Quaternary Intertidal Deposits Intercalated with Volcanic Rocks on Isla

Journal of Coastal Research

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West Palm Beach, Florida

July 2010

Quaternary Intertidal Deposits Intercalated with Volcanic Rocks on Isla Sombrero Chino in the Gala´pagos Islands (Ecuador) Markes E. Johnson{, Paul M. Karabinos{, and Victor Mendia{ { Department of Geosciences Williams College Williamstown, MA 01267, U.S.A. [email protected]

{

www.cerf-jcr.org

P.O. Box 17-21-890, Quito, Ecuador

ABSTRACT JOHNSON, M.E.; KARABINOS, P.M., and MENDIA, V., 2010. Quaternary intertidal deposits intercalated with volcanic rocks on Isla Sombrero Chino in the Gala´pagos Islands (Ecuador). Journal of Coastal Research, 26(4), 762–768. West Palm Beach (Florida), ISSN 0749-0208. A stratigraphic succession composed of limestone intercalated with volcanic ash and basalt capped by a conglomerate of mixed limestone and basalt cobbles was deposited in a trough-shaped depression approximately 25 m wide and 50 m long to a thickness of 1.62 m on the southwest side of Isla Sombrero Chino in the Gala´pagos Islands of Ecuador. Two layers of well-cemented calcarenite up to 20 cm thick accumulated as beach deposits with bioclasts of gastropods dominated by the Gala´pagos Periwinkle (Nodilittorina galapagiensis), a representative of the Beaded Hoofshell (Hipponix grayanus), broken crab fragments, and bird bones. Crustacean remains most likely belong to the Sally Lightfoot Crab (Graspus graspus). The bird bones are attributed to Audubon’s Shearwater (Puffinus iherminieri). Distinctly intertidal in origin, such a mixed assemblage of invertebrates and vertebrates is unusual, and the association with basalt flows is seldom met in the rock record. The pristine state of the volcanic cone on Sombrero Chino is consistent with a 3He exposure age of 13 6 0.8 ka. The age of the basalt-limestone sequence is unknown but must be younger than the 3He exposure age. The basaltlimestone sequence is elevated approximately 3 to 4 m above current sea level. This implies that the intertidal limestone was deposited during an interval of higher sea level or, more likely, was uplifted by magmatic inflation. Such intertidal deposits, in conjunction with more precise dating, have the potential to constrain the history of relative sea-level change during island growth and isostatic subsidence related to volcanism and lithospheric cooling. Intertidal deposits of the kind reported here also help to distinguish between monogenetic as opposed to polygenetic history for volcanic islands.

ADDITIONAL INDEX WORDS:

Ash beds, basalt flows, intertidal biotas, gastropods, crabs, shore birds.

INTRODUCTION Intertidal deposits are common near unconformities in the rock record, but more often from the Neogene (10 Ka to 23 Ma) than older parts of the chronostratigraphic record. In a review based on 230 published reports on rocky shores spanning all geological ages, nearly half (48%) are Neogene (Johnson, 2006). Less than 10% of those 230 reports identify intertidal deposits related to volcanic shores, mostly continental shores composed of andesite flows. Given the huge number of islands in today’s oceans, it appears that the Cenozoic and Mesozoic record of intertidal deposits on unconformities with basalt is underrepresented in the literature. The small number of such intertidal deposits reflects both the ephemeral nature of volcanic oceanic islands, which subside once volcanic growth ceases, and sea-level rise, which has the potential to submerge many intertidal deposits. Uplift of a volcanic island’s shore by magmatic inflation at a rate that exceeds both isostatic subsidence and sea-level rise is another mechanism for exposing intertidal deposits.

DOI: 10.2112/JCOASTRES-D-10-00010.1 received and accepted in revision 19 January 2010. ’ Coastal Education & Research Foundation 2010.

