17th Caribbean Geological Conference 2005, San Juan PR

Relocation Of Earthquakes Western Puerto Rico Region Using Waveform Cross Correlation And Double Difference Techniques Abreu Rafael, Eugenio Asencio and Jay Pulliam Department of Geology, University of Puerto Rico at Mayagüez; Stephanie Ross, Andrew Michael and Shirley Baher USGS Menlo Park, California

The Puerto Rico Region has a significant seismic hazard due to large local, although relatively infrequent, earthquakes. To properly quantify this hazard we need to improve our understanding of this seismicity by identifying and understanding specific fault structures in the region. It is important to determine the location of such faults because the hypocentral distance affects the amount of on-land shaking, which is a factor used for earthquake planning by government agencies. Determining fault structure is important because it helps define fault segmentation, which controls the sizes and expected repeat times of earthquakes. In this study, we seek to improve earthquake locations recorded by the Puerto Rico Seismic Network (PRSN) by using waveform cross-correlation and double- difference relocation techniques. This project is a collaborative effort between the U.S. Geological Survey, in Menlo Park, the Department of Geology of the University of Puerto Rico at Mayagüez and the Puerto Rico Seismic Network. Standard PRSN locations for the region show a diffuse cloud of seismicity distributed over a broad region, preventing proper correlation of events to specific active seismogenic sources. The methods mentioned above have the advantage of simultaneous analysis of large seismic datasets, significantly improving the accuracy of earthquake locations and allowing the identification of clusters of earthquakes belonging to specific faults. Our preliminary results show improved definition of active seismogenic sources in the western part of the island of Puerto Rico.

Receiver Functions And SKS Splitting Measurements At Three Tectonically Distinct Locations Around The Caribbean Support The Continental Undertow Hypothesis Baez Sanchez Gisela, Rafael Abreu París, Antonio Cameron Gonzales, Eugenio Asencio, and Jay Pulliam Red Sísmica de Puerto Rico, Dept. de Geología, Universidad de Puerto Rico, Mayagüez, PR

The degree to which plate tectonic processes are controlled and/or affected by the Earth’s mantle is unclear, yet tectonic processes that deform the Earth’s crust and upper mantle apparently leave seismically-observable signatures in the form of large-scale anisotropy and some structural features of the crust appear to have analogs in the upper mantle. To examine remanent deformation we can study shear waves that penetrate the Earth’s core. These waves (called “SKS phases”) are converted to compressional waves for their path through the outer core and, when they re-enter the mantle and are converted back into shear waves, their energy is polarized in the SV plane. If, when recorded at broadband seismographic stations at the Earth’s surface, rotated into the proper, great-

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circle frame of reference, and examined, these SKS phases have energy polarized in the SH direction, it means that the waves have encountered an anisotropic material somewhere along their path from the core to the surface. We observed such “bi-refringence” or “SKS splitting” on the three broadband stations around the Caribbean that have been operating the longest: SDV in Venezuela, FDF in Martinique, and SJG in Puerto Rico. We measured the polarization direction and time lag indicated by the bi-refringence. SDV completes a transition between station BOCO, to the southwest, and stations MNVV,HSPV, and ECPV, to the northeast that suggests bending of the upper mantle deformation around the continental root of South America. This is similar to the pattern shown—more densely in their case—for SKS splitting parameters around the continental root of North America by Fouch et al. (2000). The two oceanic islands have very different signatures. Results for SJG indicate a generally east- west polarization and are consistent with the results of Russ et al. (1996). The polarization found for FDF differs dramatically, however—it is approximately north- south in orientation. Potential interpretations—including possible sources of error—will be discussed for this result. “Receiver functions”, formed by deconvolving the vertical seismic trace from the radial trace to isolate the shear wave reverberations in the crust and upper mantle, allow us to build an image of sharp boundaries (“layers”) in the Earth. We applied this technique to stations SDV, FDF, and SJG in order to study the deep structure beneath these distinct Caribbean locations. A synthesis of the receiver function and SKS interpretations will be presented in the context of Caribbean seismicity, plate motions, and other geophysical observables.

Late Cretaceous and early Tertiary Radiolaria from the Pacific coast of Costa Rica Bandini, A.N. & Baumgartner, Institute of Geology and Palaeontology, BFSH2, University of Lausanne, 1015 Lausanne, Switzerland. [email protected], [email protected]

We are in the process of a systematic study of late Cretaceous and early Tertiary radiolarian bearing siliceous mudstones and cherts from the Nicoya and Osa peninsulas. In these areas a variety of oceanic and arc derived terranes include mafic volcanics and associated pelagic and hemipelagic rocks rich in biogenic silica which has favoured the preservation of common moderately to well preserved radiolarians. Late Cretaceous to early Tertiary palaeoenvironments along the pacific margin were characterised by high terrestrial nutrient input derived from volcanic sources and active up-welling. High radiolarian productivity is mostly caused by high nutrients concentration in surface waters (Yamashita et al., 2002). Radiolarian preservation in the sediment is often enhanced by the presence of silica-saturated volcanic tuffs and debris. Currently, we have dated the Berrugate Formation and rocks mapped as Sabana Grande Formation in the Nicoya Peninsula. The Berrugate Formation is a thick hemipelagic- turbiditic sequence containing arc-derived volcanoclastic deposits (Flores et al. 2003). On the bases of published zonations we can state a Coniancian radiolarian age for the Berrugate Formation. We have determined the co-occurrence of Dictyomitra koslovae,

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Pseudoaulophacus florensis, Pseudoaulophacus lenticulatus and Theocampe salillum (species that have not been cited earlier than Coniacian) of with Stichomitra communis (a species that has not been cited later than Coniacian). The Sabana Grande formation consists of pelagic, hemipelagic and turbiditic siliceous and calcareous shales and mudstones (Flores et al. 2003). This formation is currently assumed to be of Cenomanian-Turonian age on the base of its stratigraphic position below the Nambi and Piedra Blancas formations that only indicate a pre-Campanian age. However, the formation itself has not been directly dated. In addition, many isolated outcrops of Sabana Grande lithologies are not stratigraphically constrained and could therefore have a different age. Such an outcrop, sampled east of Nicoya, has yielded an early Eocene age by the occurrence of Phormocyrtis striata striata. More data will be presented during the conference, since our laboratory work is currently in progress. Figure 1 SEM-illustrations of late Cretaceous and early Tertiary radiolarians from the Nicoya Peninsula, Costa Rica : 1. Dictyomitra koslovae Foreman, 2. Theocampe salillum Campbell & Clark, 3. Stichomitra communis Squinabol, 4a-b. Pseudoaulophacus lenticulatus White, 5a-b. Pseudoaulophacus floresensis Pessagno, 6. Phormocyrtis striata striata Brandt References Flores. K., Denyer, P. & Aguilar, T. (2003): Nueva propuesta estratigráfica: Geología de las hojas Matambú y Talolinga, Guanacaste, Costa Rica.- Rev. Geol. América Central, 28, 131-138. Yamashita, H., Takahashi, K. & Fujitani, N. (2002): Zonal and vertical distribution of radiolarians in the western and central Equatorial Pacific in January 1999. Deep- Sea Research, II, 49, 2823–2862.

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Water Resources Development In Barbados--- A Geological Perspective. Barker Leslie H. 2005

Barbados is a small island developing statewhich is the most easterly of the Lessser Antilles Island Arc. Stratigraphically it is composed of three main rock groups: The Basals or Scotland formation , a group of deep water turbidites of mid. to upper Eocene age ; The Oceanic formation, a group of deep water argillaceous deposits of contemporaneous age with the Scotlands; and a thin cover of Pleistocene to Recent reefal limestones which cover some six- sevenths of the island. This stratigraphic sequence together with the Pleistocene to Recent tectonic history of the island have formed the basis for the mode of occurrence of ground water on the island. The general lack of surface water is due to the widespread occurrence of permeable limestone on the island. The ground water occurs in a coastal phreatic aquifer which stretches almost entirely around the island except in the east where the Scotland formation outcrops. With the increasing demand for potable water one of the major problems facing us todayis the need for optimizing the exploitation of groundwater in the face of increasing seawater intrusion. Although engineering science has played a major role in our water resources development thus far we need a clear understanding of the island’s hydrogeology in order to achieve this optimization of groundwater exploitation.

Barremian (Lower Cretaceous) Ammonites From Cuba: An Assemblage Rich On Representatives Of The Family Pulchelliidae Ricardo Barragán-Manzo1 and Consuelo Díaz-Otero2 1, Departamento de Paleontología, Instituto de Geología, UNAM, México. 2, Instituto de Geología y Paleontología, Vía Blanca y Carretera Central, 11000 La Habana, Cuba.

Barremian (Lower Cretaceous) ammonites from Cuba are studied for the first time for systematic and biochronostratigraphic purposes. The fossils under study come from previous and recent sampling from different Barremian stratigraphic exposures within the Las Villas Province. A rich stratigraphic-controlled assemblage of taxa belonging to the Family Pulchelliidae conforms the focus of the studied material, allowing new discussions on the geographical distribution of this taxon within the Tethyan Realm. Preliminary results suggest that the ammonite association is predominated by representatives of the Subfamilies Pulchelliinae and Psilotissotiinae. The data herein discussed represent the first detailed systematic reports of these taxa in the Caribbean, widening their paleobiogeographic significance and allowing for precise long distance correlations of standard Barremian ammonite zonations between Cuba and other areas of the world.

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Remnants Of Pacific Ocean Foor : Jurassic-Lower Cretaceous Radiolarites In Central America And The Caribbean

Baumgartner, P.O.(1), Bandini, A.N.(1) & Denyer, P.(2) (1)Institut de Géologie et Paléontologie, BFSH2, Université de Lausanne, 1015 Lausanne Switzerland. [email protected]; (2)Escuela Centroamericana de Geología, Universidad de Costa Rica. P.O. Box 214-2060 UCR, San José Costa Rica. [email protected]

Mesozoic ribbon-bedded radiolarites are widespread in Tethyan and circumpacific orogenic belts, but they are unknown from the Atlantic, Gulf of Mexico and the Venezuelan Mesozoic passive margin. Mesozoic radiolarites formed in detritally starved, oceanic areas beneath moderate to high surface productivity. The Jurassic-Early Cretaceous Central Atlantic – Paleo-Caribbean ocean basins formed a mediterranean sea of generally low surface productivity, resulting in clay-rich and/or calcareous pelagic facies throughout. However, ribbon-bedded radiolarites occur in various tectonostratigraphic within the Modern Caribbean Plate. In the Nicoya Complex (NW- Costa Rica), the Siuna Oceanic Complex (NE-Nicaragua), Tambor Group (Montagua, Guatemala), Duarte Complex (Hispaniola), Mariquita Chert (Puerto Rico) and in the Phare Unit (Désirade). These radiolarites are associated with mafic/ultramafic igneous rocks of diverse petrogenetic origin: Association with MORB is the exception, more often radiolarites are incorporated as exotic blocks in: Cretaceous plateaus (Nicoya Complex), or subduction-related mélanges (Santa Elena, N Costa Rica, Puerto Rico). On La Désirade, radiolarites are interbedded with pillow basalts of a back-arc setting. Occurrencs of Nicaragua, Honduras and Guatemala are currently under study. Faunal characteristics of radiolarian assemblages have been interpreted in terms of paleo-latitude of formation. However, paleobiogeography of Tertiary to Recent radiolarians shows that higher latitude radiolarian assemblages are very similar to upwelling assemblages that occur throughout the tropical ream along the American Pacific Margin. Several Caribbean radiolarian assemblages studied from La Désirade closely resemble coeval faunas from the Califonian Coast Range Ophiolite, formed along this margin. We consequently interpret Mesozoic radiolarites associated with the Caribbean Plate, as remnants of Pacific ocean floor, some of which formed in arc-related settings. Radiolarian faunas do not allow for paleo-latitudinal interpretation, but suggest paleo-longitudinal displacement from the Eastern Pacific/Western American Margin into their present position in Central America and the Eastern Caribbean. This interpretation supports an allochthonous, Pacific origin of the Modern Caribbean Plate.

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Late Oligocene Caribbean Assemblages Of Larger Foraminifera Calibrated By 87Sr/86Sr (Nicoya, Costa Rica And Carriacou, Lesser Antilles) Claudia Baumgartner-Mora (1), Pascal Tschudin (1), and Peter O. Baumgartner (1) (1) Instuitut de Géologie et Paléontologie, BFSH2, Université de Lausanne, 1015 Lausanne Switzerland. [email protected]

Upper Oligocene shallow water formations unconformably overlie Paleocene- Eocene deepwater sediments in outcrops between Punta Peladas and Nosara River (Nicoya Peninsula, Costa Rica). The bioclastic limestones of these outcrops yielded rich assemblages of Larger Foraminifera that we studied in oriented sections, SEM for split material and polished rock thin sections for transmitted light and cathodoluminescence (CL). CL observation was essential for taxonomic determination of miogypsinids. CL observation also revealed planktonic Foraminifera associated with the shallow water material confirming the open marine environment indicated by the sedimentology. We determined: Heterostegina antillea Cushman, Miogypsina tani Drooger, Miogypsina gunteri Cole, Miogypsina cf. (Miolepidocyclina) panamensis (Cushman), Miogypsina sp., Miogypsinoides bermudezi (Drooger),Miogypsinoides cf. bantamensis (Tan Sin Hok), Lepidocyclina (Nephrolepidina) vaughani Cushman, Lepidocyclina yurnagurensis Cushman, Lepidocyclina undosa Cushman. At Windward, Carriacou (Lesser Antilles) scattered outcrops of the Belvedere Formation contain calciturbidites rich in Larger Foraminifera associated with a lower upper Oligocene (NP24) nannofossil assemblage. Planktonic Foraminifera recovered south of Windward in rocks slightly downsection indicate an upper middle Oligocene age. Larger Foraminifer species collected from a coastal outcrop just north of Windward include Lepidocyclina undosa Cushman and Miogypsina gunteri Cole. The 87Sr/86Sr ratio was measured in 11 specimens of megalosphaeric Lepidocyclina spp. Mechanically extracted from 2 rock samples collected at Punta Peladas (Costa Rica). 87Sr/86Sr ratios range from 0.709088 to 0.708196. which corresponds to a model age of 27.4 to 24.94 Ma. Very similar 87Sr/86Sr ratios, ranging from 0.708150 to 0.708167 were obtained from 2 specimens extracted from a sample collected in a coastal outcrop just N of Windward Village (Carriacou, Lesser Antilles). All measured 87Sr/86Sr ratios fall within a Chattian (Late Oligocene) age. The biochronologic range of the larger foraminifera listed above is currently controversial, and has to be considered as poorly known. French authors have restricted the range Miogypsina gunteri to the lower Aquitanian and Miogypsina. tani to the upper Aquitanian. Nannofossils, planktonic foraminifera and identical 87Sr/86Sr ratios form Punta Peladas and Windward clearly indicate a Chattian (upper Oligocene) occurrence of Miogypsina gunteri and Miogypsina tani and confirm this age range for the other Larger Foraminifera cited above.

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Puerto Rico Digital Earth-Science Data and the US Geological Survey Mineral Resource Assessment Methodology By: Walter J. Bawiec United States Geological Survey 954 National Center Reston, Virginia 20192

A mineral resource assessment of the Commonwealth of Puerto Rico was conducted by the U.S. Geological Survey, the Puerto Rico Department of Natural Resources, and the University of Puerto Rico (Bawiec, 2001). The purpose of this mineral resource assessment is to provide an inventory of the known mineral occurrences, to give an estimate of the potential for undiscovered mineral resources, and to provide a multi- purpose earth-science database. The earth-science data presented in this report will assist in long-range planning for environmental, health, and mineral-resource concerns in the Commonwealth of Puerto Rico and will provide a clearer understanding of the mineral potential of the island. The mineral resource assessment of Puerto Rico represents a compilation of several decades of mineral investigations and studies. The data used in the assessment are in a digital format and may be used in geographic information systems (GIS). The data includes maps of geology (and derivative maps), geophysics (Bouguer gravity, aeromagnetics), geochemistry (stream sediments), mines and mineral occurrences, and tracts permissive for various mineral deposit types. Although much of this information existed and was published prior to the assessment, this is the first time it has appeared in a single comprehensive publication.

The compiled earth-science data served as input into the three-part assessment method for estimating undiscovered non-fuel mineral deposits. This assessment includes the following steps:

1. Delineating areas permissive for undiscovered mineral resources according to the types of deposits permitted by the geology; 2. Estimating the number of undiscovered deposits of each type for each delineated area; 3. Estimating the amount of resources contained in the undiscovered deposits by using appropriate grade and tonnage models for each deposit type.

Reference:

Bawiec, Walter J., 2001, ed., Geology, Geochemistry, Geophysics, Mineral Occurrences, and Mineral Resource Assessment for the Commonwealth of Puerto Rico, USGS Open- File Report 98-38, 1 CD-ROM.

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Structural Development of the Columbus Basin, offshore S.E. Trinidad bpTT Exploration, Port of Spain, Trinidad and Tobago

The Columbus Basin, offshore S.E. Trinidad, marks the eastern extent of the Eastern Venezuelan foreland Basin, bounded to the north by the transpressional Darien Ridge, and southwards by the progressive onlap of the palaeo-Orinoco derived Plio – Pleistocene depositional fill onto the Cretaceous and Early Palaeogene age passive margin of the Venezuelan Plataforma Deltana. On a regional scale the basin is located along the transpressional plate margin between the South American and Caribbean plates, and lies west of the southern extension of the Barbados accretionary prism.

Essentially the basin is a modified foreland basin superimposed over the frontal, partly detached, structures of a Late Miocene to Early Pliocene transpressional foldbelt. The basin was subsequently re-inverted in Pleistocene times with the southern buttress to the contraction marked by the onlap edge of deepwater Palaeogene through Early Miocene age mudstones onto the relict passive margin. The extent of these facies has played a critical role in the evolution of the internal geometry of the basin with the major Plio- Pleistocene aged structures regionally detached from the north dipping Cretaceous passive margin succession.

Internally, there are two obvious structural elements that characterise the Columbus Basin in Trinidad waters: NNE dipping regional growth faults and NE-SW trending inversion anticlines. The superimposition of these trends provides the majority of the structural containers that provide the petroleum traps. However, the major extension in the Columbus Basin has occurred along NW-SE trending counter regional faults that were initiated by the rapid loading of the palaeo-Orinoco sediments and the consequent seaward excavation of the underlying over-pressured and mobile deepwater mudstones. The extension systematically shifted from counter regional faults, and was accommodated progressively eastwards on regional listric ‘growth’ fault sets.

3D Visualisation of the Columbus Basin, Offshore S.E. Trinidad bpTT Exploration, Port of Spain, Trinidad and Tobago

The Columbus Basin, offshore S.E. Trinidad is an areally rich petroleum province (12-15 bcf/km2), bounded to the north by the transpressional Darien Ridge, and southwards by the progressive onlap of the Plio – Pleistocene depositional fill onto the Venezuelan foreland. The structural geometry in Trinidad waters is dominated by WSW-dipping counter-regional, and NNE-SSW oriented regional faults, and internally is characterised by stacked deltaic and shelfal sandstone reservoirs in extensional fault roll-overs.

Historically, the interpretation of the basin had been on a piecemeal basis, with a local stratigraphic scheme for each of the fault blocks, covered by small-area 3D seismic volumes. Through the merging of fifteen 3D seismic surveys, bpTT has constructed a “mega-merge” volume, which for the first time has allowed a confident stratigraphic correlation throughout the basin, calibrated by an extensive well dataset collected over the forty-year exploration history of the basin.

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More than sixty regional surfaces have been mapped from the seismic volume to date. Using GeoProbe software, the interpretation of these surfaces can be actively viewed in 3D together with well paths, proven reservoir segments, fault surfaces, attribute extractions and pressure surfaces, overlain on the regional seismic cube. The visualisation permits the identification of structural traps, the distribution of potential reservoir facies and locally direct hydrocarbon detection. Collectively, the integration of all these data allows a 3-dimensional understanding of the basin and its development through time.

Plio-Pleistocene Depositional fill of the Columbus Basin – Gross Depositional Environment mapping. bpTT Exploration, Port of Spain, Trinidad and Tobago

During Late Pliocene through Pleistocene times, the palaeo-Orinoco River, confined within the Venezuelan and Central Trinidadian foreland basin, incised into the continental shelf, where it formed a braided-river complex that transported sediment to a series of shelf-edge deltas. During the progradation phase, river systems dumped large amounts of sand and silt onto the delta front to form a “delta platform”. From the shelf edge there was an abrupt transition into the slope and basin environment. During episodes of low accommodation space creation, sand was conveyed past the shelf edge onto the slope by channels, chutes, slumps and debris flows. Where the delta was building at a rapid rate the depositional geometries were modified by sediment collapse scars, growth faulting, turbidite channels and shelf edge canyons. This description is derived from high resolution regional seismic imaging below the present day shelf margin of the Columbus Basin and Plataforma Deltana which provides new understandings of the interaction of active tectonics, fluvial process, and the accommodation space fluctuations that influence deltaic and shelfal architecture. 3D seismic attributes remarkably portray the most recent (16,000 - 12,000yr) shelf edge deltaic system which is seen as a prograding sigmoid oblique clinoform bundle that represents the most significant period of sediment accumulation. The package highlights the syn-depositional tectonic influence on the deltaic architecture in terms of local accommodation space creation.

The depositional model has been used as an analogue for the deeper depositional sequences of the basin, which contain the bulk of the gas resource. This stratigraphy has been divided into a series of sequence sets that relate to regional accommodation space development, and a detailed Gross Depositional Environment (GDE) interpretation has been made for 39 of the 97 sequences within these sequence sets. Regional seismic surface mapping, seismic attributes and seismic facies calibrated to well data show the progressive infilling of the Columbus Basin by Palaeo-Orinoco shelf edge deltas. GDE maps are drawn at the time of the maximum extent of each delta to show the greatest extent of sand that would be encountered in the reservoir sections. The maps provide an easily understandable view of the deltaic geologic setting, helping us to constrain the distribution of different reservoir facies and provide the basis for defining prospective

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play fairways. GDE’s also show the geographic distribution of key deltaic facies belts with time, which include the active delta plain, delta front, shelf, and slope.

Common Risk Segment Mapping - focusing the exploration effort in the Columbus Basin, Offshore S.E. Trinidad. bpTT Exploration, Port of Spain, Trinidad and Tobago

Common Risk Segment (CRS) mapping is the key tool that allows the mapping of relative risk on the individual petroleum play elements across an entire sedimentary basin. Combining these elements to form a Composite CRS allows the description of play risk on a regional scale and focuses the exploration effort to areas of lowest common risk. Play Fairway risk is simply depicted using a traffic light scheme, where green indicates areas of low risk, yellow moderate risk and red high risk.

The Columbus Basin, offshore S.E. Trinidad, is a prolific petroleum province, with multiple reservoir targets. The stratigraphic interpretation of the basin has divided the Plio-Pleistocene basin fill into Sequence Sets, and for each of these a Composite CRS analysis has been made. The primary inputs to the analyses, the Gross Depositional Environment (GDE) maps, are used to identify low risk areas for both reservoir and seal presence. Reservoir quality distribution is determined from depth versus porosity plots and depth structure maps. Petroleum systems analysis provides information to generate individual CRS maps that describe seal effectiveness, source presence and potential, and petroleum charge access. Biogenic charge CRS maps are created using temperature versus depth plots. The maps are produced using Arc Gis software, which makes them easy to update and edit when new data are acquired.

The Composite CRS interpretation provides an objective, map-based understanding of the distribution of petroleum in the Columbus Basin, and is a powerful tool for inventory ranking, portfolio analysis and as a framework for yet to find analysis. Identifying areas that have low play risk determines where exploration dollars should be spent to access and test the most attractive opportunities in the basin.

From Regional to the Shotpoint. Chachalaca Discovery, Columbus Basin, Offshore S.E. Trinidad bpTT Exploration, Port of Spain, Trinidad and Tobago

After an intense eighteen month study of the Columbus Basin, offshore SE Trinidad, the exploration unit of bpTT, resumed operations in an untested region within bpTT’s eastern acreage. On 13th December, 2004, the Chachalaca well was drilled as a deviated hole to a total depth of 15633ft below rotary table, at a location about 52 miles east south east off Trinidad’s east coast, in 335 feet of water. The well was plugged and abandoned as a Gas Discovery well which resulted in the booking of a total resource of about 2 trillion cubic feet (tcf).

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The Chachalaca well was drilled to evaluate the exploration potential of three target reservoirs of Pleistocene age within two depositional sequence sets. These reservoirs were predicted from regional and detailed Gross Depositional Environment (GDE) mapping, and Common Risk Segment interpretation that identified the areas of the basin with the lowest geological risk. The reservoir sequences at Chachalaca are supported by a NE-SW oriented inversion geometry, orthogonal to the NE-SW regional faults, and on trend with another earlier field discovery, Corallita/Lantana. The well successfully tested these reservoirs, which were vertically stacked within five thousand feet, but laterally separated by different fault blocks. The oldest and most significant reservoir lies in the rollover to an early counter- regional fault, and confirmed the depositional model developed in the regional interpretation. The success in defining this prospect was based on a thorough regional understanding of the basin focusing the effort and spend to areas of lowest risk. This understanding was based on detailed work on all aspects of the petroleum system: structural setting, stratigraphy, facies distributions and petroleum migration and timing. Integration has been the backbone of Chachalaca’s success. Similar work for future exploration, can provide similar results.

Stratigraphy of the Cretaceous Succession in the Benbow Inlier, Jamaica Ian C. Brown and Simon F. Mitchell Department of Geography and Geology, University of the West Indies, Mona Campus, Kingston 7, Jamaica.

A minimum 9-km-thick succession of lavas, volcaniclastic sediments, shales and limestones is developed in the Benbow Inlier of central east Jamaica. This Lower Cretaceous succession is amongst the most complete within the Caribbean, with a minimum of seven limestones (several newly recognised), interbedded with volcanics and clastics) containing diagnostic rudist-foraminifer faunas indicating the following ages: Hauterivian; Late Barremian, early Aptian?; early Albian; late Albian; and possibly early Cenomanian. The uppermost part of the succession has yielded a Turonian nannofloral assemblage. Tholeiitic lavas in the lower part of the section are regarded as part of the tholeiitic island arc suite, whereas the overlying Albian to Turonian rocks have a calc-alkaline island arc suite. A new geologic map and the lithostratigraphy of the rocks exposed in this inlier will be presented and the age-diagnostic faunas reviewed.

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Earthquake Monitoring In Panama

Eduardo Camacho Instituto de Geociencias Universidad de Panama Panama, Panama [email protected]

The first seismic instrument in the Western Hemisphere was installed in Panama City, Panama by The French Canal Company in early 1882. This instrument recorded the great tsunamigenic earthquake (M8.0) of September 7, 1882, with epicenter offshore the northeast Caribbean coast of the Isthmus.

BALBOA HEIGHTS PANAMA (BHP). Since 1909 the Panama Canal Company installed two sets of Bosch Omori seismographs at Balboa Heights Panama (BHP). In 1932 these instruments were replaced by two Wood Anderson seismographs and in 1934 the first accelerograph outside the continental USA was installed at BHP. All these instruments were replaced in 1962 by short period and long period instruments of the WWSSN. BHP operated uninterruptedly until 1977.

UNIVERSITY OF PANAMA NETWORK (UPA). In 1983 the University of Panama received the WWSSN instruments that had operated at BHP before and installed them with the help of the USGS at the Panama City Campus.

Nowadays the UPA has 5 one component short period telemetric analog stations. Additionally, there are one digital accelerograph and 3 three component short period digital stations linked via INTERNET. The analog records of the telemetric stations are digitized at the UPA observatory, at Panama City and the records from the three digital stations are digitized on site.

In cooperation with the Geophysical Institute of the University of Mexico (UNAM), a STS-2 broad band sensor has been installed at the UPA observatory at Panama City

CHIRINIET. In western Panama operates a private network which consists of 6 digital short period three component stations, deployed in that part of the country. The data transmission of this network is via INTERNET and the records are digitized on site..

PANAMA CANAL AUTHORITY NETWORK

The Panama Canal Authority (ACP) operates since the beginning of 2005 a network of 3 short period 3 component digital stations and 4 digital accelerographs. This network is deployed around the Panama canal Basin.

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All seismic networks in Panama: UPA, CHIRINET and ACPN exchange data and cooperate very closely, through institutional agreements, to improve the seismic monitoring of the country.

