bioturbated, muddy, The islands in the northern region of the silty sandstone with common horizons of Bocas del Toro archipelago have a different abundant thick-shelled mollusks and aher- geologic history than the southern region. matypic corals. Occasional horizons of Volcanic arc columnar basalts of the Va- pebble conglomerate and very coarse- liente Formation form the basement that grained volcaniclastic sandstone are com- underlies the marine late Neogene succession, as in the southern region. While no radiometric dates for these basalts are available, we can presume they are part of the same volcanic arc that went extinct and cooled after the middle Miocene (∼12 Ma). In all the Northern Region, the sediments unconformably overlying the Valiente For- mation basalt are Plio-Pleistocene in age. The upper Miocene succession of Tobobe Sandstone, Nancy Point, and Shark Hole formations are absent. Furthermore, the northern units are characterized by a major component of coral reef limestone. The geology of Colon and Bastimentos islands are currently being studied and the FIG. 6. Geological map of Cayo Agua. Ages in mil- formal designation of the lithostratigraphic lions of years. units and their ages is not yet finalized. In

Fi 5 li 4/C Fi 6 li 4/C GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 383

general, the sequence is younger than the Valiente Formation.—The spectacular ex- section to the south with the exception of posures along the northwestern coast of the Escudo de Veraguas Formation. The Bastimentos Island (Fig. 7) of columnar ba- oldest units on Colon and Bastimentos is- salt and flow breccia are assigned to the lands may overlap in time with the top of Valiente Formation solely on their great the Cayo Agua and Shark Hole Point se- similarity in lithology. The exposures range quences at ∼3.5 Ma. from Toro Point to the eastern side of

FIG. 7. Geologic map and section (a-a’) of Bastimentos

Fi 7 li 4/C 384 A. COATES ET AL.

Dreffe Beach and occur also at the western Twenty species of corals have been iden- end of Long Beach. These basalt units prob- tified from the limestone near Hill Point, ably form the basement of the entire Bocas the most abundant being Caulastraea porto- del Toro Archipelago. ricensis, Stylophora granulata, Agaricia (= Un- Unnamed Formations of Colon and Basti- daria agaricites), Colpophyllia natans, Mon- mentos islands.—There are three major litho- tastraea faveolata, and Mycetophyllia danaana stratigraphic units (Fig. 2). (Ann Budd, pers. comm. 2005). Exposure of Old Bank Unit (informal field name).—This similar limestone also occurs immediately is the oldest unit, and it crops out exten- to the North of Paunch, on the east coast of sively in the southern half of Colon Island Colon Island, and on Carinero Island (Fig. (Fig. 8) where it is crossed by the Bocas del 8). At Paunch, an entirely extant fauna of Drago road along which there are several corals includes Colpophyllia natans, Diploria good exposures. It also occurs in the north- strigosa, Meandrina meandrites, Montastraea east of the island where it forms a distinct faveolata, and Agaricia (Undaria) agaricites escarpment parallel to the coast. Many (Ann Budd, pers. comm. 2005). streams have waterfalls where they cross On Bastimentos Island (Fig. 7), similar this scarp with good exposures. The same reef deposits appear to sit directly on the unit crops out on Bastimentos Island (Fig. Miocene basalt of the Valiente Formation 7). There are exposures from Juan Brown where they are well exposed on Wild Cane Point eastwards along, and inland of the Key and along the coast for 2 km to the east. south coast, in steep stream courses flow- The reef limestone here is extensively re- ing down from the ridge formed by its out- crystallized but many coral colonies can be crop, which parallels the coast. observed. A particularly well preserved ex- On Colon Island the Old Bank Unit con- ample of the La Gruta reef, packed with sists mostly of a blue-grey mudstone with large and diverse coral colonies is exposed occasional thin sandstone stringers, fine at the base of the cliffs in three small bays at volcanic conglomerate and volcanic boul- Fish Hole, at the southern end of Long der beds. On Bastimentos, it may be mica- Beach. The most abundant species are Di- ceous and sandier, with wood fragments chocoenia stokesi, Manicina (Teleiophyllia) gei- and sparse mollusks including turritellids steri, Montastraea faveolata, M. canalis, Placo- and Anadara. Preliminary field observa- cyathus variabilis, Porites waylandi, P. tions suggest it is an inner shelf deposit macdonaldi, Antillia gregorii, Goniopora im- flanking volcanic islands and that it is peratoris, Agaricia (Undaria) crassa, and Sty- about 3.5-2.0 Ma. lophora granulata. Because >50% of this La Gruta Unit (informal field name).—On fauna is extinct, the La Gruta Formation on Colon Island (Fig. 8), an extensive recrys- Bastimentos appears to be older than that tallized reef and reef rubble deposit is ex- on Colon Island (Ann Budd, pers. comm. posed in the north central part of the island. 2005). Eastward from Hill Point it forms distinc- Ground Creek Unit (informal field name).— tive ridge running parallel to the north Interbedded with and overlapping onto the coast towards Mimitimimbi Creek. The La Gruta Unit are back reef/reef flank de- limestone extends southward as far as La posits, dominantly shelly coral bearing bio- Gruta, a locally famous bat cave. Around clastic carbonate and volcaniclastic sand- La Gruta, the limestone is a reef deposit stone and siltstone. They are typically with numerous large coral colonies but the exposed in several stream courses in the limestone grades into fore-reef rubble northwest of Colon Island in a region northeastwards toward the mouth of Mim- known as Ground Creek (Fig. 8). Near itimimbi Creek where it is well exposed on Ground Creek, the unit has yielded 90 gen- the coast. Both the reef and fore-reef depos- era of bivalves and gastropods in siliciclas- its are heavily fractured to produce a rub- tic mudstone and fine sandstone, where bly rock unit when exposed. Earthquakes they are intercalated with thin carbonate and uplift are likely responsible for this sand containing poritid thickets and other pervasive fracturing. reef patches with platy Caulastraea portori- GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 385