Darwin (1844) made detailed observations pertaining to a limestone deposit trapped between basalt flows on the island of Santiago in the Cape Verde Archipelago. Since the voyage of the HMS Beagle in which Darwin participated (1831–1836), few studies have surpassed his level of observation on this particular topic. A notable exception is the study by Ladd and Hoffmeister (1945) regarding limestone-basalt relationships on 26 islands in the eastern part of the Fiji Archipelago. Research by Lietz and Schminke (1975) regarding Las Palmas Terrace on gran Canaria (in the Canary Islands) is a more recent example of a stratigraphic study that interprets the relationship between volcanic flows and fossil-bearing coastal sediments of Miocene to Pliocene age. Fossils from intertidal deposits reflect both the preservation of organisms with hard parts that lived in a coastal setting and those whose remains were transported to the shore from other places. Among the former are marine invertebrates from a wide range of phyla that adopted habits of encrusting, clamping, or boring on rocky shores (Johnson and Barli, 1999). Among vertebrate fossils, there are many kinds, such as marine mammals, turtles, fishes, and sharks, most of which spent little or no time ashore (Johnson, Ledesma-Va´zquez, and Baarli, 2006). It is unusual to find an intertidal deposit that includes a mix of invertebrate and vertebrate fossils with a proven affinity

Quaternary Fossils and Volcanism in the Gala´pagos Islands

Figure 1. Maps: (A) Gala´pagos Islands, (B) Isla Santiago (part) and Isla Sombrero Chino, and (C) study site on the southwest side of Isla Sombrero Chino.

for shore life. Yet more seldom is discovery of an intertidal deposit with invertebrate and vertebrate fossils related to basaltic shores. The purpose of this report is to describe fossil-rich limestone beds intercalated with basalt flows and volcanic ash from Isla Sombrero Chino in the Gala´pagos Islands of Ecuador. Most visitors come to the islands to see and study the living fauna and flora, but the volcanic Gala´pagos also feature some limestone and volcaniclastic deposits with fossils. Darwin (1844) was the first to mention marine fossils from the Gala´pagos on Isla San Cristobal (Figure 1A), but relatively little interest has been devoted to this topic in the many years since Darwin’s historic stopover. Hickman and Lipps (1985) compiled a classification of several kinds of fossiliferous deposits found on six of the Gala´pagos Islands, the most widespread being volcanic tuffs with fossils. Another category is ‘‘limestones and sandstones interbedded with basalt’’ (Hickman and Lipps, 1985), but heretofore the only known example has been the extensive limestone plate with a diverse assemblage of Upper Pliocene fossils (Hertlein, 1972) from the basaltic cliffs of Baltra and northeastern Santa Cruz (Figure 1A). Although modest in scope, our contribution shows that it is possible to glean new data and insights on the fossils and strata of the Gala´pagos Islands in some of the most heavily visited parts of the archipelago.

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elevation about 30 m above sea level, the summit rim of the spatter cone is approximately 70 m in diameter. The islet is separated from the southeast coast of Isla Santiago by a 180 m wide channel (Figure 1B). According to Swanson et al. (1974), volcanic activity on Isla Santiago spanned much of the last 700 ka, the age of the oldest dated rock. However, Geist (personal communication) suggests that Isla Santiago emerged between 1.4 and 1.0 ma. Sombrero Chino is a popular stopping place in the Gala´pagos National Park (Site 38) with a 450 m long nature trail that requires a wet landing near the northwest end of the island at the narrows across from Isla Santiago (Anonymous, 2002). Visitors are strictly prohibited from climbing the volcano, and all activities are restricted to the trail. The official handbook for naturalist guides attributes the steepness of the volcanic cone to spattered lava ‘‘which erupted in the form of thick globs, that fell near where they left the earth’’ (Anonymous, 2002, p. 126). No additional information is provided in the handbook regarding other geologic features. Part of the park trail is littered with broken coral fragments and carbonate sand close to the shore. In other places, the trail intersects empty lava tubes up to 50 cm in diameter that run down the volcano’s slope toward the sea. Sombrero Chino is within sight of several other islets that occur as spatter, cinder, and tuff cones, known as the Rocas Bainbridge. These cones were the result of phreatic and littoral eruptions during late-stage volcanic activity on Isla Santiago that channeled the upward migration of magma away from the island core to the margins through an extensive fracture system (Swanson et al., 1974). The largest of the Rocas Bainbridge features a crater lake with cored sediments dated by 14C as approximately 7.13 ka (calendar years; Riedinger et al., 2002). This is in accord with a 3He-exposure age of 9.7 6 0.6 ka for the Rocas Bainbridge reported by Geist (personal communication). As recently as 1897, lava flows on Isla Santiago reached the narrow channel, separating it from Isla Sombrero Chino (Simkin and Siebert, 1994).