Development Of Rapid Moment Tensor Seismic Inversion Procedures For Incorporation Into The Emergent Puerto Rico-Virgin Islands Tsunami Warning System Antonio Cameron González1, Eugenio Asencio1, Víctor Huérfano1, Carlos Mendoza2 (1) Puerto Rico Seismic Network, Dept. of Geology, University of Puerto Rico Mayaguez (2) Centro de Geociencias de la UNAM, Campus Juriquilla, Quéretaro, Mexico

We present a preliminary result of moment tensor inversion procedures for regional events within the Caribbean Region. Our ultimate goal is to incorporate these procedures into the emergent Puerto Rico-Virgin Islands Tsunami Warning System (PRVITWS). Using three-component digital broadband waveforms that were recorded by the Puerto Rico Seismic Network (PRSN) for events between December 2004 and March 2005 we estimate the source mechanism for 2 earthquakes with moment-magnitudes (Mw) higher that 4.0 near the highly oblique oceanic subduction-strike-slip transition area along the North America-Caribbean plate boundary.

Regional tectonic setting of the Caribbean showing

the epicenters of 2 regional events examined for this

study (red stars), and layout of seismic stations

operated by the PRSN.

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The procedures use the reflection-matrix method of Kennett (1983) to identify source parameters that best reproduce the regional waveforms. The method used by Randall et al. (1995) for regional event inversions was applied, with source depth fixed at 10 km. The synthetic Green’s functions were estimate using a general Caribbean crustal velocity model (Mann and Burke, 1984). A Butterworth passband filter with corners at 20 sec and 50 sec was applied to synthetic and observed data. The inversion scheme provides rapid estimation of source parameters such as earthquake size (Mw) and fault geometry (Mendoza and Huérfano, 2004), which are critical to the identification of possible tsunamigenic events in the Caribbean region.

Geoprico-Do Project: A new marine geophysical study at northeastern Caribbean Plate Boundary Zone (Dominican Republic-Puerto Rico-Islas Vírgenes). A. Carbó and GEOPRICO-DO Working Group [ A. Carbó (1), D. Córdoba (2), J.M. Dávila (3), P. Herranz (4), A. Muñoz (1), A. Pazos (2), M. Catalán (2), M. Gómez (4), C. Von Hilldebrandt (6), U. Ten Brink (5), J. Payero (7), S. Dabreo (9), J.L. Granja (1) ,P. Llanes (1), J. Álvarez (1), L.M. Agudo (1), M. Druet (1)

(1) Departamento de Geodinámica, Universidad Complutense de Madrid, Spain, (2) Departamento de Geofísica, Universidad Complutense de Madrid, Spain, (3) Real Observatorio de la Armada en San Fernando (Cádiz), Spain, (4) Instituto Español de Oceanografía, Madrid, Spain, (5) U.S. Geological Survey, (6) Puerto Rico Seismic Network, (7) Universidad Autónoma de Santo Domingo-Instituto Sismológico Universitario, Dominican Republic, (8) Instituto Nacional de Recursos Hidráulicos, Dominican Republic, (9) Department of Disaster Management,B.V.I.]

The Northeastern Caribbean Plate Boundary Zone presents an area of complex and very active tectonics, where different processes interaction have been proposed: strain partitioning (Calais et al, 2002), microplates (Mann et al, 1995), oblique subduction to strike-slip transitions (Dolan & Mann, 1998; Dillon et al, 1994), opposing subducted slabs (Deng and Sykes, 1995), crust arching (Van Gestel et al, 1998), tear fault (ten Brink et al, in press), block rotation (Mason and Scanlon, 1991) among other. All these processes produce a high seismic activity due tectonic deformation. The proof of this activity is the constant record of events in the seismic networks and the historical seismic record (Mona Passage, 1943, Ms = 7.6 offshore Northeastern Hispaniola, 1946 Ms = 8.1 Dolan et al, 1997). Moreover, these earthquakes can unleash submarine landslides, which could be triggered by earthquakes, could be generated in the region because of the steep slopes offshore (ten Brink, 2004). Recent GPS's studies have contributed to clarify the kinematics of the zone (Calais et al, 2002).

The Northeastern Caribbean Boundary Zone (Hispaniola and Puerto Rico zone) has been widely studied from 50's, but most studies have focused on northern Hispaniola and Puerto Rico islands (e.g. Puerto Rico Trench, Bahamas Bank, Mona Rift, (Mann et al, 1995; Dolan et al, 1998; ten Brink et al, 2004)), very few studies have been carried out to the south, resulting in a lack of information. During April, 2005 a marine geophysics

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cruise aboard the Spanish Oceanographic Research Vessel “Hespérides” was carried out in this area of the Northeastern Caribbean Plate. In the project GEOPRICO-DO, which are coordinated by Univesidad Complutense de Madrid (Geodynamics Department, Geophysics Department, Spain) and Real Obsevatorio de la Armada de San Fernando (Spain), also participate the Instituto Español de Oceanografía (Spain), Universidad de Barcelona (Spain), U.S. Geological Service/Woods Hole Oceanographic Institution (USGS/WHOI), Puerto Rico Seismic Network (University of Puerto Rico, Mayaguez), Universidad Autónoma de Santo Domingo-Instituto Sismológico Universitario, Red Sísmica del Instituto Dominicano de Recursos Hidráulicos and the Department of Disaster Management (Virgin Islands). The data acquired in the cruise were; multibeam bathymetry, potential fields (gravity and magnetism), multichanel reflection seismic, deep seismic sounding with record on stations onland and streamer and OBS`s. The OBS will remain at seabed recording seismicity for a continuous period of 6 months.

We present here the data acquired during the recently finished survey and some preliminary results: geomagnetic anomaly maps, gravimetric (Bouguer) anomaly maps, one brut stacked of seismic section and one section interpreted and acquired with a high resolution topographic parametric seismic system (TOPAS), in the northeastern Puerto Rico Trench and to the south of the Hispaniola and of Puerto Rico islands (Muertos Trench). Besides, with the integration of all data we have elaborated a preliminary crustal model for the plates boundaries in the Muertos Trench region.

Evaluation of Instability of Unsaturated Soil Slopes during Heavy Rainfall By Migdalia Carrión1, Ana María Hagan2, Hebenly Celis3, and Miguel Pando4*

Rainfall-induced slope instabilities and landslides are common in Puerto Rico (PR). The island has an area of 9103 square kilometers, about 70 to 80 percent of which is hilly or mountainous. The presence of steep slopes in the mountainous terrain, coupled with weathered soils and intense rainfall, lead to severe slope-stability problems throughout the island. Natural hazards such as hurricanes further exacerbate these problems. All physiographic provinces of the island have experienced landslides.

This poster presents an overview of the slope stability problem in PR with particular emphasis on the problem of instability of unsaturated residual soil slopes during wet periods. This type of slope failure is a recurring problem in PR. Infiltration during rainfall decreases insitu soil suctions, resulting in decrease in shear strength due to the loss of insitu suction, and ultimately slope failure. This triggering mechanism is investigated with particular reference to recent slope failures in the Mayaguez area.

1 Undergraduate student, Department of Civil Engineering, University of Puerto Rico at Mayaguez, P.O. Box 9041, Mayaguez, PR, 00681-9041 2 Visiting undergraduate student, Department of Civil Engineering, University of Rhode Island

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3 Graduate student, Department of Civil Engineering, University of Puerto Rico at Mayaguez, P.O. Box 9041, Mayaguez, PR, 00681-9041 4 Assistant Professor, Department of Civil Engineering, University of Puerto Rico at Mayaguez, P.O. Box 9041, Mayaguez, PR, 00681-9041. E-mail: [email protected]

*: Corresponding author.

The Geometry Of The Basement In NW Colombia: Implications In The Evolution Of The Colombia Basin. John Ceron and R. Hernández Empresa Colombiana de Petróleos, Bogotá, Colombia

Potential fields data, MBES and numerous seismic profiles, have contributed to the mapping of the basement in the NW corner of South America. The type of crust underlying the sedimentary accretionary prism has relevance on the exploration for hydrocarbons in the region. The geometry of the prism is revealed by MBES which, in turn, exposes new questions to the understanding of the evolution of the Colombia basin, such like the meaning of the La Aguja submarine Canyon and the geometry of the conjunction (?) of the Santa Marta and Oca faults Strain partitioning at the Caribbean – NW South America collision zone have not been clearly explained, and the amount of displacement required for present plate slip rates requires considerable movement along strike-slip faults that has not been demonstrated by displacements of known faults. The Romeral Fault Zone plays the role of a paleo-suture but it might also represent a zone of strike slip displacement that will help explain present slip vectors in the SW Caribbean plate. With this Poster we seek to create the scenario for discussion on the implications of all these geometrical and geophysical considerations to the understanding of the evolution of the Colombia basin, the postulation of Caribbean plate evolutionary models and the clarification of the geological risk in the assessment of hydrocarbon plays.

BOLIVAR: A Cross-Section of the Caribbean-South American Plate Boundary at 64W S.A. Clark, A. Levander, M.B. Magnani, D.S. Sawyer and the BOLIVAR Working Group Department of Earth Science, Rice University, Houston, TX, USA

BOLIVAR, the Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region, is an NSF and Venezuelan funded, collaborative seismic experiment in the southeast Caribbean region. The purpose of the BOLIVAR project is to understand the diffuse plate boundary formed by the oblique collision between the Caribbean and South American plates (see Levander, this meeting). Profile 64W of the BOLIVAR experiment, a 415 km-long, N-S transect onshore and offshore Venezuela approximately located at 64 deg W longitude, images the deep crustal structures formed by this process early in its development, ~15 My after the Antilles arc collided with the continent at this longitude.

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The active source components of profile 64W include 275 km of MCS data, 33 coincident OBSs, and 344 land seismic stations which recorded 7500 offshore airgun shots and 2 explosive land shots. A passive source experiment, consisting of 17 broadband seismometers in the vicinity of the profile, complements the active source data.

We hypothesize that 64W transects a north-dipping, remnant subduction zone (VanDecar et al., 2003) underlying the Serrania del Interior and Maturin Basin, formed at 16 Ma by collision of the Caribbean forearc overriding South American crust. Backthrusting of this subduction inverted and closed the Grenada Basin. This initial subduction gradually choked on continental crust, causing a polarity reversal and jump to the north. Subduction could not evolve in the Grenada Basin backthrust because it choked on the Aves Ridge/La Blanquilla High. Instead, down-to-the-south subduction initiated further to the north, where Caribbean oceanic crust of the Venezuela Basin began to subduct beneath the Aves Ridge/La Blanquilla High in the Pliocene (~4 Ma) and appears to continue today. Between the remnant subduction zone and the modern/nascent one, the El Pilar and Coche strike-slip faults accommodate most of the transform motion of the plate boundary. From the remnant subduction zone to the modern one, ~350 km of orogenic float comprises the diffuse plate boundary.

Honduran seismic stations: Necessity of enhancing seismic monitoring in the Caribbean Region of Central America Gonzalo Cruz Calderón ([email protected]) (Universidad Nacional Autónoma de Honduras Departamento de Física, Sección de Geofísica)

The Honduras status of the seismic observations is presented toward the future plans of strengthens such a network. In this contest, we also review the limitations of regional monitoring capabilities along some of the northern Central American coasts due to the uneven distribution of several systems or the absence of stations in other areas which do not allow the adequate observation of significant seismic events for hazard evaluation purposes. Most of the Central American networks are concentrated along the pacific coast, even though seismic events have also affected the northern and western regions. This fact is especially crucial in the Gulf of Honduras (Honduras – Guatemala tectonic environment), where some important seismic events have taken place in historical and instrumental periods. For example, data from 1505 through 2000, show that about 60-70 seismic events grater than M = 4.5 have occurred in the Caribbean region shared by Honduras and other countries, and some of them have generated tsunamis that have affected cities and towns along the coast. Also, on July 11 of 1999 an earthquake (M= 6.4) occurred in the Honduras Gulf region and was felt strongly creating panic in Puerto Cortes, San Pedro Sula (Honduras), Puerto Barrios in Guatemala and other regions of northern and western Central America

In view of the worldwide awareness, we believe that it is of much importance for the whole Caribbean Region to start building a broad regional and integral seismic hazard

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program for tsunami warning. Such an effort would require the enhancement of the seismic monitoring of significant seismicity along the Caribbean region of Central American counties. For Honduras, it would be crucially important to be part of such a regional network. After reviewing the geological, seismological and strategic aspects for our participation in such an effort, we suggest that the site of Puerto Cortes (the main port facility of the country) would be the appropriate place for installing a seismic station.

Development of the Mid-Holocene Cañada Honda fossil reef, Dominican Republic: Preliminary results and implications to modern trends of reef degradation in high sedimentation environments

Cuevas-Miranda, David*, Ramírez, Wilson**, Sherman, Clark*, Hubbard, Dennis***

*Department of Marine Sciences, University of Puerto Rico at Mayagüez, **Department of Geology, University of Puerto Rico at Mayaguez *** Department of Geology, Oberlin College, Oberlin, OH 44074

Many modern coral reefs are in decline, in many areas related to high sedimentation rates and sediment resuspension. However, there is evidence in the fossil record of reefs developed in high sedimentation environments, such as the Cañada Honda outcrop in the Dominican Republic, with a record of accretion spanning over a thousand years. The Holocene coral reefs of the Enriquillo Valley, Dominican Republic provide a unique record of coral development in an environment that seems to have been exposed to high sediment input. They exhibit excellent preservation and offer an exceptional opportunity to examine in detail the internal coral assemblage and sedimentary patterns of a Holocene coral reef. In particular, the Cañada Honda outcrop reveals several sediment layers that appear to represent single depositional events such as storms, probably with elevated rainfall as is typical of the region today. These layers are rich in coral, bivalve and gastropod fragments and can be traced several meters within the outcrop, where a paleoreef surface can be followed. Coral and sediment samples were collected below and above these sedimentary horizons for the purpose of dating and documenting any changes in the coral-species assemblage, growth rate, siltation stress and carbon isotopes before and after their deposition. Additional coral and sediment samples were collected throughout the entire outcrop to observe similar changes through time. Quantitative measurements of coral importance, diversity and sediment were obtained throughout the whole stratigraphic section using quadrats along vertical transects. In addition, sediments incorporated in coral skeleton and from the reef matrix are being examined to quantify the input and variations in terrigenous sedimentation through the section. The information obtained from this study will be instrumental to better understand modern reefs since direct comparisons of this fossil reef with modern counterparts (with high sedimentation in a restricted environment) will be possible.

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Nicoya Complex (Costa Rica) – a Cretaceous Plateau containing Middle Jurassic to Cretaceous radiolarite blocks

Denyer, P.(2) & Baumgartner, P.O.(1) (1)Institut de Géologie et Paléontologie, BFSH2, Université de Lausanne, 1015 Lausanne Switzerland. [email protected]; (2)Escuela Centroamericana de Geología, Universidad de Costa Rica. P.O. Box 214-2060 UCR, San José Costa Rica. [email protected]

We re-examined igneous and sedimentary rocks and radiolarian biochronology in the NW-Nicoya Peninsula, where the Nicoya Complex s.st. was originally defined. The geologic data mapping, and the new Ar/Ar-dates and igneous isotope geochemistry done by other authors, do not confirm either one of the current hypotheses on the tectonostratigraphy of the area. Neither alpine-type nappe structures, nor a threefold magmatostratigraphy, in which an oceanic basement and its Jurassic-Cretacecous sediment cover would be overlain by Upper Cretaceous plateau basalts. Herein, we re- assess field relationships between igneous rocks and radiolarites, and document refined. We now interpret the Nicoya Complex s. str. as a fragment of a Cretaceous plateau created by uplift and southward tilting during an early Campanian collisional event. The deepest levels of the Plateau are exposed in NW-Nicoya, where over 50 % of the igneous rocks are intrusives (gabbros and plagiogranites) that have a single mantle plume source, common with the basalts. Ar/Ar-dates range from Valanginian to Campanian. Radiolarian-dated, Bajocian (Middle Jurassic) to Albian (middle Cretaceous), Mn-rich radiolarites, are set as stratigraphically incoherent blocks in a “matrix” of multiple basalt flows, subsequent intrusions and cross-cutting dykes and sills. Chilled margins of magmatites, and hydrothermal baking and leaching of the sediments confirm the Ar/Ar- dating of igneous rocks being consistently younger than most of the radiolarian cherts. No Jurassic oceanic basement has been identified so far at the outcrop level in the Nicoya Peninsula, but it could be buried beneath the surface. The Jurassic-Cretaceous chert sediment pile became disrupted and detached from its original basement by multiple intrusions during the formation of the Plateau. Radiolarian-dated, Coniacian - Santonian (Late Cretaceous) thin, Fe-rich radiolarites are largely synchronous and associated with late phases of the Plateau.

Tectonic control of the Barbados accretionary prism on the Orinoco turbidite system (Southeastern Caribbean) Deville Eric, Callec Yannick, Desaubliaux Guy, Mascle Alain, Institut Français du Pétrole, 1-4, av. de Bois-Préau, 92 506 Rueil-Malmaison, France e-mail:[email protected] Huyghe-Mugnier Pascale, Maison des Geosciences, BP 53, Université de Grenoble, 38041 Grenoble, France

Recent marine acquisitions (multibeam, seismic and 3.5 kHz profiles, piston cores) provide a better understanding of the whole interference area between the Barbados

19 17th Caribbean Geological Conference 2005, San Juan PR accretionary prism and the Orinoco turbidite system. It appears that due to its location in an active margin, the Orinoco turbidite system is not a passive deep delta. The depositional system is morphologically and tectonically controlled by the compressional structures of the Barbados prism, and as a consequence the system does not exhibit classic fan geometry. The hinge between the slope of the front of the Barbados prism and the slope of the Guyana margin induces the convergence of the turbidite channels in the abyssal plain, at the front of the prism. Above the prism, upward the system is multi- source with several distributaries, whereas downward the channel courses are more complex with frequent convergences or divergences that are emphasized by the effects of the undulating seafloor morphologies. Indeed, tectonics, shale diapirism, and mud volcanism force the topography of the substratum generating local highs and confined piggyback basins that control the courses of the channels. Erosion processes are mostly absent in the upper part of the turbidite system. Erosion develops in the deep-water area between 2000 and 4000 m above the compressional structures of the Barbados prism. Incisions show irregular meandering and sinuous courses in the low relieve segments and less sinuous courses where channels cut the structures. Larger canyons are 3 km wide and 300 m deep. The occurrence of different phases of successive incisions is responsible for the development of similar terraces in both flanks of the canyons. This is probably the consequence of two superimposed mechanisms: the tectonic activity of the deformation front characterized by progressive uplift and thrusting of recent sediments, and the superimposition of the fluctuations of Orinoco turbidite system activity.

Isotopic Correlation Between The Cotui Formation Exposures In The Cerro Buena Vista Area And On Road Pr100, Southwestern Puerto Rico Viviana Díaz¹, Alvin Bonilla and Hernan Santos Department of Geology, University of Puerto Rico, Mayagüez, PR

This work is based on the comparison of the isotopic signatures of two stratigraphic sections: the Cotui Limestone in the Cerro Buena Vista area and from road PR100, Km 11.9, Cabo Rojo. The work is part of an investigation that aims to resolve recent debates on whether the limestone exposed on PR100 is a depositional event between the older Cotui Limestone and the younger Guaniquilla Formation; or part of the Cotui Limestone. Samples were collected from both outcrops. After XRD analysis, the samples were analyzed for C¹²/C¹³ ratios on a Stable Isotope Ratio Mass Spectrometer (GASI Lab- Department of Geology, UPRM). C¹²/C¹³ ratios were plotted against height in stratigraphy. After comparison no match was found between the two graphs, however, the PR 100 isotopic profile did match with a part of the Cotui Limestone profile. This match suggests that the PR100 limestone correlates with part of the middle Cotui Limestone.

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Cuaba Gneiss, Dominican Republic: An ultra high pressure metamorphic terrane in the northern Caribbean

Grenville Draper, Department of Earth Sciences, Florida International University, Miami, FL 33199, USA Richard .N. Abbott, Department of Geology, Appalachian State Univ., Boone, NC 28608, USA Shantanu Keshav, Geophysical Laboratiry, Carnegie Institution of Washington, Washington DC 20015, USA

The Cuaba Gneiss is narrow belt of mafic gneisses and minor schists that occurs as one the of the units of the subduction- Rio San Juan Complex related in the northern Dominican Republic. The gneisses consists of banded eclogite that have been retrograded to amphibolite grade. The banding is near vertical and trends N-S, across the major trend of the outcrop. kinematic indicators suggest that the gneisses underwent consitent dextral shearing at eclogite conditions. Meter-scale bodies of garnet peridotite and garnet pyroxenite occur as pods in the gneisses. Some blocks have been found that contain coexisting garnet-clinopyroxene-spinel and corundum assemblages and magmatic cumulate textures. Mineralogic phase relations indicate that such a magmatic assemblage had to have formed at greater than 3.6Gpa and 15500C, that is to say at UHP (greater than 2.7 Gpa) conditions. We interpret these rocks as having formed in the hangingwall of the Late Cretaceous, SW-dipping Greater Antillean (GA) subduction zone at depths of greater than ~110km. They then became entrained in the downgoing, eclogitized oceanic crust represented by the Cuaba Gneiss. This means that the Cuaba Gneiss itself must have descended to these depths ans hould therefore be viewed as a UHP terrane. The exhumation of the Cuaba terrane is problematic as it would not have had the buoyancy of continental crust9the usual host for UHP rocks) and so buoancy cannot be invoked as the exhumation mexchanism.

Revisión sobre los recursos minerales metálicos del Distrito de Bayaguana, al Este de la República Dominicana Por Julio E. Espaillat L. Corporación Minera Dominicana, S.A.

El Distrito mineralizado de Bayaguana, se encuentra en la parte oriental de la isla de la Hispaniola, aproximadamente 60 km. Al Noreste de la ciudad de Santo Domingo.

Las mineralizaciones descubiertas en la zona, consisten de diseminaciones y vetas hidrotermales de pirita y sulfuros de cobre con enriquecimiento local de oro y plata. Estas están contenidas en rocas volcánicas e intrusivas bi-modales basálticas y dacíticas con pequeñas proporciones de sedimentos clásticos y carbonosos de la denominada Formación Los Ranchos de edad Cretácica Inferior.

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Las mineralizaciones estudiadas están relacionadas con grandes zonas de alteración hidrotermal que se extienden por mas de 50 kilómetros cuadrados de afloramientos dentro de un edificio volcánico, claramente definido por mapeo geológico y visible en los estudios de magnetometría aerotransportadas realizados en 1996 sobre la República Dominicana.

Métodos convencionales de prospección minera fueron inicialmente usados para definir las mineralizaciones del área incluyendo: mapeos geológicos, levantamientos geoquímicos, geofísicos y excavación de trincheras. Mediante sondeos diamantados, la Corporación Minera Dominicana, S.A., ha establecido tres prospectos con inventarios minerales: (1) El prospecto de Cerro Kiosko, consistente en una estructura tabular silicificada de mas de 1.1 Km de longitud a lo largo de su rumbo, contenida en rocas máficas alteradas. Esta mineralización se considera como una veta telescópica epitermal de cuarzo con pequeñas cantidades de caolinita, rutilo y muscovita, conteniendo un ensamblaje mineral de pirita, calcopirita, energita y bornita en formas diseminadas y en vetillas (stockwork) enriquecidas con oro y plata. El inventario calculado es de 4,920,000 toneladas métricas de mineral con leyes de 2.0 gr./t Au, 5.06 gr./t Ag. y 1.0% Cu. (2) Las mineralizaciones porfiríticas de cobre diseminado de Cerro Managuá, consistentes en un manto o blanket de enriquecimiento supergénico de unos 100 metros de espesor y que se extiende dentro de una zona fuertemente silicificada de rocas volcánicas máficas intruidas por dacitas porfiríticas consanguíneas. El inventario mineral calculado en la zona de enriquecimiento secundario y donde predomina la calcocita y la covelita es de unas 45 millones de toneladas métricas con 0.45% Cu y 0.22 gr./t Au. Esta zona apárece superpuesta a minealizaciones hipogénicas de baja ley conteniendo pirita, calcopirita y trazas de molibdenita. (3) Mineralizaciones de Ceja del Coco, consistente en una amplia zona de alteración hidrotermal asociada a domos porfiríticos de cuarzo y feldespatos, fuertemente silicificados y argilitizados, conteniendo diseminaciones y vetillas (stringers) de pirita, calcopirita y bornita, parcialmente reemplazados por cantidades menores de calcocita y covelita. El inventario mineral calculado preliminarmente mediante sondeos es de 7.0 millones de toneladas métricas con 0.5% Cu.

Otros prospectos dentro del Distrito Bayaguana que han sido ensayados mediante sondeos diamantados, han retornado valores anómalos y elevados de metales bases y preciosos. Para la ejecución de los programas de exploración se ha cumplido con todos los requisitos ambientales establecidos en las normas y leyes ambientales de la República Dominicana. Review of the exploration for metallic mineral resources within the Bayaguana District in the eastern Dominican Republic. The mineralized district of Bayaguana is located in the eastern part of Hispaniola, approximately 60 km. northeast of the city of Santo Domingo.

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Occurrences of mineralization discovered in the district consist of hydrothermal disseminations and stringers of sulphides, dominated by pyrite, chalcopyrite and bornite, and locally enriched with gold and silver. The mineralization is hosted by bi-modal volcanic and intrusive rocks of basaltic and dacitic composition, with a minor proportion of clastic and carbonaceous sediments of the Lower Cretaceous Los Ranchos Formation.

The known mineralization is related to a volcanic center that is clearly defined by geological mapping and is visible on the 1996 magnetic airborne survey of the Dominican Republic. Large hydrothermal alterations zone of over 50 square kilometers envelopes the mineral occurrences.

Conventional exploration tools were used, including geological mapping, geochemical and geophysical surveys and trenching initially to detect these prospects.

Throuh drilling, Corporación Minera Dominicana, S.A., has established three prospects as follows: (1) Cerro Kiosko prospect, in which a silicified, tabular mineralized structure has been traced for 1.1 km, along strike, and is hosted by altered mafic volcanics. The mineral assemblage observed in the epithermal telescopic quartz vein consists of dissemination and stringers of pyrite, chalcopyrite, enargite and bornite, enriched with gold and silver with an inventory of 4,920,000 metric tons @ 2.0 g/t Au, 5.06 g/t Ag and 1.0% Cu. (2) Porphyritic disseminated copper mineralization of Cerro Managua. It consists of a supergene blanket of approximately 100 meters thick that overlies a strongly silicified zone of mafic volcanic rocks intruded by consanguineous porphyritic dacites. The mineral inventory of the secondary enriched zone is 45.0 million metric tons @ 0.45% Cu and 0.22 g/t Au. (3) Ceja del Coco mineralization, consists of a broad zone of hydrothermal alteration associated with porphyritic quartz and feldspar dacite and rhyolite domes, that are strongly silicified and argillitized. The domes are mineralized with dissemination and stringers (stockworks) of pyrite, chalcopyrite and minor amount of chalcocite and covellite. The preliminary mineral inventory calculated by drilling is 7.0 million of metric tons @ 0.5% Cu. Other prospects within the District tested by drilling returned elevated and anomalous base and precious metals values. For the execution of the exploration programs, all environmental procedures and requirements established in the Dominican environmental norms and laws were followed.

(English Version) Review of the exploration for metallic mineral resources within the Bayaguana District in the eastern Dominican Republic.

The mineralized district of Bayaguana is located in the eastern part of Hispaniola, approximately 60 km. northeast of the city of Santo Domingo.

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Occurrences of mineralization discovered in the district consist of hydrothermal disseminations and stringers of sulphides, dominated by pyrite, chalcopyrite and bornite, and locally enriched with gold and silver. The mineralization is hosted by bi-modal volcanic and intrusive rocks of basaltic and dacitic composition, with a minor proportion of clastic and carbonaceous sediments of the Lower Cretaceous Los Ranchos Formation.

The known mineralization is related to a volcanic center that is clearly defined by geological mapping and is visible on the 1996 magnetic airborne survey of the Dominican Republic. Large hydrothermal alterations zone of over 50 square kilometers envelopes the mineral occurrences.

Conventional exploration tools were used, including geological mapping, geochemical and geophysical surveys and trenching initially to detect these prospects.

Throuh drilling, Corporación Minera Dominicana, S.A., has established three prospects as follows: (4) Cerro Kiosko prospect, in which a silicified, tabular mineralized structure has been traced for 1.1 km, along strike, and is hosted by altered mafic volcanics. The mineral assemblage observed in the epithermal telescopic quartz vein consists of dissemination and stringers of pyrite, chalcopyrite, enargite and bornite, enriched with gold and silver with an inventory of 4,920,000 metric tons @ 2.0 g/t Au, 5.06 g/t Ag and 1.0% Cu. (5) Porphyritic disseminated copper mineralization of Cerro Managua. It consists of a supergene blanket of approximately 100 meters thick that overlies a strongly silicified zone of mafic volcanic rocks intruded by consanguineous porphyritic dacites. The mineral inventory of the secondary enriched zone is 45.0 million metric tons @ 0.45% Cu and 0.22 g/t Au. (6) Ceja del Coco mineralization, consists of a broad zone of hydrothermal alteration associated with porphyritic quartz and feldspar dacite and rhyolite domes, that are strongly silicified and argillitized. The domes are mineralized with dissemination and stringers (stockworks) of pyrite, chalcopyrite and minor amount of chalcocite and covellite. The preliminary mineral inventory calculated by drilling is 7.0 million of metric tons @ 0.5% Cu. Other prospects within the District tested by drilling returned elevated and anomalous base and precious metals values. For the execution of the exploration programs, all environmental procedures and requirements established in the Dominican environmental norms and laws were followed.

