Geological History

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Miocene

During the Miocene (some 23 to 5 million years ago), sedimentation of volcanic materials and those generated by the erosion of surfaced lands continued.  Compaction and consolidation of these materials generated sedimentary rocks.  At the same time, along the Talamanca mountain range, magmatic materials intruded  through fissures and tectonic faults in the earth’s crust, and also through the previously mentioned sedimentary rock formations, favoring the emplacement of bodies of variable-size intrusive rocks, formed during different successive stages.  During this sequence, the granite rocks appear to be the youngest and gabbros the most ancient ones.  Currently, these intrusive rocks receive the name of Puerto Nuevo Formation and particularly the gabbros were the ones used by indigenous populations to create the spheres.

Later, towards the end of the Miocene (some 10 to 8 million years ago), the tectonic uplift of the region, the erosion and accumulated deposits of sediments transported by rivers and deposited as alluvial fans (on the low part of the mountains) and deltas (in the coast), made water depth of the littoral decrease gradually, establishing a continuous continental bridge, and allowing some animals to transit and migrate from North America to South America and vice-versa.  The resulting rocks, of this era were formed by various sized sediment particles, called conglomerates, sandstones and shales, and receive the name of Curré Formation.

The islands that would later form the base of the Osa peninsula began to emerge from the waters and became more stable and continuous hereafter.

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