METHODS AND MATERIALS Faculty and students from Williams College visited Isla Sombrero Chino on March 29, 2009, led by Park Naturalist Victor Mendia on the M/Y Floreana. All activities and observations were limited to the park trail. All strata and fossils were photographed in place and left intact. The guidebook by Hickman and Finet (1999) was used to identify marine invertebrate shells. Commentary by Jackson (1994) and Heinzel and Hall (2000) on shore birds and crabs in the Gala´pagos Islands were consulted for insight on the most likely identifications of other fossil materials. Time limitations prevented us from making a detailed survey of the small study site on Isla Sombrero Chino. However, we created a map of the study area using a camera enabled by a global-positioning system (GPS) and the many photographs taken while at the site. The GPS positions are accurate to within 63 m.

GEOGRAPHIC AND GEOLOGIC SETTING Isla Sombrero Chino is a volcanic islet approximately 700 m long and 450 m wide with a low cone-shaped profile that resembles a Chinese laborer’s hat, hence the name. At an

LOCAL STRATIGRAPHY AND TOPOGRAPHY The volcanic terrain near the end of the Parque Nacional Gala´pagos trail on the southwest side of Isla Sombrero Chino

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Figure 2. Photographs of interbedded volcanic and sedimentary strata near the end of the Parque Nacional Gala´pagos trail on Isla Sombrero Chino (for map location, see Figure 1C). Numbers correspond to layers in the column in Figure 3.

features a thin basalt flow with an extensive surface exposure of polygonal cooling cracks (Figures 2A–D). Strata below this flow are exposed on the margin of a local topographic swale, which reveals an underlying limestone bed separated from an older basalt flow by a tuff bed (Figure 2E). Careful examination of the site further demonstrates traces of a second limestone bed found only in thin patches above the upper basalt with the polygonal joints. In some places, the overlying limestone fills the joints between the basalt polygons. The two basalt flows can easily be distinguished because the lower layer is vesicular basalt, whereas the upper layer contains polygonal joints but

lacks vesicles (Figure 3). Locally, a conglomeratic deposit consisting of basal cobbles and boulders mixed with platy pieces of broken limestone is piled atop the polygonally jointed basalt (Figure 3). The conglomerate is restricted to the lower elevations of the study area near the shore (Figure 1C). The troughlike depression in which the stratigraphic sequence occurs is approximately 25 m wide and 50 m long with a 5u downward slope trending 280u toward the shore. We were unable to survey the area in detail to determine the precise elevation of the intertidal deposits but based on visual estimates and average GPS elevation data, the basalt-lime-

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Figure 3. Measured stratigraphic column representing interbedded volcanic and sedimentary strata in a topographic swale near the end of the Parque Nacional Gala´pagos trail on Isla Sombrero Chino.