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Pre-Campanian Terranes in Nicoya area (Costa Rica, Middle America)

Kennet Flores (1), Peter O. Baumgartner (1), Percy Denyer (2), Alexandre Bandini (1), and Claudia Baumgartner-Mora (1) (1) Instuitut de Géologie et Paléontologie, BFSH2, Université de Lausanne, 1015 Lausanne Switzerland. [email protected] (2) Escuela Centroamericana de Geología, Universidad de Costa Rica. P.O. Box 214- 2060 UCR, San José Costa Rica. [email protected]

Field mapping, isotopic and palaeontologic dating in Nicoya reveals coeval pre- Campanian, middle to late Cretaceous magmatic/sedimentary sequences of different geodynamic paleoenvironments. 1- The Nicoya Complex is a pile of plateau basalts and intrusives of Berriasian to Campanian igneous ages, including Middle Jurassic to Santonian radiolarites. 2- The Matambu Terrane comprises a basaltic basement of unknown origin and age, overlain by late Albian bituminous, siliceous shales (Loma Chumico Formation). This formation is thermally affected by younger basaltic flows and intrusives of the Nicoya (plateau) Complex. The Loma Chumico Formation is overlain by pelagic, hemipelagic/turbiditic siliceous and calcareous shales and mudstones of the Sabana Grande Formation (estimated as Cenomanian to Coniancian in age). Upsection, the Nambi Formation is characterized by volcaniclastic turbidities derived from the Nicoya Complex. 87Sr/86Sr isotopic analysis of Inoceramus gave a value of 0.70738, interpreted as a Coniacian age. The top of Nambi is marked by the presence of reworked Campanian shallow water bioclasts, announcing the transition to the overlap sediments. 3- The Manzanillo Terrane is floored by a basaltic basement intruded by the Tortugual Komatiitic suite of Turonian (89 ma) age. Upsection, a thick hemipelagic- turbiditic sequence containing arc-derived volcaniclastic deposits is defined as Berrugate Formation, dated by radiolarian biochronology as Coniancian/Campanian.

The Manzanillo Terrane documents pre-Campanian evolved arc volcanism that resulted from active subduction of ocean floor once located between the exotic Nicoya Complex (1) /Matambu Terrane (2), and the Manzanillo Terrane (3). The Manzanillo Terrane could represent a fore-arc area at the foot of the western edge of the future Caribbean Plate. Subduction stopped when (1) and (2) reached the trench and collided with the Caribbean Plate during the Campanian.

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Subduction events in Cuba

Antonio García-Casco(1), Rafael Torres-Roldán(1), Guillermo Millán(2), Manuel Iturralde- Vinent(4), Kenya Nuñez Cambra(2), Concepción Lázaro Calisalvo(1), Antonio Rodríguez Vega(4) (1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002 Granada, Spain. (2) Instituto de Geología y Paleontología, Via Blanca y Carretera Central, La Habana, Cuba. (3) Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana 10100, Cuba. (4) Instituto Superior Minero-Metalúrgico, Departamento de Geología, Las Coloradas de Moa, Holguín, Cuba.

The diversity of P-T paths, ages, and tectonic settings of formation of high-pressure complexes of oceanic material in Cuba documents a protracted history of subduction at the northern margin of the Caribbean Plate during the Mesozoic that is analyzed within the framework of available geological data and plate-tectonic models. In Western and Central Cuba, HP blocks within serpentinite-mélanges separated ca. 800 km along strike of the belt document cold (i.e., mature) subduction of oceanic lithosphere at pre-Aptian times and mélange formation and uplift at the Aptian-Albian. The P-T evolutions are clockwise, with subtle changes in P-T during the prograde sections of the paths and relatively hot geothermal gradient during exhumation (i.e., “Alpine-type”) incompatible with steady-state subduction. Petrological arguments favor an intra-oceanic collision setting at the Aptian-Albian that caused arrest of subduction. Either a Pacific or a Proto- Caribbean subduction system can explain the formation of these rocks at the mid- Cretaceous. In Eastern Cuba, HP blocks within serpentinite mélanges document hot subduction of oceanic lithosphere, with partial melting of amphibolites and formation of trondhjemitic melts at ca. 750 ºC 15-18 kbar followed by cooling at high pressure (i.e., counterclockwise P-T paths). This petrologic evolution makes the correlation of Eastern and West-Central Cuban mélanges doubtful. Indeed, available data support formation of hot-subduction complexes at the Aptian-Albian upon the onset of a new subduction system that evolved to normal (cold) subduction during the Upper Cretaceous. A SW- dipping Proto-Caribbean subduction system can be proposed, though geological and structural data indicate a complex arrangement of subduction systems in Eastern Cuba during the Upper Cretaceous. Finally, HP ophiolitic material tectonically juxtaposed within subducted platform metasediments of the Escambray complex (Central Cuba) decompressed at relatively cold geothermal gradients (“Franciscan-type” P-T paths), suggesting syn-subduction exhumation at the uppermost Cretaceous (ca. 70 Ma). Geological, petrological and structural data suggests subduction of the Proto-Caribbean.

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Upper Cretaceous Stratigraphy Of The Oriental Cordillera (Dominican Republic)

Jesús García Senz1, Jacques Monthel2, Alberto Díaz de Neira3, Pedro Pablo Hernáiz- Huerta4, Andrés Pérez Estaún5 1Dept. de Geodinàmica i Geofísica, Universitat de Barcelona (formerly Inypsa Group) 2Bureau de Rechereches Geologiques et Minières, BRGM, France 3Geoprin, Spain (formerly Inypsa Group) 4Iniciativas y Proyectos S.A, Inypsa, Spain 5Consejo Superior de Investigaciones Científicas, CSIC, Spain

Extensive mapping in the Oriental Cordillera allows to define the stratigraphy of a 6 km- thick upper Cretaceous sequence, deposited in a fore-arc basin at the northern margin of the Caribbean plate.

Las Guayabas Fm (Cenomanian-upper Coniacian) consists of well stratified lithic- feldespatolithic sandstones with volcanic grains and lesser amounts of metamorphic and sedimentary grains, radiolaria and planktonic foraminifera, interpreted as deep-water epiclastites and tuffs derived from a volcanic arc source. The lower part of the formation includes debris-flow conglomerates of ultrabasic rocks (El Cujano Mb, Lower Coniacian) possibly eroded from the accretionary prism located to the north, and a basaltic-andesitic lava horizon (Loma La Vega Mb) with geochemical affinities to magmas generated above the subduction zone. The upper part of Las Guayabas Fm intercalates gravely sandstones (Hato Mayor Mb), interpreted as concentrated turbidites. Capping the succession, the Arroyo La Yabana Mb (upper Coniacian-Santonian), is a key level made of centimetric beds of radiolarites interbedded with silt, indicative of the temporal cease of volcanism.

The overlying Las Auyamas Mb (Campanian-Maastrichtian) consists of thin beds of volcanic lithic sandstones and silt, interbedded with biomicrites. They grade in lateral and in vertical to calcareous turbidites (Río Chavón Fm) with sporadic volcanic gravel and clasts of shallow-water biota derived from the destruction of a southern carbonate platform. These resedimented deposits are gradually replaced by hemipelagic biomicrites and marls, ending the cretaceous sequence by red calcarenites with ondulated stratification and cross-bedding (Loma de Anglada Fm, Maastrichtian), volcanic-lithic sandstones and rudist biostromes, deposited on a serpentinite seamount. The correlative deposits to the north are calcareous turbidites.

The overall sedimentary trend is a reduction of the volume of detritics of volcanic origin and the increase of detritics from a sedimentary source, coeval with the filling of the fore- arc basin.

This contribution is a result of the SYSMIN Program (2002-2004) financed by the European Union.

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The Structure Of The Oriental Cordillera Of The Dominican Republic

Jesús García Senz1, Jacques Monthel2, Alberto Díaz de Neira3, Pedro Pablo Hernáiz- Huerta4 & Andrés Pérez Estaún5 1Dept. de Geodinàmica i Geofísica, Universitat de Barcelona (formerly Inypsa Group) 2Bureau de Rechereches Geologiques et Minières, BRGM, France 3Geoprin, Spain (formerly Inypsa Group) 4Iniciativas y Proyectos S.A, Inypsa, Spain 5Consejo Superior de Investigaciones Científicas, CSIC, Spain

The Oriental Cordillera extends 135 km adjacent to the south coast of the Samaná peninsula, exposing little-metamorphosed rocks of the Lower Cretaceous island-arc and the Late Cretaceous fore-arc basin. Regional maps clearly shows a big domal structure plunging to the east, with their north limb cut by the Samaná strike-slip fault. Map-scale folds with upright axial surfaces outcrop along the southern limb of the dome, eroded by the Paleocene conglomerates. They are refolded by NW-SE folds, giving a Type 1 interference pattern, which is best developed on the east-plunging end of the dome. The most important structure in this area is the NW_SE Yabón fault, pierced by serpentinite intrusions. Other prominent features are pop-up structures that made up the highs of the sierra, right-stepping conical folds with the apex pointing to the NW, and WNW-ESE Riedel shears cutting previous and contemporaneous folds as half-anticlines and half-synclines. The region of maximum shortening is located between the villages of Miches and Las Lisas, as deduced by extensive cleavage development. The cleavage disappears following the fold axis to the SE, a fact previously interpreted as the evidence of two terranes, El Seibo and El Oro, with different deformational grade. The arrangement of structures described in the Oriental Cordillera indicate contraction and uplift simultaneous with wrench along sinistral E-W and NW-SE strike-slip faults, characteristic of transpressional tectonics. Transpression is an active process today forcing the retreat of the sea and the doming of the Plio-pleistocene reef 400 m above sea level.

This contribution is a result of the SYSMIN Program (2002-2004) financed by the European Union.

Preliminary Description Of A Bed Containing Glass Spherules In The Bejucalito Section (Oriental Cordillera, Dominican Republic). A New Possible K/T Boundary Layer Jesús García Senz1 & José Pedro Calvo2 1Dept. de Geodinàmica i Geofísica, Universitat de Barcelona 2 Instituto Geológico y Minero de España, IGME

A spherule layer in the Bejucalito section, 20 km southeast of the El Seibo village (Oriental Cordillera, UTM: 051220, 206535) possibly represents impact glass from the Chicxulub crater and a new K/T boundary site. The Bejucalito section contains shallow- water deposits spanning the Maastrichtian to Eocene, deposited non-conformable on a serpentinite seamount in the upper Cretaceous fore-arc basin.

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The Maastrichtian Loma de Anglada Fm on top of the serpentinite, consists of about 100 m of red sandstones with nodular stratification enhanced by iron oxides, quartz grains, volcanic minerals, coral fragments, bivalves, echinoids, gastropoda and Sulcoperculina sp. A Maastrichtian age has recently been stablished in the close río Mana section based on rudist bivalves (Pons, García Senz and Bernárdez, this Conference). The top of Loma de Anglada Fm is an erosional surface filled by an up to 2 m-thick breccia with reworked centimetric clasts of serpentinite and sandstone in a red matrix. The absence of age diagnostic fossils in this breccia has prevented age determination of the erosional event capping the maastrichtian platform. Above lies the Paleocene-Eocene Bejucal reefal limestone, starting with a 2 m-thick polymict microbreccia with reworked rock inclusions of glass spherules, serpentinite, corallinae algae, bivalves and echinoids. Glass spherules, ranging 0.2 – 6.8 mm in size, are loosely distributed in limestone showing a packstone- grainstone fabric. At the time of redaction of this abstract, the microprobe analysis of the glass is in progress, but based on the age of the section and their position close to the Chicxulub crater, we tentatively interpret the spherules level as a K/T boundary ejecta deposit.

This contribution is a result of the SYSMIN Program (2002-2004) financed by the European Union.

Validation Of Remote Sensors For Benthic Habitat Studies In Southwestern Puerto Rico Fernando Gilbes and Jeanette Arce Geological and Environmental Remote Sensing Laboratory Department of Geology University of Puerto Rico at Mayaguez

Different remote sensing techniques were employed to study benthic habitats in La Parguera, Puerto Rico. These include the comparison of two sensors with different spatial and spectral resolution, IKONOS (1 m, 4 bands) and Hyperion (30 m, 220 bands). Image processing of IKONOS included atmospheric, sun glint, water column corrections, and supervised classifications for the characterization of sea grass, sand and coral. Hyperion data analyses included destriping, atmospheric correction, sun glint correction and classifications. Field data collection was performed by the establishment of three transects with ten quadrants for each habitat class. The benthic composition from transects were compared with those generated by the image classifications. Field validation shows the potential of the techniques used, but demonstrates that these processing methods require improvement. Preliminary analyses show that the most appropriate remote sensing technique for benthic habitat classification is merging the data of these two sensors.

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Spectral Characterization Of Sandy Beaches In Western Puerto Rico Fernando Gilbes and Gretchen Chiqués Geological and Environmental Remote Sensing Laboratory Department of Geology University of Puerto Rico at Mayaguez

Remote sensing applications to beach system in Puerto Rico have been limited by low spatial resolution of the available images and lack of appropriate equipment for field validation. A GER-1500 spectroradiometer was used to collect reflectance measurements with a spectral range from 350 to 1050 nanometers in 15 sandy beaches in western Puerto Rico. Samples of the beaches were analyzed in the laboratory to determine the composition. Results indicate a change in magnitude in the reflectance curve compared with the composition. Higher magnitude correlated with more carbonate material concentration in the sand and lower magnitude correlated with higher concentration of dark mineral. The reflectance shows a change in the curve between 450 to 550 nanometer that is present in all 15 beaches. The spectral slope in that range was calculated and related to the composition. The results of the field reflectance measurements were compared to a high resolution (1m) of IKONOS satellite image. Using band math these images show a correlation between the field measurement and the satellite image. A methodology to obtain information about composition in sand beaches using remote sensing was developed. For the first time a spectral library of beach sand sediment for western Puerto Rico was created.

Carbonate Diagenesis from Evaporated Seawater Goldstein1, Robert H. and Csoma1,2, Anita, E., 1University of Kansas, Department of Geology, 1475 Jayhawk Blvd., Lawrence, Kansas 66045; 2Current Address, ConocoPhillips Company, Upstream Technology, Integrated Geological Analyses, 600 N. Dairy Ashford, PR 3064, Houston, TX 77079-1175.

Many of the Plio-Pleistocene diagenetic phases, that previously have been interpreted as forming from low-temperature seawater, precipitate, at least in part, from evaporated seawater. These phases include Mg-calcite, calcite, and dolomite from the Clino core of the western Bahamas, Hope Gate Formation of Jamaica, and Eocene section of Enewetak Atoll. Each of these examples contains diagenetic phases which have been interpreted as forming in water of normal marine salinity on the basis of petrographic relationships and stable isotopic compositions. Fluid inclusion data, however, provide strong evidence for evaporated seawater. Dolomites from Enewetak Atoll are found below 1200 meters and lie at the base of a permeable slope deposit. The Sr isotopic composition is more radiogenic than the depositional carbonate, indicating that dolomitizing fluids were young. Fluid inclusion data (Tm ice = -2.4 to -4.4°C) indicate dolomitization from fluids of 44 to 85 ppt salinity. Thus, dolomitization was at least in part from deeply refluxing evaporated seawater. Samples from the drill core Clino, western Bahamas, show significant calcite cementation after compaction in grainy carbonates of Pliocene age. Fluid inclusion data

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from calcite cements (Tm ice = -2.2 to -10.8°C) indicate elevated salinity, ranging from 37 ppt to highly saline brines of 148 ppt. Clear Mg-rich calcite from the Plio-Pleistocene Hope Gate Formation of Jamaica contains fluid inclusions with Tm ice values ranging from -1.9 to -2.4ºC, indicating precipitation from normal to slightly evaporated seawater (35 to 45 ppt). These data provide a climatically significant record of ancient seawater evaporation that has been previously unrecognized. Generation of such high density fluids at the surface could lead to deep reflux of fluids, resulting in the precipitation of either calcite, Mg-rich calcite, or dolomite, strong evidence that mineralogy and process are controlled more by microbial processes than fluid origin and salinity.

Petrography And Stable Isotope Geochemistry Of Upper Cretaceous Carbonate Concretions And Veins In The Cariblanco Formation Of Southcentral Puerto Rico: Implications For Hydrocarbon Generation And Migration Luis A. González , Department of Geology, University of Kansas, Lawrence Kansas 66049 Rubén Uribe, ExxonMobil Exploration Company, Houston Texas 77210

Calcite cements in concretions and veins of the Upper Cretaceous Cariblanco Formation of south-central Puerto Rico contain the only documented occurrence of live hydrocarbons in Puerto Rico. Concretions preserve the complex diagenetic history of the Upper Cariblanco Formation and provide important clues about the generation and migration of hydrocarbons. Paragenetic sequence preserved by concretions consist of 1) Synsedimentary pyrite formation; 2) three distinct events of vein/fracture formation accompanied by sediment infilling; 3) pyrite formation throughout the concretion matrix and sediment vein fills; 4) four events of larger vein and fracture formation and infilling by distinct calcite cements; 5) late barite and quartz void filling cements; and 6) very late formation of calcite-filled veinlets. Stable isotopic values of concretion components and vein calcite define two distinct diagenetic trends of progressive δ18O depletion and δ13C enrichment. δ18O depletion in both cases resulted from progressive warming of circulating seawater as magma emplacement proceeded and/or from the fluid interaction with the volcaniclastic materials during burial diagenesis. The 13C-depleted CO2 involved in calcite cementation in both concretion matrix and vein calcite is most likely sourced from the oxidation of methane. Marked differences are observed between the oxygen isotopic composition of early diagenetic concretion components and the oxygen isotopic compositions of concretion late diagenetic cement phases as well as vein calcite precipitation. Early diagenetic fluids were most likely marine in origin and presumably circulated through the sediments as a result of thermally driven advection. The fluids precipitating vein calcite and late concretion cements were sourced deeper in the basin and were certainly warmer than earlier fluids. The presence of hydrocarbon fluid inclusions, the common fluorescence of vein calcites, and the exclusive association of the live hydrocarbon with calcite veins and late cements in concretions clearly indicate that this later fluid mobilized the hydrocarbons. A better knowledge of the source rock potential of the Cariblanco Formation will provide a

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better foundation for assessing the paradigm that no appreciable quantities of hydrocarbons exist in the Cretaceous rocks in and around Puerto Rico.

A New Seismotectonic Model For The Chortis Block Marco Guzmán-Speziale Centro de Geociencias, UNAM, México +52 442 238 1119 ext 125 +52 442 238 1101 (fax) [email protected]

Using centroid moment-tensor solutions (CMTs) published by Harvard University, we study the state of stress in the northwestern corner of the Caribbean plate. Plate boundaries are located in the vicinity of this region: the convergent margin between the Cocos and the Caribbean plate along the Middle America trench, and the transform plate boundary between the North America (NOAM) and Caribbean (CARB) plates along the Motagua-Polochic fault system, both of them seismically very active. There are also tectonic earthquakes (right-lateral, strike-slip mechanisms) along the Central America Volcanic Arc (CAVO), parallel to the trench. P axes of events along the CAVO show horizontal, N-NW compression whereas strike- slip events along the NOAM-CARB margin show P axes oriented S-SW. Compression, then, is directed towards the corner of the Caribbean plate. T axes show SE orientation for the NOAM-CARB boundary, and a NE general azimuth for events along the CAVO, both of which add to a general eastern tensional regime. Eigenvalues associated to P and T axes are similar in magnitude for both groups of events, along the NOAM-CARB plate boundary and along the CAVO, which together with orientations of P and T axes, suggest that the northwestern corner of the Caribbean plate is under NNW horizontal compression, probably due to subduction of the Cocos plate, and SSW horizontal tension because of the relative motion of the North America plate. Superposition of bot stress regimes suggest that this parto f the Caribbean plate is being extruded to the East.

The Coniacian Santonian Boundary in the Oil Fields of Northern Iraq Rund A. Hammoudi Dept. of Geology ,College of Science, Mosul University Mosul , Iraq Phone 00964 60 812609 Mobile 00964 770 160 1990 e-mail [email protected] [email protected]

Biostratigraphic data from the subsurface sections in the oil fields of northern Iraq provides evidence for defining the Coniacian - Santonian boundary . Depending on the distribution of foraminifera in Kirkuk and Balad oil wells , the Coniacian - Santonian boundary is located within the upper part of the Concavata Zone . The last appearance of

32 17th Caribbean Geological Conference 2005, San Juan PR the Marginotruncana renzi and the first appearance of the Globotruncana linneana marks this boundary .Other foraminiferal assemblages have been recognized for determining the end of Coniacian.

Use of Seismic Techniques to Locate and Define Sinkholes James C. Hasbrouck, B.S., R.Gp., Suelos Inc., Hato Rey, Puerto Rico Carlos Rodriguez Molina*, M.S., P.E., C.E., Suelos Inc., Hato Rey, Puerto Rico *Speaker

Within many parts of the Caribbean the presence of sinkholes create financial and logistical problems in the development of public and private infrastructure. Surface seismic surveys are used for regional mapping of limestone depth and topography to identify subsurface depressions within the buried limestone that are typically associated with the existence of sinkholes or sinkhole related phenomena. Once anomalous areas have been identified, surface to borehole seismic surveys aid in the detailed geometry mapping of possible sinkholes with only a small amount of drilling. Thus the application of these geophysical techniques to locate and define sinkholes makes it possible to prepare, at minimal costs, development plans that provide usage of good land.

Examples are shown of the combined use of surface and surface to borehole seismic techniques to locate and define sinkholes along the axis of a planned highway in Puerto Rico. Using surface refraction seismic and the delay-time processing method several anomalous topographic depressions within the subsurface limestone are identified to depths greater than 100 feet. Seismic techniques are well suited for use in most urban areas because of the limited influence of electrical utilities and metal fences (both of which can adversely affect electrical resistivity and electromagnetic data) and noise from nearby traffic can be minimized through careful data acquisition procedures.

Anomalous areas identified along the proposed highway axis from surface refraction seismic data, aerial photography and field reconnaissance are surveyed with the surface to borehole seismic technique to detail the geometry of suspected sinkholes. To adequately map the sinkholes and enable three dimensional representations, data are acquired along four overlapping lines centered on each of three boreholes at an anomalous area. Thus two seismic survey types and a minimal amount of boreholes at selected anomalous areas enable the cost-effective and safe design of highways and other infrastructure.

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The tectonic evolution of the Caribbean Plate: Insights from volcanic rocks in Jamaica and the Virgin Islands. Alan R. Hastie1, Andrew C. Kerr1, Simon F. Mitchell2 and Trevor A. Jackson2. School of Earth Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, U.K. Department of Geography and Geology, University of the West Indies, Mona, Kingston 7, Jamaica, W.I.

The complex question of Caribbean plate tectonic evolution requires a multidisciplinary approach involving volcanology, igneous petrology, structural geology and palaeontology. Plate tectonic models of Caribbean plate evolution are widely debated, and this study on the Cretaceous-Tertiary igneous rocks of Jamaica and the Virgin Islands will aim to clarify the existing models. Information relating to volcanic rocks in Jamaica and the Virgin Islands is sparse with Information relating to volcanic rocks in Jamaica and the Virgin Islands is sparse with few geochemical and geochronological studies having been carried out. Some of the volcanics have been identified stratigraphically, but their petrogenesis is still unknown i.e. did they originate in a subduction-related setting, a mid-ocean ridge or an oceanic plateau? The temporal and spatial identification of the volcanic rocks in these islands will be valuable in determining plate evolution by identifying when, where and how the different volcanic rocks formed.

Fieldwork has demonstrated the variety of volcanic and plutonic rocks on Jamaica. During the summer of 2004 samples were collected from the Blue Mountains, Central,

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Above Rocks and Benbow Cretaceous Inliers throughout the island. Recent major and trace element data has been obtained by state of the art ICP-OES and ICP-MS facilities at Cardiff University, U.K. The data has confirmed the presence of a plateau section and a number of primitive and evolved Cretaceous island arc sequences. Due to intense tropical weathering many elements have been mobilised, and it is for this reason that most of the samples analysed were interpretated using immobile trace elements. These new findings are presented here, and it is hoped that together with the stratigraphical and temporal location of the igneous rocks that the “Pacific” model of Caribbean plate evolution can be supported and/or refined.]

Holocene Coral-Reef Development In Canada Honda, SW Dominican Republic HUBBARD, Dennis K. 1, RAMIREZ, Wilson2, DAVIS, Allicia1, LAWSON, Gregory R. 1, ORAM, Jessica1, PARSONS-HUBBARD, Karla1, CUEVAS, David2, and DEL CORO, Monica2, (1) Dept. of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074, (2) Dept. of Geology, University of Puerto Rico, PO Box 9017, Mayaguez, PR 00681 contact: [email protected]

Facies preserved in a 400-m long outcrop at Cañada Honda in the western Dominican Republic span a depth range of over 40 m, and mimic the zonation pattern seen on modern Caribbean reefs. Twenty-seven scleractinean species have been recorded in the outcrop, along with 56 species of mollusks. Coral abundance in 53 quadrats from 21 vertical transects averaged over 60%, and ranged from 35% in the platy coral zone to 76% in the mixed-coral facies. Taphonomic data from corals buried by a prominent storm-debris layer (mostly Madracis mirabilis) that crosses the outcrop indicate that roughly half the buried colonies were already dead. This infers that the 60% coral abundance in quadrats probably reflects live-coral cover near 30%. This value is similar to that seen on modern Caribbean reefs, and closely matches the coral recovery from Holocene reef cores throughout the region. Facies geometry reflects early transgression starting ca. 10,000 years ago, followed by the outbuilding of shallow facies by 6,000 years CALbp, as sea-level rise slowed.

Despite the high diversity within the outcrop, the reefs were probably exposed to high levels of sedimentation. The dominant corals were Siderastrea siderea and Montastraea faveolata, both sediment-tolerant species. Elevated sedimentation is further supported by the absence of Acropora palmata, a coral without a biological strategy for sediment removal. Massive corals vary from hemispheres to conical to columnar forms as sedimentation presumably increased. Siderastrea spp. are dominantly conical, while Montastraea spp. tend to form columns. Many corals show interrupted growth that is manifested in flared colony margins, giving an appearance likened to a stack of pancakes. Thus, colony shape provides a useful proxy for both the magnitude and constancy of sedimentation.

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Where’s The Reef? – Clues To Gaps In The Caribbean Record Of Acropora Palmata At 5,800 And 3,000 Calpb HUBBARD, Dennis K., LAWSON, Gregory R., and TOMLINSON, M., Dept. of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074 contact: [email protected]

It has been proposed that the recent decline of coral reefs is an event unprecedented over Holocene time or perhaps longer. In apparent contrast, two Caribbean-wide gaps in the Holocene record of Acropora palmata appear to have occurred approximately 5,800 and 3,000 years ago. Oceanographic and meteorological patterns vary significantly across the sites where these gaps have been seen, and a regional or global mechanism is required to explain the pattern. Existing sea-level data seem to preclude a sudden rise as a factor. Of the possible causes that we can envision, only bleaching and disease have not been ruled out. However, the lack of proof for other mechanisms is not a priori proof that either of these was responsible for the two millennial-scale gaps described above. It is nevertheless interesting that the two remaining possibilities are important elements of the recent decline.

In 2002, we collected over 200 branch segments from still-standing colonies of A. palmata killed in the early 1980s by White Band Disease. Each was cut in cross section and made into a thin section. Preliminary analyses indicate that the standing-dead branches are dominantly encrusted by coralline algae, vermetid gastropods and the foraminifer Gypsina spp. The total thickness and diversity within the crust vary between the branch top and bottom. In contrast, samples of A. palmata recovered from two 2-m deep excavations in the adjacent substrate are generally less encrusted and have significant quantities of the foraminifer Carpenteria spp. Homotrema rubrum is common in both sample sets, but exhibits a markedly different morphology between standing-dead and buried branches. The presence of an encrusting “signature” that is unique to standing- dead colonies may be useful in understanding the origins of the gaps in the Caribbean A. palmata record.

Telemetred multichannel system for geophysical cable

Mr. Florin Ionica Earthquake Unit, University of the West Indies Kingston – Jamaica E-mail: [email protected]

A new telemetred multichannel system for geophysical cable is presented.The investigation of the boreholes is very important to be done using as many measuring channels as possible in order to have fast and effective results. Multiwire cables which are now used in multichannel systems are very problematic due the connectors, durability and wear. Water tightness must be very high because of the high pressure which exists in boreholes over 1000 meters. Also noises and disturbances

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generated by external electromagnetic fields are big problems especially in VSP or HSP measuring where all the signals, including the weakest reflections must be recorded at sufficient resolution. Taking in account these requirements it was designed one modular system which is constructed to function on one coaxial cable where all the channels are located in parallel in frequency domain. This kind of system is called telemetry system and it is used mostly in airplane and space equipment. This telemetry system consist of transducer units (each one with three geophones), preamplifiers, circuits to transfer signals to cable, electronic controls and power supply components. All units are connected on a strong main coaxial cable as many as needed. Physically they are in series with cable but electrically are in parallel as on a bus line. The power supply is delivered via the same cable as single DC-supply voltage where units take their power from switching regulators.

