Toa Baja Research Articles

Retinitis Pigmentosa in the Puerto Rican Population: A Geographic Distribution.

BackgroundPrevious studies have reported on retinitis pigmentosa (RP) in Puerto Rico. Information on the geographic distribution of RP mutations in Puerto Rico may lead to higher rates of diagnosis and co-management. We aimed to evaluate whether there are areas with increased incidence of genes leading to RP in the Island.Materials and MethodsWe conducted a non-concurrent prospective study on the genotype of 241 patients with RP in Puerto Rico. We evaluated their townships to determine whether there are clusters of genes leading to RP. Genetic studies were done using the Invitae inherited retinal diseases panel analyzing 330 genes.ResultsA total of 100 patients were evaluated. Clusters of patients with mutations were found in certain townships. As depicted in the map, a cluster of patients with a mutation in the PDE6B gene was found in San Juan (9), those with the BBS1 gene occurred in San Juan (6) and Bayamón (4), mutations on the USH2A gene were found in Toa Baja (5), mutations in the CRB1 gene appeared in Ciales (4), and mutations in the BBS7 were found in Aibonito (2). Other mutations are scattered throughout the Island.ConclusionClusters of mutations were identified in several townships including San Juan, Bayamón, Toa Baja, Ciales, and Aibonito. Some of these are isolated geographically. Additional mutations were identified but only the most pertinent were reported. Genetic studies are warranted in all patients with RP in Puerto Rico.

Medical and psychosocial needs of the Puerto Rican people after Hurricane Maria

ABSTRACTA community clinic in Puerto Rico, the Bantiox Clinic, was developed to serve the medical needs of Toa Baja and the surrounding communities after Hurricanes Irma and Maria in response to an urgent need for medical treatment of the community residents. Within 4 months, the clinic had 4941 total visits. The Toa Baja residents used the clinic more than the offsite residents. Certain offsite towns needed medical care more than others, suggesting a lack of medical access in the mountainous areas. Elderly patients with chronic diseases were served more than younger patients. Hypertension, diabetes, and medication refills appeared to be the primary reasons for treatment. The suicide rate increased 16% from 2016. The unemployment rate and the migration rate in all occupations have continued to increase after Hurricane Maria. Puerto Rico is a human laboratory that shows the medical needs of an island after devastating climate events and provides insight on ways to better prepare for such emergencies.

Manatee Mortality in Puerto Rico.

/ The most pressing problem in the effective management of the West Indian manatee (Trichechus manatus) in Puerto Rico is mortality due to human activities. We assessed 90 cases of manatee strandings in Puerto Rico based on historical data and a coordinated carcass salvage effort from 1990 through 1995. We determined patterns of mortality, including type of event, condition of carcasses, spatial and temporal distribution, gender, size/age class, and the cause of death. The spatial distribution of stranding events was not uniform, with the north, northeast, and south coasts having the highest numbers. Six clusters representing the highest incidence included the areas of Fajardo and Ceiba, Bahía de Jobos, Toa Baja, Guayanilla, Cabo Rojo, and Rio Grande to Luquillo. The number of reported cases has increased at an average rate of 9.6%/yr since 1990. The seasonality of stranding events showed a bimodal pattern, from February through April and in August and September. Most identified causes of death were due to human interaction, especially captures and watercraft collisions. Natural causes usually involved dependent calves. From 1990 through 1995, most deaths were attributed to watercraft collisions. A reduction in anthropogenic mortality of this endangered species can be accomplished only through education and a proactive management and conservation plan that includes law enforcement, mortality assessment, scientific research, rescue and rehabilitation, and inter- and intraagency cooperation.