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brates. Hipponix grayanus (Beaded Hoofshell) is a limpet that occurs as a fossil from this level (Figure 4C). This extant species is common in the Gala´pagos Islands, but also occurs today from Mazatla´n, Mexico, in the north to Peru in the south. The habitat of the Beaded Hoofshell is intertidal and shallow subtidal to 20 m (Hickman and Finet, 1999). A large worn shell that probably belongs to the genus Neorapana (not figured) was spotted at the same level. Extant species are carnivorous gastropods that thrive in intertidal to shallow subtidal settings. Other fossils from the lower limestone unit include bits of crab claws and bird bones. Figure 4D shows a segment of a crab claw slightly more than 2 cm in length. The most likely candidate is Graspus graspus, the Sally Lightfoot Crab (also known as the Red Rock Crab), which is ubiquitous on the rocky shores of the Gala´pagos Islands and mainland rocky shores from the Pacific coast of Mexico to Chile. The fossil fragment has a porcelainlike quality and is pure white. Loss of original coloration probably was due to bleaching, but the increased hardness may have been the result of volcanic baking. Bits and pieces of small fossil bones that clearly demonstrate the hollow characteristics of bird bones are firmly incorporated into the limestone matrix. Figure 4E illustrates a bone fragment 1.75 cm in length along the shaft with a diameter of 3 mm, expanding to 7 mm at the intact end of the shaft. The shape of this fragment suggests that it is a femur bone. Another bone fragment that is 4 cm long parallel to the shaft (Figure 4F) has a diameter of about 3 mm with a notable increase at the proximal epiphysis. This shape suggests a long bone characteristic of the tibiotarsus. Any number of shore birds could be the donor species for these particular bones, but the likely candidate is Puffinus iherminieri (Audubon’s Shearwater) for reasons outlined in the Discussion section.

stone sequence is approximately 3 to 4 m above present sea level.

DISCUSSION Habitat Coherence of Fossil Representatives

FOSSIL CONTENT The lower limestone unit is the thicker of the two limestone beds (Figure 3) and includes laminations of calcarenite with abundant fossils. On the upper surface of a loose limestone slab that probably comes from this level (Figure 4A), there is a dense accumulation of small fossil gastropods, all of which belong to the extant species Nodilittorina galapagiensis. The concentration of shells on the bedding surface is about 40 individuals/25 cm2 with approximately half the shells showing signs of physical wear. A single fossil representative of this species is shown in Figure 4B. According to Hickman and Finet (1999, p. 47), this endemic species is the dominant gastropod mollusk in the upper and mid intertidal zone with a ubiquitous presence on rocky shores throughout the Gala´pagos Islands. The Gala´pgos Periwinkle (common name) is an herbivorous gastropod that makes a living by rasping encrusting microscopic algae from the rock surface (Hickman and Finet, 1999). Fossil specimens of this species from the bedding plane exposed on the lower limestone unit are not nearly as prolific as seen in loose slabs, but well represented. Sparsely fossiliferous by comparison, the upper limestone unit also yields some valuable information on marine inverte-

All fossil gastropods found in the limestone units from the southwest side of Isla Sombrero Chino are indicative of an intertidal, rocky-shore setting. If the fossil crab fragments belong to the common Sally Lightfoot Crab, this interpretation of habitat source is further strengthened. Bird fossils are more difficult to identify and several possible candidates among the shore birds could include Audubon’s Shearwater (P. iherminieri), the Oystercatcher (Haematopus ostralegus), the Semipalmated Plover (Charadrius semipalmatus), the Ruddy Turnstone (Arenaria interpres), the Wandering Tattler (Heteroscelus incanus), and the Sanderling (Crocethia alba) based on comparative bone sizes. Among these, all but Audubon’s Shearwater and the Oystercatcher are migrants with no permanent breeding populations in the Gala´pagos Islands (Harris, 1973; Jackson, 1994). Migrant birds visiting the Gala´pagos from among these species tend to be small in numbers (Harris, 1973). Low population counts also are typical of the resident Oystercatcher. In contrast, Audubon’s Shearwater is a native tropical seabird maintaining yearlong residency. It is also a slightly larger bird with an adult body mass up to 170 g, and it habitually nests in colonies in rock crevices or in small burrows on the coast (Jackson, 1994). This

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Figure 4. Fossils from limestone deposits on Isla Sombrero Chino, including (A) loose slab with dense concentration of the gastropod Nodilittorina galapagiensis; coin for scale: 2.5 cm: (B) individual loose specimen N. galapagiensis, shell height 1 cm): (C) individual specimen from bedding plane Hipponix grayanus, maximum shell diameter 1 cm: (D) piece of crab claw, possibly G. graspus: (E) proximal end of bird femur bone, possibly from P. iherminieri: (F) bird long-bone fragment, possibly from P. iherminieri.