Transmission of seismic data using High Voltage Electrical Lines –Power Line Carrier Systems

Mr. Florin Ionica Earthquake Unit, University of the West Indies Kingston – Jamaica E-mail: [email protected] Section: Seismology-Poster

Among the different kind of communication systems to be used like bearer, the Power Line Carrier (PLC) Systems represent in many countries a main part of utility-owned transmission system. The PLC technology remains in fact always cost attractive because, by using as transmission bearer the same power network, is able to: - connect exactly all the main points involved with the required exchange of information reducing the number of the communication equipment and maintenance work - guarantee good communication also on High Voltage (H.V.) power lines of some hundred kilometers, without any need of repeaters, in any climatic conditions and independently of natural barriers (hills, mountains, etc.) - guarantee highly reliable communications for the high mechanical safety of the H.V. power lines which are designed to withstand the worst Nature can do. Some aspects regarding the using of the PLC Systems for seismic data transmission are presented. A PLC System is generally composed of a few main elements such as: - line traps - coupling devices - PLC equipment - teleprotection equipment Transmission of the signals in PLC Systems is using high frequency carriers (generally in the 40 to 500 KHz band) between two or more locations.

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The PLC equipment converts the low frequency signals (e.g. VCO’s) or serial outputs from seismic data-loggers into high frequency signals to be transmitted on the High Voltage lines: the opposite conversions are performed for the received high frequency signals.

Biogeographic implications of Caribbean Paleogeography: The origin and evolution of an inter-oceanic seaway Manuel A. Iturralde-Vinent Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana 10100, Cuba; [email protected]

Since latest Triassic the Caribbean started to be formed as a system of Jurassic rift valleys within west-central Pangaea, later evolving into a mediterranean sea where distinct volcanic and non volcanic island evolved. Since its very early formation this sea has been playing an important roll controlling the historical patterns of ocean water circulation, moderating the world climate, and determining the possibilities of biotic exchange of the surrounding terrestrial and marine ecosystems. The formation of a Mesozoic marine seaway between the western Tethys and the eastern Pacific, across west-central Pangaea, has been postulated for the Early Jurassic (Hettangian-Pliensbachian) according to biogeographic thesis, but supporting stratigraphic data is lacking. Probably since the Bathonian but certainly since the Oxfordian, the stratigraphic record indicate that this connection was fully functional and the Circum Tropical marine current was active. Overland dispersal between western Laurasia (North America) and western Gondwana (South America) has been interrupted since the Callovian when the continents were separated by a marine gap. Later, a connecting landbridge may have been present during the latest Campanian/Maastrichtian (~75-65 Ma), and since the Plio-Pleistocene (2.5-2.3 Ma). Evidence for a precursor bridge late in the Middle Miocene is ambiguous at this time. Since the formation of the first volcanic archipelago within the Caribbean realm, at about the Jurassic-Cretaceous transition, volcanic islands, shallow banks, and ridges have been present in the paleogeographic scenario of the area. But these lands were generally ephemeral, as they lasted just a few million years. Only after the Middle Eocene (<40 Ma ago) permanent lands were present within the Caribbean geographic scenario, providing the substrates for the formation and development of the present terrestrial biota.

Keywords: Paleogeography, paleoceanography, biogeography, Caribbean, Mesozoic, Cenozoic.

This paper is a contribution to IUGS/UNESCO International Geological Correlation Programe Project 433: Caribbean Plate Tectonics

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Paleoproductivity in the Caribbean Sea During Closure of the Central American Seaway Sreepat Jain and Laurel S. Collins, Department of Earth Sciences, Florida International University, Miami, Florida 33199, USA

Increased Caribbean oligotrophy is a predicted effect of the closure of the Caribbean – Eastern Pacific seaway about 4 Ma. We examine nutrient proxies at sites ODP 999 and DSDP 502, Colombian Basin, from before (8 Ma) to after (2.5 Ma) this event. PpP (paleoproductivity) is based on a transfer function converting carbonate mass accumulation rates, and BFAR is the rate of accumulation of benthic foraminifers (>63 μm), a proxy for organic matter accumulation on the seafloor.

Between 7.3–6 Ma, paleoproductivity and Site 502 BFAR decreased from moderately high values, although Site 999 values were low. The trend agrees with high global paleoproductivity associated with the Late Miocene Carbon Isotope Shift (7.6–6.8 Ma). From 6–5.3 Ma, paleoproductivity and seafloor accumulation of organic matter increased, and PpP increased to its highest values. This interval corresponds to the onset of the Messinian Salinity Crisis around 6 Ma and higher productivity. From 5.3–4.75 Ma, PpP and BFAR decreased, reflecting decreased global productivity associated with the Terminal Messinian Flood and eustatic rise at 5.3 Ma. During the last stages of seaway closure 4.75–4.0 Ma, paleoproductivity and seafloor accumulation of organic matter increased again. Enhanced ventilation of the deep Caribbean Basin and better carbonate preservation has been documented starting at 4.6 Ma. From 4–2.5 Ma, PpP values declined slightly. BFAR values generally agree with PpP estimates until 4 Ma, after which the proxies diverge. Site 999 BFAR peaked at 3.5 Ma, but Site 502 BFAR has its highest values at 4 and 3 Ma.

Conclusions: 1) Paleoproductivity and accumulation of organic matter on the seafloor varied within the Colombian Basin. 2) Paleoproductivity reached a high around the Miocene/Pliocene boundary and, after a drop and recovery 5–4 Ma, gradually declined. 3) Both proxies effectively track global and regional signals.

Comparison of the Stratigraphy of the Tertiary Limestone Across Central Jamaica Ennika James and Simon F. Mitchell University of the West indies, Mona, Kingston 7

This study is concerned with understanding the distribution of carbonate-microfacies on a Middle Eocene, carbonate platform (Chapelton Formation) in Jamaica. Three sections across central Jamaica (Watermont, St. Catherine in the east, Coleyville, Clarendon in central Jamaica and Litchfield, Manchester, in the west) were investigated. Representative samples were collected and thin sections for microfacies analysis prepared. In the eastern part, the Chapelton Formation is represented by poorly developed limestones with pellatisperella- dominanted sparse biomicrites interbedded with fossiliferous mudstones and clastic

39 17th Caribbean Geological Conference 2005, San Juan PR sandstones. In the western sections the carbonates consist of fossiliferous (foraminiferan and molluscan) packstones and grainstones. Sporadically dolomitization of the facies has occurred with either mimick replacement or the development of cross-cutting dolomite rhombs. The succession forms a part of a back stepping depositional system with the progressive restriction of clastic components to the south-east and the development of thick foraminiferan and molluscan dominated microfacies in an extensive shallow marine carbonate sea to the north-west. The distribution of microfacies has importance to ongoing hydrocarbon exploration in Jamaica.

Geochemistry And Formation Of Horizontal Elongate Concretions In A Mixed Sand-Gravel Shoreface Sherene A. James1, Simon F. Mitchell1, Jim D. Marshall2 and Steve F. Crowley2 1Department of Geography and Geology University of the West Indies, Mona Kingston 7, Jamaica 2Department of Earth and Ocean Sciences, University of Liverpool, United Kingdom.

Horizontal, highly elongate concretions occur in Late Pleistocene, marine shoreface sandstones at the base of a 4 m high Pleistocene sea cliff at Roselle, St. Thomas, Jamaica. These concretions have width:length ratios of 3-5, are orientated perpendicular to the modern shoreline, and cut by vadose-zone rhizocretion columns. This study examined the method of formation of these concretions using geochemistry and petrography. The cements in the concretions consist of large (up to 1 cm) polikotopic plates, which are confirmed as calcite by X-ray diffraction. In cathodoluminescence and backscatter scanning electron microscopy, these cements show strong luminescence. Trace element analysis demonstrates relatively high concentrations of Mn and low concentrations of Fe, with the Mn likely the cause of the luminescence. The high Mn would suggest a marine environment; and the lack of pyrite, coupled with the high Mn, indicates crystallization occurred within the sub-oxic zone, before Fe reduction. Oxygen isotopes (-4.9-5.8‰ PDB) indicate near-surface temperatures consistent with a marine or meteoric water source. The relatively negative δ13C (-10.3 to -13.9‰ PDB) values suggest the incorporation of bicarbonate from bacterial reduction of organic matter. The lack of pyrite, the near surface temperatures for oxygen isotope data, the high Mn values, and the presence of poikilotopic plates indicate growth in the suboxic zone in a phreatic environment created by stagnant mixed marine and meteoric water. The source of calcium ions could be either internal (dissolution of marine bioclasts and Ca-rich minerals) or external. Cementation is envisaged to have occurred as the system was flushed by mixed marine-meteoric waters as sea level fell following the Sangomonian high stand, prior to the establishment of a vadose diagenetic environment. These results indicate that cementation of sandstones beneath sequence boundaries occur during sea- level fall.

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Remote sensing evaluation of regional chemistry and element dispersion of porphyry copper deposits in the Silver Bell Mountains, Arizona Jaramillo-Nieves, Lorna G. (Ph.D., Geology) [Department of Physical Sciences, UPR, Río Piedras]

Porphyry copper deposits in southeastern Arizona belong to a cluster of 38 mineralized centers covering a region extending from northern Mexico to western New Mexico and southern Arizona. Presently, some of these deposits are being actively mined and the rest are prospects or abandoned mining sites. As a result of the large number of porphyry copper deposits in this region, research on the interaction between mineralized centers and the environment is important; in particular, the dispersion characteristics of acid- generating metal-enriched materials at the shallow alluvial margins of these centers. The present research uses remote sensing techniques, groundwater chemistry, trace element, and mineralogical analysis to characterize dispersion chemistry surrounding porphyry copper deposits in the Silver Bell Mountains. Hyperspectral imagery obtained by the Airborne Visible/Infrared Spectrometer and HyMap are used to map supergene minerals by analyzing their spectral profiles in the visible and short wave infrared regions of the electromagnetic spectrum. Reflectance profiles are characteristic of each mineral and shifts in absorption features within one mineral are a result of differences in cation content. Image reflectance profiles are compared with stream sediment mineralogy and reflectance spectral profiles to better outline concentrations of Fe, S, K, Na, Ca, Mg, Cu, and Al. In addition, groundwater modeling in the Silver Bell Mountains is considered for various flow paths within shallow aquifers in the region and compared to actual groundwater chemistry and surface lithology. The Silver Bell Mountains serve as a case study for element mobility and concentration distribution in other areas where undisturbed deposits, historic and present-day excavation activity occurs, where semi- arid climate and a deep vadose zone are variables that influence element mobility and concentration. Results obtained from hyperspectral image processing indicate the possible enrichment of stream sediment samples in iron and/or magnesium, based on absorption shifts observed for phyllosilicates in the region. The extent of alteration patterns in porphyry copper deposits located in the Silver Bell Mountains supports the concept of narrow dispersion haloes in semi-arid environments.

Role of crustal melting in petrogenesis of the Cretaceous Water Island Formation, Virgin Islands Northeast Antilles Island Arc Wayne T. Jolly, Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1 Edward G. Lidiak, Department of Earth and Planetary Sciences, University of Pittsburgh, Pittsburgh, Penna., USA 15260

The Late Aptian to Early Albian (~115 Ma) Water Island Formation in the Virgin Islands is comprised of approximately 20% degraded island arc basalt (spilite; 46-56% SiO2) and 80% dacite and rhyolite (keratophyre; 65-85% SiO2). Trace element patterns of both end- members, characterized by pronounced negative normalized high field-strength element (HFSE) anomalies, relatively flat rare earth element (REE) patterns, and highly depleted

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Sr/Y, have analogues in plagiorhyolite suites from bimodal Cenozoic arcs, including the western Aleutians, Izu-Bonin, and the Kermedacs. Incompatible element patterns are consistent with melting models involving partial fusion of amphibole-bearing oceanic crust at low pressures within the stability range of plagioclase. Predominance of plagiorhyolite relative to basalt, and simultaneous extrusion of basalt and plagiorhyolite throughout volcanism, indicate basaltic melts were underplated along the crust-mantle boundary from earliest stages of volcanism. Moreover, truncation of the erupted fractional crystallization series at SiO2 = 56% indicates evolved basaltic fractionates were gradually displaced from crustal magma conduits as the volume of more buoyant plagiorhyolite melt increased and eventually became trapped in sub-crustal magma chambers by density contrasts. Volcanism occurred in two successive eruptive cycles. First cycle basalts have borderline boninitic compositions, characterized by flat to slightly depleted normalized REE patterns, and depleted light rare earth element concentrations. Interlayered first cycle plagiorhyolites contain a significant basalt component (~25%), indicating intermingling between basaltic melt and crustal source material. Second cycle basalts have flat to slightly enriched REE patterns with elevated LREE abundances, analogous to modern intra-oceanic island arc basalts. Associated plagiorhyolites are free of basalt contamination, reflecting greater physical isolation of second cycle plagiorhyolite melts compared with the previous cycle, probably due to migration of the melting zone to higher crustal levels, out of a restate zone produced during the first cycle.

Late Cretaceous to Mid-Eocene Pelagic Sediment Budget in Puerto Rico and the Virgin Islands, Northeast Antilles Island Arc Wayne T. Jolly, Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1 [email protected] Edward G. Lidiak, Department of Earth and Planetary Sciences, University of Pittsburgh, Pittsburgh, PA., USA 15260 [email protected] Alan P. Dickin, Department of Geology and Geography, McMaster University, Hamilton, Ontario Canada L8S 4M1 [email protected]

Island arc basalts (IAB) in the extinct Greater Antilles, dating between Albian and mid-Eocene time (~125 to 45 Ma), consist of an early low-K, primitive island arc (PIA) basalt series and a later, predominantly intermediate calcalkaline (CA) series. The rocks resemble modern sediment-poor, low-light rare earth element (LREE)/heavy rare earth element (HREE) arc basalts from intra-oceanic tectonic settings and sediment-rich, high-LREE/HREE types from continental margin arcs, respectively. Isotope and incompatible trace element distribution along a 450 km segment of the arc in the northeast Antilles demonstrates that low-LREE/HREE basalts predominate in Albian to mid-Santonian (~85 Ma) stratigraphic sequences in the Virgin Islands (VI) and northeast Puerto Rico (NEPR), while there is a gradual but spectacular increase in both LREE/HREE and absolute abundances of incompatible elements in central Puerto Rico (CPR). Northeastern Antilles basalts have consistently elevated La/Nb and relatively low Nb/Zr, both inconsistent with the presence of a significant ocean island basalt (OIB) component. Hence, observed differences are interpreted to reflect variation in proportions of pelagic sediment subducted by the south-dipping Antilles arc system as it

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swept northeastward across the Caribbean region and eventually approached the Bahama Banks along the southeastern fringes of the North American Plate. Trace element mixing models indicate sediment proportions in VI and NEPR were limited, averaging considerably below 1.0%. In comparison, sediment content in CPR increased from an average slightly above 1.0% in Albian (~125-95 Ma) basalts to as high as 8% in Cenomanian (90-95 Ma) types. Following collision of neighboring Hispaniola with the Bahamas, and a shift from predominantly northeast to east-northeast convergence, sediment budgets in the northeast Antilles stabilized at moderate levels from 2 to 3%, reflecting widespread subduction of North Atlantic Cretaceous pelagic sediment (AKPS).

Impact of the November 2003 Rains on Hillslopes, Embankments, Rock Cuts and Ghuts in the British Virgin Islands. Joyce J. and Santos H., Dept. of Geology, University of Puerto Rico Mayagüez PR

Heavy rains fell over the northeastern Caribbean during the week of November 9- 17, 2003 . Rainfalls recorded at the Tortola airport exceeded 7 inches on 12th and 13th and 6 inches on 14th. The rainfall data clearly show that the distribution of rain was irregular and did not appear to have a geographic control. The greatest rainfall accumulation of 34 inches occurred at Beef Island airport, a relatively low area at the eastern end of Tortola whereas only about 13 inches accumulated at the highest elevation recording station located in Chalwell, in the west central portion of the island. The two primary causes of the extent of the impact were uncontrolled roadway drainage and inadequate drainage capabilities in the ghuts. The problem was worsened where ghut culverts were clogged by debris flows and overflowed on to the roadway. The slope failures not related to roadway runoff largely occurred on over steepened rock cuts along roads and behind homes. Natural slope failures were limited to debris flows in the ghuts and sea cliffs. Most of the debris flows on natural and man-made slopes occurred along joint intersections. The cut slope failures were generally superficial and largely controlled by rock type. The stronger massive rock layers failed by sliding along joints and joint intersection wedges creating rock falls and avalanches. The thin bedded weaker units failed by superficial debris avalanches. The intrusive batholithic rocks of eastern Tortola and Virgin Gorda exhibited joint controlled rock sliding and a granodiorite tor topple. The common occurrence of thick colluvial deposits in many road cuts indicates that rainfall events of this magnitude have occurred in the past and are likely to occur again.

November 2004 Mogote Topple Manati Puerto Rico Joyce, J. and Velez, R., University of Puerto Rico, Mayagüez, Puerto Rico

An enormous portion of a hilltop mogote toppled off of a 50 meter high limestone hill and crushed houses in the urbanization that lay below. As the mogote section fell it broke up into blocks and pieces, the largest of which was 2-3 times the size of the impacted homes. Although damage was severe there were no personal injuries due largely to the fact that the home dwellers were not present at the time. The cause of the event was

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natural, a combination of paleo-karst dissolution features, the orientation of the mogote bounding joints and the thin bedded limestone that lay below the mogote. The mogote formed part of a northeast trending mogote karst ridge in the Aymamon Limestone. The mogote top was composed of recrystallized massive limestone and underlain by thin bedded recrystallized grainstone. The remainder of the hill slope below the mogote was composed of thick to very thick bedded recrystallized limestone. The base of the remaining section of the mogote ridge was marked by a prominent notch. Smaller notches and weathering at the base of the largest fallen block indicates the notch was continuous along the mogote ridge. The notch tracked into a small cave suggesting it represents a paleo-phreatic level. The mass of the remaining mogote ridge was clearly inclined over the notch and towards the urbanization. This tilt and the undercut notch caused a section of the mogote ridge to peel off the underlying thin beds and topple on to the urbanization below. The remaining thin beds of limestone were heaved up and tilted the topple direction. Although the topple required the combination of several geologic features it may not represent a unique event. Similar conditions may be found elsewhere in the mogote karst and present a hazard to other urbanizations.

The Amorphous Mystery Shakira Khan and Simon F. Mitchell Department of Geography and Geology, University of the West Indies, Mona, Kingston, Jamaica

Jamaica’s carbonate sand beaches consist of skeletal and non-skeletal sand-sized grains. The skeletal grains can be identified in thin section and consist of fragments of marine organisms, including foraminifers, red algae, green algae, echinoids, molluscs and corals. The non-skeletal fraction consists of crystalline, amorphous and clastic grains. Compositional analysis, of sediment collected around the island of Jamaica, shows that amorphous grains contribute up to 50% of the total beach in many areas. Previously, several ways have been suggested for the formation of amorphous grains (for instance, alteration of skeletal grains, fecal pellets, mud balls, etc.). Because of their importance as a major constituent of beach sand, an understanding of the origin of these non-skeletal grains is critical in modeling the production of beach sediment. This study focuses on identifying the origin of amorphous grains; two techniques were used: petrography and scanning electron microscopy (SEM). For petrographic analysis, sand samples were resin impregnated, and thin sections prepared from the blocks. Individual amorphous grains were studied for traces of internal structure that might indicate their origin. For SEM analysis, individual grains were fractured and mounted on a stub. They were coated with gold-palladium and viewed under the SEM, with attention being drawn to internal features. The results indicate the origin for the amorphous grains in Jamaican beaches – but like any good who-done-it you don’t want to know the answer yet!

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Pressure-temperature-time paths critically constrain Cretaceous subduction-zone dynamics in the Rio San Juan Complex (Northern Dominican Republic) Krebs, M.*, Maresch, W.V.*, Schertl, H.-P.*, Draper, G.**, Idleman, B.*** *Institute of Geology, Mineralogy and Geophysics, Ruhr-University of Bochum, 44780 Bochum, Germany ** Dep't of Geology, Florida International University, University Park, Miami FL 33199, USA ***Dept. of Earth and Environmental Sciences, Lehigh University, Bethlehem, PA 18015, USA

Serpentinite melanges associated with Cretaceous subduction at the leading edge of the eastward-drifting Caribbean plate now decorate the trace of the Caribbean / North- American suture zone exposed in Cuba and northern Dominican Republic. Blocks of various types of metamorphic rocks (e.g., eclogites, blueschists, metagranitoids) in the melanges exhibit a series of different but interrelated P-T-paths. Comparison with numerical models yields critical information on the dynamics of a young and maturing subduction-zone / island-arc complex. The P-T paths can be summarized into three categories: 1) oldest, "nascent" stage: Typically shallow ("hot") P/T gradients and peak conditions of 700°C/22 kbar. Unusual anticlockwise P-T paths with isobaric cooling and later isothermal exhumation are common in eclogites. U-Pb-zircon protolith ages of 139.9 ± 4.1 Ma constrain the beginning of subduction. Lu-Hf-data on Grt-Ep-Amp-Omp- WR yield an age of 103.9 ± 2.2 Ma for peak metamorphic conditions. Rb-Sr-ages of 74.7 ± 0.5 Ma (Phe-Grt-WR) and Ar-Ar (Phe) of 73.18 ± 0.99 Ma constrain the exhumation path. 2) maturing stage: Continuous cooling and steepening of the subduction-zone P-T gradient is recorded. Omphacite blueschists yield an age of 80.3 ± 1.1 Ma (Rb-Sr on Phe- Amp-WR) for peak metamorphic conditions (550°C/18 kbar) and an age of 72.97 ± 1.01 Ma for cooling below 400°C (Ar-Ar on Phe) during exhumation. 3) mature stage: Typified by jadeite-lawsonite blueschists (380°C/>16 kbar) recording very steep, "cold" P/T-gradients. Rb-Sr-ages (Phe-Amp-WR) of 62.1 ± 1.4 Ma date peak metamorphic conditions. This distinctive array of P-T paths in space and time is in accord with subduction-zone models calling for progressive serpentinization, weakening and incorporation into channel-flow circulation of the hanging-wall lithospheric mantle, induced by fluids emanating from the downgoing slab.

Preliminary Study of Serpentinite Deformation in Southwest Puerto Rico Laó-Dávila, D.A.1, Campbell, P.2, and Anderson, T.H.1 1 Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA, USA 15260 2 Department of Geography, Geology, and the Environment, Slippery Rock University, Slippery Rock, PA, USA 16057

In southwest Puerto Rico, three belts of ultramafic rocks crop out: Monte del Estado peridotite belt (MEPB), Guanajibo serpentinite belt (GSB), and the Bermeja Complex. Preliminary field studies in the GSB and the MEPB reveal common brittle (kernel joints, serpentinite veins, and cataclasites) and ductile structures (S-C fabrics and

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folded foliations) in the serpentinite. Within the GSB, foliated serpentinite is characterized by steeply dipping E-W striking S-C fabric that distinguishes a left-lateral shear zone. The steep S-C fabric overprints an earlier fabric. The easterly strike and steep dip of the youngest fabric suggest its development along a Tertiary strike-slip fault. Serpentinite at the southern contact of the MEPB is topographically high and locally structurally overlies Late Cretaceous rocks along contacts with gentle apparent dips. Quarry exposures reveal moderately dipping NW-SE striking faults and shear zones. Some of which contain foliated serpentinite that records folds with hinges trending NW-SE. Drag and offset of distinctive features suggest southwest-directed transport. Previous interpretations of the geologic history of these ultramafic rocks include: 1) northward-directed obduction during Early Cretaceous subduction followed by weathering, and formation of conglomerate and breccia containing clasts of serpentinite that constitute the base of the overlying Late Cretaceous rocks; 2) diapirism of the serpentinite through the overlying Late Cretaceous rocks; and 3) serpentinite deformation in response to early Tertiary contraction. None of the above interpretations is supported by the results of our preliminary structural studies in the GSB and MPB. The presence of nearby ductile and cataclastic structures indicates a more complex tectonic history than previously recognized. Our results from three locations suggest: 1) emplacement of cold, somewhat deformed, serpentinite above Late Cretaceous units, and 2) development of left-lateral steep shear zones that may be related to regional late Eocene strike-slip faults. Older, yet unrecognized events are not precluded.

BOLIVAR: Continental Growth and Deformation along the South American- Caribbean Plate Boundary A. Levander* and the BOLIVAR Working Group *Department of Earth Science, Rice University, Houston, TX, USA 77005 [email protected]

BOLIVAR (Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region) is a 5 year seismic, geological, and geochemical study funded by the NSF Continental Dynamics Program to investigate continental growth and deformation along the South American-Caribbean (SA-Car) plate boundary. The study area extends from western Venezuela to the Atlantic Ocean. Since the SA-Car collision at 55 Ma, the Americas have migrated westward with respect to the Caribbean plate, with SA passing the leading edge of the Antilles subduction zone across the entire northern SA margin. This oblique continent-arc collision has simultaneously formed a foreland fold and thrust belt on the SA mainland, a strike slip system separating SA from the Caribbean Leeward Antilles arc, and incorporated elements of the volcanic arc into the continental margin. Offshore a new west striking, southward-dipping subduction zone has formed beneath SA due to SA-Car convergence.

Our investigations of this region have included an active seismic program acquiring 6000 km of marine reflection profiles, 4 onshore-offshore and 5 OBS profiles as well as seismic recordings on the islands of the Leeward Antilles and Venezuelan arcs. Five

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major reflection/wide-angle transects are designed to give cross-sections of the arc and margin showing the evolution of the plate boundary from 55 Ma to the present.

To investigate the upper mantle of this complex region we are currently operating a 35 element PASSCAL broadband array in Venezuela and a 14 element longterm OBS array in the southeastern Caribbean to complement the 35 element permanently installed Venezuelan broadband seismic network operated by FUNVISIS.

Geological studies include age dating of rocks along the Leeward Antilles arc, field mapping, exhumation rate, and fault studies on the ABC islands and in northern Venezuela, and basin analysis of a number of the Venezuelan and offshore sedimentary basins.

New Petrological And Geochemical Constraints On The Origin Of Loma Caribe Peridotite (Dominican Republic) J.F. Lewis(1), J.A. Proenza(2), F. Longo(3), (1) Dept. of Earth and Environmental Sciences, George Washington University, Washington, D.C. 20052. [email protected] (2) Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí i Franquès, s/n, 08028 Barcelona, Spain. [email protected] (3) Falconbridge Dominicana, Bonao, Dominican Republic

Loma Caribe peridotite is exposed along the Median Belt in the northeastern part of the Cordillera Central, Dominican Republic. The peridotite body is about 4-5 km wide and extends for 95 km from La Vega to Cerro Prieta north of Santo Domingo. These mantle rocks are considered to have been exposed because of the collision of an oceanic plateau (Duarte plateau terrane) with the primitive Caribbean island–arc (Maimon-Amina terrane) at Aptian time. The Loma Caribe peridotite is composed of mainly harzburgite with Cpx-rich harzburgite, lherzolite and dunite. The peridotites typically show porphyroclastic and coarse-grained granoblastic textures. These metamorphic textures together with the presence of strongly deformed orthopyroxene phenocrysts are consistent with the view that the peridotites represent remnants of depleted upper mantle. The Cr/(Cr+Al# in accessory Cr-spinel from Loma Caribe peridotites vary from 0.30 to 0.88. These large compositional variations indicate the occurrence of peridotites with very different melting histories. In addition, the olivine Mg# of dunite (91-92) is slightly higher than that of harzburgite (90-91), and higher than lherzolite (89.5-90.5). Opx composition in harburgite shows higher Mg# (90.6-91.4), and Al2O3 contents ranging from 2.8 to 3.1 wt.%. Opx from lherzolite in Loma Caribe exhibits lower Mg# (< 90.5) and higher Al2O3 (up to 3.3 wt.%). The equilibration temperature estimates (according to three thermometric formulations using pyroxenes) give large ranges of equilibration temperature between 980º and 1260º C.