FIG. 8. Geologic map and section (a-a’) of Colon Island.

censis, Porites baracoaensis, Agaricia, ?Clado- The Ground Creek unit also crops out on cora, small domed ?Favia, Manicina (Teleio- Bastimentos Island (Fig. 7), where it is in- phyllia) and serpulids. Also occasionally terbedded with and overlying the La Gruta interbedded are horizons of reworked large unit on Wild Cane Key, and it may also coral heads. crop out around the Valiente Formation

Fi 8 li 4/C 386 A. COATES ET AL. outlier at the northern end of Long Beach the Punta Alegre Formation and are early and overlie the reefs at Fish Hole. Miocene in age (ca. 19-18.3 Ma). They re- Swan Cay Formation.—The formation is cord oceanic muddy and silty ooze depos- named for the small island of the same ited in lower bathyal depths (1000-2000 m) name that lies 1.7 km off the northern coast and the unit is interpreted to represent the of Colon Island (Fig. 8). The stratotype runs pre-isthmian Neotropical ocean. Coeval de- from north (youngest) to south (oldest) posits, like the Uscari Formation in the across Swan Cay. The formation has three southern Limón Basin (Cassell and Sen components. The lower 15 m is exposed on Gupta 1989; Bottazzi et al. 1994), the Clarita the southerly low hill of the island and con- Formation of the Darien (Coates et al. 2004) sists of silty sandstone and shelly calcaren- and the Uva and Naipipi formations of the itic siltstone, with coral rubble and red al- Atrato Basin (Duque Caro 1990) in north- gal fragments and balls. The middle 4 m west Colombia were also deposited at consists of calcarenitic clayey siltstone, bathyal depths. Thus, prior to the collision with dense, fine shell-hash horizons, and of the southern Central American arc with abundant large coral colonies in the lower South America, upper Cretaceous to lower part. The upper 60 m of the formation con- middle Miocene rocks were deposited in sists of massively thick-bedded, pale tan- abyssal to lower bathyal depths in an open- white limestone. The upper 30 m includes ocean, low energy, essentially non- a 4-m-thick coral bed with large Mon- siliciclastic sedimentary environment that tastraea colonies, other corals and mol- was distant from South America (Coates et lusks. The lower 30 m contains silty cal- al. 2004). carenite with common red algae and large Evidence from the overlying Valiente foraminifera, shell hash, and micromol- Formation indicates the rapid growth of a lusks. This limestone also shows evi- pre-isthmian volcanic arc (whose southern dence of frequent microfracturing, many of end was still some distance from South which are healed with secondary calcite ce- America) from about 16.5-12.3 Ma. During ment. Cave deposits, about 5 m above the the deposition of the Valiente Formation base of the calcarenite, consist of silty, (Coates et al. 2003), paleodepths (Fig. 9) in shelly, volcaniclastic sandstone, mixed the region shallowed in general to upper with abundant volcanic cobbles and boul- bathyal depths (200-600 m). However, sub- ders, and calcareous reef rubble contain- marine topographic relief was high as vol- ing