Discover Puerto Rico and Explore the Fossils & Geodiversity of the Caribbean and Greater Antilles
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Puerto Rico is a tropical island rising from the Caribbean Sea and Atlantic Ocean and features a volcanic Cordillera Central, limestone Northern Karst Belt, and diverse coastal plains. Fossils from the San Sebastián Formation and Ponce Limestone reveal Oligocene to Holocene marine and terrestrial life, while coral reefs, raised terraces, and El Yunque National Forest highlight dynamic landscapes shaped by tectonics and climate change. Easily accessed via San Juan, Puerto Rico combines volcanic peaks, karst formations, and fossil assemblages that make it a geotourism hotspot in the Caribbean.
Rising from the turquoise waters of the Caribbean Sea and the Atlantic Ocean is Puerto Rico located at the northeastern edge of the Caribbean Plate. The island forms a mountainous arc shaped by tectonic forces, volcanic activity, and marine sedimentation over more than 135 million years. Its central Cordillera Central mountains, Northern Karst Belt, and coastal plains that tell a deep time story over a number dramatic landscapes.
Easily accessible via direct flights to San Juan from North America and Europe, Puerto Rico sits east of Hispaniola and west of the Virgin Islands. Its strategic location makes it a natural gateway to the Caribbean. Visitors can explore golden beaches along the northern Atlantic coast, calmer southern Caribbean shores perfect for snorkeling and sailing, and the interior mountains for rainforest trekking.
At the island’s core lies the Cordillera Central, a steep volcanic and plutonic mountain range formed during the Early Cretaceous through volcanic island arc processes. The Cordillera Central forms the mountainous backbone of Puerto Rico, recording over 120 million years of volcanic island arc activity linked to tectonic interactions between the Caribbean Plate and the North American Plate. Built from Cretaceous to Eocene volcanic lava flows, breccias, sedimentary turbidites, and resistant intrusive rocks such as diorite and granodiorite, the range reflects a complex subduction-driven geological history within the Greater Antilles. Deep erosion has sculpted steep slopes and rugged ridges, while major fault zones divide the mountains into southwest, central, and northeast structural blocks. Serpentinite belts and metallic mineralization, including nickel, cobalt, iron, and chromium, highlight the region’s volcanic origins and later tectonic deformation.
Beyond the Cordillera Central, Puerto Rico’s geology is organised into three major provinces: the volcanic mountains, extensive limestone carbonate regions, and low-lying coastal plains shaped by marine processes. Some of the island’s oldest rocks, found in Sierra Bermeja, may represent fragments of ancient oceanic crust, pointing to a long and dynamic tectonic evolution. The island sits along an active plate boundary, where compression, faulting, and uplift continue to reshape the landscape and drive frequent earthquakes.
Just north of Puerto Rico lies the Puerto Rico Trench, the deepest feature in the Atlantic Ocean, formed as the North American Plate subducts beneath the Caribbean Plate. This immense tectonic system influences seismic activity, tsunami risk, and regional volcanism across the Caribbean.
Stretching from Aguadilla to Loíza the Northern Karst Belt (Cinturón del Carso Norteño) spans roughly 1,600 km², covering about 20% of Puerto Rico’s north coast and is among the Caribbean’s most extensive tropical karst regions. This limestone region, formed from Middle Oligocene to Miocene deposits such as the Aymamón and Aguada limestones, is renowned for its dramatic topography of mogotes, sinkholes, and caves.
The Aymamón and Aguada limestones of northern Puerto Rico preserve an exceptional Middle to Late Miocene fossil record that documents a warm, shallow tropical sea once covering the island’s northern coast. These marine limestone formations are rich in bivalves, gastropods, corals, benthic foraminifera, and bryozoans, reflecting thriving reef and lagoon ecosystems. The Aymamón Limestone is particularly famous for large oysters such as Ostrea haitensis, diverse molluscs, coral reef remnants, and remarkable vertebrate discoveries from Isabela, including Megalodon shark teeth dated to roughly 16.4 to 11.2 million years ago. These fossils confirm the presence of giant prehistoric sharks in the Caribbean during the Miocene epoch. In contrast, the slightly more ferruginous Aguada Limestone records calm back-reef and shallow lagoon environments enriched with red algae, shell beds, and microfossils. Together, these fossil-rich units offer valuable insights into ancient sea levels, reef evolution, and the dynamic coastal environments that shaped Puerto Rico’s geological past.