species is one of the most common birds throughout the Gala´pagos Islands (Heinzel and Hall, 2000, p. 166), which statistically makes it a good candidate for fossilization. Flocks of nesting P. iherminieri are reported in the hundreds on Isla Sombrero Chino (Heinzel and Hall, 2000, p. 96). More important, the bird’s nesting habits are consistent with an overall rocky-shore setting. It must be emphasized that bird bones rarely are described from the fossil record. No occurrences are noted in the survey by Johnson et al. (2006) on vertebrate remains from former rocky shorelines. One of the few sea birds identified from fossil bones in coastal deposits is described by Seguı´ et al. (2001) as a petrel from the Miocene of Minorca in the Balearic Islands of the western Mediterranean. Quaternary bird bones are widely known to occur in lava tubes, where the bones are preserved in

owl pellets. Among other vertebrate groups, Steadman (1986) recognized more than a dozen bird species from cave deposits on Isla Floreana based on fossil bones that included Audubon’s Shearwater (P. iherminieri). The novel aspect of bird bones from Isla Sombrero Chino is that they represent burial in what was clearly a coastal setting.

Depositional Setting and Volcanism Although the study site on Sombrero Chino is close to a modern rocky shore and features a fossil assemblage typical of a rocky-shore environment, the depositional setting of the limestone beds in which those fossils occur is a small pocket beach. The primary evidence for this interpretation is that the fossils constitute the coarse fraction of a calcarenite composed

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of bioclastic materials. The lower and thicker carbonate unit also is distinctly laminated parallel to master bedding planes on a 5u slope toward the nearest shore. Beach sands were apparently trapped in the shallow swale at this locality, where wave action contributed many whole shells and some bone debris washed from adjacent rock surfaces. Hence, the fossils from this locality represent a transported assemblage; although the rock surfaces where the organisms lived were clearly nearby. A lava flow on the southwest flank of Sombrero Chino capped and armor plated the lower limestone deposit that accumulated there. The upper limestone bed is locally preserved above the polygonally jointed basalt (Figures 2B and C). We did not observe the upper limestone bed directly below the conglomerate composed of limestone rip-up clasts and basalt cobbles (Figure 3). We interpret the limestone clasts in the conglomerate as recycled fragments from the upper limestone bed. The sharp contact between the conglomerate (unit 6 in Figure 3) and the polygonally jointed basalt (unit 4 in Figure 3) is inconsistent with a weathering origin for the conglomerate (Figures 2D and E). Also, it is important to note that the conglomerate is restricted to the lower elevations of the site close to the shore. Thus, we interpret the conglomerate as a chaotic storm deposit. Vigorous wave activity was necessary to rip up the limestone layers and polygonally jointed basalt that form the conglomerate, as discussed further on. The basalt-limestone succession on Sombrero Chino sits approximately 3 to 4 m above current sea level. There is no evidence for a eustatic sea-level increase of this magnitude during the last 13 ka. Thus, it seems more likely that at least this part of the shore on Isla Sombrero Chino was uplifted by magmatic inflation after the formation of the intertidal deposits. If the limestone beds or the adjacent basalt flows can be more accurately dated, the magnitude of inflation could be more confidently estimated in conjunction with eustatic sealevel curves. Geist (personal communication) suggests that the satellite islets around Isla Santiago are monogenetic centers and that the 3 He exposure ages also date the emergence of those islets. The latter interpretation is certainly reasonable, but the intertidal limestone and basalt sequence described herein suggests that Isla Sombrero Chino experienced a more protracted and polygenetic history characterized by multiple lava flows.

Local Topography and Coastal Dynamics Attuned to the geological underpinning of landscapes, Darwin (1844, p. 113) observed that all 28 tuff craters visited by the Beagle in the Gala´pagos Islands ‘‘had their southern sides either much lower than the other sides, or, quite broken down and removed.’’ This is certainly true of the Rocas Brainbridge in the vicinity of Sombrero Chino, including the largest island with its 7.13 ka crater lake (Reidinger et al., 2002). Darwin interpreted this phenomenon as a consequence of the prevailing trade winds that regularly bring ocean swells and waves from the south and southeast in the Gala´pagos Islands. The soft tuff construction of many volcanic cones easily might be eroded on any side, but the line of wave attack arrives mainly from the south.