an abundant and diverse molluscan as- canoes in the chain grew and coalesced, semblage. The most abundant corals are giving rise to steep sided slopes on which Acropora palmata, A. cervicornis, Diploria the sediments were deposited. Thus, near labyrinthiformis, Montastraea faveolata, Punta Alegre in the Valiente Peninsula, and Porites furcata, Agaricia (Undaria) agaracites, Deer Island (Coates et al. 2003) sediments Meandrina meandrites, and Dichocoenia were deposited in middle bathyal depths stokesi. Organisms from a range of depths (1000-600 m) and at Avispa Point, Toro indicate that the deposit is reworked fore- Point and Cusapin Village deposition was reef debris formed at about 100 m (Collins at upper bathyal paleodepths (600-200 m). et al. 1999). Microfossils are similarly re- Widespread development of columnar ba- worked. Abundant large and freshly pre- salt lava, flow breccia, fluviatile to estua- served globigerinid planktonic foraminif- rine, coarse volcaniclastic deposits, lahars era combined with paleomagnetic data (terrestrial mudflow deposits), and interca- strongly suggest that the deposit is early lated reef lenses, packed with large coral Pleistocene (0.78-1.77 Ma). heads, testify to the extensive emergence of the isthmian volcanic arc in the Bocas del Toro area by 12 Ma (Fig. 3). GEOLOGIC HISTORY Fig. 10 outlines paleogeographic recon- structions for these events. The volcanic arc The oldest sediments recorded in the Bo- underlying the Neogene sediments of Bo- cas del Toro Archipelago (Fig. 9) belong to cas del Toro was an active and emergent GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 387

FIG. 9. Chronological chart showing bathymetric ranges of various formations from the Valiente Peninsula, Popa Island, Cayo Agua, and the southern Limón and Panama Canal basins. Dashed lines enclose the same geologic section. Dotted lines show the biochronologic ranges of sections that are placed according to physical stratigraphy.

FIG. 10. A. Schematic paleogeographic reconstruction of the Panamanian Isthmus at 15-16 Ma. Circles represent reliably dated sections that have yielded rich benthic foraminiferal assemblages useful for paleobathy- metric analysis. The Central Cordilleran Volcanic Arc is shown as a line of islands; the triangles represent volcanoes. Evidence of middle Miocene volcanism in western Panama is from de Boer et al. (1988, 1991) and references therein. Land areas to the south of the arc are interpreted as exotic terrains. The Panamanian Isthmus at this stage was a volcanic island arc with a narrow neritic zone. The Southern Limón and Bocas del Toro Basin sediments indicate bathyal paleodepths in contrast to the Panama Canal Basin where neritic to emergent condition persist through most of the Cenozoic. B: Schematic paleogeographic reconstruction of the Panamanian Isthmus at 11-12 Ma. Symbols as for part A. The neritic zone has by this time expanded significantly and an emergent active volcanic back-arc has developed in the Bocas del Toro Basin. We assume that the Central Cordilleran volcanic arc had become emergent at this time.