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REE analyses of harzburgite and dunite show homogeneous HREE contents and are characterized by relatively flat LREE patterns and a steep HREE fractionated segment. These patterns are similar to those of depleted peridotites from the eastern Cuban ophiolite, and to peridotites from the Izu-Bonin-Mariana forearc. The REE compositions can be interpreted as the result of partial melting and mantle interaction with ascending melt at a suprasubduction zone. In contrast, lherzolites from the Loma Caribe peridotite are enriched in MREE and HREE compared to harzburgite and dunite. REE pattern show low LREE/MREE and MREE/HREE ratios consistent with partial melting in the garnet peridotite facies. In addition, Loma Caribe peridotites are relatively enriched in Cs, Rb and U, and depleted in Th. It therefore appears that the upper mantle rocks present in Loma Caribe peridotite are probably from several suboceanic mantle sources, including mantle slices from beneath an ceanic ridge, oceanic plateau and island arc.

Composition And Mineralogy Of PGE-Rich Loma Peguera Chromitites, Dominican Republic

J.F. Lewis(1), F. Zaccarini(2), J.A. Proenza(3), F. Longo(4), G. Garuti(5) (1)George Washington University, USA, [email protected] (2)University of Leoben, Austria, [email protected] (3)Universitat de Barcelona, Spain, [email protected] (4)Falconbridge Dominicana, Bonao, Dominican Republic, [email protected] (5)University of Modena and Reggio Emilia, Italy, [email protected]

Loma Peguera chromitites are located in the central part of the Loma Caribe peridotite in the Cordillera Central, Dominican Republic. The chromitite forms small podiform bodies enclosed in dunite, and shows mainly massive textures, with intergranular silicates such as olivine, serpentine and chlorite accompanied by minor pentlandite and Fe-Ni alloys. Primary chromite composition from the Loma Peguera chromitite is Cr-rich. The Cr# varies from 0.75 to 0.78, the Mg# from 0.47 to 0.50. These values are typical of ophiolitic chromitites elsewhere. However, Loma Peguera chromite exhibits systematically high TiO2 (0.79-0.93 wt%) and Fe2O3 (7.23-8.46 wt%) contents. Total PGE concentrations in the Loma Peguera chromitites are high, ranging from 1.82 to 2.04 ppm. Chondrite-normalized PGE patterns show an enrichment in Os+Ir+Ru relative to Rh+Pd+Pt, causing a negative slope between IPGE and PPGE. Consistent with the high PGE concentrations, PGM are very abundant in Loma Peguera chromitites. Platinum-group minerals (PGM) were discovered in 14 polished sections of chromitite with an average frequency of about 2 grains per square centimeter. Generally, they are less than 10 µm in size. The mineralogy of PGM is made up of Ru, Os, Ir and Pt phases, including laurite, irarsite, ferronickelplatinum, Ru-Os-Ir-Fe oxides, unknown Ru-Os-Ir-Pt-Fe-Ni-Cu compounds, native Ru and Ru- rich Ni-Fe alloy.

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Loma Peguera chromitites are hosted in typical mantle peridotites in terms of mineralogy, composition and texture, and seem to be derived from a magma characterized by high Cr, Fe and PGE contents. The composition of chromitite from Loma Peguera is similar to that reported for Cr-spinel from oceanic plateau basalts (e.g. Nauru Basin Oceanic Plateau, SW Pacific; Tokuyama and Batiza, 1981). It is therefore likely that Loma Peguera chromitite represents an example of chromitite formed in a suboceanic upper mantle affected by a mantle plume (Duarte plume).

Anomalous Granitoid Compositions From The Northwestern Cayman Trench: Implications For The Composition And Evolution Of The Cayman Ridge. John F. Lewis, Michael R. Perfit, Giuseppina Kysar Mattietti, Ricardo Aravalo, James Mortensen. Thomas Ullrich, Richard Friedman and George Kamenov

Perfit and Heezen (1979) showed that granitoid rocks crop out along the steep walls of the Cayman Ridge. Six of the granitoid rock samples, dredged from the western Cayman Trench, immediately south of the Rosario Bank area, between 83°W and 84°54’W, have been radiometrically dated and analyzed for major and trace element geochemistry, and Pb isotope compositions. The granitoid rocks range from 55% to 72% SiO2 and are characterized by high concentrations of Th (up to 41ppm in acid rocks), Zr (112-261 ppm), Nb (5-18ppm), and LREE (La=16-65ppm). Yitrium and HREE concentrations are very low (Yb < 0.22 ppm in 5 samples with sample 2172F at 0.56ppm). Ce/Yb ratios ** John might be better to quote this as the chondrite normalized ratio*** range from 116 to 1150. These values are more typical of continental arc granitoids (eg Sierra Nevada batholith) and contrast with the oceanic island arc compositions of granitoids from the Greater Antilles islands including the Sierra Maestra of Cuba. Three of the western Cayman Trench granitoids have Pb isotope compositions that are decidedly more radiogenic than other granitoids from the Greater Antilles and are consistent with the incorporation of an isotopically more evolved component such as continental crust or sea floor sediment. West Cayman granitoids yield satisfactory U/Pb ages on titanite and Ar/Ar ages on hornblende and biotite from 62 to 64 Ma with one biotite plateau age at 66.35 ± 0.34 Ma, slightly older than previous K/Ar determinations (Perfit and Heezen,1979). These ages and compositions contrast with those of the Sierra Maestra of Cuba, considered to be an uplifted extension of the Cayman Ridge. Sierra Maestra granitoids yield U/Pb ages on zircon that range from 46.8 ± 0.2 to 60.5 ± 2.2Ma (Mattietti et al. 1998; Rojas et al. 2004). Trace element plots of Sierra Maestra granitoids show geochemical signatures intermediate between oceanic arc granitoids and MOR plutonic rocks **Is this what you mean?). Pb isotope compositions lie along the MORB array and indicate a minimal subduction component

There have been no reliable dates of greater than 60.5 Ma for granitoid rocks in the Sierra Maestra although Paleogene volcanism, which lasted for about 20 Ma, might have begun in early Danian time. ??? confusing sentence?? On the other hand there have been no reliable dates younger than 62 Ma recorded for granitoid rocks from the western Cayman Ridge.

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Although volcaniclastic turbidites, of early Eocene age, similar to those in the Sierra Maestra, have been drilled (DSDP Hole XXX) on the western Cayman Rise at 83°W, the crust underlying the western Cayman Ridge appears to include granitoid rocks with a distinct continental affinity, very different from the Sierra Maestra. The deeper crustal rocks of the western Cayman Ridge are likely to be a rifted eastern extension of the northern marginal basement complex of the Chortis block of Honduras, as has been suggested previously (who?). It is concluded that the composition and Cretaceous-early Paleocene history of the western Cayman Ridge probably differed significantly from that of the Sierra Maestra.

Cretaceous (115-75 Ma) Geochemical Stratigraphy In The Northern Virgin Islands, Northeast Antilles Island Arc Edward G. Lidiak, Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA., USA 15260. e-mail: [email protected] Wayne T. Jolly, Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1. e-mail: [email protected]

Island arc volcanism in the northern Virgin Islands consists of a conformable sequence of flows, breccias, tuffs, and their volcaniclastic equivalents that range in age from Aptian- Albian (125-110 Ma) to Campanian-Maastrichtian (75 Ma). The earliest strata are rocks of the Water Island Formation, a bimodal basalt-plagiorhyolite suite, dominated by a mixture of mantle-derived basalt (20%) and crust-derived felsic lava (80%). The mafic end-member contains transitional intermediate-Ti boninites and high-Ti island arc basalts that are highly depleted in incompatible elements. In contrast, rocks from the overlying Louisenhoj Formation are tri-modal (basalts, 65%; andesite, 20%; plagiorhyolite, 5%) and contain slightly higher incompatible element concentrations. A low LREE content places both the Water Island and the Louisenhoj in the Antillean primitive island arc (PIA) suite. The sequence in the US Virgin Islands is capped by a series of basaltic andesite-to-andesite lavas (Tutu Formation) with distinctly elevated LREE, indicating that they belong in the Antillean calcalkaline (CA) suite. The compositional shift from PIA to CA is consistent with a gradual increase in the proportion of pelagic sediment derived from source regions. Compositional similarities and structural relations in the British Virgin Islands, where strata are dominated by a basalt-to-dacite fractional crystallization series (Tortola Fm), indicate correlation with Louisenhoj strata. Plagiorhyolite lavas in the Virgin Islands, characterized by low Na, Al2O3, and Sr/Y, represent melts generated by low-pressure fusion of oceanic crust. The proportion of plagiorhyolite decreases significantly from 80% in Water Island strata, to 15% in the Louisenhoj, to 0% in the Tutu Formation, reflecting decreasing temperatures and decreasing proportion of crustal melt generated in the system. Andesitic lavas in the Louisenhoj Formation represent products of fusion within under plated arc gabbros produced during initial Water Island volcanism. A significant proportion of Tutu volcanic rocks were contaminated by similar remelted arc-related material.

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Seizing the opportunity to build more resilient hazard monitoring networks in the Eastern Caribbean

Lloyd L. Lynch Seismic Research Unit University of the West Indies St. Augustine, TRINIDAD and TOBAGO

A major initiative is currently underway to establish a program for reducing the risk to various coastal hazards in the Inter Americas Seas. This initiative is lead by the Caribbean Charter of the International Oceanic Commission (IOCARIBE). It involves most regional institutions and agencies that are already engaged in the monitoring and study of coastal and other hazards as well as several disaster management organizations. Initially, priority is being given to the development of a Tsunami Warning System (TWS) and support programs to empower threatened communities to respond correctly to alerts and warnings.

Although the consequences of future tsunamis are likely to be more severe than past events, it is a fact that the recurrence rate of these events is quite low. Decision-makers usually devote limited resources to current and the most salient problems rather than to problems that may not occur during their term of office. To do otherwise, a decision- maker must have a cost-effective justification. Not only are Tsunami Warning Systems expensive to establish, they are also difficult to sustain and require high levels of coordination and commitment to function effectively. Close collaboration among institutions and organizations of several countries is a needed for rapid exchange of data and warnings and to maintain the seismic and ocean observing system. An initial goal in establishing the TWS is to pool and use resources from existing regional monitoring and disaster management systems in a synergistic manner so as to attain cost-efficiency at all levels of design and operation. The same principle will also be applied to new overlapping networks being established by adjacent jurisdictions.

The Seismic Research Unit (SRU), University of the West Indies currently operates a 60- station seismic volcano and earthquake monitoring network in the Eastern Caribbean. The Unit is well positioned to provide meaningful contributions to the TWS and the broader hazard mitigation initiative. It brings to the pool, several dedicated staff members with a wealth of experience, a substantial amount of resources and a network of support that has played a key role in its operation that has been sustained for over fifty years. Some level of upgrade is needed to transform strategically located SRU installations to the status required to contribute to the TWS network and for the Unit headquarters to function as a TWS sub-focal center. It is however anticipated that the cost/benefit advantage of the target multi-hazard system will attract the support needed and spawn the development of techniques to overcome technical and other obstacles. Through collaboration with other institutions SRU will secure improved data communication links and other resources that will facilitate real-time transfer of data on current Volcano Surveillance, Seismic and Sea observing networks and support complementary programs such as real-time geo-dynamic monitoring .

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BOLIVAR: A Snapshot of the Caribbean-South American plate Boundary at 67.5W M.B. Magnani, C.A. Zelt, A. Levander, S.A. Clark and the BOLIVAR Working Group Department of Earth Science, Rice University, Houston, TX, USA

The active seismic component of the BOLIVAR experiment (Broadband Ocean Land Investigation of Venezuela and the Antilles arc Region), funded by NSF Continental Dynamics involved the acquisition of ~6000 km of marine reflection profiles, four onshore/offshore/OBS profiles across the Venezuelan margin and seismic recording on six of the Leeward Antilles arc and Venezuelan islands (see Levander et al., this session).

The five main transects were designed to image the upper mantle and crustal structure of the South American-Caribbean (SA-Car) plate boundary at different stages of its evolution as the Americas moved west and the Caribbean collided obliquely with SA. The multi-channel marine reflection data and the onshore/offshore wide-angle data along one of these transects approximately along the 67.5W meridian and adjacent reflection profiles provide a snapshot of the plate boundary processes since the Antilles subduction zone passed this point of the margin at ~30 My. The seismic data document the complex evolution of the plate boundary starting from the development of the Caribbean Mountain system and the accretion of the volcanic arc on the SA continental margin, and the opening of the Falcon-Bonaire-Grenada basins (~55 Ma). The south-dipping subduction of the Caribbean plate started at 28 Ma and the Moron-El Pilar dextral strike-slip system developed at about 12 Ma, inverting several Paleogene extensional features on the southern edge of the Bonaire-Grenada basin. The wide-angle data show a complex crustal velocity structure underneath the volcanic arc, where the Moho is at about 27 km depth, under the Bonaire basin, where the Moho rises to about 25km depth, and across the Moron-El Pilar strike-slip system, where the Moho drops abruptly to about 40 km underneath the South American continent. The Moron - El Pilar fault is associated with high velocities (~6.5-7.0 km/s) visible to about 15 km depth. A similar high velocity structure characterizes the northern edge of the Los Aves and Los Roques block, where the reflection data image the backstop of the Caribbean Deformed Belt.

For more information: http://earthscience.rice.edu/BOLIVAR.html

Subduction Zone Dynamics And Interpretation Of Caribbean Fossil Suture Zones Maresch, W.V.* and Gerya, T.V.** *Institute of Geology, Mineralogy and Geophysics, Ruhr-University of Bochum, 44780 Bochum, Germany ** Geological Institute, ETH - Zürich, CH-8092 Zürich, Switzerland,

The Caribbean area is characterized by well-preserved fossil collision zones to the north and south, in which oceanic subduction-zone/island-arc complexes have been

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sutured to and preserved along the adjoining continents. The dynamics of these extinct subduction-zone/island-arc systems and the processes accompanying the actual collision are of both general interest in understanding "subduction-zone factories" world-wide, and of particular interest in reconstructing the tectonic history of the Caribbean area. The study of exposed metamorphic rocks in suture zones allows the "depth dimension" to be incorporated into terrane analysis. The study of exposed magmatic rocks yields information on input, output, conveyor belts and plant facilities of the subduction-zone factory. It has become possible in recent years not only to formulate realistic models of the subduction-zone factory in general and of oceanic subduction-zone/island-arc complexes in particular, but also to allow visualization of these multi-parameter numerical models, so that interactive optimization on the basis of field and laboratory data becomes possible. This presentation will focus on the following specific topics and relate them to Caribbean examples: 1) Why can arrays of pressure-temperature-time paths determined for high-pressure metamorphic rocks provide critical constraints on the history and development of a particular subduction zone rather than providing evidence for different subduction zone types? The San Juan Complex of the Dominican Republic provides a text-book example. 2) Can subduction-unrelated simple overthrusting/stacking of rock series produce blueschists? Are blueschist belts without an accompanying volcanic arc possible? What, for instance, is the significance of blueschist pods in the Cangre belt of western Cuba? 3) Arc volcanics are one end-product of the subduction- zone factory. How variable can geochemistry be for a given geometry and constant type of input? 4) Can a subduction-zone "flip" really be a true flip? Can high-pressure rocks be "keel-hauled" from one side to the other of a "flipped" volcanic arc?

Late Cretaceous Charophytes From Puerto Rico

Michael Martínez(1), Adriana García(2), Shirley Mercado(1), Simon Mitchel(3), and Eduardo A. Musacchio(4). (1) GeoScience Education Program, Universidad del Este, PR; (2) School of Earth and Environmental Sciences, University of Wollongong-Australia; (3) Department of Geology, University of West Indies-Jamaica; (4) Universidad Nacional de la Patagonia- Argentina

Late Cretaceous (Uppermost Maestrichtian) sediments and sedimentary rocks from the Upper El Rayo Formation, southwest Puerto Rico, has yielded the first occurence of fossil charophytes (Charales). The fauna consists of Feistiella gildemesteri (Maestrichtian-Paleocene), Platychara grambastii (Maestrichtian), Platychara cf. cruciana, Feistiella cf. anluensis and Amblyochara sp. Fossil charophytes have been described elsewhere in the Caribbean-Greater Antilles but this assemblage reassembles those found in Peru and Argentina during the Late Cretaceous (Maestrichtian). In the Central Inlier in Jamaica, the Thomas River Formation, formerly known as Slippery Rock Formation, fossil charophytes have been described as: Platychara grambastii, Porochara cf. anulensis, Porochara oblonga. This formation was assigned an age of 68mya based on 87Sr/86Sr analysis on the rudistid Chiapasella radiolitiformis. The charophyte faunal

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assemblages, although sparse, never have been studied in detail in terms of distributional patterns, biogeographical interrelationship between islands, and as a possible Cretaceous/Tertiary boundary indicator in the Caribbean. Cretaceous rocks of the Upper El Rayo Formation, are composed of basaltic to andesitic volcanic flows interbedded with volcaniclastic conglomerates, sandstones, and limestones. The charophyte bearing sediments are altered and weathered pyroclastic materials overlying rudistid-bearing limestones. These altered materials marked the last Cretaceous volcanic episode of the southwest Igneous Province of Puerto Rico. Sedimentary analysis shows the development of deltaic environments contemporaneous with the appearance of the charophytes. The discovered charophyte assemblage provides supporting evidence, for the first time, of the presence of non- marine (fresh water/brackish water) environments by the end of the Maestrichtian in Puerto Rico.

Paleoecological Distribution (Benthic Foraminifera) along the Oligocene/Miocene Boundary in Southern Puerto Rico: Local or Global Implication? Michael Martínez1, Carmen Urbina1, Wilfredo Morales1, Rosángela Pérez1, James Galluzzo2, and Wilson Ramírez3 (1) GeoScience Education Program, Universidad del Este, PR; (2) Department of Geology, Tulane University, New Orleans; (3) Department of Geology, University of Puerto Rico-Mayaguez Campus Benthic foraminifera distribution patterns, in the Santa Helena and Playa Jaboncillos sections, of the Juana Díaz Formation are strongly related to relative sea level changes with a global influence. These patterns not only show changes on species dominance along the stratigraphic sequence but also show extinction events of larger foraminifera (i.e. Lepidocyclina undosa, Lepidocyclina canelli) prior to the Oligocene/Miocene boundary (planktic biozone: P21-M1; benthic biozone: Miogypsinoides sp., ~23.8 Ma). This extinction event was not abrupt indicative of a non-catastrophic climatic change allowing the slow demise of these larger foraminifera. Distribution patterns showed a relative shallow water environment that prevailed during the Late Oligocene. An abrupt decrease in sea level, during and after the Oligocene/Miocene boundary, evidenced a stress to the Oligocene fauna and environment and is attributed to tectonic uplift. This event favored an increase in species richness (opportunistic foraminifera) and a more diverse fauna in the Early Miocene. This is indicative of a more stable tectonic setting, hence, a more suitable environment for the foraminifera to flourish on the southern coast of Puerto Rico.

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Holocene Ostracods/Foraminifera assemblages on reef/deltaic environments on Lake Enriquillo-Dominican Republic: Preliminary survey Michael Martínez(1), Rebecca Abréu(2), Wilson Ramírez(3),and Carlos J. Santos(4) (1) GeoScience Education Program, Universidad del Este, PR; (2) Department of Microbiology, Universidad del Este, PR; (3) Department of Geology, University of Puerto Rico-Mayagüez; (4) Department of Biology, University of Puerto Rico- Mayagüez Lake Enriquillo, once a small seaway, is a hyper-saline lake in western Dominican Republic formed by the enclosure of the area due to tectonic uplift. It is surrounded by well developed fossil reef facies overlain by deltaic sequences containing very diverse ostracod assemblages. The main purpose of this work is to document, for the first time, the distribution patterns of fossil ostracods and foraminifera through the transition between these environments (reef vs. deltaic). Scarce benthic and planktic foraminifera were found in the reef facies (carbonate rich sediments). Ostracods were also scarce and had the morphological characteristics of those found in fresh/brackish waters, indicative of transport. This trend is persistent throughout the studied reef facies sequence. On the other hand, rich epiclastic sediments of the deltaic facies showed a dominance and high diversity of non-marine ostracods. Morphological differences between ostracods are a result of different wave energy regimes or environments. Highly ornamented morphologies (i.e. primary reticulation, tubercle, and dense tests) are associated with sand rich sediments, indicative of a proximity to a shoreline. Less ornamented morphologies (i.e. non-reticulated, punctae, smooth and delicate tests, etc.) are characteristic of lower energy regimes or environments, associated with silty rich sediments. Distribution cycles of ornamented and non-ornamented ostracods are the result of changes in the sedimentation regimes due to changes in climate (i.e. precipitation) and possible tectonics (uplift) of the studied area.

Upper Cretaceous (Maestrichtian) microfauna of the Thomas River and Guinea Corn Formation in Jamaica (Central Inlier) Michael Martinez(1), Shirley Mercado(1), Simon Mitchel(2), Adriana Gracia(3) and Eduardo A. Mussacio(4) (1) GeoScience Education Program, Universidad del Este; (2) Department of Geology, University of West Indies-Jamaica; (3) School of Earth and Environmental Sciences, University of Wollongong-Australia; (4) Universidad Nacional de la Patagonia- Argentina

Sedimentary sequences on Late Cretaceous (Maestrichtian) Central Inlier Jamaica, represents different paleoenvironmental settings. These are represented by the Thomas River and Guinea Corn Formations part of the Kellits Synthem. The studied section of the Thomas River Formation consists of tidal influenced environment based on sedimentary structures (sandstones/mudstone interbedding, laminated heterolithics, flaser-wavyy-lenticular bedding, and rythmites), lack of marine fossils, and abundance of fossil charophytes (fresh/brackish waters). Marine environments, on the other hand, are represented by Guinea Corn Formation (late Maestrichtian) consisting of a diverse coral

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and rudist bivalve assemblages (i.e. Titanosarcolites giganteus and Chiapasella radiolitiformis), abundant echinoid assemblages, and micrite matrix dominated limestones. Preliminary fossil microfaunal analyses on both formations show a relationship between sediment grain size and type of microfossil. Siltstones and mudstones are characterized by being barren and occasionally ostracods (poorly ornamented indicative of low energy environments) are in abundance with some benthic foraminifera (Kathina jamaicensis). Abundant smaller benthic foraminifera are associated with fine grained silty sandstones. The Thomas River Formation represent a two stage Highstand System Tract (HST): stage 1- marine tidal flat deposits; and stage 2- fresh/brackish water charophyte bearing tidal flat.

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Geochemical interpretation of Jamaican rocks displaying pozzolanic properties to be used

in the manufacture of cement

Mr. N. Mckenzie, Research Student/Mining Engineer

Department of Geography and Geology

University of the West Indies, Mona Kingston, 7 Jamaica.

Caribbean Cement Company LTD.

Rockfort, Kingston, Jamaica

[email protected]

The effect of pozzolan replacement for clinker in the cement industry is well known and has developed over the years among major cement producers. The Caribbean Cement Company Ltd (CCCL) a subsidiary of Trinidad Cement Company (TCL) has being using pozzolanic material purchased from Martinique since 2002 as a replacement for clinker in their blended cement product. This study looks at two alternative sources locally for pozzolanic material as a means to reduce cost and to optimise cement late days strength (28 days). The high correlation (r value) between pozzolan from Martinique and local material (volcanic tuff and andesite) is noted for the geochemistry and mineralogy. It is expected that over similar geologic environment such as volcanics and ignimbrite that the concentrated values would be similar and within the range of pozzolanic material used in cement production. Experimental data indicates that rocks of the study area show similarity in weight percentage of SiO2, FeO3 and Al2O3 and that the pozzolan reactivity index is similar to natural pozzolan. The material can be used as a percentage substitute for clinker in cement production. The results show that rocks of both study area when used as a mineral admixture show progressive increases in strength with increasing percentages of replacement, up to the 15% level.

Capability Analysis of a Proposed Nine Station Seismic Network in the Caribbean D. McNamara, H. Benz, P. Earle, J. Odum, J. McCarthy, B. Presgrave, J. Weaver, B. Leith, C. Hutt, D. Oppenheimer

The USGS will deploy nine seismic stations to monitor earthquake activity in the Caribbean region as a part of the Global Seismograph Network (GSN) by September of 2006. The new seismic network is part

57 17th Caribbean Geological Conference 2005, San Juan PR of a larger effort to monitor and mitigate tsunami hazard in the region. Destructive earthquakes and tsunamis are known to be a threat in various parts of the Caribbean. These natural hazards cause damage, not only from strong ground shaking and surface rupture, but also from liquefaction, extensive land sliding and tsunami waves. A critical component for the accurate assessment of earthquake hazards in the region is local and regional monitoring of seismic activity and deformation. Long-term monitoring of active faults provides critical information needed for response activities, local and regional planning and, ultimately, building resilient communities throughout the Caribbean. Installation of the new seismic network is a collaborative effort that will involve contributions from several participants from the United States Geological Survey (USGS), the Puerto Rico Seismic Network (PRSN), Seismic Research Unit of the University of the West Indies, and several additional institutions in the Caribbean region. In this presentation we assess the capabilities of the proposed seismic network using three different measures of capability. The three measures of network capability are: 1) minimum Mw detection threshold; 2) response time of the automatic processing system and; 3) theoretical earthquake location errors. For the proposed upgrade scenario we demonstrate that considerable improvement in network magnitude threshold, response time and earthquake location error can be achieved. We also demonstrate that the technique used in this analysis is valuable for quantifying seismic network capability improvements and a useful tool for network design planning.

A Preliminary Evaluation of Tsunami Hazard and Risk in Jamaica Using A Geographical Information System (GIS) Mr. S. Miller, Research Student

Dr. Martin Degg, Senior Lecturer

Department of Geography,

University College Chester,

Parkgate Road, Chester,

Cheshire,

CH1 4BJ, UK.

[email protected] , [email protected]

The December 26, 2004, tsunami in the Indian Ocean served to highlight the dramatic escalation of tsunami risk that has occurred in low-lying regions with significant tourist development. Island economies of the Caribbean region are strongly dependent on tourism for their economic survival, and low-lying coastal areas of the region have witnessed phenomenal rates of development during the last three decades. This paper shows that many of these areas are exposed to significant tsunami hazard, and that this hazard has been largely overlooked compared to the attention and resources devoted to mitigating the seemingly more immediate threats posed by hurricane activity.

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The paper presents a regional review of tsunami hazard that sets the context for a specific assessment of tsunami hazard and risk on the island of Jamaica. This country experienced damaging tsunamis in 1688, 1692, 1780, 1812, 1881 and 1907, but the coastal zone was far less intensively developed then than is now the case. A Geographical Information System (GIS) is used to create a preliminary tsunami hazard map for Jamaica. This highlights that the severity of the tsunami hazard varies quite considerably around the coastal zone, and that some of the most highly urbanised and most economically important parts of the country are potentially at risk. The paper concludes by considering risk reduction strategies that might be employed in these areas to reduce the potential for catastrophic human and economic impact from future tsunami occurences.

GIS and Landslide hazard mapping in St. Thomas Jamaica Mr, S. Miller, Research Student

Department of Geography,

University College Chester,

Parkgate Road, Chester,

Cheshire CH1 4BJ.

[email protected]

Landslides are a major natural hazard in Jamaica, and have resulted in loss of life, major economic losses, social disruption and damage to public and private properties. The parish of St. Thomas has the highest incident of slope instability on the island and is extremely prone to catastrophic landslides. The Judgement Cliff landslide in the parish is arguably the most infamous landslide on the island, and in 1692, killed 19 people and moved a settlement half a mile from its original location. St Thomas is particularly prone to slope instability due to its geology, steep and partially bare slopes, deeply weathered soils, improper land-use and high rainfall intensity. There is a need to delineate the areas that are prone to landslippage in order to mitigate their effects. One way of achieving this is to create landslide susceptibility maps in a Geographical Information System (GIS). There are a number of GIS methodologies that may be employed to create susceptibility maps but care must be taken to choose the best method that is suitable for the terrain and the contributing factors to slope instability unique to Jamaica. Five methods were

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examined, these were; Simple overlay, Index overlay, Fuzzy logics, Multiple logistic regression and Bayesian conditional probability. Of these five methodologies, the Bayesian, Fuzzy Logics and Multiple logistic regression methods has the highest rate of success in classifying the existing and ‘future’ landslides into the high and very high susceptibility zones and may be useful in creating models for other areas of Jamaica.

Stratigraphy of the Sunning Hill Inlier, SE Jamaica: rudist faunas upside down Simon F. Mitchell Department of Geography and Geology University of the West Indies, Mona Kingston 7, Jamaica

The geological succession in the Sunning Hill Inlier has been determined by geological mapping at a scale of 1:12,500 and the collection of rudist assemblages. The oldest rocks are a thick pile of andesitic lavas. These are succeeded by a thin red-bed sequence of locally derived conglomerates and sandstones with occasional calcrete palaeosols. The red beds are succeeded by a thin sequence of limestones and shales with abundant in situ fossils. The fauanl assemblage includes abundant actaeonellid gastropods, the echinoid Hemiaster, and rare rudists. Rudists from loose blocks include ‘Barrettia’ sp. nov. aff. “B.” gigas and Torreites chubbi. This assemblage is of Early Middle Campanian age. The limestones are succeeded by a sequence of mudstones and conglomerates. The conglomerates contain a diverse assemblage of individual transported rudists including: Barrettia coatesi (Chubb), Durania lopeztrigoi (Palmer); Durania curasavica (Martin), Bournonia sp. and Biradiolites sp. This assemblage is clearly of Middle Santonian age. The conglomerates are replaced up section by interbedded sandstones and shales (?turbidites). The succession is interpreted in terms of pre-rift and syn-rift deposits. The andesites and red beds at the base of the succession are interpreted as pre-rift deposits. Rifting began in the Early Campanian and the rift was flooded by marine waters producing a marine limestone. Further subsidence saw the appearance of extensive reworked material from the rift margins including abundant Santonian rudists. The results of this study indicate that care must be taken when reworked rudist assemblages are used to date succession, as such assemblages may be reworked into younger stratigraphic intervals.