Diagenesis of Middle Tertiary carbonates in the Toa Baja Well, Puerto Rico

The Toa Baja Well drilled in northern Puerto Rico to adepth of 2705 m (8872 ft.) penetrated over 550 m (1800 ft.) of Tertiary carbonates. The limestone‐dominated portion of the well consists mostly of shallow‐water backreef carbonates. Metastable carbonates have been either calcitized, dolomitized or dissolved. The pétrographie character of the Tertiary carbonates in the Toa Baja Well, and those reported by Monroe [1980], the cathodoluminescence petrography, and the stable isotopic compositions indicate that these carbonates were rapidly cemented in the marine environment (limiting compaction), that replacement of metastable carbonates by calcite and precipitation of sparry calcite took place mostly in meteoric diagenetic environments and dolomitization probably occurred in a meteoric‐marine mixing zone. Given the history of numerous drainage systems that dissected the Tertiary carbonates throughout their depositional history [Monroe, 1980] and the repeated Cenozoic sea level oscillations [Monroe, 1980; Seiglie and Moussa, 1984], it is likely that alteration of metastable carbonates took place during lowstands. Interstratified fluvial deposits suggest the continued influence of meteoric fluids in local highlands [Monroe, 198O].

Carbon and oxygen stable isotopes in the Toa Baja Well, Puerto Rico: Implications for burial diagenesis and hydrocarbon generation

The Toa Baja Well was drilled on the coastal plains of northern Puerto Rico with a total depth of 2705 m [Larue, 1990]. Interstratified limestone, quartz‐bearing calcareous sandstones, and shales dominate the uppermost 580 m and are separated from underlying rocks by an unconformity. Below this unconformity continuing to total depth, lithologies encountered consist of volcaniclastic sandstones/siltstones, pelagic carbonates, volcanic flows and either plutonic rocks or coarse‐grained immature sandstones derived from plutonic bodies.Stable isotopic data of carbonates suggest diagenetic modification under a meteoric and meteoric‐marine mixing environments for sediments above 915 m. A fracture zone near 915 m coincides with an abrupt shift in δ18O compositions indicating the presence of hotter fluids during alteration of these sediments. The depleted δ13C signatures occurring above a fault at 1220 m are suggestive of isotopically light gaseous hydrocarbons migrating through the fault and being oxidized as they dispersed through the sediment column. The abrupt shift in δ18O compositions and its coincidence with the fracture zone at 915 m suggest geopressuring and thermal buildup due to accumulation of hotter, upward migrating formational fluids. Estimated burial temperatures for the interval above 915 m do not exceed 40°C and are possibly lower due to circulating colder meteoric fluids. Maximum estimated burial temperatures for sediments below 915 m range from 80° to a a maximum of 150°C at 2400 m. The data suggests that the bulk of the sediment pile has not been exposed to temperatures above the oil window and possibly hydrocarbons have been generated deeper in the basin.

Clay mineral and zeolite diagenesis in the Toa Baja Well, Puerto Rico

Several diagenetic reactions typical of volcaniclastic sediments have been identified in the Toa Baja well. The zeolites heulandite and (less commonly) analcite, present in the upper half of the drilled section, give way to laumontite at depth. A decrease with depth in the expandability of mixed layer chlorite/smectite was observed. Corrensite was detected over the depth range 1676–2286 m. Temperatures implied by the depth ranges of diagenetic and indicator minerals are consistent with a paleothermal gradient of about 30–50°C/km, assuming little or no erosion of section.

Origin of reflectors in seismic line 2, Toa Baja, Small gas horizons associated with enhanced reflector amplitudes, and recognizing leaky and sealing faults using gas chromatography data

Reflectors imaged in a multichannel seismic line at Toa Baja, Puerto Rico, were studied by comparing the positions of reflection events with changes in rock properties determined through analysis of logs and cuttings. Reflectors appear to be associated primarily with changes in rock properties across facies or formation boundaries, and more rarely unconformities and faults. Faults that seal versus faults that leak can be recognized on the basis of gas Chromatograph data. Several laterally discontinuous reflectors characterized by modest amplitude anomalies seem to correlate in depth with minor shows of methane gas, measured by onsite gas chromatography. Gas was not recognizeable using geophysical logs indicating small quantities. The gas is apparently associated with rock types and rock properties which affect reflector amplitude rather than directly enhancing reflector amplitude.