Fi 9 li 4/C 388 A. COATES ET AL.

Fi 10 li 4/C GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 389 back-arc, parallel to the main Central Cor- to the overlying upper bathyal (200-600 m) dilleran arc. The environment of the Bocas Chagres Formation (∼6 Ma; Collins et al. del Toro back arc archipelago, by 12 Ma, 1996a). It is not clear whether deepening had patchy shallow-water fringing reefs represents a eustatic (sea level) or a re- around active volcanic islands whose emer- gional tectonic event caused by cooling and gent flanks were characterized by laharic sinking of the Bocas del Toro volcanic arc. breccia and basalt flows. The lahars and By the early Pliocene (Zanclean, 5.2-3.5 flows graded laterally into fluviatile and Ma), marine regression had caused rapid deltaic sequences, and then into resedi- shallowing throughout the Bocas del Toro mented near-shore deposits. Major volcanic Basin (Shark Hole Point and Cayo Agua activity in the area ceased about 12 Ma (the formations). Coeval deposits (4-1 Ma) in youngest radiometric date on columnar ba- the southern Limón Basin (Rio Banano, salt flows,) although there are younger ba- Quebrada Chocolate, Moin, and Suretka salt dykes intruding the Valiente Formation formations) also record rapid shallowing sediments, e.g., at Laurel point, Isla Popa and emergence (McNeill et al. 2000). Simi- (Fig. 4), dated about 8.5 Ma. larly, shallowing to neritic (<100 m) or To the northwest, in the southern Limón emergent conditions was occurring in the Basin, a similar general shallowing pattern Darien region (Yaviza Formation, Tuquesa is observed (Coates et al. 2004, Fig. 9). From and Chucunaque formations; Coates et al. ∼18-13 Ma, the Uscari Formation shallows 2004). These patterns are evidence of the from middle bathyal (1000-600 m) to outer shoaling of Central American isthmus vol- neritic (100-200 m) depths. The record is canic arc (4.7-2.8 Ma). In the Northern Re- absent after 13 Ma. The Gatun Formation gion of the Bocas del Toro archipelago (11.8-11.4 Ma) an inner neritic (<50 m) de- there is an extensive Plio-Pleistocene se- posit in the Panama Canal Basin (Collins et quence, ranging in age from about 3.5 to al., 1996a) is evidence that the emergence of 0.78 Ma, that displays a widespread devel- the isthmus had developed to a similar de- opment of coral reef formation. This is in gree in that region. In the central Darien marked contrast to the very limited coral region (Coates et al. 2004), middle Miocene reef lenses intercalated into the siliciclastic deposits shallowed from middle bathyal Miocene sediments the Southern Region. depths (1000-600 m) in the Clarita and Collins et al. (1996b) have demonstrated the Tapaliza formations (∼16.4-11.2 Ma) to increase, from the late Miocene, of carbon- neritic depths (<200 m) in the Tuira, ate dwelling benthic foraminiferal species Yaviza, and Chucunaque formations (11.2- and of corals associated with increased 5.6 Ma). warming and salinity (and decreased pro- In the Bocas del Toro region, the Valiente ductivity) in the western Caribbean as a re- Formation is unconformably overlain by sult of closure of the Isthmus of Panama. the Tobobe Sandstone Formation (Coates et The Northern Region of the Bocas del Toro al. 1992; Coates 1999), indicating flooding archipelago demonstrates the same trend. of the eroded extinct volcanic arc rocks by very shallow water. Deposition of the mar- CONCLUSIONS ginal marine conglomerate and sandstone signals the start of a marine transgressive/ 1) Prior to the collision of the southern regressive cycle (Fig. 9). Sediments of the Central American arc with south conformably overlying Nancy Point For- America, upper Cretaceous to lower mation (Messinian 7.26-5.32 Ma; Aubry and Miocene rocks of the Bocas del Toro Ba- Berggren 1999) show that deepening pro- sin (lower Miocene, Punta Alegre For- ceeded to upper bathyal depths (200-600 m; mation) were deposited in abyssal to Collins 1993). This deepening is also re- lower bathyal depths in an open-ocean, corded in the Panama Canal Basin (Coates low-energy, essentially non-siliciclastic et al. 2004, Fig. 9) where a rapid transition sedimentary environment distant from occurs from the inner neritic (20-40 m), South America. middle-upper Gatun Formation (∼11-8 Ma) 2) The Valiente Formation records the 390 A. COATES ET AL.