Tidal deposits in the Kellits Synthem (Maastrichtian) of the Central Inlier, Jamaica Simon F. Mitchell Department of Geography and Geology University of the West Indies, Mona Kingston 7, Jamaica

The Thomas River, Guinea Corn and Green River formations form part of the major (3rd Order) transgressive-regressive, Maastrichtian-Paleocene Kellits Synthem. The synthem is extensively exposed across the Central Inlier of central Jamaica and all available stratigraphic sections have been logged. Using a sequence of faunal event beds and biostratigraphic markers (mainly rudists and corals) it is now possible to correlate small- scale cycles (circa 40 kyrs) across the inlier. The sedimentology of these cycles has been investigated and a strong tidal signature has been recognised. The following major tide- dominated facies associations are recognised. 1, Supratidal red mudstones with paleosols.

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2, Intertidal mud-flat deposits with mm-scale interlaminated mudstones and organic-rich (plant debris) layers with a restricted marine/brackish water fauna/flora. 2, Laminated mudstones and sandstones with symmetrical and asymmetrical ripple form sets. 4, Tidal channel heterolithics (interlaminated mudstones and sandstones) with flaser, wavy and lenticular bedding, and basal erosion surfaces/shell beds. 5, Tidal channel sandstones and granule conglomerates with erosional bases. 6, Tidal sandwave complexes with low angle cross bedded sets up to several meters thick consisting of carbonate or mixed clastic- carbonate sands in 20-40 cm thick beds. The tidal deposits characterise the transgressive systems tracts of the high frequency cycles in the Kellits Synthem, and there is a significant spatial separation of diverse rudist-coral assemblages and the tidal deposits (although some rudists occur as reworked elements in some tidal deposits, they are invariably interpreted as reworked from older limestones). This suggests a tidally dominated inshore zone with clastic and mixed clastic-carbonate deposits and an offshore carbonate or mixed clastic-carbonate zone with diverse rudist and coral assemblages.

Cretaceous and Cainozoic evolution of Jamaica. How does it test the current models? Simon F. Mitchell Department of Geography and Geology, University of the West Indies, Mona Campus, Kingston 7, Jamaica.

Throughout the Cretaceous and Cenozoic Jamaica has been situated close to the northern boundary of Caribbean Plate and contains a record of the changing geological development of this plate boundary. Extensive studies on this succession have resulted in the development of a well-constrained chronology, and can be used to compare the various models suggested for the evolution of this part of the Caribbean. Jamaica is divided into two terrains with different geological histories: the Cornwall-Middlesex Block, and the Blue Mountains Block. The Cornwall-Middlesex Block has a three-fold stratigraphy: a pre-Santonian sequence of volcanics and rudist- bearing limestones; the Crofts Synthem (Santonian to Campanian rudist-bearing limestones and deep water clastics); and the transgressive-regressive Kellits Synthem (Upper Maastrichtian-Paleocene). The Blue Mountain Block has a Turonian-Conician ophiolite suite, and a Santonian to Early? Maastrichtian island arc suite (limestones indicating the Santonian, Early Middle Campanian and Early? Maastrichtian). Rifting progressed across the island from late Maastrichtian time onwards: Latest Maastrichtian to Early Paleocene in the John Crowe Trough; Late Paleocene to Early Eocene in the Wagwater Trough and North Coast Belt, and Middle Eocene in the Montpelier–Newmarket Trough, Negril–Sav-la-Mar Trough and Walton Basin. The resultant Block and Trough topography/bathymetry controlled Neogene sedimentation patterns, with mixed deltaics (Middle Eocene) and shallow-water platform limestones (Middle Eocene to Miocene) on the blocks, and deep-water pelagic and mass-flow deposits in the troughs. In the Miocene, tanspression affected Jamaica with differential uplift and subsidence. The Tertiary limestone cover of the uplifted regions was stripped off and the volcano-sedimentary successions beneath exposed to erosion. This provided extensive

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clastic detritus that were shed into the adjacent basins to form thick mixed clastic- carbonate sequences.

Cretaceous (Campanian and Aptian) Radiolarians of the Washikemba Formation, Bonaire, Netherlands Antilles Homer Montgomery, Emile Pessagno, Mohsen Kariminia University of Texas at Dallas

The Cretaceous Washikemba Formation of western Bonaire is composed of a 3-km-thick package of pillow lavas, volcaniclastic sediments, and rhyodacite flows in the Southern Complex and a 5-km-thick accumulation of volcanics, pelagic sediments, and volcaniclastic sandstones in the Northern Complex. The formation is reported to contain upper Albian ammonite imprints in the Southern Complex and Coniacian inoceramids and Turonian and Coniacian planktonic foraminifera in the Northern. Ar-Ar dating suggests a minimum age of 95 + 2 Ma for a rhyodacite flow. This age is not completely reliable due to the degree of alteration. Recently, 18 outcrops of chert in the Washikemba were sampled with only two, both dark blue-gray to black chert in the Southern Complex located near Punt’l Wekua, yielding radiolarian microfossils in HF residue. One sample contains a well-preserved radiolarian assemblage of low diversity. The occurrence of Archaeospongoprunum hueyi, a taxon presently known only from the upper Campanian, suggests that at least part of the Washikemba may be younger than previously reported. Campanian radiolarians are common in the Caribbean being reported in Puerto Rico, Hispaniola, Cuba, Panama, and DSDP Site 146 drilled between Hispaniola and Venezuela. The second sample contains a diverse fauna of well-preserved radiolarians that are likely Aptian based on the presence of Thanarla conica, Pseudodictyomitra carpatica and Sethocapsa sp. among many other forms. The discovery of radiolarians in the Southern Complex of the Washikemba that are both older (by 10-20 Ma) and younger (by 10 Ma) than any previously reported fossils will necessitate rethinking the stratigraphy of the formation as well as perhaps reevaluating the significance of the reported geochemistry characteristics.

USGS Seismic Hazard Maps for Puerto Rico and the U.S. Virgin Islands Charles S. Mueller, Arthur D. Frankel, Mark D. Petersen, and E. V. Leyendecker U.S. Geological Survey, Golden, CO

New seismic hazard maps for Puerto Rico and the U. S. Virgin Islands were developed by the U.S. Geological Survey in 2003. Modeled seismic sources include: 1) subduction- interface and crustal faults with known rates, 2) gridded seismicity to account for subduction-intraslab activity and crustal activity not associated with specific faults, and 3) zones of crustal extension in the Mona Passage and Anegada Passage regions with activity rates determined by GPS geodesy. Attenuation relations are derived from worldwide data for subduction sources and from western North America data for crustal sources; alternative relations are combined using logic trees. A new Caribbean-specific relation gives large high-frequency ground motions, and is used with low weight; it has

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since been revised, and we will show the sensitivity of the computed hazard to the revision. We map mean, time-independent, probabilistic peak ground acceleration and 1.0-, 0.3-, and 0.2-s spectral acceleration for a Vs30= 760-m/s site condition. Example pga values for 10% probability of exceedance in 50 years are 0.23 g at San Juan, 0.25 g at Mayaguez, 0.21 g at Ponce, and 0.28 g at Charlotte Amalie. At San Juan contributions from shallow and deep gridded seismicity and Puerto Rico Trench subduction dominate the hazard about equally for pga greater than about 0.10 g, with shallow seismicity increasingly dominant above 0.40 g. At Mayaguez and Ponce shallow and deep gridded seismicity dominate over the Mona Passage extensional source and Puerto Rico Trench subduction for pga equal to about 0.10 g, but the Mona Passage source dominates above 0.25 g. At Charlotte Amalie shallow and deep gridded seismicity dominate for all pga. Deaggregations indicate that the South Lajas Fault can be a major contributor to local hazard in southwestern Puerto Rico for some exceedance probabilities, showing the importance of identifying other active onshore faults.

Timing And Duration Of The Last Interglacial Period From U-Series Ages Of Unaltered Reef Corals, Northern And Western Puerto Rico MUHS, D.R., U.S. Geol Survey, MS 980, Box 25046, Federal Center, Denver, CO 80225, [email protected], SIMMONS, K.R., U.S. Geological Survey, MS 980, Box 25046 Federal Center, Denver, CO 80225, TAGGART, B.E., U.S. Geol Survey, 10 Bearfoot Road, Northborough, MA 01532, PRENTICE, C.S., U.S. Geol Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025, JOYCE, J., Dept. of Geology, Univ of Puerto Rico, Mayagüez, PR 00681, and TROESTER, J.W., U.S. Geol Survey, 651 Federal Drive, Suite 400-15, Guaynabo, PR 00965-5703

Although there have been many studies of last-interglacial (LIG) shorelines (emergent reefs and terraces), there are still uncertainties about the timing and duration of LIG sea level elevations near or above the present sea level. The island of Puerto Rico has probably experienced slow, long-term uplift in the late Quaternary (on the order of 0.03- 0.05 m/ka) and therefore sea level records need to be interpreted with caution. Nevertheless, LIG reef tract deposits are common along much of the northern and western coasts of Puerto Rico and contain well preserved corals (95-100% aragonite). We analyzed corals from localities near Palmas Altas, El Vigia, Punta Agujereada and Punta Higüero for U-series dating. Corals in growth position are common in most reef tracts and are found at elevations between about 0.5 and 1.5 m above high tide level. Of 19 LIG corals analyzed, all have U contents similar to their modern counterparts and low common Th contents. Fifteen of the corals have back-calculated initial 234-U/238-U

63 17th Caribbean Geological Conference 2005, San Juan PR activity ratios of 1.140 to 1.154, overlapping the range of values found in modern seawater. These 15 samples indicate probable closed-system histories with respect to U- series nuclides and yield ages with a high degree of confidence. Ages range from 127.7 ± 0.7 ka to 114 ± 2 ka (two-sigma errors); one sample gave an age of 105.0 ± 0.5 ka. In the Holocene, sea level rose to present levels several thousand years after the high-latitude, Northern Hemisphere summer insolation peak at ~11 ka. The Puerto Rico coral data presented here indicate that sea level was near or above present at the time of the previous summer insolation peak at ~127 ka. Further, the Puerto Rico data indicate that the LIG high sea level probably lasted a minimum of 12 ka. This contrasts with the deep- sea oxygen isotope record, wherein the LIG high sea stand is thought to have had a duration of only about 7 ka at most.

Aquifer Recharge thru Sinkholes Presented by: Omar Negrón, P.G. President GEOWORKS, INC

20 of the most beautiful sinkholes in the north of the island aretested to obtain their aquifer recharge potentials. Sinkholes varying in diameter from 10 to 160 feet wide and varying in depths from 10 to 70 feet. Field tests were developed by GEOWORKS, INC. to obtain detailed modeling of their natural potentials. Results were used to define their collapse potentials, water management capabilities and engineering mitigation to its surroundings. Previous methods used pumping water at high gpm’s, but a different approach was developed to emphasize on testing the sinkholes via rapid massive water discharges in excess of 75 CFS using aluminum containers that served as water reservoirs. Over 20 sinkholes tested in various projects presented convincing results of how the sinkholes managed the massive water outputs. 7,000 to 20,000 gallons of water were observed to be managed thru this natural systems within seconds of receiving the massive water output almost Hollywood style. Obtained data was followed by comprehensive drilling, geophysical and geothecnical analysis. The presentation is a combination of the methodologies used, comparison with other modeling techniques and data extrapolation. Various types of sinkholes are seen trhu video at the moment of the modeling and others are presented trhu photographs and aerial views. A great display of the awesome power of water and limestone geology.

Seismic Study Of The Subduction To Strike-Slip Transition Of The North American-Caribbean Plate Boundary In The Dominican Republic Denisse Ocasio Campos1, Jay Pulliam1, Victor Huérfano1, Christa von Hillebrandt- Andrade1, Ivelisse Camacho1, Luis Odonel Gomez2, Juan Payero3

(1) Red Sísmica de Puerto Rico, Dept. de Geología, Universidad de Puerto Rico, Mayagüez, PR (2) Instituto Nacional de Recursos Hidráulicos, República Dominicana

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(3) Instituto Sismológico Universitario de la Universidad Autónoma Santo Domingo, Ciudad Universitario, Apto. Postal 1335, Santo Domingo, República Dominicana

The Northern Caribbean Plate Boundary Zone is a complex region that has been modified extensively by the relative eastward movement of the Caribbean Plate and the plate’s impact with the buoyant Bahama carbonate platform (see Figure). The results include extensive subduction of oceanic crust belonging to the North American Plate, a broad zone of deformation to accommodate strain, the development of several new transform and normal faults to relieve stress after collisions, the formation and rotation of microplates, and the rearrangement and aggregation of crustal fragments into new islands.

On 22 September 2003, a large (mW=6.5) earthquake struck the Dominican Republic, causing widespread damage that included partially collapsed buildings and bridges in the cities of Santiago and Puerto Plata and landslides in the mountainous outlying areas. Aftershocks reaching mW =5.1 followed for weeks afterward. This earthquake sequence is the strongest to affect the Dominican Republic since a series of powerful thrust events, including five earthquakes ranging in magnitude from 7.1 to 8.1, occurred between 1943 and 1953. Prior to 1943, significant earthquakes occurred in 1564 (in which the city of Santiago was destroyed), 1783, 1842, 1887, and 1897. Following the 2003 Puerto Plata main shock we deployed 10 broadband seismographs borrowed from IRIS’ PASSCAL Instrument Center around the aftershock zone for a period of two months and analyzed the data jointly with data from two permanent seismic networks in the DR. Analyses included estimating a new 1D model of earth structure, re-locating more than 300 aftershocks, producing a 3D tomographic model of the fault zone from phase arrivals, and computing focal mechanisms. We will report the results of these analyses and their implications for regional structure, processes and seismic hazard.

Schematic of the Northern Caribbean Plate Boundary Zone with the location of the 22 September 2003 main shock (red star).

(inset) Map of currently and recently operating seismic stations in the Dominican Republic. The symbol indicates the station’s network affiliation: ISU stations are S1-10 and ISU01-10; INDRHI stations are DR01-16; PRSN/UT temporary stations are YB01-10. The star is a broadband

65 17th Caribbean Geological Conference 2005, San Juan PR station at PUCMM in Santiago. Symbol color indicates the sensor’s passband: red = short- period, green = intermediate-period, black = broadband. Black outlines indicate three-component sensors.

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Near-Surface S- And P-Wave Velocities, Vs30, And NEHRP Site Classification At Selected Urban And Seismograph Sites Within The Commonwealth Of Puerto Rico Jack K. Odum1, Robert A. Williams1, William J. Stephenson1, Christa von Hillebrandt-Andrade2, Eugenio Asencio3, and Antonio Cameron2

1U.S. Geological Survey, Geologic Hazards Team, Golden, CO

2Puerto Rico Seismic Network, University of Puerto Rico- Mayagüez, PR

3 Department of Geology, University of Puerto Rico-Mayagüez, PR

Studies over the last few decades have established that shear-wave seismic velocity (Vs) in the upper 30 to 60 m can greatly influence the amplification and duration of earthquake ground motions observed at the surface. The determination of near-surface seismic velocities is motivated by their use in the National Earthquake Hazards Reduction Program (NEHRP) model code provisions (Building Seismic Safety Council, 1997). In 2004 and 2005, the Puerto Rico Seismic Network (PRSN), the Puerto Rico Strong Motion Program (PRSMP) and the Geology Department, all of the University of Puerto-Rico- Mayagüez (UPRM), collaborated with personnel from the U.S. Geological Survey to study Vs and compressional-wave velocities (Vp) in and around major urban areas of Puerto Rico and at some seismic stations of the PRSN and PRSN (see arrows on figure). Using noninvasive seismic refraction-reflection profiling techniques, we acquired velocities at 27 locations. Sites within the urbanized areas were selected to sample near-surface materials associated with the primary geologic units within the urbanized areas. Geologic units surveyed included Cretaceous intrusive and volcanic bedrock, Tertiary sedimentary units, and Quaternary and Holocene fluvial, beach, and lagoon unconsolidated deposits.

From the acquired data we constructed Vp and Vs depth columns, calculated average VS to 30-m depth (VS30), and derived NEHRP site classifications for the 14 sites from the 2004 campaign. The distribution of determined NEHRP classes is as follows: two class “E” (Vs30 below180 m/s), six class ”D” (Vs30 between 180 and 360 m/s), five class “C” (Vs30 between 360 and 760 m/s), and one class “B” (Vs30 greater than 760 m/s). Results will be used to calibrate site response at seismograph stations and in the development of regional and local Shake Map models for the Commonwealth of Puerto Rico. The data from the 13 additional sites surveyed in 2005 are currently being processed. Relief map of Puerto Rico showing (white arrows) location of Vs and Vp sites.

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Sedimentation And Coral-Reef Development: Enriquillo Valley, Sw Dominican Republic ORAM, Jessica1, HUBBARD, Dennis K. 1, BREWER, Joshua1, STEIN, Alexandra1, TOMLINSON, Michael1, TIMMONS, Erikson1, RAMIREZ, Wilson3, and DAVIS, Allicia1, (1) Dept. of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074, (2) Dept. of Geology, University of Puerto Rico, PO Box 9017, Mayaguez, PR 00681 contact: [email protected]

A well-developed Holocene reef exposed at Cañada Honda in the western Dominican Republic provides an ideal opportunity to map coral-reef facies, and to relate both species distribution and colony shape to location on the reef, paleo-water depth and presumed rates of sedimentation. Where sedimentation was slower, hemispherical colonies similar to those seen in the massive-coral zone of most Caribbean reefs dominate. Where sedimentation was higher, colonies progressively take on conical and then columnar morphologies as lateral growth is increasingly discouraged. Regardless of average sedimentation rate, ragged colony margins accurately record periodic increases in sedimentation, followed by lateral overgrowth of the substrate by the remaining live colony. The result is a fluted colony that resembles a “Christmas tree” or a “stack of pancakes”. Detailed measurements of density banding seen in X-radiographs reveal that average growth rate in the Dominican corals (1-4 mm/yr) is lower than that for similar species in less stressed settings (5-10 mm/yr) throughout the Caribbean. Sedimentation pulses responsible for the “pancake” morphology described above recur with a roughly decadal periodicity. Data from 1-m2 quadrats along vertical transects throughout the outcrop provide quantitative information on overall coral abundance (>60%) and species diversity (27) in the reef. Storm layers provide “time lines” along which species patterns can be measured and compared to similar data from modern Caribbean reefs. Together, these data provide a detailed picture of a diverse but slower-growing coral community that was well-adapted to elevated sedimentation. The surprising diversity in this reef is to some degree contrary

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of our perceptions of reef-community structure in sediment-stressed areas, and may provide a valuable tool for separating reefs exposed to chronic natural stress from those under the increasing influence of anthropogenic sedimentation.

Micro-Boudinage In Blueschists Of Eastern Jamaica Pallov Pal and Grenville Draper Department of Earth Sciences Florida International University Miami, FL 33199, USA

The ?lower Cretaceous blueshist-greenschist grade Mt. Hibernia Schists in eastern Jamaica show well-developed examples of micro-boudinage in relict, originally igneous, augite grains. The rocks have been examined using conventional quantitative microscopy and a new, promising technique that successfully combines digital, microscopic images and GIS to make measurements easier and more accurately. Comparison of bulk strain estimated from elongated sphene aggregates, that appear as white streaks in the XZ and XY sections in hand specimens of the rock, with that of the boudinaged augites indicate that the boudin trains underestimate elongation by ~50% using Ramsay’s classic method. The more recently devised Strain Reversal (SR) method, which takes into account far- field matrix strain, also produces similar underestimates. Relict igneous augites are boudinaged with the inter-boudin gaps being successively filled by secondary grains of quartz, crossite and actinolite sometimes in a quasi-symmetrical, other times in an asymmetric manner. The infilling minerals in the boudin gaps indicate a crack and fill mechanism, taking place syn-metamorphically. It is suggested that the gaps opened as metamorphic fluid composition changed. Thus, the textures may provide a test of the mid-point fracture model of Ramberg’s classical study, and SR method.. This analysis may further lead to methods of assessing strain rate and relative differential stress conditions during deformation of these rocks. .

Field Development in a Challenging Geological Environment The Angostura Story

The Greater Angostura Structure, comprising the Kairi, Canteen, Aripo and Angostura structurally defined areas, lies offshore Trinidad and Tobago in Block 2(C). Development drilling on the structure began in September of 2003 and First Oil was achieved in January of 2005. The Angostura Development is centered on the production of oil and gas reservoired within the Angostura Sandstone, a thick Early to Middle Oligocene sequence of sediment gravity flows that are interpreted to have been deposited in a slope type setting. Hydrocarbons were first discovered on the structure with the drilling of Angostura-1 in the second quarter of 1999, but it was not until the discovery of a moderately thick oil column underlying an extensive gas cap in Kairi-1, drilled in August of 2001, that the pace of field appraisal and subsequent development quickened.

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With data from a limited number of exploration and appraisal wells and a seismic data set of moderate to poor quality covering a fairly large structure with a varied and complex history, the field development plan needed to have a strong focus on technical risk mitigation. Since development drilling began, a combination of nineteen appraisal and development wells have been drilled on the structure with data from each successive well assisting in modifying and refining the forward drilling plan. Technical challenges encountered during the development programme have been reduced and overcome by maintaining flexibility within the plan and by maintaining and developing contingencies on both a well-by-well and whole programme basis.

Proto-Caribbean slab-window origin for the Caribbean Large Igneous Province James Pindell, Dept. of Earth Science, Rice University, 6100 Main Street, Houston, Texas, 77005 USA [email protected]

A common belief is that the Caribbean large igneous province (CLIP) was extruded as Caribbean lithosphere passed over Galapagos hot spot (GHS) before entering the inter-American gap from the Pacific. However, (1) Guatemalan and Andean stratigraphies indicate Caribbean-American tectonic interactions by Turonian during CLIP extrusion, such that the Caribbean was east of paleo-GHS [if fixed mantle reference] by then; (2) GHS can be dated to Oligocene only, leaving doubt about is Cretaceous existence; (3) it is unclear how GHS might have affected an area as large as CLIP; (4) Costa Rica arc began in Albian according to sandstone mineralogy, thus the Galapagos model requires the Costa Rica Benioff Zone to have passed over GHS after CLIP extrusion (unlikely). I propose instead that a slab window formed as the Proto- Caribbean spreading ridge was subducted beneath Caribbean Plate during entry into the widening inter-American gap, through which Proto-Caribbean mantle convection reached the base of Caribbean lithosphere. Caribbean migration between the Americas from the Pacific began ~120 Ma, as shown by (1) Hi-P suites along the Caribbean’s eastern edge dating back to Aptian, (2) “Antillean-Cycle” Caribbean arcs dating back to Albian. Atlantic magnetics show that Proto-Caribbean spreading continued to Santonian. Thus the Proto-Caribbean Ridge was subducted from Aptian to Santonian, exactly matching the period of CLIP extrusion. Paleotectonic maps integrate Caribbean-American interactions and the formation of Hi-P suites, Antillean arcs, and the slab window whose size approached that of the CLIP by 90Ma (most common age of CLIP). Observed mid- Cretaceous Caribbean crustal extension and CLIP volcanism is reminiscent of Basin and Range geology, but in oceanic crust. Field examples of the CLIP (Aruba, Hispaniola) indicate partial subaerial exposure during extrusion, carrying thermal implications for Caribbean sedimentary basins. The slab window model may explain why certain batholiths (e.g., Aruba Batholith) are not necessarily arc related. This work forms part of the regional framework of the BOLIVAR NSF-funded research program assessing crustal structure and continental growth along northern South America.

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The Paleogene Proto-Caribbean Subduction Zone and the arc-arc collision between South America and the Caribbean Plate James Pindell, Dept. of Earth Science, Rice University, 6100 Main Street, Houston, Texas, 77005 USA [email protected]

Plate kinematic, seismic tomographic (Hilst, 1990), stratigraphic, and heavy mineral data are synthesised to show that the long-held model of E-wardly diachronous arc-continent collision between the Caribbean Plate (CA) and northern South America (SA) is overly simple. The SA passive margin was converted into an active, S-dipping subduction margin in the Maastrichtian, at which several hundred km of Proto-Caribbean (P-CA) lithosphere was subducted beneath SA prior to the progressive arrival of CA from its Pacific origin. Thus, CA-SA interaction has been an E-wardly progressive “arc-arc” collision of sorts, although SA did not develop arc magmatism because the magnitude and rate of P-CA subduction was too small. The P-CA trench can be seen in gravity and basement structure maps emerging E-ward from beneath from Barbados Ridge ahead of Barbados to Atlantic magnetic anomaly 31 (Late Maastichtian). Thus the P-CA trench probably formed a simple triple junction with a ridge-transform corner of the Atlantic Spreading Ridge at that time. Subsequent kinematics can be described by a simple rotation of SA toward North America since that time. Field studies and heavy-mineral patterns constrain a dynamic model for “hanging wall” uplift just prior to arc-arc collision. This uplift is E-wardly diachronous but culminates in the Serranía Oriental at end-Eocene. The new tectono-stratigraphic model for the evolution of northern South America explains long-standing controversies such as Paleogene flysch-like deposition in Eastern Venezuela-Trinidad (northern Vidoño, Chaudiere, Scotland fms) earlier than the Late Oligocene arrival of CA along the Serranía Oriental, the apparent depth of incision in the SA hanging wall (N and E fringes of the Serranía), and the magnitude of normal fault throws that cannot be explained by a forebulge model in arc-continent collision. The model also provides a framework in which to understand the Early Oligocene clastic play along the Central Range of Trinidad. This work forms part of the regional framework and onshore basin analysis components of the BOLIVAR NSF-funded research program assessing crustal structure and continental growth along northern South America.

Natural Rock Drainage Associated With Unmined Porphyry Copper Deposits In The Rio Grande De Arecibo Watershed, Puerto Rico 1 1 2 1 M. Plaza Toledo , J.H. Schellekens , R.R. Seal II , F. Gilbes Santaella 1University of Puerto Rico Department of Geology, P.O. Box 9017, Mayagüez P.R. 00681 2 U.S. Geological Survey 954 National Center, Reston V.A. 20192

The Río Grande de Arecibo is located at the north-central part of the island of Puerto Rico; its watershed is unique because it contains most of the discovered porphyry copper deposits of Puerto Rico. Several of them were extensively explored but were never mined. The premining geochemical signature for areas around mineral deposits, known as geochemical background in pristine areas, or a geochemical baseline in areas that have

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experienced anthropogenic activity, is essential for realistic reclamation goals for after mining at proposed mines and at abandoned mines (Runnels et al. 1998). This study represents a geochemical background characterization that can be used as a remote analogue for porphyry copper deposits in tropical climates. This will be performed on the basis of water geochemical analysis of the Río Viví in Utuado, which passes through the deposits, and Río Pellejas in Adjuntas which drains the deposits. In addition to these analyses, processed images from the IKONOS satellite will be used to better characterize vegetation on the vicinity of the deposits. A comparison will be made using the information obtained by these images and the water quality data obtained in this study.

A Maastrichtian Rudist Bivalves Association Found In The Oriental Cordillera (Dominican Republic) Jose Maria Pons1, Jesús García Senz2 & Enrique Bernárdez3 1Dept. de Geologia, Facultat de Ciències, Universitat Autònoma de Barcelona 2Dept. Geodinàmica i Geofisica, Facultat de Geologia, Universitat de Barcelona 3Dept. de Paleontología, Facultad de Geología, Universidad Complutense, Madrid

A rudist bivalves association has been found in the Río Mana section (UTM: 052125, 206408), 28 km southeast of the village of El Seibo, in the Oriental Cordillera of Dominican Republic. The discovery expands the record of this bivalve group in the Greater Antilles and has importance to study their decline and extinction pattern close to the K/T boundary. The Loma de Anglada Fm, within which the rudists are found, was deposited in a sedimentary high in a fore-arc basin adjacent to the northern boundary of the Caribbean plate. It is made of 450 m of shallow-water calcarenites with ondulated bedding and cross-stratification, followed by limestones with volcanic rock gravel and volcanic lithic sandstones. The rudist beds form biostromal bodies at the upper part of metric-thick parasequences starting with lithic sandstones, and bearing broken and slightly rounded shells belonging to the rudist families Antillocaprinidae, Radiolitidae and Hippuritidae, together with gastropods and orbitoidal foraminifers. The following species have been identified in 23 m of section: Titanosarcolites giganteus (Whit.), Antillocaprina sp., Thyrastylon cf. adhaerens (Whit.) and Praebarrettia sparcilirata (Whit.). All of them are well known from the lower part of the Titanosarcolites Limestones of Jamaica, dated as Maastrichtian. This contribution is a result of the SYSMIN Program (2002-2004) financed by the European Union .