The Toa Baja Drilling PRoject and current studies in Puerto Rican geology: Introduction and summary

This volume concerns information learned by drilling the Toa Baja well on the north coast of Puerto Rico, and current studies of Puerto Rican geology and tectonics.The Toa Baja Drillsite is located in the North Coast basin of Puerto Rico about 10 km west of San Juan. The hole was spudded on August 23, 1989, and plugged and abandoned on November 7,1989 at a total depth of 2704m. Two lithologies were encountered during drilling: an upper series consisting of Oligocene‐Miocene shallow‐water limestone and sandstone facies, and a lower series consisting of Eocene deep‐water volcaniclastic strata, including some lava flows or shallow intrusions, pelagic marls, and altered igneous rocks or coarsegrained sandstones. Principal findings made during drilling include: 1) the important unconformity separating the upper and lower series at about 579 m; 2) 8 faults defined clearly by dipmeter log; 3) changes in rock type probably associated with reflection events in seismic reflection profiles crossing the drillsite; 4) confirmation of overall low geothennal gradients and heat flow, but presence of a thermal anomaly near 2683 m; 5) documentation of high paleogeothermal gradients using petrographic, isotopic, X‐Ray diffraction and electron microprobe studies; 6) presence of fractures indicating a current extensional tectonic setting.Current studies in the Puerto Rico region include: 1) paleomagnetic evidence for Late Miocene counterclockwise rotation; 2) geochemical evolution of Cretaceous and Eocene igneous rocks; 3) evidence of transtension in the northeast Caribbean plate boundary zone; 4) results of studies of ancient fault zones on Puerto Rico; and 5) stratigraphic studies of the Tertiary of Puerto Rico.

Paleontology of the Toa Baja #1 Well, Puerto Rico

The Toa Baja well penetrated 585.2 m of fossiliferous Oligocene and Miocene limestone, sandstone, and shale above 2119 m of Eocene, dominantly volcaniclastic strata. Oligocene and Miocene rocks were deposited on a broad, shallow shelf. The unconformity between Eocene and Oligocene strata spans at least the Late Eocene, and probably part of the Early Oligocene at Toa Baja. Below the unconformity, unfossiliferous volcaniclastic and igneous rocks are interstratified with fossiliferous limestone beds containing Middle and possibly late Early Eocene planktic foraminifera probably deposited in deep water. No Paleocene or Cretaceous fossils were recovered.

Observations of wellbore failure in the Toa Baja Well-Implications for the state of stress in the North Coast Tertiary Basin, Puerto Rico

Borehole televiewer (BHTV) and 4-arm caliper (dipmeter) logs were obtained in the Toa Baja well (drilled to a depth of 2704 m into sediments of the North Coast Tertiary Basin, Puerto Rico) from 704 to 2676 m depth. The only observations suggesting that stress-induced wellbore failure (breakouts) had occurred were small intermittent features at a depth of approximately 2600 m with azimuths of 70° and 250° and the fact that, during drilling, wellbore stability became a problem near total depth. An increase in mud weight to 10 Lb/gal required to stabilize the deteriorating wellbore was accompanied by loss of drilling fluid into the formation, suggesting that hydraulic fracturing or the reopening of pre-existing near vertical fractures had occurred. A series of vertical fractures at a variety of azimuths (averaging N3l°W) was detected by the BHTV. The loss of circulation due to an increase in mud weight, combined with the absence of well-developed breakouts, enables us to estimate stress magnitudes near the well for reasonable values of rock strength: S1=Sv; S3=Shmin ≈ 0.5v; SHmax ≈ (0.55–0.63)Sv, and an associated incipient normal faulting stress regime. This stress regime is consistent with focal mechanisms determined for earthquakes with epicenters near the drillsite.

Geophysical logs from the Toa Baja Scientific Drillhole, Puerto Rico

Geophysical logs from the Toa Baja drillhole on the north central coast of Puerto Rico are used to distinguish the variation in physical properties with depth in this non‐volcanic island arc massif. A marked unconformity separates shallow Oligocene to Miocene limestones with considerable permeability contrast from a deeper sequence of volcaniclastic rocks with decreasing shaliness. A volcanic sill or flow overlying a strongly mineralized zone is found to cause the impedance contrast responsible for the strong seismic reflection anomaly (bright spot) that was the exploration target.