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Despite its well-preserved profile, 3He exposure ages from Sombrero Chino (13 6 0.8 ka) are older than the one 3He exposure age from the more eroded cones belonging to the Rocas Bainbridge (9.7 6 0.6 ka; Geist, personal communication). Thus, the well-preserved profile of Isla Sombrero Chino reflects greater resistance to erosion rather than a younger age. Isla Sombrero Chino is oval in outline, and the steepest slope from the crater rim to the shore is on the southeast flank, suggesting that erosion may be faster on this side and caused by exposure to greater wave activity. The west-trending trough, in which the basalt-limestone deposits were deposited, is sheltered from waves from the south or southeast. In fact, the opening of the shallow swale on the southwest side of Sombrero Chino is roughly 100u out of alignment with wave fronts affecting the islet from the open ocean to the south. Ocean swells from the south may be amplified as they enter the narrow and shallow south-facing channel between Isla Santiago and Isla Sombrero Chino. This mechanism may have provided sufficient energy to create the conglomerate preserved on the southwest end of Isla Sombrero Chino.

CONCLUSIONS As tourists, geologists are prepared to see and appreciate things that visitors otherwise well attuned to nature might overlook. This was the case during a recent excursion to the Gala´pagos Islands that included a stopover on Isla Sombrero Chino in the center of the archipelago close by Isla Santiago. Regular advances have been made regarding the fossil history of the islands (Hertlein, 1972; Hickman and Lipps, 1985; Steadman, 1986 among others), but the Gala´pagos are better known for the enigma of distinct faunas and floras that evolved on a chain of volcanic islands without leaving a significant fossil record. Not only in the Gala´pagos Islands, but elsewhere with regard to oceanic islands, there is a notable lack of observations on the interplay between extrusive volcanic rocks and the sort of sedimentary deposits that normally include fossils. The geographic distribution of sedimentary deposits and volcanic flows on rocky islands must conform to the larger oceanic and atmospheric circulation patterns of any given region. Although there are some peculiarities, Quaternary relationships on Isla Sombrero Chino can be explained and may be useful in predicting where to look for intercalated limestone and basalt strata on other, older islands. In summary, the following conclusions pertain to this study: (1) Two limestone beds up to 20 cm thick are interpreted as beach calcarenites intercalated with volcanic ash and basalt flows not far from the present shoreline on the southwest side of Isla Sombrero Chino. They are younger than 13 ka and sit 3 to 4 m above present sea level. (2) The coarsest bioclasts in the beach calcarenites consist of abundant gastropods, roughly 50% whole shells mixed with the broken debris of crabs and bird bones. The small Gala´pagos Periwinkle (Nodilittorina galapagiensis) is most plentiful. Present but uncommon are the Beaded Hoofshell (Hipponix grayanus), pieces of crab shell that fit with the Sally Lightfoot Crab (G. graspus), and bone

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fragments tentatively identified as belonging to Audubon’s Shearwater (P. iherminieri). These faunal elements lived on rocky shores and their postmortem remains were transported to the pocket beach. Previously, fossil bird bones in the Gala´pagos Islands were known principally from lava tubes. (3) Beach deposits on rocky islands are ephemeral, awaiting the next high tide with strong waves to sweep them away. In this case, one of the limestone beds was covered by a basalt flow that retarded later erosion. The basalt flow, however, was partially eroded to produce a conglomerate of basalt cobbles and platy limestone recycled from a younger limestone bed. (4) The preservation of intertidal limestone beds on Isla Sombrero China suggests that such deposits, if located and precisely dated, can help to constrain the timing of relative sea-level changes during island growth and isostatic subsidence resulting from volcanism and lithospheric cooling. Magmatic inflation appears to have uplifted at least the southwest part of Isla Sombrero China by at least 3 to 4 m. The intertidal deposits on Isla Sombrero Chino support a polygenetic volcanic history characterized by multiple lava flows.