Paleoseismology in the Caribbean: A review of studies in Hispaniola, Puerto Rico and Trinidad Carol S. Prentice, U.S. Geological Survey, 345 Middlefield Rd, MS 977, Menlo Park, CA 94025, [email protected], 1-650-329-5690, Paul Mann, Institute for Geophysics, University of Texas, Austin, TX, 78713, John Weber, Department of Geology, Grand Valley State University, Allendale, MI 49401, PEÑA, L.R., Avenue Cuesta Colorada, #2, Santiago, Dominican Republic, and Christopher Crosby, U.S. Geological Survey, 345 Middlefield Rd, MS 977, Menlo Park, CA 94025

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We have applied paleoseismic techniques to the study of faults on three of the islands in the Caribbean region: Hispaniola, Puerto Rico, and Trinidad. The Septentrional fault zone (SFZ) is the major North American-Caribbean plate-boundary fault in Hispaniola, where it traverses the densely populated and rapidly developing Cibao Valley in northern Dominican Republic. Our studies show that the most recent ground rupture on the SFZ east of Santiago, in the central part of the valley, occurred about 800 years ago, and was associated with a minimum of about 4 m of left-lateral strike-slip displacement. The penultimate event occurred after AD30, suggesting a recurrence interval of 800 to 1200 years. Studies of offset Holocene stream terraces suggest a SFZ slip rate of 6-12 mm/yr, indicating that this structure accommodates about half of the geodetically determined total plate- boundary motion of approximately 19 mm/yr. These paleoseismic data suggest that the seismic hazard associated with the SFZ is high.

The major structures of the North American-Caribbean plate boundary are offshore north of Puerto Rico. However, the location of the island within the plate-boundary zone suggests the possibility of onshore Holocene faults, though no faults with Holocene displacement have previously been documented on the island, and current seismic hazard assessments only consider the impact of distant, offshore seismic sources. Our mapping and paleoseismic studies demonstrate that repeated Holocene surface rupture has occurred on a previously unrecognized fault in the Lajas Valley of southwestern Puerto Rico. We identified an approximately east-west trending scarp crossing an alluvial fan on the southern side of the Lajas Valley, and several excavations across this scarp exposed faulted alluvium. In one of our excavations, we see evidence for two, and possibly three earthquakes. In addition, relations exposed in both fault-perpendicular and fault-parallel trenches suggest a right-lateral component of slip in addition to a normal component. Very little material suitable for radiocarbon analysis was present in the sediments exposed in the trenches. We collected five samples, which we hope will yield age constraints on the timing of these earthquakes. Based on the ages of samples collected and analyzed in 2000, we conclude that there have been at least two earthquakes in the last 5000 years on this fault. We anticipate that additional radiocarbon analyses will provide additional age constraints.

Trinidad is located along the transform plate boundary between the South American and Caribbean plates. Analysis and comparison of historic triangulation and GPS data suggest that a significant fraction (14+/-3 mm/yr) of the total plate-boundary motion (about 20 mm/yr) is being accommodated across the Central Range Fault in central Trinidad. Geomorphic evidence of Quaternary faulting along the Central Range Fault includes linear drainages, aligned topographic saddles and troughs, offset ridges, right-laterally deflected streams, and linear scarps, supporting the geodetic evidence for youthful fault slip. We exposed a 6-m-wide shear zone within Pliocene(?) material in a trench cut into a fluvial terrace across the Central Range Fault. The overlying Holocene fluvial gravel is faulted and folded across the shear zone, and Holocene fluvial deposits are faulted against the shear zone on the north side. Our paleoseismic studies demonstrate that surface rupture has occurred within the past 4500 years on this previously unrecognized, active fault.

Holocene marine terraces in Puerto Rico: Evidence for tectonic uplift? Prentice, C.S. McGeehin, J., Simmons, K.R., Muhs, D.R., Roig, C., Joyce, J., Taggart, B.

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We identified paleo-shorelines and associated marine deposits at elevations of approximately 3-5 m above modern sea level on the island of Puerto Rico in four widely separated locations: Patillas, Salinas, Rincón, and Ramey. Near Patillas (southeastern Puerto Rico), a paleo-seacliff extends up to 200 m inland and has a shore-parallel extent of ~5 km. Pits excavated into the terrace surfaces seaward of these paleo-shorelines exposed fossiliferous marine sand beneath soils. Seven radiocarbon analyses of samples from the Patillas terrace range in age from 400-520 yr BP to 730-900 yr BP (two-sigma ages). Near Salinas (southern Puerto Rico), well-developed paleo-sea cliffs extend up to 800 m inland and at least 8 km parallel to the modern shore. Eleven radiocarbon ages and two U-series ages of samples collected from the Salinas terrace range from 670-860 yr BP to 2740-2870 yr BP. Near Rincón, in northwestern Puerto Rico, ongoing commercial sand extraction activities on a terrace approximately 1 km inland exposed fossiliferous marine sand approximately 3 m above sea level that underlie fluvial and marsh deposits. Radiocarbon analyses of two coral samples yield ages of 1350-1550 yr BP and 1680-1870 yr BP. At the Ramey locality, a well-developed paleo-seacliff extends up to 20 km parallel to the coastline and up to 500 m inland. Sand extraction activities have removed deposits associated with this terrace, but fossil corals left behind on the bedrock platform approximately 3-5 m above sea level yield eight U-series ages ranging from 4000 yr BP to 7000 yr BP. Studies in the Caribbean suggest that sea level has been steadily rising in this region for the last 10 ka and has not been higher than it is today during the Holocene. Glacio-hydro-isostatic models do not predict a relative high sea level for the Caribbean during the Holocene. In addition, the preliminary ages suggest that the marine terraces are not all of the same age. These data suggest Holocene tectonic uplift as a possible mechanism of formation for the terraces.

PAST, PRESENT AND FUTURE OF SEISMIC MONITORING IN THE DOMINICAN REPUBLIC

Rafael Pujols, Juan Payero and Félix Martínez Instituto Sismológico Universitario, Universidad Autónomo de Santo Domingo

The “Instituto Sismológico Universitario (ISU)” was founded following a major earthquake that occurred on August 4, 1946 in the Scottish Bay. This earthquake, which registered a magnitude 8.1 on the Richter scale, caused damage in San Francisco de Macorís, Moca, La Vega, Santiago, Samaná, and Nagua, among others localities and the total destruction of the municipality of Matancitas, located in the Province María Trinidad Sánchez (Nagua), due to a tsunami. Approximately 300 human casualties were reported.

ISU began its operations on February 26, 1948, under the direction of Father Joseph Lynch, with two three-component seismic stations: one Sprengnether Series H short- period instrument and one Sprengnether broadband. These stations operated until 1987. Following the construction of the Tavera-Bao dam in 1979, seven additional short period stations that utilized, for the first time, digital recording were installed. These stations

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were a contribution from the University of Texas at Austin. In 1984, under an agreement with several national and international institutions, six short period stations that operated via telemetry and a central, three-component station in Santo Domingo were installed. This network consisted of Geotech Model S-13 seismometers. This network operated with its maximum capacity from 1985 to 1988. Eight digital short-period stations were also added to the Tavera-Bao project in 1984, for a total of fifteen. In 1996 the Dominican government contributed three single-component, short-period telemetered stations, consisting of Kinemetrics Ranger SS1 seismometers.

In 1998, with the SYSMIN project, a network was constructed in the northeast that consisted of ten digital short period stations. Equipment included a Kinemetrics Altus K2 digitizer, SS1 seismometer, and a spread spectrum digital radio at each station and a central acquisition and data analysis center near the town of San Francisco de Macorís. In addition, five accelerometers were installed with Kinemetrics Altus K2 digitizers and FBA23 sensors.

In 2002, six new short period analog telemetered stations were installed broadly around the Dominican Republic. Each station consists of a Geotech Instruments S-13J sensor with Geotech DSPA64 and DSP32C digital data acquisition systems located at the ISU laboratory in Santo Domingo. A broadband, three-component station, consisting of a KS-2000 sensor plus a DL-24 digitizer, is also located in a basement vault beneath ISU’s laboratory. In 2004, following a cooperative agreement with the Puerto Rico Seismic Network, a VISEIS digital acquisition system and EARTHWORM real time data transfer were introduced. Earthworm permits data exchange between both networks in real time through the Internet.

In the near future, also with the collaboration of the Puerto Rico Seismic Network, two broadband stations will be installed in Punta Cana and Samaná, respectively. In addition, with financial support from the Dominican government, additional short period and broadband stations may be installed, data processing capabilities expanded, computer capacity upgraded, and a new, modern building constructed to house the improved monitoring network.

The University Of Trinidad And Tobago Dr. Sally Radford

The University of Trinidad and Tobago is a new entrepreneurial university established as a partnership between government and industry. It aims to commercialise research and development in the fields of energy and environment in the Caribbean Basin and is pleased to announce a new Master of Science degree in Oil and Gas Exploration and Production. Further details may be obtained from

UTT Point Lisas Campus

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Esperanza Road, Brechin Castle, Couva, Trinidad, WI. www.utt.edu.tt

Conservation Of Reefs Around Tobago

Several projects have been established with the aim of conserving the coastal resources around Tobago. The University of the West Indies in Trinidad is currently conducting a survey of foraminifera in habitats of Buccoo Reef. These have recently been mapped by GIS. The Buccoo Reef Marine and Coastal GIS database may be obtained from

Buccoo Reef Trust Cowie's Building Auchenskeoch Road Carnbee, Tobago, WI. www.buccooreeftrust.org

Evaluating the Effects of Land Development on Sediment Production and Sediment Yields in Dry Tropical Areas of the Eastern Caribbean Author: Ramos-Scharrón, Carlos E. Island Resources Foundation 3605 Steck Ave. #1132 Austin, TX 78759 Tel. 787/587-0416 Email: [email protected]

Anecdotal evidence suggests that an observed long-term decline in coral reef cover within the Caribbean Region may be associated with localized increases in anthropogenic stresses. Of particular concern is the rise in sediment loading rates that typically accompanies land development. This study describes the impacts that land development has had on sediment production and delivery rates on dry tropical areas of the Eastern Caribbean. The objectives of this study were to: (1) measure erosion rates from a variety of anthropogenic and natural sources; and (2) develop a GIS-based model to estimate basin-scale sediment delivery.

Sediment production rates were measured from unsurfaced roads, road cutslopes, undisturbed hillslopes, streambanks, and treethrow on St. John-USVI and La Parguera-Puerto Rico. Unsurfaced roads had the highest erosion rates with values up to 23 kg m-2 yr-1, while road cutslopes generated only about 0.8 kg m-2 yr-1. Since undisturbed areas produced only 0.001 kg m-2 yr-1, unsurfaced roads can increase hillslope-scale sediment production rates by up to four orders of magnitude. Sediment production rates from erodible streambanks were estimated to be nearly 13 kg m-2 yr-1, while uprooting of trees along stream margins was estimated to deliver 0.17 kg yr-1 of sediment per meter of stream length. The St. John Erosion model (STJ-EROS) uses a series of empirical sediment production models and sediment delivery ratios to estimate watershed-scale sediment yields in a

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GIS-based system. The model has been applied to four watersheds in St. John representing a disturbance gradient and the results suggest that current sediment yields are four to forty times higher than undisturbed conditions. Predicted sediment yields are consistent with measured sediment yields and bay sedimentation rates. Actively-used unsurfaced roads were identified as the dominant source of sediment in each of the four watersheds. Cutslopes and streambanks played a secondary role in total sediment yields, while undisturbed hillslopes and treethrow contributed only minimal amounts.

Sedimentology and tectonic evolution of the Campanian to Paleocene succession in northern Blue Mountains, eastern Jamaica Ryan Ramsook and Simon F. Mitchell Department of Geography and Geology, University of the West Indies, Mona, Kingston 7, Jamaica

Detailed mapping and logging of the Campanian-Paleocene succession in the northern Blue Mountains, eastern Jamaica, has produced a revised geological map and tectonic evolution for the area. The region underwent NW-SE directed extension and rifting related to a change from north-eastward to eastwards motion of the Caribbean Plate following collision between the Nicaragua Rise and the Yucatàn Block in the late Campanian/early Maastrichtian. The geologic history is divided into pre-rift, syn-rift and post-rift stages. The Campanian to Early? Maastrichtian pre-rift sequence consists of andesitic volcanics and associated marine limestones and clastics. In the northern part of the study area, the succession consists of the Bonnie View Andesite (Campanian? porphyritic pyroxene and plagioclase andesite) with pillow structures and the fault bounded Providence Formation (calcareous poorly sorted conglomerates and graded sandstones, siltstones, shales and mudstones with Campanian ammonites). In the central study area the succession was deposited closer to an active island arc volcano and consists of a thick andesitic pile (including the Bellevue Formation) with a thin early Middle Campanian marine incursion (Back Rio Grande Formation) and is overlain by ?Early Maastrichtian rudist-bearing limestones and associated proximal volcaniclastics (Rio Grande Formation). The Bowden Pen Formation (? latest Maastrichtian) represents the base of the syn-rift sequence and is represented by poorly sorted conglomerates and sandstones deposited in alluvial fans and proximal submarine fans as the rift system developed. This is succeeded by a coarsening upwards (rift-filling) sequence of abyssal turbiditc sandstones and shales passing up into thick sandstones. Post-rift deposition is marked by a change to carbonate deposition in the late Paleocene, and marks the cessation of uplift on the rift’s margins and westward migration of rifting to the Wagwater Trough.

Identifying Submarine Slides on Jamaica’s Southern Island Slopes. by Edward Robinson1, Deborah-Ann. C. Rowe1 and Rafi Ahmad2

Submarine slides have occurred in Jamaica during storms or earthquakes, as for example following the Port Royal earthquake of 1692, and as suggested by telephone cable breaks related to earthquakes in1907 and 1993.

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The vulnerability of Jamaica’s coastline to storm surge from hurricanes has been amply demonstrated. Although tsunami have occurred in historical times, their sources and extent in the Jamaican coastal environment and damage potential is not known. Tsunami may arise locally from submarine slides on the island shelf or slope, generated by storms or earthquakes, as well as from seismic events themselves. Warning times for such local events will usually be very short, as was the case following the 1907 earthquake. Signatures from past tsunami events are probably preserved as tsunamigenic sediments on the island,s shelf/slope..

Direct investigation of the incidence of slides on the island’s south slope has been initiated by the Marine Geology Unit at the University of the West Indies, through analysis of high-density bathymetric data. Of slide deposits so far identified, one exceeds 20 million cubic metres in volume. However, bathymetry for most of the north coast shelf and slope is lacking, although such data are crucial in determining the likely parameters of future tsunami and surge events.

1Marine Geology Unit, 2Unit for Disaster Studies, Department of Geography & Geology, University of the West Indies, Mona, Kingston 7, Jamaica. [email protected]

SO2 conversion rates at Soufrière Hills volcano, Montserrat, B.W.I. LA Rodríguez1; IM Watson1,2; V Hards3, 4; G Ryan3; M Edmonds5; C Oppenheimer6; WI Rose1; GJS Bluth1 1. Geological and Mining Engineering & Sciences, Michigan Technological University, Houghton, MI 49931 2. Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK 3. Montserrat Volcano Observatory, Flemings, Montserrat, BWI 4. British Geological Survey, Keyworth, Nottingham, UK 5. USGS-Hawaiian Volcano Observatory, Hawaii National Park, HI 96718 6. Department of Geography, Cambridge University, Cambridge, UK

Volcanic SO2 emission rates are commonly measured on plume cross sections some distance downwind from the active vent; after interacting with other volcanogenic gases, particles and droplets of volcanogenic and/or meteoric origin, and atmospheric gases. The emission rates therefore do not -2 necessarily represent the real fluxes, due to the conversion of SO2 to SO4 . It is important to quantify volcanic SO2 conversion rates as a function of meteorological environment and plume age as near source plume chemistry can have significant effects on climatologically active species. We used two mini-UV spectrometers to measure SO2 emission rates at Soufrière Hills volcano, Montserrat, which is a low altitude volcano (summit altitude <1100 m above sea level) in a wet atmosphere. Helicopter and boat traverses where conducted in March and April 2004. Here we present our results from measurements taken at a variety of distances from the vent downwind (maximum of ~16 km), which represent different plume ages. Weather data will help clarify the effects of Montserrat’s low, moist, and absorptive atmosphere upon conversion rates. Preliminary results indicate that the average loss rates are in the order of 10-4 s-1; however they are not constant throughout the plume. The variations could be caused by plume puffing, plume interactions at the coast, turbulence, and aerosol evolution. This research is complemented by measurements at Lascar and Etna volcanoes, which represent dry and intermediate atmospheric conditions.

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Bioturbation by the sea urchin Diadema antillarum: Effects on sediment and diversity Rodriguez-Iglesias, Esther M. Graduate Student University of Puerto Rico, Mayaguez Campus Department of Marine Sciences P.O. Box 3342, Mayaguez, P.R. 00681-3342 [email protected]

Yoshioka, Paul Professor University of Puerto Rico, Mayaguez Campus Department of Marine Sciences P.O. Box 9013, Mayaguez, P.R. 00681-9013 [email protected]

The sea urchin Diadema antillarum is a keystone species of the Caribbean reefs. Its grazing activity both cleans and produces sediments by bioerosion. Diadema suffered a mass mortality across the Caribbean in 1983-84 (95-99% eliminated). Effects of this event included macroalgal blooms, drops in coral cover and transition from coral to algal dominance. Although recruitment of corals increased in “hard ground” habitats, coral cover remained low because of higher recruit mortality. We believe that the latter effects result from changes in the bedload regime arising from Diadema’s effect on sediments and its interaction with water motion, topographic relief, and the slope of the terrain. We are studying these effects of Diadema with caging experiments at Media Luna reef in La Parguera, Lajas. Areas inside and outside of 8 (0.5x0.5x0.25m) cages will be monitored before, during and after transplants of Diadema for periods of 1, 1 and 2 months respectively. Four of the cages will serve as controls. Photographs, sediment collection, estimates of bedload transport (measured with nylon-mesh sediment traps), and macrofauna and flora identifications will be made on a weekly basis in the field during this period. Laboratory analyses include characterization of sediment, granulometry, angularity and composition. Sediment consolidation will be estimated by extracted chlorophyll a concentrations in sediments. We expect a change in sediment composition, especially in terms of organic material, as well as in grain characteristics during the study. We also anticipate that bedload transport will increase in the presence of Diadema due to its bioerosional and sediment cleaning effects. We then expect that it will be difficult for coral recruits to become established because of this bedload regime.

Post-Jurassic Evolution of the Chortis Block and its role in the evolution of the Caribbean Robert Rogers, Department of Geology, University of Puerto Rico- Mayagüez, P.O. Box 9017 Mayaguez, PR 00681

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Four post-Jurassic tectonic events are recorded in the geology of the Chortis block of northern Central America within the context of the regional evolution of the Caribbean plate and the southernmost North American Cordillera. The earliest event is Aptian-early Cenomanian, intra-arc rifting followed by late Cretaceous inversion of the rift basin in the Frey Pedro range of east-central Honduras. A 3.5-km-thick stratigraphic section of clastic, carbonate, volcaniclastic and volcanic rocks were deposited in the intra-arc rift and on its rift shoulders. The geochemistry of rift-related volcanic rocks shows magmatic arc affinity. The northwest-directed Colon fold-thrust belt of eastern Honduras and the Nicaragua Rise and adjacent island arc Siuna belt of northern Nicaragua, record the late Cretaceous collision between the south-facing margin of the Chortis block and the northeastward-moving Caribbean arc system. This previously unrecognized arc- continent collision can be traced for a distance of 350 km across Honduras and the Nicaragua Rise. North trending rifting of the western Chortis block and NNW-SSE transtensional extension of northern Honduras and the offshore Honduran borderlands reveal Miocene to Recent divergence between the Caribbean and North America plates. Observed boundary-normal extension occurs where the angle between the plate boundary fault and the Caribbean motion vector is greater than 10º and boundary-parallel transtension where the angle is between 5 and 10º. P-wave tomographic images of the mantle beneath northern Central America reveal a detached slab of the subducted Cocos plate. Landscape features of the region above the detached slab are consistent with epeirogenic uplift produced by mantle upwelling following slab breakoff between 10 and 4 Ma. Correlation of regional aeromagnetic data with outcrop exposures allows subdivision of the Chortis block into five terranes: 1) Central Chortis with continental Paleozoic basement; 2) Eastern Chortis with Jurassic metasedimentary basement; 3) Southern Chortis of low magnetic intensity and covered by Miocene volcanic strata; 4) Siuna with oceanic island arc basement; and 5) Northern Chortis where early Tertiary magmatism overprints the Central and Eastern Chortis terranes. Common geologic and geophysical characteristics of the Chortis terranes and Mexico terranes allow improved reconstructions of the region prior to its Tertiary fragmentation. LATE GLACIAL STAGE-HOLOCENE TRANSITION RECORDED IN A NORTHERN VENEZUELA STALAGMITE S.M. Rosner1, L.A. Gonzlalez1, H. Cheng2, L. Edwards2, and F. Urbani3, R. Gomez4 1University of Kansas, Department of Geology, Lawrence KS USA 66045; 2University of Minnesota, Department of Geology and Geophysics, Minneapolis MN USA 55455; 3Universidad Central de Venezuela, Escuela de Geologia, Minas y Geophisica, Departamento de Geologia, Caracas Venezuela; 4MFG Inc., Austin TX USA, 78703

Northern South America and the southern Caribbean have undergone major climatic and environmental changes during the Late Glacial through the Holocene. Foraminifera isotope data from the Cariaco Basin off the coast of Venezuela indicate a major temperature change (~ 4°C) from Late Glacial to Holocene (Lin et al., 1997). Lacustrine records from Lake Miragoane, Haiti and Lake Valencia, northern Venezuela indicate a change from dry to wet climate in the early Holocene (Hodell et. al., 1991,

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Curtis et al., 1999). This climatic/environmental change in the region has been attributed to migration of the mean position of the Inter Tropical Convergence Zone (ITCZ) in response to insolation changes (Seltzer et al., 2000; Haug et al., 2001). Presently the average northern most position of the ITCZ over South America lies over northern Venezuela. Thus, paleoclimate proxies from northern Venezuela record critical information needed to understand climatic changes from Late Glacial to Present. Data has/is been generated from a stalagmite from Cueva Zarraga located in northern Venezuela. Isotope records span the last 20,000 years, during which time decreases in both δ13C and δ18O indicate a change to warmer and wetter conditions from the Late Glacial to the early Holocene. Presently the chronology of the stalagmite is not well constrained before about 10,500 years BP. Further isotope work, stable and radiogenic, is in progress to better determine the timing of the environmental change preserved in the stalagmite.

Geologic uncertainty in the assessment of undiscovered oil and gas resources of the Jurassic- Cretaceous Composite Total Petroleum System, Northwestern Cuba Christopher J. Schenk, U.S. Geological Survey The U.S. Geological Survey (USGS) recently assessed the undiscovered oil and gas potential of the Jurassic-Cretaceous Composite Total Petroleum System (TPS) in northwestern Cuba (mostly offshore). The USGS assessed three assessment units (AU) within the TPS: 1) North Cuba Fold and Thrust Belt AU, 2) North Cuba Foreland Basin AU, and 3) North Cuba Platform Margin Carbonate AU. The proposed geologic model for the composite TPS has oil and gas generated from Jurassic and Cretaceous organic-rich shales within the Paleogene thrust belt. Petroleum migrated updip during the Paleogene into structurally controlled reservoirs in the fold and thrust belt and below and within the foreland basin, and into reservoirs along the margins of the carbonate platform. For the North Cuba Fold and Thrust Belt AU, the USGS estimated a mean of 0.49 billion barrels of undiscovered oil (BBO) (with 0.6 trillion cubic feet [TCF] of associated gas); a mean of 3.2 BBO (with 6.4 TCF of associated gas and 1.2 TCF non-associate gas) in the North Cuba Foreland Basin AU, and a mean of 0.9 BBO (and 1.6 TCF associated gas) in the Platform Margin Carbonate AU, for a total mean undiscovered resource of about 4.6 BBO and 9.8 TCFG. Geologic uncertainties in the assessment involved the efficacy of petroleum fluid migration from sources in the thrust belt into reservoirs of the foreland basin and platform margins, reservoir quality in all assessment units, and the preservation of reservoired petroleum since possible trapping during the Paleogene.

Age and facies of submerged Late Pleistocene reefs, Oahu, Hawaii: Implications for stage 7 and late stage 5 sea levels C.E. Sherman*, C.H. Fletcher, K.H. Rubin, K.R. Simmonsb, W.H. Adey Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, 1680 East-West Road, Honolulu, Hawaii 96822, USA, bU.S. Geological Survey, MS980, Federal Center, Denver, Colorado 80225, USA, cDepartment of Botany, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, USA * Corresponding author. Address: Department of Marine Sciences, University of Puerto Rico, Mayagüez Campus, Isla Magueyes, Laboratories, PO Box 908, Lajas, PR 00667. PH: 787/ 899-2048 E-mail: [email protected]

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In situ Pleistocene reefs form a gently sloping nearshore terrace around the island of Oahu. The windward margin of the terrace is dominated by coralline algal bindstones (algal ridge) that formed in a shallow, high-energy environment within 1-2 m of paleosea level. The leeward margin of the terrace is dominated by coral framestones, bindstones, and rudstones. TIMS Th-U ages of in situ corals indicate that most of the terrace on both the windward and leeward sides of Oahu is composed of reefal limestones correlating to marine oxygen isotope stage 7 (186-242 ka). This in situ stage 7 reef complex is informally referred to as the Waianae Reef. The position of the Waianae Reef indicates that it formed during periods when sea level was ~ 9 to 20 m below present sea level. Its extensiveness and geomorphic prominence as well as a paucity of emergent stage 7 deposits on Oahu suggest that much of isotope stage 7 was characterized by sea levels below present. Later accretion along the seaward front of the terrace occurred during the latter part of isotope stage 5 (i.e., <120 ka, post-5e). The position of the late stage 5 reefal limestones is consistent with formation during a period when sea level may have been below present. The general trend of decreasing Th-U age of stage 5 corals with distance offshore may suggest that accretion along the seaward front of the terrace occurred during a period of general sea-level fall during the latter part of stage 5. The dearth of Holocene accretion over the submerged Pleistocene reefs of Oahu is a result of insufficient time and accommodation space for reefs to develop during the Holocene.

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Tectonic Evolution of the Caribbean Mountain System, Northern Venezuela: Evidence for an Atypical Origin for a Fold and Thrust Belt Virginia B. Sisson and Hans G. Avé Lallemant, Dept. of Earth Science, MS-126, Rice University, Houston TX 77251-1892

Superficially, the Caribbean Mountain system resembles a fold and thrust belt with a foreland and an igneous-metamorphic hinterland. However, the foreland formed in the Tertiary whereas the metamorphism is generally Mesozoic, and igneous rocks are Mesozoic to Lower Paleozoic. The Cordillera de la Costa belt is a subduction mélange with eclogite, granite, and granitic gneiss knockers in a mica schist and serpentinite matrix. The eclogite formed at ~75 km in mid-Cretaceous, and retrograded following a path typical of collisional terranes. Geochemistry of the eclogites and matrix indicate MORB and active margin sedimentary protoliths. Deformation structures formed during retrograde metamorphism, indicate NS shortening, EW dextral simple shear, and EW plate boundary parallel extension as an important mechanism of exhumation. Near Puerto Cabello, exhumation did not occur until after 35 Ma. The Caucagua-El Tinaco belt consists of gneisses, amphibolites, peridotites, and volcanic and sedimentary rocks. A new amphibole 40Ar/39Ar determination of the Tinaco complex yielded 146 Ma. The Tinaquillo peridotites are mylonites formed during Jurassic rifting at 190 Ma. The mid-Cretaceous Villa de Cura belt is a sequence of blueschist facies volcanic arc basalts and volcaniclastic rocks. There is little retrograde overprint, typical of Franciscan-type terranes. The Serranía del Interior fold and thrust belt is older in the west (Eocene) and younger in eastern Venezuela (Miocene). Apatite fission-track ages indicate a deformation event related to the passage of the Antilles volcanic arc. In north-central and eastern Venezuela, there are two populations of apatite fission-track ages: one Eocene age and the other Miocene. The older dates suggest NS contraction occurred long before the Antilles reached the area. Significant new findings indicate a range in tectonic processes from orogenic events correlated with the Appalachians, Jurassic rifting, Cretaceous subduction, Cretaceous-to-Tertiary exhumation and contraction, as well as formation of the Tertiary fold and thrust belt.

