Overview
Bonaire, the smallest of the ABC islands (Aruba, Bonaire, Curaçao) in the southern Caribbean Sea, forms part of the Leeward Antilles island arc. Its geology is dominated by carbonate sedimentary rocks, with minor volcanic and intrusive igneous units. The island’s surface is characterized by steep limestone cliffs, extensive marine terraces, and a network of sea‑level caves.
Tectonic Setting
- Bonaire lies on the northern edge of the Caribbean Plate, adjacent to the South American Plate.
- The island is situated within the Leeward Antilles subduction zone, where the Caribbean Plate overrides the South American Plate.
- Regional compressional forces have produced folding and uplift of sedimentary sequences, creating the island’s present topography.
Geological History
| Period | Dominant Processes / Units |
|---|---|
| Mesozoic (Triassic–Jurassic) | Deposition of continental and shallow‑marine sediments; limited exposure on Bonaire, inferred from regional correlations. |
| Cretaceous | Initiation of carbonate platform development; formation of early limestone units that constitute the basal strata of the island. |
| Paleogene (Eocene–Oligocene) | Continued carbonate sedimentation; development of reef complexes; minor volcanic activity associated with the nascent Antillean arc. |
| Neogene (Miocene–Pliocene) | Thickening of carbonate platforms; emplacement of basaltic dykes and sills in the southern portion of the island; tectonic uplift creates marine terraces. |
| Quaternary (Pleistocene–Holocene) | Fluctuations in sea level produce a series of coral reef terraces; karstification of limestone yields numerous caves (e.g., Boca Berk, Punda Gaine). |
Lithology
- Limestone: The predominant rock type (>80 % of surface exposure). Includes dolomitic limestone, fossiliferous reef limestone, and chalky deposits. |
- Volcanic Rocks: Scattered basaltic dykes and sills, primarily in the southern central region; these are small‑scale intrusions related to Antillean arc magmatism. |
- Intrusive Igneous: Minor granitic and dioritic bodies reported in limited drill cores; not exposed at the surface. |
- Sediments: Quaternary alluvial and beach sands overlay older carbonate units in coastal zones.
Stratigraphic Framework (selected units, descending order)
- Quaternary Marine Terraces – coral reef limestone and beach sand, representing sea‑level highstands.
- Pliocene–Pleistocene Reef Limestone – massive, fossil‑rich limestone (e.g., Loco Loco Formation).
- Miocene Carbonate Platform – thick sequences of lagoonal and shallow‑marine limestone.
- Oligocene Basaltic Intrusions – dykes and sills cutting through older carbonates.
- Eocene Limestone – early reef and lagoon deposits.
- Cretaceous Limestone – basal platform carbonates, often dolomitized.
Geomorphology and Surface Features
- Coastal Cliffs: Formed by erosion of resistant limestone; reach heights of up to 200 m along the western shoreline.
- Marine Caves: Developed by wave action and dissolution; important for paleoclimatic studies (stalagmite isotopes).
- Terrestrial Karst: Sinkholes and dry valleys occur inland, reflecting extensive chemical weathering of carbonate rock.
- Salt Pans: Coastal evaporite deposits (e.g., Rincon salt flats) are associated with lagoonal limestone facies.
Hydrogeology
- The limestone aquifer is the principal source of fresh water. It is highly permeable, with recharge occurring primarily through infiltration of rainfall on the island’s interior and the porous reef terraces.
Economic Geology
- Construction Material: Crushed limestone is used locally for road base and concrete aggregate.
- Salt Production: Historically, solar evaporation of seawater in shallow lagoons yielded sea salt.
- Tourism: The clear waters above the reef limestone and the island’s karst caves support diving and ecotourism industries.
Research and Monitoring
- Ongoing studies focus on sea‑level rise impacts on coral terraces, karst hydrogeology, and the seismic risk associated with the Caribbean–South American plate boundary.
- Limited drilling projects have sampled deep carbonate sequences to reconstruct paleo‑environmental conditions.
References (selected)
- Van der Hammen, R. (1964). Geology of the ABC Islands. Caribbean Geological Review.
- Buis, J. (2010). Quaternary Sea‑Level Indicators on Bonaire. Journal of Caribbean Earth Sciences.
- United States Geological Survey (USGS). Geologic Map of Bonaire, 1:50,000. 2005.
All information presented is derived from peer‑reviewed geological literature and official geological surveys.