The Northern Karst Belt also hosts complex hydrological systems, including the Camuy River and underground rivers that sustain wetlands like Caño Tiburones, while providing a vital aquifer for freshwater supply. Rich in biodiversity, the region supports endemic forests and wildlife, and landmarks like the Arecibo Observatory highlight its unique geological character, making the Northern Karst Belt a key site for conservation, ecotourism, and scientific study.
Río Camuy Cave Park exemplifies these subterranean wonders, with multi-level rivers, collapsed chambers, and fossiliferous walls preserving both marine and terrestrial remains. The karst functions as a natural aquifer, supplying freshwater while offering rare geological and ecological insights. Visitors can explore stalactites, stalagmites, and fossil deposits that illuminate island evolution and Caribbean paleoenvironments.
Puerto Rico’s fossil record spans the Oligocene to Holocene, offering unique insights into Caribbean evolution. The San Sebastián Formation in northwestern Puerto Rico preserves early terrestrial fossils, including the oldest known common coquí frog (Eleutherodactylus), rodents, Aktiogavialis puertoricensis an extinct species of gavialid (gharial) crocodilian, sirenian sea cows, and sharks. Meanwhile, the Ponce Limestone in the southwest contains rich Miocene-Pliocene marine fossils, including corals, mollusks, decapods, and large foraminifera. Quaternary cave deposits across the island reveal Pleistocene vertebrates, including extinct ground sloths of Acratocnus, Neocnus and endemic rodents, insectivores, and diverse bats. Recent discoveries of 6-million-year-old Sebecid land-crocodiles hint at ancient dispersal events from South America.
Puerto Rico’s coastal zones display contrasting geological provinces. The northern coast, narrow and exposed to higher wave energy, features terrigenous sediments and rugged cliffs. In contrast, the east, south, and west coasts form carbonate platforms with coral reefs, shallow lagoons, and calm waters ideal for snorkeling, scuba diving, and marine biology exploration. Coral fossils in raised marine terraces along the southern coast provide evidence of past sea-level changes, combining tectonic uplift and glacial–interglacial cycles. Despite environmental pressures, including sediment influx and overfishing, these reefs remain critical for biodiversity, tourism, and conservation.
Inland, El Yunque National Forest offers lush rainforest experiences unmatched in the Caribbean. Waterfalls cascade through dense canopies alive with endemic wildlife, including tropical birds, and insects. Misty trails reveal the interplay of geology and ecology, as streams cut through volcanic substrates and weathered limestone, creating nutrient-rich soils that sustain tropical flora.
Old San Juan the historic heart of Puerto Rico, known for its colourful Spanish colonial buildings, blue cobblestone streets, and massive 16th-century fortresses like Castillo San Felipe del Morro invites exploration alongside modern culinary and nightlife experiences. Local cuisine reflects the island’s environment: slow-roasted lechón, fresh seafood, tropical fruits, and locally distilled rum connect visitors to centuries of agricultural and coastal traditions.
The island remains tectonically active due to subduction at the Puerto Rico Trench, generating earthquakes, uplift, and faulting. This activity has sculpted rugged terrain, raised terraces, and dramatic coastlines. Conservation efforts aim to protect fragile marine and terrestrial habitats, including the Northern Karst Belt, coral reefs, and cave ecosystems.
From Cretaceous submarine volcanoes and rudist reef frameworks to Oligocene coastal ecosystems and Pleistocene cave faunas, Puerto Rico showcases the major geological and biological processes shaping Caribbean island arcs. Visitors can hike volcanic peaks, descend into limestone caves, kayak through bioluminescent waters, and study fossil-bearing riverbeds. Puerto Rico is a unique destination for curious visitors providing unparalleled access to Earth’s history, from Cretaceous volcanic arcs to Ice Age vertebrates.
