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| Arecibo Limestone | |
|---|---|
| Name | Arecibo Limestone |
| Type | Formation |
| Period | Late Oligocene–Miocene |
| Primary lithology | Limestone, dolomite |
| Other lithology | Marl, phosphorite |
| Region | Puerto Rico, northern Caribbean |
| Named for | Arecibo |
Arecibo Limestone
The Arecibo Limestone is a Cenozoic carbonate formation of northern Puerto Rico known for its fossiliferous limestones, dolomites, and phosphatic horizons. It has been studied in contexts ranging from regional Caribbean Plate tectonics to local hydrogeology and engineering projects in municipalities such as Arecibo, Puerto Rico, Manatí, Puerto Rico, and Isabela, Puerto Rico. Researchers from institutions including the United States Geological Survey, University of Puerto Rico, and international partners have integrated stratigraphic, paleontological, and geochemical data to interpret its depositional history.
The formation consists predominantly of massive to bedded carbonate lithologies including micritic and bioclastic limestone, dolomitized successions, and interbedded marls with localized phosphatic nodules. Lithofacies range from peloidal and packstone textures to boundstone dominated by framework builders such as corals and coralline algae, with diagenetic overprints producing stylolites and recrystallized sparry calcite. Petrographic studies have referenced techniques used at facilities like the Smithsonian Institution and analytical methods comparable to those at the Scripps Institution of Oceanography and the Lamont–Doherty Earth Observatory to characterize porosity, matrix composition, and trace-element signatures. Structural mapping relates the unit to fold-and-thrust features associated with the interaction of the North American Plate and the Caribbean Plate, and outcrops show karstic weathering similar to carbonate terrains documented in Florida and the Bahamas.
Stratigraphically, the unit overlies older Paleogene deposits and is unconformably overlain by younger Neogene and Quaternary sediments associated with coastal plains and reefal sequences near Ponce, Puerto Rico and San Juan, Puerto Rico. Biostratigraphic control derives from foraminifera, mollusks, and coral assemblages correlated with stages recognized in International Commission on Stratigraphy chronologies and regional frameworks used by the Geological Society of America. Radiometric constraints and correlation with isotope stratigraphy, including correlations to shifts recorded in the Oxygen isotope record and regional events such as the Messinian Salinity Crisis, place much of the succession in the Late Oligocene to Miocene timeframe, with local variation reflecting tectonically driven accommodation changes.
Facies analysis indicates deposition primarily in shallow tropical to subtropical marine settings including protected lagoons, shallow open-shelf carbonates, and fringing reef environments analogous to those documented in contemporaneous deposits of the Greater Antilles and Yucatán Peninsula. Paleoenvironmental reconstructions draw on comparisons to carbonate platform models developed for the Bahamas Bank, the Florida Platform, and Miocene reef tracts of Cuba and the Dominican Republic. Sea-level oscillations recorded in global eustatic charts and plate reconstructions such as those by the Paleomap Project influenced stacking patterns, while paleocurrent and isotopic data hint at episodic upwelling and phosphogenesis related to oceanographic features traced in studies of the Caribbean Sea and Atlantic Ocean gateways.
The fossil assemblage includes diverse benthic foraminifera, scleractinian corals, bivalves, gastropods, echinoids, and coralline algae, permitting paleoecological comparisons with faunas cataloged at institutions like the American Museum of Natural History and the Natural History Museum, London. Microfossil suites have facilitated biozonation tied to frameworks developed by paleontologists studying Neogene microfaunas from the Tethys-derived provinces and the Panama Isthmus closure interval. Notable taxa resemble those reported from Miocene Caribbean reefs, often referenced in monographs by researchers affiliated with the Smithsonian Tropical Research Institute and the Royal Society. Trace fossils and bioturbation indicate active benthic communities, and occasional vertebrate remains have been compared to regional records of marine mammals and fishes curated by museums such as the Caribbean Museum Center for Arts and Culture.
Prominent exposures occur along coastal cliffs, river gorges, and road cuts near Arecibo, Puerto Rico, the Río Grande de Arecibo, and coastal sectors facing the Atlántico Norte (Atlantic Ocean), with classic sections documented in geological surveys and map compilations by the United States Geological Survey and the Puerto Rico Department of Natural and Environmental Resources. These localities have been used for academic field courses by universities including the University of Puerto Rico Río Piedras Campus and international field programs organized by the Society for Sedimentary Geology (SEPM). Comparisons are frequently drawn with coeval Caribbean carbonate units exposed in Hispaniola, Jamaica, and Cuba.
The carbonate rocks serve as important aquifers within karstified zones supplying groundwater to municipalities, implicating agencies such as the Puerto Rico Aqueduct and Sewer Authority and studies by the Environmental Protection Agency. Quarrying of limestone and dolomite has supported local construction, aggregate, and cement raw material industries, interfacing with regulatory frameworks of the Puerto Rico Planning Board and environmental assessments reviewed by the National Oceanic and Atmospheric Administration. Phosphatic horizons have attracted attention for nutrient resource potential and for their role in paleoceanographic studies linked to basin-scale phosphogenesis researched by geoscientists at the University of Texas at Austin and the Massachusetts Institute of Technology.
Category:Geologic formations of Puerto Rico