Milankovitch Cycles in electrical resistivity logs from the Toa Baja Scientific Drillhole, Puerto Rico

Milankovitch cycles in the upper part of the Toa Baja drillhole, detected by geophysical logs, are used to estimate sedimentation rates, and to localize the depths at which sedimentation rate changes occur. The log‐derived age information is then combined with reference dates from palaeontological data and the “Vail” global sea‐level curve to build a detailed record of the chronology of the upper stratigraphic sequence in the well.

Structural analysis of cores and cuttings from the Toa Baja (Puerto Rico) Borehole

Deformation structures in core samples and well cuttings from the Toa Baja borehole in Puerto Rico, obtained from depths of 580 to 2700 meters, can be divided into two major categories: (1) structures resulting from compression and shear and (2) structures formed by extension. Generally, the first ones are older and they are somewhat more abundant at horizons where fault zones occur as deduced from dipmeter readings and televiewer log. These structures may have formed during an Eocene thrusting event, recognized regionally in Puerto Rico. The extensional structures which almost always crosscut the compressional ones are filled with zeolite, calcite, prehnite, or quartz. There is poor correspondence between the abundance of these fractures and the position of the major fault zones. The largest abundance of veins occurs between 1700 and 2100 meters depth. They may be related to a phase of regional extension during the Late Paleogene.

Wellbore heat flow from the Toa Baja Scientific Drillhole, Puerto Rico

Heat Flow values, determined from temperature logs and estimates of thermal conductivity from geophysical logs range from 23 to 37 mW/m2 from 800 to 2500 m depth in the Toa Baja scientific drillhole on the north, central coast of Puerto Rico. Near the target seismic reflector at the base of the well, an active hydrothermal system was encountered in which heat flow of up to 90 mW/m2 was found in a mineralized zone beneath a volcanic sill or flow. The heat flow then dropped to 50 mW/m2 beneath this subhorizontal flow zone. The mining of heat from downdip is proposed to account for this thermal anomaly, as well as the scatter in the heat flow determined from the few other wells drilled into Puerto Rico. The time‐temperature history of the well indicates that Eocene volcaniclastics of the lower 2 km were deposited into a geothermal gradient of 60°C/km north of an active arc (heat flow estimated to have been 120–180 mW/m2). Uplift, erosion and cooling occurred between 40 and 30 Ma. Reburial and deposition of Oligocene‐Miocene Limestones produced the present‐day geothermal gradient of 15 °C/km (heat flow of 30–50 mW/m2). Based upon comparisons with slab cooling models, the crustal thickness beneath Puerto Rico is estimated to be closer to continental than oceanic.

Zeolite to prehnite‐pumpellyite facies metamorphism in the Toa Baja Drill Hole, Puerto Rico

Secondary mineral assemblages in Eocene volcanic and volcaniclastic rocks of the Toa Baja drill hole progressively change as a function of depth. Four metamorphic zones are delineated with increasing depth: Caclinoptilolite→heulandite→laumontite→prehnite–purnpellyite zone. The deepest belongs to the prehnite‐pumpellyite facies, whereas the three zones at shallower depths (<2350 m) belong to the zeolite facies. Ca‐clinoptilolite and heulandite exhibit continuous solid solution with varying Si/Al (2.9–5.2) and Ca/(Ca+Na+K) ratios (0.45–0.89). Pumpellyites are characterized by extensive variation in the Fe/(Fe+Al+Mg) ratio (0.29–0.74) and extreme Fe‐enrichment in the laumontite zone. Temperatures estimated from mineral assemblages and fades transitions suggest that the North Coast Basin, Puerto Rico, has been subject to a metamorphic field gradient of ∼50 to 70°C/km.