rapid growth of an active volcanic arc tasks. Janet Coates, Gloria Jovane, Lidia which by ∼12 Ma was an extensive Mann, Isis Estribi, and the crews of the RV emergent archipelago of volcanic is- Benjamin and RV Urracca provided invalu- lands flanked by coral reefs. able logistical support over many years. We 3) After a prolonged period of emergence also thank Rachel Collin, Ann Budd, and and erosion, marine sediments began to Aaron Odea for very helpful reviews. cover the extinct volcanic arc starting about 7.2-5.3 Ma. 4) The deposits of this transgressive/ LITERATURE CITED regressive marine cycle are named the Astorga, A., et al. 1991. Cuencas sedimentarias de Bocas del Toro Group. The oldest units Costa Rica: Evolución geodinámico y potencial de (Tobobe Sandstone and Nancy Point hidrocarburos. Rev. Geol. Am. Central 13:25-59. Formation), record deepening to 200 m. Aubry, M-P., and W. A. Berggren. Newest Biostatig- The younger units (Shark Hole Point, raphy. 1999. Appendix 1, In A Paleobiotic Survey of Caribbean Faunas from the Neogene of the Isthmus of Cayo Agua, and Escudo de Veraguas Panama, ed. L.S. Collins, and A. G. Coates, 38-40, formations) represent the regressive se- Bull. Am. Paleontol., No. 357. quence. Berggren, W.O., D. V. Kent, C. C. Swisher, and M-P. 5) In the Plio-Pleistocene, an extensive Aubry. 1995. A revised geochronology and chro- coral reef system developed either on a nostratigraphy. In Time scales and Global Strati- basement of siliciclastic sediments (Co- graphic Correlation, ed. W. A. Berggren, D. V. Kent, M-P. Aubry and J. Hardenbol, 129-212, Society of lon Island, Swan Cay) or on the basalt of Economic Paleontologists and Mineralogists Special the Miocene Valiente Formation (Basti- Volume, No. 54. mentos Island), reflecting the oceano- Bottazzi, G., J. A. Fernandez, and G. Barboza. 1994. graphic changes taking place in the Sedimentología e historia tectonosedimentaria de western Caribbean as a result of shal- la cuenca Limón Sur. Profi, 7:351-391. lowing and closure of the Isthmus of Burke, K. and A.M.C. Senghor. 1986. Tectonic escape Panama. in the evolution of the continental crust. In Reflec- tion seismology: The continental Crust ed. M. Bara- zangi, and L.D. Brown, 41-53, Am. Geophys. Union Acknowledgments.—This research was Geodynamics Ser., 14:41-53, Washington D.C. supported by the National Science Founda- Budd, A.F. and K.G. Johnson. 1997. Coral reef com- tion grants BSR-9006523, DEB-9696123 and munity dynamics over 8 million years of evolu- DEB-9705289 to AGC, LSC, and Jeremy tionary time: stasis and turnover. Proc. 8th Internat. Jackson; several grants from the National Coral Reef Symp., Panama, 423-428. Geographic Society to AGC and LSC, and Budd, A.F. and K.G. Johnson. 1999. Origination pre- Scholarly Studies and Walcott Fund ceding extinction during Late Cenozoic turnover of Caribbean reefs. Paleobiology 25:188-200. awards from the Smithsonian Institution to Case, J.E., W.D. MacDonald, and P.J. Fox. 1990. Car- AGC. We are grateful to the staff of the ibbean crustal provinces. In The Geology of North STRI field station in Bocas del Toro and to America, ed. G. Dengo and J.E. Case, 15-36, vol. H, numerous field assistants of the Panama The Caribbean Region. Decade of North American Ge- Paleontology Project, who have helped ology, Geological Society of America, Boulder, Colorado. with the complex logistics of fieldwork in Cassell, D.T. and B.K. Sen Gupta. 1989. Foraminiferal this region since 1986 (see Collins and stratigraphy and paleoenvironments of the Ter- tiary Uscari Formation, Limón Basin, Costa Rica, J. Coates, 1999 for details), but particularly to Foram. Res., 19:52-71. Beatrice, Lucien Ferrenbach and Doroteo Coates, A.G. 1999. Lithostratigraphy of the Neogene Machado, and whose constant efforts to strata of the Caribbean coast from Limon, Costa maintain motors and vessels, and to orga- Rica to Colon, Panama. In A paleobiotic survey of nize food and gasoline, allowed us to work Caribbean faunas from the Neogene of the Isthmus of with maximum efficiency. We are also very Panama, ed. L.S. Collins, and A.G. Coates, 15-36. grateful to Xenia Saavedra for laboratory Bull. Am. Paleontol., No. 357. Coates, A.G. and J. A. Obando. 1996. The geologic technical and logistical support, including evolution of the Central American isthmus. In Evo- organizing (and sometimes preparing) lution and environment in tropical America, ed. J.B.C. samples, tracking them in the data base, Jackson, A.F. Budd, and A.G. Coates, 21-56, Uni- producing field maps, and numerous other versity of Chicago Press, Chicago. GEOLOGY OF BOCAS DEL TORO ARCHIPELAGO 391