Pre-historic volcanism of the Soufrière Hills-South Soufrière Hills volcanic complex, Southern Montserrat, West Indies A. L. Smith1, M. J. Roobol2, J. H. Schellekens, and G. Mattioli3 Department of Geology, University of Puerto Rico, Mayaguez, Puerto Rico

The Soufrière Hills-South Soufrière Hills volcanoes although morphologically distinct, on the basis of stratigraphy and petrology appear to belong to a single volcanic complex. Although considerable attention has been focused on the current eruption of the Soufrière Hills volcano, the pre-historic record of the complex is less well known. Stratigraphic studies indicate that the Soufrière Hills volcano is dominated by the extrusion of Pelean domes and their associated block and ash flow deposits. In contrast, the South Soufrière Hills center is composed mainly of deposits from scoria and ash flows and scoriaceous falls characteristic of St. Vincent-style activity. Their combined stratigraphies record over 400,000 years of history. The recent history of the complex, based on age dating and stratigraphy, has been subdivided into 7 episodes (Soufrière Hills subunit I, South Soufrière Hills, Soufrière Hills subunits II-VI). Subunit I (< 175 ka) is essentially composed of deposits from Pelean-style eruptions, however near its top ignimbrites characteristic of Plinian-style activity are abundant. The South Soufrière Hills (~130 ka) is characterized by deposits from open crater St. Vincent-style eruptions. Subunits II to V (~112,000 to ~400 years B.P.) represent a return to the characteristic Pelean activity, although the period between 22,000 and 20,000 years B.P. is dominated by deposits of semi-

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vesicular andesite. Similar deposits have been described from the present eruption, thus providing a mechanism for their formation. Age dating suggests that the Soufrière Hills was active just prior to European settlement in 1632 AD. Since then there have been four volcano-seismic crises, the last of which was a precursor for the present eruption (subunit VI). This eruption, dominated by dome growth and the generation of associated pyroclastic flows appears to be typical of the eruptive style characteristic of this volcano. (1) Department of Geological Sciences, California State University, San Bernardino, California; (2) Saudi Geological Survey, PO Box 54141, Jeddah, 21514, Saudi Arabia; (3) Department of Geology, University of Arkansas, Fayetteville, Arkansas

Biostratigraphic Study Of The Rio Maton Limestone Member Of The Robles Formation And The Torrecilla Breccia, Along The Pr # 1 In Cayey, Puerto Rico Ailec D. Soto Feliciano and Hernán Santos Department of Geology, University of Puerto Rico, Mayagüez Campus

A detailed stratigraphic section along the PR #1 in Cayey, Puerto Rico, between the Río Matón Limestone Member of the Robles Formation and the Torrecilla Breccia was developed. This stratigraphic section will allow for the reconstruction of the paleofacies, depositional environments, and relative sea level changes in the area. A stratigraphic section was measured, and fossils were collected to determine the age of the Formations. Gastropods, bivalves, echinoderms, corals and plant fragments were found. The presence of the rudist bivalve fossil Coalcomana ramosa, an index fossil of Lower Albian age, established the age of the formation. On the basis of the composition of carbonate rocks mixed with volcaniclastic sediments, as well as the presence of the shallow water fossil fauna, the paleofacies reconstruction made suggests the area was located in an inner platform environment. The Río Matón Limestone Member ended with a transgressive event that resulted in the deposition of the Cayey Siltstone Member.

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Contrasting high-pressure and low-pressure P-T-t-d paths in a single nappe pile: a case study from the Cuban collisional suture

Stanek, K.P., Institut für Geologie, Technische Universität Bergakademie Freiberg, D-09596 Freiberg, Germany Maresch, W.V., Institut für Geologie, Mineralogie und Geophysik; Ruhr-Universität Bochum, D-44780 Bochum, Germany Grafe, F., IBeWa Consulting, Lessingstraße 46, D-09599 Freiberg, Germany Grevel, Ch. ERFTCARBON GmbH & Co KG, Aluminiumstraße 4, D-41515 Grevenbroich, Germany Baumann, A., Institut für Mineralogie, Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany Millán Trujillo, G., Instituto de Geología y Paleontología, Via Blanca y Linea del Ferrocarril, Ciudad de La Habana CP 11000, Cuba Brix, M.R., Institut für Geologie, Mineralogie und Geophysik; Ruhr-Universität Bochum, D-44780 Bochum, Germany Hames, W.E., Department of Geology and Geography, Auburn University, Auburn, AL, 36830, USA Idleman, B., Department of Earth & Environmental Sciences, Lehigh University, Bethlehem, PA 18015-3188, USA Thomson, N.S., Department of Geology & Geophysics, Yale University, P.O. Box 208109, New Haven, CT, 06520-8109, USA

The eastern part of the Escambray Massif in Central Cuba comprises four nappe units, of which at least two indicate high-pressure (HP/LT) metamorphism and represent a former subduction-accretion complex. Tectonic features and fabric analyses argue for a northward thrusting and stacking of the metamorphic rocks. Boudins of eclogite and blueschist-facies rocks corroborate maximum conditions of 16-25 kbar and 580-630ΕC. An island-arc unit with LP/HT metamorphism of ~7 kbar at 620-700ΕC was thrust over the HP-nappes. Late Cretaceous (88-81 Ma) pegmatoids cross-cutting the shear zone between island-arc and HP-metamorphic rocks give a minimum age for the juxtaposition and metamorphism of these distinctly different nappes. SHRIMP zircon ages of ~170 Ma likely date the eclogite protolith and U/Pb, Rb/Sr and Ar/Ar data suggest a Middle to Late Cretaceous (106 to 88 Ma) age for the HP-metamorphism of the metasediments and eclogites, which originated off southeast Yucatán. The origin of the subducted rocks, the arc polarity, the timing of metamorphism, and preliminary paleomagnetic data support a Pacific origin of the Cretaceous Great Antillean island arc and its final exhumation together with the subduction-accretion complex in the Caribbean along the southwestern edge of the Bahamas platform.

Early Cenozoic Recovery Of Caribbean Reef Coral Communities Stemann, Thomas A. Department of Geography and Geology, The University of the West Indies, Mona, Kingston 7 Jamaica

Recent collections from latest Maastrichtian successions in Jamaica reveal that diverse reef coral communities persisted up until the very end of the Cretaceous. Faunas at this time include 60 species from 40 genera of scleractinians and octocorals. This level of species richness is comparable to that typically found on modern Jamaican reefs or in diverse mid to late Cenozoic faunas. Paleocene and early Eocene Caribbean corals, however, are scarce and poorly known.

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New collections of early Cenozoic corals from Jamaica are providing new insight into Caribbean reef communities immediately following the K-T boundary event. Systematic studies are on-going but presently < 5% of the Jamaican Cretaceous corals are found to range into the Cenozoic. Collections from the Paleocene of eastern Jamaica contain less than 5 coral species from each sample site and total sampled richness is lower than at any time in the Cenozoic or Cretaceous. Endemism is high in early Cenozoic faunas but ecologic diversity is significantly lower with communities composed only of thin branching colonies or small solitary corals. Richness rises slightly in the early through middle Eocene but remains low compared to typical levels found in Oligocene and younger units. Dense accumulations of reef corals including large massive, branched and plate shaped colonies do not become common until the late middle Eocene.

Part of this pattern may result from the paucity of ‘reefal’ environments preserved in the Paleocene-Eocene rocks of Jamaica. Still, known reef coral associations from throughout the Caribbean contrast markedly with the rich faunas recorded from Europe, Africa and Asia. After significant extinctions at the end of the Cretaceous, coral community recovery is slow in the Caribbean and faunas here remain species poor and ecologically simple considerably longer than elsewhere in the world.

Connectivity Within a Field: How Production Startup Data Can Answer Some of the Questions. Greater Angostura Development, Trinidad and Tobago Chris Taylor Trinidad and Tobago Asset Team BHPBilliton 1360 Post Oak Bvld., Suite 150 Houston, Texas, 77056

The Greater Angostura Structure, comprising the Kairi, Canteen, Aripo and Angostura structurally defined areas, lies offshore Trinidad and Tobago in Block 2(C). Development drilling on the structure began in September of 2003 and First Oil was achieved in January of 2005.

The Angostura Development is centered on the production of oil and gas reservoired within the Angostura Sandstone, a thick Early to Middle Oligocene sequence of sediment gravity flows that are interpreted to have been deposited in a slope type setting.

The first Phase of the development targets the two oil bearing fault blocks of Kairi and Canteen. To date, 10 oil production, 3 gas injection, and a single dual-duty (oil production followed by gas injection) well have been drilled and completed. A total of 10 bottom hole gauges have been installed for reservoir performance monitoring.

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This presentation reviews the pre-production expectation and post-production interpretation of the inter-well connectivity within the Kairi fault block based upon the bottom hole pressure data. The actual data will be shown and the justification for the interpretations given. The impact of the interpreted results on the next phase of the Greater Angostura development will also be presented.

Volcanic Activity in all Caribbean Plate Margins: Forecast and Risk Assessment R. B. TROMBLEY, Ph.D. Southwest Volcano Research Centre 3405 S. Tomahawk Rd., Suite # 31 Apache Junction, Arizona USA 85219-9169 (480) 671-1601 e-mail: [email protected] website: http://www.swvrc.org

The following presents the current eruption status and forecast for all volcanoes within the Caribbean Plate boundaries. It is upgraded from time to time as

appropriate and as necessary. The forecasting and risk assessment has been compiled, using presently loaded data, from the SWVRC software programme,

ERUPTION Pro 10.5, the only known long-range and reasonably accurate forecasting programme of it kind in the world.

The Caribbean area primarily consists of the countries of Mexico, Guatemala, Honduras, Nicaragua, Costa Rica, Panama, Columbia and Venezuela and the island nations represented in the Lesser Antilles. Some countries such as Cuba, Dominican Republic, Puerto Rico, Jamaica and Venezuela, do not have any active volcanoes within.

Pattern of saltwater contamination resulting from tsunami inundation of small islands Dr. Lensyl Urbano Department of Earth Sciences University of Memphis Memphis, TN 38152 Email: [email protected] Phone: (901) 678-4543

The inundation of coastal regions and small islands by the Indian Ocean tsunami on December 2004 resulted in extensive salinization of shallow groundwater resources. In

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order to investigate the spatial and temporal consequences of tsunami inundation, I employ an idealized numerical model that simulates the effects of inundation on natural and anthropogenically impacted freshwater lenses of small islands. On unimpacted islands the primary determinant of saline contamination of the aquifer is local topography. Saline water is collected in local depressions that serve as focus points for infiltration into the aquifer. A second major parameter affecting saline infiltration is the heterogeneity of the aquifer permeability; infiltration is focused through high permeability regions. On islands with significant anthropogenic groundwater withdrawals, however, the location and size shallow wells are extremely important. Unprotected wells can serve as direct paths for salt water into the aquifer, while the cones of depression surrounding wells focus saline recharge water toward the wells. Once the saline recharge is focused, density effects drive the saline water deeper into the aquifer and continues to focus flow even without further withdrawals. The results of these numerical experiments suggest that wellhead protection and a strategic water extraction scheme may help ameliorate the adverse effects of tsunami inundation.

Puerto Rico Seismic Network, Geology Dept. , UPRM

José Vélez González, Victor Huerfano and Christa von Hillebrandt-Andrade

The Puerto Rico Seismic Network (PRSN) has generated hypocentral information for earthquakes in the Puerto Rico and Virgin Islands region (PR-VI) since 1974 when the network was installed by the USGS for the Puerto Rico Electrical Power Authority. Although there are data for the last 30 years, the PRSN has reliable instrumental information as of 1987 when the Network was transferred to the Geology Dept. of the University of Puerto Rico at Mayag|ez.

The PRSN has been significantly upgraded since 1999 when the first broadband station was installed. At present the network operates 14 broadband and 11 short period stations installed throughout Puerto Rico and the US and British Virgin Islands. Along with the improvements in seismic instrumentation, new computer tools, as well as numerical algorithms have been implemented to analyze the data. These improvements include new magnitude computations, extended format in the parametric data, community accepted waveform formats, the inclusion of instrumental responses and the use of a new locator.

Independent of the method, the assessment of seismic hazard and seismic research relies on published catalogues. The PRSN catalogue of both parametrical and associated waveforms is available as of late 1991 when the digital recording systems were implemented. Nevertheless, this earthquake catalogue has not been significantly revised since 1994 when it was recompiled with the magnitude equations of von Hillebrandt and Bataille and the crustal model of Huirfano. To proceed with the evaluation of seismic hazard and related research for the Puerto Rico and Virgin Island region, a substantial revision of the earthquake database is required. The main goal of this project is to produce a unified earthquake catalogue for Puerto Rico and the Virgi n Islands and to

88 17th Caribbean Geological Conference 2005, San Juan PR build a comprehensive and homogeneous database based on current cross platform MySQL tools. This is being achieved by collecting and re-analyzing automatically primary sources of data, merging all available information using the new algorithms and saving the outputs in the new MySQL tables.

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Tertiary Crocodylians From Puerto Rico JorgeVélez-Juarbe 1, Christopher A. Brochu 2, Hernán Santos1, Ángel M. Nieves-Rivera 3 and Juan D. Daza-Vaca4 1 Department of Geology, P.O. Box 9017, University of Puerto Rico, Mayagüez, PR 00681-9017 2 Department of Geoscience, University of Iowa, Iowa City, IA 52242 3 Department of Marine Sciences, P.O. Box 9013, University of Puerto Rico, Mayagüez, PR 00681-9013 4Department of Biology, University of Puerto Rico, PO Box 23360, San Juan, PR 00931

During the Tertiary, the groups of islands known today as the Greater Antilles were host to a fauna different to the one found in modern times. The complex geological history of these islands makes difficult the study of the origin of these organisms. One of the organisms present (now extinct) during part of the Tertiary in Puerto Rico was the crocodylians. These have been poorly studied, mostly due to the incompleteness of their remains. Even though the remains are not enough for species-level diagnosis, they are sufficient to rule out any crocodylian currently found in the Americas and any of the Tertiary longirostrine species known from the region. Morphological aspects suggest the possibility of an endemic group of crocodylians from the Greater Antilles during the middle Tertiary of the region, this in congruence with the dispersal models for the biography of Crocodylus and of similar Neogene endemic radiations in other regions of the world. The purpose of this work is to briefly describe the evidence found in Puerto Rico.

Cretaceous To Tertiary Echinoderms From Puerto Rico Jorge Vélez-Juarbe and Hernán Santos Department of Geology, University of Puerto Rico, Mayaguez Campus, Mayaguez PR

Fossil Echinodermata, from six Cretaceous age formations, eight Tertiary age formations and one Quaternary age formation were collected and identified to the lowest taxonomic level possible. These were collected from a total of 35 localities, around the island of Puerto Rico, but mostly along the northwest and southwest parts of the island. This is the first attempt to include most of the groups within the Echinodermata, including the starfishes, brittle stars, crinoids, sand dollars and sea urchins that can be found the fossil record of Puerto Rico. Distribution and occurrence of several of the species herein identified can be used in the determination of paleoenvironment, age, and formation where they are found.

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Seismic Monitoring of the Northeastern Caribbean Region Christa G. von Hillebrandt-Andrade, Víctor Huérfano and Juan Lugo Puerto Rico Seismic Network, Dept. Geology, UPR-Mayagüez [email protected] José Martínez Cruzado, John Clinton and Georgia Cua Puerto Rico Strong Motion Program, Dept. of Civil and Surveying Engineering, UPR-Mayagüez [email protected]

The seismicity of the northeastern Caribbean region is monitored jointly by the Puerto Rico Seismic Network (PRSN) and the Puerto Rico Strong Motion Program (PRSMP) of the University of Puerto Rico at Mayagüez. The objectives of the two networks are to record, process, analyze, and research local, regional and teleseismic earthquakes. The ultimate goals are to produce high quality data and information in order to be able to respond to the needs of emergency management and the industrial, academic and research communities, as well as the general public.

The PRSN was established in 1974 to monitor the seismicity and identify earthquake sources in the Puerto Rico Region (latitudes 17.00N-20.00N and longitudes 63.5W- 69.00W). In 1987 it was transferred to the Geology Department, University of Puerto Rico at Mayagüez. It presently operates 10 short period stations and 12 broadband stations throughout Puerto Rico and the US and British Virgin Islands. The analogue short period seismic stations consist of Teledyne S-13 and Mark L-4 seismometers and the data is continuously digitized at 100 sps at the offices of the PRSN. The broadband stations (BB) consist of Guralp CMG 40T, CMG 3 ESP and CMG 3T seismometers and 24 bit Refraction Technology, DAQ and Quanterra digitizers sampling at 40 sps. The BB’s are linked in real time to the central data collection center via Monitron UHF digital radios, DDS 56K telephone lines, spread-spectrum radios and Internet service. The Earthworm system is used to store and distribute the data. PR-DANIS software developed at the PRSN is used for locating and processing earthquakes. The data is saved in GSE2.1 format. As part of the emergent Puerto Rico and Virgin Islands Tsunami Warning System, the Early Bird system developed by the Alaska Tsunami Warning Center was installed in 2003 to automatically locate, calculate magnitudes and distribute earthquake information. This system monitors the PRSN stations as well as some 15 other stations operating in the America’s and Atlantic. A system to automatically determine Regional Moment Tensors is currently being developed.

The Puerto Rico Strong Motion Program (PRSMP) has also been in operation since the 1970’s. Currently the Program maintains a network of 75 3-component ETNA stations, which are primarily located in the urban areas – in fire stations and church grounds. In addition there are 7 densely instrumented structures (2 bridges, 3 concrete dams and 2 high-rise buildings) with 9-12 channel K-2 systems. Recent initiatives have concentrated on introducing real-time communications and recording systems with higher dynamic range to the network. At the moment, 47 ETNA stations have dial-in capability, and 8 ETNA’s have been installed at free field sites with continuous ethernet telemetry to Mayagüez. The PRSMP has 8 strong motion sensors co-located with PRSN broadband

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sensors, ensuring the entire seismic frequency and amplitude bandwidth is covered at these stations. Communication with the stations (as well as PRSN) is supported by ANTELOPE software which also allows location and magnitude determinations (in backup to PRSN operations). Research initiatives that are currently being pursued at the PRSMP include ShakeMap production, regional Mw magnitude calculations, real-time structural health monitoring, and the installation of 2 more joint stations in the Dominican Republic.

Sinking of obducted oceanic forearc-arc terrane in Caribbean-South American plate boundary zone John Weber1, Shimon Wdowinski2, and Edmundo Norabuena2 1Geology Department; Grand Valley State University, Allendale, MI 49403 USA; [email protected] 2University of Miami, RSMAS-MGG, 4600 Rickenbacker Causeway, Miami, FL 33149 USA

On April 22, 1997 the largest (M 6.6) recorded earthquake in Trinidad-Tobago occurred near the boundary between the obducted oceanic arc-forearc of the Tobago terrane and continental South America. A WSW striking (250° azimuth), shallowly dipping, dextral- normal fault ruptured a shallow (≤ 5-15 km deep) fault patch ~10 km south of Tobago. This event is anomalous given the current ~E-W dextral shearing in the plate boundary.

We use GPS data before and after the earthquake at two sites in Tobago to determine coseismic offsets. The north-directed GPS-derived offsets are largest in southern Tobago, closest to the epicenter, and taper off to the north. We used an elastic dislocation model, with fault dimensions (30 km along strike x 25 km down dip) fixed by aftershocks, and fault strike fixed to the 250° CMT value. We obtained a best-fit model with a fault dip of 28° NW, a slip rake of –142°, and a 100 cm average fault slip. We get a close model match to our GPS-derived and empirically calculated displacements. The 250° strike of the fault patch ruptured matches that of the mapped terrane boundary; the fault plane is brought into coincidence with the subsurface projection of the mapped boundary using a ~5 km epicentral depth.

We conclude that this event simply reactivated and inverted the Tobago terrane boundary, which initially had a low dip angle and opposite (thrust) dip-slip sense of motion. During the event, the southern, oceanic edge of the Tobago terrane largely “sunk” into a gravitationally more stable position. Similar earthquakes acting over the past few m.y. can explain the peculiar sunken geomorphic expression of the entire accreted oceanic arc-forearc terrane (i.e., the Aruba-Bonaire-Curacao island chain) in the plate boundary zone.

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Trinidad’s mega-geomorphology records neotectonic ups and downs on edge of the Gulf of Paria pull-apart basin John Weber1, John Ritter2, Carol Prentice3 and Laurent de Verteuil4

1Geology Department, Grand Valley State University, Allendale, MI 49403 USA; [email protected] 2Geology Department, Whittenberg University, PO Box 720, Springfield, OH 45501 USA 3U.S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025 4Latinum Ltd Saddle Road, Maraval, Trinidad

GPS (Global Positioning System) and GPS-to-triangulation geodesy has provided a precise short-term snapshot of Trinidad’s horizontal neotectonics; it is now clear that the Caribbean plate moves ~20 mm/yr eastward relative to South America, and that such dextral wrenching is concentrated on the El Pilar Fault in Venezuela, and on the Central Range Fault in Trinidad. This motion must thus step across the intervening Gulf of Paria (pull-apart basin). Geodesy, however, does a poor job resolving Trinidad’s vertical motions.

We are studying a suite of geomorphic features that record Trinidad’s Quaternary vertical neotectonics. Young (Pleistocene ?) alluvial fans near the southern foot of the Northern Range are elevated and dissected in the east (near Valencia), and buried in the subsurface beneath Caroni swamp deposits in the west (near Port-of-Spain). Northern Range stream valley bottoms and peaks both show a systematic and correlative east-to-west decrease in elevation. Drainage basins in the range tend to widen toward the west. The northern Trinidad coastline is sharp and straight in the east (i.e., emergent), and scalloped and highly embayed in the west (i.e., submergent), with a sharp ~N-S-trending transition (hinge) near Chupara Bay. Uplifted wave-cut marine terraces are present in the high northeastern Northern Range, and the western islands like Monos and Chachachacare are drowned Northern Range peaks.

We interpret that a quasi-rigid block encompassing all of the Northern Range, Northern Basin, and Central Range (and perhaps all of Trinidad) is tilting westward into the Gulf of Paria pull-apart basin. A good semi-quantitative match is obtained in a comparison made between the observed east-to-west elevation changes, the magnitude of crustal stretching in the Gulf (~5 km), and a simple 1-D crustal stretching model. Additional mapping and dating of Trinidad’s geomorphic features are needed to better quantify Quaternary uplift and subsidence rates and to better flesh out the titling model.

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Jamaican Seismicity & The Jamaica Seismograph Network Margaret D. Wiggins-Grandison ([email protected]) The Earthquake Unit, University of the West Indies, Mona, Kingston 7, Jamaica

Jamaica’s seismicity is associated with the proximity of the island to the North America- Caribbean plate boundary on which the sense of faulting is left-lateral. The fault regime on the island itself is predominantly strike-slip, with some reverse faulting in central Jamaica. At least one magnitude 4 event is expected per year and as many as three have occurred in some years. The largest event in recent times occurred in January 1993. The magnitude was 5.4 and the epicentre was located in the Blue Mountains of eastern Jamaica. Intensities of VII were experienced in the epicentral region falling off to IV in western Jamaica. This year a magnitude 5.1 earthquake in central Jamaica triggered intensities of VII in the epicentral area.

However, earthquakes are not new to Jamaica. The history dates back to the 17th century, when in 1692 the city of Port Royal was destroyed. And to date, fourteen earthquakes of intensity VII and higher are documented, along with numerous smaller events. In 1957 a magnitude 6.8 earthquake with epicentre near Montego Bay caused intensities of VIII in western Jamaica. Following this event the Jamaica Seismograph Network (JSN) was started. Annually, about 200 earthquakes on and near to Jamaica are recorded.

The JSN consists of twelve analogue, short-period stations. These are linked in real-time by radio telemetry to the Central Recording Station (CRS) which is located at the Mona campus of University of the West Indies in Kingston. Four stations have three- components while the remaining eight have vertical seismometers only. Mark L-4C 1- Hertz seismometers are used along with Geotech amplifiers, modulators and demodulators. One Guralp CMG 40-T broadband seismograph and DM24 digitiser is located at Mona and there are seven Kinemetrics digital accelerographs installed across the island.

At the CRS the signals are digitized at 50 Hertz using a National Instruments AMUX- 64T 16-bit AD board and a PC-based DOS-driven seismic data acquisition (SDA) system. A Trimble SVee8 GPS is used for timing. The signals are demultiplexed and processed on a PC-based windows-driven seismic data processing (SDP) system. Both the SDA and SDP are products of the Geophysical Institute of Israel. That particular digitizer board and on-board GPS are no longer being manufactured therefore the EQU is embarking on changing from the SDA to SEISLOG data logging software from the University of Bergen (UiB). SEISLOG is more versatile and can be configured to operate with a number of standard digitisers, including Earth Data, SARA and others. SEISAN, also from UiB, running on a UNIX platform is already being used for more advanced data processing and analyses.

In the last five years a number of studies have been conducted using local earthquake data. These include determining a new Jamaican crustal model from inversion of travel times; measuring crustal attenuation using coda and S-wave decay envelopes; and

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modelling the stress regime of the island’s crust by analysing fault plane solutions of local earthquakes.

Reservoir Characterization and Hydrocarbon Implications of the Early Pliocene Deltaic Sedimentary Succession of the Columbus Channel, Trinidad René Winter – MS Candidate, University of Texas, Austin. Ron Steel - Supervisor, University of Texas, Austin Ian Stewar - Advisor, Exploration Advisor, BPTT, Trinidad.

The Pliocene–Pleistocene succession of the Columbus Basin off SE Trinidad has been a prolific hydrocarbon province. A recent stratigraphic initiative achieved basinwide correlation of the stacked, 4th/5th-order sequences of the Plio-Pleistocene shelf succession that record the regional cyclic shelf transits of the Plio-Pleistocene Orinoco Delta. This new stratigraphy has the potential to drive new play concepts that can sustain reserve growth as the current reservoirs mature. Integration of well, outcrop and seismic data between the onshore Southern Basin and offshore Columbus Channel is allowing reconstruction of the evolution of the Early Pliocene shelf margin as it accreted eastwards. The earliest Pliocene growth of the paleo-Orinoco shelf margin in the inner Columbus Channel and back into Venezuela shows a spectacular development of shelf- edge collapse and canyons, suggesting sediment by-pass into the deepwater basin at this time. This rapid regressive growth of the shelf margin reflects a shift and re-organization of the Orinoco Delta into this region. This was followed by a time of significant transgression and eastward backstepping of the delta. Subsequent early Pliocene regression brought the delta back to the shelf edge and initiated a new period of vigorous shelf-margin growth. In contrast to the preceding regressive period, there was now abundant growth-fault development but apparently little canyon generation accompanying shelf-margin accretion. Detailing the role of the paleo-Orinoco and this early history of development of the Orinoco Shelf Margin will involve an integration of seismic and well data with outcrop studies along the south coast of Trinidad.

Origin Of The Caribbean Plate: A View From Aruba And Curacao J. E. Wright and S.J. Wyld, Department of Geology, University of Georgia, Athens GA 30602; [email protected]

Geochemical studies of widely dispersed basaltic igneous rocks believed to be accreted fragments of the Caribbean plate are interpreted to indicate an oceanic plateau origin. Some recent models suggest that the plateau formed in the Pacific and that arrival of the plateau at the subducting boundary of a west-facing arc led to subduction reversal trapping the overthickened plateau crust behind the newly formed east-facing arc. Basaltic lavas and diabasic intrusions on the Leeward Antilles islands of Aruba and Curacao are believed to represent fragments of the Caribbean plate. Detailed mapping coupled with ongoing geochronological investigations of these islands, leads us to an alternative model for the development of the Caribbean plate. Field relations on Aruba and Curacao indicate that both islands became emergent in the Late Cretaceous. Basalt and diabase on both islands exhibit abundant evidence for Late Cretaceous weathering .

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In addition, on Aruba a distinctive unit of Late Cretaceous basaltic accretionary tuff overlies weathered basalt and diabase, further indicating subaerial conditions. Following emergence , the geologic evolution of the two islands significantly diverged. Aruba underwent regional deformation and metamorphism prior to emplacement of a tonalite batholith at 89 ± 1Ma, whereas Curacao records subsidence and deep marine sedimentation. We suggest that the basaltic rocks on Aruba and Curacao formed at the intersection of a spreading ridge and mantle plume. While both islands were above the plume thermal anomaly they ultimately became emergent and underwent subaerial erosion. Following this Aruba was partially subducted beneath an east-facing arc along with the mantle plume. Curacao moved off the axis of the thermal anomaly due to sea- floor spreading, subsided and continued to receive hemipelagic sedimentation while Aruba was still at depth. Subduction of the mantle plume led to crustal thickening in the backarc region producing the overthickened crust of the Caribbean plate.

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