Geologic implications of the oxygen isotope profile of the Toa Baja Drill Hole, Puerto Rico

The whole‐rock O‐isotopic compositions of volcanic and volcaniclastic samples from the Toa Baja drill hole demonstrate that low‐temperature (<200°C) processes have strongly enriched the island arc materials in 18O. Subsequent to eruption, processes such as subaerial weathering, alteration during transport and deposition in volcaniclastic aprons, submarine weathering, burial diagenesis, and prograde regional metamorphism through the beginning of the prehnite‐pumpellyite facies have raised average whole‐rock δ18O values by ∼4‰ for basalt and andesite lava flows, and by ∼8‰ for volcaniclastic sandstones. These O‐isotopic disturbances were probably caused by oxygen exchange with regionally circulating seawater under rather high water/rock conditions. The processes associated with “ageing” of volcanic and volcaniclastic materials in the oceanic environment are probably more important to the global budgets of the oxygen isotopes than has been assumed in the past. Integration of these results into global models for the oxygen isotopes awaits analysis of more varied oceanic terranes, to determine the generality of the O‐isotopic conclusions preferred here, and to more carefully evaluate the relative sizes of volcanic, volcaniclastic, and oceanic oxygen reservoirs and their variabilities in time.

Rb‐Sr and Sm‐Nd isotopic characterization of Eocene volcanic and volcaniclastic rocks from Puerto Rico

Sm‐Nd and Rb‐Sr data are presented for six volcanic and volcaniclastic samples from the Eocene belt and the Toa Baja drill hole of Puerto Rico in order to provide a preliminary isotopic description of Greater Antilles arc rocks. The lava samples have trace and rare earth element compositions typical of island arc rocks. The isotopic compositions of the volcaniclastic samples are displaced from those of the lavas, and suggest that they include an authigenic or detrital crustal component. The similarity of Sr and Nd isotopic ratios of Puerto Rican lavas and northern Lesser Antilles volcanic rocks suggests that they may have been produced from similar magma sources.

Stratigraphy, geochemistry and mineralogy of Eocene rocks from the Toa Baja Drillhole

The stratigraphy of the Eocene rocks of the Toa BaJa drillhole is dominated by volcaniclastic sediments which are interbedded with marly pelagic limestones, especially in the lower part of the hole, and lava flows. Petrological, geochemical and paleontological evidence suggest that the site of deposition was a deep marine basin and the source of the volcanics were subaerial or shallow submarine island arc volcanoes.

Cross section through the Toa Baja Drillsite: Evidence for northward change in Late Eocene deformation intensity

A 55 km geologic cross section through the Toa Baja Drillsite, generated by integrating geologic mapping data from the foothills of the Central Mountains of Puerto Rico with onshore and offshore multichannel seismic reflection data, provides an opportunity to examine in profile from the arc interior northward to within 40 km of the current trench slope break. Three structural divisions are recognized. In the foothills of Puerto Rico, Cretaceous and Eocene rocks are separated by transpressional strike‐slip faults. In the vicinity of the Toa Baja drillsite where both seismic reflection and borehole data are available, Eocene rocks, deformed by thrust faults, lie above a lower unit, interpreted to be of Cretaceous age. Offshore, north of the drilling site, seismic reflections suggest Eocene rocks onlap structural basement, thought to be Cretaceous rocks, and both units appear only slightly deformed. All Eocene and Eocene (?) rocks are overlain by little deformed Oligocene to Recent rocks. From south to north, or from the arc massif interior toward the present‐day trench, there is an apparent decrease in amount of Late Eocene to Middle Oligocene strike‐slip and shortening deformation. Deformation events occurred mostly in the arc‐interior and were not directly associated with the plate boundary which was probably near the Puerto Rico Trench.

Acoustic televiewer log images of natural fractures and bedding planes in the Toa Baja Borehole, Puerto Rico

Although borehole conditions made acoustic televiewer logging difficult in the Toa Baja borehole, more than 180 meters of continuous, acceptable quality televiewer logs were obtained in the intervals from 730 to 880 meters and from 2,515 to 2,675 meters in depth, indicating the presence of fractures that appear to be open in situ. Most of the largest, possibly open fractures in these intervals are either nearly parallel to directions given by the dipmeter log and may represent solution openings or minor washouts along bedding planes, or dip steeply to the south or southwest across bedding. The televiewer log confirms the presence of an apparently open set of fractures near 867 meters in depth, where circulation was lost during drilling, and in the interval from 2,600 to 2,650 meters in depth, where the temperature log indicates anomalous heat flow in the surrounding formation.