Coates, A.G., J.B.C. Jackson, L.S. Collins, T.M. Cronin, Panama Seaway. Palaeogeogr. Palaeoc. Palaeoecol., H.J. Dowsett, L.M. Bybell, P. Jung, and J.A. 77:203-234. Obando, 1992, Closure of the Isthmus of Panama: Gussone, N., A. Eisenhauer, R. Tiedemann, G.H. the near-shore marine record of Costa Rica and Haug, A. Heuser, B. Bock, Th.F. Nagler, and A. western Panama. Geol. Soc.Am. Bull., 104:814-828. Muller. 2004. Reconstruction of Caribbean Sea sur- Coates, A.G., M-P. Aubry, W.A. Berggren, L.S. Collins, face temperatures and salinity fluctuations in re- and M. Kunk. 2003. Early history of the Central sponse to the Pliocene closure of the Central American arc from Bocas del Toro, western American Gateway and radiative forcing using Panama. Geol. Soc. Am. Bull., 115:271-287. ␦44/40Ca, ␦18O and Ca/Mg ratios. Earth Planet. Sci. Coates, A.G., Collins, M-P. Aubry, W.A. Berggren. Lett., 227:201-214. 2004. The Geology of the Darien, Panama, and the Jackson, J.B.C., and L. D’Croz. 1999. The Ocean Di- late Miocene-Pliocene collision of the Panama arc vided. In Central America, A Natural and Cultural with northwestern South America. Geol. Soc. Am. History, ed. A.G. Coates, 38-71, Yale University Bull., 116:1327-1344. Press, New Haven. Collins, L.S. 1993. Neogene paleoenvironments of the Jackson, J.B.C., J. Jung, A.G. Coates, and L.S. Collins. Bocas del Toro Basin, Panama. J. Paleontol., 67:699- 1993. Diversity and extinction of tropical American 710. mollusks and emergence of the Isthmus of Collins, L.S. and A.G. Coates, Ed. 1999. A paleobiotic Panama. Science, 260:1624-1626. survey of Caribbean faunas from the Neogene of Haug, G.H. and R. Tiedemann. 1998. Effect of the for- the Isthmus of Panama. Bull. Am. Paleontol., 357:1- mation of the Isthmus of Panama on Atlantic 351. Ocean thermohaline circulation. Nature, 393:673- Collins, L.S., A.G. Coates, J.B.C. Jackson, and J.A. 676. Obando. 1995. Timing and rates of emergence of Keigwin, L.D. 1982. Isotopic paleoceanography of the the Limón and Bocas del Toro basins: Caribbean Caribbean and East Pacific: role of Panama uplift in effects of Cocos Ridge subduction? In Geologic and late Neogene time. Science, 217:350-352. tectonic development of the Caribbean plate boundary in Kolarsky, R.A., P. Mann, and W. Montero. 1995. Island southern Central America, ed. P. Mann, 263-289, arc response to shallow subduction of the Cocos Geol. Soc. Am., Spec. Pap., No. 295. Ridge, Costa Rica. In Geologic and tectonic develop- Collins, L.S., A.G. Coates, W.A. Berggren, M-P. Aubry, ment of the Caribbean plate boundary in southern Cen- and J. Zhang. 