ACKNOWLEDGMENTS Our excursion to the Gala´pagos Islands occurred in March– April 2009 and was part of a semester-long course on the region’s biology and geology made possible through the Freeman Foote Travel Fund for the Sciences at Williams College. The fund was established through the generosity of Dr. Joseph Lintz, a geology major and member of the graduating class of 1942. Isla Sombrero Chino was one of more than a dozen venues visited by faculty and students during a 7-day tour on the M/Y Floreana, under the able command of Captain Freddy Pen˜aherrera. Gudveig Baarli helped with the drafting of the stratigraphic column in Figure 3 and arranged the photos in Figure 4. We thank Dennis Geist (University of Idaho) and Mark Wilson (The College of Wooster) for their valuable comments on an earlier draft of this paper.

LITERATURE CITED Anonymous, 2002. Visitors Sites Guide of the Galapagos National Park. Parque Nacional Gala´pagos, Ministerio del Ambiente, 197 p. Darwin, C.R, 1844. Geological Observations on the Volcanic Islands Visited during the Voyage of the H.M.S. Beagle. London: Smith, Elder & Co., 175 p. Harris, M.P., 1973. The Galapagos avifauna. The Condor, 75, 265– 278. Heinzel, H. and Hall, B., 2000. Gala´pagos Diary: A Complete Guide to the Archipelago’s Birdlife. Berkeley, California: University of California Press, 272 p. Hertlein, L.E., 1972. Pliocene fossils from Baltra (South Seymour) Island, Gala´pagos Islands. Proceedings of the California Academy of Sciences, 39, 25–46. Hickman, C.P., Jr., and Finet, Y., 1999. A Field Guide to Marine Mollusks of Gala´pagos. Lexington, Virginia: Sugar Spring Press, 150 p. Hickman, C.S., and Lipps, J.H., 1985. Geologic youth of Gala´pagos Islands confirmed by marine stratigraphy and paleontology. Science, 227, 1578–1580. Jackson, M.A., 1994. Galapagos: A Natural History, 2nd edition. Calgary, Alberta: University of Calgary Press, 335 p. Johnson, M.E., 2006. Uniformitarianism as a guide to rocky-shore ecosystems in the geological record. Canadian Journal Earth Sciences, 43, 1119–1147. Johnson, M.E. and Baarli, B.G., 1999. Diversification of rocky-shore biotas through geologic time. Geobios, 32, 257–273. Johnson, M.E.; Ledesma-Va´zquez, J., and Baarli, B.G., 2006. Vertebrate remains on ancient rocky shores: a review with report on hadrosaur bones from the Upper Cretaceous of Baja California (Me´xico). Journal of Coastal Research, 22, 574–580. Ladd, H.S. and Hoffmeister, J.E., 1945. Geology of Lau, Fiji. Bernice P. Bishop Museum Bulletin, 181, 1–399 (with 62 plates). Lietz, J. and Schminke, H.U., 1975. Miocene-Pliocene sea-level changes and volcanic phases on gran Canaria (Canary islands) in the light of new K-Ar ages. Palaeogeography, Palaeoclimatology, Palaeoecology, 18, 213–239. Riedinger, M.A.; Steinitz-Kannan, M.; Last, W.M., and Brenner, M., 2002. A ,6100 14C yr record of El Nin˜o activity from the Gala´pagos Islnds. Journal of Paleolimnology, 27, 1–7. Seguı´, B.; Quintana, J.; Forno´s, J.J., and Alcover, J.A., 2001. A new fulmarine petrel (Aves: Procellariiformes) from the Upper Miocene of the western Mediterranean. Palaeontology, 44, 933–948. Simkin, T. and Siebert, L., 1994. Volcanoes of the World, 2nd edition. Tucson, Arizona: Geosciences Press, 349p. Steadman, D.W., 1986. Holocene vertebrate fossils from Isla Floreana, Gala´pagos. Smithsonian Contributions to Zoology, 413, 103 p. Swanson, F.J.; Baitis, H.W.; Lexa, J., and Dymond, J., 1974. Geology of Santiago, Ra´bida, and Pinzo´n islands, Gala´pagos. Geological Society of Ameica Bulletin, 85, 1803–1810.

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