1996. The late Miocene Panama isth- tral America, ed. P. Mann, 235-262, Geol. Soc. Am. mian strait. Geology, 24:687-690. Spec. Pap. 295. Collins, L.S., A.F. Budd, and A.G. Coates. 1996. Earli- Mann, P. and R.A. Kolarsky. 1995. East Panama de- est evolution associated with closure of the Tropi- formed belt: Structure, age, and neotectonic signifi- cal American Seaway. Proc. Nat. Acad. Sci., 93:6069- cance. In Geologic and tectonic development of the Car- 6072. ibbean plate boundary in southern Central America, ed. Collins, L.S., O. Aguilera, P.F. Borne, and S.D. Cairns. P. Mann, 111-130, Geol. Soc. Am. Spec. Pap. 295. Mc- 1999. A paleoenvironmental analysis of the Neo- Neill, D.F., A.G. Coates, A.F.Budd, and P.F. Borne, gene of Caribbean Panama and Costa Rica using 2000, Integrated biological and paleomagnetic several phyla. In A Paleobiotic Survey of Caribbean stratigraphy of Late Neogene deposits around Faunas from the Neogene of the Isthmus of Panama, ed. Limón, Costa Rica: a coastal emergence record of L.S. Collins, and A.G. Coates, 81-87, Bull. Am. Pa- the Central American Isthmus. Geol. Soc. Am. Bull., leontol. No. 357. 112:963-981. de Boer, J.Z., M.J. Defant, R.H. Stewart, J.F. Restrepo, Silver, E.A., D.L. Reed, J.E. Tagudin, and D.J. Heil. L.F. Clark, and A.H. Ramirez. 1988. Quaternary 1990. Implications of the north and south Panama calc-alkaline volcanism in western framework. J. S. deformed belts for the origin of the Panama oro- A. Earth Sci., 1:275-293. cline. Tectonics, 9:261-282. Donnelly, T.W., G.S. Horne, R.C. Finch, and E. Lopez- Webb, S.D. 1999. The Great American Faunal Inter- Ramos. 1990. Northern Central America; the Maya change. In Central America, A Natural and Cultural and Chortis blocks. In The Geology of North America, History, ed. A.G. Coates, 97-122, Yale University ed. G. Dengo, and J.E. Case, 37-76, vol. H, The Car- Press, New Haven. ibbean Region, Geological Society of America, Boulder, Webb, S.D. and A. Rancy. 1996. Late Cenozoic Evolu- Colorado. tion of the Neotropical Mammal Fauna. In Evolu- Duque-Caro, H. 1990. Neogene stratigraphy, palae- tion and Environment in Tropical America, ed. J.B.C. oceanography and palaeobiogeography in north- Jackson, A.F. Budd, and A.G. Coates, 335-358. The west South America and the evolution of the University of Chicago Press, Chicago.